An optical micro-coupling system of whispering-gallery mode usually consists of a resonator (e.g. a sphere) and a coupler (e.g. a taper). In this report, silica microspheres of 50–500 μm in diameter are fabricated by hydrogen flame fusing of an end of a single mode fiber or fiber taper. Fiber tapers are fabricated by the method of heating and pulling that meets an adiabatic condition. Taper’s waist diameter can routinely be made less than 1 μm and almost zero transmission loss in a taper is achieved which allows an effective and phase-matched coupling for a wide range sizes of microspheres. Both resonators and couplers’ surface microstructure and shapes are examined by scanning electronic microscopy. Three regimes of coupling are achieved, enabling a good flexibility to control Q value and coupling efficiency of a micro-coupling system. Whispering gallery mode shift is used to demonstrate a novel temperature micro-sensor. Its sensitivity determined from actual experimental results agrees well with the theoretical value. A concept of using the photon’s cavity ring down (CRD) in the microsphere to make a novel high-sensitivity trace gas micro-sensor is proposed. The CRD time constant when ammonia is chosen as the analyte gas is predicted using the simulated absorption lines.
High-Sensitivity Sensor Fabricated on the Basis of Single-Mode Fiber Loop Using Frequency-Sweeping-Generated Ringing Effect
