Home-made Spectrometer to Study Whispering Gallery Mode Resonators*

Whispering gallery mode (WGM) resonances are promising phenomena for fiber-based photonic applications such as directional couplers, spectrometers, and light generators. These resonances can also be useful for applying forces to dielectric microbeads and sorting them. We designed and built a simple system to excite and detect the WGM resonances of microbeads in atmosphere and in a liquid environment. The system consists of a tunable laser, an optical fiber with a tapered region where the WGM resonators are placed, and a photo detector to monitor the power transmitted through the fiber. The tunable laser has a wavelength range of approximately 1500-1600 nm and a peak output power of 1.5 mW. The tapered region is produced by chemical etching with hydrofluoric acid of a standard SMF-28 optical fiber. The WGM resonances are excited in plastic or glass microbeads with diameters in the 10 to 45 micron range. The preliminary results were obtained at steps of 1 and 0.1 nm/s in a wavelength sweeping mode. The power transmission was more than 40% which is sufficient to overcome the substantial power loss occurred in a liquid environment.