Output coupling of light from a whispering- gallery-mode (WGM) optical resonator directly to a photodetector has recently been demonstrated. By "directly" is meant that the coupling is effected without use of intervening optical components. Heretofore, coupling of light into and out of WGM resonators has been a complex affair involving the use of such optical components as diamond or glass prisms, optical fibers, coated collimators, and/or fiber tapers. Alignment of these components is time-consuming and expensive.
To effect direct coupling, one simply mounts a photodetector in direct mechanical contact with a spacer that is, in turn, in direct mechanical contact with a WGM resonator disk. The spacer must have a specified thickness (typically of the order of a wavelength) and an index of refraction lower, by an adequate margin, than the indices of refraction of the photodetector and the WGM resonator disk. This mechanically simple approach makes it possible to obtain an optimum compromise between maximizing optical coupling and maximizing the resonance quality factor (Q).
This work was done by Anatoliy Savchenkov, Lute Maleki, Makan Mohageg, and Thanh Le of Caltech for NASA's Jet Propulsion Laboratory.
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Refer to NPO-43178, volume and number of this NASA Tech Briefs issue, and the page number.