Abstract
Low-loss photonic integrated circuits and microresonators have enabled a wide range of applications, such as narrow-linewidth lasers and chip-scale frequency combs. To translate these into a widespread technology, attaining ultralow optical losses with established foundry manufacturing is critical. Recent advances in integrated Si3N4 photonics have shown that ultralow-loss, dispersion-engineered microresonators with quality factors Q > 10 × 106 can be attained at die-level throughput. Yet, current fabrication techniques do not have sufficiently high yield and performance for existing and emerging applications, such as integrated travelling-wave parametric amplifiers that require meter-long photonic circuits. Here we demonstrate a fabrication technology that meets all requirements on wafer-level yield, performance and length scale. Photonic microresonators with a mean Q factor exceeding 30 × 106, corresponding to 1.0 dB m−1 optical loss, are obtained over full 4-inch wafers, as determined from a statistical analysis of tens of thousands of optical resonances, and confirmed via cavity ringdown with 19 ns photon storage time. The process operates over large areas with high yield, enabling 1-meter-long spiral waveguides with 2.4 dB m−1 loss in dies of only 5 × 5 mm2 size. Using a response measurement self-calibrated via the Kerr nonlinearity, we reveal that the intrinsic absorption-limited Q factor of our Si3N4 microresonators can exceed 2 × 108. This absorption loss is sufficiently low such that the Kerr nonlinearity dominates the microresonator’s response even in the audio frequency band. Transferring this Si3N4 technology to commercial foundries can significantly improve the performance and capabilities of integrated photonics.
Highlights
Low-loss photonic integrated circuits and microresonators have enabled a wide range of applications, such as narrow-linewidth lasers and chip-scale frequency combs
In particular soliton microcombs, Si3N444 has emerged as a leading material due to its ultralow optical losses, absence of two-photon absorption in the telecommunication bands, strong Kerr nonlinearity, high refractive index, space compatibility[45] and exceptionally high power handling capability[46,47]
Among all integrated photonic platforms[48], optical losses near or below 1 dB m−1 have only been demonstrated in Si3N4 photonic integrated circuits (PICs)
Summary
Low-loss photonic integrated circuits and microresonators have enabled a wide range of applications, such as narrow-linewidth lasers and chip-scale frequency combs. To translate these into a widespread technology, attaining ultralow optical losses with established foundry manufacturing is critical. We report a high-yield, wafer-scale fabrication technology to build tight confinement, ultralow-loss, dispersion-engineered Si3N4 waveguides of length exceeding one meter. This Si3N4 fabrication technology is based on the photonic Damascene process[61] using standard CMOS fabrication techniques such as DUV stepper lithography, dry etching, and low-pressure chemical vapor deposition (LPCVD). Integrated Si3N4 microresonators fabricated using this process are systematically characterized and analyzed, showing quality (Q) factors above 30 × 106, linear losses of 1 dB m−1, and wafer-level yield
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