All-Optical Contention Resolution with TTL-Aware Selective 3R ...

All-Optical Contention Resolution with TTL-Aware Selective 3R ...

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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 [6], 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

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