S Optical Networks Course Lecture 11: Future Directions in Optical Networking

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S-72.3340 Optical Networks Course Lecture 11: Future Directions in Optical Networking Edward Mutafungwa Communications

1 S Optical Networks Course Lecture 11: Future Directions in Optical Networking Edward Mutafungwa Communications Laboratory, Helsinki University of Technology, P. O. Box 2300, FIN TKK, Finland Tel: , edward.mutafungwa@tkk.fi

2 Lecture Outline Introduction Past and present predictions Non-optical technologies Optical switching evolution Alternative optical multiplexing schemes Novel optical device technologies Conclusions April 07 EMU/S /FutureDirections/ Slide 2 of 46

3 1. Introduction The field of optical networking has had some up and downs Boom time characterized by bold predictions and huge injection of funds for R&D Followed by downturn, pessimism and reduced funding Current gradual upturn, more realistic predictions and targets Prolonged recovery will inevitably bring back the bold predictions This lecture highlights some of optical technological activities in those recent boom-bust cycles April 07 EMU/S /FutureDirections/ Slide 3 of 46

4 2. Past and Present Predictions Some predictions on optical networking where made 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 Union project HORIZON (Horizontal Action on Optical Networks) Summarized in a report titled Roadmap towards the Optical Communication Age: A European view by the HORIZON project and the ACTS Photonic Domain November April 07 EMU/S /FutureDirections/ Slide 4 of 46

5 2. Past and Present Predictions Technology evolution WDM rings with full connectivity ROADM Interconnected rings and mesh topologies ROADM OXC OXC ROADM OXC OXC OXC *Ref: Roadmap towards, EU HORIZON project and ACTS, Nov WDM rings with node addressing OADM OADM ROADM OADM ROADM Pt-pt WDM transmission OADM OADM ROADM WDM transmission with add/drop OADM OADM: Optical add-drop multiplexers ROADM: Reconfigurable OADM OXC: Optical cross-connects ? April 07 EMU/S /FutureDirections/ Slide 5 of 46

2. Past and Present Predictions WDM-based networks were expected to be dominant by now Timetable distorted by the emergence of next-generation SDH solutions

6 2. Past and Present Predictions WDM-based networks were expected to be dominant by now Timetable distorted by the emergence of next-generation SDH solutions and post-bubble reduced investment NG-SDH *Ref: Roadmap towards, EU HORIZON project and ACTS, Nov April 07 EMU/S /FutureDirections/ Slide 6 of 46

7 2. Past and Present Predictions Optical 3R, optical signal processing yet to mature *Ref: Roadmap towards, EU HORIZON project and ACTS, Nov April 07 EMU/S /FutureDirections/ Slide 7 of 46

percentage of the total number of transceiver sales in 2003.

8 2. Past and Present Predictions Cautious but gradual migration from 10 to 40 Gb/s Cisco s CRS1- routers (with 40 Gb/s [STM-256] optical interfaces) Figure: Unit sales of long-haul transceivers, shown as a percentage of the total number of transceiver sales in The 40 Gbit/s values quoted include short-reach transponders. Source: Strategies Unlimited/FiberSystems Europe. April 07 EMU/S /FutureDirections/ Slide 8 of 46

2. Past and Present Predictions Evolutions of the Ethernet standard Ethernet Line Rate 10 Mb/s 100 Mb/s 1 GbE 10 GbE 100 GbE Year Launched 1983 1994 1996 2002 Standard being developed 2.

9 2. Past and Present Predictions Evolutions of the Ethernet standard Ethernet Line Rate 10 Mb/s 100 Mb/s 1 GbE 10 GbE 100 GbE Year Launched Standard being developed 2.5 Gb/s Gb/s 10 Gb/s 40 Gb/s 160 Gb/s Activities in 160 Gb/s development have actually started! 160 Gb/s ADM, clock recovery. 160Gb/s x 640km 160 Gb/s serial transmission 160Gb/s x 350km, technoeconomics, demultiplexing April 07 EMU/S /FutureDirections/ Slide 9 of 46

10 2. Past and Present Predictions Evolution trend of protocol stacks for IP-over-WDM IP IP/MPLS IP/GMPLS IP/GMPLS AAL-5/ATM SDH SDH Thin SDH WDM WDM WDM & Optical Switching WDM & Optical label switching Adapted from article by S. Yoo, J. Lightwave Tech., Dec April 07 EMU/S /FutureDirections/ Slide 10 of 46

11 3. Non-Optical Technologies Major strides in digital signal processing (DSP) for non-optical communications systems Pressure to squeeze out ever better performance from very bandwidth limited systems Multipath RF wireless channels High-speed DSL and cable modems Audio echo cancellation etc. Same technologies can reduce cost and improve performance of optical systems April 07 EMU/S /FutureDirections/ Slide 11 of 46

12 3. Non-Optical Technologies The immediate future is not all-optical (Capacity x Distance)/Cost Current Optical Comm. Systems Optical Technologies Coded Modulation Adaptive Equalization Optical Non-Binary Dispersion Modulation Compensation Error- Correction WDM Coding Optical Adaptive Amplifiers Threshold, FDM/ Transversal Non-Optical Technologies SCM Filters OEO - Transponders Time *Ref: J. Kahn & K. Ho, Proceedings of SPIE, Vol. 4872, July 2005 April 07 EMU/S /FutureDirections/ Slide 12 of 46

13 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 such as 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 April 07 EMU/S /FutureDirections/ Slide 13 of 46

Reduce transmit power requirements Figure: BER vs OSNR comparison of the two

14 3.1 Non-Binary Modulation DPSK has the advantage of requiring about 3 db lower 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 modulation schemes for a 40 Gb/s system. April 07 EMU/S /FutureDirections/ Slide 14 of 46

15 3.1 Non-Binary Modulation Differential Quadrature PSK (DQPSK) is even better but more complex enabler for 160 Gbit/s line rates Figure: Research trends in optical modulation formats *Ref: K. Kitayama, J. Lightwave Tech, October April 07 EMU/S /FutureDirections/ Slide 15 of 46

16 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 April 07 EMU/S /FutureDirections/ Slide 16 of 46

17 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? April 07 EMU/S /FutureDirections/ Slide 17 of 46

18 3.3 Forward Error Correction (FEC) Adapted from article by T. Mizuochi, IEEE JSTQE May/June 2006 April 07 EMU/S /FutureDirections/ Slide 18 of 46

19 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 slower electronics operating in parallel Complicated architectures Larger dimensions or footprint Large power consumption Optical signal processing still necessary for future April 07 EMU/S /FutureDirections/ Slide 19 of 46

20 4. Future Optical Switching Optical switching enables switching of optical signal without the need of OE or EO conversions OE OE EO EO 2x2 electrical switch Types of optical switching Optical Circuit Switching Optical Packet Switching Optical Burst Switching 2x2 optical switch April 07 EMU/S /FutureDirections/ Slide 20 of 46

21 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 λ OSC λ 1 Switch controller λ OSC λ OSC λ 1 λ 1 2x2 optical switch λ OSC λ 1 April 07 EMU/S /FutureDirections/ Slide 21 of 46

22 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 Payloads Packet Headers Header processing, Synchronization, Routing, Forwarding Synch. Control Switch Control Header rewrite Input Buffers Output Buffers 2x2 optical packet switch April 07 EMU/S /FutureDirections/ Slide 22 of 46

23 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 range Burst Burst control packet Time offset BCP processing Switch Control 2x2 optical switch April 07 EMU/S /FutureDirections/ Slide 23 of 46

24 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 April 07 EMU/S /FutureDirections/ Slide 24 of 46

25 5. Alternative Optical Multiplexing Otherwise increase reuse of existing wavelength channels Use alternative optical multiplexing schemes to share a single wavelength channel xdm MUX λ 1 WDM MUX xdm MUX λ 2 April 07 EMU/S /FutureDirections/ Slide 25 of 46

26 5.1 Optical TDM (OTDM) OTDM combines slow optical data streams in to higher speed streams Either by optical bit-interleaving or optical packetinterleaving Electrical TDM line rates limited by speed of electronic circuits OTDM would be necessary for line rates beyond 40 Gb/s e.g. four 40Gb/s streams multiplexed into single 160 Gb/s B bit/s streams OTDM MUX 4 B bit/s streams Figure: Example TDM by bit interleaving April 07 EMU/S /FutureDirections/ Slide 26 of 46

27 5.1 Optical TDM (OTDM) Challenges in implementing high-speed OTDM Need for ultrashort optical pulse sources Synchronization between the receiver and input signal is difficult Fiber impairments at OTDM signal rates will be very significant optical 3R necessary April 07 EMU/S /FutureDirections/ Slide 27 of 46

28 5.2 Optical Code Division Multiplexing Similar to conventional CDMA for RF systems, but now applied 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 λ 1 Optical Transmitter Modulator Modulator Data stream 2 OCDMA Encoder OCDMA Encoder Combiner λ 1 WDM MUX Combiner λ 2 April 07 EMU/S /FutureDirections/ Slide 28 of 46

29 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/T c ) increased dispersion penalties Amplitude Amplitude Amplitude Data Bits 1 T Amplitude Encoding T Phase Encoding 0 1 Spreading Code [ ] Time Chip Time π 0 π π 0 π 0 π 0 π π 0 π 0 Time T Chip phase c T April 07 EMU/S /FutureDirections/ Slide 29 of 46

30 5.2 Optical Code Division Multiplexing Comparison between RF/Wireless and Optical CDMA Attributes Medium Wireless CDMA Air Optical CDMA Fiber waveguides Processing Mature VLSI Chips Underdeveloped, bulky Bit Rate Low (in Mbps) High (in Gbps) Impairments Multipath Near-far effect Severe attenuation Dispersion Fiber nonlinearities April 07 EMU/S /FutureDirections/ Slide 30 of 46

31 5.3 Polarization Division Multiplexing A light signal has two orthorgonal polarization components Polarization division multiplexing (PolDM) different data streams carried on each polarization component Data stream 1 λ 1 Optical Transmitter Polarization Beam Splitter Modulator Modulator Polarization Beam Combiner λ 1 Data stream 2 WDM MUX λ 2 April 07 EMU/S /FutureDirections/ Slide 31 of 46

32 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 April 07 EMU/S /FutureDirections/ Slide 32 of 46

33 6. Novel Optical Device Technologies The need to process signal optically still remains for future systems Ultra fast line rates beyond electronic processing speed limits 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 April 07 EMU/S /FutureDirections/ Slide 33 of 46

6. Novel Optical Device Technologies Example: currently electronic 3R transponders only feasible option Transponder or OEO O/E Electronic 3R regeneration E/O All-optical

34 6. Novel Optical Device Technologies Example: currently electronic 3R transponders only feasible option Transponder or OEO O/E Electronic 3R regeneration E/O All-optical (OOO) 3R regenerators Simplify designs Eliminate electronic processing bottlenecks Might also be cost-effective OOO April 07 EMU/S /FutureDirections/ Slide 34 of 46

35 6. Novel Optical Device Technologies Optical 3R would significantly increase line rates and/or distance without performance degradations Figure: Comparison of receiver sensitivities for 40 Gb/s transmission over km with 1R and 3R regeneration. *Ref: K. Kitayama, J. Lightwave Tech, October April 07 EMU/S /FutureDirections/ Slide 35 of 46

or medium scale integration Figure: A compact mini EDFA module. Single function: amplify WDM signal.

36 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 April 07 EMU/S /FutureDirections/ Slide 36 of 46

37 6.3 Photonic Integrated Circuits Extensive optical DSP will be possible with fully fledged 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 April 07 EMU/S /FutureDirections/ Slide 37 of 46

38 6.3 Photonic Integrated Circuits Example: planar arrayed-waveguide grating (AWG) A dual function (demultiplexing or multiplexing) PIC April 07 EMU/S /FutureDirections/ Slide 38 of 46

6.3 Photonic Integrated Circuits Example: 10 wavelength (@10 Gb/s) DWDM transmitter A 50

modulator DFB: Distributed feedback laser OPM: Optical performance monitors *Ref: R.

39 6.3 Photonic Integrated Circuits Example: 10 wavelength Gb/s) DWDM transmitter A 50 function large scale PIC VOA: Variable optical attenuator EAM: Electro-absorption modulator DFB: Distributed feedback laser OPM: Optical performance monitors *Ref: R. Nagarajan, J. Lightwave Tech, January April 07 EMU/S /FutureDirections/ Slide 39 of 46

$John 1987) Manipulate and control light using photonic band-gap effect created by periodic refractive index variations Like semiconductor devices controlling flow of electrons using energy band-gap$

40 6.4 Photonic Crystals Candidate technology future optical signal processing devices (inventors: E. Yablonovitch & S. John 1987) Manipulate and control light using photonic band-gap effect created by periodic refractive index variations Like semiconductor devices controlling flow of electrons using energy band-gap 1D photonic crystal 1D periodicity like a fiber Bragg grating 2D photonic crystal 2D planar periodicity Relatively easy to fabricate 3D photonic crystal 3D planar periodicity Difficult to fabricate Potentially many functions April 07 EMU/S /FutureDirections/ Slide 40 of 46

41 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 April 07 EMU/S /FutureDirections/ Slide 41 of 46

42 6.4 Photonic Crystals Photonic crystal fibers have some distinct and easily tailorable 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 regimes possible in holey fibers, dependent upon the hole diameter/spacing ratio. April 07 EMU/S /FutureDirections/ Slide 42 of 46

43 6.4 Photonic Crystals 2D/3D photonic crystal slabs For future realization of photonic integrated circuits (PIC) Figure: Photonic crystal waveguide (source: Nature Photonics, pp. 11, Jan 2007). April 07 EMU/S /FutureDirections/ Slide 43 of 46

44 6.4 Photonic Crystals Figure: A typical photonic crystal PIC envisioned for the future (source: Nature Photonics, pp. 11, Jan 2007). April 07 EMU/S /FutureDirections/ Slide 44 of 46

7. A Glimpse Further Into the Future Ref: M. Jinno, Y. Miyamoto, Y. Hibino, Optical Transport Networks in 2015, Nature Photonics, March 2007.

45 7. A Glimpse Further Into the Future Ref: M. Jinno, Y. Miyamoto, Y. Hibino, Optical Transport Networks in 2015, Nature Photonics, March 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) April 07 EMU/S /FutureDirections/ Slide 45 of 46

46 Thank You! April 07 EMU/S /FutureDirections/ Slide 46 of 46

WDM. Coarse WDM. Nortel's WDM System

WDM. Coarse WDM. Nortel's WDM System WDM wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e. colors) of laser light.