a1291_1.pdf OMG3.pdf OFC/NFOEC 2008 switching controller and tune the tunable laser diode (TLD) to a corresponding wavelength, and allow the semiconductor optical amplifier based Mach-Zahnder interferometer (SOA-MZI) to copy the payload onto the new wavelength. The arrayed waveguide grating router (AWGR) will then switch this payload to the desired output port corresponding to the new wavelength of the TLD. When the time-to-live (TTL) content in the label indicates near-expiration or severe signal degradations, the payload will be directed to a designated burst-mode 3R output port of the AWGR instead. After experiencing 3R, the packet goes through the AWGR again to be routed to its originally-intended destination output. The burst-mode 3R regeneration includes a SOA-MZI module for reshaping and reamplification, and then burst-mode reclocking using a clock recovery module, where a Fabry-Perot filter (FPF) extract out the clock component and a saturated SOA equalizes the amplitude , and a LiNbO 3 modulator to carve the recovered clock onto the data payload. Fig. 1 Experimental setup BERT: bit-error-rate tester, LO: local oscillator, DFB: DFB laser diode, MOD: LiNbO3 modulator, EDFA: Erbium-doped fiber amplifier, FBG: fiber Bragg grating, CIR: optical circulator, BMRX: label burst-mode receiver, FDL: fixed delay line, TDL: tunable delay line, PC: polarization controller, ATT: variable attenuator, BPF: band-pass filter, O/E: optical-to-electrical converter, LEAF: large-effective-area fiber, DCF: dispersion compensation fiber The experiments included wavelength domain and time domain contention resolution cases at Node 3. The space domain resolution is not addressed in this case, as its results will be synonymous with those of the wavelength domain, from a local OLS router’s standpoint. Fig.2 shows the timing of this demonstration. Packet with label i on the top wants to go to output fiber i. Channel 1 input reaches the AWGR earlier than channel 2 and therefore has the priority to occupy port (1, 1)out. As a result, P1’(8192 bits) from channel 2 input cannot access (1, 1)out and contention arises. The wavelength domain resolution assigns P1’ to another wavelength and forwards it to (1, 2) out, which shares the same output fiber with (1, 1)out. When P2’(5120 bits) arrives with nearly expiring TTL in the label associated with it, the switch controller realizes that it needs 3R regeneration and direct it to the 3R output port, as illustrated in Fig. 2 (a). After experiencing 3R regeneration, P2’ should continue on to its original destination. However, (1, 1)out is still occupied by P2(5120 bits), so another contending condition rises. Meanwhile, (1, 2)out is taken by P2” (8192 bits) from channel 3 so the wavelength domain resolution is not available. Thus, P2’ is sent to a fixed length buffer and then fed back into the main traffic at (1, 1)out with no more contention, as shown in Fig. 2b This scheme of delaying the contending packet in time is the contention resolution in the time domain. The packet sequences repeat with a period of 23x1024 bits (2.355μs) to facilitate bit-error-rate (BER) measurements. After Node 3, payloads on the first output fiber travel through another 60 km fiber transmission and are then analyzed by the receiver for performance evaluation. 3. Results and Discussions As the oscilloscope screen images in Fig. 3 has shown, this OLS router produces the expected packet sequence; the Authorized licensed use limited to: Univ of Calif Davis. Downloaded on March 28, 2009 at 15:18 from IEEE Xplore. Restrictions apply.
a1291_1.pdf OMG3.pdf OFC/NFOEC 2008 contentions are successfully solved by either wavelength domain or time domain resolution. Fig. 3 shows the eye diagram and BER measurement results. For 2 23 -1 pseudo-random-bit-sequence (PRBS) payloads, all BER curves reach below 1E-11 at the average power level of -13 dBm, indicating error-free operation. Each 60 km fiber transmission brings in about 2 dB power penalty. The TWC and switching fabric, on the other hand, causes little power penalty, primarily because the SOA-MZI modules used in wavelength conversion effectively reshape and reamplify the payload. The burst-mode 3R regeneration introduces about 1.5 dB of negative power penalty. The eye-diagrams of P2’, which has experienced 3R regeneration, has much less timing-jitter than P1’ and has much clearer space- and mark- levels after 3R regneration. (a) Fig. 2 Timing diagram and corresponding packet sequence (b) Fig. 3 Eye diagram and BER measurements 4. Summary We demonstrated comprehensive contention resolution for variable-length, mix-rate optical-packet switching in an OLS router network capable of supporting selective 3R regeneration. Experiment results indicate successful TTL-aware contention resolution with error-free operation. The burst-mode 3R regeneration obtained approximately 1.5 dB negative power penalty measured at 1E-9 BER. This work indicates a practical OLS system application in an intelligent optical network capable of selectively regenerating packets while resolving contention between them. 5. References  Z. Pan, et al., IEEE Photon. Technol. Lett., vol. 16, pp. 1772-1774, Jul. 2004  F. Xue, et al., J. Lightwave Technol., vol. 22, pp. 2570-2581, Nov. 2004  G. Gavioli, et al., IEE Electron. Lett., vol. 41, pp. 146-148, Feb. 2005.  Z. Zhu, et al., Tech. Dig. OFC2007, Feb. 2007  Z. Zhu, et al., IEEE Photon. Technol. Lett., vol. 17, pp. 426-428, Feb. 2005.  C. Bintjas, et al., IEEE Photonics Technology Letters, vol. 14, pp. 1363-5, Sept. 2002. Authorized licensed use limited to: Univ of Calif Davis. Downloaded on March 28, 2009 at 15:18 from IEEE Xplore. Restrictions apply.