Optical Communications (EPM755)

Prof Tong Sun (module leader and module lecturer)

– Office: C151

– Phone: 020 70408128; Fax: 020 70408568

– Email: t.sun@city.ac.uk

– http://www.staff.city.ac.uk/~tong

Mr Mohammad Karimi (lab supervisor)– Phone: 02070403641

– Email: mohammad.karimi.1@city.ac.uk

Course outline

– Part 1. Theory and Devices

– Part 2. Systems

List of Readings

Recommended books– Harry J. R. Dutton, Understanding Optical

Communications, Prentice-Hall, Inc. 1998

– Gerd Keiser, Optical Fiber Communications, third edition, McGraw-Hall, 2000

– John M Senior, Optical Fiber Communications Principles and Practice, second edition, Prentice Hall, Inc. 1992

– Jeff Hecht, Understanding Fiber Optics, fifth edition, Pearson Prentice-Hall, 2006

– Harold Kolimbiris, Fiber Optics Communications, Pearson / Prentice Hall, 2004

– Joseph C Palais, Fiber Optic Communications, fifth edition, Pearson Prentice Hall, 2005

Credit Assessment and Programme Specification (CAPS)

Module: 15 credit points

A typical pattern of a 15 credit module– 3 hours each week (lecture, tutorial) + lab

demonstration/coursework, total 10 weeks» Weeks 1-5 and week 7-11

» Week 6 is a reflective week

– 7 hours of private study per credit point

Lab sessions (CG17)– Group 1: 11:00-13:00, 22 Feb + 1, 8, 15, 22 March

– Group 2: 11:00-13:00, 25 Feb + 4, 11, 18, 25 March

Module Assessment

15 credit module (MSc)– 50% aggregate mark is required – Written exam: Lab work = 75%: 25%

Lab reports will be returned to students within three weeks after the submission, showing written feedback from the lab supervisor

Optical Communications

Theory and devices– Introduction to optical fibre communications– Optical fibre (optical communications channel)– Optical sources– Optical detection and optical receivers

Systems– Optical communications systems– System performance– System design and analysis

Cable Communications (1)

Modern Communications began with the invention of cables capable of carrying electrical signals

1839: first electrical telegraph built by Sir William FothergillCooke in England

Map of the 1858 transatlantic cable route

Cable Communications (2)

A number of inventions:

twisted pair cable (telephony, Ethernet)

coaxial cables (TV distribution, cable modem)

Coaxial cables

The Telephone (1)

Invention: Antonio Meucci, Charles Bourseul, Johann Philipp Reis, Alexander Graham Bell, Elisha Gray and Thomas Edison

The Telephone (2)

1896 telephone (Sweden)

The Telephone (3)

1987: ADSL (Asymmetric Digital Subscriber Line) technology is introduced to transport digital information as well as voice

ADSL Router by UTStarcom

Radio (1)

1897: Guglielmo Marconi established the world’s first radio station on the Isle of Wight, England

Equipped ships with life-saving wireless communications

Radio (2)

1901: Broadcast of the first transatlantic wireless signal

1954: US manufacturer Regency introduced the first transistor radio

Regency TR-1

Television (1)

March/April 1925: Scottish inventor John Logie Baird staged a three-week public demonstration of moving silhouette images captured by a ‘camera’ and shown on a monitor at Selfridges department store in London

1925: Baird successfully transmitted the world’s first greyscale television picture at a paltry resolution of 30 vertical lines per picture and 5 pictures per second.

Television (2)

1927: transmitted a long-distance TV signal between London and Glasgow through a telephone line

Television (3)

1928: first transatlantic television transmission from London to New York

1928: Baird invented colour television New trends: HDTV, IPTV, Interactive TV and

Mobile TV

Difference between standard definition and high definition

Satellite (1)

1945: The concept of geostationary satellite communications by British author Sir Arthur C Clarke was published in Wireless World

Satellite (2)

1965: COMSAT launched the world’s first commercial communications satellite, Intelsat 1, to orbit

Today some 350 communications satellites are stationed in the so-called ‘Clarke Orbit’

Engineers work on Intelsat I, a.k.a. Early Bird

Fibre Optics (1)

1965: Charles Kao and George Hockham (working for British firm Standard Telephones and Cables, now part of Nortel) demonstrated optical fibre principle to create new means of communications

Fibre Optics (2)

1970: US glass-making company Corning Glass Works manufactured the world’s first usable optical fibre for telecoms applications with an attenuation of 17 dB/km

1977: first telephone call was routed via a fibre link in Long Beach, California with a data throughout of 6 Mbit/s

Today: 15 Tbit/s with losses of less than 0.2dB/km

The Mobile Phone (1)

3 April 1973: Motorola’s Martin Cooper grabbed his shiny new, double-brick-sized DynaTAC prototype while walking the streets of New York and dialled the number of rival engineer Joel Engel, Bell Labs’ head of research

The Mobile Phone (2)

1983: First commercial version, a $4000 priced DynaTAC8000X, hit the market, starting the on-going trend of handset miniaturisation

The Mobile Phone (3)

1947: Bell Labs’ DH Ring proposed the use of hexagonal cells to form an interconnected network of transceiver base stations

1970: Bell Lab’s engineer Amos Joel invented a call handover method that allowed mobile phones to maintain an active call while moving from one cell to another

1992: Finnish mobile phone operator Oy Radiolinja Ab went live with Europe’s first GSM network

Mobile phone tower

The Internet (1)

1969: The set up of Advanced Research Projects Agency (ARPA) by the US military

ARPANET: world’s first computer network to use packet switching technology to interconnect several Universities and the Stanford Research Institute

The Internet (2)

The Father of the Internet: American Computer Scientist Vint Cerf developed TCP/IP

New Year’s day 1983: TCP/IP was used for the first time and the network of networks was officially born

1989: researcher Tim Berners-Lee in Geneva, who wrote the world’s first pages using HTML and HTTP, has effectively created the World Wide Web

The Internet (3) The Wireless Internet (1)

Mid-to-late 1990s: the father of Wi-Fi, Vic Hayes, developed various versions of the 802.11 standard

In the middle of an evolution process from providing secluded, hotspot connectivity at offices, homes, airports and cafes to offering city-wide coverage

The Wireless Internet (2)

The aim is to embed Wireless Internet access functionality directly inside portable electronic devices

Converged Devices (1)

Engineers are able to design a range of devices that incorporate two or more of different technologies together in the same package

Converged Devices (2)

Example: Sony’s PlayStation Portable console launched in 2005: play games, watch downloaded movies, live television and surf the web via built-in 802.11b modem

What is purpose of communications system?

To transfer information from one location to another

– Data

– Video

– Audio

Desirable attributes

– Fast

– Accurate

– Secure

– Scalable

– Routable/switchable

– Capable of handling multiple types of information (data)

– Cheap

Components of a telecommunications system -physical view

Source EncoderModulator/ transmitter

Receiver/ demodulator Decoder Receiver

Link

Cable

Microwave

Other wireless

Light

Smoke signals

Transmission Media (a)

Ref: COBRA

Transmission Media (b)

Transmission Medium, or channel, is the actual physical path that data follows from the transmitter to the receiver.

Copper cable is the oldest, cheapest, and the most common form of transmission medium to date.

Optical Fiber is being used increasingly for high-speed and long-distance applications.

Transmission by Light: why?

Growing demand for faster and more efficient communication systems

Internet traffic is tripling each year

It enables the provision of Ultra-high bandwidth to meet the growing demand

Increased transmission length

Improved performance

etc.

Demand for Bandwidth

BandwidthDemand

1990 2000 2010

• Raw text = 0.0017 Mb• Word document = 0.023 Mb• Word document with picture = 0.12 Mb• Radio-quality sound = 0.43 Mb• Low-grade desktop video = 2.6 Mb• CD-quality sound = 17 Mb• Good compressed (MPEG1) video = 38 Mb

Typical data bandwidth requirement

20,000 x

Communications Technologies

Year Service Bandwidth distance product1900 Open wire telegraph 500 Hz-km

1940 Coaxial cable 60 kHz-km

1950 Microwave 400 kHz-km

1976 Optical fibre 700 MHz-km

1993 Erbium doped fibre amplifier 1 GHz-km

1998 EDFA + DWDM > 20 GHz-km

2001- EDFA + DWDM > 80 GHz-km

2001- OTDM > 100 GHz-km

Optical Technology - Advantages

• High data rate, low transmission loss and low bit error rates• High immunity from electromagnetic interference• Bi-directional signal transmission• High temperature capability, and high reliability• Electrical isolation• Signal security• Small size, light weight, and stronger

448 copper pairs5500 kg/km

62 mm

21mm

648 optical fibres363 kg/km

Optical communication system concepts (a)

The basic components– A serial bit stream in electrical form is presented to a

modulator, which encodes the data appropriately for fibre transmission

Optical transmission

Optical communication system concepts (b)

– A light source (laser or Light Emitting Diode -LED) is driven by the modulator and the light focused into the fibre

– The light travels down the fibre (during which time it may experience dispersion and loss of strength)

– At the receiver end the light is fed to a detector and converted to electrical form

– The signal is then amplified and decoded to restore the original bit stream

Optical communications systems (a)

Basic building blocks of communication systems:

Point-to-point systems– Carry signals back and forth between two points

Point-to-multipoint (or broadcast) systems– Distribute identical signals from a central facility to multiple terminals,

which may (or may not) be able to send signals back» One central transmitter serving many terminals.

» Terminals may return signals (at lower speed) to central transmitter.

» Central transmitter is more powerful than point-to-point transmitter because it serves many terminals.

» Distribute identical signals to all terminals (e.g., cable-TV distribution system).

Point-to-point transmission

Optical communications systems (b)

Networked systems– Transmit signals among many terminal points somehow linked to each

other» All terminals can send and receive signals to any terminal

» LAN – small networks; MAN and WAN – large networks

» For reconfiguration, use patch panels for attaching and removing terminals.

Point-to-multipoint transmission

Optical communications systems (c)

Optical communications systems (d)

– Ring network» Signals may be tapped from loop to serve each terminal.» Signals may pass through each terminal and be modified.» Due to high attenuation of couplers, better to build networks as

collection of point-to-point links that can be regenerated at each terminal.

– Star network» Signals to and from each terminal pass through central point.» Central point can be passive coupler dividing input signal or

active coupler receiving and retransmitting signal. (Ethernet uses this configuration.)

– Network of networks» Link networks to form larger network.» Each small-scale network (department) interfaces with larger-

scale network (floor-wide), which then interfaces with an even larger network (building-wide).

Optical communications systems (e)

A hierarchy of networks, interconnected to Large-scale networks

Optical communications systems (f) Switched systems

– Make temporary connections between pairs of terminals or subscribers attached to the system

» For temporary connections between pairs of terminals.

» Any pair of terminals can both send and receive signals.

» Mostly electronics but optics is catching up.

Simplified optical network with ring architecture

Source: Tektronix

ADM: Add/drop wavelength multiplexer; DCS: Dense communications system

What is optical networking?

Use of optical components in place of electronic components in anetwork environment– Light waves (including infrared) as a signal for the

transmission or switching of data– Pure optical or all-optical networks use light exclusively from

end to end Most commonly, optical elements (optical fiber, optical

amplifiers) are used in transmission links– Known as opto-electronic networks (OEO)– Switching still done electronically (“in silicon”)– No pure optical networks at present– All-optical switching is a laboratory project at present, though

opto-mechanical systems exist which use flipping mirrors

What is optical networking? (continued)

Long-term goal is the all-optical network, with all switching, transmission, and routing done optically

How are optical networks different?

Optical networks differ from conventional electronic or “wireline” networks– Rely upon light waves to carry data, rather than

electron-based transmission in wires

Differ from conventional wireless networks– Operate at much higher frequencies

» Hundreds of terahertz vs. 30 GHz

» Wavelength () of 1600 nm ~ 188 THz

– Use waveguides (in the form of optical fiber) to carry the data-bearing waves.

Optical and electronic networks

Modulator

Input signal Connector Optional optical amplifier

Amplifier Decoder

Output signal

Optical fiber Optical fiber

Light Wavelength = 800-1600 nm

ElectricityElectricity

Light source

Detector

Modulator

Input signal

Amplifier Decoder

Output signal

Electromagnetic Radiation Frequency = 100 Kz to 30 GHz ElectricityElectricity

Trans-mitter

Detector Receiver

CSU/DSU

Input signal Optional repeater

CSU/DSU

Output signal

T1, T45 cable T1, T45 cable

Electricity

Opt

ical

Ele

ctro

nic

Wire

less

CSU: Channel service unit; DSU: Data service unit

Why optical networks?

Advantages

Cost-effective bandwidth

Noise isolation

Security

Smaller physical presence

Readily upgradable

Drivers

Demand for bandwidth

Commoditization of optical networking components

Reduced number of components

Shorter service contracts

Promise of rapid provisioning

Advantages

Cost-effective bandwidth– Above a certain threshold price per unit of bandwidth is

lower– For very high bandwidths (~Gbit/second and higher) and

even relatively short distances (~100 m), optical fiber is usually the only practical choice

Noise isolation– Optical fibers are not affected by electrical noise-

producing sources» Can be used in environments where adequate

shielding of electrical cables would be difficult or impossible

– Only in environments with high levels of radioactivity is there a potential problem

Advantages (continued)

Greater security– Optical fiber does not emit electromagnetic radiation

which can be intercepted» Much more secure than many other types of wiring,

such as category 5 untwisted pair used for Ethernet applications

– Tapping optical fiber is also much more difficult Smaller physical presence

– Single optical fiber cable with a diameter of less than 6 mm can replace a bulky cable with hundreds of wires

– Critical in applications where space is at a premium» Ships and aircraft» Retrofitting buildings and rewiring cities, where

space in conduits may also be very limited

Advantages (continued)

Ready upgrade path– Constant improvements to fiber optic cable itself

– In most cases, increased bandwidth can be had by installing new optical multiplexing equipment

Disadvantages

Higher cost per meter

Greater difficulty in splicing and maintenance– Technicians need to be retrained

Need to convert optical signals back to electronic signals for processing

Optical Communications Historical Developments (1)

• 800 BC Use of fire signal by the Greeks• 400 BC Fire relay technique to increase transmission distance• 150 BC Encoded message

• 1880 Invention of the photophone by Alexander Graham Bell

Optical Communications Historical Developments (2)

• 1930 Experiments with silica fibres, by Lamb (Germany)• 1950-55 The birth of clad optical fibre, Kapany et al (USA)• 1962 The semiconductor laser, by Natan, Holynal et al (USA)• 1960 Line of sight optical transmission using laser:

- Beam diameter: 5 m- Temperature change will effect the laser beam

Therefore, not a viable option

•1966 - A paper by C K Kao and Hockham (UL) was a break through

- Loss < 20 dB/km - Glass fibre rather than crystal (because of high viscosity)- Strength: 14000 kg /m2.

Contd.

Optical Communications Historical Developments (3)

• 1970 Low attenuation fibre, by Apron and Keck (USA) from 1000 dB/km - to - 20 dB/km

- Dopant added to the silica to in/decrease fibre refractive index.

• Late 1976 Japan, Graded index multi-mode fibre- Bandwidth: 20 GHz, but only 2 GHz/km

Start of fibre deployment. • 1976 800 nm Graded multimode fibre @ 2 Gbps/km.• 1980’s

- 1300 nm Single mode fibre @ 100 Gbps/km- 1500 nm Single mode fibre @ 1000 Gbps/km- Erbium Doped Fibre Amplifier

Optical Communications Historical Developments (4)

• 1990’s - Soliton transmission (exp.): 10 Gbps over 106 km with no error- Optical amplifiers - Wavelength division multiplexing, - Optical time division multiplexing (experimental) OTDM

• 2000 and beyond- Optical Networking - Dense WDM, @ 40 Gbps/channel, 10 channels- Hybrid DWDM/OTDM ~ 50 THz transmission window > 1000 Channels WDM > 100 Gbps OTDM Polarisation multiplexing

- Intelligent networks

Applications of fibre optics and lasers

Two major applications:

– Optical communications systems

– Non communication applications

» Sensors (gyroscopes, pressure, temperature, strain etc.)

» Illumination

» Imaging and inspection

» Medical applications

» Broad Optoelectronics

» Electronics and Computers

Undersea Cables Residential Area Networks

Ref: COBRA

In-house Network

Ref: COBRA

System Block Diagram

Laser Display

Designer apartment

Illumination woven structures

Fabric woven from steel (warp) and Trevira CS (weft) with 0.025mm notched 0.5mm PMMA POF weft floatings

Ref: A Harlin et al, Development of polymeric optical fibre fabrics as illumination elements and textile displays, AUTEX Research Journal, Vol.3, 2003

Lasers: Transforming Life

Laser Cutting Laser Welding

Laser-arc-hybrid-welding with Nd:YAG and CO2 lasers