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.
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Funding: National Natural Science Foundation of China under Grant 11704199, in part by the National Science Foundation of Jiangsu Province under Grant BK20150858 and Grant BK20161521, in part by the Distinguished Professor Project of Jiangsu under Grant RK002STP14001, in part by the Talents Projects in Nanjing University of Posts and Telecommunications under Grant NY214002 and Grant NY215002, and in part by the STITP of NUPT under Grant XZD2017040.
- Cavity resonators
- Fiber laser
- Fiber lasers
- Laser modes
- Measurement by laser beam
- Monte Carlo methods
- Optical fibers
- Taper-coupled double-microsphere-cavities
- Vernier effect