Single-longitudinal-mode Fiber Ring Lasers With Taper-coupled Double-microsphere-cavities

摘要

This letter proposes and demonstrates a fiber ring laser using taper-coupled double-microsphere-cavities (DMC) to achieve single-longitudinal-mode operation. Whispering-gallery-mode (WGM) intensity distributions and transmission spectra of the DMC with different microsphere diameters are investigated both theoretically and experimentally. Due to the Vernier effect, the DMC can produce WGM spectra with a higher extinction ratio, a higher side-mode-suppression ratio (SMSR), a larger FSR and a narrower bandwidth, as compared to a single-microsphere cavity. A single-longitudinal-mode fiber ring laser operating near 1.5 μm with a bandwidth of < 0.01 nm and a signal-to-background ratio of about 60 dB is demonstrated using the taper-coupled DMC as an all-fiber mode selector.