Tunable filter based on a pair of special long-period fiber gratings and its application in fiber ring laser

Abstract

A filter based on a Mach-Zehnder interferometer (MZI) formed by cascading a pair of longperiod fiber gratings (LPFGs) written by CO2 laser in a twisted single-mode fiber is proposed. The transmission spectrum of the filter is tuned by modifying the bending curvature of the MZI, and thus wavelength tuning is achieved. And a tunable erbium-doped fiber (EDF) ring laser employing the filter as a wavelengthselection component is experimentally demonstrated. The laser can be tuned continuously from 1573.05 to 1595.75 nm with a side-mode suppression ration of ∼50 dB over the total tuning range.