利用飞秒激光直写技术实现高品质因子三维微腔研究

The extremely short pulse duration and ultrahigh peak power offered by femtosecond laser pulses lead to the highly nonlinear interaction between the femtosecond laser pulses and materials. Therefore, femtosecond laser microfabrication can facilitate internal modification of transparent materials through a multiphoton absorption process, which is difficult to achieve by use of longer laser pulses. In addition, due to the extremely short interaction period, the heat effect can be minimized, by which the fabrication precision can be greatly promoted. Using femtosecond laser direct writing, three-dimensional micro/nanofabrication can be realized inside transparent materials. Due to these unique advantages, the technology has attracted great attention for its promissing applications in the fields of microfuidics, microelectronics, microoptics, micro-electro-mechanics, biomedicine, etc. In particular, as one of the frontiers in photonics, whispering-gallery-mode (WGM) optical microcavities that can strongly confine optical energy within small volumes for long periods of time through total internal reflection have found broad applications in quantum optics and quantum electrodynamics. However, the current WGM microcavities are fabricated by planar lithographic technique, making it impossible to achieve non-inplane optical modes. We attempt to solve this problem by fabrication of microcavities with non-inplane features (i. e., three-dimensional microcavities) using femtosecond laser direct writing. This project will focus on the fabrication of high-Q WGM microcavities in glass chips by femtosecond laser direct writing, the characterization of the optical modes in the cavities, and the exploration of the related applications.

飞秒激光脉冲具有极短的脉冲宽度和极高的峰值功率，与物质相互作用时呈现出强烈的非线性效应。它的多光子吸收机制可用来加工长脉冲无法加工的透明介质。由于飞秒脉冲作用时间极短，热效应非常小,因而大大提高了加工精度。利用飞秒激光直写技术，可以在透明材料内部实现三维立体微纳加工。基于上述优点，该技术已成为微制造领域的研究热点，在微流体、微电子、微光学、微机电系统和生物医学等领域已展露出重要的应用前景。特别是作为光子学领域的重要前沿，回音壁模式的光学微腔能把光能量长时间限制在小体积内，在量子光学及量子电动力学领域具有广泛的应用。然而利用平面光刻技术，无法实现三维结构微腔，从而对形成三维可控的光场模式与实现光与微腔的三维耦合造成显著障碍。飞秒激光直写能够突破二维光刻技术的瓶颈，有望解决上述困难。本课题将利用飞秒激光直写技术制备具有高品质因子的三维光学微腔，并尝试表征腔中的光场调控特性及开拓相关应用。

作为光子学领域的重要前沿，回音壁模式的光学微腔能把光能量长时间限制在小体积内，在量子光学及量子电动力学领域具有广泛的应用。然而利用已有平面光刻技术，无法实现三维结构微腔，从而对形成三维可控的光场模式与实现光与微腔的三维耦合造成显著障碍。本项目利用飞秒激光直写技术特有的三维微纳加工优势，在多种透明材料中实现回音壁模式的光学微腔，并发展了有效抑制微盘腔光损耗的新技术，实现了腔中的光场调控特性表征，并围绕光学微腔展开相关非线性光学与量子光学研究，结合现有的微流、微光子器件，集成和构建新型功能性器件，开拓相关应用。课题负责人作为通信作者在Optica (IF=5.205)，Phys. Rev. Appl. (IF=4.061)，Sci. Rep.(IF=5.228)等国际知名SCI 刊物发表论文10篇。负责人作为第一报告人，应邀在光电子领域权威性国际会议（如Photonics West、APLS、PULMM、COLA等）做邀请报告11次。申请发明专利2项。期间培养博士生2名，硕士生3名。取得的重要成果包括：1、采用水辅助的飞秒激光刻蚀及二氧化碳激光回流技术，首次在钕玻璃衬底上制备了高品质因子的光学回音壁模式有源微腔，品质因子超过10^6，并在室温下，实现低阈值激射；2、首次利用飞秒激光直写结合聚焦离子束研磨微腔的方案，制备了尺寸小于50微米的氟化钙晶体微腔，为芯片上的亚百微米尺寸的晶体微腔的制备及非线性光学应用、实现量子光源开辟新的路径；3、利用飞秒激光直写与聚焦离子束研磨制备高品质晶体回音壁模式光学微腔，所得铌酸锂薄膜微腔品质因子在1550 nm波段高达10^6，并演示了微腔中的二次谐波产生，归一化转换效率可达1.1×10^(-3) /mW, 为实现紧凑的频率转换器、单光子光源、光学频率梳等功能器件奠定了基础；4、研究了集成光纤锥和微流通道的微腔传感器的加工技术及性能参数，具有高探测灵敏度（氯化钠溶液中实现1.2×10^(-4)RIU),在生化分析探测领域具有重要的应用前景。

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