DFB Laser Injection-Locked to PM Fiber Ring Cavity with 75-Hz Lorentzian Linewidth

Low-noise lasers are critical in precision spectroscopy, displacement measurements, and optical atomic clock development. These fields require lasers with minimal frequency noise, combining cost-effectiveness with robust design. We introduce a simple, single-frequency laser that uses a ring fiber cavity for self-injection locking in a standard semiconductor distributed feedback (DFB) laser. Our design, unique in its use of polarization-maintaining (PM) single-mode optical fiber components, offers a maintenance-free operation and enhanced stability against environmental noise. Achieving continuous wave (CW) single-frequency operation, it maintains this state with low-bandwidth active optoelectronic feedback. The laser operates at similar to 8 mW, reducing the Lorentzian linewidth to similar to 75 Hz and achieving phase and intensity noise levels below -120 dBc/Hz and -140 dBc/Hz, respectively. Additionally, its thermal stabilization limits frequency drift to < 0.5 MHz/min with a maximum deviation of < 8 MHz. Implementing this design in integrated photonics could significantly cut costs and space requirements in high-capacity fiber networks, data centers, atomic clocks, and microwave photonics.