Fiber Optics: Engineering from Global to Nanometer Dimensions

Prof. Craig Armiento

Fall 2003 1Armiento Intro to E.E.

Optical Fiber Communications

What is it?Transmission of information using light over an optical fiber

Why use it? Extremely high data rate and wide bandwidth Low attenuation (loss of signal strength) Longer distance without repeaters Immunity to electrical interference Small size and weight Longer life expectancy than copper or coaxial cable Bandwidth can be increased by adding wavelengths

Fall 2003 2Armiento Intro to E.E.

Electromagnetic Spectrum and Communication Services

0.8 1.6 m

Fall 2003 3Armiento Intro to E.E.

What is an Optical Fiber?

Made from silica glass Light is contained in an

inner core which is only 9 m in diameter

Very low loss of signal strength (0.3 dB per kilometer - which is 7%/km)

Despite being made of glass, fiber is strong and bendable!

Fall 2003 4Armiento Intro to E.E.

Basic Optical Link Design

Electrical-to-Optical Conversion

Optical-to-Electrical Conversion

Fall 2003 5Armiento Intro to E.E.

Using Wavelengths to Increase Capacity

Engineers can increase the information capacity between two locations by using extra wavelengths

All of the wavelengths are added to a single fiber

This is called Dense Wavelength Division Multiplexing (DWDM)

Eliminates the need for multiple fibers Each wavelength is generated by a

different source and carries its own data

The wavelengths dont interfere with each other when in the same fiber

Fall 2003 6Armiento Intro to E.E.

Information Capacities in Optical Fiber Each wavelength can carry a signal operating at 10

gigabits/sec (1010 bits/sec) A fiber can transport up to 64 different wavelengths

Each wavelength can carry 10 Gb/s Unlike electrical signals, optical signals inside the same fiber at

different wavelengths dont interfere with each other Each fiber can have an aggregate data rate of 640 Gb/s

This is 640,000,000,000 bits per second! This rate translates to:

10 million simultaneous telephone calls (64 kb/s each) Download the contents of the Library of Congress takes:

84 years using a 56 kp/s modem 0.22 seconds using the aggregate fiber rate

These rates can go much higher! Researchers have developed operation of 40 Gb/s per wavelength A fiber cable can contain as much as a hundred fibers Researchers are working towards hundreds of wavelengths

Fall 2003 7Armiento Intro to E.E.

Cable Size Comparison: Copper vs. Fiber

This is a standard copper cable used for telephone service. This carries about 300 phone calls

One of these fibers can carry up to 10 million telephone calls

Fall 2003 8Armiento Intro to E.E.

Fiber Optics Engineering Disciplines

Network Design Optical power levels, routing and switching

Communications Theory Multiplexing multiple data streams

Optical Physics Fiber design, optical component design

Material Science Fiber manufacturing, new materials for sources, detectors

Semiconductor Physics Designing lasers, photodetectors

Electronics High speed IC design for transmitter and receiver

Fall 2003 9Armiento Intro to E.E.

Optical Fiber is Everywhere!

Fall 2003 10Armiento Intro to E.E.

Optical Network DesignEngineering on a Global Scale

Designing fiber optic networks that carry information over thousand of miles How to get the photons to travel that far How to keep the bits of information intact Protocols to use analog or digital?

Designing fiber networks for different applications Telecommunications and data Cable TV Local Area networks e.g., campus network

Fall 2003 11Armiento Intro to E.E.

Managing Global Networks

Network Operations Center

Fall 2003 12Armiento Intro to E.E.

Attenuation vs. Wavelength

Optical fiber systems use sources and detectors that work in the near infrared wavelengths because fiber has the lowest losses

Fiber has losses as low as 0.2 dB/km. Coaxial cable has losses as high as 60 dB/km

Fall 2003 13Armiento Intro to E.E.

Manufacturing Fiber: Draw Tower

Fall 2003 14Armiento Intro to E.E.

Fiber Cables

Multi-purposeCable

SubmarineCable

Telephone Pole Mounted Cable

Fall 2003 15Armiento Intro to E.E.

Optical Sources Lasers are used as optical sources

Sufficient power for long distances Pure optical spectrum - single wavelength Can be modulated at high data rates (gigabits per

second) Designed to emit at infrared wavelengths from

1.3-1.55 m where fiber has the lowest loss Made from semiconductor materials and are

designed to couple light into the fiber core Semiconductor lasers are very different from more

conventional lasers such as CO2 and HeNe lasers

Fall 2003 16Armiento Intro to E.E.

Diode Lasers are Small!

Laser

Fall 2003 17Armiento Intro to E.E.

Component Manufacturing for Fiber Optics

Semiconductor devices such as ICs and lasers are produced in clean rooms

Semiconductor devices such as lasers are often made with very thin layers (

Materials Engineering

Example of layers grown with a spacing of 1.2 nm (10-9 m)

Thin layers of semiconductor materials are grown on an atomic level using MBE

Fall 2003 19Armiento Intro to E.E.

Packaging a Laser

Laser packaging requires submicron accuracy to align a micron size emitting spot to the core of a fiber. These parts must be soldered in place and keep their alignment for 20 years

Fall 2003 20Armiento Intro to E.E.

Microelectromechanical Systems (MEMS)

There is a new class of components micro-sized moving components for different applications

MEMS are fabricated in silicon using processes used in IC manufacturing

MEMS are used in many applications Air bags, biological analysis, fiber optics, etc

MEMS have been used to create tiny mirrors that can be used to switch and deflect light

Fall 2003 21Armiento Intro to E.E.

Optical Switch

Fall 2003 22Armiento Intro to E.E.

Optical Switching

Route optical communication signals without conversion to the electronic domain using microscopic mirrors based on MEMS technology

Fall 2003 23Armiento Intro to E.E.

MEMS: Miniature Motors

Fall 2003 24Armiento Intro to E.E.

MEMS Mirror Array for Projectors Digital Light Processing (DLP)

Texas Instruments

Fall 2003 25Armiento Intro to E.E.

Engineering on a Global to Nano Scale

Global Optical Networks A network engineer designs optical networks that transmit high speed data over

thousands of kilometers across continents and oceans The physical scale is 106 meters

Communication Equipment Design An equipment engineer must integrate high speed electronic ICs and optical

components into subsystems that are used in telecom centers The physical scale in on the order of a meter

Fiber and Laser Packaging A packaging engineer must design alignment accuracy on a scale of a micron

between the fiber core and laser emission spot The physical scale is 10-6 meters

Optical Component Design A component engineer can design quantum well lasers with device dimensions

of 1 nanometer (2 atoms thick!) The physical scale is 10-9 meters

Thats a range of 1015 !

Fall 2003 26Armiento Intro to E.E.