Transcript Why Optical Communications?

Fibre-Optic Communication Systems
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
Why Optical Communications?
– Almost all long distance phone calls
– Most Internet traffic (Dial-up, DSL or Cable)
– Most Television channels (Cable or DSL)
‘Triple Play’
• Optical Fiber is the backbone of the modern
communication networks
• The Optical Fiber Carries:
• 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
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
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
Fiber in Smart Grid
Intra Chip Optical Links
Biomedical Optical Sensing Example
An optical fiber sensor
for the continuous
monitoring of carbondioxide partial pressure
in the stomach.4
The sensor is based on
the color change of a
CO2-sensitive indicator
layer
Fiber Optic
Sensors
Source BCC Market Research
Elements of a Fiber Optic Link
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
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
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, cleansup, amplifies and retransmits (O/E/O)
• Optical Amplifier: Amplifies light in fiber
without O/E/O
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
Multiplexing
Is the set of technique that allow the
simultaneous transmission of multiple signals
across a single data link.
Types of multiplexing
Multiplexin
g
Digit
al
Analog
FDM
TDM
WDM
diagram
Wavelength division mutliplexing
• a multiplexing technique working in the
wavelength domain
• An analog multiplexing technique to
combine optical signal.
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.
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.
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.
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.
1)installing more cables,
Three methods exist for expanding capacity
2) increasing system bit rate to multiplex more signals
3) wavelength division multiplexing.
Type of WDM
1)CWDM
2)DWDM
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.
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
CWDM&DWDM
• CWDM system have channel at
wavelengths spaced 20 nanometers (nm).
• DWDM 0.4 nm spacing
• Energy
• tolerance
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.
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
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 44.736 Mb/s
Limitation:
• Fiber attenuation (repeater spacing ≈ 6 km)
Deployed since 1978
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 2.488 Gb/s
Limitations:
• Fiber attenuation (repeater spacing ≈ 40 km)
• Fiber dispersion
Deployed since 1982
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:
• Propagation distance without regeneration/re-clocking
Evolution of Optical Networks
History of
Attenuation
Fiber Network Topologies
Who Uses
it?
Span
(km)
Bit Rate
(bps)
Multiplexing
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/C
WDM/TD
M
SMF/
LWPF
DFB
APD/ PIN
Access/
LocalLoop
Small
Business,
Consumer
~10
~109
(56kbps1Gbps)
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
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
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
Last Mile Bottle Neck and
Access Networks
Infinite Bandwidth Backbone
Optical Fiber Networks A few (Gb/s)
Few Mb/s
The Last Mile ?
Virtually infinite demand end user
Additionally, supporting different QoS
?
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 (FibreWireless) Systems
Currently Drives the Market
PON Bit-Rates & Timeline
Hybrid/Fiber Coax (HFC)
Cable TV Networks
This is a sub carrier multiplexed analog access network
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
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
ROF for Fiber-Wireless Networks
Central
Base
Station
Y
Radio over Fiber (ROF)
RAP
(Simple)
Up/Down links
Y
RAP
802.11
Y
RAP
Single ROF link can support voice and
data simultaneously
Micro
Cell
voice