Low-SWaP, tunable, and narrow-linewidth laser systems for deployable quantum technologies

With quantum optical technologies advancing toward real-world deployment, their success depends on reducing the size, weight, and power (SWaP) of the laser sources that drive them. While photonic integrated circuit (PIC)-based lasers have emerged as promising replacements to traditional bulky lasers, achieving a PIC-based laser system that satisfies both optical and functional requirements demands a system-level co-design of optics, electronics, and software that has not yet been realized. Here, we demonstrate a low-SWaP, tunable, and narrow-linewidth laser system based on PICs and programmable control electronics for the 780 nm region of the near-infrared spectrum. By leveraging the Vernier effect between a Fabry-Pérot laser diode (FPLD) and a microring resonator (MRR), we design the PIC to serve as an external cavity to self-injection lock the FPLD, resulting in a tunable laser with narrow linewidth. We package this PIC-laser into a standard butterfly package and drive it using a custom digital laser controller with a user-friendly interface. We design the programmable control electronics to meet the specific requirements of a PIC-laser as well as enable advanced functionalities that support cutting-edge quantum and classical optical applications. The complete laser system, which also includes optical isolators and fiber coupling, achieves up to 9.5 nm coarse tuning, 50 GHz mode-hop-free fine tuning, 30 mW free-space output power (before isolators), kHz-level intrinsic linewidth, and over 50 dB side-mode suppression ratio (SMSR). To exemplify the applicability of our laser system for quantum technologies, we perform spectroscopy on rubidium D2 transition lines and frequency-lock it to the cycling transition for days in a non-controlled environment with significant temperature fluctuations. We envision that our compact, fully integrated laser system will be a key enabler for scalable and deployable quantum and classical optical technologies.