Comb filter based on an all polarization maintaining fiber loop and its applications

Abstract

All polarization maintaining fiber Sagnac interferometers with linearly birefringence are proposed for the construction of stable comb filters. The transfer functions of the filters can be determined if stress-induced birefringence fiber is used because its birefringence is more or less independent of wavelength. The transfer function of the simplest filter, which acts as a comb filter, with only one polarization mode-coupling point is obtained. Several filters have been realized; they exhibit channel isolation of about 22 dB and can be used as frequency selectors in multi-wavelength fiber lasers. We also discuss the potential applications of the proposed filter that include add-drop multiplexers in wavelength division multiplexing (WDM) systems, gain flattening in fiber amplifiers, and switches/modulators.