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 www.techbriefs.com/tsp 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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Overview
The document discusses the Phase-Array Approach to Optical Whispering Gallery Modulators (WGM), highlighting their significance in high-frequency optical modulation, particularly for telecommunications and NASA applications. Optical modulators are essential components in high-speed optical links, which are crucial for communication between ground and space, as well as between airborne or space objects. The document emphasizes the importance of size, mass, and power efficiency in these technologies, especially for NASA missions.
A key issue with traditional high-frequency modulators is that they primarily function as phase modulators, while amplitude modulation is often desired for various applications. The document outlines the challenges associated with phase/amplitude modulation conversion and the need for single sideband (SSB) modulation, which eliminates one of the sidebands. The proposed solution leverages the unique properties of WGM optical modulators, which can manipulate the phases of different modes to achieve desired modulation outcomes.
The WGM resonator operates based on well-defined orbital numbers, which connect the phase variation of the field in the mode with the azimuthal angle between coupling locations. By adjusting the angle, one can control the interference patterns and achieve complete constructive or destructive interference, enabling advanced modulation functions such as phase to amplitude conversion and higher-order harmonic filtering.
The document also highlights the novelty of the WGM resonator, noting that it is the only type of high-frequency electro-optical modulator capable of implementing these advanced functions with relative ease compared to conventional modulators, which often require more complex maintenance and stabilization.
In terms of NASA relevance, the innovation enhances the capabilities of compact and power-efficient high-speed optical modulators, which are vital for optical ranging and data transfer in missions, including Mars exploration. The document suggests that the advancements in WGM technology will significantly expand its applications and improve the performance of optical links in future NASA missions.
Overall, the Phase-Array Approach to Optical Whispering Gallery Modulators represents a promising advancement in optical modulation technology, addressing existing challenges and enhancing the potential for high-speed communication in aerospace and other fields.
