lecture 11_future directions in optical networking
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7/30/2019 Lecture 11_Future Directions in Optical Networking
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S-72.3340 Optical Networks Course
Lecture 11: Future Directions inOptical Networking
Edward MutafungwaCommunications Laboratory, Helsinki University of Technology,
P. O. Box 2300, FIN-02015 TKK, FinlandTel: +358 9 451 2318, E-mail: [email protected]
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Lecture Outline
Introduction
Past and present predictions
Non-optical technologies
Optical switching evolution
Alternative optical multiplexing schemesNovel optical device technologies
Conclusions
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1. Introduction
The field of optical networking has had some upand downs
Boom time characterized by bold predictions and hugeinjection of funds for R&D
Followed by downturn, pessimism and reduced funding
Current gradual upturn, more realistic predictions andtargets
Prolonged recovery will inevitably bring back the bold
predictions
This lecture highlights some of optical technologicalactivities in those recent boom-bust cycles
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2. Past and Present Predictions
Some predictions on optical networking wheremade in the 1990s during the telecomm/dot-com
boom Some were accurate, albeit delayed in realization
Some were a too optimistic
Example predictions from the European Unionproject HORIZON (Horizontal Action on OpticalNetworks)
Summarized in a report titled “Roadmap towards theOptical Communication Age: A European view by theHORIZON project and the ACTS Photonic Domain” November 1999.
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2. Past and Present Predictions
OADM OADM
OADMOADM
OADM
OADM
ROADM
ROADMROADM
ROADM
ROADM
ROADM
OXC
OXC
OXC
OXC
OXC
1996 1998 2000 2002
T e c h n o l o g y
e v o l u t i o n
Pt-pt WDM transmission
WDM transmission with add/drop
WDM rings withnode addressing
WDM rings withfull connectivity
Interconnected ringsand mesh topologies
OADM: Optical add-drop multiplexersROADM: Reconfigurable OADMOXC: Optical cross-connects
*Ref: “Roadmap towards…,”
EU HORIZON project and
ACTS, Nov. 1999.
2007?2005
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2. Past and Present Predictions
WDM-based networks were expected to be dominant by now
Timetable distorted by the emergence of next-generation SDH solutionsand post-bubble reduced investment
NG-SDH
*Ref: “Roadmap towards…,”
EU HORIZON project and
ACTS, Nov. 1999.
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2. Past and Present Predictions
Optical 3R, optical signal processing yet to mature
*Ref: “Roadmap towards…,” EU
HORIZON project and ACTS, Nov. 1999.
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2. Past and Present Predictions
Evolutions of the Ethernet standard
1983 YearLaunched
EthernetLine Rate
10 Mb/s
1994
100 Mb/s
1996
1 GbE
2002
10 GbE
Standardbeingdeveloped
100 GbE
160 Gb/s ADM,clock recovery.
160Gb/s x 640km160 Gb/s serialtransmission
160Gb/s x 350km, techno-economics, demultiplexing
2.5 Gb/s⇒ Gb/s 10 ⇒ Gb/s ⇒ 40 Gb/s ⇒ 160 Gb/s
Activities in 160 Gb/s development have actually started!
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2. Past and Present Predictions
Evolution trend of protocol stacks for IP-over-WDM
IP IP/MPLS IP/GMPLS IP/GMPLS
WDM & Optical label
switching
AAL-5/ATM
SDH SDHThin SDH
WDM WDM WDM & Optical
Switching
Adapted from article by S. Yoo, J. LightwaveTech., Dec. 2006.
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3. Non-Optical Technologies
Major strides in digital signal processing (DSP) fornon-optical communications systems
Pressure to squeeze out ever better performancefrom very bandwidth limited systems Multipath RF wireless channels
High-speed DSL and cable modems Audio echo cancellation
etc.
Same technologies can reduce cost and improveperformance of optical systems
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3. Non-Optical Technologies
The immediate future is not “all-optical”
*Ref: J. Kahn & K. Ho, Proceedingsof SPIE, Vol. 4872, July 2005
( C a p a
c i t y x D i s t
a n c e ) / C o s
t
Time
Optical
Amplifiers
-
Optical Technologies
Non-Optical Technologies
WDM
FDM/SCM
Compensation
AdaptiveThreshold,TransversalFilters
Error-CorrectionCoding
Non-BinaryModulation
Current Optical
Comm. Systems
Adaptive
Equalization
CodedModulation
( C a p a
c i t y x D i s t
a n c e ) / C o s
t
Time
Optical
Amplifiers
OEOTransponders
-
Optical Technologies
Non-Optical Technologies
WDM
FDM/SCM
OpticalDispersion
AdaptiveThreshold,TransversalFilters
Error-CorrectionCoding
Non-BinaryModulation
Current Optical
Comm. Systems
Adaptive
Equalization
CodedModulation
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3.1 Non-Binary Modulation
Conventional binary NRZ or RZ on-off keying (OOK) 0 bit ⇒ No light in bit interval
1 bit ⇒ Light in bit interval
Simple and good performance for ≤10 Gbit/s line rates
Interest in phase-shift keying (PSK) schemes suchas differential PSK (DPSK) for ≥40 Gbit/s line rates Increased tolerance to fiber nonlinearities
Information carried in optical phase changes Light always present for 0 and 1 bits
0 bit ⇒ Apply π phase change whenever you see 0 bit
1 bit ⇒ Do not change phase if you see 1 bit
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3.1 Non-Binary Modulation
DPSK has the advantage of requiring about 3 dBlower OSNR than OOK to achieve given BER
Doubles the reach of a DPSK link compared to OOK
Reduce transmit power requirements
Figure: BER vs OSNR comparison of the two modulationschemes for a 40 Gb/s system.
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3.1 Non-Binary Modulation
Differential Quadrature PSK (DQPSK) is even better butmore complex ⇒ enabler for 160 Gbit/s line rates
Figure: Research trends inoptical modulation formats
*Ref: K. Kitayama, J. Lightwave
Tech, October 2005.
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3.2 Adaptive Equalization
Plenty of R&D in adaptive equalizers to combat dispersion(electronic dispersion compensators) and nonlinearity Linear or Feed-forward equalizers (FFE)
Decision-feedback equalizers (DFE) Maximum likelihood sequence estimation (MLSE) equalizers
Source: Q. Yu, J. Lightwave Tech., Dec. 2006.
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3.3 Forward Error Correction (FEC)
1st/2nd generation FEC codes
Reed–Solomon codes , concatenated RS codes
Future 3rd generation FEC codes Turbo codes, low-density parity-check (LDPC) codes
4th generation FEC codes ?
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3.3 Forward Error Correction (FEC)
Adapted from article by T. Mizuochi, IEEE J STQE May/J une 2006
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3.4 Limitations of Electronics
Difficulties in implementing high-speed (≥ 40 GHz)analog, digital or mixed-signal integrated circuits
Current 40 Gbit/s linecards usually employ slowerelectronics operating in parallel
Complicated architectures
Larger dimensions or footprint
Large power consumption
Optical signal processing still necessary for future
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4. Future Optical Switching
Optical switching enables switching of optical signalwithout the need of OE or EO conversions
OE
OE
EO
EO
2x2 electricalswitch
2x2 opticalswitch
Types of optical switching Optical Circuit Switching Optical Packet Switching
Optical Burst Switching
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4.1 Optical Circuit Switching (OCS)
Current optical systems mostly use OCS Switching of all traffic (usually gigabytes) on a wavelength channel
or multiple wavelength channels Out-of-band switch control using optical supervisory channel (OSC)
on a different wavelength Required switching speed in millisecond range Inefficient utilization of large wavelength channel capacities
Switchcontroller
λOSC
λOSC λ1
2x2 optical switch λOSC λ1
λ1λOSC
λ1
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4.2 Optical Packet Switching (OPS)
OPS introduces statistical multiplexing in the optical layer Switching of optical packets (40 to 1500 bytes long) In-band (same wavelength) switch control using optical packet
headers Required switching speed in nanosecond range Optical buffering techniques still limited, bulky, lossy and expensive OEO conversions required for electronic header processing
2x2 opticalpacket switch
PacketHeaders
Header processing, Synchronization,Routing, Forwarding
SwitchControl
Payloads
InputBuffers
OutputBuffers
Synch.Control
Headerrewrite
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4.3 Optical Burst Switching (OBS)
OBS is a combines the advantages of OCS and OPS Switching of aggregated bursts or megapackets (tens of kB long) In-band or out-of-band switch control using a burst control packet
(BCP) transmitted ahead of the burst BCP alerts switching nodes of size and destination of coming burst Burst sent without requiring confirmation after time offset period Eliminates need for optical buffering
Required switching speed in microsecond rangeBurst control
packet BCP processing
SwitchControl
Burst
Time offset
2x2 optical switch
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5. Alternative Optical Multiplexing
Wavelength division multiplexing (WDM)
If wavelength channel number insufficient add more
wavelengths by reducing channel spacing Deploy more stable lasers with negligible wavelength drifting
Use filters with sharper skirts (high selectivity) to retriever channels
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5. Alternative Optical Multiplexing
Otherwise increase reuse of existing wavelengthchannels
Use alternative optical multiplexing schemes toshare a single wavelength channel
WDM
MUX
xDMMUX
λ1
λ2
xDMMUX
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5.1 Optical TDM (OTDM)
OTDM combines slow optical data streams in tohigher speed streams
Either by optical bit-interleaving or optical packet-interleaving
Electrical TDM line rates limited by speed of electroniccircuits
OTDM would be necessary for line rates beyond 40 Gb/s• e.g. four 40Gb/s streams multiplexed into single 160 Gb/s
Figure: Example TDM by bit interleaving
OTDMMUX
4×B bit/sstreamsB bit/s
streams
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5.1 Optical TDM (OTDM)
Challenges in implementing high-speed OTDM
Need for ultrashort optical pulse sources
Synchronization between the receiver and input signal isdifficult
Fiber impairments at OTDM signal rates will be very
significant ⇒ optical 3R necessary
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5.2 Optical Code Division Multiplexing
Similar to conventional CDMA for RF systems, but nowapplied to optical signals
Different streams share a wavelength channel by being
assigned distinct signature codes Corresponding decoder used to recover data at receiver
Data stream 1
OpticalTransmitter
OCDMA Encoder
WDMMUX
Combiner
λ1
λ2
Data stream 2
OCDMA Encoder
λ1
Combiner
Modulator
Modulator
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5.2 Optical Code Division Multiplexing
Optical CDMA or OCDM
Mostly direct-spreading
Amplitude encoding Phase encoding
Longer code lengths (i.e.
larger code weight) More distinct codes possible
Reduced limitations due to
multiple access interference Higher chip rate (1/Tc) ⇒
increased dispersionpenalties
Amplitude Encoding
A m p l i t u d e
Time1 0 1 1 0 1 0 1 0 1 1 0 1 0
Phase Encoding
A m p l i t u d e
Timeπ 0 π π 0 π 0 π 0 π π 0 π 0
Chip
Chip phase
Data Bits
1
Time
0 1
Spreading Code[1 0 1 1 0 1 0]
T
Tc
T
T
A m p l i t u d
e
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5.2 Optical Code Division Multiplexing
Comparison between RF/Wireless and Optical CDMA
Wireless CDMA Optical CDMA Attributes
Medium
Processing
Bit Rate
Impairments
Air
Mature VLSI Chips
Low (in Mbps)
Multipath
Near-far effect
Severe attenuation
Fiber waveguides
Underdeveloped, bulky
High (in Gbps)
Dispersion
Fiber nonlinearities
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5.3 Polarization Division Multiplexing
A light signal has two orthorgonal polarization components
Polarization division multiplexing (PolDM) ⇒ different datastreams carried on each polarization component
Data stream 1
PolarizationBeam Splitter
WDMMUX
λ1
λ2
Data stream 2
Modulator
Modulator
OpticalTransmitter
λ1
PolarizationBeam Combiner
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5.3 Polarization Division Multiplexing
PolDM challenges and limitations Only two data streams can share single wavelength
channel
State of polarization of a light not preserved in fiber ⇒
dynamic polarization control required at demultiplexer
Polarization dependent losses
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6. Novel Optical Device Technologies
The need to process signal optically still remains forfuture systems
Ultra fast line rates beyond electronic processing speedlimits
Tighter wavelength channel spacing
Applications include: Monitoring signal quality (e.g. BER, Q-factor) optically
Optical header or control packet processing
All-optical wavelength conversion
All-Optical 3R (re-amplify, reshape, retime) regeneration
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6. Novel Optical Device Technologies
Example: currently electronic 3R transponders only feasibleoption
Transponder
or OEO O/EElectronic 3R regeneration E/O
All-optical (OOO) 3R regenerators
Simplify designs
Eliminate electronic processing bottlenecks
Might also be cost-effective
OOO
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6. Novel Optical Device Technologies
Optical 3R would significantly increase line rates and/ordistance without performance degradations
Figure: Comparison of receiver sensitivitiesfor 40 Gb/s transmission over 12000 kmwith 1R and 3R regeneration.
*Ref: K. Kitayama, J. Lightwave
Tech, October 2005.
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6.3 Photonic Integrated Circuits
Most of current optical devices compared to electronic ICs Bulky, costly, difficult to scale, low volume production and relatively
low reliability
Limited to mostly small or medium scale integration
Figure: A compact mini EDFA module.
Single function: amplify WDM signal. Figure: TI's OMAP730 single-chip GSM/GPRS baseband processor
6 3 h i d Ci i
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6.3 Photonic Integrated Circuits
Extensive optical DSP will be possible with fullyfledged photonic integrated circuits (PICs) Processing digital optical bits instead of analog optical
signals
Photonic integration criteria includes: Low coupling and absorption losses
Polarization insensitivity
Diverse operating wavelengths and temperatures
Interaction between optical active and passive devices
Package mechanically stable
Reproducibility on a manufacturing scale
6 3 Ph t i I t t d Ci it
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6.3 Photonic Integrated Circuits
Example: planar arrayed-waveguide grating (AWG)
A dual function (demultiplexing or multiplexing) PIC
6 3 Ph t i I t t d Ci it
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6.3 Photonic Integrated Circuits
Example: 10 wavelength (@10 Gb/s) DWDM transmitter A 50 function large scale PIC
*Ref: R. Nagarajan, J. Lightwave
Tech, January 2005.
VOA: Variable optical attenuator
EAM: Electro-absorption modulator
DFB: Distributed feedback laser
OPM: Optical performance monitors
6 4 Ph t i C t l
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6.4 Photonic Crystals
Candidate technology future optical signal processingdevices (inventors: E. Yablonovitch & S. John 1987)
Manipulate and control light using photonic band-gap effectcreated by periodic refractive index variations
Like semiconductor devices controlling flow of electrons usingenergy band-gap
1D photonic crystal
•1D periodicity like a
fiber Bragg grating
2D photonic crystal
•2D planar periodicity
•Relatively easy tofabricate
3D photonic crystal
•3D planar periodicity
•Difficult to fabricate
•Potentially many functions
6 4 Ph t i C t l
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6.4 Photonic Crystals
Photonic crystal fibers (holey fibers)
Transparent solid material (e.g., glass) and air contained in holes
Diameter (size) and spacing (pitch) of holes determines blocked
wavelengths
6 4 Photonic Crystals
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6.4 Photonic Crystals
Photonic crystal fibers have some distinct and easilytailorable optical properties compared to conventional fibers
Could be custom-made for ultrafast rate and/or long distance links
Useful for making various fiber-based devices e.g. fiber amplifiers
Figure: Various dispersion regimespossible in holey fibers, dependent uponthe hole diameter/spacing ratio.
6 4 Photonic Crystals
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6.4 Photonic Crystals
2D/3D photonic crystal slabs
For future realization of photonic integrated circuits (PIC)
Figure: Photonic crystalwaveguide (source: Nature
Photonics, pp. 11, Jan 2007).
6 4 Photonic Crystals
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6.4 Photonic Crystals
Figure: A typical photonic crystal PIC envisioned for the future (source: Nature Photonics,pp. 11, Jan 2007).
7 A Glimpse Further Into the Future
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7. A Glimpse Further Into the Future
Ref: M. Jinno, Y. Miyamoto, Y. Hibino, ”Optical Transport Networks in2015,” Nature Photonics, March 2007.
Sept 2006 record by NTT (Japan) 14 Tbit/s over 160 km fiber (140
WDM/PolDM channels, each a 111 Gbit/s DQPSK signal with FEC)
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Thank You!