Concave diffraction grating for whispering-gallery mode selection

Owing to a high Q-quality factor of whispering-gallery modes and relatively small size the dielectric disk resonators are extensively used as an oscillating circuit of high-stable microwave oscillators and serve to measure the electro-physical properties of different materials at microwaves. At the same time, the spectrum of whispering-gallery oscillations represents a rather thick grid of equidistant azimuthal oscillations of both E and H polarizations. The subject of the present report is the frequency sparsing of the forced oscillation spectrum of quasioptical dielectric resonators. It has been suggested that the strip-like concave diffraction grating be used for the mode selection of dielectric resonators.