In-fiber wavelength-selective reflector based on Y-junction coupled whispering gallery mode resonator

Abstract

An in-fiber wavelength-selective reflector based on a compact Y-junction coupled whispering gallery mode (WGM) resonator is proposed and experimentally demonstrated. The Y-junction used to simultaneously excite and collect the WGM field through evanescent field coupling is fabricated by femtosecond laser ablation, where the common port of the Y-junction connects to the original single-mode fiber core. As a proof of concept, a microsphere functioning as a WGM cavity is embedded into a femtosecond laser ablated hole in the middle of the two branches of the Y-junction. A reflection passband with a full width at half maximum (FWHM) less than 0.1 nm is experimentally achieved, corresponding to a quality factor (Q-factor) on the order of 104. Such a highly integrated in-fiber WGM reflector holds the potential for remote sensing with high resolution or providing narrow band optical feedback to lasers.