Liu Junqiu, Huang Guanhao, Wang Rui Ning, He Jijun, Raja Arslan S, Liu Tianyi, Engelsen Nils J, Kippenberg Tobias J
Institute of Physics, Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland.
Nat Commun. 2021 Apr 16;12(1):2236. doi: 10.1038/s41467-021-21973-z.
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 SiN photonics have shown that ultralow-loss, dispersion-engineered microresonators with quality factors Q > 10 × 10 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 × 10, corresponding to 1.0 dB m 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 loss in dies of only 5 × 5 mm size. Using a response measurement self-calibrated via the Kerr nonlinearity, we reveal that the intrinsic absorption-limited Q factor of our SiN microresonators can exceed 2 × 10. This absorption loss is sufficiently low such that the Kerr nonlinearity dominates the microresonator's response even in the audio frequency band. Transferring this SiN technology to commercial foundries can significantly improve the performance and capabilities of integrated photonics.
低损耗光子集成电路和微谐振器已实现了广泛的应用，如窄线宽激光器和芯片级频率梳。要将这些应用转化为广泛使用的技术，利用成熟的代工制造实现超低光损耗至关重要。集成氮化硅光子学的最新进展表明，在芯片级产量下可实现品质因数Q > 10×10的超低损耗、色散工程微谐振器。然而，对于现有和新兴应用，如需要米级光子电路的集成行波参量放大器，当前的制造技术在产量和性能方面还不够高。在此，我们展示了一种满足晶圆级产量、性能和长度尺度所有要求的制造技术。通过对数万次光学谐振的统计分析确定，在完整的4英寸晶圆上获得了平均品质因数超过30×10的光子微谐振器，对应1.0 dB·m的光损耗，并通过光子存储时间为19 ns的腔衰荡进行了确认。该工艺在大面积上以高产量运行，能够在仅5×5 mm尺寸的芯片中制造出损耗为2.4 dB·m的1米长螺旋波导。通过利用克尔非线性进行自校准的响应测量，我们发现我们的氮化硅微谐振器的本征吸收限制品质因数可超过2×10。这种吸收损耗足够低，以至于即使在音频频段，克尔非线性也主导着微谐振器的响应。将这种氮化硅技术转移到商业代工厂可显著提高集成光子学的性能和能力。
