This technology leverages the well-defined orbital number of a whispering gallery modulator (WGM) to expand the range of applications for such resonators. This property rigidly connects the phase variation of the field in this mode with the azimuthal angle between the coupling locations.

A WGM with orbital momentum L has exactly L instant nodes around the circumference of the WGM resonator supporting such a mode. Therefore, in two locations separated by the arc α, the phase difference of such a field will be equal to φ = αL. Coupling the field out of such locations, and into a balanced interferometer, once can observe a complete constructive or distractive interference (or have any situation in between) depending on the angle α. Similarly, a mode L + ΔL will pick up the phase φ + αΔL.

In all applications of a WGM resonator as a modulator, the orbital numbers for the carrier and sidebands are different, and their differences ΔL are known (usually, but not necessarily, ΔL = 1). Therefore, the choice of the angle α, and of the interferometer arms difference, allows one to control the relative phase between different modes and to perform the conversion, separation, and filtering tasks necessary.

This work was done by Dmitry Strekalov of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at under the Physical Sciences category.

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, NASA Management Office–JPL. Refer to NPO-45730.

This Brief includes a Technical Support Package (TSP).
Phase-Array Approach to Optical Whispering Gallery Modulators

(reference NPO-45730) is currently available for download from the TSP library.

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This article first appeared in the August, 2010 issue of NASA Tech Briefs Magazine.

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