All-optical format conversions from NRZ to BPSK and QPSK based on nonlinear responses in silicon microring resonators.

We propose and numerically verify a novel scheme of all-optical format conversion from non-return-to-zero (NRZ) to binary phase-shift- keying (BPSK) at 160 Gb/s using cascaded microring resonators (CMRR) on a single silicon chip. The conversion is based on large phase shift and flattened intensity-response characteristics in the CMRR. A continuous-wave light experiences different phase shifts controlled by the power of an input NRZ signal with an ~8.8-dB extinction ratio, while maintaining approximately the constant intensity. All-optical format conversion from NRZ to quadrature phase-shift-keying (QPSK) is also demonstrated based on parallel NRZ/BPSK converters in a Mach-Zehnder interferometer structure.