Tilted Fiber Bragg Grating-Based Few-Mode Fabry-Perot Filter for Mode Conversion

We propose and demonstrate a narrow-bandwidth few-mode Fabry-Perot (FP) filter based on the tilted fiber Bragg gratings (TFBGs). The proposed filter is based on the few mode fiber which possesses ring-core structure. The two TFBGs function as the reflecting mirrors in the FP cavity as well as the mode converters. Therefore, compared with the traditional FP filter and mode converter, the proposed FP filter can realize the conversion of vector modes at specific wavelengths with narrow-bandwidth characteristic. The proposed FP filter can find applications in fiber lasers, mode/wavelength division multiplexing system.