Non-linear optics in whispering gallery mode resonators

Whispering Gallery Mode (WGM) Resonators trap light in a konvex dielectric via total internal reflection. Such optical resonators are known to possess ultra high quality factors, limited only by material absorption and surface roughness (and for very small resonators by radiative losses). We fabricate and study such Whispering Gallery Mode (WGM) Resonators made out of crystalline materials to either study extremely low loss cavities for frequency standards or highly non-linear chi^(2) crystals for extremely efficient non-linear optics. As such resonators work throughout their whole transparency window, we study them in the visible/near infra-red as well as in the THz domain. Furthermore, we investigate the polarization properties WGM resonances of birefringent crystals, which might lead to novel non-linear phase-matching schemes.

Two coupled dielectric whispering gallery mode resonators, showing strong coupling between the two resonators. We investigated such coupling in the THz domain. (picture by Harald Schwefel)