All-Normal-Dispersion Mode-Locked Fiber Laser with a Tunable Angle-Spliced Polarization-Maintaining Fiber Lyot Filter

We have proposed and implemented an all-polarization-maintaining mode-locked fiber laser operating in all-normal-dispersion regime based on nonlinear amplifying loop mirror. The required spectral filtering on the circulating chirped pulse was realized with a Lyot filter that was constructed by two carefully angle-spliced polarization-maintaining single-mode fibers within the laser resonator. The intrinsic inline fiber optical filter exhibited desirable features such as compact layout, adjustable versatility, and long-term stability. By changing the specific fiber length, our laser could deliver pulses with spectral bandwidth from 0.5 to ∼4 nm. Furthermore, a continuously tunable single-wavelength operation and an asynchronous dual-wavelength operation can both be obtained with the laser setup including an improved Lyot filter, and the experimental observations agreed well with numerical analysis.