On-Chip Integrated Laser and Magnetless PiezoMEMS Transduced Optical Isolator for Mass Manufacturable, Chip-Scale Rubidium Optical Clocks

The DoD has identified low-loss, magnet-free optical isolators as a key technology enabling the next generation of quantum integrated photonics applications. Quantum sensors face the challenge of being excessively large, expensive, and delicate, rendering them unsuitable for practical operational settings. A primary and crucial factor for advancing TRL and facilitating commercialization is resolving the persistent challenge of integrated laser stability when confronted with multiple reflections and components within PICs and downstream components of the optical module. Particularly at near-IR and visible wavelengths, the integration of optical isolators poses a significant obstacle due to their cumbersome size, high cost, and incompatibility with integration. The Oxide MEMS Lab at Purdue University has developed and demonstrated magnetic-free optical isolators utilizing aluminum nitride (AlN) piezoelectric modulators, which are seamlessly integrated on Si3N4 Photonic Integrated Circuit (SiN-PIC) and which meet the performance criteria of this solicitation (isolation > 30 dB, insertion loss < 3 dB) albeit in C-band operation. Stress optic modulation is wavelength agnostic. This isolator technology is compatible with monolithic integration on the LIT 780nm wavelength ultra-low loss SiN-PIC platform. Due to the narrow bandwidth of isolation at 780nm wavelength required by the Rubidium quantum systems application, there is much freedom in the design space for optimizing the piezoelectric transducer for achieving large isolation and low insertion loss. Furthermore, it is CMOS compatible and manufacturable enabling reduced c-SWAP and technology transfer to commercial silicon photonics foundries such as AIM Photonics and Tower. Ensuring vertical confinement in the transducer design prevents modulator crosstalk and phase smearing, preserving isolation and eliminating unpredictable in-plane acoustic waves. In this Phase I program, LIT and Purdue University will design the low-loss magnetless isolator monolithically integrated on ultra-low loss 780nm wavelength SiN-PIC platform with on-chip lasers heterogeneously integrated by micro-transfer print. In collaboration with the Time & Frequency Division at NIST we will develop the performance requirements for Phase II, where we will demonstrate the challenging performance requirements through the fabrication and test of a prototype photonic chip for laser stabilization to a Rb atomic vapor cell, leveraging our developments in this program. As detailed in our proposal, each component of the platform with the required performance has been previously developed and demonstrated by our teams, albeit at different wavelengths and operating conditions. We will adapt and integrate these developments into the 780nm wavelength platform for quantum integrated photonics applications.