高灵敏度电场传感在学术与工业领域均有着广阔的应用前景。薄膜铌酸锂（TFLN）的出现为实现高灵敏度、宽频带、微型化的光学电场传感器提供了可能。本论文研究了基于TFLN的高灵敏度电场传感器的设计优化、微纳加工、耦合通光及实验应用，主要内容如下：首先，针对厚度为百纳米的铌酸锂薄膜，设计了宽度为亚微米的脊型波导，通过优化波导的刻蚀深度并减小电极间距，增加了电光调制效率；提出了基于TFLN的尺寸为百微米的微环谐振腔电场传感光路，通过减小微腔的光学总损耗，增加了光波传播的等效长度，延长了光场和电场相互作用的时间，相比于基于体铌酸锂的长度为厘米级的马赫-曾德尔干涉光路，灵敏度提高了50余倍。其次，针对TFLN材料难于刻蚀的共性问题，研发了基于TFLN平台的低损耗、高效率的加工工艺。实验探究了电子束胶、光刻胶、金属和非金属掩膜的加工方法与效果，揭示了重沉积是波导侧壁粗糙和非垂直倾角产生的主要原因。通过优化干法刻蚀参数，电子束胶和非晶硅掩膜方案分别实现了传输损耗为0.52和0.13 dB/cm的TFLN波导，刻蚀速率达到105 nm/min，传输损耗可通过制作SiO2覆层和退火工艺进一步减小。再次，针对亚微米宽度TFLN波导与十微米直径光纤的耦合难题，提出了aSi/TFLN混合光栅的垂直耦合结构，通过优化aSi与TFLN之间氧化层的厚度，实现了一维偏振不敏感光栅和理论耦合效率达到70%的单偏振光栅，揭示了其与直接刻蚀TFLN光栅的不同之处；加工了混合光栅并搭建了垂直耦合平台，实验得到单偏振光栅的单端耦合效率为38%。采用高数值孔径光纤的水平耦合方案，实现了总插入损耗为10 dB的高耦合效率、高稳定性的电场传感器封装。最后，提出利用Pound-Drever-Hall激光锁频方法的微腔电场传感方案，建立了电场传感系统的理论模型，使传感灵敏度进一步提高1倍。实验得到了不同品质因子的传感器的带宽、最小可测场强和线性动态范围；测量了不同应用场景对应的电场波形，证明了传感器的宽频时域响应能力；定量分析了传感系统的噪声来源，并实现了系统降噪；研制的传感器的最小可测场强为5.2 uV/m/Hz^(1/2)、动态范围为123 dB、3 dB带宽为414 MHz，为经典物理领域已有研究成果中灵敏度最高的电场传感器。
High sensitivity electric field sensors have broad applications in both academic and industrial fields. The emergence of thin-film lithium niobate (TFLN) makes it possible to achieve high sensitivity, wide bandwidth, and miniaturized optical electric field sensors. This paper studies the design and optimization, micro-nano fabrication, light coupling, and experimental application of high sensitivity electric field sensors based on TFLN. The main contents are as follows:Firstly, a ridge waveguide with a width of submicron scale was designed for the lithium niobate thin film with a thickness of hundreds of nanometers. The electro-optic modulation efficiency was improved by optimizing the waveguide‘s etching depth and reducing the electrode spacing. Next, a microring resonator electric field sensing optical path based on TFLN with a size of hundreds of microns was proposed. By reducing the total optical loss of the microcavity, the effective length of light propagation was increased, prolonging the interaction time between the optical and electric fields. Compared with the Mach-Zehnder interferometer based on bulk LiNbO3 with a length of centimeters, the sensitivity was increased by more than 50 times.Secondly, aiming at the common problem of TFLN material being difficult to etch, a low-loss and high-efficiency fabrication strategy based on the TFLN platform was developed. The fabrication methods and qualities of electron beam resist, photoresist, metal and non-metal masks were explored in the experiments. It was revealed that redeposition was the main cause of waveguide sidewall roughness and non-vertical angle. By optimizing the dry etching recipes, TFLN waveguides with transmission losses of 0.52 dB/cm and 0.13 dB/cm were achieved using the electron beam resist and amorphous silicon mask schemes, respectively. The etching rate reached 105 nm/min. The transmission loss could be further reduced by depositing SiO2 cladding and annealing process.Thirdly, to address the coupling challenge between submicron-width TFLN waveguides and 10-micron diameter fibers, aSi/TFLN hybrid gratings with vertical coupling structure were proposed. By optimizing the thickness of the oxide layer between aSi and TFLN, one-dimensional polarization-insensitive gratings and single-polarization gratings with a theoretical coupling efficiency of up to 70% were achieved. Their differences from directly etched TFLN gratings were revealed. The hybrid gratings were fabricated and a vertical coupling platform was built. The one-end coupling efficiency of the single-polarization grating was measured to be 38%. By using high numerical aperture fibers, a horizontal coupling scheme was implemented to package the electric field sensor with high coupling efficiency and stability, achieving a total insertion loss of 10 dB.Finally, a microcavity electric field sensing scheme using Pin-Drever-Hall laser frequency-locking method is proposed. The theoretical model of the electric field sensing system was established, which further doubled the sensing sensitivity. The bandwidth, minimum detectable field, and linear dynamic range of sensors with different quality factors were obtained experimentally. The electric field waveforms corresponding to different application scenarios were measured, demonstrating the broadband time-domain response capability of the sensor. The noise sources of the sensing system were analyzed, and noise reduction was achieved. The developed sensor has a minimum detectable field of 5.2 uV/m/Hz^(1/2), a dynamic range of 123 dB, and a 3 dB bandwidth of 414 MHz. It is the most sensitive electric field sensor among existing research results in the field of classical physics.
