Sub-20 kHz Low Frequency Noise Near Ultraviolet Miniature External Cavity Laser Diode

We present a compact InGaN fiber Bragg grating (FBG) semiconductor laser diode operating below 400 nm in the single-mode emission regime. This compact coherent laser source exhibits an intrinsic linewidth of 14 kHz in the near-UV range. We report a side-mode suppression ratio reaching up to 40 dB accompanied by a mW-level output power. Furthermore, the properties of the FBG, including its central wavelength, bandwidth, and reflectivity, can be readily customized to fulfill specific requirements. The combination of small footprint design, wavelength tunability, low frequency noise, and access to the fibered output signal positions these FBG laser systems as strong candidates for hybridization into integrated photonic platforms tailored for quantum information processing and metrology.