Razali Ngah, and Zabih Ghassemlooy Optical Communication Research Group

1. An All Optical OTDM Router Based On SMZ Switch Razali Ngah, and Zabih Ghassemlooy Optical Communication Research Group School of Engineering & Technology Northumbria University, United Kingdom http: soe.unn.ac.uk/ocr/

2. Contents • Aim and objectives • Introduction • Optical time division multiplexing (OTDM) • Ultrafast optical time-domain technology - Issues • All optical switches • All OTDM router • Simulations and results • Conclusions + further work • Publications

3. Aim and Objectives Aim: To develop a novel synchronization technique using all optical switches for ultra high speed OTDM networks • Objectives: • To study the requirement of ultra high speed OTDM packet switching • To investigate all optical demultiplexing techniques and devices • To develop a novel synchronization technique using all optical switch

4. Introduction • Multiplexing:- To extend a transmission capacity • Electrical • Optical • Drawbacks with Electrical: • Speed limitation beyond 40 Gb/s (80 Gb/s future) of: • Electo-optics/opto-electronics devices • High power and low noise amplifiers • Bandwidth bottleneck due to optical-electronic-optical conversion Solution: All optical transmission, multiplexing, switching, processing, etc.

5. Multiplexing : Optical • Wavelength division multiplexing (WDM) • Optical time division multiplexing (OTDM)  • Hybrid WDM-OTDM

6. OTDM • The total capacity of single-channel OTDM network = DWDM • Overcomes non-linear effects associated with WDM: (i) Self Phase Modulation (SPM) – The signal intensity of a given channel modulates its own refractive index, and therefore its phase (ii) Cross Phase Modulation (XPM) – In multi-channel systems, other interfering channels also modulate the refractive index of the desired channel and therefore its phase (iii) Four Wave Mixing (FWM) – Intermodulation products between the WDM channels, as the nonlinearity is quadratic with electric field • Less complex end node equipment (single-channel Vs. multi-channels) • Can operate at both: • 1500 nm • 1300 nm

7. Data (10 Gb/s) Data (10 Gb/s) Rx Span N*10 Gb/s 10 GHz Rx Network node Light source N Rx Drop Add Clock Clock recovery Transmitter Receiver Fibre delay line Fibre Modulators Amplifier OTDM MUX OTDM DEMUX OTDM :Principle of Operation • Multiplexing is sequential, and could be carried out in: • A bit-by-bit basis (bit interleaving) • A packet-by-packet basis (packet interleaving)

8. OTDM : Multiplexing of Clock Signal • Space division multiplexing: separate transmission fibre • time varying differential delay & high cost • Wavelength division multiplexing: different wavelength • only practical for predetermined path • Orthogonal polarization: orthogonally polarized clock pulse • polarization mode dispersion and other non linear effects • Intensity division multiplexing: higher intensity for clock pulse • difficult to maintain in long distance transmission • Time division multiplexing: self-synchronization - clock is located at the beginning of the packet)

9. Ultrafast optical time-domain technology : Issues • Synchronization (all optical clock recovery) • Clock recovery: using all optical switch combined with optical feedback • Contention resolution • Type: Optical buffering, deflection routing & wavelength conversion • Routing strategies • Switch-level routing and contention resolution

10. All Optical Switches • Key components required in all optical signal processing for ultrahigh speed OTDM networks • Applications: • Optical cross-connects: provisioning of lightpaths • Protection switching : rerouting a data stream in the event of system or network failure • Optical Add/Drop multiplexing: insert or extract optical channels to or from the optical transmission system • Optical signal monitoring

11. All Optical Switches – contd. Terahertz Optical Asymmetric Demultiplexer (TOAD) Non-linear Optical Loop Mirror (NOLM) • Requires high control pulse energy and long fiber loop • Asymmetrical switching window profile due to the counter-propagating nature of the data signals

12. All Optical Switches – contd. Symmetric Mach-Zehnder (SMZ) • Symmetrical switching window profile • Integratable structure

13. All Optical Switches – contd. Comparative study of all optical switches [Prucnal’01]

14. SMZ Switch :Principle (i) No control pulses (ii) With control pulses

15. SMZ : Switching Window G1 and G2 are the gains profile of the data signal at the output of the SOA1 and SOA2, ΔФ is the phase difference between the data signals, and LEF is linewidth enhancement factor

16. SMZ :Switching Window (simulation) TABLE I. SIMULATION PARAMETERS Parameter Value SOA . LengthLSOA 0.3 mm . Active area, 3.0x10-13 m2 . Transparent carrier density, No 1.0x1024 m-3 . Confinement factor,  0.15 . Differential gain, g 2.78x1020 m2 . Linewidth enhancement, 4.0 . Recombination coefficient A 1.43x108 1/s . Recombination coefficient B 1.0x10-16 m3/s . Recombination coefficient C 3.0x10-41 m6/s . Initial carrier density 2.8x1024 m-3 . Total number of segments 50 Data and control pulses . Wavelength of control & data 1550 nm . Pulse FWHM 2 ps . Control pulse peak power 1.2 W . Data pulse peak power 2.5 µW

17. SMZ :Switching Window (comparison) Theoretical Simulation

18. SMZ :Switching Window (experimental) Experimental switching window profile of the SMZ [Toliver’00 Opt. Comm]

19. SMZ :On-Off Ratio • The ratio of the output power in the on-state to the output power in the off-state Target signal Crosstalk Input signal of the SMZ Transmitted output of the SMZ

20. SMZ :On-Off Ratio – contd. On-off ratio at different data rate On-off ratio and normalised transmission power Against linewidth enhancement factor

21. Receiver parameters ___________________________________ Parameter Value Pre-amplifier Mode Gain controlled Noise Figure 4 dB Gain 25 dB PIN detector Responsivity 1 A/W Thermal noise 10 pA/Hz1/2 Cutoff frequency 7.0x109 Hz __________________________________________ SMZ :BER Performance

22. SMZ :BER Performance – contd. BER against the average received power for (a) back-to-back without demultiplexer, (b) 40 – 10 Gb/s demultiplexer, (c) 80 – 10 Gb/s demultiplexer and (d) 160 – 10 Gb/s demultiplexer

23. SMZ :BER Performance – contd. Comparison with experimental results

24. ( a) ( c) (e) Port 1 (f) SMZ1 SMZ2 SMZ3 (clock (read (route extract) address) payload ) ( b) Port2 (d) (a) OTDM Signal (b) Extracted Clock (c) Address + Payload (d) Address (e) Payload (f) Payload 1x2 All OTDM Router

25. OTDM Router : Synchronization • Self-synchronization: • low hardware costs and control control complexity • require a single pulse in the first bit position of the packet Clock, Address and payloads have the same intensity, polarization, width and wavelength

26. OTDM Router : Synchronization (simulation)

27. OTDM Router : Simulation Results Crosstalk OTDM packet signal Extracted clock from the OTDM packet

28. OTDM Router : Simulation Results –contd. The on-off ratio against the bit period

29. OTDM Router : Simulation Results – contd. Clock extraction and demultiplexing for OTDM packet signal Crosstalk Demultiplexed payload at the transmitted port

30. OTDM Router : Simulation

31. OTDM Router : Simulation Results OTDM input packet Clk Add Payload

32. OTDM Router : Simulation Results – contd. Extracted clock signal at the reflected output of SMZ1

33. OTDM Router : Simulation Results – contd. Add Payload Data packet at the transmitted output of SMZ1

34. OTDM Router : Simulation Results – contd. Address bit at the reflected output of SMZ2

35. OTDM Router : Simulation Results – contd. Payload at the transmitted output of SMZ2

36. OTDM Router : Simulation Results – contd. Payload at the port 1 of SMZ3

37. Performance Issues (1) Relative Intensity Noise (RIN) • Relative timing jitter between the control and the signal pulses induces intensity fluctuations of the demultiplexed signals

38. Relative Intensity Noise (RIN) • The output signal can be described by: where Tx(t)is the switching window profile and p(t) is the input data profile • The expected of the output signal energy is given as: • pt(t)probability density function of the relative signal pulse arrival time: where tRMSis the root mean square jitter

39. Relative Intensity Noise (RIN) – contd. • The variance of the output signal, depending on the relative arrive time is: • Assuming that the mean arrival time of the target channel is at the centre of the switching window, RIN induced by the timing jitter of the output signal can be expressed as: • The total RIN for the router is three times the value of single SMZ

40. Performance Issues – contd. (2) Channel Crosstalk (CXT) • Due to demultiplexing of adjacent non-target channels to the output port when the switching profile overlaps into adjacent signal pulses

41. Channel Crosstalk (CXT) – contd. • CXT is defined by the ratio of the transmitted power of one non-target channel to that of a target channel • Et is the output signal energy due to the target channel • Ent is the output signal energy due to the nontarget channel • The total crosstalk for the router

42. BER Analysis • Assuming 100% energy switching ratio for SMZ and the probability of mark and space are equal, the mean photocurrents for mark Im and space Is are: where R is the responsivity of the photodetector, ηinand ηout are the input and output coupling efficiencies of the optical amplifier, respectively; G is the optical amplifier internal gain, L is optical loss between amplifier and receiver, and Psigis the pre-amplified average signal power for a mark (excluding crosstalk) • The variance of receiver noise for mark and space:

43. The noise variance of RIN and • The average photo-current equivalent of ASE • The expression for calculating BER is given as: where • The total variance BER Analysis – cont. • The noise variance of optical amplifier

44. Receiver Incoming 1x2 Router t = t OTDM s Signal P Photo - P k in SMZ SMZ SMZ BER detector Filter 1 2 3 Optical Amp. Clock Address Optical path Electrical path BER: Theoretical Results Block diagram of a router with a receiver System Parameters

45. RIN and CXT : Results RIN against control pulse separation for a single SMZ and a router CXT against control pulse separation for a single SMZ and a router

46. BER : Results BER against average received power for baseline and with an optical router

47. BER : Simulation Results BER increases with the number of SMZ stages due to the accumulation of ASE noise in the SOAs hence, resulting the RIN increases. BER against average received power for baseline and with an optical router

48. Conclusions • All optical demultiplexer and 1x2 router based on SMZ has been implemented in a simulation environment using VPI. • BER analysis has been performed. • The application of low noise SOA will reduce the power penalty. • SMZ switch becomes a key component for ultra high speed OTDM networks.

49. Publications Conference (1) R. Ngah, Z. Ghassemlooy, G. Swift, T. Ahmad and P. Ball, “Simulation of an all Optical Time Division Multiplexing Router Employing TOADs”, 3rd Annual Postgraduate Symposium on the Convergence of Telecommunications, Networking & Broadcasting, Liverpool, 17-18 June 2002, pp. 415-420. (2) R. Ngah, Z. Ghassemlooy, and G. Swift, “Simulation of an all Optical Time Division Multiplexing Router Employing Symmetric Mach-Zehnder (SMZ),” 7th IEEE High Frequency Postgraduate Student Colloquium, London, 8-9 Sept. 2002, pp. 133-139. (3) R. Ngah, Z. Ghassemlooy, and G. Swift, “40 Gb/s All Optical Router Using Terahertz Optical Asymmetric Demutiplexer (TOADs)” International Conference on Robotics, Vision, Information and Signal Proceeding, Penang Malaysia, 22-24 Jan 2003, pp. 179-183. (4) R. Ngah, Z. Ghassemlooy, and G. Swift, “Simulation of 1 X 2 OTDM router employing Symmetric Mach-Zehnder (SMZ)” Postgraduate Research Conference in Electronic, Photonics, Communication & Networks, and Computing Science, Exeter, 14-16 April, pp 105-106. (5) R. Ngah, Z. Ghassemlooy, and G. Swift, “Comparison of Interferometric all-optical switches for router applications in OTDM systems” 4th Annual Postgraduate Symposium on Convergence of Telecommunications, Networking and Broadcasting, Liverpool, 16-17 June 2003, pp. 81-85. (6) A. Als, R. Ngah, Z. Ghassemlooy, and G. Swift, “Simulation of all-optical recirculating fiber loop buffer employing a SMZ switch” 7th World Multiconference on Systemics, Cybernetics, and Informatics, Florida, 27-30 July 2003, pp 1-5. (7) R. Ngah, and Z. Ghassemlooy, “BER performance of an OTDM demultiplexer based on SMZ switch” Postgraduate Research Conference in Electronic, Photonics, Communication & Networks, and Computing Science, Hetfordshire, 5-7 April 2004, pp 228 –229. (8) R. Ngah, and Z. Ghassemlooy, “Bit Error Rate Performance of All Optical Router Based on SMZ Switches,” First IFIP International Conference on Wireless and Optical Communications Networks (WOCN 2004), Oman, 7 – 9 June 2004, Accepted for publications. (9) R. Ngah, and Z. Ghassemlooy, “The Performance of an OTDM Demultiplexer Based on SMZ Switch,” IEE Seminar on Future Challenges and Opportunities for DWDM and CWDM in the Photonic Networks, University of Warwick, 11 June 2004, Accepted for publications. (10) R. Ngah, and Z. Ghassemlooy, “Simulation of Simultaneous All Optical Clock Extraction and Demultiplexing for OTDM Packet Signal Using SMZ Switches,” 9th European Conference on Networks & Optical Communications (NOC 2004), Eindhoven, 29 June – 1 July 2004, Accepted for publications. (11) R. Ngah, and Z. Ghassemlooy, “Noise and Crosstalk Analysis of SMZ Switches,” International Symposium on Communication Systems, Networks and Digital Signal Processing, University of Newcastle, 20 - 22 Juuly 2004, Accepted for publications.

50. Publications – contd. Journal (1) R. Ngah, and Z. Ghassemlooy, “Simulation of 1x2 OTDM Router Employing Symmetric Mach-Zehnder Switches” Accepted for publications in IEE Proceeding Circuits, Devices & Systems.