All-optical PPLN-based tunable NRZ-to-RZ and NRZ-DPSK-to-RZ-DPSK format conversions

Abstract

We experimentally demonstrate 20 Gbit/s all-optical tunable format conversion from non-return-to-zero (NRZ) to return-to-zero (RZ) based on cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) in a periodically poled lithium niobate (PPLN) waveguide. Moreover, PPLN-based 40 Gbit/s all-optical format conversion from non-return-to-zero differential phase-shift keying (NRZ-DPSK) to return-to-zero differential phase-shift keying (RZ-DPSK) is also theoretically investigated by using cascaded second-order nonlinearities including cSHG/DFG and cascaded sum- and difference-frequency generation (cSFG/DFG).