Potential applications of ring resonators for astronomical instrumentation

Ring resonators are a looped waveguide coupled to an input and an output waveguide. They can be used to filter, and drop, a series of wavelengths at the resonant frequencies of the ring. Both these properties are useful for astronomical applications. The dropped signal provides a frequency comb that can be used to provide accurate wavelength calibration. The free spectral range of such a device is larger than that from a laser comb, removing the requirement to perform subsequent filtering. The filtered signal could be used to suppress specific wavelengths, e.g. corresponding to atmospheric emission lines. We present the expected performance of devices designed for both applications and discuss their advantages and limitations.