Spectral peak filtering using nonlinear polarization interferometer based on polarization maintaining fiber

Abstract

Periodical spectral peaking is an attractive phenomenon for selecting optical frequency comb modes for highly sensitive comb spectroscopy. Here we proposed and demonstrated a spectral peak filtering technique using a nonlinear polarization interferometer (NPI). When we introduce an ultrashort pulse suffering from sharp absorption or phase modulation into the NPI, the ultrashort pulse and spectral peaks emerge from different output ports as a result of interference and the difference in nonlinear phase shift. The characteristics were examined both experimentally and numerically. Spectral peaks with a high signal-to-background ratio of 20 dB were obtained experimentally. The experimental results were almost in agreement with the numerical ones. The system consists of polarization-maintaining fiber devices and shows long-term stable operation. In principle, the proposed technique is applicable to any wavelength range and is useful for spectroscopic applications.