High-Q SiO/sub 2/ whispering gallery mode resonator

We have implemented two whispering gallery mode resonators in order to test the potential of such a structure using SiO/sub 2/ monocrystals as a dielectric resonator. Permittivity measurements and a 3D finite elements model enable us to calculate the resonance frequencies of the WGH and WGE modes with a good accuracy. The SiO/sub 2/ whispering gallery mode resonator presents at 16 GHz a Q-factor of the order of 50,000 at the ambient temperature with a temperature frequency stability of 26 ppm/K. These results are comparable to those obtained with a sapphire dielectric resonator. Attempts have been made in order to reach higher performances by cooling the resonator down to 77 K, but the obtained results show only a small increase in Q-factor. We can conclude that the main advantages of the SiO/sub 2/ resonator are its low cost and its availability. It could be used as frequency reference operating at the ambient temperature when no extreme performances are required.