1. Fibre-Optic Communication Systems

2. History of Fiber Optics
John Tyndall demonstrated in 1870 that
Light can be bent
Total Internal Reflection (TIR) is the basic idea of fiber optic

3. Why Optical Communications?
Optical Fiber is the backbone of the modern communication networks
The Optical Fiber Carries:
Almost all long distance phone calls
Most Internet traffic (Dial-up, DSL or Cable)
Most Television channels (Cable or DSL)
One fiber can carry up to 6.4 Tb/s (1012 b/s) or 100 million conversations simultaneously
Information revolution wouldn’t have happened without the Optical Fiber
‘Triple Play’

5. Why Optical Communications?
Lowest Attenuation: 0.2 dB/km at 1.55 µm band resulting in 100s of km fiber links without repeaters Highest Bandwidth of any communication channel: Single Mode Fiber (SMF) offers the lowest dispersion  highest bit rate  rich content (broadband) up to 100 Gb/s or more Enormous Capacity: Via WDM that also offer easy upgradability, The ‘Optical Layer’: Wavelength routing, switching and processing all optically, which adds another layer of flexibility

6. Why OPTICOM for you? Optical communications is a huge area
Basic knowledge in optics is required in many other fields
Power Engineering
Fiber optics in smart grids, optical ground wire
Biomedical
Optical Coherent Tomography, video sensors
Optical sensing
Structural monitoring
VLSI – Intra chip communications

7. Fiber in Smart Grid

8. Intra Chip Optical Links

9. Biomedical Optical Sensing Example
An optical fiber sensor for the continuous monitoring of carbon-dioxide partial pressure in the stomach.4 
The sensor is based on the color change of a CO2-sensitive indicator layer

10. Source BCC Market Research
Fiber Optic Sensors

11. Elements of a Fiber Optic Link3

12. Elements of OPTICOM System
The Fiber – that carries the light
Single Mode Fiber (only one EM mode exists), offers the highest bit rate, most widely used
Multi Mode Fiber (multiple EM modes exist), hence higher dispersion (due to multiple modes) cheaper than SMF, used in local area networks
Step Index Fiber – two distinct refractive indices
Graded Index Fiber – gradual change in refractive index

13. Elements of OPTICOM System
Optical Transmitter converts the electrical information to optical format (E/O)
Light Emitting Diode (LED): cheap, robust and used with MMF in short range applications
Surface emitting and edge emitting LED
LASER Diode: high performance and more power, used with SMF in high speed links
Distributed Feedback (DFB) Laser – high performance single mode laser
Fabry-Perrot (FP) lasers – low performance multimode laser

14. Elements of OPTICOM System
Optical Receiver converts the optical signal into appropriate electrical format (E/O)
PIN Photo Diode: Low performance, no internal gain, low cost, widely used
Avalanche Photo Diode (APD): High performance with internal (avalanche) gain
Repeater: receives weak light signal, cleans-up, amplifies and retransmits (O/E/O)
Optical Amplifier: Amplifies light in fiber without O/E/O

15. Wavelength Division Multiplexing
Fiber has the capability to transmit hundreds of wavelengths
Coarse WDM (CWDM) has ~20 nm wavelength spacing
Dense WDM (DWDM) has up to 50 GHz spacing
Once the fiber is in place, additional wavelength can be launched by upgrading transceivers

16. Multiplexing
Is the set of technique that allow the simultaneous transmission of multiple signals across a single data link.

17. Types of multiplexing
diagram
Multiplexing
Digital
Analog
TDM
FDM
WDM

18. Wavelength division mutliplexing
a multiplexing technique working in the wavelength domain
An analog multiplexing technique to combine optical signal.

19. History
The concept was first published in 1970, and by 1978 WDM systems were being realized in the laboratory. The first WDM systems only combined two signals. Modern systems can handle up to 160 signals and can thus expand a basic 10 Gbit/s fiber system to a theoretical total capacity of over 1.6 Tbit/s over a single fiber pair.

20. WDM
In fiber-optic communications Wavelength –division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different (colours) of laser light to carry different signals.

21. Most WDM systems operate on single mode fiber optical cables, which have a core diameter of 9 µm. Certain forms of WDM can also be used in multi-mode fiber cables (also known as pre mises cables) which have core diameters of 50 or 62.5 µm.

22. Why Is WDM Used?
With the exponential growth in communications, caused mainly by the wide acceptance of the Internet, many carriers are finding that their estimates of fiber needs have been highly underestimated. Although most cables included many spare fibers when installed, this growth has used many of them and new capacity is needed.

23. Three methods exist for expanding capacity
1)installing more cables,
2) increasing system bit rate to multiplex more signals
3) wavelength division multiplexing.

24. Type of WDM
1)CWDM
2)DWDM

25. Dense Wavelength Division Multiplexing
DWDM
No official or standard definition
Implies more channels more closely spaced that WDM
DWDM-based networks create a lower cost way to quickly respond to customers' bandwidth demands and protocol changes.
A key advantage to DWDM is that it's protocol- and bit-rate independent.

26. Coarse wavelength division multiplexing
CWDM
No official or standard definition
number of channals is fewer than in dense wavelength division multiplexing (DWDM) but more than in standard wavelength division multiplexing (WDM).
Laser emmission

27. CWDM&DWDM
CWDM system have channel at wavelengths spaced 20 nanometers (nm).
DWDM 0.4 nm spacing
Energy
tolerance

28. Benefits of WDM
WDM technology allows multiple connections over one fiber thus reducing fiber plant requirement.
This is mainly beneficial for long-haul applications.
Campus applications require a cost benefit analysis.
WDM technology can also provide fiber redundancy.
WDM provides a managed fiber service.

29. First Generation Fiber Optic Systems
Purpose:
Eliminate repeaters in T-1 systems used in inter-office trunk lines
Technology:
0.8 µm GaAs semiconductor lasers
Multimode silica fibers
Limitations:
Fiber attenuation
Intermodal dispersion
Deployed since 1974

30. Second Generation Systems
Opportunity:
Development of low-attenuation fiber (removal of H2O and other impurities)
Eliminate repeaters in long-distance lines
Technology:
1.3 µm multi-mode semiconductor lasers
Single-mode, low-attenuation silica fibers
DS-3 signal: 28 multiplexed DS-1 signals carried at Mb/s
Limitation:
Fiber attenuation (repeater spacing ≈ 6 km)
Deployed since 1978

31. Third Generation Systems
Opportunity:
Deregulation of long-distance market
Technology:
1.55 µm single-mode semiconductor lasers
Single-mode, low-attenuation silica fibers
OC-48 signal: 810 multiplexed 64-kb/s voice channels carried at Gb/s
Limitations:
Fiber attenuation (repeater spacing ≈ 40 km)
Fiber dispersion
Deployed since 1982

32. Fourth Generation Systems
Opportunity:
Development of erbium-doped fiber amplifiers (EDFA)
Technology (deployment began in 1994):
1.55 µm single-mode, narrow-band semiconductor lasers
Single-mode, low-attenuation, dispersion-shifted silica fibers
Wavelength-division multiplexing of 2.5 Gb/s or 10 Gb/s signals
Nonlinear effects limit the following system parameters:
Signal launch power
Propagation distance without regeneration/re-clocking
WDM channel separation
Maximum number of WDM channels per fiber
Polarization-mode dispersion limits the following parameters:

33. Evolution of Optical Networks

34. History of Attenuation5

35. Fiber Network Topologies
Who Uses it?
Span (km)
Bit Rate
(bps)
Multi-plexing
Fiber
Laser
Receiver
Core/
LongHaul
Phone Company, Gov’t(s)
~103
~1011
(100’s of Gbps)
DWDM/
TDM
SMF/ DCF
EML/ DFB
APD
Metro/
Regional
Phone Company, Big Business
~102
~1010
(10’s of Gbps)
DWDM/CWDM/TDM
SMF/ LWPF
DFB
APD/ PIN
Access/
LocalLoop
Small Business, Consumer
~10
~109
(56kbps- 1Gbps)
TDM/ SCM/
SMF/ MMF
DFB/ FP
PIN
Core - Combination of switching centers and transmission systems connecting switching centers.
Access- that part of the network which connects subscribers to their immediate service providers
LWPF : Low-Water-Peak Fiber, DCF : Dispersion Compensating Fiber, EML : Externally modulated (DFB) laser

36. Synchronous Optical Networks
SONET is the TDM optical network standard for North America (called SDH in the rest of the world)
De-facto standard for fiber backhaul networks
OC-1 consists of 810 bytes over 125 us; OC-n consists of 810n bytes over 125 us
Linear multiplexing and de-multiplexing is possible with Add-Drop-Multiplexers

37. SONET/SDH Bandwidths SONET Optical Carrier Level SONET Frame Format
SDH level and Frame Format
Payload bandwidth (kbps)
Line Rate (kbps)
OC-1
STS-1
STM-0
50,112
51,840
OC-3
STS-3
STM-1
150,336
155,520
OC-12
STS-12
STM-4
601,344
622,080
OC-24
STS-24 –
1,202,688
1,244,160
OC-48
STS-48
STM-16
2,405,376
2,488,320
OC-192
STS-192
STM-64
9,621,504
9,953,280
OC-768
STS-768
STM-256
38,486,016
39,813,120
OC-3072
STS-3072
STM-1024
153,944,064
159,252,480

38. Last Mile Bottle Neck and Access Networks
Infinite Bandwidth Backbone
Optical Fiber Networks A few (Gb/s)
Virtually infinite demand end user
Few Mb/s
The Last Mile ? ?
Additionally, supporting different QoS

39. Fiber in the Access End
Passive Optical Networks (PON) – No active elements or O/E conversion
Fibre-Coaxial (analog) or DSL (digital) fibre-copper systems
Radio over fibre (Fibre-Wireless) Systems
Currently Drives the Market

40. PON Bit-Rates & Timeline

41. Hybrid/Fiber Coax (HFC) Cable TV Networks
This is a sub carrier multiplexed analog access network

42. Digital Subscriber Loop (DSL)
Fiber Link
Digital fiber-copper (fiber-twisted pair) link
Multimedia (video, voice and data)
At least 3.7 Mb/s streaming is needed for quality video
Bit rate heavily depend on the length of the twisted pair link
New techniques like very high rate DSL (VDSL)
Many buildings in GTA have access to video over DSL

43. Radio over Fiber (ROF)
RF signals are transmitted over fiber to provide broadband wireless access
An emerging very hot area
Many advantages
Special areas
Underground
Olympics London
Niagara Tunnel

44. ROF for Fiber-Wireless NetworksY
Central
Base
Station
Radio over Fiber (ROF)
RAP
(Simple)
Up/Down links Y
RAP
802.11
voice Y
RAP
Single ROF link can support voice and
data simultaneously
Micro
Cell