RAJ T , HANIM H F , BASERI H A , et al . A survey on LiDAR scanning mechanisms [J ] . Electronics , 2020 , 9 ( 5 ): 741 . DOI: 10.3390/electronics9050741 http://doi.org/10.3390/electronics9050741 https://www.mdpi.com/2079-9292/9/5/741 https://www.mdpi.com/2079-9292/9/5/741 In recent years, light detection and ranging (LiDAR) technology has gained huge popularity in various applications such as navigation, robotics, remote sensing, and advanced driving assistance systems (ADAS). This popularity is mainly due to the improvements in LiDAR performance in terms of range detection, accuracy, power consumption, as well as physical features such as dimension and weight. Although a number of literatures on LiDAR technology have been published earlier, not many has been reported on the state-of-the-art LiDAR scanning mechanisms. The aim of this article is to review the scanning mechanisms employed in LiDAR technology from past research works to the current commercial products. The review highlights four commonly used mechanisms in LiDAR systems: Opto-mechanical, electromechanical, micro-electromechanical systems (MEMS), and solid-state scanning. The study reveals that electro-mechanical scanning is the most prominent technology in use today. The commercially available 1D time of flight (TOF) LiDAR instrument is currently the most attractive option for conversion from 1D to 3D LiDAR system, provided that low scanning rate is not an issue. As for applications with low size, weight, and power (SWaP) requirements, MEMS scanning is found to be the better alternative. MEMS scanning is by far the more matured technology compared to solid-state scanning and is currently given great emphasis to increase its robustness for fulfilling the requirements of ADAS applications. Finally, solid-state LiDAR systems are expected to fill in the gap in ADAS applications despite the low technology readiness in comparison to MEMS scanners. However, since solid-state scanning is believed to have superior robustness, field of view (FOV), and scanning rate potential, great efforts are given by both academics and industries to further develop this technology.

HE J W , DONG T , XU Y . Review of photonic integrated optical phased arrays for space optical communication [J ] . IEEE Access , 2020 , 8 : 188284 - 188298 . DOI: 10.1109/Access.6287639 http://doi.org/10.1109/Access.6287639 https://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=6287639 https://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=6287639

WU Y H , SHAO S , LI Y X , et al . Multi-beam optical phase array for long-range LiDAR and free-space data communication [J ] . Optics & Laser Technology , 2022 , 151 : 108027 .

NAKAMURA K , NARUMI K , KIKUCHI K , et al. Liquid crystal-tunable optical phased array for LiDAR applications [C ] //Proceedings of Smart Photonic and Optoelectronic Integrated Circuits XXIII. Washington, D.C. , US : SPIE , 2021 , 11690 : 94 - 99 .

HOY C , STOCKLEY J , SHANE J , et al . Non-mechanical beam steering with polarization gratings: a review [J ] . Crystals , 2021 , 11 ( 4 ): 361 . DOI: 10.3390/cryst11040361 http://doi.org/10.3390/cryst11040361 https://www.mdpi.com/2073-4352/11/4/361 https://www.mdpi.com/2073-4352/11/4/361 Polarization gratings (PGs) enable a novel architecture for dynamic non-mechanical steering of light over large angles and with large clear apertures. This beam steering approach has many applications in active sensing and optical communications. In this review, we describe some of the defining characteristics of this beam steering architecture and highlight several applications of the technology.

LI Z , ZANG Z H , HAN Y Q , et al . Solid-state FMCW LiDAR with two-dimensional spectral scanning using a virtually imaged phased array [J ] . Optics Express , 2021 , 29 ( 11 ): 16547 - 16562 . DOI: 10.1364/OE.418003 http://doi.org/10.1364/OE.418003 The beam-steering device is a critical component in LiDAR systems for 3D imaging. Solid-state beam-steering devices attract the most attention for their advantages of robustness, fast beam-steering speed, and stability. However, solid-state beam-steering devices, such as optical phased arrays (OPAs), are challenging to realize 2D scanning ability. Here we employed a virtually imaged phased array (VIPA) in the LiDAR system to realize all solid-state two-dimensional (2D) beam-steering based on dispersion only. A frequency swept laser source is used for performing optical frequency-modulated continuous-wave (FMCW) ranging and 2D beam steering simultaneously. The 2D disperser is compact and can be easily implemented owing to its simple structure. The mechanism of continuous scanning and ranging is beneficial for obtaining high lateral resolution, and a lateral resolution of 0.06° is achieved. 3D maps of the object at a distance of 2 m are obtained with cm-level ranging precision. The frame rate of the proposed LiDAR system only depends on the wavelength-tuning speed of the swept laser source, with the potential to realize ultrafast solid-state LiDAR systems.

马阎星 , 吴坚 , 粟荣涛 , 等 . 光学相控阵技术发展概述 [J ] . 红外与激光工程 , 2020 , 49 ( 10 ): 20201042-1-20201042-14 .

MA Y X , WU J , SU R T , et al . Review of optical phased array techniques [J ] . Infrared and Laser Engineering , 2020 , 49 ( 10 ): 20201042-1-20201042-14 . (in Chinese)

郑青泉 . 液晶偏振光栅斜入射下光束偏转技术研究 [D ] . 西安 : 西安工业大学 , 2022 . ZHENG Q Q. Study on beam deflection technology under oblique incidence of liquid crystal polarization grating [D]. Xi'an:Xi'an University of Technology , 2022. (in Chinese)

王琦 , 高旭峰 , 张大伟 , 等 . 液晶光学相控阵技术的研究进展 [J ] . 激光与光电子学进展 , 2021 , 58 ( 17 ): 94 - 105 .

WANG Q , GAO X F , ZHANG D W , et al . Research progress of liquid crystal optical phased array technology [J ] . Advances in Laser and Optoelectronics , 2021 , 58 ( 17 ): 94 - 105 . (in Chinese)

扈航 , 刘磊 , 李聪 , 等 . 深空合作目标高概率捕获复合扫描策略研究 [J ] . 中国空间科学技术 , 2022 , 42 ( 3 ): 58 - 66 .

HU H , LIU L , LI C , et al . Research on composite scanning strategy for high-probability acquisition of deep space cooperative targets [J ] . Chinese Space Science and Technology , 2022 , 42 ( 3 ): 58 - 66 . (in Chinese)

WANG X R , HUANG Z Q , TAN Q G , et al. Stochastic scanning method to shorten acquisition time using liquid crystal optical phased array [J ] . Optical Engineering , 2016 , 55 ( 2 ): 026109 . DOI: 10.1117/1.OE.55.2.026109 http://doi.org/10.1117/1.OE.55.2.026109 http://opticalengineering.spiedigitallibrary.org/article.aspx?doi=10.1117/1.OE.55.2.026109 http://opticalengineering.spiedigitallibrary.org/article.aspx?doi=10.1117/1.OE.55.2.026109

袁光福 , 马晓燠 , 刘爽 , 等 . 激光雷达扫描方式 [J ] . 强激光与粒子束 , 2020 , 32 ( 4 ): 65 - 70 .

YUAN G F , MA X Y , LIU S , et al. Lidar scanning method [J ] . Strong Laser and Particle Beam , 2020 , 32 ( 4 ): 65 - 70 . (in Chinese)

汪相如 , 谭庆贵 , 黄子强 , 等 . 液晶光学相控阵的双波束成形和2维扫描技术 [J ] . 激光技术 , 2013 , 37 ( 5 ): 631 - 635 .

WANG X R , TAN Q G , HUANG Z Q , et al . Dual beam formation and 2-D scan technique of liquid crystal optical phased array [J ] . Laser Technology , 2013 , 37 ( 5 ): 631 - 635 . (in Chinese) DOI: 10.1016/j.optlastec.2004.10.001 http://doi.org/10.1016/j.optlastec.2004.10.001 https://linkinghub.elsevier.com/retrieve/pii/S0030399204001823 https://linkinghub.elsevier.com/retrieve/pii/S0030399204001823

GOLMOHAMMAGY S , GHAFARY B . Stokes parameters of phase-locked partially coherent flat-topped array laser beams propagating through turbulent atmosphere [J ] . Laser Physics , 2016 , 26 ( 6 ): 066201 . DOI: 10.1088/1054-660X/26/6/066201 http://doi.org/10.1088/1054-660X/26/6/066201 https://iopscience.iop.org/article/10.1088/1054-660X/26/6/066201 https://iopscience.iop.org/article/10.1088/1054-660X/26/6/066201

王承邈 . 基于液晶光学相控阵的高精度光束指向控制技术 [D ] . 长春 : 中国科学院大学(中国科学院长春光学精密机械与物理研究所) , 2021 .

WANG C M . High precision beam pointing control technology based on liquid crystal optical phased array [D ] . Changchun : University of Chinese Academy of Sciences (Changchun Institute of Optics, Precision Mechanics and Physics, Chinese Academy of Sciences), 2021 . (in Chinese)

赵志伟 . 大偏转角液晶偏振光栅的研究 [D ] . 长春 : 中国科学院大学(中国科学院长春光学精密机械与物理研究所) , 2020 .

ZHAO Z W . Research on large deflection angle liquid crystal polarization grids [D ] . Changchun : University of Chinese Academy of Sciences (Changchun Institute of Optics and Precision Mechanics and Physics, Chinese Academy of Sciences), 2021 . (in Chinese)

GARCIA B M , GEDAY M A , OTON J M , et al . Two-dimensional digital beam steering based on liquid crystal phase gratings [J ] . Applied Sciences , 2021 , 11 ( 8 ): 3632 . DOI: 10.3390/app11083632 http://doi.org/10.3390/app11083632 https://www.mdpi.com/2076-3417/11/8/3632 https://www.mdpi.com/2076-3417/11/8/3632 Electrically tunable phase gratings are able to steer an incoming light beam without employing movable parts. Here, we present the design and implementation of a 2D beam steering device by cascading two orthogonal 1D liquid crystal (LC) based phase gratings, each having an array of 72 rectangular individually controlled pixels and driven by a custom 12-bit Pulse-Width Modulation (PWM) electrical driver. High-resolution structures in glass wafers coated with transparent Indium-Tin Oxide (ITO) have been prepared using Direct Laser Writing (DLW) techniques. With DLW, a high number of pixels can easily be drawn with an interpixel space of less than 3 μm, leading to devices with a high fill factor. The active area of the cascaded device is 1.1 × 1.1 mm2. We present a 72 × 72 point efficiency map corresponding to a maximum diagonal steering angle of 1.65°. Special attention has been paid to make the device compatible with space application by avoiding electronics in the active area.

王丽娜 , 李明秋 , 王春阳 , 等 . 级联液晶偏振光栅的衍射特性分析 [J ] . 激光与光电子学进展 , 2020 , 57 ( 3 ): 88 - 92 .

WANG L N , LI M Q , WANG C Y , et al . Diffraction characteristics of cascaded liquid crystal polarizing gratings [J ] . Laser & Optoelectronics Progress , 2020 , 57 ( 3 ): 88 - 92 . (in Chinese)

刘壮 , 王启东 , 王超 , 等 . 正交级联液晶偏振光栅角度偏转模型 [J ] . 光子学报 , 2021 , 50 ( 11 ): 1105003-1-1105003-10 .

LIU Z , WANG Q D , WANG C , et al. Deflection angular model of orthogonal cascade liquid crystal polarization gratings [J ] . Acta Photonica Sinica , 2021 , 50 ( 11 ): 1105003-1-1105003-10 . (in Chinese)

WANG Z S , WAMG C Y , LIANG S L , et al . Diffraction characteristics of a non-mechanical beam steering system with liquid crystal polarization gratings [J ] . Optics Express , 2022 , 30 ( 5 ): 7319 - 7331 . DOI: 10.1364/OE.452397 http://doi.org/10.1364/OE.452397 The non-mechanical beam steering system is composed of multiple liquid crystal polarization gratings (LCPGs) cascaded by binary or ternary technologies. However, cascading multiple LCPGs cause the beam from one LCPG to obliquely enter the subsequent LCPGs, changing their diffraction efficiency and working voltage at different steering angles. This paper uses the elastic continuum theory of liquid crystals to simulate the tilt angle of liquid crystal molecules under different voltages. The transmission process of the beam in the system at oblique incidence is described with an extended Jones matrix, and the highest diffraction efficiency and working voltage of each LCPG at different steering angles are calculated using vector diffraction theory. It is convenient to calibrate the LCPGs' working voltage and analyze the system's diffraction characteristics. In addition, we used an improved binary cascade technology to design a LCPG non-mechanical beam steering system with a steering angle of ±10° and an angular resolution of 0.67°. Compared with binary cascade, this technology can effectively reduce the number of cascaded devices and increase the system throughput under the same maximum beam steering angle and angular resolution.

丁海婷 , 周琳 , 刁伟峰 . 基于背包问题的多相控阵雷达多目标跟踪时间资源管理算法 [J ] . 兵工学报 , 2021 , 42 ( 5 ): 997 - 1003 .

DING H T , ZHOU L , DIAO W F . Multi-phased array radar multi-objective tracking time resource management algorithm based on backpack problem [J ] . Acta Armamentarii , 2021 , 42 ( 5 ): 997 - 1003 . (in Chinese)

张浩为 , 谢军伟 , 张昭建 , 等 . 基于混合自适应遗传算法的相控阵雷达任务调度 [J ] . 兵工学报 , 2017 , 38 ( 9 ): 1761 - 1770 . DOI: 10.3969/j.issn.1000-1093.2017.09.013 http://doi.org/10.3969/j.issn.1000-1093.2017.09.013 针对相控阵雷达任务调度NP难题，提出一种混合自适应遗传算法进行求解。在构建相控阵雷达任务调度优化模型的基础上，通过混沌理论优化初始种群，采取精英保留和混合排名的选择策略以及设计自适应的交叉、变异算子来提升算法的搜索性能；在自适应遗传算法的框架下，提出启发式脉冲交错算法，以利用雷达任务中的等待期来交错执行其他任务的发射期或接收期。仿真结果表明：相比于基于遗传算法的调度方法，改进算法的搜索效率更高、结果更优；相比于传统启发式算法，改进算法的调度成功率、时间利用率和实现价值率均得到了提升，并有效降低了时间偏移率。

ZHANG H W , XIE J W , ZHANG Z J , et al . Task scheduling of phased array radar based on hybrid adaptive genetic algorithm [J ] . Acta Armamentarii , 2017 , 38 ( 9 ): 1761 - 1770 . (in Chinese)

宋海生 , 傅仁毅 , 徐瑞松 , 等 . 求解多背包问题的混合遗传算法 [J ] . 计算机工程与应用 , 2009 , 45 ( 20 ): 45 - 48 .

SONG H S , FU R Y , XU R S , et al . Hybrid genetic algorithm for multi knapsack problem [J ] . Computer Engineering and Application , 2009 , 45 ( 20 ): 45 - 48 . (in Chinese)

贾冰 , 吕琼莹 , 曹国华 . 脉冲激光分布式扫描参数的优化分析 [J ] . 中国激光 , 2017 , 44 ( 12 ): 198 - 205 .

JIA B , LÜ Q Y , CAO G H . Optimization analysis of pulse laser distributed scanning parameters [J ] . China Laser , 2017 , 44 ( 12 ): 198 - 205 . (in Chinese)

杨善超 , 田康生 , 李宏权 , 等 . 综合优先级下反导预警相控阵雷达任务调度算法 [J ] . 兵工学报 , 2020 , 41 ( 2 ): 315 - 323 . DOI: 10.3969/j.issn.1000-1093.2020.02.013 http://doi.org/10.3969/j.issn.1000-1093.2020.02.013 针对相控阵雷达跟踪多弹道导弹目标时的资源分配问题，提出一种综合优先级下的价值优化调度算法。基于弹道导弹目标特性，构建目标威胁度模型；设计二维优先级表，结合目标威胁度和截止期进行综合优先级规划；基于任务优先级建立任务动态价值函数，并从调度及时性原则出发，构建任务调度的价值优化模型；对遗传算法进行改进，设置自适应选择、交叉、变异算子，并利用该算法求解调度模型；通过仿真实验将所提算法与传统工作方式优先级加截止期调度算法进行性能对比，对任务价值函数参数对调度性能的影响进行分析。结果表明：相比传统调度算法，所提调度算法的调度时间偏移率减小了46%，实现价值率提升了12%.

YANG S C , TIAN K S , LI H Q , et al. Comprehensive priority-based task scheduling algorithm for anti-missile early warning phased array radar [J ] . Acta Armamentarii , 2020 , 41 ( 2 ): 315 - 323 . (in Chinese) DOI: 10.3969/j.issn.1000-1093.2020.02.013 http://doi.org/10.3969/j.issn.1000-1093.2020.02.013 A comprehensive priority-based task scheduling algorithm is proposed for the resource allocation problem about anti-missile early warning phased array radar tracking multiple ballistic missile targets. A target threat level model is established for ballistic missile targets. Target threat level and task deadline are combined together to calculate the comprehensive priority by designing a two-dimensional priority table. A dynamic value function of tasks is established based on the comprehensive priority. A value optimization model for task scheduling is constructed according to the principle of scheduling timeliness. The genetic algorithm is improved by setting adaptive selection, crossover and mutation operators, and then the modified algorithm is used to solve the scheduling model. The performance of the proposed algorithm is compared with the traditional scheduling algorithms by simulation experiments, and the impacts of task value function parameters on scheduling performance are analyzed. Simulated results show that, compared to the traditional scheduling algorithm, the proposed algorithm reduces the average time shift ratio by 46%, and improves the hit value ratio by 12%. Key