Wideband Microfiber Fabry–Pérot Filter and Its Application to Multiwavelength Fiber Ring Laser

A microfiber Fabry-Pérot (MFP) filter consisting of two microfiber Sagnac loop mirrors as the reflectors and a section of microfiber as the cavity is proposed and fabricated. Owing to the high coupling efficiency induced by the large evanescent field of the microfiber, a broadband comb spectrum with high extinction ratio and flat amplitude can be obtained. The MFP with the extinction ratio of 15 dB as well as the free spectrum range of 0.18 nm is fabricated by bending and twisting a microfiber tapered from a single mode fiber. Consequently, the MFP is applied to an erbium-doped fiber ring laser as the wavelength filter. Assisted by a section of highly nonlinear fiber to suppress the mode competition, 42-wavelength lasing oscillations are achieved at room temperature.