Precise Stabilization of the Optical Frequency of WGMRs

This technique results in whispering gallery mode resonators with absolute frequency stability.

NASA’s Jet Propulsion Laboratory, Pasadena, California

Crystalline whispering gallery mode resonators (CWGMRs) made of crystals with axial symmetry have ordinary and extraordinary families of optical modes. These modes have substantially different thermo-refractive constants. This results in a very sharp dependence of differential detuning of optical frequency on effective temperature. This frequency difference compared with clock gives an error signal for precise compensation of the random fluctuations of optical frequency. Certain crystals, like MgF₂, have “turnover” points where the thermo-refractive effect is completely nullified.