Analysis of polarization dependence for OTDM demultiplexers based on four-wavelength mixing in semiconductor optical amplifier

In optical time-division multiplexing (OTDM) systems using the four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) for time demultiplexing, the polarization states of control pulse and OTDM data lights are an important factor in the optical time demultiplexing process, which can influence the bit error rate (BER) of OTDM systems. In this paper, we analyze the effect of light polarization states on the FWM of a SOA, and use a simulation approach to study the BER performance of 100 Gbit/s OTDM systems that use the FWM in a SOA for optical time demultiplexing. It reveals that the BER or Q factor of OTDM systems is dependent on the misalignment θ between the polarization states of OTDM data and control lights. With increasing θ, both the optical power of resulting FWM component and the BER performance (or Q factor) of OTDM systems is degraded. For linearly polarized lights, our results show that the increase of BER and the reduction in Q factor are made smoothly when θ changes its value from 0° to 75°, whereas the degradation of BER and Q factor becomes rapid when θ exceeds 75°. Although the best system BER is obtained for θ = 0°, the BER performance can still tolerate some misalignment θ (e.g., up to 20° in our simulation). This is useful for the engineering design and applications of SOA-based optical time demultiplexers.