Low-power Integrated Acousto-Optics for Atomic Quantum Sensors

Quantum measurement techniques based on matter-wave interferometry have matured from early laboratory experiments into field-useable systems capable of precision remote sensing of Earth's gravitational field. The unprecedented sensitivity of atom-based gravimeters and gradiometers is further enhanced when operating in microgravity environments, opening the possibility for high-resolution gravity cartography from orbit. The strong potential for atom interferometry in space is exemplified by NASA's Cold Atom Laboratory which has been operated onboard ISS since 2018 and provides multi-purpose capabilities as a technology demonstration. A common requirement for atom interferometers, and other atom-based quantum sensors such as Rydberg-atom-based RF-electric sensors and atomic clocks, is the need for complex laser and optical systems (LOS) used for atomic state preparation, control, and interrogation. Typically, these occupy bulky optical breadboards and require operating powers in the hundreds of Watts. While there has been much progress toward micro-integration of high-performance lasers, amplifiers, and detectors, there is currently no compact integrated alternative to free-space acousto-optic frequency shifters, which are used to precisely control laser spectra for atom manipulation. As a result, component-level advances are required for reduction in size weight and power and complexity of future space-deployable atomic quantum sensors. To overcome the limitations of existing acousto-optic components, we propose a new integrated photonic architecture based on a GaN-on-Sapphire piezo-optic platform to realize energy-efficient and compact acousto-optic devices. This material system allows simultaneous excitation and guidance of acoustic waves, as well as low-loss optical waveguiding suitable to produce extremely efficient acousto-optic interactions, with high optical power handling capabilities at the wavelengths of 780-852 nm used for Rb and Cs-based atomic sensors. This work will result in flexible acousto-optic frequency shifters and modulators with mW-drive powers (>100x improvement over state of the art) that can be readily implemented in existing quantum sensor systems. Existing state-of-the-art atomic quantum sensors utilize bulk acousto-optic modulators (AOMs) to precisely tune the frequency and amplitude of optical beams. Commercial AOMs are mature components that harness optical scattering from piezoelectrically-driven hypersound waves inside of a crystal. Due to their bulk-optical nature, they are relatively large (inch-scale) and require high RF drive powers >0.1-1 W—corresponding to wall-plug power consumption of several Watts per individual component. For future space-capable quantum sensors, that rely on numerous AOMs to operate, this represents a substantial barrier to size and power reduction. Under the ACT program, we will design and fabricate integrated acousto-optic devices in GaN-on-Sapphire, with the target goal of achieving high-performance single-sideband modulators/frequency shifters with mW-level drive powers. This superb efficiency is enabled through confinement of optical and elastic waves on wavelength-scales, radically enhancing acousto-optic coupling as compared to bulk devices. Preliminary studies show the potential for near-unity conversion efficiency of optical signals to different frequencies with >40 dB single-sideband rejection. Through this first-generation effort, these devices will be fiber-coupled to be compatible with existing breadboard-based quantum sensor systems with immediate benefit to power consumption. Future work to implement switching, routing, and attenuation based on the same piezo-optic interactions will allow fully chip-based synthesis of the numerous beams needed to perform atomic quantum sensor experiments, significantly reducing the footprint and complexity of future space-deployable systems.

Accelerate mission development and reduce risk by developing critical components and subsystems for advanced instruments and observing systems

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