Showing papers in "Infrared and Laser Engineering in 2020"

Infrared image adaptive inverse histogram enhancement technology

Abstract: In infrared images, when the traditional histogram equalizes the image, the detail pixels are easily immerged by the background pixels, resulting in the image being too bright and too dark. Based on this situation, an adaptive inverse histogram equalization algorithm was proposed in this paper. The algorithm enhanced image details by inverse statistics, adaptive selection threshold and segmentation mapping. Compared with the traditional histogram equalization algorithm, the inverse histogram equalization algorithm significantly improve the image visual effect in different gray level distributions and enhance the details of different areas of the image to different degrees. Moreover, under the premise of achieving better image processing effects, this algorithm can still guarantee real-time performance and high efficiency by optimizing calculation methods, and is suitable for FPGA hardware transplantation.

Has 3D finally come of age? ——An introduction to 3D structured-light sensor

Abstract: Three-dimensional (3D) imaging and sensing technologies, as valuable information acquisition tools for perceiving the real 3D world, provide data bases for the reconstruction of the geometric shape of objects and subsequent 3D modeling, detection, and recognition. Recently the development of computer vision and optoelectronic imaging technology, as well as the growing demand for 3D technologies in consumer electronics and personal authentication, have promoted the thriving growth of 3D imaging and sensing technologies. After the imaging revolution from monochrome to color, low resolution to high resolution, and static image to dynamic video, the transition of the camera from 2D to 3D will become the new "fourth imaging revolution." This issue of "Infrared and Laser Engineering" organizes a special topic on "Optical 3D Imaging and Sensing", which contains 20 high-quality articles, including 15 review papers and 5 research papers. These papers systematically introduce the research progress or trends of the cutting-edge research topics in the field of optical 3D imaging and sensing, and their themes comprehensively cover the current hot research directions in the field of 3D optical imaging: structured-light 3D imaging, fringe projection profilometry, interferometry, phase measuring deflectometry, 3D display technologies (such as holographic display, and integral/light field display), and the interdisciplinary fields of 3D sensing technologies and computational imaging technologies (such as 3D ghost imaging). As the preface of this issue, this paper summarizes the typical 3D sensing technologies and focuses on the current status, key technologies, and typical applications of the 3D structured-light sensor technologies, discusses its existing challenges, and looks forward to its future development directions.

Three-dimensional imaging technique based on Gray-coded structured illumination

Abstract: Three-dimensional (3D) imaging technique based on structured illumination has been deeply studied and widely applied in recent years Among numerous 3D imaging methods, the imaging technique based on Gray-coded structured illumination has been applied in industrial inspection, digitalization of antique, biomedicine detection and so on, owing to its robustness and anti-noise ability To realize 3D imaging, the projected Gray-coded pattern can either be used to modulate the height information or be used to assist acquisition and computation of the height information of the tested object In this paper, a review was given to introduce principles and progresses of the imaging techniques based on Gray-coded structured illumination and the research achievements of the author's research group about this technique were also shown In addition, the advantages, disadvantages and application scope of binary Gray-coded patterns in 3D shape measurement were discussed and the developing trends of this technique was pointed out as well

Research progress of ICESat-2/ATLAS data processing and applications

Abstract: The ICESat-2/ATLAS employed a micro-pulse multi-beam photon-counting laser altimeter system for the first time ICESat-2/ALTAS was significantly different from ICESat-1/GLAS in terms of detection mechanism, data processing methods and the breadth and depth of data applications Firstly, the key configuration parameters, data and products of ICESat-2/ATLAS were introduced Secondly, the key technologies of noise removal and classification algorithms for ICESat-2/ATLAS data as well as the adaptability and problems of each algorithm were elaborated Thirdly, the applications of ICESat-2/ATLAS data in ice sheet and sea ice elevation measurement and change monitoring, ground elevation and forest height extraction, forest biomass estimation, lake level and storage change monitoring were summarized Finally, the development trend and prospect of photon-counting LiDAR data processing methods and applications were expected

Progress of micro-nano fabrication technologies for optical metasurfaces

Abstract: The metasurface is composed of carefully arranged sub-wavelength units in a two-dimensional plane, which provides a new paradigm for designing ultra-compact optical elements and shows great potential in miniaturizing optical systems. In less than ten years, metasurfaces have caused extensive concern in multidisciplinary fields due to their advantages of being ultra-light, ultra-thin and capable of manipulating various parameters of light waves to achieve multi-functional integration. However, in the optical band, high-degree-of-freedom, aperiodic, and densely arranged metaunits put forward many extreme parameter requirements for fabrication, such as extremely small size, extremely high precision, high aspect ratio, difficult-to-process materials, cross-scale, etc. This poses a great challenge for metasurfaces from laboratory to practical applications. Here, the principles, characteristics and latest developments for micro-nano fabrication of metasurfaces in recent years were summarized, including small-area direct writing methods, large-area template transfer methods, and some emerging fabrication methods. Finally, the current challenges and future development trends of metasurface fabrication were summarized and prospected.

Research progress of APD three-dimensional imaging lidar

Abstract: Due to the advantages of rich information, strong anti-interference ability and high resolution, three-dimensional (3D) imaging lidar has been widely used in defense and civil fields, such as geomorphology surveys, autopilot, smart transportation and visual tracking. With the development of avalanche photodiode detector (APD) and the multiplicities of 3D lidar (e.g., MEMS, optical phased array, flash, etc.), the performances of lidar has been greatly improved compared with that of initial 3D systems. According to the new requirements on 3D lidar for the military and civilian fields, novel methods and mechanisms were proposed to improve comprehensive performances of 3D imaging. First of all, the three key technologies of APD-based 3D imaging lidar were analyzed, including the transmitting unit, the receiving unit, and the algorithm unit (data processing unit). Then, 3D imaging lidar was classified and discussed according to the different applications for loading. Among them, 3D imaging lidar based on unmanned vehicle was selected as the typical example for illustrating the application status and the difficulties faced with military and civilian applications. Based on the diversified development of 3D imaging methods, two novel 3D imaging methods (heterogeneous resolution and ghost imaging) suitable for APD devices were discussed. Finally, based on the analysis of the research status of 3D imaging lidar, it is concluded that 3D imaging lidar is developing towards the large field of view, high resolution, high precision, real-time, modularity and intelligence, which paves the way for developing high performances of 3D imaging lidar.

Recent development of low noise laser for precision measurement ( Invited )

Abstract: The measurement accuracy of laser precision measurement is mainly limited by optical field noise and various technical noises. After the de-coupling technical noises, quantum noise becomes the main factor limiting the measurement accuracy. Based on the intensity noise characteristics of solid-state single-frequency lasers, the main sources of intensity noise and their influence on the power noise spectrum were described, and three kinds of intensity noise suppression techniques, including traditional DC feedback control, optical AC coupled feedback control and quantum squeezer, were reviewed in this paper. By reviewing the development history of relevant technologies, the current development level and future development trend of intensity noise suppression technology were summarized-the noise suppression scheme combining three technologies is an important approach to solve high sensitivity detection.

Thermal damage of monocrystalline silicon irradiated by long pulse laser

Abstract: In view of the thermal damage law and mechanism of monocrystalline silicon for millisecond pulsed laser, the temperature of monocrystalline silicon irradiated by millisecond pulsed laser is measured by high precision point temperature meter and spectral inversion system. Then the temperature evolution process is analyzed. Also, the temperature state during the whole process of thermal damage of monocrystalline silicon irradiated by millisecond pulsed laser and the corresponding damage structure are studied. The results of this study show that the peak temperature of laser-induced monocrystalline silicon increases with the increase of energy density when the pulse width is fixed, When the pulse width is between 1.5 ms-3.0 ms, The temperature decreases with the increase of pulse width. Temperature rise curve shows inflection point when it is close to the melting point (1687 K), the reflection coefficient is from 0.33 to 0.72. During the gasification and solidification stages, it also shows the gasification and the solidification plateau periods. Thermal cleavage damage of monocrystalline silicon precedes thermal erosion damage. Stress damage dominates under low energy density laser irradiation, while thermal damage dominates under high energy density laser irradiation. The damage depth is proportional to the energy density and increases rapidly with the increase of the number of pulses.

Review of the system model and calibration for fringe projection profilometry

Abstract: Fringe projection profilometry (FPP) can well balance the system flexibility and the measurement accuracy, which is the mainstream technology of optical 3D imaging and shape measurement. When working with FPP, first an appropriate system should be established, and then the system parameters describing the system model should be determined via system calibration, finally the 3D shape is generated with 3D reconstruction by using the calibrated system model. System calibration and system model are tightly coupled, which have a direct impact on the performance of 3D imaging. The principle of FPP can be divided into two categories, i.e. the phase-3D mapping and the binocular stereo vision. This paper reviewed the system model and calibration strategy of FPP, which corresponded to the above two categories. Finally the method and basis for the accuracy evaluation of FPP were summarized.

Picosecond multi-pulse burst pump KGW infrared multi-wavelength Raman laser

Abstract: Picosecond infrared multi-wavelength Raman laser which adopted multi-pulse pumped KGW crystal was reported. A mathematical model was developed to investigate the effect of multi-pulse burst pumping regime on the vibrational mode of the Raman active molecule. The simulated results show that the response oscillation of the Raman active molecule to the multi-pulse burst pumping regime is more active and durable compared with the traditional single pulse pumping regime, which promotes the weakened molecule oscillation to return the natural frequency multiple times. The enhancement effect is beneficial to improve the Raman gain, reduce the Raman threshold, and increase the Raman conversion efficiency. During the experiment of picosecond multi-pulse pump KGW Raman crystal, the three-pulse burst pumping regime improves the Raman gain more than two times, reduces the threshold of stimulated Raman scattering more than 50%, and increases the Raman conversion efficiency more than 16% for 768 cm–1 Raman mode and 22% for 901 cm–1 Raman mode. Based on the three-pulse burst pumping regime, a 1 kHz mJ-level picosecond infrared multi-wavelength Raman laser was designed, which achieved the pulse energy of 1.39 mJ, the maximum Raman conversion efficiency of 29.6% for the 768 cm–1 vibrational mode of KGW, and the pulse energy of 1.38 mJ, the maximum Raman conversion efficiency of 25.7% for the 901 cm–1 vibrational mode of KGW. In addition, the Raman laser can radiate up to eight infrared Raman lines simultaneously for both the two vibrational modes of the KGW crystal, which covers the range of 800–1 700 nm.

Speckle projection profilometry with deep learning

Abstract: Traditional single speckle pattern matching algorithms always suffer from the low measurement accuracy and cannot be used to measure complex surface objects A speckle projection profilometry with deep learning was proposed to realize the pixel-by-pixel matching The siamese convolutional neural network structure was applied and extended where the main speckle pattern and the auxiliary speckle pattern were fed into the neural network patch by patch It was expected that the feature from the speckle pattern patches could be extracted by the convolution operation In this way, the features were fused and the matching coefficient between the two patches was obtained, which could be further used to formulate the disparity data and then the three-dimensional (3D) object was reconstructed The experiment results demonstrate that with the proposed method 3D measurement with an accuracy of about 290 μm could be achieved through a single speckle pattern

Development of an underwater spectral imaging system based on LCTF

Abstract: Underwater spectral imaging technology plays an important role in underwater object recognition and ocean ecological monitoring. An underwater spectral imaging system using liquid crystal tunable filter (LCTF) was designed based on the actual engineering environment. The system obtained spectral information by using LCTF as a filter structure. Under the illumination of a wide-spectrum LED, a pool experiment was performed to obtain 31 channel spectral images of the target between 400 and 700 nm. The spectral information of objects with similar colors under water was discussed and analyzed. The results show that the system is helpful for underwater target recognition and classification. In-situ observation of corals in the sea trial successfully obtained underwater spectral images of coral reefs. The system is expected to be applied to ocean remote sensing, ocean ecological environment monitoring and other fields.

Control method of adaptive optical system based on conjugate combined model of aberration

Abstract: In the concentric aperture circle of the unit circle, some special Zernike modes have interrelated relationship. When the modes with strong negative correlation is superposed with a certain coefficient, the aberrations in a certain concentric aperture will cancel each other and the wave surface will become smoother. This phenomenon is called the conjugate property between modes. In this paper, a set of distorted wavefront was set up, and the residual error was corrected by adaptive optical system. Then Zernike polynomials were used to decompose the corrected residual of deformable mirror. Through analysis, it was found for the first time that there was an obvious negative correlation between the lower and higher order aberrations in the residual wavefront with large mean square error. The aberration coefficients of the two parts will change regularly with the adjustment of the control signal of the deformable mirror, and in a certain combination of the coefficients, the two parts of aberrations will show conjugation. Based on the above research results, a control method was proposed. By optimizing the control voltage of the deformable mirror, the shape of the mirror surface can be adjusted so that the low-order and high-order aberration coefficients in the residual error can achieve the best matching. In this way, the root mean square (RMS) of the aberration in the concentric aperture circle of the pupil can be reduced, and the imaging quality of the system within this aperture range can be improved. The point target imaging and extended target imaging were simulated respectively. The results show that compared with the traditional closed-loop conjugate correction method, this method can obtain better optical imaging quality in the face of complex aberrations, and can effectively expand the application range of traditional adaptive optical system. This control method has a good application prospect when the deformable mirror has large fitting residual.

Effects of low emissivity material coating site on wall temperature and infrared characteristics of exhaust system

Abstract: In order to study the effects of the parts coated by infrared low-emissivity material on the wall temperature and infrared radiation (IR) characteristics of the exhaust system, the wall temperatures and IR characteristics of the axisymmetric and serpentine 2-D exhaust system were measured in three coating schemes, i.e., (1) only central cone was coated; (2) only mixer inner surface was coated; (3) both central cone and mixer inner surface were coated, under the same experimental condition. The experimental results show that the temperature of the surfaces coated with low-emissivity materials increases, and that of the non-coating surfaces is also affected by the coating layer. When high-temperature parts are coated with low-emissivity materials, the IR intensity of the exhaust system can be effectively suppressed in detection angles where the coating surface can be directly detected, while in other angles the IR intensity varies with the coating scheme. It is appropriate to only coat the inner surface of the mixer for serpentine 2-D exhaust system, and coat the central cone and the inner surface of the mixer together for an axisymmetric exhaust system in order to achieve better IR suppression.

Towards application of mobile devices: the status and future of glasses-free 3D display

Abstract: Mobile device has been the most important personal computational platform. Researches increasingly focus on glasses-free 3D display that features thin form factor and low power consumption. Once glasses-free 3D display is applied in the mobile devices, it will affect or even change the observation habit and thinking manner of human being. In this paper, the solutions that were compatible with flat display were introduced. Parallax barrier, lenticular lens array, spatio-temporal multiplexing 3D display, integral 3D display, compressive lightfield display, and vector 3D display were successively introduced in detail. Furthermore, the limitations that currently prevent these technologies from commercialization were discussed in depth. Finally, the potential research trends were highlighted.

Study on techniques of anti-aerosol-interference for active optical target-detection device

Abstract: Aerosol-interference is a serious interference source for active optical target-detection device (AOTD) when it is used in lower sky or super low sky When AOTD in a vehicle passes through aerosol, it may be wrong armed, even give out execution signal before right time In order to increase the ability in aerosol environment, how the AOTD worked and how the aerosol interfered the AOTD were analyzed It also showed out the techniques of anti-aerosol-interference used in engineering The general techniques for anti-aerosol-interference were settings of cut-off distance method, weaken methods by optical parts, optical field restraining method, cancellation by symmetric views, setting reference view field, body recognition method, composite with Ka detectors, decreasing the width of transmitted pulse, image recognition method et al Among these methods, the multimode detection method was a valuable way Effects of different anti-interference methods were listed, the results shows integrated application of all the methods can increase the ability of AOTD

Techniques of structured light measurement network with 3D sensors

Abstract: For achieving automatic, high-precision, high-density, and photorealistic 3D imaging and measurement of large-scale complex objects, the techniques about multi-node 3D sensor measurement network were described based on 3D sensing with the fringe structured light. It mainly involved the analysis of two key technologies (fringe analysis and phase reconstruction, system calibration and 3D reconstruction) of single 3D sensing, construction and optimization of multi-node 3D sensor measurement network, calibration of multi-node 3D sensor measurement network, matching and fusion of 3D depth data and texture data. Some experimental prototypes and experimental results were given.

Miniaturized mid-infrared MgO: PPLN optical parametric oscillator with high beam quality

Abstract: In order to meet the engineering application of mid-infrared laser, a miniaturized mid-infrared MgO: PPLN optical parametric oscillator (MgO: PPLN-OPO) with high beam quality was presented. The pump source was an acousto-optical Q-switched Nd: YVO4 laser. By pumping the MgO: PPLN crystal, the mid-infrared laser with high efficiency and high peak power was obtained. And the mid-infrared beam quality was improved by adding an aperture in the cavity. The whole laser was cooled by thermoelectric cooling and air cooling. Therefore, the size of the laser was miniaturized. Experimental results indicate that the acousto-optical Q-switched Nd: YVO4 laser can realize the pulse laser with the highest power of 9.3 W at 1.064 μm. The corresponding optical to optical conversion efficiency is 27.2% and the peak power is ~27.5 kW. With the Nd: YVO4 laser pump, the MgO: PPLN-OPO can output the pulse laser at 3.765 μm. When adding the aperture in the cavity, the maximum output power of the MgO: PPLN-OPO decreases from 1.20 W to 1.08 W. However, the beam quality improves obviously. The Mx and Myfactors change from 1.89 and 1.98 to 1.20 and 1.29, respectively. The pulse width and 收稿日期:2020−04−02; 修订日期:2020−05−16 基金项目:国家重点研发计划战略性国际科技创新合作重点专项 (2018YFE0203203);国家自然科学基金面上项目 (61975203);中国科学院 青年创新促进会 (2017259);激光与物质相互作用国家重点实验室开放基础研究课题 (SKLLIM1815) 作者简介:白翔 (1978−),男,助理研究员,主要从事固体激光器和航天器跟踪测量设备方面的研究。Email:bxiang@sina.com 第 49 卷第 7 期 红外与激光工程 2020 年 7 月 Vol.49 No.7 Infrared and Laser Engineering Jul. 2020

Nonlinear absorption and optical limiting of platinum(II) terpyridine complexes (Invited)

Abstract: The reported work in 2003-2019 on the reverse saturable absorption (RSA) or two-photon absorption (TPA) and/or optical limiting (OPL) of platinum(II) terpyridine complexes was summarized in this minireview. Photophysical properties, including the ground-state absorption (GSA), excited-state absorption (ESA), excitedstate lifetimes, and the quantum yields of triplet excited-state formation, RSA/OPL at 532 nm for ns laser pulses, TPA characteristics in the near-IR spectral regions, and the structure-property correlations were reviewed. This paper is composed of four sections. First, the current status of OPL materials and devices, the general requirements for reverse saturable absorbers and two-photon absorbing materials, and the different types and characteristics of square-planar platinum(II) complexes were briefly introduced. Then the photophysics and RSA/OPL of six series of Pt(II) terpyridine-analogous complexes and the structure-property correlations were discussed. Following it the TPA of five series of Pt(II) terpyridine complexes and the impacts of structural variations on the TPA cross sections (σ2) were reviewed. Finally, brief conclusions were drawn based on the reported studies. A general trend discovered was that the charge transfer absorption band(s) and the ESA can be readily tuned by substituents on the acetylide or the terpyridine ligand. Introducing electron-donating substituent to the acetylide or terpyridine ligand or improving the coplanarity between the aromatic substituent and the terpyridine ligand red-shifted the ground-state charge-transfer absorption band(s) at the price of decreasing/ quenching the triplet ESA, which consequently reduced the RSA/OPL at 532 nm. Extending the π-conjugation of the terpyridine ligand dramatically improved the σ2 values of the Pt(II) terpyridine complexes. Incorporation of electron-withdrawing π-conjugated aromatic substituent restrained the GSA to < 500 nm while keeping a longlived triplet excited state with broadband ESA in the visible spectral regions and moderately strong TPA in the NIR regions. This approach could provide a solution for developing broadband OPL materials.

Development and application of lidar mapping satellite

Abstract: The rapid development of laser altimetry satellite has a great impact on the traditional satellite earth observation field. The accurate elevation data can effectively compensate the lack of optical satellites, while laser altimetry satellite data processing and mapping applications are worthy of attention. Firstly, the principle and characteristics of laser altimetry satellite was introduced, and the its development history was presented. Then, the current on-orbit LiDAR satellite ICESat-2 was focued on, which had a high degree of attention. The satellite configuration characteristics and data processing methods were discussed, and its surveying and mapping capabilities in many fields, such as image joint adjustment, multi-source terrain fusion, global vegetation survey, and shallow water bathymetry et al. were analyzed and revealed. Finally, some thoughts about the development and construction of laser altimetry satellite in China were shared.

Filter-based technology for evaluating proportions of high-order harmonics and its application

Abstract: In order to meet the high requirements of the data measurement in the inertial confinement fusion(ICF) experiment, experimental instruments must be developed in the direction of absolute measurement, and the requirements for calibration are also higher. Beijing Synchrotron Radiation Facility (BSRF) provides a good X-ray source for calibration in China. The characteristics of the light source, such as the numerical study of the high-order harmonics content, are very important for the calibration work and the precise diagnosis of ICF. By measuring the current of a standard detector with or without a filter on a soft-X-ray source of beam line 4B7B in BSRF, the transmittance curves of different filters for monochromatic X-ray were studied and a fitted theoretical transmission curve was established. According to this, the proportion of second harmonic in the monochromatic light source was calculated. The results show that the second harmonic in the soft X-ray energy segment is mainly concentrated in the 180-300 eV and 450-800 eV, the share is mostly 15% below, the maximum can reach about 25%. Then, the calibration of the flat-response filter transmittance and the X-ray diode sensitivity was corrected 收稿日期:2020−02−26; 修订日期:2020−04−18 基金项目:中国工程物理研究院科学基金 (YZJJLX2016007);国家自然科学基金 (11775203) 作者简介:孙奥 (1995−),男,研究实习员,本科,主要从事 X射线线谱诊断方面的研究。Email:sunao2013@163.com 通讯作者:杜华冰 (1979−),男,助理研究员,硕士,主要从事 X射线辐射能流诊断方面的研究。Email:duhb@outlook.com 第 49 卷第 8 期 红外与激光工程 2020 年 8 月 Vol.49 No.8 Infrared and Laser Engineering Aug. 2020

Yb-doped all-fiber laser based on fiber saturable absorber

Abstract: An Yb-doped all-fiber Q-switched laser based on fiber saturable absorber was reported. In order to obtain laser pulses output with a higher peak power and a narrower pulse width, the saturable absorption effect of Ytterbium-doped fiber was used with laser. The 20/130 μm large mode double cladding Yb-doped fiber was used as the gain fiber. The 10/130 μm single mode double cladding Yb-doped fiber was used as saturable absorber. The laser adopted a all fiber-optic structure, and a relatively stable pulse output was obtained at a relatively low cost. The maximum average power was 3 W, the slope efficiency was 30%, the repetition rate was 10–100 kHz, and the minimum pulse duration was 344 ns with the spectral width of 0.05 nm and the central wavelength of 1 064 nm.

Deblurring methods for underwater 2D and 3D range-gated imaging

Abstract: Compared with traditional underwater cameras, the detection distance of underwater range-gated imaging can be increased by 2-3 times. Furthermore, based on this technology, fast high-resolution 3D imaging can be achieved. It has great potentials in underwater target detection and recognition, automatic navigation, marine scientific research and natural resources exploration. Although range-gated imaging can suppress the backscattering noise by space slicing, and achieve higher quality images, the backscattering noise of the sampling water volume still exists in gated images, resulting in low image signal-to-noise ratio and contrast, especially for distant targets or low reflectance targets. This paper systematically introduced author's research of deblurring methods for 2D and 3D range-gated imaging. In 2D imaging, two methods were proposed:the first was an algorithm of self-adaptive double-plateau histogram equalization to improve image contrast and better meet human vision; the second was to use a water-noise-reference denoising algorithm to improve the signal-to-noise ratio of target gated images. In 3D imaging, there were also two methods proposed:one was to use the water-noise-reference denoising algorithm for 3D reconstruction, and the other was to use the threshold-dependent joint bilateral filter algorithm for enhancing 3D images. The four proposed methods can be used independently or in combination for denoising enhancement of underwater range gated imaging.

Advances in the technology of 850 nm high-speed vertical cavity surface emitting lasers (Invited)

Abstract: Vertical-cavity surface-emitting lasers (VCSELs) have important applications in the short-distance optical interconnection attributed to their advantages, such as low cost, low threshold current, high modulation bandwidth and low power consumption. With the development of big-data and supercomputer technology, the performance demand of short-distance optical interconnection is increasing quickly, which also proposes a challenge for high-speed 850 nm VCSEL. In this paper, the latest development of high-speed 850 nm VCSEL technology was reviewed from the aspects of bandwidth-limited factors and new modulation methods, and the growing trend of this technology is prospected and summarized.

Three-dimensional shape measurement techniques of shiny surfaces

Abstract: There are a large number of three-dimensional (3D) shape measurement requirements and applications for objects with shiny surfaces, such as ceramics, ancient artifacts, and metal workpieces. However, the traditional fringe projection method cannot accurately measure shiny surfaces due to the large range of reflectivity of the objects with shiny surfaces and the limited maximum gray level of the camera. This paper reviewed the recent developments, application fields and future research directions of high dynamic range 3D shape measurement technologies of shiny surface. First, according to the principle and measurement method, the existing 3D measurement technologies of high dynamic range were divided into the following six categories: multiple exposures methods, projected patterns intensities adjusting methods, polarizing filters methods, color invariants methods, photometric stereo technology and miscellaneous technologies. Then, the advantages and disadvantages of these technologies were compared in detail and their adaptability was summarized. Finally, this 收稿日期:2019−12−28; 修订日期:2020−02−05 基金项目:国家重点研发计划资助 (2017YFF0106404);国家自然科学基金 (51675160) 作者简介:张宗华 (1974−),男,教授,博士,主要从事光学检测、三维数字成像和造型、条纹自动分析等方面的研究。Email:zhzhangtju@ hotmail.com 于瑾 (1993−),女,博士生,主要从事三维形貌测量、条纹分析和机器视觉等方面的研究。Email:yujin_15222125021@ hotmail.com 第 49 卷第 3 期 红外与激光工程 2020 年 3 月 Vol.49 No.3 Infrared and Laser Engineering Mar. 2020

Ultrathin invisibility cloaks based on metasurfaces

Abstract: The invisibility cloak as a longstanding fantastic dream for humans is now within the realm of possibility, thanks to the development of metamaterials. Transformation-optics-based invisibility cloaks have been proposed and realized in many frequency ranges by utilizing gradient-index metamaterials. However, due to the large size of device and difficulty in fabrication, transformation-optics-based invisibility cloaks are significantly limited in practical applications. Recently, metasurfaces as the 2D counterpart of metamaterials have attracted tremendous interests because of its thin thickness and strong capability in manipulating the electromagnetic waves. Ultrathin invisibility cloaks based on metasurfaces release the demand on bulky sizes and extreme parameters, thus promoting further development of invisibility cloaks. This review overviewed recent progress in ultrathin invisibility cloaks based on metasurfaces, focusing particularly on the working principles, implementation methods, advantages and disadvantages. Finally, some advice was put forward on the trends of this fast-developing research field.