For data communication between single wavelength laser communication terminals, good isolation between signal transmission and reception is the key to establishing duplex bidirectional laser communication. In this paper, with respect to the transmission and reception scheme of a single laser wavelength laser communication terminal and its overall communication performance, the influence of the surface roughness and contamination level of key components on the isolation performance of the laser communication terminal is analyzed. The model parameters are derived from Harvey model and ABg model, and the designed scheme is analyzed using TracePro software. When the surface roughness or contamination level of λ/2 wave plate, λ/4 wave plate and optical antenna structure in the signal transmission channel is improved, the backscattering caused by these elements will reduce the isolation performance in the signal transmission channel. At the same time, the measurement result of laser communication terminal isolation is 77.86 dB, which is basically consistent with the software simulation result of 78.35 dB. This can be applied in laser communication system. © 2023 Editorial Office of Chinese Optics. All rights reserved.

Metasurfaces represent a group of artificially designed structures capable of efficiently manipulating the transmission properties of incident waves, have attracted considerable attention in terahertz (THz) radiation, and gradually overcome the complexity of bulky optical systems. Although the introduction of meta-optics has made great progress in full-span phase modulation schemes within orthogonal polarization channels, flexible phase functions can still effectively alleviate the design complexity of wavefront engineering. Here, we experimentally demonstrate several designs of general-purpose all-silicon THz metasurfaces applied in different scenarios. By combining geometric phase and propagation phase, switchable multiple phase modulation in orthogonal circularly polarized (CP) channels can be realized by switching the handedness of the incident wave. The advantage of the proposed scheme is that not only a locked phase modulation profile can be generated within the cross-polarized channels with opposite handedness, but also the phase distribution within each channel can be arbitrarily tailored to break the locking, demonstrating the flexible wavefront manipulation capability of the spin-decoupled phase control. Two different metalens are experimentally demonstrated to verify the feasibility of the multiple phase modulation scheme, mainly exploiting the topological charge and type of the focused beams. This work allows the metasurface to show a higher degree of freedom in wavefront manipulation by using a simpler phase-composite algorithm. © 2023 Elsevier Ltd

Vortex and vector terahertz (THz) beams with inhomogeneous polarization states have become a considerable hot topic in the last decade due to their important roles in multiplexed wireless data transmission. However, the technical instruments to form and evaluate such beams are rather limited, as they are mainly collected in the visible range. The emergence of coded metasurfaces has reinvigorated the design of functional devices with multiple degrees of freedom. Here, we demonstrate a versatile design inspired by a binary encoding approach for generating off-axis vectorial THz beams on all-silicon metasurfaces. Experimentally, simultaneous manipulation of the encoding method within the orthogonal circularly polarized (CP) channel provides strong support for developing versatility in vector THz beams, including the generation of arbitrary polarization profiles and the directional emission of multiplexed vector vortex beams (VVBs) with specified polarization states. The introduction of the latitudinal polarization control factor guarantees that continuously rotating or independently designed vector polarization profiles can be obtained on a pre-defined focal plane. Subsequently, a universal parametric theoretical model is developed to analyze the evolutionary trend of off-axis VVB in detail. Notably, the proposed monolayer vector metasurface bypasses the requirement of multiple cascaded optical elements, further inducing the advancement of ultra-thin vector THz sources, and also facilitating the generation of vector fields with tailored polarization distributions in 3D space. © 2023, Science China Press.

导引头在3 Ma(1 Ma≈340.3 m/s)超音速飞行状态下,受到气动加热的光学窗口温度急剧上升,产生大量红外热辐射,干扰探测器的成像质量。为研究气动热辐射对导引头红外成像的影响:采用ANSYS软件对导引头进行三维建模、有限元网格划分及温度

In recent years，photoelectric tracking technology has developed rapidly and has been widely used in space laser communication，laser weapons and other fields. Traditional optoelectronic tracking systems mostly use servo turntables or optical mirrors to achieve beam adjustment to ensure accurate tracking of the target. However，they usually have a large size and weight，and excessive sensitivity to vibration also affects their dynamic tracking performance. A typical representative of a small-inertia beam servo system is the rotating double prism，which consists of a pair of circular optical prisms with specific wedge angles. Both prisms rotate with the same central axis to achieve fast beam deflection，which has the advantages of high accuracy，low rotational inertia，fast beam pointing，and low vibration sensitivity，which makes the double prism system of important practical value in laser communication，interferometry，photoelectric detection，and other fields. The key to achieving target tracking using double prisms is to reveal the nonlinear variation mechanism of beam delivery and to develop an effective prism control strategy. In this paper，a beam compound tracking technology based on a rotating double prism is proposed to replace the traditional servo turntable to achieve precise optical tracking. Firstly，the beam deflection model of the double prism is established，the relationship between the beam deflection vector and the prism angle is deduced in detail，and the nonlinear problem of the prism rotation in the tracking process is analyzed. A double-prism composite tracking system is designed to change the direction of the beam by using two independently rotating prisms，each of which is rotated under the drive of a motor. In the double-prism tracking system，an improved controller is designed to improve the tracking performance，and an FSM is added behind the double prisms，and the beam passing through the prisms will be deflected by the FSM for the final error complement. Among them，the rotating double prism is responsible for a wide range of beam adjustment，and a large field-of-view target viewing camera is added to the system for searching the target position and initial alignment of the optical axis. The FSM is used to compensate for the beam control error of the double prism，and the tracking camera is used as the target detection element in the system to obtain the aiming error of the optical axis in real time. The inertial measurement unit is mounted on an optical abutment. Unlike traditional two-dimensional servo turntable，the rotating dual prism system has a special structure and beam deflection mechanism，which cannot achieve optical axis stabilization through on-axis gyroscopic feedback as in traditional two-dimensional servo turntable，so the dynamic compensation of the optical axis is achieved through attitude decoupling. An experimental system is built to verify the compound tracking technology of the rotating double prism. A collimator is used in the direction along the center axis of the rotating double prism to generate near-parallel light to simulate a long-range target，and the rotating double prism system is fixed to a six-degree-of-freedom swing table for simulating attitude perturbations of a moving pedestal platform. In the dynamic tracking experiment，the control accuracy of the biprism using the improved controller is obviously improved. Compared with the PID controller and the linear active disturbance rejection controller，the control accuracy of the prism is increased by 58.33% and 32.81% respectively，and the corresponding tracking errors are reduced from 49.03 μrad and 38.88 μrad to 31.15 μrad. After turning on boresight compensation， the tracking performance is further improved，with the total tracking error reduced to 7.49 μrad and the tracking accuracy increased by 4.16 times. The experimental results show that the beam compound control can effectively improve the tracking accuracy of the rotating double prism，which verifies the effectiveness of the proposed method. © 2023 Chinese Optical Society. All rights reserved.

Polarization plays a key role in fundamental science, and manipulating the evolutionary trends of longitudinal polarization states can provide new implements for light–matter interaction. However, existing 3D optical devices can only manipulate the polarization conversion in a single transverse plane. Recently, methods to control polarization by cascading bulky optical systems are miniaturized using metasurfaces. Nevertheless, it is quite challenging to generate focused beams with vectorial properties for metasurfaces carrying inhomogeneous polarization profiles. Here, a single-layer all-silicon metasurface operating in the terahertz (THz) band is demonstrated to address all those aforementioned challenges in one go, and pencil-like beams with inhomogeneous polarization profiles can be imparted along the propagation direction. The introduction of a latitudinal polarization control factor representing the initial phase difference enables near-even manipulation of the evolutionary trend of the longitudinal polarization state according to the extended focal depth. By manipulating the topological charges within two orthogonal circularly polarized channels to accomplish coherent superposition, a focused vortex beam with vectorial properties can be generated in desired planes. Two functional demonstrations based on this approach are established experimentally, offering promising opportunities for structured light on meta-optics. © 2022 Wiley-VCH GmbH.

提出一种基于旋转双棱镜的光束复合跟踪技术，用于取代传统伺服转台实现精密的光学跟踪。首先，建立双棱镜的光束偏转模型，详细推导光束偏转矢量与双棱镜转角间的转换关系，并对跟踪过程中的棱镜旋转非线性问题进行了分析。提出基于快速反射镜进行光轴修正的双棱镜光束复合跟踪方法，通过建立偏转光轴与光学基台间的扰动耦合关系，实现了对双棱镜转速的实时补偿，并改进棱镜控制器以提高光束控制性能。搭建实验系统，对旋转双棱镜复合跟踪技术进行验证。在动态跟踪实验中，采用改进控制器的双棱镜的控制精度明显提高，相较于比例-积分-微分控制器和线性自抗扰控制器，所提出的改进控制器使棱镜的控制精度分别提高58.33%和32.81%，并使跟踪误差由改进前的49.03μrad和38.88μrad降低为31.15μrad。开启视轴补偿后跟踪性能进一步提高，总跟踪误差降至7.49μrad，跟踪精度提高4.16倍。实验结果表明，光束复合控制能有效提高双棱镜的跟踪精度，验证了所提方法的有效性。

Polarization plays a key role in fundamental science, and the improvement in miniaturization and practicability of polarization conversion devices could provide more degrees of freedom for light-matter interactions. Metasurfaces that can manipulate arbitrary polarization states at subwavelength scales can significantly reduce the complexity of meta-optical systems. Here, a general design of an all-silicon diatomic metasurface operating in the terahertz band that can generate a tailorable linear polarization state by the superposition of two meta-atoms with individual geometric parameters is experimentally demonstrated. By periodically arranging polarization-converting and polarization-maintaining meta-atoms, the existence of interference effects enables the proposed diatomic meta-platform to act as an optimal linear polarization operator. The gradient arrangement of the meta-molecules under the profile of the propagation phase is deduced by using the advanced Jones matrix, so that the polarization filtering and wavefront manipulation can be realized simultaneously, including the generation of tightly converged vortex and bifocal focusing beams. This demonstration of generating tailorable linear polarization states located on the Poincare sphere directly from arbitrarily polarized waves can significantly facilitate the development of functional polarization meta-devices.

Chiral metasurfaces have been widely used in sensing, imaging and other fields because they can manipulate light through the efficient circular dichroism (CD). However, its on-demand design is still a very challenging task. In this work, we propose an on-demand multiple reverse design based on deep learning, named target-driven conditional generative network (TCGN). It can reverse design the metasurface structure that meets the required CD, and its mean square error (MAE) is 0.0089. We use this method to inversely design multiple sets of metasurfaces with different structures, and all their CD values can exceed 0.36. Both simulations and experiments prove the feasibility and effectiveness of using deep learning to reverse design metasurfaces. In addition, the designed metasurface can realize chiral wavefront control under dual frequency. This design method based on deep learning can rapidly and efficiently design the chiral metasurfaces, which provides a new way for the design of metasurfaces.

Space-based gravitational-wave observatories (SGOs) promise to measure pico-meter variations in gigameter separations of a triangular constellation. Telescopes play an essential role in transmitting and receiving laser beams measuring the constellation arms with the heterodyne laser interferometry. The wavefront aberrations of the telescopes are coupled with the unavoidable misalignments caused by jitters and pointing tilts and induce additional phase changes into the heterodyne signal. As a critical aspect of achieving the measuring stability of 1 pm/v Hz, we analytically investigate the above process and determine that by properly controlling the relevant key aberrations in the design of the telescopes, the phase noise can be reduced exponentially, which makes the heterodyne signal insensitive to jitter and reduces the demand for wavefront quality. This method is validated whether the LISA Pathfinder (LPF) signal definition or the Average Phase (AP) signal definition is adopted, underpinning the guidance for the design and manufacturing of the optical telescope in SGOs.