Piezo-tunable second-harmonic-generation in a whispering-gallery resonator

Whispering-gallery resonators gain more and more interest in optical applications. Their combination of small dimensions, strong light confinement, and high quality factors make them ideally suited for optical frequency conversion. Here, their unique features not only allow operation with very small pump powers, they also allow covering the optical spectrum from the UV up to the mid-IR [1, 2, 3]. So far, a common way to change whispering-gallery resonance frequencies is to vary the resonator temperature. While this approach allows far tuning by altering the geometry and the refractive index at the same time, it is inherently slow. Further, due to dispersion, the tuning efficiency changes with wavelength and polarization. Especially in nonlinear-optical applications with many interacting waves, this is often a limiting factor as phase matching is destroyed.