Optical phase matching of high-order azimuthal WGM in a water droplet resonator

We observe the optical phase matching between a fiber taper and a high-order azimuthal whispering gallery mode (WGM) in a water droplet for the first time. The eccentricity of the droplet separates the wavelength of azimuthal modes. We evaluate the optical phase matching between the fiber taper mode and different azimuthal modes. In the experiments, the phase matching of a high-order azimuthal WGM (l-|m|=6) is realized around 1550 nm. The lifted azimuthal modes make high-efficient coupling easier for a probing light with narrow spectral range. They also have potential applications in detecting the shape fluctuation and eccentricity of water droplets.