Abstract-Metasurfaces for Terahertz Wavefront Modulation: a Review

Jingwen He, Tao Dong, Baihong Chi, Yan Zhang,

https://link.springer.com/article/10.1007/s10762-020-00677-3

Metasurface is an artificial material composed of a series of subwavelength structure units and has unique electromagnetic characteristics. Based on the ability of manipulating the phase, amplitude, and polarization of electromagnetic wave, various kinds of metasurfaces are designed to realize wavefront manipulations, such as beam focusing, beam steering, vector beams generating, and holographic imaging. This paper reviews the design methods of metasurfaces for wavefront modulation and evolution of the metasurfaces designed for wavefront manipulation in the terahertz (THz) region. The metasurfaces can be divided into two categories: passive and active metasurfaces. For the passive metasurfaces, the single-functional metasurfaces, multifunctional metasurfaces, and high diffraction efficient metasurfaces designed for various THz wavefront shaping, such as focusing, imaging, and special beams generating, are reviewed. For the active metasurfaces, the metasurfaces with fixed structure and all-optical metasurfaces without fixed structure for THz wavefront modulation are summarized. Furthermore, a comparison on the performance of different kinds of metasurfaces for THz wavefront modulation is presented and the development direction and challenges of the THz wavefront modulation metasurfaces in the future are discussed.

Abstract-Metasurfaces for Terahertz Wavefront Modulation: a Review

Jingwen He, Tao Dong, Baihong Chi,  Yan Zhang,

https://link.springer.com/article/10.1007%2Fs10762-020-00677-3

Metasurface is an artificial material composed of a series of subwavelength structure units and has unique electromagnetic characteristics. Based on the ability of manipulating the phase, amplitude, and polarization of electromagnetic wave, various kinds of metasurfaces are designed to realize wavefront manipulations, such as beam focusing, beam steering, vector beams generating, and holographic imaging. This paper reviews the design methods of metasurfaces for wavefront modulation and evolution of the metasurfaces designed for wavefront manipulation in the terahertz (THz) region. The metasurfaces can be divided into two categories: passive and active metasurfaces. For the passive metasurfaces, the single-functional metasurfaces, multifunctional metasurfaces, and high diffraction efficient metasurfaces designed for various THz wavefront shaping, such as focusing, imaging, and special beams generating, are reviewed. For the active metasurfaces, the metasurfaces with fixed structure and all-optical metasurfaces without fixed structure for THz wavefront modulation are summarized. Furthermore, a comparison on the performance of different kinds of metasurfaces for THz wavefront modulation is presented and the development direction and challenges of the THz wavefront modulation metasurfaces in the future are discussed.

Abstract-High-efficiency terahertz devices based on cross-polarization converter

• Huan Zhao, 
• Xinke Wang, 
• Jingwen He, 
• Jinying Guo, 
• Jiasheng Ye, 
• Qiang Kan,  
• Yan Zhan

• https://www.nature.com/articles/s41598-017-18013-6#Sec2

Metasurface-based devices have been investigated intensively because of their attractive properties but these devices generally suffer from low efficiency. Here we demonstrate several high-efficiency terahertz (THz) devices based on cross-polarization converters that is composed of bilayer metasurface-based structures. The converter can transfer the polarization states of transmitted THz waves from the x-direction into the y-direction with an experimental conversion efficiency of 85%. This high-efficiency transfer mechanism is investigated in detail. Furthermore, this kind of devices can be fabricated easily. A THz metalens is designed and fabricated and its focusing and imaging properties are investigated experimentally. A pure phase THz hologram that can generate different images on different propagation planes is also designed and the image reconstruction capabilities of the phase holograms are demonstrated experimentally. The performance levels of all designed devices show excellent agreement between the theoretical expectations and the corresponding experimental results. This technology may pave the way towards practical applications of such metasurface devices.

Abstract-Metasurfaces in terahertz waveband

Jingwen He and Yan Zhang

http://iopscience.iop.org/article/10.1088/1361-6463/aa8dc6

Metasurface, composed of subwavelength antennas, allows us to obtain arbitrary permittivity and permeability in electromagnetic (EM) waveband. It can be used to control the polarization, frequency, amplitude, and phase of the EM wave. Conventional terahertz (THz) components, such as high impedance silicon lens, polyethylene lens, and quartz wave plate, rely on the phase accumulation along the wave propagation to reshape the THz wave front. The metasurface employs the local resonance to modulate the wave front. Compared with the conventional THz components, metasurface has advantages of ultrathin, ultralight, and low cost. In recent years, a large number of THz devices based on metasurface have been proposed. We review a broad outline of the metasurface devices in the THz region and describe the progress of static and tunable THz field modulated metasurfaces in detail. Finally, we discuss current challenges and opportunities in this rapidly developing research field.

Abstract-A broadband terahertz ultrathin multi-focus lens

• Jingwen He
• , Jiasheng Ye
• , Xinke Wang
• , Qiang Kan
•  & Yan Zhang

http://www.nature.com/articles/srep28800

Ultrathin transmission metasurface devices are designed on the basis of the Yang-Gu amplitude-phase retrieval algorithm for focusing the terahertz (THz) radiation into four or nine spots with focal spacing of 2 or 3 mm at a frequency of 0.8 THz. The focal properties are experimentally investigated in detail, and the results agree well with the theoretical expectations. The designed THz multi-focus lens (TMFL) demonstrates a good focusing function over a broad frequency range from 0.3 to 1.1 THz. As a transmission-type device based on metasurface, the diffraction efficiency of the TMFL can be as high as 33.92% at the designed frequency. The imaging function of the TMFL is also demonstrated experimentally and clear images are obtained. The proposed method produces an ultrathin, low-cost, and broadband multi-focus lens for THz-band application

Abstract-Exciton localization in solution-processed organolead trihalide perovskites

• Haiping He,
• Qianqian Yu,
• Hui Li,
• Jing Li,
• Junjie Si,
• Yizheng Jin,
• Nana Wang,
• Jianpu Wang,
• Jingwen He,
• Xinke Wang,
• Yan Zhang
• & Zhizhen Ye
• http://www.nature.com/ncomms/2016/160321/ncomms10896/abs/ncomms10896.html

Organolead trihalide perovskites have attracted great attention due to the stunning advances in both photovoltaic and light-emitting devices. However, the photophysical properties, especially the recombination dynamics of photogenerated carriers, of this class of materials are controversial. Here we report that under an excitation level close to the working regime of solar cells, the recombination of photogenerated carriers in solution-processed methylammonium–lead–halide films is dominated by excitons weakly localized in band tail states. This scenario is evidenced by experiments of spectral-dependent luminescence decay, excitation density-dependent luminescence and frequency-dependent terahertz photoconductivity. The exciton localization effect is found to be general for several solution-processed hybrid perovskite films prepared by different methods. Our results provide insights into the charge transport and recombination mechanism in perovskite films and help to unravel their potential for high-performance optoelectronic devices.

Abstract-Generation of terahertz vector beams with a concentric ring metal grating and photo-generated carriers

Generation of terahertz vector beams with a concentric ring metal grating and photo-generated carriers Zhenwei Xie, Jingwen He, Xinke Wang, Shengfei Feng, and Yan Zhang  »View Author Affiliations

Optics Letters, Vol. 40, Issue 3, pp. 359-362 (2015)
http://dx.doi.org/10.1364/OL.40.000359

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-40-3-359

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A scheme for vector terahertz (THz) beam generation is proposed. A subwavelength metal grating is utilized to adjust the polarization of the THz radiation. The amplitude and phase distributions of the THz beam are dynamically regulated by a THz computer-generated hologram (CGH) pattern of the photo-generated carriers. A radially polarized THz beam and a vector THz vortex beam with a topological charge of 1 are generated to demonstrate the validity and the effectiveness of the proposed scheme. Experimental results correspond to the theoretical simulations well. Moreover, the proposed method is applicative for a broadband THz radiation. These results could be applied in the THz sensing, THz imaging, and THz communication in the future.

© 2015 Optical Society of America