A polarization-insensitive mode-order converting power splitter using a pixelated region is presented and investigated in this paper. As TE₀ and TM₀ modes are injected into the input port, they are converted into TE₁ and TM₁ modes, which evenly come out from the two output ports. The finite-difference time-domain method and direct-binary-search optimization algorithm are utilized to optimize structural parameters of the pixelated region to attain small insertion loss, low crosstalk, wide bandwidth, excellent power uniformity, polarization-insensitive property, and compact size. Experimental results reveal that the insertion loss, crosstalk, and power uniformity of the fabricated device at 1550 nm are 0.57, -19.67, and 0.094 dB in the case of TE polarization, while in the TM polarization, the relevant insertion loss, crosstalk, and power uniformity are 0.57, -19.40, and 0.11 dB. Within a wavelength range from 1520 to 1600 nm, for the fabricated device working at TE polarization, the insertion loss, crosstalk, and power uniformity are lower than 1.39, -17.64, and 0.14 dB. In the case of TM polarization, we achieved an insertion loss, crosstalk, and power uniformity less than 1.23, -17.62, and 0.14 dB.

A flexible-grid 1×(2×3) mode- and wavelength-selective switch which comprises counter-tapered couplers and silicon microring resonators has been proposed, optimized, and demonstrated experimentally in this work. By carefully thermally tuning phase shifters and silicon microring resonators, mode and wavelength signals can be independently and flexibly conveyed to any one of the output ports, and different bandwidths can be generated as desired. The particle swarm optimization algorithm and finite difference time-domain method are employed to optimize structural parameters of the two-mode (de)multiplexer and crossing waveguide. The bandwidth-tunable wavelength-selective optical router composed of 12 microring resonators is studied by taking advantage of the transfer matrix method. Measurement results show that, for the fabricated module, cross talk less than -10.18dB, an extinction ratio larger than 17.41 dB, an in-band ripple lower than 0.79 dB, and a 3-dB bandwidth changing from 0.38 to 1.05 nm are obtained, as the wavelength-channel spacing is 0.40 nm. The corresponding response time is measured to be 13.64 µs.

复合折射透镜（compound refractive lens, CRL）因具有结构紧凑、焦距可调、准直方便等优点，被用作硬X射线自由电子激光（X-ray free electron laser, XFEL）装置的光束聚焦器件。面向XFEL光束高精度聚焦对高性能CRL的实际需求，从CRL的几何结构设计原理出发，分析了不同材料CRL的性能参数，证明了单晶金刚石材料是适用于XFEL光束聚焦的CRL优选材料。同时，考虑超硬金刚石材料的难加工特性以及低重频钛宝石飞秒激光不能实现大厚度材料高效加工的实际问题，探索了高重频光纤飞秒激光对大厚度单晶金刚石材料进行高效加工的可行性。研究结果表明，高重频飞秒激光精密加工技术是实现金刚石CRL制备的有效手段。

提出了一种基于锥形渐变耦合结构的可扩展多模弯曲波导。该器件利用模式等效折射率匹配原理，通过对称的锥形渐变耦合结构，实现高阶模式与基模的相互转化，完成多模弯曲传输功能。同时，结合时域有限差分方法和粒子群优化算法，优化锥形渐变耦合结构区域，提升器件性能。实验测试结果表明，在1 520~1 600 nm的波长范围内，当输入模式分别为TE₀、TE₁、TE₂、TE₃和TE₄时，该器件的插入损耗分别小于1.71 dB、3.04 dB、2.90 dB、3.16 dB和4.00 dB，对应的串扰分别小于-10.60 dB、-11.35 dB、-10.92 dB、-10.35 dB和-11.45 dB。

为实现各类暂现源及暗弱目标的宽波段、高效率光谱后随观测，以1.9 m光学望远镜为例，设计了一种基于Faint Object Spectrograph and Camera型的双通道中低色散光谱仪，可实现三种光谱分辨率（R=500、2 000和5 500），工作波段覆盖紫外-近红外（310~1 000 nm）。根据光栅方程和光谱分辨率等各项指标，确定光谱仪的初始结构参数，针对光谱仪在全波段的高效率需求以及仪器随动的包络限制，确定光学系统采用双通道设计并近似对称分布：准直系统采用了不同于传统Faint Object Spectrograph and Camera型光谱仪的折反射式系统，在提高了系统效率的同时压缩了空间。色散系统根据直视棱栅的不同工艺，通过棱镜材料和角度的调整对工作波段的光栅效率进行优化并得到8种棱栅参数；红蓝通道相机系统在设计过程中优化选取光学材料，同时结合二次非球面和单透镜的主动调焦补偿，实现大动态温度范围（-30 ℃~20 ℃）全视场（φ16°）最大弥散斑半径均方根小于5 μm的优良像质。该系统结构紧凑、分布对称，设计结果满足各项指标，光谱仪全波段峰值效率优于60%，最低效率优于20%，具有较高的可实现性。基于曲面芯片工艺，以红通道为例，简化的相机系统至少可提高整体光谱效率约4%，可以为未来光谱仪相机系统的设计提供参考。