A whispering gallery mode microsphere resonator integrated with angle polished multimode fiber

We demonstrate a robust whispering-gallery-mode (WGM) microsphere resonator, fabricated by splicing two sections of multimode fiber (MMF) with end face polished to an angle of 45 degree. The polished end faces are etched by hydrofluoric (HF) acid to form an elliptical-shaped cavity to embed a microsphere before being firmly connected by UV adhesive. Part of the incident light traveling along the fiber core is coupled into the microsphere in the tangential direction to the surface of the microsphere and excites WGM. Such a microsphere resonator is highly robust and compact in size, and has a Q-factor of 5.15 $ \times $ 103. When used as a temperature sensor, the sensitivity obtained is 6.4 pm/°C.