Ultra-narrow Linewidth Lasers for Deployed Quantum Timing Applications

Vescent Photonics, LLC (Vescent) in collaboration with the Massachusetts Institute of Technology Lincoln Laboratory (MIT-LL) proposes to develop a compact ultra-narrow linewidth laser based on photonic integrated chip (PIC) technology for next-generation fieldable quantum sensor applications including optical atomic clocks, two-way time transfer, and precision inertial force and gravity sensing. Atomic clocks represent the most precise and accurate instruments developed by scientists to date and enable applications including the measurement of weak gravitational fields in near-zero gravity as well as accurate positioning, navigation, and timing (PNT) onboard a spacecraft. However, high-performance optical atomic clocks, including Sr+ trapped-ion clocks, currently only exist in laboratory settings due to constraints on the size, weight, power, and cost (SWaP-C) and environmental susceptibility of critical technology subsystems. One of the key subsystems so far hindering the transition of these high-performance optical clocks outside the laboratory is the ultra-narrow-linewidth ( 100 Hz) laser required to interrogate the atoms. The solution proposed here for the development of an ultra-narrow linewidth laser is an extension to the initial demonstrations by Dr. William Loh at MIT-LL with fiber-based stimulated Brillouin scattering (SBS) lasers which have been demonstrated in an operating Sr+ trapped-ion clock, resulting in an ADEV of 3.9E-14/(Tau)^(0.5). Using these fiber-based results as a baseline, recent measurements conducted by the MIT-LL team have shown an evolution toward PIC-based waveguide cavities that can support ultranarrow-linewidth lasers via SBS. The effort proposed here seeks to integrate necessary chip-scale components to move towards a design where the entire ultra-narrow-linewidth laser system is contained on a chip-scale device. Vescent Photonics, LLC (Vescent) in collaboration with the Massachusetts Institute of Technology Lincoln Laboratory (MIT-LL) proposes to develop a compact ultra-narrow linewidth (UNL) laser based on photonic integrated chip (PIC) technology for next-generation fieldable quantum sensors, including optical atomic clocks. High-performance optical atomic clocks currently only exist in laboratory settings due to the size, weight, power, and cost (SWaP-C) and environmental susceptibility of critical subsystems. One key subsystem hindering this transition from laboratory to deployment is the UNL (< 100 Hz) interrogation laser. The solution proposed here is an extension of work done by Dr. William Loh at MIT-LL demonstrating a compact UNL SBS fiber laser that was integrated into an operating Sr+ trapped-ion clock, resulting in an ADEV of 3.9E-14/Tau^(1/2). The MIT-LL team has since demonstrated PIC-based SBS cavities as well – the proposed effort seeks to integrate necessary chip-scale components to move towards a design where the entire UNL laser system is contained on a chip-scale device. The proposed effort consists of three components: Design PIC architecture for chip-scale SBS laser frequency doubled to the visible Sr+ clock transition: Vescent and MIT-LL will use requirements captured from NASA to design and fabricate photonic integrated circuits (PICs) with both a stimulated Brillouin scattering (SBS) cavity and a doubling circulator cavity which directs ultra-narrow linewidth (UNL) 674 nm light to a separate output. MIT’s extensive PIC fabrication experience will be heavily leveraged. Deliverables: reports containing PIC designs and fabrication data. Validate SBS performance using laboratory breadboard setup: Vescent will construct a fiber testbed to verify the supporting infrastructure and perform initial SBS measurements. This testing will include investigations into mitigating the long-term drift, which is a known issue with current SBS lasers. Deliverables: Reports containing test data and results of drift mitigation. Develop brassboard prototype for a low-SWaP, chip-scale SBS laser at the visible Sr+ transition: Vescent will design and build a low-SWaP PIC-based SBS laser prototype, containing all optics and electronics. Performance will be tested first at Vescent and then MIT-LL, where their 1348 nm UNL laser will be used to verify laser linewidth and drift. Deliverables: A low-SWaP 674 nm UNL laser, including documentation and installation.

This proposal directly addresses two of NASA’s research topic areas: S1.10 Atomic Quantum Sensors and Clocks and T8.07 Photonic Integrated Circuits. The laser hardware developed under this effort will be suitable for optical atomic clocks, atomic interferometers, and any applications requiring small, low-power lasers for remote sensing including the following missions: Moon to Mars, CLPS, Flight OPPS, and ISS. Vescent has identified several applications that would benefit from a low SWaP ultranarrow linewidth laser and include: optical atomic clocks, time and frequency transfer, ultralow microwave phase noise generation, dual comb and precision spectroscopy, precision inertial force and gravity sensing, and lidar.

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