The conversion efficiency can be optimized if instead of a short segment, the entire length of the optical resonator also carries the THz radiation. This is achieved by exciting a THz whispering gallery mode, in addition to the optical ones.

Microwave-to-optical frequency converters based on whispering-gallery-mode (WGM) resonators have been proposed as mixers for the input ends of microwave receivers in which, downstream of the input ends, signals would be processed photonically. A proposed frequency converter would exploit the nonlinearity of the electromagnetic response of a WGM resonator made of LiNbO3 or another suitable ferroelectric material: up-conversion would take place by three-wave mixing in the resonator.

Phase matching of diverse electromagnetic modes (specifically, coexisting optical and microwave modes) in a whispering-gallery-mode (WGM) resonator has been predicted theoretically and verified experimentally. Such phase matching is necessary for storage of microwave/terahertz and optical electromagnetic energy in the same resonator, as needed for exploitation of nonlinear optical phenomena.

We propose to use the difference in thermo optical constants of whispering gallery mode resonators’ mode families for precise measurements of temperature. The sensor consists of the whispering gallery mode dielectric resonator made of transparent media with two different sets of modes with different thermooptical constants, and optoelectronic circuit to compare the relative temperature-dependent shift of their resonant frequencies.

This custom optic allows one to redirect any unabsorbed pump diode radiation back into a side-pumped, two-pass, solid state laser slab for a total of four pump passes. Therefore, a 1-mm slab behaves like a 2-mm thick slab, produces higher inversion densities, small laser beam apertures, and higher efficiencies for small cavities. This technique can also be used in small end-pumped designs for minimizing cavity length and pulse width.