Multichannel Optical Signal Processing in NRZ Systems Based on a Frequency-Doubling Optoelectronic Oscillator

Optical signal processing, including clock recovery, nonreturn-to-zero (NRZ) to return-to-zero (RZ) or to carrier-suppressed return-to-zero (CSRZ) format conversions, serial-to-parallel conversion, and optical regeneration in NRZ systems using a frequency-doubling optoelectronic oscillator (OEO) is investigated. The key device in the OEO is a dual-output intensity modulator (IM), which is implemented using a polarization modulator (PolM). If a continuous-wave (CW) probe along with a multichannel NRZ signal is injected into the OEO, an electrical clock at half the data rate of the NRZ signal will be generated. When the electrical clock is fed back into the PolM-based IM, it will modulate the later injected CW probe and the NRZ signal, thus carving the NRZ signal to be an RZ/CSRZ signal at the same data rate or an RZ signal at half the data rate of the NRZ signal. Meanwhile, the CW probe is also carved to be an optical pulse train with a frequency equal to the data rate or half the data rate of the NRZ signal. Multichannel line-rate and prescaled clock recovery, NRZ-to-RZ/CSRZ conversion, 1:2 serial-to-parallel conversion, and synchronous-modulation-based regeneration are thus realized. An experiment is performed with all the aforementioned signal processing functions verified.