infrared

UNIVERSITY OF QUEENSLANDDEPARTMENT OF ELECTRICAL AND

COMPUTER ENGINEERINGUNDERGRADUATE THESIS

By:

Davin Briner

Supervisor:

Dr. M. Majewski

Submission Date:

16 October 1998

16 October 1998

Davin Briner51 Kildare StreetCarina Heights QLD 4152Tel. (07) 3398 2772October 16, 1998

The DeanSchool of EngineeringUniversity of QueenslandSt Lucia, Queensland, 4072

Dear Sir,

In accordance with the requirements of the degree of Bachelor of Engineering

(Honours) in the division of Electrical and Electronic Engineering, I present the

following thesis entitled “Infrared Alarm Security System”. This work was performed

under the supervision of Dr M. Majewski.

I declare that the work submitted in this thesis is my own, except as acknowledged in

the text and footnotes, and has not been previously submitted for a degree at the

University of Queensland or any other institution.

Yours sincerely

Davin Briner

i

ACKNOWLEDGEMENTS

The author wishes to sincerely thank his project supervisor, Dr. M. Majewski, and the

Microwave and Optics Laboratories Manager, Aleksandar Rakic, for their great

guidance, encouragement and assistance during the course of this thesis.

Thanks must be given to the Hawken Electronics Workshop Team for the use of their

facilities and the high quality printed circuit boards they produced. The author also

wishes to thank Mr V. Borris, Dr. Y. Ryan and his parents for the grammatical checking

of this document.

ABSTRACT

The aim of this thesis is to design and test a prototyped infrared alarm security system.

It was decided to construct an active system over its passive counterpart, because the

active system is unaffected by the Doppler effect and is thus more versatile and

effective in hotter, wetter, windier and more humid environments. The system is very

commercially attractive and only costs $191.84.

The thesis is concerned with the analysis and design of the basic elements of the optical

and electrical systems of an active alarm system and uses an optical source never used

before in such an application. The source is a Vertical Cavity Surface Emitting Laser

(VCSEL), and possesses outstanding electrical and optical properties that may ensure its

place in the future as the only choice for an active alarm source.

A battery-powered VCSEL driver that modulates a constant current at 1kHz, a detector

and Alerting Apparatus have been constructed. The alarm proved to be very efficient; it

had a noise equivalent power of 0.5473 µW and could monitor a maximum distance of

950 m with very low power consumption. An optimal optical design has also been

achieved using Gaussian theory.

The organisation of this thesis is as follows. It begins with a brief overview of existing

active alarm security systems, states the disadvantages of each and identifies a gap in

the commercial market that can be exploited. Australian Standards are discussed for

allowable radiation limits and alarm systems. The specifications of the system are then

given. There is an overview of Vertical Cavity Surface Emitting Laser (VCSEL)

operation, and a comparison is made between this and the edge-emitting laser - a source

that is used commercially today.

A method for optimal optical design is presented, followed by the electrical modules

used for this system. Finally, a critical system evaluation is completed.

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iii

TABLE OF CONTENTSU

ACKNOWLEDGEMENTS.................................................................................................................. i

ABSTRACT.......................................................................................................................................... ii

GLOSSARY: LIST OF SYMBOLS .................................................................................................... x

CHAPTER ONE: INTRODUCTION ................................................................................................. 1

1.1 CHAPTER OBJECTIVES........................................................................................................ 1

1.2 IMPORTANCE OF INFRARED ALARM SECURITY SYSTEM............................................ 1

1.3 OBJECTIVES OF MY SECURITY SYSTEM.......................................................................... 1

1.4 ACTIVE INFRARED: THE ONLY SOLUTION...................................................................... 2

1.5 MOTIVATION FOR DESIGN................................................................................................. 3

1.5.1 Understanding of Commercial Market and relevant Standards ...................................... 3

1.5.2 Optoelectronic Exercise.................................................................................................. 4

1.6 BREAKDOWN OF THESIS.................................................................................................... 4

1.7 CONCLUSION........................................................................................................................ 5

CHAPTER TWO: COMMERCIALLY AVAILABLE ACTIVE INFRARED ALARM SECURITY

SYSTEMS.......................................................................................................... 6

2.1 CHAPTER OBJECTIVES........................................................................................................ 6

2.2 IPID RAPID DEPLOYMENT INTRUSION DETECTION SYSTEM (RDIDS)....................... 6

2.2.1 Operational Concept ...................................................................................................... 7

2.2.2 Operational Characteristics............................................................................................ 7

2.2.3 Technical Characteristics............................................................................................... 7

2.2.4 Cost and Applications..................................................................................................... 8

2.2.5 Commentary on RDIDS ................................................................................................. 8

2.3 COMMERCIALLY AVAILABLE PULNIX PRODUCTS ....................................................... 8

2.3.1 Pulnix Photoelectric Beam Receivers and Sensors ......................................................... 8

2.3.2 Indoor and Outdoor Applications................................................................................... 8

2.3.3 Setup .............................................................................................................................. 9

2.3.4 Features and Specifications ........................................................................................... 9

2.3.5 Commentary on Pulnix Range ..................................................................................... 10

2.4 CONCLUSION...................................................................................................................... 10

CHAPTER THREE:AUSTRALIAN LASER AND INTRUDER ALARM SYSTEM

STANDARDS................................................................................................... 12

3.1 CHAPTER OBJECTIVES...................................................................................................... 12

3.2 LASER SAFETY – AS/NZS 2211.1:1997.............................................................................. 12

3.2.1 Laser Classification...................................................................................................... 12

3.2.2 Required Warning Labels............................................................................................. 13

3.2.3 Accessible Emission Limits for Class 3B Laser Products ............................................. 13

3.2.4 Maximum Permissible Exposures (MPE)..................................................................... 14

3.2.4.1 MPE at cornea for direct ocular exposure.................................................................................14

3.2.4.2 MPE of skin to laser radiation..................................................................................................15

3.3 INTRUDER ALARM SYSTEM REQUIREMENTS .............................................................. 15

3.3.1 Requirements for Beam Interruption Detectors – AS 2201.3-1991 .............................. 15

3.3.2 Classification of Systems: AS 2201.4 – 1990 ................................................................ 16

3.3.3 Monitoring of System: AS 2201.5-1992 ........................................................................ 17

3.3.3.1 Transmission Characteristics and Requirements .......................................................................17

3.3.3.2 Performance of System ...........................................................................................................18

3.4 CONCLUSION...................................................................................................................... 18

CHAPTER FOUR: SYSTEM SPECIFICATION............................................................................. 19


4.2 SPECIFICATIONS BASED ON THE DISADVANTAGES OF COMMERCIAL ACTIVE

INFRARED SECURITY SYSTEMS...................................................................................... 19

4.3 SPECIFICATIONS BASED ON IMPORTANT ISSUES OF RELEVANT AUSTRALIAN

STANDARDS ....................................................................................................................... 20

4.4 SPECIFICATIONS BASED ON CHAPTER ONE OBJECTIVES.......................................... 21

4.5 SUMMARY OF SYSTEM COMPONENTS TO MEET SPECIFICATIONS......................... 23

4.6 CONCLUSION...................................................................................................................... 25

CHAPTER FIVE: OPTICAL DESIGN THEORY AND OPTIMISATION METHODS................ 26


5.2 INFRARED LIGHT AND THE ELECTROMAGNETIC SPECTRUM.................................. 26

5.3 INTRODUCTION TO VERTICAL CAVITY SURFACE EMITTING LASERS ................... 28

iv

5.3.1 Solid State Lasers .............................................................................................................. 28

5.3.2 Shortcomings of the edge emitting laser ............................................................................ 31

5.3.3 VCSELs: Overcoming the shortcomings ........................................................................... 32

5.3.4 Comparison between VCSELs and Edge Emitting Lasers ................................................. 34

5.4 OPTICAL OPTIMISATION .................................................................................................. 35

5.4.1 Goal One: Beam Collimation ............................................................................................ 35

5.4.2 Goal Two: Optimising system’s performance .................................................................... 36

5.4.3 ABCD Matrix Method: Achieving the goals ...................................................................... 37

5.5 ATTENUATORS................................................................................................................... 40

5.6 THEORETICAL POWER NEEDED TO EXTEND BEAM LENGTH.................................... 41

5.7 CONCLUSION...................................................................................................................... 43

CHAPTER SIX: ELECTRICAL DESIGN ....................................................................................... 44


6.2 IMPORTANCE OF CIRCUIT SIMULATION ....................................................................... 44

6.2.1 PSPICE............................................................................................................................. 44

6.2.2 LogicWorks ....................................................................................................................... 45

6.3 VCSEL DRIVER ................................................................................................................... 45

6.3.1 Timer Chip ........................................................................................................................ 46

6.3.2 Constant Current Source................................................................................................... 47

6.4 RECEIVER CIRCUIT ........................................................................................................... 48

6.4.1 Silicon IR Light-to-Voltage Sensor.................................................................................... 49

6.4.2 Precision Full-Wave Rectifier ........................................................................................... 49

6.4.3 Inverter with Schmitt Trigger Input .................................................................................. 51

6.5 BATTERY POWER SUPPLY FOR VCSEL DRIVER AND RECEIVER .............................. 52

6.6 ALERTING APPARATUS .................................................................................................... 52

6.7 CONCLUSION...................................................................................................................... 53

CHAPTER SEVEN: RESULTS AND DISCUSSION....................................................................... 54


7.2 VCSEL PERFORMANCE ..................................................................................................... 54

7.2.1 Far Field Distribution and associated full angle beam divergence .................................... 54

7.2.2 DC Electrical and Optical Characteristics ......................................................................... 56

7.2.3 Spectrum Analysis ............................................................................................................. 57

7.3 SYSTEM AND RECEIVER PERFORMANCE...................................................................... 59

7.3.1 Noise Equivalent Power: Determining the Limts............................................................... 59

v

7.3.2 Responsivity of Detector .................................................................................................... 61

7.3.3 Width of Monitoring Beam................................................................................................ 62

7.3.4 Response Time .................................................................................................................. 62

7.3.5 Safety Criteria ................................................................................................................... 62

7.3.6 System’s Durability ........................................................................................................... 63

7.3.7 System’s Costing ............................................................................................................... 63

7.4 CONCLUSION...................................................................................................................... 63

CHAPTER EIGHT: CONCLUSION................................................................................................ 65

8.1 SUMMARY........................................................................................................................... 65

8.2 FUTURE WORK................................................................................................................... 67

REFERENCES................................................................................................................................... 69

APPENDIX ONE: SYSTEM COSTING.................................................................................................72

A1.1 VCSEL DRIVER ...................................................................................................................... 72

A1.2 RECEIVER................................................................................................................................ 72

A1.3 ALERTING APPARATUS ............................................................................................................ 73

A1.4 BATTERY SUPPLY .................................................................................................................... 73

A1.5 OPTICAL COMPONENTS............................................................................................................ 73

APPENDIX TWO: SCHEMATICS .................................................................................................. 75

A2.1 VCSEL DRIVER ...................................................................................................................... 75

A2.2 RECEIVER................................................................................................................................ 76

A2.3. BATTERY POWER SUPPLY ....................................................................................................... 77

A2.4 ALERTING APPARATUS ............................................................................................................ 78

APPENDIX THREE: GAUSSIAN BEAMS...................................................................................... 79

A3.1 THE WAVE EQUATION ............................................................................................................. 79

A3.1.1 Amplitude of Field .......................................................................................................... 80

A3.1.2 Longitudinal Phase Factor ............................................................................................. 81

A3.1.3 Spot Size of Beam ........................................................................................................... 81

A3.1.4 Divergence angle ............................................................................................................ 81

A3.1.5 Higher order Gaussian modes ........................................................................................ 82

vi

A3.1.6 Q parameter.................................................................................................................... 82

A3.1.7 ABCD Law for Gaussian Beams..................................................................................... 83

APPENDIX FOUR: MATHEMATICA CODE ................................................................................ 85

APPENDIX FIVE: DATA SHEETS ................................................................................................. 86

A5.1 VCSEL DATASHEET ............................................................................................................... 86

A5.2 SILICON DETECTOR DATASHEET .............................................................................................. 87

APPENDIX SIX: PSPICE CODE ..................................................................................................... 88

A6.1 VCSEL DRIVER CODE............................................................................................................. 88

A6.2 DETECTOR CODE ..................................................................................................................... 88

APPENDIX SEVEN : RECEIVER FLOW CHART DIAGRAM .................................................... 90

APPENDIX EIGHT: ACCOMPANYING DISK.............................................................................. 91

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viii

LIST OF FIGURESS

FIGURE 2.1: ACTIVE INFRARED INTRUSION DETECTION SYSTEM 6

FIGURE 2.2: PULNIX INFRARED SECURITY SYSTEM 9

FIGURE 3.1: WARNING LABEL 14

FIGURE 3.2: EXPLANATORY LABEL 14

FIGURE 3.3: ALARM TRANSMISSION SYSTEM 17

FIGURE 4.1: INFRARED ALARM SECURITY SYSTEM SETUP WITHOUT ALERTING

APPARATUS 24

FIGURE 4.2: PHOTOGRAPH OF SYSTEM 24

FIGURE 5.1: CLASSICAL VIEW OF AN ELECTROMAGNETIC WAVE 27

FIGURE 5.2: THE ELECTROMAGNETIC SPECTRUM 27

FIGURE 5.3: BASIC LASER OPERATION 28

FIGURE 5.4: POPULATION INVERSION PROCESS 29

FIGURE 5.5: GAIN THRESHOLD FOR OSCILLATIONS 30

FIGURE 5.6: ELLIPTICAL BEAM SHAPE OF EDGE EMITTING LASER 31

FIGURE 5.7: PHYSICAL STRUCTURE OF VCSEL 33

FIGURE 5.8: OUTPUT BEAM OF VCSEL 34

FIGURE 5.9: APPROXIMATE RELATIONSHIP BETWEEN SOURCE AND LENS 1 35

FIGURE 5.10: INTENSITY PROFILE OF GAUSSIAN BEAM 37

FIGURE 5.11: 1D OPTICAL SYSTEM 38

FIGURE 6.1: PHOTOGRAPH OF DRIVER CIRCUIT 46

FIGURE 6.2: CURRENT OUTPUT WAVEFORM OF VCSEL DRIVER 48

FIGURE 6.3: PHOTOGRAPH OF RECEIVER CIRCUITRY 49

FIGURE 6.4: BREAKUP OF PRECISION FULL-WAVE RECTIFIER 50

FIGURE 6.5: PSPICE SIMULATION OF FULL-WAVE PRECISION RECTIFIER 50

FIGURE 6.6: TRANSFER CHARACTERISTIC DISPLAYING HYSTERISIS 51

FIGURE 6.7: DURABLE CASING OF ALERTING APPARATUS 53

FIGURE 7.1: SETUP FOR MEASURING THE FAR FIELD DISTRIBUTION 55

FIGURE 7.2: POLAR PLOT OF THE FAR FIELD DISTRIBUTION 55

FIGURE 7.3: VCSELS V-I-L-ηWP RELATIONSHIP 56

FIGURE 7.4: EXPERIMENTAL SETUP FOR SPECTRUM ANALYSIS 57

FIGURE 7.5: VCSEL’S SPECTRUM 58

FIGURE 7.6: MODE PATTERNS 58

FIGURE A3.1: ORIGIN OF THE PHASE FRONT CURVATURE 80

FIGURE A3.2: GAUSSIAN BEAM PROFILE OF A TEM0,0 MODE. 80

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LIST OF TABLESTABLE 2.1: TECHNICAL CHARACTERISTICS OF THE RDIDS SYSTEM 7

TABLE 2.2: SPECIFICATIONS OF VARIOUS PHOTOELECTRIC BEAM SENSORS 10

TABLE 4.1: ALARM SYSTEM COMPONENTS AND THEIR ASSOCIATED ROLES 23

TABLE 5.1: VCSEL VS EDGE EMITTING LASER 34

TABLE 5.2: KNOWN AND UNKNOWN PARAMETERS 37

TABLE 5.3 METHOD OF CALCULATING VCSEL’S ELECTRICAL POWER FOR INCREASED

BEAM LENGTH 42

TABLE 6.1: RECEIVER’S LOGIC 51

TABLE A1.1: COMPONENTS AND COSTING OF VCSEL DRIVER 72

TABLE A1.2: COMPONENTS AND COSTING OF RECEIVER 73

TABLE A1.3: COMPONENTS AND COSTING OF ALERTING APPARATUS 73

TABLE A1.4: COMPONENTS AND COSTING OF BATTERY-POWER SUPPLY 73

TABLE A1.5: COMPONENTS AND COSTING OF OPTICAL SYSTEM 74

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GLOSSARY: LIST OF SYMBOLS

Symbol Meaning

D Duty cycle (%)d1 Distance between source and lens 1 (m)d2 Distance between lenses (m)d3 Distance between lens 2 and detector (m)E Irradiance (mW/mm2)FL Fresnel LossF Frequency (Hz)f Focal length (m)Hm Hermite polynomialH Radiant exposure (J/m2)k Wave NumberL Output Optical power (mW)MPE Maximum Permissable ExposurePelec Input electrical power (mW)R Responsivity (A/W)R(z) Radius of spherical equiphase surfacesRL Reflective LossT Transmission Matrixw0 Beam width at source (m)w1 Beam width at detector (m)τoxygen Absorption coefficient of oxygenτWV Absorption coefficient of water vapourθ Beam divergence (°)φR Radial phase factorφL Longitudinal phase factorηwp Wall plug efficiency (%)

Infrared Alarm Security System 1

CHAPTER ONE

INTRODUCTION

1.1 CHAPTER OBJECTIVES:

• Outline the importance of infrared alarm security systems

• Define the objectives of the system

• Explain why only an active system can satisfy objectives

• Discuss the motivation for designing an infrared security system

• Show the logical breakdown of this thesis.

1.2 IMPORTANCE OF INFRARED ALARM SECURITY

SYSTEM

There is enormous commercial potential in industry and business for infrared security

applications. Today we live in a dangerous world – protecting one`s family’s

business(es), possessions is of prime concern. Security systems are ubiquitous and have

become an integral part of society. The demand for security systems will increase in the

future. Improvements to these systems are inevitable as technology advances with time.

1.3 OBJECTIVES OF MY SECURITY SYSTEM

The objectives of the my security system are to:

1 Monitor the perimeter of a factory or military installation

2 Achieve a high system efficiency

3 Achieve a competitive system cost (see Appendix One)


4 Exceed industry’s maximum beam monitoring length of 600 metres [S2]

5 Achieve a low power consumption for a monitoring distance of at least 160

metres

6 Determine the system limits obtained when the system’s signal is equal to

the system’s noise

7 Produce a prototyped product that is durable and can withstand harsh

environmental conditions such as excessive heat, fog and humidity

8 To integrate special casing into the system to protect the receiver, detector

and their associated circuitry, from these harsh elements

9 Ensure that the monitoring beam can not be seen by the naked eye; thus, the

source must generate an infrared wave

10 Alert the intruder that the alarm has activated when the beam is broken.

1.4 ACTIVE INFRARED: THE ONLY SOLUTION

Infrared alarms can be classified as either active or passive. A passive system detects

the infrared rays that are emitted from a moving object. In contrast, an active infrared

system is triggered when the beam, emitted from a source and detected at the receiver,

is broken.

Active systems are the only choice to fulfil the objectives of Section 1.3. Active

systems are much more versatile than their passive counterparts, and can be

implemented in excessive heat and humidity. The active systems are not subject to

difficulties arising from the Doppler Effect1 [S2]. This makes the active system much

more appealing to the commercial market.

1 The Doppler effect was named after Chrsitan Doppler (1803-1853) and states that the frequency at pointB will be different to that at Point A relative to the viewer. Consider when an atom in a low-pressure gasemits radiation, a sharp monochromatic line at frequency F0 is emitted in the atom’s rest frame. If theatom is moving at a relative velocity v towards or away from the viewer, the observer will see a

frequency

±=

c

vFF 10 .


1.5 MOTIVATION FOR DESIGN

This section deals with the reasons for undertaking the design of an infrared alarm

security system.

1.5.1 Understanding of Commercial Market and relevant Standards

One of the goals of this thesis is to understand and gain an appreciation of the

methodology used to produce a commercial product. It is intended that the prototyped

infrared security system should overcome the weaknesses of existing commercial

products.

The steps involved in the methodology used to produce a commercial product are:

1. Choose product field – in this case, Active Infrared Alarm Security Systems.

Realise the industrial potential for this field

2. Analyse commercial Active Infrared products and note drawbacks

3. Consider relevant Australian Standards

4. Define system’s specifications; ensure that the system:

a) Capitalises on the disadvantages of existing commercial products

b) Pertains to all relevant Australian Standards

5. Build a prototype of the system

6. Expand the prototype system for commercial use. It is intended that the final

product would incorporate two beams instead of one. This would overcome

the problem of small insects intercepting a beam and triggering a false alarm.

The two transmitters and receivers would be concealed so the intruder is

unaware of the monitoring region.


1.5.2 Optoelectronic Exercise

The construction of an infrared alarm security system is also an exercise in

Optoelectronics. It is fascinating to integrate physical and optical principles into a

useable state of the art detection apparatus.

1.6 BREAKDOWN OF THESIS

This thesis shows the logical steps involved in understanding and gaining an

appreciation of the methodology used to produce an active infrared alarm security

system prototype that overcomes the drawbacks of commercial designs.

The breakdown of the thesis is as follows:

Chapter Two: Analyses the drawbacks of existing commercial active infrared alarm

systems

Chapter Three: Discusses the relevant Australian Standards of active infrared alarm

security systems; maximum permissable exposure levels and intruder

alarm system requirements are examined

Chapter Four : Defines the system’s specifications that:

1. Capitalise on the drawbacks of commercial products reviewed

in Chapter Two

2. Satisfy the relevant Australian Standards of Chapter Three

Chapter Five: Discusses the optical theory needed to satisfy system’s specifications

Chapter Six: Discusses the electrical design needed to satisfy system’s

specifications

Chapter Seven: Gives a critical analysis of the system; a determination is made on

whether the system’s objectives have been met

Chapter Eight: Gives a summary of the thesis and recommends future work.


1.7 CONCLUSION

This Chapter has outlined the importance of infrared alarm security systems. An active

system was chosen over its passive counterpart because of its versatility and its capacity

to operate in harsher environments. In comparison, the passive system is less effective

in these conditions and is affected by the Doppler Effect. The most important goal of

the prototype system is to improve on weaknesses of current existing technology.


CHAPTER TWO

COMMERCIALLY AVAILABLE ACTIVE

INFRARED ALARM SECURITY SYSTEMS


• Review Commercially available Pulnix and EAG Elektronik products

• Focus on the leading active infrared military system, the IPID Rapid

Deployment Intrusion Detection System (RDIDS)

• Analyse the shortcomings, cost, advantages and applications of each device

2.2 IPID RAPID DEPLOYMENT INTRUSION DETECTION

SYSTEM (RDIDS)

The American Company, Cooperative Monitoring Center (CMC) specialises in active

infrared security systems for military applications. The RDIDS utilises infrared break

beam sensor technology [T1]. The system consists of six sources and six detectors and

is shown in Figure 2.1

Figure 2.1: Active Infrared Intrusion Detection System


2.2.1 Operational Concept

The operational concept of the detection system is akin to all active infrared security

systems. The active infrared transmitter transmits modulated pulses of infrared energy

from the focal point of a transmitter lens to the focal point of a receiver lens. If an

intruder breaks this beam of energy, the signal strength monitored at the receiver lens is

reduced. The sensor then triggers the alarm. This system has a 100-metre long

perimeter detection zone in the shape of a vertical plane.

2.2.2 Operational Characteristics

The RDIDS has a variety of features that makes it attractive for security applications.

Features include:

• a high intruder detection accuracy − the probability of triggering a false

alarm is small

• high system durability to withstand harsh temperature, wet and foggy

conditions; this is to be expected from a military-intended security system.

• a choice between a fixed or portable security system [T1].

2.2.3 Technical Characteristics

The technical characteristics of the RDIDS are outlined in Table 2.1.

Table 2.1: Technical Characteristics of the RDIDS system

Parameter ValueLens Diameter 88.9mm

Pulse Frequency 1200 HzPower 120Vac/12VdcCurrentrequirement

200mA

OperatingTemperature

-30 C to +60 C


2.2.4 Cost and Applications

The portable sensor can be set up quickly across road and paths and around the

perimeter of a facility to detect people and vehicles. The base model of the RDIDS is

capable of covering a zone of approximately 100m. This system detects the crawling,

running or walking of intruders and costs approximately $10,000.

2.2.5 Commentary on RDIDS

The IPID Rapid Deployment Intrusion Detection System possesses all the qualities of

an excellent security system. The purpose of the RDIDS is to monitor military

institutions such as air bases and weapon factories. Because of this, the RDIDS is

designed to withstand harsh environments, has a wide operating temperature range and

can monitor a 100m perimeter zone. The only drawback of this system is its high cost

of $10 000.

2.3 COMMERCIALLY AVAILABLE PULNIX PRODUCTS

2.3.1 Pulnix Photoelectric Beam Receivers and Sensors

Pulnix caters for indoor and outdoor applications. The principle of operation is

identical to the RDIDS system and the infrared security system designed for this thesis.

2.3.2 Indoor and Outdoor Applications

Pulnix infrared security systems designed for indoor applications monitor:

• entrances and exits

• corridors

• staircases

• bank counters.

Pulnix infrared security systems designed for outdoor applications monitor building

perimeters (such as in factories or prisons), and can work efficiently in harsh


environments. A special hood is attached on the sensor cover to protect the system

against frost and dew.

2.3.3 Setup

Pulnix utilises twin beam technology. The beams are synchronised to work together to

reinforce the range and stability in severe weather conditions [P1].

For outdoor applications, the synchronised twin beams reduce the probability of

triggering false alarms caused by flying birds and falling leaves. Figure 2.2 shows a

graphical representation of the system.

Beam

Beam

Figure 2.2: PULNiX Infrared security System

2.3.4 Features and Specifications

The specifications of the various Pulnix products are outlined in Table 2.2. The features

that are common to all Pulnix products are as follows:

1. Rotary Optical System - the optical system of both transmitter and receiver can

be rotated a full 180 degrees to allow for side aiming

2. Insect Protection - sealed optical system prevents intrusion and interference by

insects

3. External light protection - the filter cuts out visible rays; the system has

excellent tolerance of sunlight, automobile head light, fluorescent light and

mercury light.

DetectorEmitter


Table 2.2: Specifications of various Photoelectric Beam Sensors

Model PR-5B PB-2OTE PB-40TE PB-60TEDetectionSystem

Breaking of 1 beam Simultaneousbreaking of 2beams

Infrared beam LEDλ=940nmModulation: 500Hz

LED pulsedbeam, Doublemodulation

Response Time 50ms or more 50msec to700msec(Variable atpot)

Supply voltage 10.5 V- 26 V (non-polarity)

12 to 30 V DC(non-polarity)

Currentconsumption

- 55mA or less 75mA orless

80mA or less

Ambienttemperaturerange

(-20 to +50) degreesCelsius

(-25 to +60)degrees Celsius

Application Indoor Indoor Outdoor OutdoorCost ($) 160.00 364.00 383.00 403.00DistanceCoverage (m)

5 40 80 120

2.3.5 Commentary on Pulnix Range

The Pulnix products are very attractive commercially. The products are relatively

cheap, minimise the probability of false alarms through an insect protection mechanism

and have external light protection. Pulnix also offers a wide range of systems to suit the

consumer market.

The drawbacks of the Pulnix products include the average efficiency that is atypical of

Light Emitting Diodes. The flimsy protective plastic coating surrounding the Pulnix

emitters and detectors also raises doubts about the durability and effectiveness of the

system operating in harsh outdoor environments.

2.4 CONCLUSION

The RDIDS and the various Pulnix systems were discussed. The main disadvantage of

the RDIDS is its cost; in comparison the Pulnix products lacked durability. It is clearly


evident that a niche exists in the commercial market for an active infrared alarm system

that is cheap and durable.


CHAPTER THREE

AUSTRALIAN LASER AND INTRUDER

ALARM SYSTEM STANDARDS


• Discuss Laser Safety pertaining to active infrared alarm security systems;

focus on issues such as manufacturing requirements, labelling, accessible

emission limits and maximum permissible exposure (MPE) at the cornea for

direct ocular exposure to laser radiation.

• Specify intruder alarm system requirements such as system classification,

requirements for beam interrupted detectors and an overview of monitoring

procedures.

3.2 LASER SAFETY – AS/NZS 2211.1:1997

Laser safety requirements are specified by the Australian Standard 2211.1:1997. The

source of the infrared alarm security system is a Vertical Cavity Surface Emitting Laser

(VCSEL). This section discusses the regulations that pertain to their use.

3.2.1 Laser Classification

Laser and laser product manufacturers must certify and label lasers [A5]. The lasers are

classified into four classes – Class 1, Class 2, Class 3A and 3B and Class 4.

The class boundaries are defined by:


1. The laser’s optical output power

2. The wavelength of the laser

3. The potential hazard of the laser to the human eye and skin.

The higher the Class, the more potentially dangerous the laser is. There are four classes

- Class 1, Class 2, Class 3A and 3B and Class 4. The VCSEL is a Class 3B laser. All

Class 3 lasers that emit invisible radiation are classified as Class 3B [A5]. VCSELs

operate at 850 nm (i.e. within the infrared range) and satisfy this condition.

3.2.2 Required Warning Labels

Clause 5.5 of AS/NZS 2211.1:1997 states that each class 3B laser product shall have

affixed a warning label and an explanatory label shown in Figure 3.1 and 3.2

respectively [A5].

3.2.3 Accessible Emission Limits for Class 3B Laser Products

The Accessible Emission Limit is defined as the safe maximum optical output power of

a laser. This limit is determined by the emission duration of the laser’s radiation.

The accessible emission limits for the VCSEL for an emission duration of t = 0.0005

seconds is given by [A5]:

EMPE = 0.03C4 J (1)

C4 = 100.002(λ-700) = 100.002(850-700) = 2.00 (2)

Substituting numbers into equation (2),

EMPE = 0.03*2.00 = 0.06 J (3)

In terms of power obtained after dividing by t,

PMPE = 120 W (4)


Figure 3.1: Warning Label Figure 3.2: Explanatory Label

3.2.4 Maximum Permissible Exposures (MPE)

Potential safety hazards exist when using a laser. The most common are damage to the

eyes and skin [A5]. Maximum permissible exposure values indicate the value of laser

radiation to which people may be exposed without adverse effects [A5]. MPE is

measured in terms of:

1. Radiant exposure – at a point on a surface, the radiant energy incident on

an element of a surface divided by the area of that element; this is expressed

in Jm-2 and is denoted by H [A5]

2. Irradiance – at a point on a surface, the radiant power incident on an

element of a surface divided by the area of that element; this is expressed in

Wm-2 and is denoted by E [A5].

3.2.4.1 MPE at cornea for direct ocular exposure

The MPE at the cornea for direct ocular exposure is the limit of radiation (in terms of

radiant exposure and irradiance) that the eye can be directly exposed to without causing

any damage. The MPE at the cornea, for direct ocular exposure for 0.0005 seconds to

laser radiation at a wavelength of 850 nm is given by [A5]:

HMPE = 18t0.75C4C6 J/m2 (5)


C4 = 100.002(λ-700) = 100.002(850-700) = 2.00 (6)

Since C6 = 1 for point source viewing conditions,

HMPE = 18 x (5 x 10-4).75 x 2.00 x 1 = 120.37 x 10-3 J/m2 (7)

In terms of irradiance obtained after dividng by t,

EMPE = 240.75 W/m2 (8)

= 0.24075 mW/mm2

3.2.4.2 MPE of skin to laser radiation

The MPE of skin to laser radiation is the maximum amount of radiation that the skin

can be subjected to without causing any damaging effects. The MPE of skin to laser

radiation at a wavelength of 850 nm is given by:

HMPE = 1.1 x 104 x C4 x t.25 J/m2 (9)

C4 = 100.002(λ-700) = 100.002(850-700) = 2.00 (10)

t = 0.0005 s = emission duration

The MPE value then is as follows:

HMPE = 1.1 x 104 x 2.00 x (5 x 10-4) 25 = 3.290 x 103 J/m2 (11)

In terms of irradiance obtained after dividng by t,

EMPE = 6.58 x 106 W/m2 (12)

3.3 INTRUDER ALARM SYSTEM REQUIREMENTS

3.3.1 Requirements for Beam Interruption Detectors – AS 2201.3-1991

The requirements for Beam Interruption Detectors are [A2]:

1. Operational spectrum: The beam interruption detectors shall operate

outside the visible spectrum (wavelengths in excess of 760 nm)


2. Maximum range: The manufacturer shall state the maximum range of the

detector as the greatest separation between the transmitter and the receiver at

which an alarm condition is not initiated as a result of a 3dB reduction in the

power level of the signal received

3. Modulation: The detector shall incorporate some method of modulation so

that the introduction of an unmodulated source of wavelength comparable

with that of the transmitter shall neither:

a) prevent an alarm condition being initiated; nor

b) initiate an alarm condition

4. Sensitivity: The detector shall initiate an alarm condition as a result of the

complete interruption of the signal received for any period longer than 40ms;

the detector shall not initiate an alarm condition as a result of the complete

interruption of the signal for any period shorter than 20ms.

3.3.2 Classification of Systems: AS 2201.4 – 1990

This standard classifies the degree to which wire-free systems are monitored, from

Class One to Class Five. Although no monitoring system will be implemented for this

thesis, this standard is of great importance; it must be followed if the product is to be

developed for the commercial market.

The graduation for these classes is determined by [A4]:

• Transmission type of the signal

• The degree to which a system distinguishes between an alarm and a fault

signal

• The method of coding to minimise the possibility of interference occcuring

between systems

The degree of complexity increases with Classes.


The commercial product would be best suited to Class One. The advantage of this

would be a cheaper system that would be more attractive to the consumer. In no

instance is the safety of a Class One wire-free system jeopardised. This is because

Class One requirements are very stringent. ‘The Class 1 system provides the following:

1. Transmission of a signal when a detector has gone into an alarm

condition

2. A means to distinguish between an alarm and a fault signal

3. A method of coding to give a minimum of 16 different system

identifications’ [A3].

3.3.3 Monitoring of System: AS 2201.5-1992

This Australian Standard discusses the communication that occurs between the

supervised premises and the monitoring station. Transmission Requirements and

Performance are discussed in this section.

3.3.3.1 Transmission Characteristics and Requirements

If the security system were to be upgraded for commercial purposes, it would have a

continuous and periodic transmission between the supervised premises and the central

station. Figure 3.3 illustrates how the supervised premises would be networked to the

central station.

SUPERVISED PREMISES CENTRAL STATION

Alarm Alarm Alarm Annunciation System Transmission Equipment Equipment

Alarm system interface Terminal Interface

Figure 3.3: Alarm Transmission System


3.3.3.2 Performance of System

It is required that the transmission system shall communicate information about the

state of the alarm system to the designated central station. The transmission system

response delay is defined as the time taken for a signal to be sent from the supervised

premises to the monitoring station. This time delay is 240 seconds for a Class 1 system.

3.4 CONCLUSION

In this chapter, four standards were reviewed:

1. AS/NZS 2211.1:1997 dealt with laser safety requirements. This standard

specified the compulsory use of warning labels and gave MPE values at the

cornea and to skin of 0.24075 mW/mm2 and 6.58 MW/m2 respectively.

2. AS2201.3 –1991 gave the requirements for Beam Interruption Detectors in

terms of operational spectrum, maximum range, modulation and sensitivity. The

prototyped system must initiate an alarm condition as a result of the beam

breaking for any period longer than 40ms.

3. AS 2201.4 –1990 gave classifications for active alarm systems. A class one

system was given for the commercial expansion of the designed prototype

system.

4. AS2201.5 –1992 discussed the conditions for an alarm transmission system that

would be implemented in the final product. The time delay between the

supervised premises and the monitoring station is 240 seconds.


CHAPTER FOUR

SYSTEM SPECIFICATION


• To clearly define the system’s specifications based on:

1. The disadvantages of commercial active infrared security systems

2. The relevant Australian Standards for Laser Emission and Security

Systems

3. Objectives of the prototyped security system outlined in Chapter

One.

4.2 SPECIFICATIONS BASED ON THE DISADVANTAGES

OF COMMERCIAL ACTIVE INFRARED SECURITY

SYSTEMS

The downfalls of commercial active infrared security systems analysed in Chapter Two

are given below:

• The IPID Rapid Deployment Intrusion Detection System’s high cost of

$10,000

• The Pulnix’s average efficiency atypical of Light Emitting Diodes

• The Pulnix’s lack of durability and effectiveness operating in harsh outdoor

environments due to its flimsy plastic emitter and detector casing


To counter these downfalls, the active security system prototype should be cost-

effective and have durable casing surrounding its modules. The system should also

implement the most effective and power-efficient laser source. This laser source is a

Vertical Cavity Surface Emitting Laser that possesses a respectable optimal wall-plug

efficiency of 11.4%.

4.3 SPECIFICATIONS BASED ON IMPORTANT ISSUES OF

RELEVANT AUSTRALIAN STANDARDS

The system must satisfy both laser safety and intruder alarm system requirements. The

maximum permissible exposure to the skin and at the cornea for direct ocular exposure

must be satisfied for the system to be considered safe. Therefore, the laser source must

possess a low input electrical power and low output optical power. The VCSEL

possesses a low threshold voltage and current of 1.45 V and 3.65 mA and has a typical

optical output Power of 2.5 mA. This reinforces the need for a Vertical Cavity Surface

Emitting Laser as the system’s source.

A highly sensitive receiver is required to detect the low optical output power of the

VCSEL. The TSL261 is an excellent detector that has an in-built amplifier and filter to

harness out any unwanted signals. The TSL261 will be discussed further in Chapter

Six.

Next, one must consider the requirements for beam interruption detectors, specified by

Australian Standard AS 2201.3-1991. According to this standard, the detector must

prevent an alarm condition being initiated by a signal other than the modulation signal.

This indicates that two system specifications are needed:

1. The VCSEL must be driven at a modulated frequency; 1kHz was arbitrarily

chosen.

2. The detector must have an in-built filter in its internal setup.


The TSL261 satisfies this latter condition, and reinforces this excellent choice of

detectors.

Another issue relevant to AS 2201.3-1991 is the system’s sensitivity. The system must

only initiate an alarm condition as a result of the complete interruption of the signal

received for any period longer than 40ms. Hence, one must carefully examine the

sensitivity of the detector to ensure that it is not over sensitive. The TSL261 will be

tested thoroughly to ensure that this alerting condition is satisfied.

4.4 SPECIFICATIONS BASED ON CHAPTER ONE

OBJECTIVES

This section outlines the objectives of Chapter One and the methods, and electrical

and/or optical equipment needed to achieve these objectives. Further information

regarding optical theory and electrical components can be found in Chapters Five and

Six respectively.

Objective 1: Monitor the perimeter of a factory or military Institution.

Proposed Solution 1: Mirrors should be utilised to minimise the number of sources

and detectors used. Two lenses should be used to collimate the

beam and then focus the beam on the detector.

Objective 2: Achieve a high system efficiency.

Proposed Solution 2: A very efficient source should be used. A VCSEL is ideal for

this. A highly sensitive detector should also be incorporated

into the design. The TSL261 satisfies this condition.

Objective 3: Achieve a competitive system cost.

Proposed Solution 3: Electrical and Optical components must be chosen that achieve

the task at hand. Cost must not be sacrificed for durability and

system’s effectiveness.


Objective 4: Exceed industry’s maximum beam monitoring length of 600

metres.

Proposed Solution 4 The source’s beam divergence should be as small as possible.

The VCSEL satisfies this condition. A good choice of lenses to

collimate the beam effectively at the laser and to focus it on the

detector is also required.

Objective 5: Achieve a low power consumption for a monitoring distance of

at least 160 metres.

Proposed Solution 5: Simulate 160 metres with the use of attenuators.

Objective 6: Produce a prototyped product that is durable and can withstand

harsh environmental conditions such as excessive heat,

humidity and cyclonic conditions.

Proposed Solution 6: Design Special casing to protect the receiver, detector and their

associated circuitry. Choose components that can function to

their full capacity under excessive temperature changes.

Objective 7: Ensure that the monitoring beam can not be seen by the naked

eye.

Proposed Solution 7: The VCSEL must emit infrared radiation. The VCSEL being

used operates at 850nm and is unseen by the naked eye. An

appropriate detector must be chosen that works efficiently at

this wavelength. Here, a Silicon detector is the best option.

Objective 8: Alert the intruder that the alarm has activated when the beam is

broken.

Proposed Solution 8: Design alerting apparatus that activates the buzzer for at least

six seconds.


4.5 SUMMARY OF SYSTEM COMPONENTS TO MEET

SPECIFICATIONS

The components, objectives and their associated uses are summarised in Table 4.1. The

infrared alarm security setup is shown in Figure 4.1. A photograph of the system can be

seen in Figure 4.2.

Table 4.1: Alarm System Components and their associated roles

Alarm System Component Purpose Objective Number2 Attenuators • Simulates real conditions

• Increases monitoringdistance from 1.6m to 160m.

• 5

1 Laser Driver • Modulates VCSEL at 1kHz • 1,2Vertical Cavity Surface EmittingLaser (VCSEL)

• Efficient laser (11.4% wallplug efficiency)

• Operates at wavelength of850nm

• 2,5,7

3 mirrors • Minimises number ofemitter and detector arrays

• Reflects beam 90 degrees

• 1

Lens A • Collimates beam• Increases monitoring beam’s

diameter

• 4

Lens B • Focuses beam onto Silicondetector

• 4

1 Silicon Detector • Receives beam• Silicon most efficient at

850nm.

• 2,3,4

Detector Circuitry • Filters out unwanted signals• Activates buzzer only when

beam is not received atdetector.

• 2

Alarm Buzzer • Acts as deterrent for intruder• Active when alarm triggers

• 8


Figure 4.1: Infrared Alarm Security System Setup without Alerting Apparatus

Figure 4.2: Photograph of System

Mirror

Lens

Detector

Attenuators

VCSEL

VCSEL

Driver


4.6 CONCLUSION

This chapter has clearly defined the prototype system’s specifications by considering

relevant Australian Standards and capitalising on the disadvantages of commercial

systems. Thus the new system is intended to be durable and cost-efficient. It has been

decided to use a VCSEL as the laser source because of its low divergent beam, its

invisible output spectrum, its respectable wall-plug efficiency, its low input electrical

power and its low output optical power. A highly sensitive Silicon Detector was chosen

due to its high sensitivity and its capacity to filter out unwanted signals.


CHAPTER FIVE

OPTICAL DESIGN THEORY AND

OPTIMISATION METHODS


• Define infrared light and the electromagnetic spectrum

• Introduce operational and physical characteristics of Vertical Cavity Surface

Emitting Lasers (VCSELs)

• Compare VCSELs to edge-emitting lasers

• Show that VCSELs are the better laser source for an active infrared security

system

• Discuss Gaussian beams, the ABCD matrix and optical principles of lenses

and atteunuators

• Examine optimisation design methods for the security system.

5.2 INFRARED LIGHT AND THE ELECTROMAGNETIC

SPECTRUM

Electromagnetic waves are related patterns of electric and magnetic force [F2]. The

direction of the electric and magnetic fields and the direction of the wave's motion are

perpendicular to one another. Figure 5.1 shows a classical view of an electromagnetic

wave.


Figure 5.1: Classical view of an Electromagnetic Wave

These waves are generated by the oscillation of electric charges and travel through free

space at the speed of light, 2.998*108 m/s [F2].

Infrared light is an invisible band in the electromagnetic spectrum. This is shown in

Figure 5.2. It is invisible to the human eye and possesses identical properties to visible

light. The light can be reflected (bounced back), collimated (directed in a straight line),

diffracted (broken up) and refracted (bent). The propagation of infrared light through

free space using traditional optical elements has been modelled using Gaussian Theory

(see Appendix Three). Thus, infrared light is ideal to use in a security system.

Figure 5.2: The Electromagnetic Spectrum


5.3 INTRODUCTION TO VERTICAL CAVITY SURFACE

EMITTING LASERS

The VCSEL is a solid state laser device. In contrast to the conventional edge-emitting

lasers, VCSELs present unique optical and electrical properties which make these

devices very attractive. These include a 99% device yield, low threshold voltage

(1.45V), low threshold current (3.68 mA), a respectable wall-plug efficiency2 (ηeff =

11.4%), single-longitudinal mode emission and a low-divergence circular output beam

[V1].

This section will introduce the basic concepts of the solid state laser. The shortcomings

of the edge-emitting laser will be discussed and it will be shown how VCSELs can

overcome these shortcomings. The importance of VCSELs over edge-emitting lasers

for an active infrared security system is also examined.

5.3.1 Solid State Lasers

The basic operation of a solid state laser is shown in Figure 5.3. Two mirrors are used

to form a cavity. Optical radiation is confined by the mirrors and causes the photons to

reflect back and forth inside the cavity. The light is then forced to pass through an

optical gain medium many times, each time the field being amplified [S3].

Figure 5.3: Basic Laser Operation

2 Wall-plug efficiency is a measure of the ratio of the optical output power to the supplied electricalpower.


Only certain wavelengths are allowed to resonate within the cavity. The resonant wave

must fit in the cavity with an integer number of half-wavelengths. Thus:

where: q is an integer

d is the cavity length

∆F is the change of frequency within the laser cavity (Hz) [D1].

From (14), the spacing of the resonant frequencies is inversely proportional to the cavity

length. That is, a small d gives widely spaced frequency modes and a large d gives

narrowly spaced frequency modes.

Optical gain within the cavity is due to the state transition between two energy bands in

the gain medium [K1]. This is shown in Figure 5.4. There is not an exact quantity in

energy difference between the two energy bands. This means that there is a range of

energies due to the finite smearing of energy levels in the crystal [C2]. Thus, different

frequencies can cause optical gain.

Figure 5.4: Population Inversion process

(13)

(14)

f

cqqd

∆==

22

λ

d

cf

2=∆∴


The frequencies that have the potential to resonate with the cavity mode are those where

the optical gain of the medium exceeds the losses encountered by the cavity. Therefore,

there are two basic conditions that the laser requires for oscillation:

(a) the optical gain of the material exceeds the losses in the cavity at the

frequency of interest

(b) the frequency of interest satisfies one of the cavity modes.

This is shown by Figure 5.5. The arrows show the cavity modes whilst the hatched area

is where the gain is higher than losses and laser action can occur. L is the cavity loss in

dB [C2].

Figure 5.5: Gain threshold for oscillations

Stimulated emission is a mechanism whereby the electromagnetic field couples to the

quantum-mechanical energy states in the gain medium [E1]. Figure 5.4 illustrates this

point.

The mechanism of stimulated emission is central to the gain medium providing optical

gain. This is attributed to the fact that some photons generate excited atoms in the gain

medium to undergo a decay into a lower energy state which releases a photon of exactly

the same energy as the initiating photon.


Atoms are raised from the ground state into some energy state E2 via the pumping

process. This effect lasts a long time. Photons create stimulated emission, exciting the

atoms to decay into an ephemeral intermediate energy level E1. Atoms from level E1 are

decayed to the ground state by a process called spontaneous emission. If E1 has a much

shorter life than E2, the atoms will be emptied at a fast enough rate to ensure that the

population of E2 exceeds that of E1. Population inversion is the name given to this

occurrence. It is the basic requirement for stimulated emission to be more dominant

than the natural absorption mechanism in the material [C2][A1].

5.3.2 Shortcomings of the edge emitting laser

There are three main shortcomings of the edge emitting laser. The first is the elliptical

beam shape of this laser. This is shown in Figure 5.6. The beam shape implies that to

obtain a good coupling to a fibre, an astigmatic lens is required which has exactly the

correct focal length. This is very hard to achieve in practice because of the wide range

of edge emitting lasers, each requiring its own astigmatic lens [C2].

Figure 5.6: Elliptical Beam Shape of Edge Emitting Laser

The second problem is the large divergence angle of the beam (60°)[S3]. This is

because the depletion layer of the pn junction (i.e. the active region) is very thin,

resulting in a very small output aperture [C2][S3]. A hetero-junction can reduce this

problem.3

3 A Hetero-Junction is a junction with a number of layers of varying doping. It increases the depletionregion width and consequently widens the aperture [C2].

Output

Beam

Output

Beam


The third problem concerns the long cavity length (many wavelengths long). From

equation (14), a large cavity length results in narrowly spaced longitudinal frequency

modes. This increases the likelihood of many more modes fitting into the lasing

frequency range [S3][C2]. Ideally, a short cavity length would allow only a few modes

within the lasing frequency range as these modes would be spaced widely apart.

5.3.3 VCSELs: Overcoming the shortcomings

VCSELs overcome the shortcoming of the edge emitting laser by using a micro-cavity.

A micro-cavity is a very short cavity that results in a widely spaced frequency range.

The use of the micro-cavity is two-fold: to reduce the number of the longitudinal modes

the laser may support, and to increase the coherence length of the VCSEL [C2][S1]. A

large aperture is also needed to increase the coupling efficiency. This is achieved by a

device called a Vertical Cavity Surface Emitting Laser. The VCSEL mirrors are grown

on the substrate and are not cleaved [C2]. Thus VCSELs may be constructed in arrays

and may be easily integrated with other electronics [S3][C2].

Band-gap engineering techniques such as molecular beam epitaxy and metal organic

vapour phase epitaxy are employed for the construction of the VCSEL [C2]. Both

methods allow the growth of many thin layers of semiconductor materials with atomic

precision [C2][S1]. This way, the band-gap energies of the resultant material can be

altered as desired and the desired electrical and optical properties of the material may be

specified [S3].

The structure of the VCSEL can be seen in Figure 5.7.


Figure 5.7: Physical Structure of VCSEL

VCSELs comprise of both thin and thick layers; thin layers (approximately 10nm)

confine electrons and thicker layers (approximately 100nm) act as Distributed Bragg

Reflector (DBR) mirrors. DBR mirrors consist of repeating pairs of quarter-

wavelength-thick high (GaAs with a n=3.5) and low (AlAs with a n=3.5) refractive

index layers. These mirrors are grown into the laser structure itself, both above and

below the active region [A1][C1]. Light is reflected vertically through this active

region.

A thin metallic layer, with a tiny aperture cut (diameter of up to 15µm), is deposited on

the top of the device [C1][C2]. The metal’s purpose is to inject current into the

junction. Population inversion occurs in the quantum well by hole-electron

recombination. This is similar to that of the edge emitting laser [S3].

VCSELs employ a mechanism called periodic gain. This mechanism creates optical

gain at the wave crests of the optical standing wave inside the cavity [C2]. As a

consequence, the frequency of the cavity is stabilised as only the correct mode will have

maximum gain. The spurious longitudinal modes are also suppressed because they

experience no loss due to the natural absorption of the material [C2].

VCSELs support only a single longitudinal mode. However, they tend to generate a

large number of transverse modes depending on the VCSEL diameter. For a small

diameter (5µm), the transverse mode TEM00 is the most dominant one. This is not the

case for larger VCSEL diameters (10µm), where the TEM00 mode tends to disappear at


bias currents above threshold. This is due to a process called hole burning where a

mode has depleted the gain in a specific spatial position over the gain medium, due to

its large amplitude at that particular spot [C2] .

5.3.4 Comparison between VCSELs and Edge Emitting Lasers

VCSELs are superior to edge emitting lasers as a source for an active infrared security

system. This is because VCSELs are much cheaper to manufacture than edge emitting

lasers as the VCSEL mirrors do not have to be cleaved. The VCSEL’s output beam is

also circular rather than elliptical (shown in Figure 5.8), and its divergence angle is very

small (approximately 6°) compared to that of the edge-emitting laser (approximately 60

degrees). Obviously, a less divergent, circular beam is easier to work with and to

manipulate according to the designer’s needs. Table 5.1 shows a comparison between

the VCSEL and the Edge Emitting Laser [C1].

Figure 5.8: Output beam of VCSEL

Table 5.1: VCSEL VS Edge Emitting Laser

Edge Emitting Laser VCSELs1. Very divergent beam. Harder to

manipulate beam.2. Astigmatic beam; hard to correct3. Emission parallel to surface4. Large cavity length. Supports multi-

modes. May cause chromaticaberration in imaging systems

5. More expensive to manufacture6. Same Driver Voltage (1.8V) as VCSEL

but higher Current (40-60mA). Lasernot power efficient.

1. Small divergent beam due to largeraperture. Easier to work with.

2. Symmetric Beam – easy to workwith

3. Emission perpendicular to surface4. Short cavity length. Supports only a

few longitudinal modes. Has manytransverse modes.

5. Cheaper to manufacture.6. Low Driver Voltage (1.8V) and

Current (15mA) makes for a morepower efficient laser


5.4 OPTICAL OPTIMISATION

This section deals with the ABCD Matrix Method employed to optimise the optical

design. Optimisation is a very broad term and must be defined exactly to ensure that the

optimisation goals are achieved.

5.4.1 Goal One: Beam Collimation

The first goal is to achieve a collimated beam to monitor the system and to determine its

maximum spot size using optical theory.

To collimate a Gaussian Beam, the divergence of the source should be as small as

possible. Thus, the maximum distance between the source and Lens 1 and the detector

and Lens 2 should equal that of the lenses’ focal length [O1][N1].

The maximum spot size is inhibited by the clear diameter (aperture), D of the lens. This

clear aperture must be at least 1.5 times the lens’s spot size, wL to intercept 99% of the

incoming intensity [V1]. That is:

The lens 4 being used has a D = 2.5 cm. Thus, the maximum collimated beam achieved

for this system is a spot size of 1.67 cm. The relationship between the source and spot

size at Lens 1 is shown in Figure 5.9.

5.1

DwL ⟨ (13)

Source

wL1

d1

θ/2

Figure 5.9: Approximate Relationship between source and Lens 1


The approximate distance from the source to Lens 1 (d1) is calculated using the

tangential rule. Thus:

where: θ/2 is the half-divergence angle = 7.255°

Using equation (14), d1 equals 13.1 cm. This exceeds the focal length of the lens and

thus does not satisfy the condition for a collimated beam. Hence, the largest possible

distance between the source and the lens is 10cm that results in a beam spot size of

1.27cm.

5.4.2 Goal Two: Optimising system’s performance

The second goal is to achieve an optimal system performance by focussing the beam on

to ninety per cent of the detector.

The Gaussian’s intensity beam profile is infinite, as shown in Figure 5.10. However,

most of the profile falls between the 1/e2 points. Thus, the Gaussian beam’s irradiance

profile should focus on at least 1-1/e2 = 86.47% (90% is used) of the detector.

Therefore, the beam width at the detector is 0.9 * 2mm = 1.8mm.

4 There was no choice of lenses due to the department’s tight financial situation. A better lens could havebeen chosen which would have given a large spot size at Lens 1 and thus have increased the monitoringdiameter of the beam

=∴

=

2tan

2tan

11

1

1

θ

θ

L

L

wd

d

w

(14)


Figure 5.10: Intensity profile of Gaussian Beam

5.4.3 ABCD Matrix Method: Achieving the goals

The ABCD Matrix Method is used to calculate the system parameters to satisfy the two

optimisation goals of 5.3.1 and 5.3.2. The known and unknown parameters of the

system can be found below in Table 5.2:

Table 5.2: Known and Unknown Parameters

Parameter Meaning of Parameter Value KnownValue?

UnknownValue?

w0 Beam width at source 6µm yesw1 Beam width at detector 0.0018m yesλ0 Laser Beam Wavelength 850nm yesd1 Distance from source to Lens 1 0.1m yesd2 Distance from Lens 1 to Lens 2 yesd3 Distance from Len 2 to detector yesf Focal Length of Lens 1 and Lens

20.1m yes

The two optimisation goals specified crucial information needed to solve the unknown

parameters of the system. Goal one, beam collimation specified the distance d1 between

the source and Lens 1 whilst goal two, optimising the system’s performance specified

the beam width at the detector.

The ABCD matrix method incorporates Gaussian Beam Theory and relates the q

parameter of one point of the optical system to the other (see Appendix Three). Using

the ABCD Matrix approach, the optical system is transformed from a two dimensional


(x-y-axis) to a one dimensional system (x-axis). The two dimensional system was

presented as Figure 4.1 in the previous chapter. The one dimensional optical system is

shown in Figure 5.11. The planar mirrors used have no effect on the beam’s profile.

Therefore, they are not incorporated in this analysis.

Figure 5.11: 1D Optical System

The system consists of five building blocks:

1. Block One: free space of distance d1

2. Block Two: collimating lens of focal length f1

3. Block Three: free space of distance d2

4. Block Four: converging lens of focal length f2

5. Block Five: Free space of distance d3.

A relationship exists between the VCSEL laser source and the detector based on the

following two assumptions:

1. The laser beam emitted from the source is a Gaussian Beam

2. The VCSEL transverse mode is a basic TEM00 mode and other higher order

modes are ignored.

The combined ABCD matrix known as the combined transmission matrix is:

(15)

−++−

+−

+−+−+−−

−+−−

=

−

−

=

=

f

d

f

dd

f

d

f

d

f

df

ddd

f

dd

f

ddd

f

dd

f

ddd

f

d

f

dd

f

d

f

d

ff

TTTTTDC

BABLOCKBLOCKBLOCKBLOCKBLOCK

COMBINED

22211

22

221

331

23212131

13

23223

123

12345

122

1

10

d11

101

10

d11

101

10

d1


where: T is the transmission matrix.

The waist of the Gaussian beam must be at the surface of the VCSEL since the phase

across the output aperture of the VCSEL is approximately constant [V1]. Thus w0 ≈ a,

where a is the radius of the VCSEL. The q parameter, which relates complex beam

parameters of one plane to another plane ,is given by:

where: z is the distance from the waist

R(z) is the radius of curvature

λ is the wavelength of the VCSEL, 850nm

The reciprocal of the q factor is easier to work with. Thus, (q(z))-1 becomes:

Assume that the beam has a planar wavefront (i.e. R(z) = ∞) at the source and detector.

The inverse of qsource is:

The reciprocal of qdetector for R(z) = ∞ is given by:

(16)

(17)

(18)

(19)

( )λ

π 20)(

wjzRzq +=

20)(

1

)(

1

wj

zRzq πλ

−=

20

1

aj

q source πλ

−=

( )2detdet 1

1

1

ector

source

source

ector wj

qBA

qDC

q πλ

−=

+

+

=


The left and right hand side of (19) are separated into their real and imaginary

components and then equated. Two equations and two unknowns, d2 and d3 are

obtained. It is expected that d3 should be less than the focal length of the lens. If d3

were to equal this focal length, the beam width at the detector would only be a point.

The specified width set by optimisation goal 2 and the system’s optimal performance

would not be achieved. Consequently, the system’s performance would not be

satisfied..

A program called Mathematica is used to solve for d2 and d3. The Mathematica code

can be found in Appendix Four. The resulting parameters calculated using Mathematica

are:

d2 = 1.51m

d3 = 0.085m

These results are valid since d3 is less than the focal length of the lens and d2 is

mathematically determined by d1, f, d2, w0 and w1.

5.5 ATTENUATORS

Attenuators are used to simulate an increase in the monitoring distance of the alarm

system without physically expanding the system. The attenuators accomplishes this by

limiting the amount of light passing through the device. The direct relationship between

transmission percent and monitoring distance is:

where: MD is monitoring distance (metres)

TP is the overall transmission percent (%)

(20)

TPMD

%1005.1 ×=


Light transmission through the attenuator is directly proportional to the wedge distance

of the device. Transmission percentages less than 5% are obtained by placing two

attenuators in series. The overall transmission percentage is then:

where:TP1 and TP2 are the transmission percentages of attenuators one and two

respectively.

5.6 THEORETICAL POWER NEEDED TO EXTEND BEAM

LENGTH

The electrical input power of the VCSEL required to extend the system’s Beam Length

is calculated by analysing the system’s components in a backward fashion, starting from

the detector and progressing through to the source [W2]. The steps undertaken are

outlined below in Table 5.3. The absorption of oxygen and water vapour are also

included for a monitoring distance of 600m [H2]. This ensures that the calculation is

accurate for conditions in harsh wet environments.

(21)21 TPTPTP ×=


Table 5.3 Method of calculating VCSEL’s electrical Power for increased BeamLength

OpticalComponent/Loss

Parameter of Interest Calculation Method

1 Detector Electrical OutputPower (Pelec)

5

Detector Gain (Av) 6:

Pout = LiAv (22)

Av = 386

3 Mirrors Reflective Loss (RL) RL = (1-(mirror absorption coefficient))3 (23) = (1-0.1)3

= 0.7292 Lenses Fresnel Loss between

glass-air interface (FL)7

FL = (FL1 lens)4 (24)

= (1 – ((nair – nglass)/(nair + nglass))2)4

= 4(1 – ((1 – 1.5)/(1 + 1.5))2)4

= 0.85AbsorptionCoefficient of O2

AbsorptionCoefficient of O2 atλ=850nm (τoxygen) for600m

τoxygen= 0.96

AbsorptionCoefficient ofwater vapout

AbsorptionCoefficient of watervapour at λ=850nm(τwv) for 600m

τev= 0.7

OpticalComponent/Loss

Parameter of Interest Calculation Mehtod

TransmissionPercentages ofAttenuators

TransmissionPercentages TPtotal

TPtotal=TP1.TP2 (25) =1% = 0.01

Source Optical Output Power(Poptical)Electrical Input Power(Pelec)

Poptical = Li/ (total system losses) (26) = Li/((TPtotal)(RL) (FL) (τoxygen)(τev))Pelec = Poptical/ηwp (27)

5 Li is defined as the incident optical power on the detector.

6 This voltage gain was calculated when the VCSEL was operating at 13mA and only 1 per cent of lightwas allowed through by the attenuators. At this current, the incident optical power was 0.00648mW andthe output electrical power was 2.5mW. It was found that when the VCSEL’s operating current wasaltered, the detector’s gain did not change.

7 For each lens, there are two losses:1. Fresnel loss of incoming light to the lens from air to glass2. Fresnel loss of outcoming light from the lens from glass to air


The theoretical electrical VCSEL input Power required to monitor 600 metres and

surpass conventional monitoring distances is 14.14mW.8 This power is remarkably low

due to the extremely high sensitivity of the receiver (see Section 7.3).

5.7 CONCLUSION

This Chapter has outlined the optical design theory and optimisation methods involved

for an infrared alarm security system. It showed the advantages of VCSELs over edge

emitting lasers. These advantages included smaller beam divergence, high power

efficiency and cheaper manufacturing costs. The ABCD Matrix method was introduced

to calculate the optimal beam parameters. It was found that d1 was 10cm, d2 was 1.51m

and d3 was 8.5cm. These values were to be expected. The chapter also outlined the

procedure used to calculate the VCSELs electrical input power for a monitoring

distance of 600 metres. It was found to be 14.14mW, a remarkably low input power.

8 This value was calculated using a wall-plug efficiency of 11% (see Section 7.2) and an Li of0.00648mW.


CHAPTER SIX

ELECTRICAL DESIGN


• Explain the electrical components of the active infrared alarm security

system specified in Chapter Four

• Stress the importance of the electrical simulation programs PSPICE and

LogicWorks in the design process

• Discuss the VCSEL Driver, Receiver Circuit, Power Supply and Alerting

Apparatus.

6.2 IMPORTANCE OF CIRCUIT SIMULATION

6.2.1 PSPICE

SPICE is an acronym for Simulation Program with Integrated Circuit Emphasis. The

program was developed by the Electronics Research Laboratory at the University of

California in the early 1970s [H1]. An enhanced version, called PSPICE Version 8, by

Microsim, is used for this thesis.

The simulation of an electronic circuit using PSPICE is a crucial step in the design

process for analogue circuits. It can save hours of time and money otherwise spent in

prototyping. However, PSPICE should not be used as a substitute for traditional circuit

design.

A Pspice program consists of the following [H1]:


1. Program Title

2. Comment statements denoted by *

3. Component statements that describe the circuit topology

4. Model statements that give device parameters

5. Analysis requests

6. Output requests

7. End Statement

6.2.2 LogicWorks

LogicWorks is designed by Capilano Computing Systems Limited. Version 3.0.2 was

used for the simulation. LogicWorks is a simulation program for digital circuits. The

circuit’s operation can be observed by placing logic probes at both inputs and outputs of

the circuit. It is an imperative design tool and can save hours of time otherwise spent

breadboarding.

6.3 VCSEL DRIVER

The VCSEL Driver Circuit is shown in Appendix Two. A photograph of the circuit can

be found in Figure 6.1. The circuit is designed to drive a VCSEL at 1.85V and 13 mA

from a five volt battery power supply. A potentiometer is used to vary the constant

output current. The laser driver consists of a modulator cascaded with a constant

current source.


Figure 6.1: Photograph of Driver Circuit

6.3.1 Timer Chip

The timer is a TLC555 CMOS chip that modulates the VCSEL’s output current at 1kHz

and 50% duty-cycle. The oscillation frequency and duty-cycle are found by:

1. Specifying a capacitor value, C

2. Solving the following two equations:

where: D is the duty cycle (%)

F is the oscillation frequency (Hz).

C is chosen to be 0.1 µF and R1 and R2 equal 330 Ω and 5.7 kΩ respectively.

(28)

(29)

( )CRRF

21 2

44.1

+=

21

2

2RR

RD

+=


6.3.2 Constant Current Source

An operational amplifier configuration is used as the constant current source. The

summing-point constraint, v- = v+ is used to obtain the constant current expression. The

steps taken to arrive at this expression are outlined below:

where: Rsh = Pot1A (from Figure 5.1),

Vsh is the voltage at the transistor’s base

Vcc is the +5V Power Supply

V- is the inverting input of the opamp

V= is the non-inverting input of the opamp

Thus, by varying the potentiometer, a current range from eight to thirty milliamperes is

obtained.

The PSPICE program can be found in Appendix Seven. The output current waveform

is depicted in Figure 6.2 for 15 mA of current.

(31)

(30)

(32)

(33)

(34)

( )

( )5

4

4

5

87

8

54

4

54

5

,

RV

VVRi

R

RVR

vvEquating

R

VVi

RR

RVv

RR

RVV

RR

RVv

i

shccout

ish

sh

shccout

cc

shccin

−=∴

=

=

−=

+=

+−

++

=

+−

+

−


6.4 RECEIVER CIRCUIT

The Receiver Circuit comprises of three components:

1. a Silicon IR Light-to-Voltage Sensor

2. a Precision full-phase wave rectifier

3. an Inverter with Schmitt Trigger input.

Figure 6.2: Current Output Waveform of VCSEL driver

An additional fourth component, the battery power supply has also been designed and

prototyped successfully9.

A flow chart of the receiver’s operation is shown in Appendix Seven. The receiver

circuit is shown in Appendix Two. A photograph of this circuit can be seen in Figure

6.3.

9 The battery power supply has not been placed on the final receiver PCB due to time constraints.


Figure 6.3: Photograph of Receiver Circuitry

6.4.1 Silicon IR Light-to-Voltage Sensor

The Silicon detector (TSL261) is a light-to-voltage optical sensor and contains an 8MΩ

photodiode and a transimpedance amplifier. This device outputs an amplified voltage

signal of the output laser. The TSL261 is an ideal alarm system detector because of its:

• high sensitivity (irradiance responsitivity of 23 mV/(µW/cm2)

• fast response time (90 µs)

• in-built visible light cut-off filter to ensure only infrared light is detected

• in-built amplifier with a voltage gain of 10.

6.4.2 Precision Full-Wave Rectifier

The precision full-wave rectifier can be considered as two functional blocks cascaded

together. This is shown by Figure 6.4. Op-amp X1 and its associated components

produce a half-wave rectified version of the input signal at point A. Op amp X2 and its

associated resistors form a summer circuit [H1]. The output voltage is given by:

Where: v0 is the full-wave rectified signal.

(35)Ain vR

Rv

R

Rv

1

2

1

20

2−−=


Figure 6.4: Breakup of Precision full-wave rectifier

The precision full-wave rectifier converts the voltage square wave into a constant DC

voltage output. This is shown by the PSPICE simulation in Figure 6.5 when the peak

input voltage equals 2 V. Note that the DC voltage is only half the peak modulation

voltage. Increasing the resistance of the potentiometer, R8 (refer to schematic in

Appendix Two), boosts the DC voltage.

Figure 6.5: PSPICE simulation of full-wave precision rectifier


6.4.3 Inverter with Schmitt Trigger Input

The output of the precision full-wave rectifier feeds into the inverter with a Schmitt

Trigger input. The inverter is used to give a high output signal when there is no input

signal at the receiver. That way, the Alerting Apparatus is triggered when the beam is

broken. The opposite happens when the receiver detects an input: the output is low and

the alerting apparatus is not activated. This is shown in Table 6.1.

Table 6.1: Receiver’s Logic

Is monitoring beam broken? Input signal (V) Output signal (V)No High10 0Yes Low 4.5

The transfer characteristic of the inverter with a Schmitt trigger input is shown in Figure

6.6. This circuit displays hysteresis because the switching threshold is different for an

increasing input compared with a decreasing input [H1]. Due to hysteresis, noise added

to the input signal does not cause unwanted multiple transitions of the output assuming

that the peak-to-peak noise is less than the width of the hysterisis zone [H1].

Figure 6.6: Transfer characteristic displaying hysterisis

10 The input voltage depends on the positioning of the detector and the light transmission characteristicsthrough the attenuators. Thus a specific voltage can not be stated. Chapter Six discusses the detectorvoltage under specific attenuator transmission settings.

Input Voltage

Output Voltage

+4.5V

0V

Vth1=1.5V Vth2=2.0V


6.5 BATTERY POWER SUPPLY FOR VCSEL DRIVER AND

RECEIVER

The Battery Power Supply is shown in Appendix Two. The MAXIM 631, a step-up

converter, is used to boost 3 V input Voltage from two C batteries in series to 5 V @

100 mA. The laser driver draws 88 mA, whilst the receiver and Alerting Apparatus

only draw 50 mA. Due to this low current consumption, the battery life is prolonged

(7750 mA hours [F1]). An ON/OFF switch is used to activate the power supply. The

LED power indicator light is activated when the Power Switch is turned on. Both the

laser driver and receiver draw currents less than 100mA.

6.6 ALERTING APPARATUS

The alerting apparatus is a digital circuit that drives a buzzer when the beam is broken.

The buzzer’s output is 76 dB at 30 cm away from the source. Once the beam refocusses

on the detector, a counter is activated.11 This ensures that the buzzer is active for an

additional amount of time (the delay time), to warn the intruder and others that a break-

in has occurred. The delay time is determined by the clock frequency, 0.375 Hz and is

given by:

)(16)( HzfrequencysTimeDelay ×=

The alerting apparatus is shown in Appendix Two. A photograph of the durable casing

of the alerting apparatus can be found in Figure 6.7.

11 The counter was simulated using a program called LogicWorks. The disk containing the file a:\countercan be found in Appendix Seven.

(36)


Figure 6.7: Durable Casing of Alerting Apparatus

6.7 CONCLUSION

This chapter has dealt with the electrical design of the alarm security system. The

transmitter consisted of a modulator cascaded to a constant current source. The receiver

rectified the input modulation signal by using a full-wave precision rectifier. The

alerting apparatus was a digital circuit that had a specified delay time to alert the

intruder that the beam had been broken. A power supply was also presented that

regulated 3V DC to 5V DC. Throughout the design process, the importance of PSPICE

and LogicWorks were shown as imperative simulation tools in the prototyping stage of

electrical design. The utilisation of these tools maximised time efficiency.


CHAPTER SEVEN

RESULTS AND DISCUSSION


• Present an analysis of the security alarm system and its components

• Analyse the performance of the VCSEL and detector

• Determine the system’s maximum monitoring distance by evaluating the

detector’s noise equivalent power for an operational VCSEL current of

13mA12

• Determine if the system’s specifications were achieved.

7.2 VCSEL PERFORMANCE

7.2.1 Far Field Distribution and associated full angle beam divergence

The Far Field Distribution of the VCSEL (driven at 13mA) is used to calculate the

divergence of the laser beam. The VCSEL is placed on a rotating stand and its beam is

directed towards the pinhole. The angle positioning of the VCSEL and the laser’s

output power behind the pinhole are then measured13. This setup is shown in Figure 7.1.

12 13mA was chosen as it gave the maximum allowable current at the detector of 10mA.

13 The pinhole ensures that the optical wattmeter detects the beam’s maximum irradiance.


Figure 7.1: Setup for measuring the far field distribution

A polar plot of the Far Field distribution can be found in Figure 7.2. The full angle

beam divergence θ is the angle subtended by the 1/e2 diameter points for distances far

from the beam waist i.e. the far field region [G3]. The divergence angle for this VCSEL

is 14.51°. This angle is very small. Therefore, it is much easier to collimate the

VCSEL’s beam and maintain an almost parallel monitoring width.

Thus the low beam divergence of the VCSEL reiterates that this laser is an outstanding

source for an active infrared alarm security system.

Figure 7.2: Polar Plot of the Far Field Distribution

Optical Wattmeter

Probe

VCSEL RayRotating Stand

VCSELPin Hole Setup


7.2.2 DC Electrical and Optical Characteristics

The electrical and optical characteristics of the VCSEL measured were:

1. output Voltage, V (V)

2. output Current, I (mA)

3. output Optical Power, L (mW)

4. wall-plug efficiency, ηwp (%)

They are shown in Figure 7.3. The V-I-L curve was measured by recording the voltage

across the VCSEL as the current was varied; the L was obtained by placing an optical

power metre (ANDO AQ-135E) as close as possible to the VCSEL. The optical power

readings were then taken as the current was varied.

The wall plug efficiency was calculated using the following formula:

Figure 7.3: VCSELs V-I-L-ηηwp relationship

(37)

ηwp

L

V

DC I-V-L-Wallplug Efficiency

0

2

4

6

8

10

12

0 5 10 15 20 25

Current (mA)

Volta

ge (V

)W

allp

lug

Effic

ienc

y (%

)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Opt

ical

Out

put P

ower

(mW

)

V

ηwp

L

I-V-L-ηηwp VCSEL Characteristics

%100

%100

×=

×=

VI

L

PowerinputElectrical

Lwpη


From the graph, an optimal wall-plug efficiency of 11.4% was obtained at 14mA drive

current. This is a quite a respectable efficiency for lasers today [S3] The threshold

current and voltages14 are 3.6mA and 1.45V. These small threshold values indicate the

beauty of the VCSEL’s low input electrical power capacity and demonstrate why this

laser is such a superb alarm source.

7.2.3 Spectrum Analysis

A spectrum analysis was taken for the VCSEL. The set up is shown in figure 7.4. The

spectrum can be found in figure 7.5. The laser was driven at 13mA constant current.

The output signal from the amplifier was taken to an RF Spectrum analyser, the

ADVANTEST R4131D.

Figure 7.4: Experimental setup for Spectrum Analysis

14 The threshold values are the minimum values required for lasing to occur.


Figure 7.5: VCSEL’s Spectrum

Two TEM (transverse electric and magnetic) modes exist in the VCSEL’s spectrum:

1. The fundamental mode – TEM00 at a wavelength of 858.14nm;

2. The first transverse mode – TEM10 at a wavelength of 858.29nm.

The mode patterns are shown in Figure 7.6.

Figure 7.6: Mode Patterns

Thus, the laser is multimode.

Spectrum Analysis

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

856.5 857 857.5 858 858.5 859 859.5 860 860.5

Wavelength (nm)

Sp

ectr

al In

ten

sity

(A

rbit

rary

Un

its)


7.3 SYSTEM AND RECEIVER PERFORMANCE

The infrared system is designed around the characteristics of the infrared detector. This

section discusses seven issues pertaining to the effectiveness of the system’s and

receiver’s performance. The results were taken for a driver VCSEL current of 13mA, a

room temperature of 22°C and a monitoring distance of 160m15. The issues are:

Issue One: The system’s limits that results when the VCSELs’ signal voltage

is equal to the detector’s noise voltage

Issue Two: The signal obtained per unit radiant power falling on the detector

Issue Three: The width of the monitoring beam

Issue Four: The system’s response time

Issue Five: The safety of the system

Issue Six: System’s Durability

Issue Seven: System’s Cost

7.3.1 Noise Equivalent Power: Determining the Limts

The Noise Equivalent Power, NEP, is used to calculate the system’s monitoring limit.

The NEP is the input optical power at the detector when the detector’s Signal to Noise

Ratio is equal to 1 [I1] [K1][G2].

The noise equivalent power, NEP, is given by:

15 The results taken in this section were for a simulated monitoring distance of 160m. This monitoringdistance is due to the series combination of attenuators that only allow 1% of light transmission throughfrom the laser to the detector.

( )1-mW.Hz 1

fV

VEANEP

S

ND

∆

= (38)


where: Ad is the area of the detector = 0.5 mm2

VN is the noise voltage = 0.25nV @ 1 kHz

VS is the VCSEL DC signal voltage = 1.85 V @ 13 mA

∆f is the bandwidth = 1000 Hz

E is the irradiance (mW/mm2) = 0.01296 mW/mm2

Thus, by substituting these values into equation (38), the NEP is equal to 0.5473µW.

This NEP value is very good and indicates that only a small amount of incident optical

power is required at the receiver to effectively detect a signal.

The maximum monitoring distance is calculated by considering the system losses and

the absorption coefficients of oxygen and water vapour. The calculation assumes an

input VCSEL current of 13mA. It is based on the same methodology used in Section

5.6.

The maximum VCSEL input electrical power at 13mA driver current is 24.05 mW (i.e.

Operating Current multiplied by output Voltage). The VCSEL’s output optical power

is calculated by multiplying the laser’s incident electrical power by its wall-plug

efficiency, 11% at 13mA. This gives an output optical power of 2.645 mW.

Alternatively, this value could be interpolated from Figure 7.3

Now that the optical power of the source and the incident power of the detector are

known, the total losses throughout the system (System Losses) can be calculated. This

is shown in (39).

0.0002 645.2

5437.0

=

=

=

mW

W

LaserOfPowerOpticalOutput

DetectorOfPowerElectricalInputLossesSysteml

µ (39)


This value is to be expected. It incorporates losses associated with the attenuators (loss

of 1%), absorption coefficients and optical components.

Next, the system losses neglecting absorption by oxygen and water vapour are

considered. They can be calculated from Table 5.3. These losses are:

1. Reflective losses of the mirror = 0.729

2. Fresnel losses associated with the thin lenses = 0.85

3. Transmission losses associated with the attenuators = 0.01.

All three losses are multiplied together to give system losses ex absorption of 0.0062.

Finally, the absorption losses can be calculated. This is done by realising that the

system losses are equal to the system loss ex absorption multiplied by absorption losses.

An absorption loss of 32% is calculated. This results in a staggering maximum

monitoring distance of approximately 950 metres with only 24.05mW of electrical

power supplied to the VCSEL. 16.

7.3.2 Responsivity of Detector

The responsivity, R of the detector is defined as the rms signal current Is per unit rms

radiant power P incident upon the detector. It is given by:

The responsivity is extremely high and is a strong player in the outstanding performance

of the system.

16 Fog and dust intervention have been neglected for this calculation

mWAmW

mA

L

IR

i

s

/2 00648.0

13

=

=

=

(40)


7.3.3 Width of Monitoring Beam

The monitoring beam width was obtained by viewing the collimated laser beam on an

infrared card and measuring its diameter. It was found to be 1.5cm. Even though this

is a reasonable size, the beam’s diameter could be increased by using a lens with a

larger focal length.

7.3.4 Response Time

The response time is the time taken for the Alerting Apparatus to activate when the

beam is cut. The system’s response time is in adherance with the Australian Standard

2201.3-1991. That is, the detector initiates an alarm as a result of the complete

interruption of the signal received for any period longer than 40ms and does not activate

the alarm for a period shorter than 20ms.

7.3.5 Safety Criteria

The allowable MPE to the eye is 0.24075 mW/mm2 according to AS/NZS 2211.1:1997 .

Working on the formula irradiance = input optical power (mW)/ocular surface area

(mm2), the calculation based on the premise of a cornea17 gives the following result for

a laser operating at 13mA:

Thus, if the laser beam intercepted a cornea, it would cause no problem to the eye. The

system would not harm the skin as its MPE does not exceed the skin’s MPE specified

by the Australian Standard AS/NZS 2211.1:1997.

17 The area of a cornea is 13.2mm2[W1]

MPE allowable

/189.0

2.13

5.2

2

⟨=

=

=

mmmW

mm

mW

A

pMPE

surfaceocular

laser

(41)


7.3.6 System’s Durability

The system’s durability is judged on:

1. Its overall sturdiness

2. It’s effectiveness in hot and wet environments

Addressing Issue One: The system’s shielding components for the laser driver and

alerting apparatus are made of a sturdy tough metal. This has been shown in the

Electrical Design Chapter. Due to time constraints, it was not possible to make a

similar casing for the detector. However, the receiver must incorporate a hard metal

casing if the prototyped product is to be developed to the commercial level.

Addressing Issue Two: It was impossible to expose the system to extreme weather

temperatures. However, the components used for this system were all capable of

functioning to their fall capacity under extreme temperature variations, from–10 to 65

degrees Celsius. Based on this, the system is expected to be highly resilient to dramatic

temperature changes and should work effectively. Dust particles from a dirty cloth were

used to simulate the beam intervention that small rain drops may have on the system..

The system was unaffected by these dust particles.

7.3.7 System’s Costing

The system’s cost can be found in Appendix One. The cost of the complete system is

$191.84. This is an extremely competitive price for a system that has low power

consumption and can monitor a distance of 950 metres.

7.4 CONCLUSION

All system’s specifications were met. The system improved on existing technology

through its durability and cost-effectiveness. The system also performed well under


simulated conditions of dust intervention and light transmission limitations imposed by

the attenuators. An excellent monitoring distance of 950 metres was achieved with a

low input power of 24.05 mW.


CHAPTER EIGHT

CONCLUSION

8.1 SUMMARY

This thesis has focussed on the design and implementation of an active infrared alarm

security system. The active infrared system was chosen over its passive counterpart

because it could operate in harsher environments. The system was measured to have an

excellent noise equivalent power, NEP of 0.5473 µW. This meant that only 0.5473 µW

of incident optical power on the detector was required to detect the VCSEL’s signal.

The system was capable of monitoring a distance of 950m (excluding fog intervention).

The system built consisted of Vertical Cavity Surface Emitting Laesr (6µm diameter)

driver circuitry, a system of mirrors, lenses and attenuators, a receiver circuit (Silicon

detector with a detection area of 0.5mm2) and alerting apparatus.

The thesis first considered the motivation for undertaking the design of an active

infrared alarm security system:

1. To realise the system’s industrial potential

2. To understand the commercial market and relevant Australian Laser and

Alarm Standards

3. To rise to the challenge of setting goals and successfully achieving them

4. For the fascination of integrating physical and optical principles into a usable

state of the art detection apparatus.

5. To capitalise on the drawbakcs of commercial systems

The thesis then reviewed current existing technology, and found that a niche existed in

the market that the active alarm system could exploit. It was found that existing


systems were very expensive and lacked durability. The new system is very cheap

($191.84) and has been designed to operate in very hot, wet, windy and humid

environments. This is because the system is an active infrared one and has strong

casing surrounding the vital components.18

Relevant Australian Laser Safety and Alarm Standards were reviewed. Specifications

were then set based on the system’s objectives, relevant Australian Standards and

drawbacks that exist in commercial active infrared systems. The maximum permissable

exposure to the cornea, 0.24075 mW/mm2 and the skin, 6580 mW/mm2 was not

exceeded by the system. Thus, the system design was safe.

The response time of the system adhered to the Australian Standard 2201.3-1991. That

is, the detector successfully initiated an alarm as a result of the complete interruption of

the signal received for any period longer than 40 ms and did not activate the alarm for a

period shorter than 20 ms.

Optical Design Theory and optimisation methods were presented. VCSELs were

compared to edge emitting lasers. VCSELs had a smaller divergent and symmetric

beam, were cheaper to manufacture and had a much lower power consumption than

their edge-emitting counterparts.

Optical Optimisation methods incorporated the use of the ABCD matrix law to calculate

the beam’s parameters. Optical optimisation dealt with beam collimation and optimising

the system’s performance. The beam was said to be collimated when the maximum

distance between the source and Lens 1 and the detector and Lens 2 equalled the lens’s

focal length. The system’s performance was optimised by focussing the beam on to

ninety per cent of the detector. In this section, a method was presented to calculate the

monitoring distance of 600 metres and surpass conventional monitoring distances.

System losses and absorption losses of oxygen and waver vapour were taken into

consideration.

18 A hard casing was not designed for the prototype detector circuit for this thesis. However, for the finalproduct, the hard case would be implemented with ease.


The system’s electrical design was discussed. Chapter Five stressed the importance of

circuit simulation programs such as PSPICE and LogicWorksas tools that maximised

time efficiency. in the design process. The VCSEL driver, receiver and alerting

apparatus circuitry were discussed in detail. A battery-powered supply for all three

modules was designed.

Chapter Six dealt with the system’s analysis. It was found that the VCSEL had a full

angle beam divergence of 14.51°. The threshold voltage and current of the VCSEL

were 1.45 V and 3.6 mA respectively. An optimal wall-plug efficiency of 11.4% was

achieved at 14 mA. The system was also analysed and a maximum monitoring distance

of 950 m was calculated when the Signal to Noise Ratio equalled one. The monitoring

distance of the prototype security system far exceeded the maximum limit of 600 m of

of commercial conventional systems.

In conclusion, the active infrared alarm security system was a success. It satisifed all

objectives and worked very effectively.

8.2 FUTURE WORK

Despite the success of the project, further work is possible to extend the capabilities of

the system.

A) Design an intelligent active alarm system that activates various alarm tones

based on the interruption time of the signal and distinguishes between pets

and intruders

B) Design hardware and software that constantly monitors the alarm system and

informs a host computer of its current status

C) Evaluate the extent to which dust particles, leaves, and loose soil particles

hinder the performance of the system and incorporate this into the maximum

monitoring distance of the system


D) Analyse and model the effect that varying detector size and VCSEL

diameters have on system performance

E) Design a flashing light that informs intruders that the system is activated.


REFERENCES

A1. Aronson, L.B., Lernoff, B.E., Giboney, K.S., “The Ideal Light Source for Data

Nets”, IEEE Spectrum, Feb., 1998, pp 43-53.

A2. AS 2201.3 – 1991, Intruder alarm system—Part 3: Detection devices for internal

use.

A3. AS 2201.4 – 1990, Intruder alarm system—Part 4: Wire-free systems installed in

client’s premises.

A4. AS 2201.5 – 1992, Intruder alarm systems—Part 5: Alarm transmission systems.

A5. AS/NZS 2211.1: 1997, Laser Safety—Part 1: Equipment classification,

reuirements and user’s guide.

C1. Choquette, K.D., Hou, H.Q., “Vertical Cavity Surface Emitting Lasers: Moving

from Research to Manufacturing”, Proc. IEEE, vol. 85, No. 11, Nov. 1997, pp

1730-1939.

C2. Cohen, M., Vertical cavity surface emitting lasers and their applications to

optical computing, Brisbane: [St. Lucia, Qld.], 1995.

D1. Desmarais, L., Applied electro-optics, Upper Saddle River, N.J. : Prentice Hall,

1998.

E1. Ebeling, K.J., Integrated optoelectronics : waveguide optics, photonics,

semiconductors, Berlin ; New York : Springer-Verlag, 1993.

F1. Farnell Electronics Catalogue, pp 4, 1998.


F2. Feinberg, G., “The Electromagnetic Spectrum,” The World Book Encyclopedia,

Field Enterprises , pp158-159, 1975.

G1. Gerrard, A., Introduction to matrix methods in optics, London ; New York :

Wiley, 1975.

G2. Gopel, W., Hesse, J., Zemel, J.N., Sensors : a comprehensive survey, Weinheim,

Germany ; New York, NY, USA : VCH, 1989.

G3. Guenther, R.D., Modern optics, New York : Wiley, 1990.

H1. Hambley, A.R., Electronics : a top-down approach to computer-aided circuit

design, Englewood Cliffs, N.J. : Prentice Hall, 1994.

H2. Hellwege K.H., Madelung O., “Physical and Chemical Properties of the Air,”

Landolt-Bornstein, vol 4-b, pp 138-142, 1998.

I1. Infrared Information and Analysis (IRIA) Center, The infrared handbook,

Washington : The Office, 1978.

K1. Kruse, P. W., Elements of infrared technology : generation, transmission, and

detection, New York : Wiley, 1962.

N1. Nussbaum, A., Geometric Optics : an introduction, Reading, Mass. : Addison-

Wesley Pub. Co, 1968.

O1. O'Shea, D.C., Elements of modern optical design, New York : Wiley, c1985.

P1. Pulnix America Inc., Unit 16, 35 Garden Road, Clayton, 3168 Victoria, Australia.

R1 RS Components Catalogue, July 1998.


S1. Sale, T. E., Vertical cavity surface emitting lasers, Taunton, Somerset, England :

Research Studies Press ; New York : Wiley, 1995.

S2. Saunders, G., retired army alarm system security specialist.

S3. Senior, J., Optical Fibre Communications, New York : McGraw-Hill Book,

1981.

T1. Tech Logistics, Inc. 955 Belmont Avenue, North Haledon, NJ 07508. Email:

[email protected].

V1. Verdeyen, J.T., Laser Electronics, Englewood Cliffs, N.J. : Prentice-Hall, 1995.

W1. Wolf T., The Anatomy of the eye and Orbit, New York: Prentice Hall, 1965.

W2. Wright, H.C., Infrared techniques, Oxford : Clarendon Press, 1973.


Appendix One: System Costing

A1.1 VCSEL Driver

DeviceDescription

Device Model Cost/Item ($) Supplier Number ofItems

Totalcost($)

VCSEL HFE4081 80.00 Honeywell 1 80.00Op-Amp 1 UA741 1.04 RS 1 1.04Modulator Chip TLC555 1.24 RS 1 1.24NPN Transistor 2N222A 0.74 RS 1 0.74Resistor 330 Ohm 0.14 RS 1 0.14Resistor 1k 0.14 RS 1 0.14Resistor 4.7k 0.14 RS 1 0.14Resistor 100 Ohm 0.14 RS 2 0.28Resistor 100k 0.14 RS 1 0.14Resistor 1k Pot 1.95 RS 1 1.95Resistor 47 Ohm 0.14 RS 1 0.14Diode 1N748A 0.75 RS 1 0.75Capacitor non-polarised

0.01µF 0.48 RS 1 0.48

Capacitor non-polarised

0.01µF 0.48 RS 1 0.48

TOTALCOST

$87.40

Table A1.1: Components and Costing of VCSEL driver

A1.2 Receiver

DeviceDescription

DeviceModel

Cost/Item($)

Supplier Number ofItems

Total cost($)

SiliconDetector

TSL261 5.55 RS 1 5.55

Op-Amp 2 LMC6042 4.99 RS 1 4.99SchmittTrigger

74LS14 0.90 RS 1 0.90

Resistor 1k 0.14 RS 3 0.42Resistor 33 Ohm 0.14 RS 1 0.14Resistor 47 Ohm 0.14 RS 1 0.14Resistor 1M Pot 1.95 RS 1 1.95Capcitorpolarised

100µF 0.48 RS 1 0.48

TOTALCOST

$14.57


Table A1.2: Components and Costing of Receiver

A1.3 Alerting Apparatus

DeviceDescription

DeviceModel

Cost/Item($)


Total cost($)

Buzzer Pico Buzzer 8.00 RSComponents

1 8.00

ModulatorChip

TLC555 1.24 RS 1 1.24

OR gates 74LS32 0.87 RS 1 0.87AND gates 74LS08 0.99 RS 1 0.99Inverter 74LS04 0.87 RS 1 0.87Counter 74LS161 1.77 RS 1 1.77

TOTALCOST

$13.74

Table A1.3: Components and Costing of Alerting Apparatus

A1.4 Battery Supply

DeviceDescription

DeviceModel

Cost/Item($)


Total cost($)

Step-Up DCto DCConverter

Maxim 631 12.25 Farnell 3 36.75

2 C batteries DuracellBattery

2.00 CrazyClarks

3 6.00

LED 3mm LED 0.282 Farnell 3 0.85ON/OFFSwitch

Double PoleDoubleThrow

2.50 Dick Smith 3 7.50

CapacitorPolarised

100nF 0.45 RS 3 1.35

Inductor 33µH 1.42 Farnell 3 4.26Resistor 47 Ohm 0.14 RS 3 0.42

TOTALCOST

$57.13

Table A1.4: Components and Costing of Battery-Power Supply

A1.5 Optical Components

DeviceDescription

DeviceModel

Cost/Item($)


Total cost($)

Mirror PlanarMirror

3.00 EngineeringOptics Lab

3 9.00

Thin Lens Focal lengthof 10cm

2.00 EngineeringOptics Lab

2 4.00


Holders Holders 6.00 EngineeringOptics Lab

1 6.00

TOTAL

COST

$19.00

Table A1.5: Components and Costing of Optical System

Total System Cost = $191.84


Appendix Two: Schematics

A2.1 VCSEL Driver


A2.2 Receiver


A2.3. Battery Power Supply


A2.4 Alerting Apparatus


Appendix Three: Gaussian Beams

A3.1 The Wave Equation

The Gaussian Beam concept arises from solving the time independent Helmholz Wave

Equation given by:

where: ψ is the Wave Function

k is the wave number

r is a cylindrical co-ordinate

One solution is:

where

where w0 is the minimum beam width of the Gaussian Beam

R(z) denotes the radius of the spherical equiphase surfaces.

k, is the wave number

(42)

(43)

(44)

(45)

(46)

02)(1

=∂∂

−∂∂

∂∂

zkj

rr

rr

ψψ

phase radial )(2

exp

phase allongitudin )(tanexp

factor amplitude )(

exp),,(

2

0

1

2

20

0

×

×

−

=

zR

kr-j

z

zkz--j

zw

r

w(z)

w

E

zyxE

-

( )

0

20

0

2

0

2

0

20

2

z

1

1)(

λπnw

z

zzzR

z

zwzw

=

+=

+=


z is distance from the waist of the beam

A3.1.1 Amplitude of Field

The amplitude of the field changes as the beam propagates along z. The 1/e point is

defined by w0/2, where w(z) is known as the beam width [V1]. Figure A1.1 shows the

origin of the phase front curvature. In this diagram, z is the distance from the waist of

the beam. Figure A1.2 shows the Gaussian beam profile of a TEM0,0 mode.

Figure A3.1: Origin of the phase front curvature

Figure A3.2: Gaussian beam profile of a TEM0,0 mode.


A3.1.2 Longitudinal Phase Factor

The Longitudinal Phase Factor shows that the phase of the wave travelling in the

positive Z direction is not constant. It is given by:

where k, the wave number of a uniform plane wave = wn/c.

The radial phase factor indicates that the lines of constant phase are spheres [C2]. Thus

for a plane perpendicular to the z axis, the phase is always varying. It is given by:

where R(z) denotes the radius of the spherical equiphase surfaces.

A3.1.3 Spot Size of Beam

The beam width, w(z), increases directly with the magnitude of z. The Spot size of the

beam occurs when w is at its smallest value. This is where z is defined to be zero. This

is illustrated in Figure A1.1.

A3.1.4 Divergence angle

The divergence angle is shown also in Figure A1.1 As the width grows as the wave

propagates, in the limit as z approaches to infinity, w(z) has a linear asymptote given by

[V1]:

where θ0 is called the Divergence or far field angle of the beam.

(47)

(48)

(49)

−=

0

1-tanz

zkzLφ

)(2/2 zRkrR =φ

nw00

2

πλ

θ =


A3.1.5 Higher order Gaussian modes

The Helmolz wave equation can be solved using Cartesian Coordinates to give higher

order modes for the gaussian beam. The solution is:

The Hermite polynomial of order m and argument u is given by:

A3.1.6 Q parameter

The Q parameter is the most important parameter for the analysis of an optical system at

any point in space using Gaussian beam theory. The two parameters which characterise

the Q parameter are:

1. beam width – w(z)

2. distance from the beam waist, z.

The Q parameter is given by:

(50)

(51)

(52)

( )( ) ( )

( )

( )

×

++−−×

+−×

=

z2R

krj-exp

tan)1(exp

exp)(

22,,

2

0

1-

2

220

,

z

zpmkzj

zw

yx

zw

w

zw

yH

zw

xH

E

zyxEpm

pm

( ) ( )m

umum

mdu

edeuH

2

2

1−

−=

( )λ

π 20)(

wjzRzq +=


A3.1.7 ABCD Law for Gaussian Beams

The ABCD Law for Gaussian Beams is an excellent tool for calculating parameters

such as beam width, lens focal length and spacing dimensions for an optical system.

The ABCD law relates the complex beam parameters q2 of a Gaussian beam at plane 2

to the value q1 at plane 1[V1]. Thus,

Consider the optical system shown in Figure A1.2. The system has one input ray and

one output ray. The input and output rays are specified by their heights y1 and y2 and

slopes y11 and y2

1 respectively measured relative to the optical axes [V1].

The output ray is a function of the input ray such that:

A Taylor series expansion is done on the above equation and only the linear terms are

kept. The constant terms disappear by choosing the correct optical axes orientations and

positions [G1]. Thus:

The ABCD matrix is called the transmission matrix. The ABCD matrix for free space of

length z is given by:

(53)

(54)

(55)

(56)

DCq

BAqq

++

=1

12

( )( )1

1121

2

11112

,

,

yyfy

yyfy

=

=

=

1

1

11

2

2

y

y

DC

BA

y

y

=

10

1

space free

z

DC

BA


The ABCD matrix for a thin lens of focal length f is given by:

The thin lens’ power, P is given by:

(57)

(58)

−=

1

101

lensthin fDC

BA

fP

1=


Appendix Four: Mathematica Code

*clears past entries*Clear[w0,w1,d1,z1,z,y,x,q0,lamda]

*Initialisation**sets d1 to 10cm*d1=0.1*sets lamda to 850nm*lamda=850 10^-9*beam width of VCSEL is 6um*w0=6 10^-6*beam width at detector is 1.8mm*w1=0.0018q0=-I lamda/pi w0^2pi = N[Pi,3]*focal length of lens is 10cm*f=0.1

*specify abcd matrix*a=1-d3/f-d2/f+(d2 d3)/(f f)-d3/fb=d1 - (d1 d3)/f - (d1 d2)/f + (d1 d2 d3)/(f f) - (d1 d3)/f + d3 - (d1 d2)/f + d2c=-2/f + d2/(f^2)d=-(2 d)/f + (d1 d2)/(f f) + 1 - d2/f

*define functions for q parameter*F[d1_,d2_,d3_,q0_,f_]:=c + d/q0G[d1_,d2_,d3_,q0_,f_]:= a + b/q0H[d1_,d2_,d3_,q0_,f_] := F[d1,d2,d3,q0,f]/G[d1,d2,d3,q0,f]Together[H[d1,d2,d3,q0,f]]x=ComplexExpand[H[d1,d2,d3,q0,f]]

*separate equation into its real part*MyRe[x_] := ComplexExpand[x /. I r_ -> 0]y=MyRe[x]

*separate equation into its imaginary part*z=x-yz1=Together[z/I]

*solve the equation*Solve [ y == 0, z1 == -pi w1^2/lamda, d2,d3 ]


Appendix Five: Data Sheets

A5.1 VCSEL Datasheet


A5.2 Silicon Detector Datasheet


Appendix Six: PSPICE Code

A6.1 VCSEL Driver Code

Analysis of VCSEL Driver*normal ciruit**transient analysis.TRAN 1MS 30MS*1kHz square waveform with 50% duty cycleVIN 1 0 PULSE (0V 1V 0SEC 1NS 1NS 0.0005SEC 0.001SEC)Vcc 100 0 5VD1 1 2 D1N914R4 2 3 100RR7 100 4 100kR8 4 0 100RR5 3 7 100kRPOT 100 7 500RR6 20 0 47RTR1 20 7 50 Q2N2222VGND 10 0 0VX1 4 3 100 10 50 UA741.model Q2N2222 NPN(Is=14.34f Xti=3 Eg=1.11 Vaf=74.03 Bf=255.9 Ne=1.307+ Ise=14.34f Ikf=.2847 Xtb=1.5 Br=6.092 Nc=2 Isc=0 Ikr=0 Rc=1+ Cjc=7.306p Mjc=.3416 Vjc=.75 Fc=.5 Cje=22.01p Mje=.377Vje=.75+ Tr=46.91n Tf=411.1p Itf=.6 Vtf=1.7 Xtf=3 Rb=10)* National pid=19 case=TO18* 88-09-07 bam creation.LIB C:\Eval.lib.PROBE.END

A6.2 Detector Code

Rectifier Circuit*transient analysis.TRAN 1MS 10MS*square wave input: 50% duty cycle at 1kHzVIN 1 0 PULSE (0V 2V 0SEC 1NS 1NS 0.0005SEC 0.001SEC)R1a 10 2 1kR1b 10 6 1kR1c 6 9 1kR1d 9 2 0.5kV2 5 0 0VVGND 4 0 0VVHIGH 8 0 5VD1a 9 7 D1N914


D1b 7 5 D1N914R2e 2 1 1kV1 3 0 0VC1 1 0 0.1uFXOP1 5 6 8 4 7 LMC6042A/NSXOP2 3 2 8 4 1 LMC6042A/NS.LIB C:\Eval.lib.LIB C:\Davin.lib.PROBE.END


Appendix Seven : Receiver Flow Chart Diagram

Turn Detector On

Is the receivedsignal high?

Yes

Rectify square wavesignal using a full-

wave rectifier

Limit rectified DCVoltage to 2V by

adjustingPotentiometer

Send 2V to inverterinput

Send low (0V) output ofInverter to input of Alerting

Apparatus

NoSend Low signal to

inverter input

Send High (4.5V) output ofInverter to input of Alerting

Apparatus


Appendix Eight: Accompanying Disk

This disk contains the counter that can be simulated in LogicWorks. The filename is

counter.cct.

infrared

Documents

alarm systems

critical system evaluation

active alarm source

davin brinersupervisor

foxit readercopyrightc

excepta of queensland

foxit software company

supervision of dr