Cryogenic electro-optic modulation in titanium in-diffused lithium niobate waveguides Thiele, Frederik vom Bruch, Felix Brockmeier, Julian Protte, Maximilian Hummel, Thomas Ricken, Raimund Quiring, Viktor Lengeling, Sebastian Herrmann, Harald Eigner, Christof Silberhorn, Christine Bartley, Tim Electrical and Electronic Engineering Atomic and Molecular Physics and Optics Electronic Optical and Magnetic Materials <jats:title>Abstract</jats:title> <jats:p>Lithium niobate is a promising platform for integrated quantum optics. In this platform, we aim to efficiently manipulate and detect quantum states by combining superconducting single photon detectors and modulators. The cryogenic operation of a superconducting single photon detector dictates the optimisation of the electro-optic modulators under the same operating conditions. To that end, we characterise a phase modulator, directional coupler, and polarisation converter at both ambient and cryogenic temperatures. The operation voltage <jats:inline-formula> <jats:tex-math><?CDATA $V_{\pi/2}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>V</mml:mi> <mml:mrow> <mml:mi>π</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> of these modulators increases, due to the decrease in the electro-optic effect, by 74% for the phase modulator, 84% for the directional coupler and 35% for the polarisation converter below 8.5<jats:inline-formula> <jats:tex-math><?CDATA $\,\mathrm{K}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">K</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. The phase modulator preserves its broadband nature and modulates light in the characterised wavelength range. The unbiased bar state of the directional coupler changed by a wavelength shift of 85<jats:inline-formula> <jats:tex-math><?CDATA $\,\mathrm{nm}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">n</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> while cooling the device down to 5<jats:inline-formula> <jats:tex-math><?CDATA $\,\mathrm{K}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">K</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>. The polarisation converter uses periodic poling to phasematch the two orthogonal polarisations. The phasematched wavelength of the utilised poling changes by 112<jats:inline-formula> <jats:tex-math><?CDATA $\,\mathrm{nm}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">n</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> when cooling to 5<jats:inline-formula> <jats:tex-math><?CDATA $\,\mathrm{K}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">K</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonac6c63ieqn6.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p> IOP Publishing 2022 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_6501 https://ris.uni-paderborn.de/record/33672 Thiele F, vom Bruch F, Brockmeier J, et al. Cryogenic electro-optic modulation in titanium in-diffused lithium niobate waveguides. <i>Journal of Physics: Photonics</i>. 2022;4(3). doi:<a href="https://doi.org/10.1088/2515-7647/ac6c63">10.1088/2515-7647/ac6c63</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1088/2515-7647/ac6c63 info:eu-repo/semantics/altIdentifier/issn/2515-7647 info:eu-repo/semantics/closedAccess