We propose a multi-hole periodic silver film array structure and explore the optical properties of the proposed structure using the finite-difference time-domain method. Simulation results reveal that when linearly polarized light is incident on the metal surface, the structure possesses extraordinary optical transmission due to the excitation of the surface plasmon polaritons and localized surface plasmon resonances. In view of this phenomenon, the optical transmission property of the proposed structure is further optimized by the angle between the central hole and side holes, polarization angle of the incident light, and structural parameters (i.e., diameters of the central hole and side holes, structural thickness, space between side holes and central hole). Further analysis of the variation of the transmission peak under different refractive indices shows that the structure has a high sensitivity to the refractive index of the surrounding environment. Thus, the proposed structure has potential applications in surface plasma filters and refractive index sensors.

To improve the accuracy of cloud detection, we propose a multi-scale dilation convolutional neural network method. Combining with the characteristic of satellite images, we design the deep convolution network structure, which includes a deep-feature coding module, a local dilation perception module, and a cloud-dense decoding module. First, the deep-features of cloud are obtained by the basic convolutional layer in conjunction with the coding module. Second, multi-scale dilation convolution layers jointed with pooling layers are used to perceive corporately. A nonlinear function is employed in each block to improve the effectiveness of network model expression. Finally, the cloud-dense decoding module integrate the features corresponding to those included in the coding module and then utilize the L1 regularization upsampling algorithm to accomplish the end-to-end pixel-level cloud detection task. Cloud detection experiments are performed in the typical cloud mask areas; the results are compared with those of the Otsu algorithm and the FCN-8S method. The results indicate that the accuracy of proposed method is higher and the Kappa coefficient is effectively improved.

The performances of a double-beam thin-film interferometric fiber (DBTFIF) microphone based on phase demodulation is studied. The effects of the direct current (DC) subentry, alternating current (AC) subentry and phase difference of three interference signals on the output performances of this DBTFIF microphone are analyzed by simulation. Through the comparison method, the output performances of this DBTFIF microphone based on phase demodulation are studied experimentally as well. The experimental results show that the measurement of acoustic signals with a sensitivity of about 193 mV/Pa at 1 kHz and the frequency response ranging from 200 Hz to 4 kHz with a fluctuation of about ±3 dB can both be achieved. This research can be well used in the fields of acoustic detection, voice recognition, and so on.

A novel video saliency detection method is proposed based on the spatiotemporal features of superpixels, which is used to the superpixel segmentation of images and extract the features of color gradient and motion gradient for the construction of a spatial-temporal gradient map of superpixels. The average weighted geodesic distance is used to measure the spatiotemporal saliency degree of each superpixel relative to its neighbor on the spatiotemporal gradient map, and thus the spatiotemporal saliency map is formed. In order to obtain the motion coherency map, the motion entropy in the multiple continuous frames is computed to represent the motion coherence of motion object over time. The fusion of spatiotemporal saliency maps and motion coherency maps is applied to locate in the salient motion using adaptive segmentation. In addition, the performance of the proposed method is compared with those of the other algorithms in experiments from two perspectives of visual analysis and qualitative evaluation. The results show that the proposed method is robust and suitable for the detection of moving targets in videos within complex background texture and changeable environment. Moreover, the detection precision is up to 92%.

The optical rotation property of a polarized alkali vapor cell is demonstrated. The polarized atomic gas chamber can be macroscopically equivalent to a Faraday polarized crystal, whose optical rotation coefficient is related to the spin precession of atoms. A novel atomic spin precession detection scheme is proposed by means of the detection of the phase difference between the left and the right circularly polarized probe lights when a circularly polarized probe light is propagating through the vapor cell. Based on the modified all-fiber reflective Sagnac interferometer, the fiber atomic spin precession detection system is built and the detection of spin precession signals in the spin exchanged relaxation free states is realized by a circularly polarized light. The detection scheme is verified and the gyroscopic effect is realized on the experimental platform of an atomic spin gyroscope. The experimental results confirm that the proposed theory is correct. The performance of this gyroscope is preliminarily tested and its zero-bias instability is 0.29 (°)/h.

The Stokes vector measurement error equation including alignment errors of half-wave plate (HWP) and quarter-wave plate (QWP) fast axes is established. The influences of alignment errors of wave plate fast axes on Stokes vector measurement accuracy for seven typical incident lights are analyzed. A calibration method of Stokes vector measurement errors for any incident light is given. The simulation results show that the greater the degree of polarization is, the larger the polarization measurement error is. The polarization measurement accuracy is selected to evaluate the system performance when the degree of polarization for the incident light equals to 1. A method for optimizing the alignment errors of wave-plate fast axes is proposed. When the condition number of the measurement matrix is less than 1.84, the selection of splitting ratio 0.772/0.228 can minimize the influences of alignment errors of wave-plate fast axes on the polarization measurement accuracy. To ensure a polarization measurement accuracy of 2%, the alignment error of HWP fast axis should be within ±0.15° and that of QWP fast axis is within ±0.52°.

An absolute distance measurement method is proposed based on coherent detection by a femtosecond optical frequency comb. The absolute distance measurement is realized by the detection of coherence patterns between measurement signals and reference signals. The measurement model of the first-order coherence function is studied. The measurement system based on an unbalanced Michelson interferometer is constructed. The target distance is obtained by the envelope fitting of the first-order coherence function and by the high-precision extraction of peaks on the overlapped pulse positions. The 3 m absolute distance measurement experiment on a long range guide is designed and a real-time comparison with those by the commercial interferometers is conducted. In addition, the ambient factors and system errors are analyzed based on a large number of experimental results. The errors are eliminated and compensated. The results show that in the 500 min long term measurement process, the maximum measurement error is 5.85 μm and the standard deviation is 2.20 μm as for the proposed method with a measurement range of 3 m.

The tunable single-frequency (SF) narrow-linewidth fiber laser with all-fiber complex cavity structure is designed, which is composed of an optical fiber tunable filter, a high-precision ring filter, and a fiber loop mirror. A 980-nm semiconductor laser is used as the pumping source, and the ytterbium-doped fiber is employed as the gain medium and saturable absorber, then a wide-spectrum tunable single-frequency narrow-linewidth laser output from 1030 nm to 1090 nm is successfully realized. When the pump power is up to 300 mW, the output power is 18.5 mW and the slope efficiency is 7.95% at the wavelength of 1070 nm. There is no mode hopping phenomenon within 1 h, and the standard deviation of power stability is less than 1%. When the pump power is 200 mW, the linewidth is measured by the delay self-heterodyne method, and the average line width in the wavelength tuning range is 8.7 kHz, and the relaxation oscillation frequency is 64 kHz.

Electromagnetic stirring technique is introduced into the processing of laser cladding for preparing Co-based alloy coatings. In this research, a detailed analysis of hot corrosion resistance is conducted for a cladding layer applied in a salt mixture at 750 ℃ for 100 h with and without the assistance of electromagnetic stirring. The cladding layer is found to have poor hot corrosion resistance without magnetic field assistance. After hot corrosion for 60 h, the inside of the coating shows severe internal oxidation and vulcanization as well as substantial weight loss. In contrast, electromagnetic stirring produces a cladding layer that effectively suppresses the inward intrusion of S and Cl- ions in the etching solution. This suppression facilitates the formation of stable protective Cr2O3 and CoCr2O4 spinel oxide films so that only slight cracking and peeling occur during the entire hot corrosion stage. The addition of electromagnetic stirring effectively refines and homogenizes the microstructure of the coating, and also promotes the rapid formation of a protective oxide film on the coating surface, which can prevent the diffusion of molten salt; thus, the hot corrosion resistance of the coating can be further improved.

As for the large size measurement, motion tracking, 3D reconstruction and visual positioning in the field of visual positioning measurement, there exist many problems of system calibration difficulty, method complexity, low precision and so on for a multi-camera positioning system with no public or less public field of view. Thus an integrated calibration method for a multi-camera positioning system is proposed based on a precision two-axis turntable, in which the two-axis turntable provides an angle reference. When the turntable passes through the fields of view of all cameras at once, each camera shoots sequentially the calibration images. The internal parameters of each camera and the external parameters from each camera to the turntable are solved. The turntable coordinates are used to calculate the external parameters of cameras. The whole calibration process is controlled by programming. The integration and automation of figure-collection calibration for the multi-camera system are achieved, which greatly reduces the workload of calibration. The calibration principle of this multi-camera positioning system is analyzed and verified by experiments as well. The reprojection errors of the internal parameters of two cameras are less than 0.17 pixel and the system positioning accuracy is less than 1 mm. The results show that the proposed method is feasible, accurate and operable, which can be applied in the calibration process of a multi-camera positioning system with no public or small public field of view.

Defect detection is a challenging problem due to the diversity of appearances, sizes and locations of button surface defects. A low-rank information based button image reconstruction method is proposed based on the spatial structure correlation of defect image information, in which the low-rank constrained defect image matrix is utilized to reconstruct the defect-free button surface images through regression and the background subtraction method is adopted to separate the residual images with defect information, and thus the defects can be effectively extracted through the locally weighted adaptive threshold. In addition, in this method, the minimum rank of the residual matrix is converted into the minimum nuclear norm, the regression coefficients are solved by the alternating direction multiplier method, and thus the image reconstruction is realized with positive samples. According to the performance test of the reconstructed button sample set, it is verified that the proposed method is effective for different types of buttons and different sizes and shapes of defects, and the accuracy of the algorithm is 99%. Moreover, the method has a certain adaptability to illumination variation.

With the rapid developments of machine vision and artificial intelligence, the visual attention mechanism, as an important part of machine vision, has attracted more and more attention. A coarse-to-fine saliency detection method is proposed based on non-subsampled contourlet transform (NSCT), which, as a frequency-domain based saliency detection method, can make full use of the low-frequency and high-frequency information of images and suppress the influence of illumination on detection as well. First, the non-subsampled contourlet transform is used to decompose the input images. The low-frequency components are enhanced by Retinex to ameliorate the brightness uniformity of images, and thus the influence of illumination on the saliency detection is suppressed. Then, the coarse saliency detection is performed. The high-frequency components are enhanced nonlinearly to suppress noises and enhance details, and thus the high-frequency feature maps are obtained via reconstruction. The global and local saliency analyses of the high-frequency feature maps are performed within the scope of low-frequency coarse saliency maps. Finally, the fine saliency maps are obtained via fusion. The contrast experiments are carried out on three datasets and the results confirm the feasibility and effectiveness of the proposed method.

In order to satisfy the requirements of visual tracking algorithm on tracking accuracy and speed, a multi-scale correlation filtering visual tracking algorithm combined with target detection is proposed. The proposed algorithm is first used to find the target location and size in the image by the target detection algorithm based on depth learning. The correlation filtering algorithm is then applied to the visual tracking of the given target features and the multi-scale search of the optimal response. When the correlation filtering response appears abnormal, the model stops updating. When the response value of several frames continues to be abnormal, the search of target location and size is then made in the whole image. By the evaluation of tracking states and the adaptive adjustment of model updating rate, the proposed algorithm solves the problem of tracking error accumulation over time in the traditional correlation filter algorithm, and possesses high tracking speed and high precision. The results show that as for the proposed algorithm on the Matlab platform, the average positioning precision is 0.593, the average overlap precision is 0.784, and the frame rate is 65.3 frame/s.

To improve the registration accuracy of three-dimensional point clouds in the complex situations of random data missing, noise interference and so on, a method of registering point clouds based on multi-dimensional mixed Cauchy distribution (MMC) is proposed. The mathematical model of point clouds is extended to the MMC model, and the parameters of this model are solved to construct a characteristic tetrahedron so that the rotation matrix and translation vector are optimized. Based on the MMC model, the data centers, covariance matrices and weights of target point clouds and point clouds to register are obtained by the expectation-maximization algorithm. The simulation data and experimental data show that the MMC algorithm can be used to realize an accurate registration and simultaneously possesses a good robustness if compared with several common algorithms under the conditions that the point cloud data are occluded, missing, size-inconsistent, interfered by random noise and out of order.

In order to assist the surgeons in the fast histological inspection of the excised tissues during the thyroid surgery, a home-made optical coherence tomography (OCT) system is used for the three-dimensional (3D) imaging of the excised tissues from the patients receiving the thyroid surgery and lymphadenectomy. The 3D OCT images are also compared with the corresponding two-dimensional OCT images and the histological images. The 67 high-resolution 3D OCT images with 1000 pixel×1000 pixel×630 pixel are acquired from the excised tissues of the 21 patients and the corresponding imaging range is 6 mm×6 mm×3.8 mm. It is convenient to observe the 3D OCT images from different perspectives or cross-sectional planes. The thyroid, parathyroid, lymph node and fat within the imaging range can be clearly identified, and the malignant lesions of lymphatic metastasis can also be distinguished. This high speed and high resolution 3D OCT imaging provides a method for the intraoperative histopathology and is promising to assist the surgeons for their intraoperative decision.

The reciprocating progressive scanning is an effective way to increase the imaging frame rate of laser confocal scanning microscopic imaging. However, serious image dislocations during image reconstruction are introduced as the frame rate increases. According to the motion characteristics of a high-speed galvanometer, the dislocation principle of reconstructed images by the laser confocal high-speed scanning microscopic imaging system is analyzed. A dislocation evaluation algorithm of reconstructed images is designed based on the morphological gradients. In addition, the single-objective constrained particle swarm algorithm is used to realize the dislocation correction of reconstructed images by combining with the search for the minimum point of dislocation evaluation. The experimental results show that the proposed algorithm is suitable for the dislocation correction of reconstructed images even when the imaging frame is up to 300 frame/s. Compared with that of the original images without dislocation correction, the imaging resolution after correction increases by 68.83%. Moreover, this algorithm is also suitable for the image reconstruction under different mirror combinations and different scanning frame rates.

Thermal deformation of 16 nm extreme ultraviolet lithography (EUVL) objective is one of the main factors influencing its high resolution imaging. In order to provide a reliable technical basis for the thermal management of EUVL system, we simulate the thermal deformation of a typical 16 nm EUVL objective with 0.33 numerical aperture. The finite element software ANSYS is used to simulate the transient temperature and thermal deformation of each mirror during exposure. The deformed mirror surface is fitted with Zernike polynomial as an interface tool to evaluate the effect of the thermal deformation on imaging performance. The results show that the maximum temperature rise and the maximum thermal deformation of the objective are 3.9 ℃ and 10.2 nm, respectively. The thermal deformation of the objective in the high temperature state causes maximum wavefront error root mean square (RMS) of 0.1λ and the distortion of 56 nm, which are beyond the reasonable range. The wavefront error RMS and the distortion caused by the thermal deformation of M3 and M4 mirrors together account for 88% and 99%, which play leading roles in the imaging performance. The temperatures of these two mirrors should be controlled strictly.

We propose a waveguide based on three graphene-coated dielectric nanowires with a non-coplanar axis using the multipole method, and analyze the real part of effective refractive index and propagation length of five supported low-order modes by changing the operating frequency, radius and height of the central nanowires, the horizontal space between the nanowires, and the Fermi energy of graphene. When the operating frequency increases from 30 THz to 40 THz, the real part of the effective refractive index increases, whereas the propagation length decreases. When the radius of the central nanowire increases from 20 nm to 55 nm, the real part of effective refractive index increases; however, the corresponding propagation length varies. When the height of the central nanowire increases from 0 to 100 nm, the real part of effective refractive index decreases, whereas the propagation length increases, except for that of mode 5. When the horizontal space between the nanowires increases from 160 nm to 200 nm or the Fermi energy increases from 0.4 eV to 0.8 eV, the propagation length increases, whereas the real part of the effective refractive index decreases.

Polarization, as an intrinsic nature of light, is certainly of great importance to serve as a degree of freedom for manipulating light. The vector optical fields with inhomogeneous polarization distribution have been applied in many areas due to the unique feature with respect to the traditional scalar optical fields. However, the early study of vector optical fields mainly focused on the local linearly polarized vector optical fields with cylindrical symmetry. In recent years, novel vector optical fields with various polarization distributions have attracted significant interest. These new vector optical fields have not only enriched the family of the vector optical fields, but also provided new degrees of manipulation freedom. As a result, these new vector optical fields have been applied in realms such as manipulation of focal fields, optical micro-machining, optical micro-manipulation, and optical information transmission. In this paper, we present an overview of the recently appearing new kinds of vector optical fields, including hybridly polarized vector optical fields in cylindrical coordinates, vector optical fields associated with Poincare sphere, array vector optical fields, vector optical fields with multiple polarization singularities, and other vector optical fields without cylindrical symmetry. The advances, design scheme, experimental generation, properties and related applications of these vector optical fields have been presented.

The basic theory and common generation methods of vectorial optical fields are reviewed. The vectorial optical field generator based on spatial light modulator and its recent improvements in performances are introduced in detail. An overview of the vector diffraction theory under tightly focusing is offered, and the methods for tailoring the intensity distribution, polarization direction and spin orientation within the optical focal fields are highlighted. The applications of the tailored focal field in microscopy, directional coupling and so on are briefly discussed.

Fiber-based structured light fields, as an important branch of light field modulation, have gradually attracted much attention of researchers. First, based on the fiber vector mode theory, the generation mechanism of fiber-based structured light fields with spatial polarization/phase singularity is discussed. Then, the generation methods of fiber-based structured light fields, such as long-period fiber grating coupling method, fiber end face microstructure method, and orbital angular momentum conversion method, are introduced. Finally, some typical applications of fiber-based structured light fields in super-resolution imaging, vortex light communication, plasmonic tip nanofocusing, nonlinear frequency conversion and so on are presented.

Vortex beams have physical properties such as spiral wave-fronts, phase singularities, and orbital angular momentum, which have important applications in particle manipulation, quantum information, super-resolution imaging, optical communication and so on, and become the spotlight of optical researches. Owing to the rapid development of the optical coherence theory, the researchers have introduced the coherence as a new degree of freedom into the vortex beams and proposed the partially coherent vortex beams as an extension of coherent vortex beams. Such partially coherent vortex beams, compared with the fully coherent ones, have their unique physical meanings and optical properties. Particularly, some new peculiar effects (such as coherence singularities, beam shaping, polarization switches, and self-healing) emerge when the coherence and the topological charges of the partially coherent vortex beams are modulated. Here, an overview on the fundamental theory and the development history of the partially coherent vortex beams is presented. The theoretical models, the propagation characteristics, the experimental generations and measurements, as well as the applications are introduced with the combination of our recent research works.

Metasurfaces, as two-dimensional artificial nanostructures, have draw a lot of attention in recent years due to the remarkable ability for flexible optical field modulation. Full-control, and all-dimensional optical field manipulation can be realized by designing metasurface. In this review, we utilize Fourier analysis to theoretically study the designed strategy of metasurface consisting of weakly coupling unit cells. The stable conditions based on Fourier analysis is proposed to mimic continuous phase profile using discontinuous phase profile, which compensates the inadequacy of subwavelength conditions. Furthermore, by combining the phase manipulation by metasurfaces with optical characteristics of polarization, amplitude, and frequency, the evolution and applications of metasurfaces in multi-dimensional manipulation of optical field are briefly reviewed, respectively. As a result, the multi-dimensional manipulation of optical field by metasurfaces not only increases the freedom degree of light-field control, but also promotes the development of integrated optical equipment.

With the rapid developments of ultrafast lasers toward even shorter pulse, it will suffer great technological and experimental challenges for further generation of optical waveforms with single-cycle or sub-cycle in optical wavelength range. The multi-channel coherent synthesis with precise carrier envelope phase (CEP)-controlled waveforms opens the frontier of ultrafast optics for sub-cycle waveforms generation. In this paper, we review the recent progresses on coherent waveform synthesis based on our research works, the mechanics and key technological approaches are analyzed and discussed, which include ultrabroadband supercontinuum generation, dispersion management and CEP-control.

Ultrafast controlling of atomic and molecular quantum states has attracted intensive attention benefited from the development of ultrafast laser and its manipulation. The related researches have led to increasing understanding of the interaction between intense laser field and quantum states of atoms or molecules. In the present paper we review the research progress in this field, particularly focusing on the quantum control of molecular rotation and dissociation in ultrafast laser fields, ionization of atoms and molecules in such ultrafast manipulated laser fields, and prospects for future development.

Complex optical fields usually refer to structured light fields with special distributions of phase, amplitude, polarization and so on, including vortex light fields represented by orbital angular momentum patterns and vector light fields with non-uniformly distributed polarization states. The construction of a multi-dimensional multiplexing optical fiber communication system using complex optical fields has become a research hotspot of the space division multiplexing optical communication technology. The methods of generation, regulation and transmittance of a complex light field through an optical fiber are introduced. In addition, the application of a new ring core fiber in the low complexity short-distance mode multiplexed optical fiber communication system is introduced. The experiment on the Q-plate-based short-distance direct detection vector mode multiplexed optical fiber communication system is introduced. The fiber grating coupled mode conversion method as well as the generation of the first-order and second-order orbital angular momentum modes using a few-mode fiber is briefly analyzed. At the same time, the technical scheme for measuring the characteristics of a vortex light field by one-dimensional and two-dimensional periodic gradient phase gratings is introduced. The fiber loss and mode crosstalk are the key factors limiting the performances of a mode-multiplexed fiber communication system based on complex optical fields. Thus, it is still a great challenge to generate and control a high-order complex optical field based on an optical fiber. However, complex light field mode multiplexing technology as a multiplexing technology based on optical fiber eigenmodes, its related researches have important research significance and potential application value in the future super-capacity mode multiplexed optical fiber communication system.

The principle of surface wave, classification of measurement technology and key technology are discussed. The historical developments of refractive index sensing based on total internal reflection, surface plasmon resonance, graphene and other optical surface waves is summarized. The technical advantages of surface wave refractive index sensing imaging are further discussed. The research results show that surface wave sensing imaging, as a high-precision quantitative label-free microscopic imaging technology, has important values in the accurate diagnosis and treatment of medical optics.

Optical imaging has been widely used in bio-medical, physical and chemical research fields due to its non-invasive characteristic. By adjusting the temporal and spatial parameters of the optical fields, we can effectively modulate the time sequence, wavefront, amplitude, phase, dispersion and other characteristics of the light, and obtain the optical image with high temporal and spatial resolution. On the basis of the principle of optical fields engineering, the recent progresses in the research of high temporal-spatial resolution imaging technology are reviewed.

Optical microfibers or nanofibers are waveguides with diameters close to or smaller than the guided wavelength. Because of the high contrast of the refractive index between the core and cladding material, they have the properties like strong light confinement, enhanced evanescent field, ultralow loss, abnormal waveguide dispersion, excellent surface uniformity and mechanical stability. In recent years, passively mode-locked fiber lasers based on nanomaterials saturable absorber have been a hotspot in the research field of ultrashort pulse generation. Benefitting from strong light confinement and large proportion of evanescent fields, the hybrid structure of nanomaterial and microfiber could enhance light-material interaction significantly and reduce the saturable absorption threshold, thus provide a flexible and innovative platform for the research on ultrashort pulse generation and nonlinear dynamics. Meanwhile, it has the properties of abnormal waveguide dispersion, spectral filtering, saturable absorption and polarization sensitivity, thus it could be applied for dispersion management and polarization induced mode-locking. This review article introduces the fabrication and characteristics of microfiber, its typical applications on mode-locked lasers, and related technology developments. The perspectives for future directions are also mentioned.

Femtosecond laser micromachining has been widely used in laser material processing because of its unique advantages of low thermal effects, high precision and three-dimensional processing capability inside materials. The recent advances of the application of femtosecond laser microfabrication combined with femtosecond laser pulse shaping to micro-nanofabrication in transparent materials are reviewed. These techniques possess an important application prospect in novel integrated optics and micro- and nano-optics.

Structured light fields are a kind of special light fields that have tailored lightwave spatial structure. The generalized structured light fields are these kinds of fields including spatially variant amplitude, phase and polarization distribution as well as space array. Structured light fields have seen wide applications in optical manipulation, microscopy, imaging, metrology, sensing, nonlinear optics, astronomy, quantum science and optical communications owing to their distinct advantages. Structured light communication techniques include multiplexing communications and coding/decoding communications. In this review article, the recent progress of structured light coding/decoding communications is retrospected. Various generation methods of structured light fields and structured light coding/decoding communications with different spatial modes (orbital angular momentum mode, non-diffraction Bessel mode, linearly polarized mode, vector mode, space array), different coding methods (direct mode coding, high-speed mapping), and different scenarios (photonic chip, free space, fiber) are comprehensively reviewed. Future trend and perspective are also discussed. Structured light coding/decoding communications exploit the space domain dimensional resources of light fields, which provide a potential solution to address the new capacity crunch of optical communications and enable sustainable expansion of optical communications.

Vectorial vortex beams are a new kind of structure beams, with anisotropic polarization distributions and carrying orbital angular momentum. Such unique features contribute to their applications in lots of domains as optical communications, optical tweezers, laser material processing, etc. Different applications need different polarization and phase distributions. So generating vectorial vortex beams with continuously adjustable polarization and phase distributions is of great importance. In this paper, we introduce some approaches for generating vectorial vortex beams developed in our group, including generation of single vectorial vortex beams outside the cavity and generation of vectorial vortex beams arrays.

A perfect vortex beam has only a single simple mode, which restricts its applications in many fields. To overcome this drawback, a concentric vectorial perfect vortex mode is proposed, whose intensity distribution presents a group of concentric vectorial perfect vortices. In addition, the property of each vectorial perfect vortex is tested. The research results show that the characteristic parameters of each vectorial perfect vortex, such as radius and polarization order, are independent on each other. Furthermore, the superposition property of intensity rings of concentric vectorial perfect vortex mode is studied. Different from the scalar superposition, the sub-vortices generated by the vectorial superposition vanish at some specific locations as a result of polarization orthogonality for these rings at these locations. This work vastly enriches the mode distributions of a perfect vortex and broadens its potential applications in the fields of micromanipulation, optical communication and so on.

The vortex beams carrying different topological values are generated based on the high efficiency transmission metasurfaces illuminated by quasi-spherical beams from standard horns. These metasurfaces are able to exhibit a transmission efficiency of over 90% in the bandwidth range of larger than 10% and an over 3-bit phase modulation. Through the theoretical derivation of a phase-compensation formula and the design of metasurfaces, high-order orbital angular momentum (OAM) vortex beams are generated on the high efficiency transmission metasurfaces at 30 GHz. The proposed scheme is verified by the full-wave simulation and the results agree well with the theoretical results.

The orbital angular momentum (OAM) of a vortex beam is measured and its performance is improved by gratings. Compared with other equipment or devices, this measurement method by gratings is simple and can make the cost of communication system reduced. The vortex beam is illuminated to an appropriate position of a period-gradually-changing grating or an annular grating. The light spot distribution in the diffraction pattern is observed and the incident vortex beam is measured. The experimental results show that the size and plus-minus of the topological charge of incident vortex beam can be determined according to the number and orientation of dark stripes in the light spot. Meanwhile, the phase correction or fan-out technique can be adopted to make the stripes more clearly visible in the diffraction results. Moreover, with these two techniques, the measured maximum number topological charges is increased to 30. This research provides a basis for the demultiplexing and generation of vortex beams in the OAM multiplexing communication.

A random speckle field is generated in the propagation of coherent light through a multimode fiber (MMF). For a non-polarization-maintaining MMF, linearly polarized incident light cannot maintain the linear polarization distribution owing to the depolarization effect. Therefore the randomness of the speckle pattern is observed in both intensity and polarization distributions. In this study, the intensity and polarization of the disordered speckle field generated by the MMF is controlled with the feedback wavefront shaping technology that generates a focal line with controllable polarization distribution.

Femtosecond laser is used to ablate a CaF2 crystal surface. By varying the laser parameters, we produce the microstructures (including ablation holes and lines) using stationary focusing ablation and dynamic scanning. The laser-induced microstructures on CaF2 crystal surface under both processing modes are investigated to obtain the parameter dependence and ablation threshold. The calculation results reveal that the incubation factor is 0.0033 in the stationary focusing case; whereas, in the case of dynamic scanning, the incubation factor is 0.0043 or 0.0052 when the scanning direction is perpendicular or parallel to the laser polarization, respectively. The results reveal that the incubation effect plays an important role in the process of femtosecond laser ablation on crystal surface.

The influence of thermal blooming effect on the flat-topped laser beam array propagating through the atmosphere is studied, where coherent beam combination and incoherent beam combination are considered. The results show that the beam spot of flat-topped laser beam array propagating through the atmosphere with cross wind is like a crescent pattern. For coherent beam combination, multiply intensity peaks exist in the beam spot. For incoherent beam combination, there is always one intensity peak. The flat-topped laser beam array for incoherent beam combination is less affected by the thermal blooming than that for coherent beam combination. The flat-topped laser beam array with larger beam order N is less affected by the thermal blooming than that with smaller one. Hence, comparing with the flat-topped laser beam array, the thermal blooming is more serious for the Gaussian beam array (N=1). With the increase of N, the propagation efficiency decreases in free space, but it increases in the atmosphere. Under the condition of the same beam power in atmosphere, the propagation efficiency of flat-topped laser beam array is better than that of Gaussian laser beam array.

The pulse shaping technology based on liquid crystal spatial light modulator is used to control the femtosecond laser filament in fused silica. The experimental results show that the filament can be generated at a designated position in fused silica. In addition, a long-distance controllable displacement of the onset of filamentation in fused silica is achieved, with a maximum displacement of 5.4 mm. Furthermore, the theoretical simulation on filamentation of shaped pulse in fused silica is performed based on the (3+1)-D nonlinear Schr dinger equation. The results are consistent with those of experiments. It is demonstrated that the onset of filamentation depends on the peak intensity and envelope of shaped femtosecond pulse.

Gaofen-4 (GF-4) satellite is the first geosynchronous high-resolution optical imaging satellite developed by China, and it has high temporal resolution and high spatial resolution. Aiming at the characteristics of GF-4 satellite data, we propose a cloud and cloud shadow detection algorithm combining spectral analysis and geometrical algorithms. Geometrically corrected and radiometrically calibrated GF-4 images are used to identify potential cloud pixels using spectral difference analysis techniques based on the spectral characteristics of clouds and typical land surfaces. The cloud probability is calculated according to the difference of spectral variability rate of clouds and cloudless features. The geometrical relationship between clouds and cloud shadows is combined with the sensor parameters to identify the projective regions of cloud shadows. Then the image-based dynamic thresholds are set in the projection regions based on the spectral characteristics of the shadows to detect cloud shadows. This algorithm can better identify thin clouds, and significantly improve the cloud shadow detection accuracy. The visual interpretation method is used to verify the detection accuracy. It finds that cloud pixels recognition in different regions are more accurate and the shapes are relatively complete. Compared with the method of cloud and cloud shadow matching, the dynamic-spectral-threshold algorithm proposed in this paper is more accurate in detecting cloud shadows.

Aiming at the various statistical characteristics such as peak tailing presented in the high-resolution synthetic aperture radar (SAR) images, we model the polarimetric features according to the Gaussian mixture model (GMM) and come up with a constrained distance estimation algorithm for the parameters of multivariate Gaussian mixture distribution. Under the framework of greedy expectation maximum algorithm, a constraint distance function is designed and the number of mixed components and model parameters are automatically estimated in this parameter estimation algorithm. Consequently the classification of polarimetric SAR images is realized under the Bayesian framework. The classification results of three groups of image data from Radarsat-2 in San Francisco and other places indicate that the proposed GMM classification algorithm possesses an overall accuracy higher by 7%-10% comparing with those by the classical classification algorithms. Moreover, its dependence on sample number is small. The more accurate classification results can be obtained in heterogeneous regions such as urban and farmland.

As for the simultaneous detection of trace Cu2+ and Co2+ in zinc solution, there exist the problems of low sensitivity, narrow effective band and serious spectral signal coverage. Thus, a multi-objective optimization fractional differentiation pretreatment method is proposed. First, the coverage degree and distortion degree in the simultaneous detection of Cu2+ and Co2+ are determined according to the spectral characteristics, and the functional relationship and constraints of differential order and index are fitted. Then, the established optimization problem is solved by the multi-objective particle swarm optimization algorithm. This multi-objective differential order optimization method is finally verified. The results show that the proposed method can be used to reconstruct the completely covered ion wave peaks with low sensitivity and narrow effective bands, and to solve the complete spectral coverage problem. Moreover, it can be used to minimize the distortion degree of differential filtering and reduce the spectral coverage of trace Cu2+ and Co2+ to the maximum extent.

A Bragg grating/graphene/metallic thin film-type optical structure is prepared to enhance light absorption in graphene, and the optical propagation properties of the structure are investigated using the transfer matrix and finite-difference time-domain methods. The light-graphene interaction can be effectively enhanced using strongly confined Tamm plasmon polaritons formed between the Bragg grating and metallic film. Thus, an approximately 36-fold increase could be observed in the near-infrared light absorption of the graphene. Additionally, the dependence of graphene absorption on the Bragg grating period number, graphene position, angle of incident light, thickness of the Bragg grating layers, and chemical potential of the graphene is investigated. The results show that the wavelength and efficiency of light absorption in graphene can be controlled by adjusting the aforementioned physical parameters. The results of this study provide a new pathway for realizing high-performance graphene devices, especially photodetectors.

In order to investigate the influence of the primary spectrum of a display device on the color discrimination difference of observers with normal color vision, five display devices with different red, green and blue color primary spectral energy distributions are selected. Based on the 5 color stimuli recommended by CIE, 30 observers aged from 20 to 27 with normal color vision are organized to carry out the color-matching experiment based on these five display devices. Meanwhile, the 108 color-matching functions (CMFs) are used for the computational simulation of the color-matching process, and the calculation results are compared with the color-matching experimental ones. The influence of different display devices on the discrimination of observers is quantified by the metamerism index. It is found that the simulation results are well consistent with the color-matching experimental ones. With the 285 CIELAB color difference data acquired from the color-matching experiment based on the selected four display devices to be matched and the target display device, the maximum of 9.59 and the minimum of 3.89 as for the metamerism index are obtained. The primary color spectrum of a display device has a strong influence on the observer metamerism and the influence of a red color device is weaker than those of yellow and blue ones.

On the basis of the analysis of the existing pupil diameter estimation models, the changes in pupil diameter of all subjects under different light environments are measured. The comparison among all existing models are made by use of the measurement data. The relationship of luminance and visual angle with pupil diameter is established according to the corneal flux density. Moreover, based on the Stanley-Davies model, the original calculation formulas are corrected and optimized, and thus the calculation precision of this model is improved. Via experiments, the field of view area is extended and the maximum field of view is increased to 40 degrees.