Hybrid integrated ultra-low linewidth coil stabilized isolator-free widely tunable external cavity laser

Precision applications such as quantum computing, quantum and fiber sensing, and mmWave and RF generation, require ultra-low phase noise stabilized lasers operating at wavelengths across the visible to near-IR. These applications employ widely tunable table-scale laser systems, bulk-optic reference cavities, and optical isolation to achieve ultra-low frequency noise and high stability across wide wavelength ranges. Photonic integration promises to bring these laser systems to the chip-scale, enabling reliable, scalable and portable precision applications. Here we report record-low integrated laser linewidths with a coil-cavity stabilized 1550 nm tunable laser, that achieves 3 to 7 Hz fundamental linewidth across a 60 nm tuning range and 27 - 60 Hz integral linewidths with an Allan deviation of 1.8E-13 at 6.4 ms across 40 nm. These results represent 5 orders of magnitude noise reduction and almost 2-orders magnitude reduction in integral linewidth for widely tunable integrated lasers. The hybrid integrated silicon nitride external cavity tunable laser is stabilized to a silicon nitride 10-meter long integrated coil-resonator without the need for an optical isolator by leveraging the inherent 45 dB isolation. The laser and reference cavity are fabricated in the same 80 nm-thick ultra-low loss silicon nitride waveguide CMOS foundry compatible process, which combined with the inherent isolation, unlocks the path towards fully integrated visible to NIR frequency-stabilized lasers.