  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 and 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. As a result, the small footprint design of this
laser is compatible with integration into a standard butterfly package to ease
the lab-to-market technology transfer. The combination of low frequency noise
and fibered output signal positions these FBG laser systems as strong
candidates for hybridization with integrated photonic platforms tailored for
quantum information processing and metrology.
