基于倾斜波导光栅结构的高偏振消光比二氧化硅光波导谐振腔

Gyro is an important inertial rotation sensor. Among available gyro technologies, the Sagnac based optical gyros are attractive since they are insensitive to vibrations and acceleration, and are capable of handling a large range of rotation rates. The well-known optical gyro is the interferometric fiber-optic gyro (IFOG). While IFOGs have been widely developed over the past 30 years, their further applications are limited in terms of size, weight, and robustness. In recent years, the resonant micro-optic gyro (RMOG) with a waveguide-type ring resonator emerges as an excellent alternative in this regard, which greatly benefits from the recent technical progress of integrated optics. The length of the sensing loop in the RMOG system can be greatly reduced, due to the enhanced Sagnac effect established by circulating lightwaves in the resonator loop. The adoption of integrated optics technology allows constructing the resonator and other individual optical elements on one substrate, enabling mass production of RMOGs featuring low cost, small size, and rugged architecture. The waveguide ring resonator is the key sensing element in the RMOG. Both the loss and polarization characteristics of the resonator affect the sensitivity of the RMOG. The applicant concentrates on the temperature-related polarization noise that has restricted the long-term stability of the RMOG. A novel resonator by inserting a titled waveguide gratings with the Brewster angle in a silica waveguide ring resonator is proposed. We will present an in-depth analysis of the polarization characteristics of this novel waveguide ring resonator and its influence of the RMOG in this project. The single-mode optical waveguides in the resonator will be fabricated using lithographic pattering and refractive ion etching. In order to avoid etching submicron structures with a high aspect ratio, the UV-written grating technique is adopted for the titled waveguide gratings fabrication. The performance of the titled waveguide gratings and its influence of the waveguide ring resonator will be studied both theoretically and experimentally. The silica waveguide ring resonator integrated with the titled waveguide gratings is expected to achieve a high polarization extinction ratio thus to improve the long-term stability of the RMOG. Our goal is to develop a silica waveguide ring resonator with a high polarization extinction ratio for tactical-performance RMOG.

陀螺是重要的惯性传感器，历经30多年的发展，以Sagnac效应为基础的干涉式光纤陀螺已获批量生产和广泛应用，理论上具有更高精度的谐振式光学陀螺仍处于实验室研究阶段。在一些对体积、重量有特殊要求以及耐振动、抗冲击的领域，谐振式微光学陀螺（RMOG）具有独特优势。光波导环形谐振腔是RMOG的核心敏感部件，除损耗特性影RMOG理论灵敏度之外，谐振腔的偏振特性也会严重影响RMOG的零偏稳定性。针对长期制约着RMOG稳定性提高的偏振噪声问题，项目首次提出集成倾斜波导光栅结构的高偏振消光比光波导谐振腔结构，开展理论和实验研究。本项目以硅基二氧化硅光波导谐振腔为研究对象，利用集成光学微加工工艺和紫外写入技术，在芯片的局部谐振腔波导上，集成倾斜角度为Brewster角大小的倾斜波导光栅结构，利用Brewster原理，研制出具有高偏振消光比的二氧化硅光波导谐振腔，并改善温度特性，满足研制战术级RMOG需要。

微陀螺是微小卫星实现高精度姿态和轨道控制的核心器件，是未来高性能微小卫星的瓶颈技术之一。谐振式微光学陀螺（RMOG）是高精度陀螺实现微小型化和集成化的重要途径。光波导环形谐振腔（WRR）是RMOG 的核心敏感部件，除损耗特性影响RMOG理论灵敏度之外，谐振腔的偏振特性也会严重影响RMOG的零偏稳定性。针对长期制约着RMOG稳定性提高的偏振噪声问题，项目首次提出采用倾斜角度为Brewster角的倾斜波导光栅（TWG）的方法，实现低损耗、高清晰度、高偏振消光比的WRR。采用体电流法建立了TWG传输特性分析模型，完成了TWG结构优化设计；利用琼斯矩阵法建立WRR偏振特性分析模型，分析了在WRR入腔、出腔及腔内局部光波导上集成TWG结构对其偏振特性的改善情况，优化设计了WRR结构；采用波长为248nm的准分子激光器在等离子体化学气相淀积（PECVD）法制作的硅基二氧化硅WRR上制作了倾斜角度为45的TWG结构，研制出低损耗、高清晰度、高偏振消光比的WRR芯片：其中研制的反射式WRR芯片测试清晰度高达196.7，是目前二氧化硅光波导谐振腔芯片中公开报道的最高值；改变WRR入腔光波偏振态和芯片温度，谐振曲线保持稳定，表明次偏振态得到了充分抑制；研究了WRR偏振消光比特性和RMOG偏振波动的关系，建立了RMOG偏振波动噪声分析模型；提出了一种基于变时间、幅度固定的调制方式，实现了高精度移频，移频器的分辨率为0.0075Hz，采用正弦波和锯齿波组合调制技术，率先将上述移频器成功应用于腔长为厘米的RMOG，在国际上首次实现了能检测到地球自转的硅基集成光学陀螺。基于该项成果，有望在更大温度范围内，抑制温度波动有关的偏振噪声，极大地提高RMOG的长期稳定性，使得RMOG的实际应用成为可能。. 项目执行过程中，发表SCI期刊论文17篇，EI会议论文12篇，授权发明专利4项，国际/国内学术会议邀请报告10次，培养硕士/博士研究生10人。