Ultra-low-noise Microwave to Optics Conversion in Gallium Phosphide

TL;DR

This paper demonstrates ultra-low-noise, bidirectional microwave-optical conversion using gallium phosphide's unique properties, enabling high-cooperativity optomechanical interactions with minimal thermal noise.

Contribution

The work introduces a gallium phosphide-based platform for efficient, low-noise microwave to optical photon conversion with high optomechanical cooperativity and minimal thermal noise.

Findings

Achieved bidirectional microwave-optical conversion on-chip.

Operated at optomechanical cooperativities exceeding one.

Induced less than one thermal noise phonon with pulsed pumping.

Abstract

Mechanical resonators can act as excellent intermediaries to interface single photons in the microwave and optical domains due to their high quality factors. Nevertheless, the optical pump required to overcome the large energy difference between the frequencies can add significant noise to the transduced signal. Here we exploit the remarkable properties of thin-film gallium phosphide to demonstrate bi-directional on-chip conversion between microwave and optical frequencies, realized by piezoelectric actuation of a Gigahertz-frequency optomechanical resonator. The large optomechanical coupling and the suppression of two-photon absorption in the material allows us to operate the device at optomechanical cooperativities greatly exceeding one. Alternatively, when using a pulsed upconversion pump, we demonstrate that we induce less than one thermal noise phonon. We include a high-impedance on-chip matching resonator to mediate the mechanical load with the 50-Ohm source. Our results establish gallium phosphide as a versatile platform for ultra-low-noise conversion of photons between microwave and optical frequencies.