A simple technique has been devised for making small, permanent changes in the eigenfrequencies (resonance frequencies) of whispering-gallery-mode (WGM) dielectric optical resonators that have high values of the resonance quality factor (Q). The essence of the technique is to coat the resonator with a thin layer of a transparent polymer having an index of refraction close to that of the resonator material.
Successive small frequency adjustments can be made by applying successive coats. The technique was demonstrated on a calcium fluoride resonator to which successive coats of a polymer were applied by use of a hand-made wooden brush. To prevent temperature-related frequency shifts that could interfere with the verification of the effectiveness of this technique, the temperature of the resonator was stabilized by means of a three-stage thermoelectric cooler. Measurements of the resonator spectrum showed the frequency shifts caused by the successive coating layers.
This work was done by Dmitry Strekalov, Anatoliy Savchenkov, Lute Maleki, Andrey Matsko, Vladimir Iltchenko, and Jan Martin of Caltech for NASA’s Jet Propulsion Laboratory.
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Refer to NPO-44383, volume and number of this NASA Tech Briefs issue, and the page number.