1
Optical networking:
Network elements, devices,
technology and transmission issues
Lars Thylén
Lab of Optics, Photonics and Quantum Electronics
Dept of Microelectroncis and Information
Technology
KTH
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· Telecommunications
· Metrology
· Sensors
· Medicine
· Biotechnology
· Display
· Storage
· Lighting and energy
· Security
Photonics
Areas of applications
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Bara fotonik kan ge kapaciteten
Only photonics can give the capacity
Kilde: Chalmers University of Technology
1st generation networks 2nd generation
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Laboratory of
PHOTONICS
and
MICROWAVE Eng.LARK'99/ A. Karlsson/2
KTH
Optical Transmission
EvolutionofTransmissionCapacity
10
100
1000
10000
100000
1000000
10000000
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
Year
Capacity[Gb/s*km]
Singlechannel
IM/DDsystem
Soliton
systems
FDM/WDM
systems
Capacity =Speed *distance
> 1Tbit/s over 1000 km
> 1500 CD-roms/sec
on single fiber
Already today!
Capacity =Speed *distance
> 1Tbit/s over 1000 km
> 1500 CD-roms/sec
on single fiber
Already today!
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Laboratory of
PHOTONICS
and
MICROWAVE Eng.LARK'99/ A. Karlsson/1
KTH
Capacity of Fiber
Shannon Channel Capacity
( )SNRBC += 1log2
B = Fiber bandwidth , 5B = Fiber bandwidth , 5--5050 THzTHz
SNR = Signal to Noise RatioSNR = Signal to Noise Ratio
plug in SNR = 50 (not too unrealistic) givesplug in SNR = 50 (not too unrealistic) gives
C = 250C = 250 TbitTbit/s/s
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Spectral efficiency in b/s/Hz vs power/(bandwidth x length)
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Contents
Øeview of optical networks
·Optical network elements
Ïevices in optical networks
«ransmission link limitations
­TDM : Time division multiplexing
­WDM: Wavelength division multiplexing
­ (SCM : subcarrier multiplexing)
· Modulation formats
· Photonic packet switching and the
time domain
·Future challenges
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Review of optical
networks
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First and second generation
optical networks
· 1st generation-> point to point, single
wavelength
· 2nd generation: routing and switching in the
optical domain, "all optical network"
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Point to point WDM
1st generation networks
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PoP
Long distance
PoP
Metro DWDM NetworkMetro DWDM Network
Metro core
Business
Area
Banks
Residential
Areas
Metro Access
Network Mgmt
Enterprise
2nd generation networks
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Development in Optical Networking
P-t-P WDM OADM OXC
GMPLS
G.709
ITU Grid
SDH
PDH Capacity
Advanced Transport Networks
Network Management
Optical Networking
Signalling
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TDM
WDM
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SCM : subcarrier multiplexing
Electronics
Multiplexer in the electric
frequency domain
Linear E/O
converter
Light
Microwave
carriers
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TDM vs WDM
WDM: # of channels?
1000 reported (difficult!) => e g 5 GHz channel separation
Potential still unexplored!!!
TDM: # of channels?
Example: 160 Gb/s at 1 Mb/s => easily 160 000 channels
 WDM gives the transmission capacity, TDM the switching capability , at least now
Optical networks3rd
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The layer concept
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data link
1 Physical
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Second generation
networks
· "All" optical WDM networks
· But the all optical network is an analog one
(cf your digital computer)=> problems with
scalability (will go into that later)
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PoP
Long distance
PoP
Metro DWDM NetworkMetro DWDM Network
Metro core
Business
Area
Banks
Residential
Areas
Metro Access
Network Mgmt
Enterprise
2nd generation networks
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(All) Optical networks
· Networks vs point to point transmission
­ Noise, dispersion and nonlinearity accumulation
­ Crosstalk accumulation
­ Alignment of (de)multiplexers, filters
­ Filter bandwidth narrowing of concatenated
(de)multiplexers, filters
­ Equalization of powers due to power and SNR variation
in the network
­ Rapid dynamic equalization of amplifier gain
· In general we have linear networks: Scaleability is
a problem!!
· Protection
· Granularity
· => Limited scalability! (as compared to point to
point transmission with electronic regneration)
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Example of limited scalability: Optical amplifiers:
Èompensate for loss -> "Optical transparency"
Òo retiming, pulse shaping etc
·Linear, analog->Noise accumulates
Power out
Power in
Power out
Power in
Digital electronics, optical bistability
Optical amplifiers
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2R, 3R
1R
Ex (1-p)^N
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Regeneration in optical networks
The signal has to be regenerated after
passage of a certain number of nodes
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What is 3R and 4R regeneration ?
1st R: Reamplifying
1R
Time
Opticalpower
1R consists in amplification and
packet leveling
1R consists in amplification and
packet leveling
1R, 2R, 3R, 4R
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What is 3R and 4R regeneration ?
1st R: Reamplifying
1R
Time
Opticalpower
1R consists in amplification and
packet leveling
1R consists in amplification and
packet leveling
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1st R: Reamplifying
1R
Time
Opticalpower
What is 3R and 4R regeneration ?
1R consists in amplification and
packet leveling
1R consists in amplification and
packet leveling
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1st R: Reamplifying
1R
Time
Opticalpower
What is 3R and 4R regeneration ?
1R consists in amplification and
packet leveling
1R consists in amplification and
packet leveling
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1st R: Reamplifying
1R
Time
Opticalpower
What is 3R and 4R regeneration ?
1R consists in amplification and
packet leveling
1R consists in amplification and
packet leveling
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1R
Time
Opticalpower
What is 3R and 4R regeneration ?
1R consists in amplification and
packet leveling
1R consists in amplification and
packet leveling
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1R
Time
Opticalpower
What is 3R and 4R regeneration ?
It is performed by fiber or semiconductor optical amplifiers (or
electronic amplifiers)
It is performed by fiber or semiconductor optical amplifiers (or
electronic amplifiers)
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2R
Time
Opticalpower
What is 3R and 4R regeneration ?
2R ...2R ...
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2R
Time
Opticalpower
What is 3R and 4R regeneration ?
2nd R consists in reshaping and
improving amplitude noise
2nd R consists in reshaping and
improving amplitude noise
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1st R: Reamplifying
2nd R: Reshaping
2R
Time
Opticalpower
What is 3R and 4R regeneration ?
2nd R consists in reshaping and
improving amplitude noise
2nd R consists in reshaping and
improving amplitude noise
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1st R: Reamplifying
2nd R: Reshaping
2R
Time
Opticalpower
What is 3R and 4R regeneration ?
2nd R consists in reshaping and
improving amplitude noise
2nd R consists in reshaping and
improving amplitude noise
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1st R: Reamplifying
2nd R: Reshaping
2R
Time
Opticalpower
What is 3R and 4R regeneration ?
2nd R consists in reshaping and
improving amplitude noise
2nd R consists in reshaping and
improving amplitude noise
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2R
Time
Opticalpower
What is 3R and 4R regeneration ?
It is done by using non-linear devices: SOA , SOA based
Mach-Zehnder, Q-switched laser, etc
It is done by using non-linear devices: SOA , SOA based
Mach-Zehnder, Q-switched laser, etc
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3R
Time
Opticalpower
What is 3R and 4R regeneration ?
3R ...3R ...
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3R
Time
Opticalpower
What is 3R and 4R regeneration ?
3rd R consists in retiming the signal to
correct jitter
3rd R consists in retiming the signal to
correct jitter
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3R
Time
Opticalpower
What is 3R and 4R regeneration ?
3rd R consists in retiming the signal to
correct jitter
3rd R consists in retiming the signal to
correct jitter
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3R
Time
Opticalpower
What is 3R and 4R regeneration ?
3rd R consists in retiming the signal to
correct jitter
3rd R consists in retiming the signal to
correct jitter
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3R
Time
Opticalpower
What is 3R and 4R regeneration ?
It requires clok recovery (E standard or self-pusating laser)
followed by gating or switching
It requires clok recovery (E standard or self-pusating laser)
followed by gating or switching
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Trade off bandwidth vs jitter
Low bandwidth
High bandwidth
Drawback?
Noise
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4R
Time
Opticalpower
What is 3R and 4R regeneration ?
4th is specific to optical regeneration ...4th is specific to optical regeneration ...
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4R
Time
Opticalpower
What is 3R and 4R regeneration ?
4th R consists in wavelength regeneration or
reallocation
4th R consists in wavelength regeneration or
reallocation
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4R
Time
Opticalpower
What is 3R and 4R regeneration ?
4th R consists in wavelength regeneration or
reallocation
4th R consists in wavelength regeneration or
reallocation
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4R
Time
Opticalpower
What is 3R and 4R regeneration ?
4th R consists in wavelength regeneration or
reallocation
4th R consists in wavelength regeneration or
reallocation
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4R
Time
Opticalpower
What is 3R and 4R regeneration ?
4th R consists in wavelength regeneration or
reallocation
4th R consists in wavelength regeneration or
reallocation
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4R
Time
Opticalpower
What is 3R and 4R regeneration ?
4th R consists in wavelength regeneration or
reallocation
4th R consists in wavelength regeneration or
reallocation
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Optical network elements
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Network elements:
­Optical cross connects (OXCs)
­Optical add drop multiplexers
(OADMs)
­Optical line amplifiers (OLAs)
­Optical line terminals (OLTs)
­...........
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Optical cross connects
· Needed for complex mesh topologies and large
number of wavelengths
· Functions:
­ Service provisioning
­ Protection switching
­ Bit rate transparency (if it is all optical)
­ Performance monitoring
­ Wavelength conversion
­ Multiplexing and grooming
56Grooming, regeneration, wavelength conversion
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In an electronic switch
one can monitor signals,
measure BER, groom, etc
In an optical one, optical power
can conveniently be measured,
but not much more
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?
?
?
?
?
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Example of optical network node
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OXC
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Wavelength Routing Optical Cross-Connect
Ericsson & KTH 1992 (!)
1-4
1-4
1-4
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Devices in optical network
elements
Requirements??
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Photonics in information transfer
and in general
·Functionality
­Photonics lacks, currently, RAM type
memory and signal processing capability
·Physical size ("footprint")
­ 100s to 1000s of wavelengths in length,
order of wavelength in transverse dimension
­ Compare electronics (FET gate lengths <
100 nm), but interconnects important for
photonics as well as electronics
Èost
­Too expensive (too much handcraft..)
·But there are ways to resolve this
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First 4x4 polarization independent switch (LiNbO3)
Ericsson, 1988
5 cm