Mechanical squeezing has been found to alter the frequency tuning of a whispering-gallery-mode (WGM) optical resonator that has an elliptical shape and is made of lithium niobate. It may be possible to exploit this effect to design reconfigurable optical filters for optical communications and for scientific experiments involving quantum electrodynamics.

Tuning Rates were calculated from resonance-frequency-vs.-voltage measurements on an elliptical WGM resonator squeezed along its semimajor axis.
Some background information is prerequisite to a meaningful description of the squeezing-induced alteration of frequency tuning: The spectrum of a WGM resonator is represented by a comblike plot of intensity versus frequency. Each peak of the comblike plot corresponds to an electromagnetic mode represented by an integer mode number, and the modes are grouped into sets represented by integer mode indices. Because lithium niobate is an electro-optically active material, the WGM resonator can be tuned (that is, the resonance frequencies can be shifted) by applying a suitable bias potential. The frequency shift of each mode is quantified by a tuning rate defined as the ratio between the frequency shift and the applied potential. In the absence of squeezing, all modes exhibit the same tuning rate. This concludes the background information.

It has been demonstrated experimentally that when the resonator is squeezed along part of either of its two principal axes, tuning rates differ among the groups of modes represented by different indices (see figure). The differences in tuning rates could be utilized to configure the resonance spectrum to obtain a desired effect; for example, through a combination of squeezing and electrical biasing, two resonances represented by different mode indices could be set at a specified frequency difference — something that could not be done through electrical biasing alone.

This work was done by Makan Mohageg and Lute Maleki of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Electronics/Computers category.

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 E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-45044, volume and number of this NASA Tech Briefs issue, and the page number.

Topics:
Electronics & Computers Lithium Metals Optics
This Brief includes a Technical Support Package (TSP).
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Squeezing Alters Frequency Tuning of WGM Optical Resonator

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This article first appeared in the July, 2010 issue of NASA Tech Briefs Magazine (Vol. 34 No. 7).

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Overview

The document discusses a groundbreaking development in photonic technology by researchers Makan Mohageg and Lute Maleki at NASA's Jet Propulsion Laboratory. It focuses on a reconfigurable photonic filter based on elliptical whispering-gallery modes (WGM) within a resonator made from lithium niobate, an electro-optically active material. The key innovation lies in the ability to manipulate the resonant frequencies of the modes through morphological modifications of the resonator.

The elliptical geometry of the WGM resonator breaks modal degeneracy, allowing individual resonant frequencies to respond differently to the same perturbation. This is particularly significant because it enables a completely reconfigurable resonance spectrum. The researchers applied both direct current (dc) and alternating current (ac) electrical biases to the resonator, which resulted in a uniform shift of all mode frequencies. Additionally, they demonstrated that by squeezing the resonator, the tuning rates of the various modes could be altered, revealing discrete tuning rates that are likely proportional to integer modal indices.

The implications of this research are vast, as the reconfigurable optical spectra can be utilized to create a variety of optical devices. Potential applications include variable optical attenuators, dispersion compensators, multipass wavelength division multiplexers, and multipass filters. Furthermore, these technologies can play a crucial role in scientific experiments related to cavity quantum electrodynamics, enhancing the capabilities of optical systems in various fields.

The document is part of a Technical Support Package under NASA's Commercial Technology Program, aimed at disseminating aerospace-related developments with broader technological, scientific, or commercial applications. It emphasizes the importance of compliance with U.S. export regulations and provides contact information for further inquiries regarding the research and technology discussed.

In summary, this document highlights a significant advancement in the field of photonics, showcasing how morphological modifications of WGM optical resonators can lead to innovative reconfigurable devices with a wide range of applications in both technology and scientific research. The findings underscore the potential for further exploration and development in this area, paving the way for future advancements in optical technologies.