Tunable and switchable erbium-doped fiber laser based on the parallel filter of the FBGs embedded in Sagnac ring and the in-line MZI

Abstract

A tunable and switchable erbium-doped fiber laser (EDFL) based on the parallel filter is proposed and experimentally verified. The parallel filter is composed of two branches. One branch is double fiber Bragg gratings (FBGs) embedded in Sagnac ring filter, which can realize the selection of two wavelengths; the other branch is an in-line Mach Zehnder interferometer (MZI) filter, which is composed of a 10 cm polarization-maintaining fiber (PMF) fused in the middle of single mode fibers (SMFs) with spheres at both ends, which can realize the selection of five wavelengths. When the parallel filter is inserted into the fiber laser cavity and the polarization controllers (PCs) are adjusted, the laser excitation from single-wavelength to quadruple-wavelength can be realized, including 7 different single-wavelength laser states, 16 different dual-wavelength laser states, 11 different triple-wavelength laser states and 2 different quadruple-wavelength laser states. In addition, the intervals of the dual-wavelength laser states are relatively regular, and the dual-wavelength laser intervals are obtained every ∼ 2 nm from 7 nm to 18 nm. And the optical signal-to-noise ratios (OSNRs) are more than 43 dB, and the highest OSNR is 60 dB. Finally, by changing the temperature applied to the FBG, tunability of dual-wavelength intervals can be achieved with a range of 1.1 nm. Due to the variety of lasing laser states of the fiber laser, easy switching, and regular intervals between the dual-wavelength laser states, the fiber laser proposed can be better applied to wavelength division multiplexing (WDM)system.