针对反射式显示器彩色电润湿电子纸在不同色温环境光下显示颜色不一致，影响显示图片色彩还原度的问题，提出一种基于彩色电润湿电子纸光谱反射率特性的色彩校正方法。通过彩色电润湿电子纸的光谱反射率特性，得到不同色温环境光下显示颜色的光谱对应关系，以此建立不同色温环境光下彩色电润湿电子纸显示颜色的映射关系，并根据该映射关系对输入颜色数据进行校正，从而减小不同色温环境光下显示颜色的色差。设置标准光源A（5 000 K）、实验光源B（3 500 K）和实验光源C（6 500 K）对样品进行测试。在两个实验光源下，测量100个测试色块在经过本文方法校正前后的色度数据。实验结果表明，校正前后显示颜色与标准光源下显示颜色的平均色差分别减小了55%和35%，校正后的显示图像平均主观评价Z得分分别为0.45和0.25。

Yb:YAG透明陶瓷由于具有宽的吸收带和发射带、高增益、低的热负载、长的荧光寿命、高的量子效率等优点而成为有应用前景的高功率固体激光器用增益介质。本研究优化了粉体的性能并制备了高透明的Yb:YAG陶瓷。以碳酸氢铵为沉淀剂, 分别以纯水或乙醇/水混合物为溶剂, 采用共沉淀法合成了5at%Yb:YAG纳米粉体。在1250 ℃下煅烧4 h得到的所有粉体均为纯YAG相。与纯水溶剂制备的粉体相比, 醇水溶剂制备的粉体具有更小的平均晶粒尺寸和更低的团聚程度。以醇水溶剂制备的粉体为原料, 采用真空烧结法在不添加烧结助剂的情况下成功制备了5at%Yb:YAG透明陶瓷, 并对1500~1825 ℃烧结20 h和1800 ℃烧结10~50 h所得陶瓷的微观结构和直线透过率进行了探究。除在1825 ℃下烧结20 h所得的陶瓷外, 其余的5at%Yb:YAG陶瓷都具有均匀的微观结构。在1800 ℃下烧结50 h制备的5at%Yb:YAG陶瓷具有最高的光学质量, 在1100和400 nm处的直线透过率分别为78.6%和76.7%(样品厚度为2.2 mm)。该Yb:YAG透明陶瓷在937 nm处的吸收截面为5.03×10^-21 cm², 在1031 nm处的发射截面为13.48×10^-21cm²。

Metasurfaces have pioneered a new avenue for advanced wave-front engineering. Among the various types of metasurfaces, Huygens’ metasurfaces are thought to be a novel paradigm for flat optical devices. Enabled by spectrally overlapped electric resonance and magnetic resonance, Huygens’ metasurfaces are imparted with high transmission and full phase coverage of 2π, which makes them capable of realizing high-efficiency wave-front control. However, a defect of Huygens’ metasurfaces is that their phase profiles and transmissive responses are often sensitive to the interaction of neighboring Huygens’ elements. Consequently, the original assigned phase distribution can be distorted. In this work, we present our design strategy of transmissive Huygens’ metasurfaces performing anomalous refraction. We illustrate the investigation of Huygens’ elements, realizing the overlapping between an electric dipole and magnetic dipole resonance based on cross-shaped structures. We find that the traditional discrete equidistant-phase design method is not enough to realize a transmissive Huygens’ surface due to the interaction between neighboring Huygens’ elements. Therefore, we introduce an extra optimization process on the element spacing to palliate the phase distortion resulting from the element interaction. Based on this method, we successfully design unequally spaced three-element transmissive metasurfaces exhibiting anomalous refraction effect. The anomalous refractive angle of the designed Huygens’ metasurface is 30°, which exceeds the angles of most present transmissive Huygens’ metasurfaces. A transmissive efficiency of 83.5% is numerically derived at the operating wavelength. The far-field electric distribution shows that about 93% of transmissive light is directed along the 30° refractive direction. The deflection angle can be tuned by adjusting the number of Huygens’ elements in one metasurface unit cell. The design strategies used in this paper can be inspiring for other functional Huygens’ metasurface schemes.

We propose and numerically investigate an efficient transmission-mode metasurface that consists of quasi-continuous trapezoid-shaped crystalline silicon nanoantennas on a quartz substrate. This metasurface provides a linear phase gradient and realizes both full 2π phase shift and high transmission efficiency in the operating wavelength range from 740 to 780 nm. At the central wavelength around 751 nm, the total transmission efficiency is up to 88.0% and the section of the desired anomalous refraction is 80.4%. The anomalous refraction angle is 29.62°, and larger refraction angle can be achieved by changing the period of the super cell. We demonstrate a refraction angle as large as 38.59°, and the anomalous transmission efficiency reaches 76.6% at wavelength of 741 nm. It is worth mentioning that the structure is much simpler than conventional metasurfaces based on arrays of discrete nanoantennas. Our research may pave the way for designing efficient all-dielectric phase-gradient metasurfaces and applying them in integrated optical devices for wavefront control.

A novel scheme for the design of an ultra-compact and high-performance optical switch is proposed and investigated numerically. Based on a standard silicon (Si) photonic stripe waveguide, a section of hyperbolic metamaterials (HMM) consisting of 20-pair alternating vanadium dioxide (VO2)/Si thin layers is inserted to realize the switching of fundamental TE mode propagation. Finite-element-method simulation results show that, with the help of an HMM with a size of 400 nm×220 nm×200 nm (width×height×length), the ON/OFF switching for fundamental TE mode propagation in an Si waveguide can be characterized by modulation depth (MD) of 5.6 dB and insertion loss (IL) of 1.25 dB. It also allows for a relatively wide operating bandwidth of 215 nm maintaining MD>5 dB and IL<1.25 dB. Furthermore, we discuss that the tungsten-doped VO2 layers could be useful for reducing metal-insulator-transition temperature and thus improving switching performance. In general, our findings may provide some useful ideas for optical switch design and application in an on-chip all-optical communication system with a demanding integration level.