600-Hz linewidth short-linear-cavity fiber laser

We proposed a short-linear-cavity (SLC) fiber laser based on a virtual-folded-ring (VFR) resonator and a fiber Bragg grating Fabry-Perot filter. Spatial hole burning effect was reduced by retarding the polarization state of the counter-propagating light waves utilizing the VFR structure. The photon lifetime of the resonator was extended due to the multi-reflection inside the FBG FP, which increased the intra-cavity power and relatively suppressed the contribution of phase diffusion from spontaneous emission. The relaxation oscillation frequency is around 160 kHz due to the slow light effect. The linewidth of the SLC fiber laser was measured to be less than 600 Hz.