满足光量子芯片品质要求的低损耗三维光波导的研制

Integrated optical quantum chip can reduce the volume of space quantum optical system, break through the constraints of its spatial geometric structure, overcome the problems of poor stability, weak signal and high noise. It has become a much expected research focus in the field of light quantum information processing. However, due to the constraints of large transmission loss and limitation of three-dimensional expansion, the optical quantum chip still stays at the stage of algorithm validation and experimental demonstration, and it is very far from preparation of practical devices. This project will focus on the cause of transmission loss and study the intrinsic absorption of the material and the absorption of new ions. We will use the space tailored femtosecond pulse local annealing strategy to reduce the scattering of inhomogeneous refractive index and the residual stress after laser scanning. We will use the three-dimensional nonlinear compensation of femtosecond pulse shaping technology, overcoming the defocusing problem of laser pulse medium internal focusing and redistribution of laser energy in three-dimensional space volume elements of focus area. It will realize the control of mode field shape, undifferentiated transmission of polarization mode field and continuous depth change of waveguide. Finally, we will realize the transmission loss of single-mode optical waveguide under 0.1 dB/cm, and the depth of longitudinal continuous non defocusing three-dimensional waveguide is more than 1 mm, which will contribute to practical application of optical quantum chips.

集成光量子芯片可降低空间光量子系统体积、突破其空间几何构架制约，克服其稳定性差、信号弱、噪声高等问题，成为光量子信息处理领域备受期待的热点方向。但受到光子传输损耗大、三维扩展受限等因素的制约，目前光量子芯片仍停留在算法验证和实验演示阶段，距离制备实用器件仍很遥远。本项目聚焦光量子芯片核心部件光波导传输损耗的成因，研究材料本征吸收及新生离子的吸收作用，采用空间剪裁飞秒脉冲局域退火方案降低激光扫描后波导折射率分布不均与残余应力对光的散射作用，实现光波导传输损耗的降低；采用非线性补偿的飞秒脉冲三维空间整形技术，克服脉冲激光介质内部聚焦的散焦问题，对焦点区域三维空间体积元内的激光能量进行再分配，实现光波导模场形状的控制、偏振模场的无差别传输和波导深度的连续变化。最终实现单模光波导传输损耗低于0.1dB/cm，三维波导纵向连续无失焦变化深度超过1mm，为光量子芯片的实用发展做出贡献。

基于飞秒激光直写的三维光量子集成芯片在量子计算、量子传感、量子通信等领域展现了重要的潜在应用。但聚焦飞秒脉冲的散焦问题致使三维波导深度不足波导截面不圆，限定了三维光量子芯片的实用化。本项目针对飞秒激光直写的散焦问题，围绕计划书中飞秒激光直写低损耗三维光波导的研制开展研究，项目研究内容和任务目标如期执行，获得了较好的预期结果。开发了基于空间光调制器的多光场叠加球形热场技术和狭缝-柱透镜圆形波导制备等技术，实现了对波导模场圆形度、模场尺寸、模式、损耗、双折射光轴、偏振态制备与转化等波导基本属性的控制，实现了对波导相位、耦合系数等关键属性的调控与控制，实现了三维编码波导器件、大纵深三维波导阵列的制备，展示了光波导在量子模拟中的应用。具体地，大纵深圆形截面三维玻璃波导深度跨越1.5mm（指标值：1mm）、圆形度96.7%（国际领先）、传输损耗0.33dB/cm（国际同种材料同等水平），从芯片制备的角度为光量子芯片的实用化提供技术支持。. 本项目立项时预期在相关领域一流国际专业杂志上发表学术论文5篇以上，申请国家发明专利1项，培养博士生3名，硕士生4名。实际培养博士研究生3人、硕士研究生6人；项目资助下，实际发表研究论文21篇，含Physical Review Letters 1篇、Advanced Optical Materials 1篇、Laser & Photonics Reviews 1篇、Opto-Electronic Advances 1篇、Journal of Lightwave Technology1篇、Optics Express 1篇、Optics Letter7篇；实际申请并获授权国家发明专利4项，较好地完成了既定的研究目标。