Electro-optic tuning of potassium tantalate-niobate whispering gallery resonators

Most centrosymmetric materials exhibit a neglectable electro-optic response; the Pockels coefficients are zero, while the DC-Kerr coefficients are typically small. For a standard material such as silica they are on the order of 10−22 m2/V2 . 1 Thus, refractive index tuning is achieved by thermal or mechanical means. Potassium tantalateniobate (KTa1−xNbxO3 with 0 < x < 1, KTN) is a rare exception. It offers outstandingly high DC-Kerr coefficients in the 10−15 m2/V2 range.2 In this contribution, the first-ever KTN whispering gallery resonators (WGR) are demonstrated with quality factors Q > 107 and electro-optic eigenfrequency tuning of more than 100 GHz at l = 1040 nm for moderate field strengths of 250 V/mm. These results potentially pave the way for applications such as electro-optically tunable Kerr frequency combs.