TCOM 503 Fiber Optic Networks

1
TCOM 503Fiber Optic Networks

• Spring, 2006
• Thomas B. Fowler, Sc.D.
• Senior Principal Engineer
• Mitretek Systems

2
Course overview

• This course, together with TCOM 513, presents
  basic material needed to understand optical
  communications
• Physical principles of optical devices and
  networks
• Components of fiber optic systems and how they
  function
• Light as a communications medium modulation,
  noise, detection of signals
• How these components work together to create
  useful fiber optic networks
• How fiber optic networks are used to create
  large-scale communications networks
• How all-optical networks will function, and their
  advantages and problems

3
Course goal

• Impart general background on optical
  communications
• Enable students to undertake more detailed study
  of any aspect of optical communications
• Give enough information so that students become
  informed consumers and decision makers on many
  optical communications issues

4
Course organization

• 7 weeks
• Main text Understanding Optical Communications,
  Harry Dutton, Prentice-Hall, 1998
• Supplementary text Fiber Optic Communications,
  4th Edition, Joseph C. Palais, Prentice-Hall,
  1998
• Other material to be downloaded from Internet
  (see syllabus)
• Student evaluation
• Homework 40
• Project outline 20
• Final exam 40

5
Topics for TCOM 503

• Week 1 Overview of fiber optic communications
• Week 2 Brief discussion of physics behind fiber
  optics
• Week 3 Light sources for fiber optic networks
• Week 4 Fiber optic components fabrication and
  use
• Week 5 Modulation of light, its use to transmit
  information
• Week 6 Noise and detection
• Week 7 Optical fiber fabrication and testing of
  components

6
Week 1 Overview of fiber optic communications

• Basics of communications systems
• Fiber optic networks compared to other networks
• Advantages of and drivers for optical networks
• Architecture of typical fiber optic networks
• Brief history of optical networking
• Fiber optic network terminology
• General communications systems background

7
What is purpose of communications system?

• To transfer information from one location to
  another
• Voice
• Data
• Video
• Audio
• Desirable attributes
• Fast
• Accurate
• Secure
• Scalable
• Routable/switchable
• Capable of handling multiple types of information
  (data)
• Cheap

8
Components of a telecommuncations systemphysical
view

Link
Modulator/ transmitter
Receiver/ demodulator
Source
Encoder
Decoder
Receiver
Cable Microwave Other wireless Light Smoke signals
9
Components of a telecommuncations systemlogical
view

Source
Interface
Interface
Receiver
Packet-switched network
10
What is optical networking?

• Use of optical components in place of electronic
  components in a network environment
• Light waves (including infrared) as a medium 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

11
What is optical networking? (continued)

• Long-term goal is the all-optical network, with
  all switching, transmission, and routing done
  optically
• Conversion to/from electrical signals occurs only
  at boundary
• Likely to be commercialized within 5 years

12
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 (l) of 1600 nm 188 THz
• Use waveguides (in the form of optical fiber) to
  carry the data-bearing waves.

13
Optical and electronic networks

Optical
Electronic
Wireless
14
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

15
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

16
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

17
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

18
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

19
Supply

• Exuberance of late 90s and early 2000s led to
  huge volumes of fiber put in the ground
• New technologies mean more bandwidth even from
  existing fibers

20
Drivers

• Huge and insatiable demand for bandwidthcooled
  after dot com crash
• May have been hyped all along
• But developments such as more video on Internet
  and anticipated use of Internet for video
  delivery in future will require optical
  connections to or close to homes
• Commoditization of optical network components
  enables more powerful and economical networks to
  be built
• Reduced number of components means network
  simplification and equipment consolidation
• Shorter service contracts implies faster
  depreciation and more rapid replacement of
  equipment with newer technology

21
Relative cost per DS3 (45 mbit/sec) mile

PPNPurely Photonic Networks
SourceQtera Networks/NGN99
22
Evolution of optical networks

Source Sycamore Networks/NGN 99
23
Problems with end-end all-optical networks

• Physical limitations of devices still limit
  scalability and performance of optical networks
• Multi-vendor environment and rapidly evolving
  technology limits plug-and-play compatibility
• Subnetworks are easier to monitor and manage

24
Optical network capacity vs. distance

25
Schematic diagram of typical optical network today

Modulator/ transmitter
Receiver/ demodulator
Source
Encoder
Receiver
Decoder
Link
Source Sycamore Networks/NGN 99
26
Simplified optical network with ring architecture

Source Tektronix
27
History of optical communications systems

• Glass invented, c. 2500 BC
• Fires have been used for signaling since Biblical
  times
• Famous opening of Aeschylus play Agamemnon (c.
  458 BC)
• I wait to read the meaning in that beacon
  light,a blaze of fire to carry out of Troy the
  rumorand outcry of its capture.
• Smoke signals have also been used for thousands
  of years, most notably by Native Americans
• Lanterns in Bostons Old North Church used to
  signal Paul Revere on his famous ride (1775)
• Flashing lights used on ships for communication
  since time of Lord Nelson (1758-1805)

28
History of optical communications systems
(continued)

• Optical telegraph built in France during 1790s by
  Claude Chappe
• Signalmen occupied a series of towers between
  Paris and Lille, 230 km
• Signals relayed using movable signal arms
• 15 minutes to send a message
• In 1840, Daniel Colladon demonstrated light
  guiding in jet of water in Geneva
• Used in opera Faust, 1853, by Paris Opera
• In 1870, John Tyndall demonstrated principle of
  guiding light through internal reflections, using
  a jet of pouring water (duplicating Colladons
  work)
• In 1880, Alexander Graham Bell patented
  photophone, which utilizes unguided light bounced
  off of vibrating mirrors to carry speech
• Intended for long distance
• Didnt work in cloudy weather

29
History of optical communications systems
(continued)

• Also in 1880, William Wheeler invented system of
  light pipes to direct light around homes
• Pipes lined with a highly reflective coating
• Single electric arc lamp placed in the basement
• In 1888, first use of bent glass rods to
  illuminate body cavities (medical team of Roth
  and Reuss of Vienna)
• In 1895, early attempt at television by French
  engineer Henry Saint-Rene using a system of bent
  glass rods for guiding light images
• In 1898, American David Smith applied for a
  patent on a bent glass rod device to be used as a
  surgical lamp
• In 1920's, idea of using arrays of transparent
  rods for transmission of images for television
  and facsimiles respectively patented by
  Englishman John Logie Baird and American Clarence
  W. Hansell

30
History of optical communications systems
(continued)

• In 1930, German medical student Heinrich Lamm was
  first person to assemble a bundle of optical
  fibers to carry an image
• Objective was to look inside inaccessible parts
  of the body (fiberscope)
• Images were of poor quality
• In 1954, Dutch scientist Abraham Van Heel and
  British scientist Harold. H. Hopkins separately
  wrote papers on imaging bundles
• Van Heel had idea of cladding bare fiber with
  material of lower refractive index
• In 1956, Narinder S. Kapany of Imperial College
  in London invented glass-coated glass rod, coined
  term fiber optics
• Not suited for communications
• Applications in fiberscopes

31
History of optical communications systems
(continued)

• 1960 ruby lasers
• In 1961, Elias Snitzer of American Optical
  published theoretical description of single mode
  fibers
• Fiber with a core so small it could carry light
  with only one wave-guide mode
• Worked for a fiberscopes
• Light loss too high for communications (one
  decibel per meter)
• 1962 lasers operating on semiconductor chips
• 1964 C. K. Kao identifies that maximum loss of
  20 db/km needed for communications
• Corresponds to 1 of energy left after 1 km
• Existing glasses not transparent enough
• Speculated that losses of 1000 db/km result of
  impurities in glass

32
History of optical communications systems
(continued)

• 1970 Corning Glass researchers Robert Maurer,
  Donald Keck and Peter Schultz invent fiber optic
  wire or Optical Waveguide Fibers
• Fused silica, which has high melting point, low
  refractive index
• 65,000 times more capacity than copper wire
• By 1972, losses down to 4 db/km
• Today, 0.2 db/km
• 1973 Navy installs fiber-optic telephone link
  on a ship
• In 1975, US Government links computers in the
  NORAD headquarters at Cheyenne Mountain using
  fiber optics to reduce interference
• In 1977, first optical telephone communication
  system installed
• 1.5 miles long, under downtown Chicago
• Each optical fiber carried the equivalent of 672
  voice channels

33
History of optical communications systems
(continued)

• 1980 first long distance fiber optic link
  (Boston-Richmond)
• 1984 First SONET networks
• 1987 fiber amplifiers invented by Dave Payne at
  U of Southampton, UK
• 1988 first transatlantic fiber optic link
  (ATT)
• 1990s Bragg filters
• 1997 Wave division multiplexing (WDM)
• 2000 dense wave division multiplexing (DWDM)

34
Thrusts of fiber optics technology

• As distribution mechanism for light
• To see in otherwise inaccessible places
• For high-speed communications

35
Speed history

• 1790 5 bits
• 1977 44.7 Megabits
• 1982 400 Megabits
• 1986 1.7 Gigabits
• 1993 10 Gigabits
• 1996 1 Terabit
• 2002 3 Terabits
• Comparison entire worlds telephone traffic 5
  Tb/sec

36
Optical network bandwidth is exploding

OC-192, 320l
37
How widespread are optical networks?

Source Teleglobe
38
Fiber optic terminology

• Lambda (l) a single wavelength of light
• SONET Synchronous Optical Networka transport
  technology for reliably sending information over
  optical fiber
• Photonic having to do with devices using light
  (photons) instead of electronics analogous to
  electronic
• Decibel (db) a unit of power gain or loss,
  relative to a source. Calculated as 10 log10
  (P/Pref). If reference is 1 mw, expression dbm
  is often used.

39
Types of optical networks

• Present
• Simplest SONET 1 wavelength of light (l)
• SONET 2 l
• SONET Dense wave division multiplexing (DWDM)
  (many ls)
• Future
• IP over ATM over SONET DWDM
• IP over ATM over SONET, private line DWDM
• IP over other transport layer
• All optical networks

40
World is changing with migration to data from
voice

• Data-driven network
• Ingress/egress 2000 km
• 80 long-haul, 20 short haul
• Traffic statistics unpredictable
• Annual growth rate 30

• Voice-driven network
• Ingress/egress 500 km
• 80 short-haul, 20 long haul
• Traffic statistics predictable
• Annual growth rate 7

Source Qtera Networks/NGN99
41
General communications system background

• Analog and digital signals
• Information theory
• Layered communications architectures

42
Digital and analog signals
43
Analog and digital transmission

44
Parts of a pulse

45
Information theory background

• Sampling
• Digitizing
• Pulse code modulation
• Multiplexing
• Time
• Frequency
• Wave
• Information content

46
Sampling

Source Cisco Systems
47
Digitizing (quantizing)

Source Cisco Systems
48
Effect of quantizing

4 bits/ sample
8 bits/ sample
3 bits/ sample
2 bits/ sample
Source U of Waterloo
49
Pulse Code Modulation (PCM)

Prefiltering
Sampling
Quantizing
Transmission or storage of string of numbers
50
Multiplexing

• Definition combining multiple signals for
  transmission over a single line or medium
• Types
• Frequency division multiplexing (FDM) each
  signal assigned a different frequency
• Wavelength division multiplexing (WDM) each
  signal assigned a particular wavelength (l) (a
  type of FDM)
• Time division multiplexing (TDM) each signal
  assigned a fixed time slot in a fixed rotation
• Statistical time division multiplexing (STDM)
  time slots assigned dynamically to signals based
  on characteristics to achieve better utilization

51
FDM multiplexing details
Source Kenneth Williams, NC AT Univ.
52
Wave division multiplexing details

Source Los Alamos National Laboratory
53
WDM demultiplexing
Source Los Alamos National Laboratory
54
Time division multiplexing details

Source Kenneth Williams, NC AT Univ.
55
Time division multiplexing details (cont)

Source Kenneth Williams, NC AT Univ.
56
Information content

• Shannon showed that the capacity in bits/second
  of an additive white Gaussian noise channel is
  given by the famous Tuller-Shannon formula
• C BW log2 (1 S/N)
• BW transmission bandwidth
• S/N signal-to-noise ratio
• This capacity only available with optimal
  encoding
• Note that bandwidth cannot be larger than
  transmission frequency, and typically is much
  smaller
• Optical systems typically operate at frequencies
  of 200 THz, so even a bandwidth of 1 of that is
  2 THz, and with S/N of 100 gives capacity 20 x
  1012 bits/second
• Electronic systems, operating at 30 GHz or so are
  limited to about 3 x 109 bits/second

57
Layered communications architecture

• What it is
• How it works
• Why it is needed
• What it looks like

58
Communications systems architecture

• An architecture is the highest-level organization
  and dynamics of a system
• What a layered communications architecture is
• Hierarchically organized set of operations
• Corresponding set of methods of encoding
  information
• Permits the reliable transmission and
  reconstruction of complex messages across
  multiple network segments
• Types of data communications systems
• Packetized
• Non-packetized

59
The five functions of a communications system

• Put information into a form suitable for
  transmission
• Send information through a physical medium,
  utilizing some type of channel
• Due to physical constraints is always
  characterized by degradation, including noise and
  distortion.
• At receiving end, extract or reconstruct the
  original message, which is the lowest level
  logical entity which has meaning to the end
  systems.
• May involve reassembly, decoding/decripting, and
  error detection and correction.
• Route message to place where it needs to be used.
• Perform control and sequencing functions
• Ensure correct action taken for multiple messages

60
Necessity of these functions

• Functions (1) and (2) are necessary because
  transmission of information through a noisy
  channel requires special coding to minimize
  errors and maximize the transmission speed
  (Shannons Theorem)
• Invariably means that information as transmitted
  is in form completely different than that
  required for its ultimate use
• Other three functions each require different
  processing capability
• Usually translates to different physical hardware
  and different software or its equivalent

61
Necessity of these functions (continued)

• Isolation of one function from another desirable
  because it permits changes to be made internally
  in the processing of each function which are
  invisible to other functions
• Facilitates incremental optimization of the
  overall system
• Allows addition of new, higher-level functions by
  adding new layer(s) to code

62
Characteristics of layered architectures

• Different parts of the requisite coding and
  processing are performed by separate layers
• Output from each layer in a standard form
• Each layer contains a logical grouping of
  functions which together provide a set of
  specific services.
• Services of layer N are available to layer N1,
  and layer N in turn utilizes the services of
  layer N-1
• Break exists between the physical layers (those
  concerned with information as coded for
  transmission through a physical channel) and the
  logical layers (those concerned with information
  as an abstract or symbolic entity)
• Latter set of layers is concerned with symbolic
  manipulation of the information with reference to
  the meaning it will ultimately have for end
  system or user

63
Layering in communications systems

64

Seven layer OSI network architecture
65
OSI and TCP/IP Comparison
TCP/IP Implementation Using Ethernet
OSI Reference Model

Application
Applications Telnet FTP SMTP HTTP
Application Protocols
Presentation
Session
Transport
TCP
TCP/IP
Network
IP
LLC Sublayer
Data Link
Ethernet (802.3)
MAC Sublayer
Physical signaling Media attachment
Physical
66
Traffic Routing Across TCP/IP Network

67
All-optical network protocol stack

Source Richard Barry, Optical Networking
Technologies, NGN99