Electro-Optic Polarisation Conversion at 0.8 K in Titanium in-Diffused Lithium Niobate Waveguides

We demonstrate an electro-optic polarisation converter for 1550nm at cryogenic temperatures in titanium in-diffused lithium niobate waveguides. The switching voltage increases, the modulation depth remains unchanged, and we show operation up to 25 MHz.

1. Introduction

Lithium niobate is an important platform for integrated quantum optics given its high second-order nonlinearity and electro-optic properties [1], [2]. In this material, high-speed electro-optic modulation as well as polarisation conversion can be realised in periodically-poled titanium in-diffused waveguides. These waveguides achieve low losses and a high coupling efficiency with optical fibres [3], [4], which is advantageous for the combination with other integrated optical platforms for quantum communication. Together with the integration of superconducting detectors [5], this platform offers a broad range of functionality. For the integration and operation of these and other low-temperature technologies, operating temperatures around 4 K are needed.