A single-longitudinal-mode, narrow linewidth fiber ring laser stabilized by taper-coupled double-microsphere-cavities

This paper proposes a novel fiber ring laser utilizing taper-coupled double-microsphere-cavities (TC-DMC) to stabilize its single-longitudinal-mode operating with a 0.01 nm narrow bandwidth. Fundamental properties including whispery gallery mode (WGM) mode distribution and transmission spectra in the DMC are investigated both theoretically and experimentally. Due to Vernier effect, the WGM spectrum of the DMC has a narrower FWHM which is compressed about 29.3% and the FSR is increased about 5.3%, as compared to the single-microsphere cavity. A 1.5 μm wavelength single-longitudinal-mode fiber ring laser with a bandwidth of 0.01 nm is also demonstrated using the taper-coupled double-microsphere-cavities (TC-DMC) as the all-fiber mode selector.