Narrow linewidth, tunable external cavity diode laser using AlGaAs-SiN hybrid integration at 1-μm band

This paper demonstrates a narrow linewidth, tunable external cavity diode laser (ECDL) operating in the 1-μm spectral region. The ECDL is constructed on a hybrid AlGaAs-SiN photonic integrated platform, comprising key elements including an AlGaAs gain chip, a SiN passive external cavity chip and a lensed fiber. By utilizing double micro-ring resonators (MRRs) with slightly different perimeters on the SiN passive chip, the ECDL achieves a wavelength tuning range of 63 nm and exhibits a side mode suppression ratio exceeding 45 dB across the entire tuning range. The spot size converter (SSC) with a trident structure was optimized to achieve a coupling efficiency of 91% between the AlGaAs gain chip and the SiN waveguide. The combination of the narrowband filtering of the double MRRs and the low-loss coupling of the SSC enables the ECDL to achieve an intrinsic linewidth of less than 18 kHz. This narrow linewidth, widely tunable ECDL with a hybrid integration design is capable of acting as a seed laser in high-power spectral beam combining systems.