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An integrated optical modulator operating at cryogenic temperatures

Abstract

Photonic integrated circuits (PICs) operating at cryogenic temperatures are fundamental building blocks required to achieve scalable quantum computing and cryogenic computing technologies1,2. Silicon PICs have matured for room-temperature applications, but their cryogenic performance is limited by the absence of efficient low-temperature electro-optic modulation. Here we demonstrate electro-optic switching and modulation from room temperature down to 4 K by using the Pockels effect in integrated barium titanate (BaTiO3) devices3. We investigate the temperature dependence of the nonlinear optical properties of BaTiO3, showing an effective Pockels coefficient of 200 pm V−1 at 4 K. The fabricated devices show an electro-optic bandwidth of 30 GHz, ultralow-power tuning that is 109 times more efficient than thermal tuning, and high-speed data modulation at 20 Gbps. Our results demonstrate a missing component for cryogenic PICs, removing major roadblocks for the realization of cryogenic-compatible systems in the field of quantum computing, supercomputing and sensing, and for interfacing those systems with instrumentation at room temperature.

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Fig. 1: BaTiO3 EO device concept.
Fig. 2: EO and electrical response of BaTiO3-based optical switches at 4 K.
Fig. 3: Temperature dependence of the Pockels effect in BaTiO3.
Fig. 4: Demonstration of low-power switching and high-speed data modulation with BaTiO3-based devices at 4 K.

Data availability

The data from the electro-optic measurements analysed and presented in Figs. 2a–c, 3 and 4 are available in an online repository with the digital object identifier: https://doi.org/10.5523/bris.3dwflddsnkun32ghpq4zufxtl1. The remaining data supporting the findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work has received funding from the European Commission under grant agreement numbers H2020-ICT-2015-25- 688579 (PHRESCO) and H2020-ICT-2017-1-780997 (plaCMOS), from the Swiss State Secretariat for Education, Research and Innovation under contract numbers 15.0285 and 16.0001, from the Swiss National Foundation project number 200021_159565 PADOMO, from EPSRC grants EP/L024020/1, EP/M013472/1 and EP/K033085/1, the UK EPSRC grant QuPIC (EP/N015126/1), and ERC grant 2014- STG 640079. J.B. thanks D. Sahin for her assistance with the experimental setup.

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F.E. and J.F. fabricated and structurally characterized the epitaxial BaTiO3/SrTiO3 layer stack with support from H.S. F.E. designed all photonic circuits and fabricated them with support from D.C. F.E., P.S. and S.A. performed optical simulations for the device design. G.E.V.-G., F.E., A.A.G., A.H., G.D.M. and J.B. characterized the electro-optic performance at different temperatures, including low-speed and radiofrequency measurements. The electro-optic data were analysed by F.E. and A.A.G. F.E. and P.S. performed all electrical measurements. The concept for this work was defined by S.A., G.D.M. and M.G.T. and implemented by F.E. with support of S.A. and J.B. F.E., J.F. and S.A. wrote the manuscript with contributions from all authors.

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Correspondence to Felix Eltes or Stefan Abel.

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Competing interests

F.E., J.F. and S.A. are involved in commercially developing barium titanate technologies at Lumiphase AG. M.G.T. is involved in developing photonic quantum technologies at PsiQuantum Corporation.

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Supplementary Notes 1–9, Figs. 1–12, Table 1 and refs 1–14.

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Eltes, F., Villarreal-Garcia, G.E., Caimi, D. et al. An integrated optical modulator operating at cryogenic temperatures. Nat. Mater. 19, 1164–1168 (2020). https://doi.org/10.1038/s41563-020-0725-5

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