Stable dual-wavelength laser combined with gain flattening ML-FMF Bragg grating filter

A stable dual-wavelength laser combined with gain flattening multi-layer few-mode fiber Bragg grating filter was proposed and experimentally demonstrated. The index profile of the multi-layer few-mode fiber was particularly designed to support LP01 and LP11 modes with approximately equal excitation coefficients. And conventional phase-mask fabrication technique was used to inscribe Bragg gratings in the multi-layer few-mode fiber core, which leads to the gain flattening filter. A switchable dual-wavelength laser combined with the gain flattening filter was successfully achieved with simple linear configuration. The lasing wavelengths spacing was 0.39 nm. The variation of the central wavelength and intensity fluctuation were as small as 0.01 nm and <0.7 dBm in both dual-wavelength and single-wavelength operation regions, respectively.