Anneal-free ultra-low loss silicon nitride integrated photonics

Heterogeneous and monolithic integration of the versatile low-loss silicon nitride platform with low-temperature materials such as silicon electronics and photonics,III–V compound semiconductors,lithium niobate,organics,and glasses has been inhibited by the need for high-temperature annealing as well as the need for different process flows for thin and thick waveguides.New techniques are needed to maintain the state-of-the-art losses,nonlinear properties,and CMOS-compatible processes while enabling this next generation of 3D silicon nitride integration.We report a significant advance in silicon nitride integrated photonics,demonstrating the lowest losses to date for an anneal-free process at a maximum temperature 250℃,with the same deuterated silane based fabrication flow,for nitride and oxide,for an order of magnitude range in nitride thickness without requiring stress mitigation or polishing.We report record low anneal-free losses for both nitride core and oxide cladding,enabling 1.77 dBm^(-1) loss and 14.9 million Q for 80 nm nitride core waveguides,more than half an order magnitude lower loss than previously reported sub 300℃ process.For 800 nm-thick nitride,we achieve as good as 8.66 dBm^(-1) loss and 4.03 million Q,the highest reported Q for a low temperature processed resonator with equivalent device area,with a median of loss and Q of 13.9 dBm^(-1) and 2.59 million each respectively.We demonstrate laser stabilization with over 4 orders of magnitude frequency noise reduction using a thin nitride reference cavity,and using a thick nitride micro-resonator we demonstrate OPO,over two octave supercontinuum generation,and four-wave mixing and parametric gain with the lowest reported optical parametric oscillation threshold per unit resonator length.These results represent a significant step towards a uniform ultra-low loss silicon nitride homogeneous and heterogeneous platform for both thin and thick waveguides capable of linear and nonlinear photonic circuits and integration with low-temperature materials and processes.

Tunable broadband two-point-coupled ultra-high-Q visible and near-infrared photonic integrated resonators

Ultra-high-quality-factor(Q)resonators are a critical component for visible to near-infrared(NIR)applications,including quantum sensing and computation,atomic timekeeping and navigation,precision metrology,microwave photonics,and fiber optic sensing and communications.Implementing such resonators in an ultra-low-loss CMOS foundry compatible photonic integration platform can enable the transitioning of critical components from the lab-to the chip-scale,such as ultra-low-linewidth lasers,optical reference cavities,scanning spectroscopy,and precision filtering.The optimal operation of these resonators must preserve the ultra-low losses and simultaneously support the desired variations in coupling over a wide range of visible and NIR wavelengths as well as provide tolerance to fabrication imperfections.We report a significant advancement in high-performance integrated resonators based on a two-point-coupling design that achieves critical coupling simultaneously at multiple wavelengths across wide wavebands and tuning of the coupling condition at any wavelength,from under-,through critically,to over-coupled.We demonstrate critical coupling at 698 nm and 780 nm in one visible-wavelength resonator and critical coupling over a wavelength range from 1550 nm to 1630 nm in a 340-million intrinsic Q 10-meter-coil waveguide resonator.Using the 340-million intrinsic Q coil resonator,we demonstrate laser stabilization that achieves six orders of magnitude reduction in the semiconductor laser frequency noise.We also report that this design can be used as a characterization technique to measure the intrinsic waveguide losses from 1300 nm to 1650 nm,resolving hydrogen-related absorption peaks at 1380 nm and 1520 nm in the resonator,giving insight to further reduce waveguide loss.The CMOS foundry compatibility of this resonator design will provide a path towards scalable system-on-chip integration for high-performance precision experiments and applications,improving reliability,and reducing size and cost.