We demonstrate an all-optical XOR logic gate for 40-Gbaud quadrature phaseshift keying (QPSK) tributaries in a silicon nanowire for the first time. The XOR logic operation is realized based on four-wave mixing (FWM) in the C-band. Experimental results show negligible power penalty at a bit error ratio (BER) of 10 À6 compared with the back-toback signals. The BER floor appears at BER of 10 À6 for both I and Q tributaries of the logic operation, and the main reasons are the optical signal-to-noise ratio (OSNR) deterioration caused by nonlinear loss due to free carrier absorption (FCA) and two-photon absorption (TPA) and the cross-phase modulation (XPM)-induced phase impairments.

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A novel phase-shifted optical quantization scheme for an all-optical analog-to-digital converter, which uses 4×4 multimode interference couplers, is demonstrated and theoretically analyzed. The whole scheme can be integrated on a chip.

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