All-Optical Format Conversion for Polarization and Wavelength Division Multiplexed System

All-optical return-to-zero (RZ) to nonreturn-to-zero (NRZ) format conversions for polarization division and wavelength division multiplexed on-off keying (OOK), differential phase-shift keying (DPSK), and quadrature phase-shift keying (QPSK) signals are proposed and demonstrated using a single delay interferometer (DI). Because of the periodical filtering property and the polarization insensitive characteristic of the free space-based DI, four wavelength division multiplexed and polarization division multiplexed RZ-OOK to NRZ-OOK, RZ-DPSK to NRZ-DPSK, and RZ-QPSK to NRZ-QPSK conversions have been achieved using the constructive interference. An average power penalty of 1.5 dB can be achieved. The proposed scheme can well accommodate the future transmission system with multiple modulation formats and multidimensional multiplexed techniques.