Narrow-linewidth photonic wirebonded silicon nitride external cavity tunable laser

Ultra-low linewidth widely tunable lasers capable of emission by design from the visible to shortwave infrared are important building blocks for a range of precision applications including quantum sensing and computing, timekeeping, metrology, optical clocks, and fiber sensing. Importantly, integration of precision tunable lasers in a CMOS foundry compatible platform that can support higher level integration with other components, such as low loss silicon nitride (Si₃N₄), is an important step towards full system on chip solutions. Integration of the III-V gain material with the Si₃N₄ tunable cavity is a critical step towards this goal and must be achieved through a low-cost, manufacturable, and reliable process. However, this co-integration has remained challenging due to tight alignment tolerances and mode mismatches between the semiconductor and silicon nitride waveguides. 3D-printed photonic wire bonding (PWB) offers a robust approach to hybrid integration due to the relaxation of waveguide alignment tolerances and the inherent low-loss mode matching. In this work, we demonstrate a narrow linewidth PWB-integrated Si₃N₄ external cavity tunable laser (ECTL) with a 3.75-7.77 Hz fundamental linewidth measured across a 60 nm tuning range and a 1.27 kHz integral linewidth: a reduction of nearly three orders of magnitude in fundamental linewidth compared with previously reported PWB-integrated ECTLs in Si₃N₄. The PWB process has the potential to realize reliable and manufacturable tunable lasers on-chip with the performance of table-top fiber lasers. These results establish photonic wirebonding as a viable integration pathway for precision photonic systems, enabling portable, scalable, and cost-effective solutions for quantum, low-noise microwave, and sensing applications.