A Reflective Whispering Gallery Mode Microsphere Resonator in Single-Mode Fiber

A whispering gallery mode (WGM) microsphere resonator is proposed and demonstrated. The resonator consists of a microsphere embedded in an open air-cavity at the end of a single-mode fiber (SMF). The open air-cavity is fabricated by firstly inscribe a waveguide in the fiber core, followed by discharging the waveguide area using a fusion splicer to form a spindle-shaped air-cavity, and finally cutting the air-cavity by femtosecond laser. The device is simple in fabrication, easy in operation, robust in structure and low in cost and has a good quality (Q) factor of <inline-formula> <tex-math notation="LaTeX">$7.5\times 10 ^{4}$ </tex-math></inline-formula>.