Terahertz (THz) radiation (0.1 THz to 10 THz) falls in between the infrared and microwave region of the electromagnetic spectrum, and it shares some properties with each of these, as shown below. The terahertz region is of particular scientific importance due to its remarkable and unique characteristics. Many common materials and living tissues are semi-transparent and have ‘THz fingerprints’, permitting them to be imaged, identified, and analyzed. Meanwhile, the non-ionizing properties of terahertz radiation and the relatively low power levels used indicate that it is safe. Terahertz radiation constitutes a gap in the science and remains to be better understood and much better exploited.
Yuanhao Lang, Quan Xu, Xieyu Chen, Jie Han, Xiaohan Jiang, Yuehong Xu, Ming Kang, Xueqian Zhang, Andrea Alù, Jiaguang Han and Weili Zhang
Published in: Laser&Photonics Reviews
（Volume 16, Issue 10, 2200242）
Abstract Since the late 19th century, enormous endeavors have been made in extending
the scope and capability of optical interferometers. Recently, plasmonic
vortices that strongly confine the orbital angular momentum to surface have
attracted considerable attention. However, current research interests in this
area have focused on the mechanisms and dynamics of
polarization-dependent single plasmonic vortex generation and evolution,
while the interference between different plasmonic vortices for practical
applications has been unexplored. Here, a method for flexible on-chip
spin-to-orbital angular momentum conversion is introduced, resulting in
exotic interferograms. Based on this method, a new form of interferometers
that is realized by the interference between customized plasmonic vortices is
demonstrated. Within wavelength-scale dimension, the proposed plasmonic
vortex interferometers exhibit superior performance to directly measure the
polarization state, spin and orbital angular momentum of incident beams. The
proposed interferometry is straightforward and robust, and can be expected to
be applied to different scenarios, fueling fundamental advances and
applications alike.
Reconfigurable and Nonvolatile Terahertz Metadevices Based on a Phase-Change Material ×
Xieyu Chen, Shoujun Zhang, Kuan Liu, Haiyang Li, Yihan Xu, Jiajia Chen, Yongchang Lu, Qingwei Wang, Xi Feng, Kemeng Wang, Zeru Liu, Tun Cao, and Zhen Tian
Published in: ACS Photonics
（Volume Online, 0）
Abstract Reconfigurable terahertz (THz) devices with nonvolatile and multilevel properties are highly desirable in many applications from imaging and high-capacity communication to nondestructive biosensing. Here, we present and experimentally demonstrate a promising platform for dynamic THz devices by exploring the reversible, nonvolatile, and multilevel modulation features of the Ge2Sb2Te5 (GST) material. These properties were fully demonstrated by characterizing the THz response of a centimeter-level area GST layer during the thermally stimulated crystallization and optically stimulated reamorphization process. As a proof of concept, a hybrid plasmonic dimer structure composed of two trapezoidal metallic rings connected by GST islands was designed, fabricated, and characterized. The modulation of this device was experimentally realized by inducing crystallization and reamorphization processes with thermal and optical activation, respectively. Moreover, electrical switching of the designed device was also realized by applying a 5 s duration electrical pulse. With these findings, this study may open an attractive direction for a wide range of design possibilities in terms of reversible, nonvolatile, and multilevel THz modulation devices.
Mechanically reprogrammable Pancharatnam–Berry metasurface for microwaves ×
Quan Xu, Xiaoqiang Su, Xueqian Zhang, Lijuan Dong, Lifeng Liu, Yunlong Shi, Qiu Wang, Ming Kang, Andrea Alù, Shuang Zhang, Jiaguang Han, and Weili Zhang
Published in: Advanced Photonics
（Volume 4, Issue 1, 016002）
Abstract Metasurfaces have enabled the realization of several optical functionalities over an ultrathin platform, fostering the exciting field of flat optics. Traditional metasurfaces are achieved by arranging a layout of static meta-atoms to imprint a desired operation on the impinging wavefront, but their functionality cannot be altered. Reconfigurability and programmability of metasurfaces are the next important step to broaden their impact, adding customized on-demand functionality in which each meta-atom can be individually reprogrammed. We demonstrate a mechanical metasurface platform with controllable rotation at the meta-atom level, which can implement continuous Pancharatnam–Berry phase control of circularly polarized microwaves. As the proof-of-concept experiments, we demonstrate metalensing, focused vortex beam generation, and holographic imaging in the same metasurface template, exhibiting versatility and superior performance. Such dynamic control of electromagnetic waves using a single, low-cost metasurface
paves an avenue towards practical applications, driving the field of reprogrammable intelligent metasurfaces for a variety of applications.
Abstract Weyl points are discrete locations in the three-dimensional momentum space where two bands cross linearly with each other. They serve as the monopoles of Berry curvature in the momentum space, and their existence requires breaking of either time-reversal or inversion symmetry. Although various non-centrosymmetric Weyl systems have been reported, demonstration of Weyl degeneracies due to breaking of the time-reversal symmetry remains scarce and is limited to electronic systems. Here, we report the experimental observation of photonic Weyl degeneracies in a magnetized semiconductor—InSb, which behaves as a magnetized plasma for electromagnetic waves at the terahertz band. By varying the magnetic field strength, Weyl points and the corresponding photonic Fermi arcs have been demonstrated. Our observation establishes magnetized semiconductors as a reconfigurable terahertz Weyl system, which may prompt research on novel magnetic topological phenomena such as chiral Majorana-type edge states and zero modes in classic systems.
Coherent Control of Optical Spin-to-Orbital Angular Momentum Conversion in Metasurface ×
Huifang Zhang, Ming Kang, Xueqian Zhang, Wengao Guo, Changgui Lv, Yanfeng Li, Weili Zhang, and Jiaguang Han
Published in: Advanced Materials
（Volume 29, Issue 6, 1604252）
Abstract Efficient control over the conversion of optical angular momentum from spin to orbital form in a metasurface system is achieved. Under coherent symmetric incidence, it can support nearly 100% conversion and unitary output, while it can support 50% conversion with 25% transmittance under one beam incidence.
