为进一步优化传统反光杯在匀光、防眩光等方面的问题，基于Zemax仿真软件设计出了一种匀光性能优越的鳞甲反光杯。仿真结果表明，在杯前25 m处的配光屏幕上，最大光照强度为234 lx，中心HV点的光照强度大于0.80 E_max，各指标均符合国标GB 25991—2010《汽车用LED前照灯》的要求。将鳞甲反光杯与微透镜阵列相结合，使配光屏幕上的最大光照强度减小至59.51 lx，在各项指标仍符合国家标准的情况下，该系统的光斑能量更加均匀，且中心区域的光强进一步降低，光斑边缘过渡更加柔和，防止汽车远光灯产生眩光的效果更好，可以大量应用于汽车前照远光灯。

There is still a lack of high-performance terahertz (THz) modulators with wide operation bandwidth and large modulation depth due to the underlying physics limitation behind existing approaches. Meanwhile, for many applications, simple compact THz modulators working straightforward in the transmission mode are also highly desired. Here, we demonstrate a THz modulator with a maximal transmission-amplitude modulation depth of 99.9% (switching ratio of 1000) based on a commonly used silica-on-silicon structure. Different from those reported graphene or metamaterials enhanced proposals, the device we proposed works within a reversible avalanche breakdown region of silicon that has not been studied yet and has the potential to modulate/switch THz waves efficiently. Further, we proved that the modulation depth exceeds 97% in the frequency range from 0.2 to 1 THz in the experiment. The simplicity and generality of this new type of near-perfect THz modulator will undoubtedly attract lots of attention of researchers in the near future due to its potential to be engineered into integrated devices.

BST(Ba0.5Sr0.5TiO3)/PZT(Pb0.52Zr0.48TiO3) photonic crystals were fabricated by magnetron sputtering and annealed at 620°C?700°C. By controlling the crystallinity and the oxygen vacancies of the ferroelectric photonic crystals, the optically and electrically controllable terahertz wave modulations were realized. The variation in refractive index of the 680°C annealed sample showed the highest modulation to the optical pump and increased to 11.9 due to the highest absorption near 532 nm. In the optical pump, the electrons from Ti3+2p3/2 ions could be stimulated and captured by Ti4+2p3/2 ions, and the ratio of Ti3+/Ti4+ observed increased with the increasing annealing temperature, indicating the increasing oxygen vacancies concentration, which increased the 532 nm optical absorption and contributed to the improved optical modulation. The excess Pb migrating to the surface at higher annealing temperature might be one reason for the degradation of optical modulation. The increasing polarization and leakage current could contribute to the increasing permittivity and loss with the increasing annealing temperature. Two different results were observed on the sample annealed at 680°C when the order of applying external optical and electric fields was changed, due to the different migration mechanisms of excited carriers. This work provides a potentially effective approach to fabricate THz sensing, imaging, and communications devices with multi-function in the modulation of optical and electric multi-fields.

We theoretically present a concise and tunable dual-band metamaterial absorber composed of a typical metal-dielectric-metal structure in the terahertz regime. The dual-band absorption originates from two different resonance modes induced in one square ring, which is different from the common dual-band absorber composed of a super unit with several different-sized structures. The proposed absorber can realize dynamic tunability through changing the permittivity of the dielectric layer by applying different temperatures. Other good performances, such as a wide incident angle and polarization insensitivity, are also available for the proposed absorber. Such a metamaterial absorber is a promising candidate for terahertz imaging and detection.