Razali Ngah, and Zabih Ghassemlooy Optical Communication Research Group

1. Bit Error Rate Performance of All Optical Router Based on SMZ Switches 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 • Introduction • OTDM • All optical switches • Symmetric Mach-Zehnder (SMZ) switch • All OTDM Router • Simulations and Results • Conclusion

3. Introduction • Multiplexing: • 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 • Router congestion and reduced throughputs: Due to optical-electronic-optical conversion • Limited modulation bandwidth of light sources, and modulators Solution: All optical transmission, multiplexing, switching, processing, etc.

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

5. OTDM • Flexible bandwidth on demand at burst rates of 100 Gb/s/ • 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 (like WDM) due to EDFA • 1300

6. 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 Modulators Amplifier OTDM MUX OTDM DEMUX Fibre 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)

7. All Optical Switches Non-linear Optical Loop Mirror (NOLM) Terahertz Optical Asymmetric Demultiplexer (TOAD)

8. All Optical Switches – contd. Mach-Zehnder Interferometer (MZI) • Colliding pulse Mach-Zehnder (CPMZ) • Symmetric Mach Zehnder (SMZ)

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

10. SMZ : Switching Window G1 and G2 are the gains profile of the data signal at the output of the SOA1 and SOA2 and ΔФ is the phase difference between the data signals

11. ( 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

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

13. 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

14. 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

15. 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

16. 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

17. 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:

18. 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

19. 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 Results Block diagram of a router with a receiver System Parameters

20. Results – RIN and CXT RIN against control pulse separation for a single SMZ and a router CXT against control pulse separation for a single SMZ and a router

21. Results - BER BER against average received power for baseline and with an optical router

22. Conclusions • Relative intensity noise and channel crosstalk of 1x2 router is investigated • BER analysis has been performed. • As expected the BER increases with the number of SMZ stages due to the accumulation of ASE noise in the SOAs hence, resulting the RIN increases.

23. THANK YOU