|
|
Whispering gallery mode (WGM) optical resonators are axially symmetric dielectric structures ranging in size from tens of microns to a few mm, which trap light in a small volume. The modes are solutions of Maxwell’s wave equation and represent waves that propagate close to the surface of the resonator structures.
The three energy loss mechanisms - radiative, surface scattering, and bending losses - are minimized in WGM resonators due to the morphology of the structure and the transparency of the dielectric material. Thus, WGM resonators generally exhibit Q’s that range from 105 in the case of ring structures, to greater than 1011 for fluorite toroidal resonators. WGM structures fabricated with semiconductor materials may also be made to have gain.
A variety of WGM resonators were fabricated to have ring, spherical, toroidal, and elliptical geometries. They were also demonstrated in a wide range of materials, including glass, silica, silicon, compound semiconductors, and crystalline materials. Attractive methods exist to allow fabrication of WGM resonators with conventional semiconductor processing techniques.
Crystalline WGM resonators exhibit nonlinear optical properties, such as the electro-optic effect, which can be used for an advantage in filter and modulator applications. Resonators fabricated with ferroelectric materials can be used for engineering of the modal spectrum with applied DC and RF fields, since an applied electrical field changes the index of refraction of the material. Taking advantage of these properties, OEwaves has demonstrated extremely efficient WGM based modulators with application of RF and microwave fields, and widely tunable filters with application of a DC field. 4mm Dia. Lithium Niobate WGM Resonator 
|
