Electro-optic eigenfrequency tuning of potassium tantalate-niobate microresonators

TL;DR

This paper demonstrates significant electro-optic eigenfrequency tuning in potassium tantalate-niobate microresonators with high quality factors, enabling tunable optical filters and frequency converters, and analyzes the tuning behavior near phase transition temperatures.

Contribution

It introduces whispering-gallery resonators made of KTN with high quality factors and achieves over 100 GHz tuning, along with a theoretical model for behavior near phase transition.

Findings

Q>10^7 quality factors achieved

Over 100 GHz eigenfrequency tuning demonstrated

Tuning behavior analyzed near phase transition

Abstract

Eigenfrequency tuning in microresonators is useful for a range of applications including frequency-agile optical filters and tunable optical frequency converters. In most of these applications, eigenfrequency tuning is achieved by thermal or mechanical means, while a few non-centrosymmetric crystals such as lithium niobate allow for such tuning using the linear electro-optic effect. Potassium tantalate-niobate ($\mathrm{KTa}_{1-x}\mathrm{Nb}_{x}\mathrm{O}_{3}$ with $0\leq x \leq1$, KTN) is a particularly attractive material for electro-optic tuning purposes. It has both non-centrosymmetric and centrosymmetric phases offering outstandingly large linear as well as quadratic electro-optic coefficients near the phase transition temperature. We demonstrate whispering-gallery resonators (WGRs) made of KTN with quality factors of $Q>10^{7}$ and electro-optic eigenfrequency tuning of more than 100 GHz at $\lambda=1040\,$nm for moderate field strengths of $E=250\,$V/mm. The tuning behavior near the phase transition temperature is analyzed by introducing a simple theoretical model. These results pave the way for applications such as electro-optically tunable microresonator-based Kerr frequency combs.