Whispering-gallery-mode (WGM) optical resonators of a type now under development are designed to support few well-defined waveguide modes. In the simplest case, a resonator of this type would support one equatorial family of WGMs; in a more complex case, such a resonator would be made to support two, three, or some other specified finite number of modes. Such a resonator can be made of almost any transparent material commonly used in optics. The nature of the supported modes does not depend on which material is used, and the geometrical dispersion of this resonator is much smaller than that of a typical prior WGM resonator. Moreover, in principle, many such resonators could be fabricated as integral parts of a single chip.
Basically, a resonator of this type consists of a rod, made of a suitable transparent material, from which protrudes a thin circumferential belt of the same material. The belt is integral with the rest of the rod (see figure) and acts as a circumferential waveguide. If the depth (d) and width (w) of the belt are made appropriately small, then the belt acts as though it were the core of a single-mode optical fiber: the belt and its adjacent supporting rod material support a single, circumferentially propagating mode or family of modes.
It has been shown theoretically that the fiber-optic-like behavior of the belt-on-rod resonator structure can be summarized, in part, by the difference, Δn, between (1) an effective index of refraction of an imaginary fiber core and (2) the index of refraction (n) of the transparent rod/belt material. It has also been shown theoretically that for a given required value of Δn, the required depth of the belt can be estimated as d ≈ R Δn, where R is the radius of the rod. It must be emphasized that this estimated depth is independent of n and, hence, is independent of the choice of rod material.
As in the cases of prior WGM resonators, input/output optical coupling involves utilization of evanescent fields. In the present case, there are two evanescent fields: one at the belt/air interface and one in the boundary region between the belt and the rest of the rod.
This work was done by Anatoliy Savchenkov, Dmitry Strekalov, Andrey Matsko, Vladimir Iltchenko, and Lute Maleki 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:
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Refer to NPO-41256
This Brief includes a Technical Support Package (TSP).
Few-Mode Whispering-Gallery-Mode Resonators
(reference NPO-41256) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory, focusing on Few-Mode Whispering-Gallery-Mode Resonators, identified by the reference NPO-41256. It is part of NASA Tech Briefs, which disseminate aerospace-related developments with broader technological, scientific, or commercial applications.
Whispering-gallery-mode (WGM) resonators are optical devices that confine light in a circular path, allowing for high-quality factor resonances. The document discusses the advancements in few-mode WGM resonators, which can support multiple modes of light propagation while maintaining the unique properties of whispering-gallery modes. These resonators are significant for various applications, including sensors, telecommunications, and precision measurements.
The document includes several figures illustrating the concepts discussed, such as the structure of silica resonators and the behavior of evanescent fields, which are crucial for understanding how light interacts with the resonator's surface. The figures serve to visually represent the technical details and enhance comprehension of the resonator's functionality.
Additionally, the document emphasizes the importance of compliance with U.S. export regulations, indicating that the information may contain proprietary content. It encourages users to adhere to applicable laws when utilizing the information provided.
For those seeking further assistance or information, the document provides contact details for the NASA Scientific and Technical Information (STI) Program Office, including a website and contact information for inquiries. This resource is aimed at facilitating access to a broader range of research and technology related to the field.
Overall, the Technical Support Package serves as a valuable resource for researchers, engineers, and industry professionals interested in the latest developments in resonator technology, particularly in the context of aerospace applications. It highlights the potential of few-mode WGM resonators to advance various technological fields and encourages collaboration and innovation through the sharing of knowledge and resources.
