Design and analysis of parallel polarization-beam-splitter-based optical filter with adjustable channel spacing

In this paper, a parallel polarization-beam-splitter-based fiber optic filter with adjustable channel spacing is proposed and demonstrated. The transmission characteristics of the proposed filter are simulated and analyzed using the transmission matrix theory. Simulation results show that the filter can generate three different channel spacings by adjusting different polarization controllers (PCs) in front of the polarization beam splitter (PBS). The experiment confirms the feasibility of a multi-wavelength fiber laser (MWFL) constructed based on this filter in achieving channel spacing switching. Its wavelength spacing can be switched between 0.46 nm, 0.66 nm, and 0.88 nm, matching the simulated results of the filter. The power fluctuations between the outputs of the three-channel spacing outputs are less than 1.17 dB, 0.89 dB, and 0.98 dB, and the wavelength fluctuations are less than 0.18 nm, 0.14 nm, and 0.13 nm, respectively.