network iq training manual chapter 1 – fibre basics

Network IQ Training ManualChapter 1 – Fibre Basics

Optical Fibre Network IQ Training Manual 2

Fibre safety rules• Keep all food and beverages out of the work area. If fibre particles are ingested they can

cause internal hemorrhaging.• Always wear safety glasses with side shields to protect your eyes from fibre shards or

splinters. Treat fibre optic splinters the same as you would treat glass splinters.• Keep track of all fibre and cable scraps and dispose of them properly. If available, work on

black work mats and wear disposable lab aprons to minimize fibre particles on your clothing. Fibre particles on your clothing can later get into food, drinks, and/or be ingested by other means.

• Never look directly into the end of fibre cables – especially with a microscope – until you are positive that there is no light source at the other end – having tested it with a power meter. Use a fibre optic power meter to make certain the fibre is dark. When using an optical tracer or continuity checker, look at the fibre from an angle at least 6 inches away from your eye to determine if the visible light is present.

• Contact lens wearers must not handle their lenses until they have thoroughly washed their hands and Do not touch your eyes while working with fibre optic systems until your hands have been thoroughly washed.

• Keep all combustible materials safely away from the curing ovens and fusion splicers.• When finished with the lab, dispose of all scraps properly. Put all fibre scraps in a properly

marked container for disposal.• Thoroughly clean your work area when you are done.


Safety Precautions

• Chemical Safety– Isopropyl Alcohol is Flammable at 12.2°C and can cause irritation to eyes on

contact. In case of eye contact. flush eyes with water for at least 15 minutes

• Laser Handling Precautions:

– Communication System Laser Light is Invisible

– Viewing it Directly does not Cause Pain. The Iris of the Eye will not Close Involuntarily as when Viewing a Bright Light. Consequently. Serious Damage to the Retina of the Eye is Possible

– Should Accidental Eye Exposure to Laser Light be Suspected. Arrange for an Eye Examination Immediately

If any of Corning's procedural recommendations conflict with your company's safety procedures. Then your company's procedures should take precedence.


Safety Precautions

• Most sources are low-power and no great risk• High power sources might burn the retina with invisible light

Healthy Cornea Damage Retina Damage


New Classification of Lasers; IEC 60825

Class Output description Health/Safety Issues Example Sources

Class 2 Emits 400-700nm (visible) light. < 1mW (Continuous)

Blink reaction normally prevents damage. Many laser pointers. Unicam CTS laser

Class 2M Emits 400-700nm (visible) light Blink reaction normally prevents damage. but can damage if viewed with optical magnifier

Rifle site. laser pointer

Class 3B 315 - 1400nm. <500mW (contin)400-700nm. <30mJ (pulsed)

May damage eye if viewed directly or reflected light but not likely. Probability low to cause fire.

Industrial. military. medical lasers. Must have key switch and lock

Class 4 > 500mW Can burn skin and damage eye; may ignite materials

Industrial. military. medical lasers. Must have key switch and lock

• Lasers defined in terms of maximum permissible exposure (MPE) • Laser classification is a function of

– power (pulsed or continuous)– beam coherence– wavelength– safety containment around beam

• More details in reference slides


Fibre Handling Precautions

• Cleaved glass fibres are sharp and can pierce the skin easily.• Find all pieces of fibre so that they do not cause problems later.• Use tweezers to pick up pieces of the glass fibres and place them

on a loop of tape or in a plastic bottle. Dispose of them properly.• Wear gloves when stripping cable.


Cable Handling Precautions

• Fibre optic cable is sensitive to excessive pulling. bending and crushing forces.

• Do not bend cable more sharply than the minimum recommended bend radius.

• Do not apply more pulling force to the cable than specified.• Crushed. kinked or over-pulled cable. may be damaged and

require replacement of the cable.

Rule of Thumb – Minimum Bend RadiusDuring Installation > 15 x Cable ODRelaxed > 10 x Cable OD


Fibre versus Copper

Media Unrepeatered Distance

Bandwidth Voice Channels (per Cu pair or per fibre)

Typ. Cable Weight

Typ. Cable Diameter

Copper 2.5km 1.544Mbps(T-1)

24 5200kg/km(400pair)

60mm(400pair)

Fibre 100+ km 2.5 Gbps +(OC-48)

32.000 + 130kg/km (24 fibre)

11.6mm(24 fibre)

• Fibre cables transmit more information over longer distance– Fibre provides 1000x more bandwidth

and up to 100x longer links• Fibre cables are smaller and

lighter– Fibre cable with the same

information-carrying capacity (bandwidth) < 1% size. weight of equivalent copper cable


Fibre Anatomy

• Core: Carries the light

• Cladding: Keeps the light in the core

• Coating : protects the core & cladding

• Cannot separate core from cladding!

125μ

m

125μ

m

50μm

or 62.

5μm

8μm

Single-mode

Multimode


Fibre Anatomy in details

• The Core: is a thin filament made of glass or plastic, measured in micra ( 1µm = 0,000001m) where the light pass through. The larger the diameter of the core, the more light it can conduct.

• Cladding: Layer that revests the core. Since it has a refraction index lower than the core, it prevents the light from being refracted, hence allowing the light to reach the reception device.

• Coating: Plastic layer that revest the skin, protecting the optical fibre from mechanical shocks and excess of bending.

• Mechanic resistance fibres: Fibres that help to protect the core against impacts and excessive tensions during their installation. They are usually made of a material called kevlar, the same used on bullet-proof vests.

• Outer Jacket: Is the jacket that covers the optical fibre.


Types Of Optical Fibre

Single-mode:Allows only one mode (ray) of light to travelthrough the core

Multimode:Allows multiple modes (rays) of light to travelthrough the core


Multimode vs. Singlemode – Total Internal Reflection

MU

LTIM

OD

E

62.5

/125 For short

distance

Easy to work with

Used in LANs

MU

LTIM

OD

E

50/1

25 For short distance

Easy to work with

Used in LANs

Provides more bandwith than 62.5/125 at 850nm wavelength

SIN

GLE

MO

DE

9/

125 For long

distance

Difficult to work with

Used by Telecom Service provider, CATV companies

125

62.5

125

50

125

9

The physical properties of singlemode fibre offer very low attenuation over distance, which is why singlemode fibre is used to connect cities, campuses and wide area telephone and data networks. Multimode fibre cables experience more attenuation, or loss, per the same distance than singlemode fibre.

Typically Multimode fibre is used within buildings and to connect buildings together in a campus environment. Lastly, plastic optical fibre has the highest attenuation, or loss of light per distance compared to the glass fibre cable types mentioned above. For many applications the maximum distance for plastic fibre cable is less than 10 meters.


Principle of Operation - Index of Refraction

Index of Refraction is abbreviated with the letter nSpeed of Light = 299.792.458 m/s (186.282 miles per sec)

Index of Refraction1.01.00031.331.461.48

MediumVacuumAirWaterCladdingCore

Speed of Light in a Medium

Speed of Light in a VacuumIndex of Refraction (n) =


Refraction

n1 sin 1 = n2 sin 2 Refraction law

1 = Angle of incidence

2 = angle of refraction

refraction index n2

Interface

Medium 1

refraction index n1

Medium 2

1

1 2

2

first wavefront

second wavefront

Lot at the interface


Law of reflection

= ´ Law of reflection

= Angle of incedence

Interface

Medium 1

Medium 2

´

´ = Angle of reflection

In most cases, refraction and reflection occur simultaneously: Only a portion of the light is reflected thereby and the remainder enters on the

other medium (according to the law of refraction).

index of refraction n1

index of refracton n2

Lot on the interface


Totalreflexion

Wenn n1 > n2

dann existiert ein Einfallswinkel G für den der Brechungswinkel = 90°sin G =n2/n1

Für Einfallswinkel > G tritt die Totalrelfexion auf

G = Grenzwinkel

Grenzfläche

Medium 1

Medium 2

G ´G

Brechungsindex n2

Brechungsindex n1

> G ´ =

Lot auf der Grenzfläche


Wenn θ1 > θG Totalreflexion

Möwe erscheint hier

Wenn θ1 < θG Brechung

nLuft = 1.0003

nWasser = 1.33

sin θG = (nLuft/nWasser) θG ≈ 49°

θ ´

θ2

Wirkungsprinzip

θG

θ1 = Einfallswinkel

θG = Grenzwinkel

θ2 = Brechungswinkel

θ ´ = Ausfallswinkel

Fisch erscheint hier

θ1θ1


Total Internal Reflection

• If (ncore > ncladding) AND If critical angle not exceeded.

– THEN Total Internal Reflection occurs

• =


System Performance Parameters

• Light sources transmit light through the fibre at various

wavelengths

• As the light travels down the fibre. attenuation occurs

• As the light travels down the fibre. dispersion occurs

which affects bandwidth


System Performance Parameters

WAVELENGTH

is a characteristic of

light that is emitted

from the light source

and is measured in

nanometers (nm)

TYPICAL OPERATIONAL WAVELENGTHS

• 850 nm (MM)• 1300 nm(MM)• 1310 nm(SM)• 1550 nm(SM)


Attenuation - Definition

• Attenuation is measured in decibels (dB)

decibel (dB) = -10 log (Pout/Pin). Pout = Received Power Pin = Transmitted Power


Attenuation SamplesAttenutation in Decible Remaining power in %

0.1 97.7

0.2 95.5

0.3 93.3

0.4 91.2

0.5 89.1

0.6 87.7

0.7 85.1

0.8 83.2

0.9 81.1

1 79.4 ≈ 80

2 63.1

3 50.1 ≈ 50

4 39.8

5 31.6

6 25.1 ≈ 25

7 19.9 ≈ 20

8 15.8

9 12.6

10 10.0

20 1.0

30 0.1

40 0.01

Performance P in mW Performance in dBm

1 W +30 dBm

100 mW +20 dBm

10mW +10 dBm

5 mW +7 dBm

1 mW 0 dBm

500 µW -3 dBm

100 µW -10 dBm

50 µW -20 dBm

10 µW -23 dBm

1 µW -30 dBm

100 nW -40 dBm

10 nW -50 dBm

1 nW -60 dBm

100 pW -70 dBm

10 p W -80 dBm

1 pW -90 dBm

in dBm = 10lg


Types of Attenuation

Attenuation - measure of optical power loss.

Two Types of Attenuation:

1. Intrinsic 2. Extrinsic

- Absorption - Macrobending

- Scattering - Microbending


Spectral Attenuation Curve

850 1300/1310

1550

“Windows of Operation”

MM SM

WaterPeak1383 nm


Intrinsic Attenuation – Absorption and Scattering

Absorption - natural impurities in the glass absorb light energy.

Scattering - Light rays interact with glass on the atomic level

and are scattered into new pathways that may be lost

through the cladding.


Extrinsic Attenuation

• Macrobending – Loss due to large scale bending from external sources

Corning’s new ClearCurve® fibres are macrobend resistant through innovative barriers between Core and Cladding

- Single-Mode ClearCurve

- Multimode ClearCurve

(see reference pages for details)

Corning’s new ClearCurve® fibres are macrobend resistant through innovative barriers between Core and Cladding

- Single-Mode ClearCurve

- Multimode ClearCurve

(see reference pages for details)


Extrinsic Attenuation

• Microbending – loss due to small scale distortions– Small bend affecting the fibre eg. cable ties installed

too tight.


System Performance Parameters: Dispersion

Dispersion is defined as the spreading of a light pulse as it travels down a fibre

Bandwidth is defined as the amount of information that a system can carry such that each pulse of light is distinguishable by the receiver


Dispersion - Modal Dispersion

• In multimode fibre. an input pulse travels in different paths. called “modes”

• Each ball is a mode• All of the balls start from

the same pulse• Modal dispersion only

occurs in MM fibre


Dispersion - Effect on SignalAffects quality of the transmission-Bandwidth

1 0 1

1 1 1

logical information

electrical input signal

transmitted optical signal

received optical signal (with

dispersion)

electrical output signal

logical information

BIT ERROR


Optical transmitters

Beam Shape Source Name Light beam Power/ Speed Relative Cost

Light Bulb Light not directed or focused. rays travel many directions

Low power (in 1 direction)

Cheap

LED

Light Emitting Diode

Large cone of light. large spectral width

Low power. Max speed 622Mbps

Cheap

LASER

Light Amplification by Stimulated Emission of Radiation

Parallel beams. focused. very small spectral width

High power. very fast 10+Gbps

Expensive

VCSEL

Vertical Cavity Surface Emitting Laser

Well focused beam. small spectral width

Mid power. very fast: 10Gbps

Economical


Optical transmitters - Spot size

The spot-size and the laser launch are factors which affect the fibre-bandwidth.

cladding/125µm

LASERTx

VCSEL

LED

Tx

Tx

core/50µmcoatings/250µm

Spot size 4-10µm

Spot size 20-30µm

Spot size > 100 µm


Pros and Cons Optical Fibre vs Copper

Pros:• High bandwidth: Using wavelength

division multiplexing allows multiple 100 Tbit / s can be transmitted per fiber

• Low attenuation, high coverage: Without Optical Amplifier typical 100km, with optical amplifiers from several hundred to one thousand kilometers

• The attenuation in the optical waveguide, as opposed to copper conductors independent of the frequency of the transmitted signal

• Glass is an insulator: Allows Isolation between transmitter and receiver.

• Immunity to electro-magnetic interferences

• No signal radiation and thus relative privacy

• Use in hazardous areas is possible

Cons• Over fiber optic cabling no power supply

is available. Requires additional copper cabling

• Fiber optic cable can not be located, if it contains no copper.

• High requirements in connection technology: Plug wiring, splicing

• Measurement consuming• The components are still expensive


Summary

• Light signal travels in the core of the fibre.

• This is possible because the cladding IOR is less than the core IOR

• (ncore >ncladding)

• The light rays travel in paths called modes.

• Two types of fibre:• Multimode• Single-mode

• Optical signal loss (attenuation) is measured in dB (deciBel)

• Attenuation in fibre caused by:

• Intrinsic Characteristics: Absorption. Scattering

• External Characteristics: Macro/Micro- bends

• An optical pulse spreads as it travels through a fibre. Called Dispersion.

• Sources/Transmitters used in Fibre Systems• LEDs• VCSELs• Lasers

network iq training manual chapter 1 – fibre basics

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