A tunable Lyot birefringent filter with variable channel spacing and wavelength using nonlinear polarization rotation in an SOA

Abstract

We experimentally demonstrate a tunable fiber-optical Lyot birefringent comb filter with independent tuning of the channel spacing and wavelength. The filter consists of a fiber-optic programmable differential group delay line (DGDL) and a semiconductor optical amplifier (SOA) sandwiched between two polarizers. The channel spacing of the filter can be tuned by adjusting the programmable DGDL. Using the nonlinear polarization rotation (NPR) effect, the output state of polarization (SOP) of the SOA can be adjusted by varying the power level of the pump light. This results in a change in the phase shift between the transverse electric (TE) and the transverse magnetic (TM) components of the SOA, and hence fast and continuously wavelength tuning of the filter can also be achieved. The wavelength tuning range is up to 50% of the channel spacing when the pump power is increased from -10 dBm to 17 dBm.