Theoretical and experimental study on wavelength conversion based on FWM for PDM-QPSK signals with digital coherent detection in HNLF

In this paper, we have theoretically analyzed that wavelength conversion for the polarization insensitive co-polarized pumps wavelength conversion for polarization-division-multiplexing (PDM) quaternary phase shift keying (QPSK) signals in highly nonlinear optical fiber (HNLF) with digital coherent detection. We found that the received polarization multiplexing signal can be obtained without crosstalk by adopting polarization diversity coherent reception. The analytical results show that variation of the signal wavelength has small effect on the conversion efficiency; the conversion efficiency increases and the signal performance becomes better as the injection power of signal light increases until the later reaches a certain value, and then the former almost keep unchanged. We have also experimentally demonstrated parallel dual-pump wavelength conversion of 112 Gbit/s PM-QPSK signal based on four wave mixing by using coherent detection in 1 km high-nonlinear fiber. The experimental results can be agreed with the theoretical analyses.