Superconducting Acousto-optic Phase Modulator

TL;DR

This paper presents a superconducting acousto-optic phase modulator on lithium niobate, demonstrating comparable performance to electro-optic modulators at cryogenic temperatures and potential for further efficiency improvements.

Contribution

It introduces a superconducting acousto-optic modulator with detailed fabrication, performance evaluation, and simulation, advancing integrated photonics at cryogenic temperatures.

Findings

Achieved a length-$V_$ product of 1.78 V$m$ at 8K.

Numerical simulations match experimental results and predict lower $V_$ with cavity enhancement.

Potential to reduce $V_$ to 0.27 V with simple device extension.

Abstract

We report the development of a superconducting acousto-optic phase modulator fabricated on a lithium niobate substrate. A titanium-diffused optical waveguide is placed in a surface acoustic wave resonator, where the electrodes for mirrors and an interdigitated transducer are made of a superconducting niobium titanium nitride thin film. The device performance is evaluated as a substitute for the current electro-optic modulators, with the same fiber coupling scheme and comparable device size. Operating the device at a cryogenic temperature (T=8K), we observe the length-half-wave-voltage (length-$V_\pi$) product of 1.78 V$\cdot$cm. Numerical simulation is conducted to reproduce and extrapolate the performance of the device. An optical cavity with mirror coating on the input/output facets of the optical waveguide is tested for further enhancement of the modulation efficiency. A simple extension of the current device is estimated to achieve an efficient modulation with $V_\pi=$ 0.27 V.