Narrow linewidth near-UV InGaN laser diode based on external cavity fiber Bragg grating

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