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.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
(818) 354-2240
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Refer to NPO-44383, volume and number of this NASA Tech Briefs issue, and the page number.
This Brief includes a Technical Support Package (TSP).
A Technique for Adjusting Eigenfrequencies of WGM Resonators
(reference NPO-44383) is currently available for download from the TSP library.
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Overview
The document outlines a significant advancement in the field of photonics, specifically focusing on a technique for permanently adjusting the eigenfrequencies of high-Q dielectric Whispering Gallery Mode (WGM) resonators. These resonators are crucial components in various optical applications, and their performance is heavily dependent on the precise control of their optical frequencies.
The primary challenge addressed in the document is the need for fixed detuning between the frequencies of coupled resonators. Traditional methods of frequency adjustment often lack the precision required for high-Q resonators, which have narrow resonant lines due to their long photon lifetimes. The document highlights that achieving the necessary manufacturing precision for microrings—on the order of 10^(-10)—is difficult, particularly for resonators with a diameter of 1mm, where absolute precision must be better than 0.001A.
To overcome these challenges, the document presents a novel solution involving the partial coating of the resonator's surface with a polymer that has a refractive index similar to that of the fluorite material of the resonator. This technique results in a permanent and controllable shift in the eigenfrequency of the resonator by distorting the evanescent field. The process is described in detail, including the method of applying the polymer coating using a hand-made wooden mini brush and the thermal stabilization of the resonator to mitigate temperature-related frequency shifts.
The document emphasizes the novelty of this technique, which allows for a permanent adjustment of the eigenfrequency, thus enhancing the utility of high-Q factor crystalline dielectric cavities in photonic applications. The ability to control the optical frequency with high precision is crucial for the development of advanced photonic components, making this technique a valuable contribution to the field.
For further inquiries or detailed information, the document provides contact details for the Innovative Technology Assets Management at NASA's Jet Propulsion Laboratory. Overall, this advancement represents a significant step forward in the precision engineering of optical resonators, with potential implications for a wide range of technological applications.
