We realize a fiber Bragg grating InGaN based laser diode emitting at 400 nm and demonstrate its high coherency. Thanks to the fabrication of a narrow band fiber Bragg grating in the near-UV, we can reach single-mode and single-frequency regimes for the selfinjection locked diode. The device exhibits 44 dB sidemode-suppression-ratio and mW output power. Detailed frequency noise analysis reveals sub-MHz integrated linewidth and 16 kHz intrinsic linewidth. Such a narrow linewidth laser diode in the near-UV domain with a compact and low-cost design could find applications whenever coherency and interferometric resolutions are needed.

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High-Q whispering gallery mode microresonators are cornerstones to develop compact coherent sources like single frequency lasers or frequency combs. This work reports a detailed characterization of a whispering gallery mode microsphere in the near ultraviolet. Light coupling in the resonator is obtain thanks to a robust angle-polished fiber allowing to investigate the different coupling regimes. An intrinsic Q0-factor of 2.2 × 10 8 and a finesse of 7.3×10 4 are reported at a wavelength of 420 nm. Physical mechanisms contributing to the Q0-factor are discussed and routes to improve the performances are drawn. Such high-Q factor and high finesse are key ingredients to ease the study of photonic devices based on WGM microresonators.