微米尺寸铌酸锂晶体回音壁模式微腔的制备和光学非线性增强研究

Whispering gallery mode (WGM) micro-resonators, based on total internal reflection and possessing high quality factor Q and small mode volume V, have found applications in many areas such as nonlinear optics, quantum optics and sensors. These applications benefit from the enhancement of light-matter interactions within or near micro-resonators. Without any doubt, micro-resonators made of nonlinear optical crystalline materials such as lithium niobate, are ideally suited for the generation and enhancement of nonlinear optical effects. However, the quality factors of micron-size resonators made of crystalline materials are in the order of 1e3 or 1e4 typically, which are much lower than that of their millimeter-size counterparts by 3 to 4 orders of magnitude. Compared with millimeter-size resonators, the micron-size crystalline resonators have many advantages, including small mode volume, easy integration, and compatibility with optical communication system. Thus, the improvement of the quality factors of micron-size resonator made of crystalline materials and the enhancement of nonlinear optical effects therein is highly demanded from both the theoretical and practical points of view. In this project, we plan to fabricate high-Q micron-size lithium-niobate WGM resonators by use of high quality crystals and optimization of the design and fabrication process, for example, ultra-high-temperature treatment to smooth the surface. The optical nonlinear optical effects, such as the optical parametric oscillation and the output of UV light via second harmonic generation, are expect to be improved significantly due to the light locolazatoin and slow light based on high-Q micro-resonators.

回音壁模式微腔依靠全内反射将光限制在腔内，因为同时具有较高的品质因子Q和较小的模式体积V，腔内光场强度及其与物质的相互作用显著增强，所以广泛应用于非线性光学、量子光学和传感等领域。由铌酸锂等非线性晶体制备而成的微腔在非线性光学应用方面具有得天独厚的优势。目前，微米尺寸晶体材料微腔的Q值普遍不高，一般为1e3到1e4，与毫米尺寸晶体材料微腔的Q值相比存在3-4个数量级的差距。微米尺寸晶体材料微腔与毫米腔相比，具有模式体积小、易于集成和与光通信系统兼容的优点，因此其Q值的提高和光学非线性增强具有重要的学术和应用价值。在本项目中，我们拟通过选用高质量铌酸锂晶体，优化微腔结构设计以及包括超高温表面平滑处理在内的加工工艺流程，来制备微米尺寸高品质因子铌酸锂晶体回音壁模式微腔，并利用微腔的光场局域增强效应和慢光增强效应，在铌酸锂微腔内开展紫外倍频输出和光学参量振荡等非线性光学效应增强的研究。

本项目利用光刻、刻蚀等传统的半导体加工工艺，成功地实现了高品质因子片上铌酸锂晶体、二氧化硅微腔的批量制备，并围绕回音廊模式光学微腔开展耦合、主动调控和非线性光学效应等方面的研究。.项目执行期间，首次实现了品质因子达到1.19e6的片上铌酸锂单晶微腔的批量制备和电光调制；在铌酸锂单晶微腔中，实现了热光振荡、倍频以及和频等非线性效应；制备了反楔形二氧化硅微腔，实现了锥形光纤和微腔之间稳定的光耦合；通过在二氧化硅反楔形微腔上镀铌酸锂薄膜的方法，成功制备出了铌酸锂/二氧化硅复合微腔，克服了纯二氧化硅微腔不具备电光效应和光学非线性效应弱的缺点；发现了微腔之间和微腔与波导之间耦合的横向振荡效应，利用微腔与光波导之间的多点耦合效应，实现了不同尺寸光纤与微腔的临界耦合，为提高微腔波导耦合体系的机械强度和系统稳定性提供了简单可行方案。.课题负责人做为通讯作者或第一作者在Adv. Mater.、Sci. Rep.、Opt. Express等国际知名SCI刊物发表论文8篇，合作发表论文5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SPIE Photonics West、META、PIERS、IMCO等）做邀请报告8次。举办学术研讨会3次。期间培养博士生1名，硕士生3名。