Ultrafast all-optical logic AND gate for CSRZ signals using periodically poled lithium niobate

Abstract

We propose and investigate ultrafast logic AND gate for carrier-suppressed return-to-zero (CSRZ) signals by exploiting two kinds of cascaded second-order nonlinearities in a periodically poled lithium niobate (PPLN) waveguide. The analytical solutions are derived under the nondepletion approximation clearly describing the principle of operation. First, based on cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) in a PPLN, an all-optical 40 Gbit/s CSRZ logic AND gate is successfully implemented in the experiment and verified by numerical simulations. It is found that the converted idler, taking the AND result, keeps the CSRZ modulation format unchanged. Second, by using cascaded sum- and difference-frequency generation (cSFG/DFG) in a PPLN, we report simultaneous CSRZ logic AND operation and format conversion from CSRZ to return-to-zero (RZ). Single PPLN-based all-optical 40 Gbit/s tunable (fixed-in variable-out) and flexible (variable-in variable-out) simultaneous CSRZ logic AND gate and CSRZ-to-RZ format conversion are successfully demonstrated in the experiment and confirmed via theoretical analyses. The obtained simulation and theoretical results, including optical spectra, temporal waveforms, eye diagrams, and phase diagrams, conform to the experimental results, thereby indicating the successful implementation of PPLN-based all-optical logic AND gate for CSRZ signals.