Dispersion of light waves is well known, but the subject deserves some comments. Certain classical equations do not fully respect causality; as an example, group velocity v_g is usually given as the first derivative of the angular frequency ω with respect to the angular spatial frequency k_m (or wavenumber) in the medium, whereas it is k_m that depends on ω. This paper also emphasizes the use of phase index n and group index n_g, as inverse of their respective velocities, normalized to 1/c, the inverse of free-space light velocity. This clarifies the understanding of dispersion equations: group dispersion parameter D is related to the first derivative of n_g with respect to wavelength λ, whilst group velocity dispersion GVD is also related to the first derivative of n_g, but now with respect to angular frequency ω. One notices that the term second order dispersion does not have the same meaning with λ, or with ω. In addition, two original and amusing geometrical constructions are proposed; they simply derive group index n_g from phase index n with a tangent, which helps to visualize their relationship. This applies to bulk materials, as well as to optical fibers and waveguides, and this can be extended to birefringence and polarization mode dispersion in polarization-maintaining fibers or birefringent waveguides.Dispersion of light waves is well known, but the subject deserves some comments. Certain classical equations do not fully respect causality; as an example, group velocity v_g is usually given as the first derivative of the angular frequency ω with respect to the angular spatial frequency k_m (or wavenumber) in the medium, whereas it is k_m that depends on ω. This paper also emphasizes the use of phase index n and group index n_g, as inverse of their respective velocities, normalized to 1/c, the inverse of free-space light velocity. This clarifies the understanding of dispersion equations: group dispersion parameter D is related to the first derivative of n_g with respect to wavelength λ, whilst group velocity dispersion GVD is also related to the first derivative of n_g, but now with respect to angular frequency ω. One notices that the term second order dispersion does not have the same meaning with λ, or with ω. In addition, two original and amusing geometrical constructions are proposed; they simply derive group index n_g from phase index n with a tangent, which helps to visualize their relationship. This applies to bulk materials, as well as to optical fibers and waveguides, and this can be extended to birefringence and polarization mode dispersion in polarization-maintaining fibers or birefringent waveguides.

非对称结构光子晶体光纤应用广泛。其良好的偏振特性、灵活的色散调控能力以及低限制损耗品质，对于优化与改善偏振光纤器件、非线性光学光纤、光通信光纤、光纤传感器等性能发挥着关键的作用。选用高折射率铋锗镓激光玻璃为材料，设计了八边形阵列、矩形晶格排列的光子晶体光纤，纤芯缺陷区包层及外包层均为圆形空气孔。模拟实验数据显示，结构参数为M=0.5，0.6时，在波长为1.55 μm处的双折射系数分别为1.16×10⁻²和1.33×10⁻²；在近红外波段短波区，矩形晶格结构光子晶体光纤的色散范围分别在±30 ps·nm⁻¹·km⁻¹之间及−18～32 ps·nm⁻¹·km⁻¹之间。色散斜率较低，曲线具有零色散点，展现了良好的连续谱调控能力；在1.00～1.90 μm波段内，当M=0.5，0.6时，光纤限制损耗稳定在10⁻⁷～10⁻⁹ dB·km⁻¹之间；在1.55 μm处，限制损耗测量值分别为2.32×10⁻⁷和1.62×10⁻⁸ dB·km⁻¹。

相位恢复是利用能观测到的强度信息恢复原始相位信息。强度传输方程（TIE）作为一种传统的非干涉相位恢复技术，只需通过测量至少两个相近平面的强度信息即可计算出相位信息。这种方法通常需要通过移动被测物体或摄像机来获取强度图像，不可避免地会产生机械误差。提出了一种新的相位恢复方法：与色散融合的混合相位恢复算法（CD-HPR）。通过设置不同波长的光通过单透镜系统得到物体在同一位置成的像，这样不需要机械运动就能获得聚焦和散焦图像强度，然后结合散焦量与波长之间的关系计算出散焦量，再用强度传输方程计算初始相位信息。角谱迭代算法的使用较好地改进了初始相位值。在仿真实验中，该方法恢复的相位与原始相位之间的均方差为0.1076；同时，通过实验恢复了透镜阵列的相位，实验结果与实际参数的误差为3.4%，证明了该方法的正确性和有效性。该方法扩展了传统方法要求光源为单色的局限性，提高了计算精度。

报道了利用50 km光纤实现4.38×10^-15@1 s和2.80×10^-18@65.5×10³ s稳定度的微波频率传递的实验研究.实验系统采用多普勒噪声消除技术，通过在本地端探测往返传递的微波信号相位获得链路上的相位变化信息，并实时控制光延迟调整机构进行补偿.光延迟控制采用压电陶瓷的快速拉伸和慢速光纤温控联合方式，可实现5 ns和千赫兹带宽的光延迟控制，能够实现光纤噪声的长期高精度补偿.与电相位补偿相比，光延迟补偿受微波泄露的影响相对较小，而微波泄露影响在类似系统难以避免，因此这种方式更利于获得高稳定度的频率传递.此外，系统采用变频往返传递消除光寄生反射效应，以及色散补偿光纤减小因色散引起的调制信号衰减等措施，提高了系统的技术指标.

The chromatic aberration of metasurfaces limits their application. How to cancel or utilize the large chromatic dispersion of metasurfaces becomes an important issue. Here, we design Si-based metasurfaces to realize flexible chromatic dispersion manipulation in mid-infrared region. We demonstrate the broadband achromatic metalens and achromatic gradient metasurface to cancel the chromatic aberration over a continuous bandwidth (8–12 μm). In contrast, the metalens and gradient metasurface with enhanced chromatic dispersion have also been realized, where the focal length and deflection angle with different wavelengths vary more significantly than the conventional devices designed with geometric phase. These demonstrations indicate promising potential applications.