Barium Titanate and Lithium Niobate Permittivity and Pockels Coefficients from MHz to Sub-THz Frequencies

TL;DR

This study measures and compares the frequency-dependent electro-optic properties of lithium niobate and barium titanate from MHz to sub-THz, revealing BTO's larger electro-optic coefficients and methods for broadband characterization.

Contribution

It provides the first comprehensive broadband measurement of Pockels coefficients and permittivity in LN and BTO, demonstrating BTO's superior electro-optic properties and flat frequency response design strategies.

Findings

BTO exhibits significantly larger Pockels coefficients than LN.

Permittivity remains constant in LN but varies in BTO across frequencies.

Method for broadband electro-optic property measurement using integrated phase shifters.

Abstract

The Pockels effect is essential for controlling optical signals at the highest speeds, particularly for electro-optic modulators in photonic integrated circuits. Lithium niobate (LN) and barium titanate (BTO) are two excellent Pockels materials to this end. Here, we measure the Pockels coefficients and permittivity in LN and BTO over a continuous frequency range from 100 MHz to 330 GHz. These properties are constant across this frequency range in LN but have a significant frequency dependence in BTO. Still, our measurements show that BTO has remarkably large electro-optic properties compared to LN. Furthermore, we show how BTO devices can be designed with a flat electro-optic frequency response despite the Pockels coefficient dispersion. Finally, we expound our method for broadband characterization of these vital electro-optic properties, utilizing specialized integrated electro-optic phase shifters. Altogether, this work empowers the design of high-speed BTO devices and the development of new electro-optic materials.