氮化硅集成微腔光频梳器件关键制备技术(特邀)

微腔光频梳，又称微腔梳，是通过腔内四波混频过程产生的一种高相干宽谱的集成光源，有着优异的时频特性，可用于超精密分子光谱、相干通信、激光雷达、轻型化装备等测量应用，是基础科学、计量学及军事装备的重要工具，是一项颠覆性的技术。报道了一种集成氮化硅（Si₃N₄）微腔光频梳器件制备的关键技术，提出了一种方法平衡Si₃N₄的应力、厚度和化学计量之间的矛盾，以满足反常色散和减少双光子吸收的要求。利用这种改进的大马士革工艺微结构降低Si₃N₄厚膜的应力，减少应力缺陷对器件性能的影响，实现高品质Si₃N₄薄膜的可控制备。在微腔刻蚀工艺中，采用30 nm氧化铝牺牲层补偿掩模抗刻蚀能力，实现微环和波导侧壁粗糙度小于15 nm，满足了微腔高Q值的要求。经双光泵浦测量得到1 480~1 640 nm波段内的宽光谱高相干克尔光频梳。

Fabrication of silicon nitride-based integrated microcavity optical frequency comb devices (Invited)

Microcavity optical frequency comb (also called the microcavity comb), a subversive technology, is an integrated light source produced from a four-wave mixing process in a nonlinear optical microcavity. As a precision device with excellent properties of optical frequency, microcavity combs can be extensively applied in many fields such as molecular spectroscopy, coherent communication, LiDAR, metrology, and lightweight equipment for airborne system. Here, the fabrication of integrated silicon nitride (Si₃N₄) microcavity optical frequency comb devices was reported. The balance between the stress, thickness and stoichiometry of Si₃N₄ was well controlled. A reliable method was proposed to fabricate Si₃N₄ optical film with enough thickness and stoichiometry to meet the requirements of anomalous dispersion and reducing light absorption. The modified technology of Damascene process with microstructures to decline the stress of thick Si₃N₄ film was developed to reduce defects. Furthermore, the mask via with a 30 nm thick alumina compensation layer was optimized and a practicable etching process was used for fabricating Si₃N₄ microresonators with sub-15 nm roughness of lateral walls of microring and waveguide. The experimental results show a high quality of Si₃N₄ microcavity. Additionally, a coherent Kerr optical frequency comb spectrum can be produced with a wide spectral range from 1480 nm to 1640 nm via dual light pumping.