Super-oscillatory lens (SOL) and super-critical lens (SCL) are the typical representatives of planar metalens which could achieve sub-diffractive focusing and imaging in far field by means of light field modulation. Through precisely modulating the interference effect of each diffractive unit, the electromagnetic wave could be oscillated faster than its maximum frequency components in a certain region of the target plane, and then the focal spot size is controllable in lateral and longitudinal directions. Compared with the traditional optical lens, the planar metalens is much more attractive in the fields of diffractive optics and nanophotonics due to its distinct advantages of powerful focusing capabilities, compact configuration, higher design freedom and the integratable properties, etc. In this review, we briefly introduce the field modulation mechanism and design principle of planar metalens. The research advances of the super-oscillatory lens and super-critical lens, as well as their applica-tions in far-field label-free super-resolution imaging, are discussed in detail. In addition, a perspective about the future outlook of planar metalens is summarized. Since the planar metalens has powerful capability in manipu-lating the light field, the rapid development in various applications would be gradually realized in the near future.

A dual-band frequency selective surface (FSS) with double screen was designed to cover the mid-infrared atmospheric window (3 μm~5 μm) and the far-infrared atmospheric window (8 μm~14 μm). This structure is composed of hexagonal metallic mesh and hexagonal resonant ring array. Simulation results show that the average transmission of FSS in atmospheric window is lower than 5%, and this structure is insensitive to the incident angle. The effect of the parameters on transmission properties was analyzed. The results show that adjusting the size of hexagonal ring structure can effectively adjust the -10 dB stopband bandwidth in 3 μm~5 μm, and increasing the size of metallic mesh can move the stopband in 8 μm~14 μm to long wave direction.

In order to study the effect of diffractive stray light on the modulation transfer function (MTF) caused by the binary phase-type Fresnel lens, the wave propagation method was used to simulate the propagation of light waves. The point spread function (PSF) of the system was obtained by coherent superposition of infinite diffrac-tive orders, and the MTF was obtained by the Fourier transform of the PSF. The differences between the modified values and the theoretical design values were analyzed when the number of level was 2, 4 and 8 at the diffrac-tion imaging system with an 80 mm Fresnel lens as primary lens. The results show that the effect of diffractive stray light on the MTF of the system decreases with the increase of the number of level. However, the deviation from the design value is less than 0.5% when the level is 4. Finally, we put forward the idea that the central region of the lens is processed into several levels and the edge part is 2-level to reduce the effect of diffractive stray light. The results show that the idea can achieve the purpose of suppressing effect of diffractive stray light.

Using the spoke structure as the elastic element, an adjustable range fiber grating torque sensor is de-signed. Two fiber Bragg gratings with different central wavelengths are symmetrically bonded on the upper and lower surfaces of the elastic plate parallel to the axial direction, respectively, as sensing elements and reference elements. By calibrating the relationship between the torque values and the central wavelength difference be-tween the two reflecting elements, the influence of ambient temperature can be eliminated, and the self com-pensation function of temperature can be realized. The elastic plate is connected with the inner wheel hub and the outer wheel hub by a bayonet, and is fixed by bolts, and the structure is easy to be disassembled so the range of the sensor can be adjusted by replacing the elastic plate. The dimension of spoke structure is optimized by using the finite element simulation software. The finite element simulation and experimental results show that the strain of the elastic element has a linear relationship with the central wavelength difference of two fiber grat-ings. When the range is 80 Nm, the average sensitivity of the sensor is 27.1 pm/Nm, the correlation coefficient is 0.997, the repeat ability error is 3.23% FS, and the hysteresis error is 1.03% FS.

It is necessary to calibrate the relative pose between the three-dimensional (3D) lidar and the GPS / INS integrated navigation system for their combination. Because of the phenomenon of point cloud distortion in vehicle moving process, a method of coordinate correction for laser scanning point in single frame point cloud is proposed. Aiming at the calibration problem, a method of extrinsic parameter calibration is proposed, based on ICP algorithm, hand-eye calibration model, and least squares method. Monte Carlo simulation results show that the algorithm is accurate and effective. The calibration experiment is carried out on the unmanned vehicle labor-atory JJUV-6, and the 3D relative pose relations are obtained. It shows that after calibration the effect of 3D point clouds reconstruction is better, and the overlapping degree of point clouds is close to the registration effect. For the purpose of applications, it can meet the needs of 2D map construction and 3D environment reconstruction.

The ability to analyze the spectra of 532 nm/354.7 nm backscatter signal of atmosphere for Mach-Zehdner interferometer is demonstrated. The Mach-Zehdner interferometer accepts return signal. The phase difference and interference contrast are measured, which are formed by the interferometer’s double arm, polarization and quadro-channels, and Doppler frequency shift of atmosphere and backscatter ratio of aerosol backscatter to molecular backscatter are derived. Transmitter laser can operate with multi-longitudinal mode, and Mie backscattering and Rayleigh backscattering analysis spectrograph is free from locking to laser frequency. Analysis method of simultaneous measurements atmosphere aerosol backscattering ratio profile and wind pro-file are also discussed. If Mach-Zehnder interferometer is employed as atmospheric backscatter signal’s fre-quency spectrum analyzer, this high spectral resolution lidar will become an atmosphere analysis instrument with excellent performance and anticipant prospect.

A control system for complex curved surface laser shock processing was introduced, which was a set of automatic and digital control system operation, and controlled by the industrial PC/PLC. And it completed the real-time online monitoring and information interaction feedback, belonging to the open distributed system, by the fact that the re-mote monitoring and control system status of processing effectively avoid the occurrence of major accidents. This system was laser shock processing core device (including laser, robot, auxiliary control, quality testing device and auxiliary system, etc.), that implemented each link of information interaction and systems work together. By the remote monitoring, control system status of processing effectively avoided the occurrence of major accidents. At the same time, the control system added process of laser shock processing test data record function. According to actual demand parameters database called the background, parameter optimization was processed effectively. In addition, the system also could realize laser shock processing model established, complex surface machining trajectory plan-ning automatically and processing strategy. The system can realize the automatic production of the whole blade la-ser impact of aero engine, and it is already in the engineering application stage. In view of the problem that the pre-sent domestic industrialization level of laser shock peening equipment is not high, a laser shock peening equipment is developed by using fixed optical system structure and modular design method. The design scheme of laser shock peening equipment, the characteristics of laser optical path arrangement and the system control method are ana-lyzed, and the technical indexes of laser shock peening equipment are tested. Keep room temperature stable at (22 ± 2) ℃ and 20 minutes after the device is switched on. The technical parameters such as the maximum output single pulse energy up to 25 J, energy instability <3%, pulse width which can be continuously adjustable between 16 ns and 20 ns, pulse width instability <±1 ns, beam divergence <2.5 mrad, beam points instability<50 μrad, the repetition frequency of 0.5 Hz ?5 Hz are achieved. The transmission efficiency of the optical system is about 92%. The thick-ness of the constraint layer is uniform and the flow rate is continuously controlled. The test results show that the performance of the laser shock peening equipment is good.

A control system for complex curved surface laser shock processing was introduced, which was a set of automatic and digital control system operation, and controlled by the industrial PC/PLC. And it completed the real-time online monitoring and information interaction feedback, belonging to the open distributed system, by the fact that the re-mote monitoring and control system status of processing effectively avoid the occurrence of major accidents. This system was laser shock processing core device (including laser, robot, auxiliary control, quality testing device and auxiliary system, etc.), that implemented each link of information interaction and systems work together. By the remote monitoring, control system status of processing effectively avoided the occurrence of major accidents. At the same time, the control system added process of laser shock processing test data record function. According to actual demand parameters database called the background, parameter optimization was processed effectively. In addition, the system also could realize laser shock processing model established, complex surface machining trajectory plan-ning automatically and processing strategy. The system can realize the automatic production of the whole blade la-ser impact of aero engine, and it is already in the engineering application stage. In view of the problem that the pre-sent domestic industrialization level of laser shock peening equipment is not high, a laser shock peening equipment is developed by using fixed optical system structure and modular design method. The design scheme of laser shock peening equipment, the characteristics of laser optical path arrangement and the system control method are ana-lyzed, and the technical indexes of laser shock peening equipment are tested. Keep room temperature stable at (22 ± 2) ℃ and 20 minutes after the device is switched on. The technical parameters such as the maximum output single pulse energy up to 25 J, energy instability <3%, pulse width which can be continuously adjustable between 16 ns and 20 ns, pulse width instability <±1 ns, beam divergence <2.5 mrad, beam points instability<50 μrad, the repetition frequency of 0.5 Hz ?5 Hz are achieved. The transmission efficiency of the optical system is about 92%. The thick-ness of the constraint layer is uniform and the flow rate is continuously controlled. The test results show that the performance of the laser shock peening equipment is good.

In the locomotive operation, because of the hunting motion caused by pure conical tread, a lateral force and com-plex creep force between the wheel and rail will emerge and result in attack angle between the wheel and rail when crossing a curve line. Although the attack angle is microscopic, it affects the wheel/rail contact loss and vehicle safety seriously and attack angle is a key index to evaluate the stability of snakelike motion in the train. Monitoring and analyzing the wheel/rail contact condition and the change of attack angle in the locomotive operation play a signif-icant role in the stability and safety of vehicle operation. Due to the complexity of the running train and the small angle of attack, it is difficult to measure the angle between the wheel and rail. A method for combining the on-board camera with the laser line is presented to complete the image acquisition and detect the attack angle based on the laser line and the direction of motion as collinear wheel on the rail surface. The laser line and orbital edge line are obtained by some algorithms such as image pre-processing algorithm, image correction, Meanshift smoothing, and Radon line detection. The angle between the laser line and orbital edge in the image can be got through a series of image processing algorithms, which can reflect the attack angle in the running of locomotive. Radon detection algo-rithm is used to detect the relative position between laser line and rail edge line, and different conditions of under-shooting changes are compared by simulation. The comparison between simulation data and experimental data shows that the method can simply realize the detection of attack angle and it is feasible enough. The results of detec-tion illustrate that the change of attack angle is between 0.355 and -0.72 degrees, and the maximum error is 0.091 degrees. Finally, the correction method of the detection error and measurement accuracy analysis is given, which increases the stability of the detection method and demonstrates that it can meet the demand in engineering applica-tions. It costs about 500 ms when the system completes primary detection of attack angle, which indicates that the detection speed is fast enough, and it can meet the detection requirements in engineering applications. However, some factors such as illumination and external vibration still need to be further studied to emphasize the robustness of the system. This method lays a foundation for further monitoring the condition of train operation and improving the safety mechanism of train.

In the locomotive operation, because of the hunting motion caused by pure conical tread, a lateral force and com-plex creep force between the wheel and rail will emerge and result in attack angle between the wheel and rail when crossing a curve line. Although the attack angle is microscopic, it affects the wheel/rail contact loss and vehicle safety seriously and attack angle is a key index to evaluate the stability of snakelike motion in the train. Monitoring and analyzing the wheel/rail contact condition and the change of attack angle in the locomotive operation play a signif-icant role in the stability and safety of vehicle operation. Due to the complexity of the running train and the small angle of attack, it is difficult to measure the angle between the wheel and rail. A method for combining the on-board camera with the laser line is presented to complete the image acquisition and detect the attack angle based on the laser line and the direction of motion as collinear wheel on the rail surface. The laser line and orbital edge line are obtained by some algorithms such as image pre-processing algorithm, image correction, Meanshift smoothing, and Radon line detection. The angle between the laser line and orbital edge in the image can be got through a series of image processing algorithms, which can reflect the attack angle in the running of locomotive. Radon detection algo-rithm is used to detect the relative position between laser line and rail edge line, and different conditions of under-shooting changes are compared by simulation. The comparison between simulation data and experimental data shows that the method can simply realize the detection of attack angle and it is feasible enough. The results of detec-tion illustrate that the change of attack angle is between 0.355 and -0.72 degrees, and the maximum error is 0.091 degrees. Finally, the correction method of the detection error and measurement accuracy analysis is given, which increases the stability of the detection method and demonstrates that it can meet the demand in engineering applica-tions. It costs about 500 ms when the system completes primary detection of attack angle, which indicates that the detection speed is fast enough, and it can meet the detection requirements in engineering applications. However, some factors such as illumination and external vibration still need to be further studied to emphasize the robustness of the system. This method lays a foundation for further monitoring the condition of train operation and improving the safety mechanism of train.

In the field of advanced processing and manufacturing, precision guide and stage are the important moving parts, which ensure the accuracy of machine tool manufacturing and instrument measurement. The precise installation and adjustment of guide and stage, the detection and control of their location and motion, need to measure multiple spatial parameters of the moving object simultaneously. The traditional commercial measurement instruments, such as the HP5529A Dynamic Calibrator and the Renishaw laser interferometer, can only measure one parameter at a time, and the measurement process is very complicated. Therefore, multi-parameter measurement has become one of the research focuses. At present, domestic and foreign research institutions and manufacturers have developed some measurement devices, but they have the disadvantages of complex structure, uneasy adjustment, small measurement range and low measurement accuracy.In order to simplify the measurement structure, expand the measurement range and improve the measurement accuracy, a three-degree-of-freedom common-path laser measurement system, which is a combination of the laser interferometer with the auto-collimator, can realize the measurement of three parameters of displacement, yaw and pitch angles simultaneously with the advantages of large stroke, high precision and non-contact.Common optical path arrangement was adopted to design the three-degree-of-freedom laser measurement system for measuring 1D displacement and 2D angles of a moving stage simultaneously on the basis of the principles of Michelson interference and laser auto-collimation. In the displacement measurement, the fine resolution of dis-placement measurement was achieved by using polarization interference and optical path difference doubling tech-nique. Adopting four-beam-signal detection technique and signal differential processing, high-quality displacement output signals were obtained. In the angle measurement, changes in yaw and pitch of a moving stage caused the position change of the mirror which was mounted on the stage. The incident beam was reflected by the mirror and detected by a four-quadrant detector. According to the position change of the spot, yaw and pitch angles were de-tected precisely. In order to verify the effectiveness of the system, the stability and resolution tests and the compari-son experiments with the British Renishaw XL-80 laser interferometer were done. Experimental results show that the system has the resolution of 0.8 nm for displacement measurement and 0.2 " for angle measurement. Compared with the results of XL-80 laser interferometer, the maximum deviation of displacement measurement is less than 100 nm within the measurement range of 50 mm. The maximum deviations of yaw and pitch are 0.5 " and 0.4 ".

In the field of advanced processing and manufacturing, precision guide and stage are the important moving parts, which ensure the accuracy of machine tool manufacturing and instrument measurement. The precise installation and adjustment of guide and stage, the detection and control of their location and motion, need to measure multiple spatial parameters of the moving object simultaneously. The traditional commercial measurement instruments, such as the HP5529A Dynamic Calibrator and the Renishaw laser interferometer, can only measure one parameter at a time, and the measurement process is very complicated. Therefore, multi-parameter measurement has become one of the research focuses. At present, domestic and foreign research institutions and manufacturers have developed some measurement devices, but they have the disadvantages of complex structure, uneasy adjustment, small measurement range and low measurement accuracy.In order to simplify the measurement structure, expand the measurement range and improve the measurement accuracy, a three-degree-of-freedom common-path laser measurement system, which is a combination of the laser interferometer with the auto-collimator, can realize the measurement of three parameters of displacement, yaw and pitch angles simultaneously with the advantages of large stroke, high precision and non-contact.Common optical path arrangement was adopted to design the three-degree-of-freedom laser measurement system for measuring 1D displacement and 2D angles of a moving stage simultaneously on the basis of the principles of Michelson interference and laser auto-collimation. In the displacement measurement, the fine resolution of dis-placement measurement was achieved by using polarization interference and optical path difference doubling tech-nique. Adopting four-beam-signal detection technique and signal differential processing, high-quality displacement output signals were obtained. In the angle measurement, changes in yaw and pitch of a moving stage caused the position change of the mirror which was mounted on the stage. The incident beam was reflected by the mirror and detected by a four-quadrant detector. According to the position change of the spot, yaw and pitch angles were de-tected precisely. In order to verify the effectiveness of the system, the stability and resolution tests and the compari-son experiments with the British Renishaw XL-80 laser interferometer were done. Experimental results show that the system has the resolution of 0.8 nm for displacement measurement and 0.2 " for angle measurement. Compared with the results of XL-80 laser interferometer, the maximum deviation of displacement measurement is less than 100 nm within the measurement range of 50 mm. The maximum deviations of yaw and pitch are 0.5 " and 0.4 ".

The ability to analyze the spectra of 532 nm/354.7 nm backscatter signal of atmosphere for Mach-Zehdner inter-ferometer is demonstrated. The Mach-Zehdner interferometer accepts return signal. The phase difference and inter-ference contrast are measured, which are formed by the interferometer’s double arm, polarization and quad-ro-channels, and Doppler frequency shift of atmosphere and backscatter ratio of aerosol backscatter to molecular backscatter are derived.Unlike the previously developed high spectral resolution lidar (HSRL) by use of Fabry–Perot interferometers or iodine filters, the Mach-Zehdner interferometer (MZI) receiver does not separate the molecule and particle scatter-ings. We perform the backscatter ratio determination by deriving the interference contrast from the signal delivered by the different channels. In the same way, the Doppler shift is calculated by the difference in the interference state between the outgoing pulse and the backscattered signal. For both retrievals it is then unnecessary to lock the emitted frequency onto the receiver as required by most HSRL devices to reduce bias in the signal analysis. Only relative frequency stability is necessary during signal averaging, which is a more easily achievable requirement. Another characteristic of the MZI receiver is that it transmits all the incident photons in contrast to most of the HSRL devices that use only the signal that is transmitted through a highly selective filter, and Michelson interferometer receiver re-flects half of all the incident photons. The MZI receiver allows larger signal to noise ratio (SNR) for the MZI com-pared with the HSRL devices, as long as the noise is not dominated by the background light contribution. It must also be noted that the measurements of the backscatter ratio and the wind velocity can be performed independently and do not require cross corrections.We prove physics theory of an HSRL using a laser that oscillates in a multi-longitudinal mode. The instrument ex-ploits the light backscattered by particles using an MZI with an optical path difference matched to the free spectral range of the laser longitudinal modes. Rayleigh and Mie scattering components are acquired using an MZI with the same free spectral range (FSR) as the transmitted laser. The transmitted laser light is measured as a reference signal with the same MZI. Using rectangular prism reflex light path built up double optical arms, one of the same class ge-ometrical model of MZI is devised. With combination magnesium fluoride crystal and mountain crystal two crystals material, a quarter wave plate is devised, and then it makes MZI adapt to two types 532 nm/354.7 nm wavelength light echo synchronously. If MZI is employed as atmospheric backscatter signal’s frequency spectrum analyzer, this high spectral resolution lidar will become an atmosphere analysis instrument with excellent performance and antici-pant prospect.

Based on the requirement of high precision map construction for unmanned vehicle, the relative pose calibration between three-dimensional lidar and GPS/INS integrated navigation system is necessary. The coordinate systems of the three-dimensional lidar and the GPS/INS integrated navigation system are established according to the charac-teristics of each type, respectively. Aiming at the problem that the relative position between the two coordinate sys-tems can not be measured accurately and the relative rotation angles between them are difficult to be measured, the calibration of three-dimensional (3D) lidar external parameters is studied. Based on the point cloud registration, the hand-eye calibration model of 3D lidar and GPS/INS integrated navigation system is established. The point cloud pose is obtained after registration by ICP algorithm. Using the multi-pairs point cloud pose, the extrinsic parameters are calculated by the least square method.The 3D lidar data are resolved into continuous single frame point clouds, and the longitude and latitude coordi-nates of GPS are converted into plane coordinates. At the same time, the data of the two kinds of sensors are syn-chronized in time, and the pose tag is attached to each point cloud frame. Aiming at the phenomenon of point cloud distortion in vehicle moving process, a method of coordinate correction for laser scanning point in single frame point cloud is proposed. The point cloud with the attitude angle changed is chosen as the point cloud pair. A point cloud registration algorithm is used to register the corresponding point cloud pairs, and the new pose after registration is obtained. The relative pose of each pair of cloud points before and after registration can satisfy the model of hand-eye calibration. Finally, a set of over determined equations is constructed by multi-pairs registration data satis-fying the “non-parallel condition”, and the transfer matrix is solved by decoupling. The rotation matrix is trans-formed into quaternion form, and the rotation parameters are solved by the least squares method. After the rotation parameters are obtained, the translation parameters are computed using the point cloud positions before and after registration.Monte Carlo simulation results show that the algorithm is accurate and effective. The calibration experiment is carried out on the unmanned vehicle laboratory JJUV-6, and the 3D relative pose relations are obtained. It shows that after calibration the effect of 3D point clouds reconstruction is better, and the overlapping degree of point clouds is close to the registration effect. For the purpose of applications, it can meet the needs of 2D map construc-tion and 3D environment reconstruction.

The torque parameters of the mechanical equipment can reflect the performance of the rotating power mechanical system and provide scientific data for the parts to be measured. Compared with the electric and magnetic torque sensors, FBG sensors have many advantages such as high temperature resistance, radiation resistance, safety and reliability. Using the spoke structure as the elastic element, an adjustable range FBG torque sensor is designed. The FBG torque sensor mainly consists of an inner wheel hub, an outer wheel hub, four elastic plates, a coupling and FBG. Two FBGs with different central wavelengths are symmetrically bonded on the upper and lower surfaces of the elas-tic plate parallel to the axial direction, respectively, as sensing elements and reference elements. In the packaging process, by applying slight adjustable pre-stressing on both sides of the FBG, it can effectively prevent the contrac-tion of FBG in the curing process, as well as the chirp of FBG reflection spectrum and nonlinear distortion of center wavelength. When the torsion force is applied to the hub, two FBGs are subjected to tension and pressure respectively, leading to the center wavelength of the grating moving to opposite directions. By calibrating the relationship between the torque values and the central wavelength difference between the two reflecting elements, the influence of ambi-ent temperature can be eliminated, and the self compensation function of temperature can be realized. The angle between adjacent elastic plates is 90o, the elastic plate is connected with the inner wheel hub and the outer wheel hub by a bayonet, and is fixed by bolts. At the same time, a new type of elastic plate with double grooves is designed on the basis of strip elastic plate, and the range of the sensor is adjusted by replacing the elastic plate without changing the overall structure of the torque sensor. The inner wheel hub is connected with the coupling, thereby improving the practicability and the versatility of the sensor. The torque sensing model of fiber grating is established and the dimen-sion of spoke structure is optimized by using the finite element simulation software. The finite element simulation and experimental results show that the strain of the elastic element has a linear relationship with the central wave-length difference of two fiber gratings. When the range is 80 Nm, the average sensitivity of the sensor is 27.1 pm/Nm, the correlation coefficient is 0.997, the repeat ability error is 3.23% FS, and the hysteresis error is 1.03% FS.

There is a contradiction between high resolution and light weight of large aperture spaced imaging system. So many research institutions have begun to explore new imaging methods. Diffractive lens through microstructure to modu-late light waves can be fabricated on thin films with very low surface mass density. With the benefits of small size, light weight and loose surface tolerance, diffraction imaging system has become a great potential technical solution. Fresnel zone plate (FZP) and photon sieves are the most commonly used microstructures, while the low diffraction efficiency limits the applications of photon sieves. FZP fabricated by binary optics technology can achieve 40.5% diffraction efficiency when the level is 2, and 81% for 4 levels. On the other hand, the diffraction efficiency is a function of the ratio of the design wavelength to the illumination wavelength. Therefore, the non design orders dif-fractive light may affect the performance of diffractive imaging system and can’t be ignored. In order to study the effect of diffractive stray light caused by non design orders on the modulation transfer function of diffractive imag-ing system, the wave propagation method was used to simulate the propagation of diffractive light waves. By co-herent superposition of finite diffractive orders, we calculated the PSF at 17 signal wavelength which evenly covers the spectral range. The sum of these results is the polychromatic PSF. After the point spread function (PSF) of the system was obtained, the Fourier transform of the PSF was done to calculate the modulation transfer function (MTF). The differences between the modified values and the theoretical design values were analyzed when the number of level was 2, 4 and 8 at the diffraction imaging system with an 80 mm Fresnel lens as primary lens. The MTF decreased at low frequency with 2-level Fresnel primary lens and the biggest decrease was 6.6%. The deviation from the design value is less than 0.5% when the level is 4 and 8. The results show that the effect of diffractive stray light on the MTF of the system decreases with the increase of the number of level. Finally, we found that only the incident light illuminating the primary’s central area can directly attach the image plane by non design diffractive orders. So, we put forward the idea that the central area of the diffractive primary lens is processed into 4 or 8 levels and the edge part is 2 levels to reduce the effect of diffractive stray light. The MTF increased apparently after opti-mized and was close to the design value. It shows that the idea can achieve the goal of suppressing the diffractive stray light.

Military infrared detection technology mainly focuses on the infrared radiation of target in mid-infrared atmospheric window (3 μm~5 μm) and the far-infrared atmospheric window (8 μm~14 μm), therefore reducing the infrared transmittance of the target in these two atmospherics can effectively decrease the possibility of detection. Frequency selective surface (FSS) has good spatial filtering characteristics and can be used to suppress the infrared transmit-tance of the target in the band of interest. In order to extend the bandwidth of FSS and realize multi-band selection, we combine hexagonal ring structure with hexagonal metal mesh. Meanwhile, we adopt double layers to further ex-pand the bandwidth. Simulation results show that the infrared transmission of the structure is lower than 5% in 3 μm~5 μm and 8 μm ~14 μm. The structure realizes the suppression of infrared transmission in mid-infrared atmos-pheric window and far-infrared atmospheric window. The absorption of the structure is nearly 10% in 3 μm~5 μm and 8 μm~14 μm, which indicates the low infrared radiation of the structure. Moreover, the reflection of the FSS is close to 90%, which suggests that the stopband characteristic of the structure is mainly due to the reflection en-hancement caused by the scattering field produced by the surface current. The surface current distributions at 4 μm and 10 μm show that the stopband characteristics at 4 μm is mainly caused by the scattering field produced by the surface current of hexagonal ring structure, while the stopband characteristics at 10 μm is mainly caused by the scattering field produced by the surface current of hexagonal metal mesh. The structure is insensitive to polarization. At oblique incidence, the structure can still maintain low infrared transmittance in 3 μm~5 μm and 8 μm~14 μm. When the line width w decreases from 0.25 μm to 0.10 μm, the equivalent size of the hexagonal metal mesh increas-es and the spacing of the hexagonal ring structure units decreases, which causes the transmission curve moves to-wards the long wave and the -10 dB bandwidth in 3 μm~5 μm increases from 2.47 μm to 3.08 μm. When L1 reduces from 0.75 μm to 0.60 μm, the spacing of the hexagonal ring structure units increases, which weakens the coupling effect between the units, and the -10 dB bandwidth in 3 μm~5 μm reduces from 2.92 μm to 1.65 μm, meanwhile grating lobe appears in 3 μm~5 μm. When L2 changes from 0.85 μm to 1 μm, the transmission curve in 8 μm~14 μm moves towards long wave due to the increase of equivalent size of the hexagonal metal mesh.

The phase measuring deflectometry (PMD) has attracted extensive attention to researchers in recent years as it has the advantage of being fast, non-coherent and high sensitivity. The high sensitivity of PMD allows measuring gradi-ent changes in the range of micro-scale and local height changes in the range of nanometers, which enables PMD as an effective tool for high precision inspection of defects or local height variation. The accuracy of the PMD is related to the phase reliability of the captured fringe pattern. Errors in the phase map influence the accuracy of the whole measurement. When testing low reflectivity specular surfaces like cell phone shell, contrast of the distorted fringe patterns is low, and there are always relatively big errors in the phase map. The phase error characteristics in PMD system when testing low reflectivity surfaces are analyzed. The results illustrate that the random phase error increas-es rapidly while the nonlinear error drops slowly with the decreasing of the tested surface reflectivity. In order to at-tain high precision measurement of low reflectivity specular surface, a robust error reduction method based on wavelet de-noising is presented to reduce the phase error. The optimal wavelet parameters for denoising the aimed noise level are carried out by simulation, which are 5 decomposition level, ‘soft’ thresholding and ‘rigrsure’ thresh-olding rule. The error reduction method is compared with the least-square TPU method and low-pass Gaussian filter method. As the result, when compared to the least-square TPU method, the method based on wavelet de-noising needs much less shooting time and has a more outstanding error reduction effect. In comparison with the low-pass Gaussian filter method, the wavelet de-noising method performs better in the preservation of phase details. The ex-periment of measuring a typical mobile shell shows clearly the superiority of the method based on the wavelet de-noising. In some situations, if the curvature maps are required for the inspection of defects, especially when the tested surfaces have low reflectivity, the method based on wavelet de-noising would be quite suitable for error reduc-tion. The method based on wavelet de-noising is also suitable to detect small defects and for the measurement of the high reflective surface to reach higher precision. In the experiment of measuring a plane mirror, the RMS phase error with the method based on wavelet de-noising is 5 times smaller than that with only 6-step phase shifting method.

Improving the imaging resolution has always been one of the most important topics since the invention of optical microscope. Due to the fundamental laws of wave optics, the focusing and imaging resolution of traditional refrac-tion and diffraction lenses are subject to the Rayleigh Criterion (0.61λ/NA), and the spatial resolution of optical mi-croscopy is restricted to ~200 nm at visible light. Tremendous efforts have been made to fight against the diffraction limit in the past decades, and several novel approaches have been invented which could be categorized as near-field and far-field modes. For the near-field techniques, such as NSOM, superlens, hyperlens, microsphere lens, they al-ways suffer from the challenges of near-field operation and small field of view, which make them not meet some requirements of practical applications. Although very high imaging resolution in far-field could be achieved by the fluorescence-based approaches, all these techniques have a common feature that is quite limited to biological do-main because of the requirement to put dyes and fluorescence into objects. Therefore, the label-free technique for super-resolution imaging in far field is very important for general applications. Recent advance in this field is the de-velopment of planar metalens which could achieve sub-diffractive focusing and imaging in far field by means of light field modulation. Super-oscillatory lens (SOL) and super-critical lens (SCL) are the typical representatives of planar metalens. Through precisely modulating the interference effect of each diffractive unit, the focal spot size in a certain region of the target plane is controllable in lateral and longitudinal directions. Combined with the confocal technique, the label-free superresolution imaging could be realized in far field with purely non-invasive manners. Compared with the traditional optical lens, the planar metalens is much more attractive due to its distinct ad-vantages of powerful focusing capabilities, compact configuration, higher design freedom and the integratable prop-erties, etc. In this review, we briefly introduce the field modulation mechanism and design principle of the planar metalens. The research progress of the super-oscillatory lens and super-critical lens, as well as their applications in far-field label-free super-resolution imaging, is presented in detail. The advantages and limitations of that planar lens are compared and briefly discussed. A perspective about the future outlook of planar metalens is summarized. Since the planar metalens has a powerful capability in manipulating the light field, the rapid development in various ap-plications would be gradually realized in the near future.

Schottky heterojunctions based on grapheme-silicon structures are promising for high-performance photo-detectors. However, existing fabrication processes adopt transferred graphene as electrodes, limiting process com-patibility and generating pollution because of the metal catalyst, and the high reflectivity of the silicon surface makes the effective absorption much lower than desired.

The chiral microstructure has special optical properties, which is of great significance in the study of circular di-chromatic and optical dispersion.

Nano-scale lasers and optical amplifiers are the core devices of optoelectronic integration of chips in the fu-ture. Rare-earth optical materials with large optical gain are of great importance for a wide variety of applica-tions in photonics and quantum information, especially in the realization of efficient lasers and amplifiers. Until now, such materials have achieved a gain of less than a few dB/cm, rendering them unsuitable for applications in nanophotonic integrated circuits.