Cryogenic electro-optic polarisation conversion in titanium in-diffused lithium niobate waveguides

Many technologies in quantum photonics require cryogenic conditions to operate. However, the underlying platform behind active components such as switches, modulators and phase shifters must be compatible with these operating conditions. To address this, we demonstrate an electro-optic polarisation converter for 1550nm light at 0.8K in titanium in-diffused lithium niobate waveguides. To do so, we exploit the electro-optic properties of lithium niobate to convert between orthogonal polarisation modes with a fiber-to-fiber transmission >43%. We achieve a modulation depth of 23.6±3.3dB and a conversion voltage-length product of 28.8Vcm. This enables the combination of cryogenic photonics and active components on a single integration platform.