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A report is presented on all-optical logic XOR operation for high-speed carrier-suppressed return-to-zero differential phase-shiftkeying (CSRZ-DPSK) signals based on cascaded sum- and differencefrequency generation (cSFG/DFG) in a periodically poled lithium niobate (PPLN) waveguide. The linear relationship of complex amplitudes between the converted idler and input signals enables a CSRZ-DPSK logic XOR gate with the converted idler carrying the RZ-DPSK format. An all-optical logic XOR gate for 40 Gbit/s CSRZ-DPSK signals is demonstrated in the experiment. Dualchannel- output and wavelength variable-in variable-out operations are also shown for the PPLN-based CSRZ-DPSK logic XOR gate.
Introduction: Ultrafast optical signal processing for phase-shiftkeying (PSK) signals has attracted increasing interest recently since the PSK modulation format shows advantages of high tolerance to fibre transmission impairments. An important function of optical signal processing is all-optical logic XOR operation for PSK signals which was previously implemented using four-wave mixing (FWM) either in a semiconductor optical amplifier (SOA) [1-3] or a highly nonlinear fibre (HNLF) [4]. We also proposed and studied the logic XOR gate for non-return-tozero differential phase-shiftkeying (NRZ-DPSK) and return-to-zero differential phase-shiftkeying (RZ-DPSK) signals based on cascaded second-order nonlinear interactions in a periodically poled lithium niobate (PPLN) waveguide [5]. In this Letter, by exploiting cascaded sum- and difference-frequency generation (cSFG/DFG) in a PPLN waveguide, we demonstrate a 40 Gbit/s all-optical logic XOR gate for carrier-suppressed return-to-zero differential phase-shiftkeying (CSRZ-DPSK) signals with the logic XOR result taking the RZ-DPSK format.
Experimental setup and operation principle: Fig. 1 shows the experimental setup. Two tunable lasers (TL1, TL2), two cascaded Mach- Zehnder modulators (MZMs) driven by a bit pattern generator (BPG), and an erbium-doped fibre amplifier (EDFA) are used to generate two 40 Gbit/s pseudorandom binary sequence (PRBS) CSRZ-DPSK signals (signal A, signal B). Two CSRZ-DPSK signals are separated by a wavelength-division-multiplexer (WDM) and introduced is a relative time delay through a tunable optical delay line (ODL). A continuous- wave (CW) pump emitted from an external cavity laser (ECL) is...