飞秒激光测距中空气色散补偿理论研究

研究了飞秒激光测距中空气色散对其脉冲宽度的影响,探讨了飞秒激光脉冲宽度随入射初始飞秒脉冲宽度、中心波长和激光传输距离等参数的变化关系。为保证飞秒激光测距精度,提出采用高密度透射式光栅的飞秒激光测距空气色散补偿方法,并详细分析了光栅周期、光栅对间距对不同中心波长的飞秒激光脉冲宽度压缩的影响。该方法具有体积小和操作方便等优点,对采用飞秒脉冲激光进行长距离高精度测量实验研究具有一定的指导意义。     

A wideband transmission metasurface for generating Bessel beam carrying orbital angular momentum

Orbital angular momentum (OAM) microwave waves have received increasing research interest because of their potential to improve communication capacity and radar resolution. However, the traditional orbital angular momentum wave has the problem of diffraction divergence. The ideal Bessel beam with orbital angular momentum has the property of nondiffraction. Hence, the Bessel beam carrying orbital angular momentum has great research potential. In this work, a wideband transmission metasurface for generating Bessel beam carrying OAM is designed, fabricated, and measured. And it is the first experimental to show that the Bessel beam carrying OAM has higher gain and lower crosstalk than the traditional OAM wave in far field transmission.     

卷曲空间型超表面对声波的调控

声学超表面具有天然材料所不具备的独特属性,为声学器件的设计提供了多样性。以广义斯涅尔定律为理论基础,设计了具有多种声波调控能力的折射型相位梯度超表面。该超表面由8个具有不同结构参数的卷曲空间单元结构组合而成,在中心频率3 500 Hz附近,8个单元结构的相位覆盖π范围且声波透射率较高。通过合理地设计超表面水平方向上的相位梯度变化,能够实现对声波的任意调控,在理论和有限元仿真上依次实现了异常折射、无衍射贝塞尔声束和声聚焦。这种厚度薄、透射率高的声超表面,在声学器件设计方面具有潜在的应用价值。     

Tailoring MoS2 Valley‐Polarized Photoluminescence with Super Chiral Near‐Field

Transition metal dichalcogenides with intrinsic spin–valley degrees of freedom hold great potentials for applications in spintronic and valleytronic devices. MoS₂ monolayer possesses two inequivalent valleys in the Brillouin zone, with each valley coupling selectively with circularly polarized photons. The degree of valley polarization (DVP) is a parameter to characterize the purity of valley‐polarized photoluminescence (PL) of MoS₂ monolayer. Usually, the detected values of DVP in MoS₂ monolayer show achiral property under optical excitation of opposite helicities due to reciprocal phonon‐assisted intervalley scattering process. Here, it is reported that valley‐polarized PL of MoS₂ can be tailored through near‐field interaction with plasmonic chiral metasurface. The resonant field of the chiral metasurface couples with valley‐polarized excitons, and tailors the measured PL spectra in the far‐field, resulting in observation of chiral DVP of MoS₂‐metasurface under opposite helicities excitations. Valley‐contrast PL in the chiral heterostructure is also observed when illuminated by linearly polarized light. The manipulation of valley‐polarized PL in 2D materials using chiral metasurface represents a viable route toward valley‐polaritonic devices.     

High gain transmitarray antenna based on ultra‐thin metasurface

This article presents a bandwidth enhanced transmitarray (TA) antenna based on ultra‐thin metasurface (MS) for high gain operating at X‐band. The antenna consists of a three layers continuous flat structure and an aperture coupled microstrip antenna as the feed source. The relative phase shift of 360° is achieved by the unit cell design based on ultra‐thin MS, and the quasi‐spherical wave could be focused as plane wave when the wave goes through TA. The aperture coupled microstrip feed is designed with a bandwidth of 20.6%, and the bandwidth enhanced property of feed source will reduce the negative effect of elements mutual coupling on TA and increase the bandwidth of the TA antenna. The TA antenna gain increases from 8.25 to 18.98 dB and with a side lobe level of ?14.3 dB. Owing to the low‐profile and easy configuration, this kind of TA antenna has great potential, wireless communication.     

A full integration of electromagnetic resonance sensor and capacitive touch sensor into LCD

We have developed a transmissive and reflective LCD that integrates electromagnetic resonance (EMR) and capacitive touch sensors using existing in‐cell process. This development has been achieved by utilizing our hybrid‐in‐cell technology with low resistance material for the RX, which is an improvement of over 80% compared with conventional indium thin oxide (ITO) material. For EMR detection, we have slightly modified the TX layer used for capacitive touch sensing, by making a coil loop that generates a magnetic field on the panel. The direction of current on the coil can be modulated by the low‐temperature polycrystalline silicon (LTPS) circuit. Our in‐cell touch sensing has separately assigned timings for display and touch units. This time‐sharing method provides immunity from display noise and consequently better signal‐to‐noise ratio (SNR) than other out‐cell types. In parallel, we have developed a new controller that can support both EMR and capacitive sensing as a one‐chip solution, with the capability of maximizing signal levels lowering noise and detecting the frequency precisely when there is pressure on the pen tip. Our in‐cell technologies contribute not only a good SNR for EMR pen but also the added benefits for thin design, lightweight panel, compared with conventional LCD techniques.     

A triple‐slotted substrate integrated cavity‐fed 2 × 2 metasurface antenna with wide bandwidth

This article presents a triple‐slotted substrate integrated cavity (SIC)‐fed 2 × 2 metasurface antenna. Three modes can be obtained including TM₁₀ mode of the metasurface, TE₂₁₀, mode and TE₃₁₀ mode of the SIC. The TE₂₁₀ mode of SIC radiates through the two side slots and is coupled to the metasurface mainly by the two side slots, while the TE₃₁₀ mode of SIC is mainly coupled to the metasurface by the middle slot. Comparing with the reported SIC‐backed slot antenna, dual‐slotted SIC‐fed patch antenna or the metasurface antenna, the proposed antenna exhibits the advantage of wide bandwidth with flat gain. One prototype operated at 10 GHz was fabricated and measured with 10‐dB fractional bandwidth of 33%, the gain of 8.1 dBi at the center frequency, the cross polarization level of 20 dB and the gain ripple of 1.5 dB.     

Smart monopole antenna with pattern and frequency reconfiguration characteristics based on programmable metasurface

Metasurfaces having ultrathin and planar structure with sub‐wavelength unit cell, have recently gained significant potential for use thanks to their control capabilities over the electromagnetic waves from microwave to the visible range. The structure and the dimensions of the sub‐wavelength elements determine the electromagnetic properties, capabilities, and functionalities of the metasurfaces providing a full control of the reflected and transmitted fields and these metasurfaces are referred to as analog metasurfaces. When adjustability is added to the unit cells, programmable or digital metasurfaces are obtained, allowing us to take multiple unique functionality advantages controlled by external stimuli. In this study, we propose a metasurface structure, also known as 1‐bit coding metasurface, which is controlled depending on the “On/Off” state. The “On/Off” state is controlled by a computer program using genetical algorithm. Depending on the operating state, electromagnetic waves can be manipulated and different functionalities of the metasurfaces can be realized. The contribution and innovation of the study is the demonstration of the beam rotation, resonance frequency shift and radiation pattern reconfiguration properties of a simple monopole antenna by using controllable metasurface composed of T shaped resonator and circular patch with an operating frequency between 4.3 and 5.6 GHz.     

An offset surface to reduce radar cross section for airborne antenna out‐band

To meet the needs of modern electronic warfare in better stealth performance of the weapon platform, we design an offset surface with metasurface structure, which greatly reduces the radar cross section for airborne antenna. The relation between surface unit size and attenuation frequency guides the design of offset surface that can work in the L‐band. The original strategy performed as cross‐array structure that plays well throughout the band at different angles, except 30° to 35°. An undesired reflection occurs at this angle gap. Therefore, we attempted to modify the structure as parallel‐array structure with same unit size. The results show that modification performs well at all angles in the passband, which meets the design requirements. We processed an offset surface sample and performed a joint test with an aircraft antenna to verify the superiority of the design.     

Wideband beam‐steerable configuration of metasurface loaded slot antenna

In this article, a wideband two dimensional (2D) beam‐steerable antenna structure is presented. The proposed structure is based on a radially gradient hybrid metasurface (RGHMS) illuminated through a slot antenna. The half aperture of the RGHMS comprises of a gradient phase profile topology, while its other half aperture consists of a constant phase profile configuration. The slot antenna possessing the bidirectional radiation pattern is printed on a relatively thin substrate, which operates over a wide bandwidth of 1420 MHz (15.10%). The placement of RGHMS tilts the main beam of slot antenna by 15° away from normal direction. Further, in‐plane movement of MS provides beam steering in both elevation and azimuth planes, with a conical region of an apex angle of 30°. Apart from the beam steering capability, the placement of RGHMS in front of slot antenna also enhances the overall bandwidth and gain by 360 MHz and 5 dB, respectively. Thus, a wide band beam steering configuration with the impedance bandwidth of 1780 MHz (18.85%) is obtained. In order to investigate the frequency dependent beam tilting capability of the RGHMS in the elevation plane, a detailed analysis is carried out using the principle of refraction.