The history and present situation of optical fiber sensors (OFS) development in China in the past 40 years are presented, and three development stages in the technology field are reviewed including quickly development and determining National Projects of OFS in China, the trough both in technology and market because of its un-completeness, and industrialization stage driven by the market. From the view of two aspects, typical OFS technology and its application, new type OFS technology and instrument developing, the main technical achievements of Chinese scholars are summarized including fiber Sagnac interferometer and its applications in gyroscope field, the applications of fiber Michelson interferometer and Mach-Zehnder interferometer in the fields of hydrophone and geophone for oil detection and acoustic detection, optical fiber grating sensing technology and its applications for fire alarming, distributed OFS technology and its typical applications in the fields of largescale smart structure and architecture, optical fiber Fabry-Perot sensing technology and applications, and new type OFS sensing technology and its biomedical applications. The development of OFS research and development exchange platform in China and its important role in promoting the academic development and technology of OFS are expounded. The problems in the development of OFS technology in China are pointed out at present. The development experiences and prospects of OFS technology are summarized and prospected in general.

The basic principle of image processing methods based on variational image decomposition, the common functional spaces, and the variational image decomposition models are introduced. We review the applications of information extraction technologies based on variational image decomposition for electronic speckle pattern interferometry (ESPI) in recent years, including the filtering process, orientation and density calculation, and skeleton line extraction of the fringes. The advantages of the mentioned methods compared with that of traditional methods are given and the development trend of the image processing methods based on variational image decomposition in optical measurement is further illustrated.

Due to the advantages of compact size, easy integration, fast response time, strong ability for controlling light, detecting without label, and flexibility in design, the photonic crystal (PC) micronano sensors show great application prospects in the fields of industrial production, ocean exploration, biological medicine testing, and environmental detection. As for the one-dimensional nanobeam and two-dimensional slab PC sensoring technologies, the key theories and experimental technique progresses of PC micronano sensing at home and abroad are analyzed from the aspects of structural design and sensoring performance improvement of sensors. Furthermore, with comparative analysis, the challenges and future development trend of PC micronano sensing technology in further application are discussed.

To meet the urgent needs of high-precision guidance, navigation and control systems in space and other fields, the research of interferometer photonic crystal fiber optic gyroscope (PCFOG) based on solid core polarization maintaining photonic crystal fiber (PM-PCFs) is carried out. Some key technologies, such as the fabrication technology of PM-PCFs and erbium-doped PCFs (ED-PCFs) for PCFOG, the coupling technology and the fusion technology of PCFs, are studied and developed. The prototype of PCFOG is developed and the typical environmental tests are carried out. The results show that PCFOG has obvious advantages in accuracy and environmental adaptability, and satisfies the conditions of engineering application.

Recently, distributed Brillouin optical fiber sensors have been extensively studied and discussed for the capacity to measure distributed strain and temperature, as well as important applications in the field of structural health monitoring. In several optical fiber sensing schemes, Brillouin optical time domain analysis (BOTDA) is widely concerned due to its good signal-to-noise ratio, high spatial resolution, and long-range sensing distance. However, due to the time-consuming averaging and frequency-sweeping processes, the classical BOTDA systems are suitable for static or slow-varying strain measurements. In this paper, we analyze the operation principle of BOTDA system and discuss some main factors for limiting fast measurement. Then, we summarize and analyze the dynamic measurement methods based on fast BOTDA, which are polarization compensation technique, frequency-agile technique, slope-assisted method, optical chirp chain technique, optical frequency comb technique. It is pointed out that the fast BOTDA system consisted of a single or multiple new techniques, has a better performance and a wider application prospect.

Plasmonics is one of the most powerful technology for biomedical detection which may realize single molecule detection. The combination of high sensitive plasmonic technology and flexible fiber-optic sensors opens up a multitude of opportunities for cost-effective and relatively simple-to-implement bio-sample detection. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo. We briefly review the principle of fiber grating based plasmonic biosensors, and the key properties to achieve unprecedented sensitivities (10-6-10-8 RIU) and limits of detection (pM-fM). Meanwhile, we also demonstrate such sensors provide very controllable cross-sensitivities, absolute and relative measurements of various parameters, and their self-calibration ability to the environmental cross-talk (especially to the temperature fluctuations). Finally, we briefly review the recent developments of the surface and localized affinity studies of the biomolecules for real life problems, the electrochemical actives of electroactive biofilms for clean energy resources and the ultra-highly sensitive sensing in gas.

Optical coherence domain polarimetry (OCDP) is a measurment method based on white light interferometry and accurately measures distributed polarization characteristics of polarization maintaining fiber devices and components by energy coupling (polarization crosstalk) in polarization transmission modes. It has advantages of ultra-high polarization sensitivity (polarization crosstalk is from -100 dB to -90 dB), high spatial resolution (5-10 cm), ultra-wide dynamic range (109-1010), and large scanning range (several kilometers), which meet ultra-high performance measurement requirements for polarization maintaining fiber devices and components including key components and optical circuits of fiber-optic gyroscopes. The principle and key technique of OCDP are reviewed including the measurment principle and accurate modeling method of distributed polarization crosstalk, and several key techniques of OCDP instrumentation. The application of OCDP in quantitative measuring as well as diagnosing and evaluating the integrated waveguide modulator with ultra-high extinction ratio and ultra-large length sensing fiber coil is demonstrated. An outlook of future developments of OCDP in measurement of key components and total optical circuits of high precision fiber-optic gyroscopes is provided aiming at complicated and changeable application environment of high performance optical fiber transducers.

The Bloch surface wave (BSW) technology is a novel optical sensing technology based on all-dielectric structures, which possesses a low optical loss, a large phase jump and a high design flexibility. It has been recently widely studied and the different structure designs and detection schemes have been proposed and confirmed. The related technologies have been confirmed to be used for label-free biosensing, gas sensing, fluorescence detection, and so on. The research progress of BSW technology at home and abroad is reviewed, from the aspects of basic principle, sensing devices, detection systems and methods.

Fiber Bragg grating is an important optical fiber sensor, which has the advantages of small size, corrosion resistance, anti-electromagnetic interference, high sensitivity and quasi-distributed measurement. Traditional fiber Bragg gratings fabricated by ultraviolet laser usually require hydrogen loading to the fiber and their poor thermal stability restricts the use in extremely high temperature environment. In recent years, with the research development in the field of femtosecond laser micromachining of glass, researchers begin to use femtosecond laser to fabricate fiber gratings. Fiber grating inscription by femtosecond laser shows good machining flexibility, no requirement of hydrogen loading and polymer coating stripping, and more importantly, femtosecond laser inscribed fiber grating shows excellent high temperature stability. The machining mechanism of femtosecond laser inscription for fiber grating and three typical optical fiber Bragg grating femtosecond laser preparation methods are introduced. At last, the research progress of high temperature sensors based on femtosecond laser induced fiber Bragg gratings is reviewed.

The Fabry-Perot interferometer based fiber optical sensor (FP sensor) was first known in the early of 1980 s. It has been experienced high speed development in recent 10 years and gradually shows the superiority in special applications such as aviation, oil exploration, source of energy and civil engineering. Because it has excellent reliability, and high sensitivity in harsh environments such as high temperature, high pressure, strong radiation and narrow space. This paper firstly reviews the history of fiber Fabry-Perot sensor, then introduces its recent progress and future development trends from the aspects of sensors, demodulation methods, hardware systems and applications based on the principle of fiber optical sensor.

Sensing principles and characteristics of some optical electric-power sensors are reviewed, and some typical problems, solutions, and research proposals are summarized and analyzed. Main advantages of optical electric-power sensors include large measurement range, broadband frequency response, and good electrically insulating capability. Optical electric-power sensors can be classified into two types according to different light modulating approaches, i.e. direct modulation and indirect modulation. Compared with conventional optical voltage and current sensing signals, the optical electric-power sensing signal is much weaker and the active power sensing signal is a direct current signal. It is difficult to distinguish the direct current sensing signal from fluctuation of the probing light intensity. The sensing material of a single crystal-based electric-power sensor should exhibit both electro-optic and magneto-optic effects, or dual transverse electro-optic Pockels or Kerr effects. In addition, we should consider multiple optical effects in sensing crystals and their mutual interference, and how to avoid or suppress the temperature drift of sensing signal. Optical electric-power sensors have potential applications to smart power grid, microwave and electro-magnetic pulse power measurement.

Methane (CH4) is one of the most important gases to be monitored in many fields such as atmospheric environment monitoring, industrial process control and coal mine production safety. Developing CH4 sensor has a wide application value. Based on the fundamental frequency absorption band of CH4 molecule near 3.31 μm and its absorption line at 3038.5 cm-1 as the target line, a CH4 sensor based on the mid-infrared room-temperature, continuous and single-mode interband cascaded laser (ICL) is developed. The sensor uses tunable laser direct absorption spectroscopy and long-path (54.6 m) absorption spectroscopy to measure CH4 gas concentrations. A high sensitivity, low power laser temperature controller and current driver are developed independently, and the program of data generation, acquisition and processing based on LabVIEW is coded. The CH4 standard gas with a volume fraction of 2.1×10-6 and a gas dilution system are used to prepare CH4 gas samples with different concentrations. And the performance test of the sensor is conducted. According to the analysis of the standard deviation of the sensor, when the sampling period is 2.5 s, the lower 1σ detection limit of the sensor is about 1.1×10-8. The sensor is used to monitor the concentration of CH4 in the outdoor air for 84 h continuously. The results confirm the engineering practical value of the developed CH4 sensor.

A multicore fiber Bragg grating (FBG)-based curvature sensor interrogated by a matched-filter technique is proposed and experimentally demonstrated. The multicore FBG-based fiber curvature sensor consists of two FBGs inscribed at two arbitrary outer cores arranged symmetrically to the center core. These two FBGs have almost same reflection spectrum and center wavelength. When the multi-core fiber is bent, the overlapping area of the reflection spectra of the two FBGs changes, which affects the matched-filter output power and is related to fiber curvature. Thus we can interrogate the curvature by monitoring output power. The proposed sensor with the sensitivity of 0.78 mW·m-1 is achieved. In addition, the performances of the multicore FBG-based curvature sensor based on matched-filter interrogation under different externally applied axial strains and temperatures are also evaluated. The results show that the proposed sensor has strong ability to resist ambient fluctuations.

A cantilever-enhanced photoacoustic signal detection method based on fiber-optic Fabry-Perot interferometric sensors is proposed, which combines the technologies of fiber-optic sensing, longitudinal resonant photoacoustic spectroscopy, wavelength modulation and second-harmonic detection. According to the characteristics of fiber coupling near-infrared exciting light, the resonant photoacoustic cell is optimally designed. A high-sensitivity laser photoacoustic spectrometer for trace acetylene gas detection is developed. Experimental results show that the detection limit of acetylene reaches 8×10-10 with the measurement time of 60 s.

A distributed optical fiber acoustic sensing system based on chaotic laser interference is proposed, which uses the external cavity feedback semiconductor chaotic laser as the sensing light source, and the non-equal length of Mach-Zehnder arms for the introduction of the interference optical path difference. The reciprocal effect of the annular interference system is overcome by the linear Sagnac structure. The spectral null-frequency point is applied to realize the distributed location of sound signals.The experimental results show that, this system can real-time extract the single-tone signal with a frequency of 1 kHz and the voice signal in the frequency range of 200-900 Hz. Compared with the traditional broadband amplified spontaneous emission laser, this acoustic sensing system based on chaotic laser interference has a better sound frequency response curve, a higher detection sensitivity and a uniform plane directivity. Moreover, a broad-spectrum sound positioning in a 12 km single-mode fiber is achieved, which provides a new sensitivity enhancement solution for the distributed optical fiber acoustic sensing system.

A kind of fiber-optic acoustic sensor based on the multi-layered graphene material is studied, which has a Fabry-Perot interferometic cavity structure, consisting of single mode fibers and multi-layered graphene films. With the multi-layered pure graphene and multi-layered graphene oxide (GO) as the acoustic pressure sensitive film respectively, the experiments of acoustic wave sensing are conducted. The results indicate that, in the audio range, the average signal-to-noise ratios of the fiber-optic acoustic sensors based on multi-layered pure graphene and multi-layered GO films reach 56 dB and 69 dB, respectively. The sensitivities of the average minimum detectable acoustic pressure are 20.8 μPa·Hz-1/2 and 6.63 μPa·Hz-1/2, respectively, far smaller than that of the electric acoustic sensor. The fiber-optic acoustic sensors based on the graphene material possess a high sensitivity, which is suitable for the micro-acoustic pressure measurement under the environment of severe electromagnetic interference and confined spaces.

The wavefront distortion occurs when vortex light transmits in atmospheric turbulence, so wavefront correction is required. Compared with the traditional adaptive optical system with wavefront sensor, the adaptive optical system of the wavefront sensorless using a stochastic-parallel-gradient-descent (SPGD) algorithm has the advantages of simple realization of hardware and good adaptability of complex environment such as light intensity scintillation. The simulation results show that the system can correct the wavefront distortion and improve the mode purity for single-mode and multimode multiplexed vortex beams. The experimental results show that the intensity correlation coefficient of single mode vortex beam can be increased to around 0.85, the intensity correlation coefficient of multimode multiplexed vortex beam can be increased to around 0.72, and the wavefront distortion correction effect of single mode vortex beam is better than that of multimode multiplexed vortex beam. Both the simulation and experimental results show that the adaptive correction technique using SPGD algorithm can effectively realize the wavefront distortion correction of vortex beam.

In order to solve the problem of low speed impact load location recognition on composite structures, the relationship of skewness, kurtosis of the impulse response signal time series sensed by fiber Bragg grating (FBG) sensors and the distance from sensors to the load is analyzed by constructing a distributed FBG sensing network. The location of impact load and the distance to each sensor are identified by the skewness and kurtosis of impulse response signals perceived by different position sensors. The weighted centroid localization algorithm is used to locate the impact load location. The experiment results show 16 test samples are randomly selected from the monitoring area of 240 mm×240 mm on the carbon fiber reinforced plastics board for low-speed impact positioning and recognition. The identifications of all impact test points are achieved. The average error of coordinate positioning is 20.7 mm. The research results provide a reliable method for the location identification of low speed impact on carbon fiber reinforced plastics structures.

As one of the greenhouse gases, ethane can promote the generation of photochemical pollution and destruction of ozone. Due to its extremely low concentration in the atmosphere, it requires a sensor with high accuracy for measurement. A continuous-wave interband cascade laser (ICL) based on mid-infrared sensor system with high-precision of 10-9 level is demonstrated for detection of ethane in atmospheric. A multi-pass gas cell with volume of 220 mL and an optical path of 54.6 m is used. The LabVIEW visual instrument platform is used to program the scan and modulation signal as well as their superposition. A date acquisition (DAQ) card is employed to output the signal of the ICL driver. The output signal from detector is acquired by the DAQ and programmed by LabVIEW for data processing such as lock-in amplifier and second-harmonic extraction. Experimental results show that an Allan deviation of 1.86×10-9 for ethane with an averaging time of 1.67 s is achieved, and it is as low as 0.026×10-9 at an averaging time of 775 s. Outdoor atmospheric ethane concentration measurement is carried out in a compressed natural gas station. The experimental result shows that this ethane sensor system has a great practical value in application.

In order to simplify the design and fabrication of optical fiber liquid level sensor, we propose an in-fiber Michelson interferometer based on fiber-core mismatching intermodal interference, which consists of a single mode fiber (SMF) fusion-spliced with a section of thinned fiber (TF). The fusion point of the SMF-TF acts as a fiber coupler to excite the high-order cladding modes. The core mode and high-order cladding modes are reflected by the end face of the TF and transmitted to SMF to generate intermodal interference. The output interference fringes are clear and in high contrast, which are sensitive to the change of environment liquid level. The sensing characteristics of a sensor sample with 12-mm-long TF to liquid level and temperature are investigated. The experimental results show that the reflection dip wavelength linearly changes for a liquid level variation of 0-9 mm, and the sensitivities to water and NaCl solution with mass faction of 4.7% are －0.116 and －0.129 nm/mm; the temperature sensitivity to water is 0.038 nm/℃ in the temperature range of 20-80 ℃. The sensor has advantages of simple structure, easy fabrication, and low cost, which offers the prospective application in petroleum industrial and chemical industry.

To test performances of different color matching functions (CMFs), we make 20 pairs of nearly metameric color patches based on 5 target colors (gray, brown, b-green, blue, and purple). The visual data from 56 observers is adopted to calculate the standardized residual sum of square and correlation coefficient. The behaviors of different CMFs from the young and old observers have large discrepancies. For young observers, S2 and S6 outperform others and CIE1931 has the worst performance. While, for old observers, CIE1931 outperforms others and CIE1964 has the worst performance. Visual data from observers under the D65 light source is used to optimize CIE1964 CMFs. After optimizing, performances for different age group improves not only for D65 light source, but also for light emitting diode source.

The electromagnetic induced gain (EIG) effects based on the degenerate two-level atomic system are theoretically and experimentally studied. By constructing a N-type degenerate two-level system, the variations of signal light gain with Rabi frequency of pumping light are theoretically analyzed under different Doppler shifts. The results show that, in the rising range, the gain spectrum keeps a single peak structure with a narrow linewidth; while in the decreasing range, it generates a Rabi-like splitting and exhibits a symmetrical two-peak profile. Based on the degenerate energy levels of Cs atoms in which the angular momenta of ground and excited states are same, the generation feature of EIG is experimentally investigated. Furthermore, the influences of pumping intensity and signal light polarization on the peak gain efficiency are also analyzed.

Based on mass bio-optical data from Taihu Lake, Poyang Lake, Pearl River Estuary and Daya Bay, we propose a method called Secchi disk depth (SD_H) to evaluate the water transparency. The method is applied to the new generation water color satellite sensor Suomi NPP VIIRS. The dynamic change characteristics of water transparency are revealed. We analyze the dominant influencing factors of transparency in different waters, compare the transparency products of VIIRS and moderate-resolution imaging spectroradiometer (MODIS) in Pearl River Estuary, and discuss their water environmental monitoring capacity. The results show that the SD_H model constructed based on VIIRS at 488, 555, 672 nm is suitable for water investigation, which can explain 79% of the transparency variation. We apply the proposed model to VIIRS satellite remote sensing images after pretreatment, and get the spatial distribution characteristics of water transparency in Taihu Lake, Poyang Lake, Pearl River Estuary and Daya Bay. Compared to phytoplankton, the suspended sediments and chromophoric dissolved organic matter are the dominant factors influencing the Secchi disk depth in coastal and inland waters. Transparency products of VIIRS and MODIS are consistent in space. However, the transparency product of VIIRS has a better spatial resolution and a stronger environmental monitoring ability.

In the applications of blue-green laser submarine communication and submarine detection, laser transmits through the atmosphere, air-sea interface, and seawater channel. The blue-green laser transmission channel presents complicated characteristics due to the influences of the sea fog over the sea surface, the variation of sea surface roughness and foams caused by wind speed, and the suspended particles in the seawater channel. Based on the Mie scattering theory, the rough surface scattering theory, and the vector radiative transfer theory, we study the laser seawater channel transmission characteristics under the above three influences, and discuss the influence of wind speed, sea fog visibility, and phytoplankton distributions on laser power attenuation in detail. The results show that the sea fog, the rough sea surface with foams, and the phytoplankton distributions in seawater channel affect the transmission laser power together. Among them, the influence of phytoplankton distributions in seawater channel on the laser power attenuation is most significant. The variations of sea surface roughness and foams caused by wind speed have a significant influence on the laser transmission angle domain and meanwhile have a certain influence on transmission extremal value of laser power.

A terahertz detector of GaN/AlGaN high electron mobility transistor (HEMT) with a high speed and a high sensitivity integrated with low-pass filters is fabricated.The experimental study indicates that, when the low-pass filters are added between the terahertz antennas and the lead electrode, the resonance performance of THz coupled antenna is restored. At the room temperature, the responsivity of the device reaches 1.05×103 V·W-1, and the noise equivalent power reaches 4.7×10-11 W when the bandwidth is 1 Hz. This detector unit is used for the fast scanning imaging of different materials, and the results show that this detector unit has a high imaging resolution and its response speed is superior to those of the commercial pneumatic detectors and pyroelectric detectors.

We analyze and compare the transmission characteristics of the metallic hollow waveguides and dielectric-coated metallic hollow waveguides with different diameters and dielectric layer thicknesses, in terms of attenuation, dispersion, and coupling efficiency. It is shown that a bigger diameter and a thinner dielectric layer can achieve a lower transmission loss. We can coat a dielectric layer to improve the single-mode transmission range and dispersion property. We study the coupling efficiency between a polarized Gaussian beam and the waveguides and find that coupling efficiencies of high-order mode are lower than that of the fundamental mode for a proper optical source. We discuss the influence of the dielectric layer on the coupling efficiency, and also analyze the influence of the dielectric layer on the electric field distribution when the transmission wavelength is close to the diameter of the waveguides.

Using the capability that an optoelectronic oscillator (OEO) can generate microwave signals and modulation polarization sensitivity of Mach-Zehnder modulator (MZM), we design a triangular wave and sinusoidal signal generator which is an OEO system embedded by the triangular waveform generator. The bias of the MZM is set at the minimum transmission point, and the polarization angle of the light beam is controlled so that light enters the MZM with an angle for the best modulation axis. The component of the light field parallel to the best modulation axis is modulated by the optical carrier suppression in MZM to generate the odd-order sidebands, but the orthogonal component keeps unchanged. After filtering the negative sidebands and projecting the light field in the same direction by the analyzer, we generate a triangular waveform signal in the photodetector (PD). When the triangular waveform signal passes an electric bandpass filter, the corresponding sinusoidal microwave signal is obtained, which can also complete oscillation feedback for the OEO system. The principle of triangular waveform generation is theoretically analyzed and simulated. In the experiments, a clear and steady triangular waveform signal with a repetition frequency of 5 GHz is generated, meanwhile the sinusoidal microwave signal can be obtained simultaneously. With only a few devices added in OEO, the proposed scheme can generate both triangular waveform and sinusoidal signal simultaneously, which has the advantages of simple structure and practicability.

Nonuniformly correlated partially coherent beams with radially symmetric coherence distributions, i.e., the radial partially coherent beams (RPCBs), can alleviate the scintillation induced by atmospheric turbulence and thus benefit the reception performance. We use wave optics simulation to study the propagation characteristics of coherent Gaussian beams, Gaussian Schell-mode beams, and RPCBs with convex Gaussian and super-Gaussian coherence distributions through anisotropic non-Kolmogorov turbulence. The effects of anisotropic parameters as well as non-Kolmogorov power spectrum index on far-field beam quality are analyzed in terms of far-field intensity profile and aperture-averaged scintillation index. The simulation results indicate that, the beam quality continues to deteriorate as the non-Kolmogorov spectrum index increases. On the other hand, the anisotropy will result in elliptical irradiance distribution in the far field. Therefore, instead of using a circular aperture with an equal-area elliptical aperture at the receiving end, the aperture-averaged scintillation index can be substantially reduced. Generally speaking, the propagation properties of RPCBs in anisotropic non-Kolmogorov turbulence remain superior to fully coherent beams as well as Gaussian Schell-model beams, especially for relatively small receiving apertures.

The combination of wireless ultraviolet (UV) communication and mobile ad hoc network technology can effectively expand communication range of wireless UV communication. Using space division multiplexing, we design a UV mobile ad hoc network communication node transceiver and propose the method of acquisition, pointing, and tracking (APT) among communication nodes. The relationship between the time of acquisition and the speed of the node is simulated and analyzed. Based on the non-line-of-sight (NLOS) UV communication theory,we simulate the transmission rate between the designed two nodes by the Monte Carlo method when the on off keying (OOK) modulation is used and the bit error rate is 10-5 . We do an outdoor NLOS UV communication experiment, and the experimental results show that the code rate curve and the simulation results have the same trend. When the transmit power is 50 mW, the maximum deflection angle of NLOS communication is set to 6°, and the bit error rate is 10-5, the originating code rate can reach 1.64×106 Baud·s-1.

To overcome the color distortion in sky regions and large white regions brought by the dark channel prior dehazing algorithm, we propose a single image dehazing algorithm based on sparse representation model and feature extraction. Firstly, the algorithm learns the sparse features of foggy images via training sparse dictionary, and optimizes the sparse coefficients of the rough medium transmission image preliminarily. Then, the algorithm refines the medium transmission image by the sparse features of foggy gray images. Finally, with the converse solution of the degradation model, the algorithm obtains the dehazing image. The experimental results demonstrate that the proposed algorithm has obvious advantages in the processing of the sky area, and at the same time, it can recover more image details and marginal information.

Three-dimensional display technology, which aims at presenting almost-realistic three-dimensional images to the observer without any auxiliary devices, has drawn great attention from both academia and industry in recent years. In this paper, we implement a flat three-dimensional display using multi-layer semitransparent thin film structure. Compared to traditional three-dimensional display technologies, the proposed display technology has higher resolution, higher contrast, and simpler structure, thus easier to fabricate. Based on our prototype of flat three-dimensional display with multi-layer, we further extend it to spatial three-dimensional display using the principle of specular reflection, which allows observers to see virtual three-dimensional objects from different directions in the air.

Utilizing the mathematical model of the orbit mechanics, the orbit prediction is to forecast the space target’s orbit information of a certain time based on the orbit of the initial time. The proper satellite radiometric calibration system (PSRCS) and calibration orbit prediction process are introduced briefly. On the basis of the research of the calibration spatial position design method and the radiative transfer model, an orbit prediction method for proper satellite radiometric calibration is proposed to select the appropriate calibration arc for the satellite to be calibrated and to predict the orbit information of the proper satellite and the satellite to be calibrated. By analyzing the orbit constraint of the proper satellite calibration, the GF-1 solar synchronous orbit is chosen as the proper satellite orbit in order to simulate the calibration visible time for different satellites to be calibrated. The results verify the feasibility of the proper satellite calibration orbit prediction method.

A kind of three-dimensional measurement system consisting of an ultra-large-scale line structured-light sensor and a two-axis guide rail is designed to realize the high-accuracy rapid three-dimensional measurement of large-scale free-form surface workpiece. The structured-light sensor acquires the image driven by the two-axis guide rail, and obtains the three-dimensional coordinates of the target workpiece by calculation. A novel approach for simultaneous calibration of the intrinsic and extrinsic parameters of ultra-large-scale line structured-light sensor is proposed to transform two-dimensional image coordinate to three-dimensional camera coordinate. The method calibrates the quasi-one-dimensional target, and calculates the intrinsic and extrinsic parameters of line structured-light sensor with the obtained images of target and laser light during translation. Experimental result shows that the calibration results are reliable and the system measurement error is within 0.6 mm, which meets the design requirement. The calibration process is simple, easy to make target, and suitable for the industrial field calibration.

Aiming at the problem that the existing salient object detection algorithms suffers from the similar background interference, the detection accuracy of the target is low and the stability is poor. We propose a salient object detection method based on binocular vision. Firstly, inspired by the visual characteristics of the human eye, we consider the depth information acquired by binocular vision model as the salient features based on human visual characteristics. Secondly, we use the depth information and the result of region segmentation based on multi-feature fusion clustering to analyze the regional level depth saliency of image quantitatively. Thirdly, we make the weighted fusion of the global saliency map and regional level depth saliency map to highlight the objection area. Finally, we suppress the background to complete salient object detection based on the regional distribution of fusion results. The results show that compared with the existing methods, the proposed method can effectively suppress the interference of similar background with high accuracy and stability simultaneously.

In order to solve the problems of traditional airplane detection methods, such as low accuracy, high false alarm rate, and low speed, we propose a fast airplane detection method based on multi-layer feature fusion in a fully convolutional neural network. Firstly, we sample the shallow and deep features separately and fuse them at the same scale, which can alleviate the problem that the deep features are too sparse to express the small-size objects. Secondly, we redesign the size of the reference boxes to adjust to the practical size of the airplane in the input image. Thirdly, we replace the fully connected layers by convolutional layers to reduce the network parameters and adapt to input images with different sizes. Fourthly, we multiplex the convolutional layers and the learning-feature parameters of the proposal network and the detection network to improve the detection efficiency. The simulation results show that compared with typical airplane detection methods, the proposed method achieves higher accuracy and lower false alarm rate and greatly accelerates the detection speed.

In order to solve the problems of weak edges, uneven illumination, and non-uniform bubble distribution in floatation surface bubble image, we propose a floatation bubble delineation method by combining nonsubsampled Shearlet transform (NSST) and multiscale boundary detection and fusion. First, we use NSST to decompose a bubble image into a low-frequency and multiscale multi-directional high-frequency subband images. Then, we use adaptive fractional order differential valley detection templates to extract valley boundary of the low-frequency subband, detect the edge information of high-frequency subband images based on scale correlation coefficient and direction modulus maximum, and extract boundary detail from the edge information by ridge characteristics determination. Finally, we implement bubble delineation through multiscale boundary fusion and morphological processing. Experimental results show that, the proposed method is affected little by noise and illumination, and can effectively delineate bubbles with different distribution types. The average detection efficiency and accuracy are much better than those of existing methods. This method meets the dynamic changes of flotation working condition well.

The existing calibration methods of zoom lens are mostly characterized by great difficulty and low dynamic accuracy. We propose a dynamical estimation method of internal and external parameters based on homography matrix for binocular camera with zoom lens and a fast plane reconstruction method. Firstly, we estimate two types of homography matrix using matching points of binocular images and matching points before and after zooming. Secondly, using mathematic model of zoom lens and the homography matrix, we calculate internal and external parameters of camera pair after zooming to realize the dynamic estimation and optimization of binocular parameters after zoom lens distortion. Finally, we achieve the fast matching and reconstruction of the planes by homography matrix of binocular images. The experiment results show that the calculated internal and external parameters are in good agreement with the calibration results. After zooming, the normalized error of computational homography matrix is less than 0.01, the error of image reprojection is less than 1 pixel, and the accuracy of reconstruction is less than 0.1 mm.

The change regulation of vigilance based on functional near-infrared spectroscopy (fNIRS) is studied. During the experiment, the hemodynamics signals of 12 participants including oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (Hb) are recorded through 10 channels fNIRS technology, and the behavior data of the participants are simultaneously recorded. The results indicate that vigilance of the participants can be labeled as three levels: the first 30 min is high vigilance level, the middle 30 min is general vigilance level, and the last 30 min is low vigilance level. Additionally, the results indicate that channel 2 on the left side and channel 9, channel 8, channel 7 and channel 6 on the right side of prefrontal have better sensitivity to vigilance change. Under support vector machine recognition model, the average accuracy over the 12 participants of three-level-classification results is 76.9%. The experimental results confirm the feasibility of fNIRS in the evaluation of vigilance, and point out the specific locations of the sensitive brain region, which provides a new way for real-time vigilance monitoring.

Biological research requires dynamic and wide-field optical microscopy with nanoscale resolution to study the biological process. To address this issue, a structured illumination microscopy based on near-field diffraction enhancement using metallic grating is proposed. The technique introduces spatial light modulator and metal grating on the basis of the conventional e-pi microscope. The sub-wavelength imaging performance of this technique is studied theoretically and numerically. The results show that the transverse spatial resolution of full width at half maximum is 65 nm at wavelength of 520 nm and numerical aperture of 1.3. Compared with the traditional wide-field microscopy, the resolution of the technology increases by about 3.7 times. This technology has potential application in biological research.

A dual cosinoidal phase modulation method is proposed to improve spectrum compression of the super-Gaussian pulse with nonlinear chirp in a highly nonlinear fiber. The results show that the temporal unlevel phase of the super-Gaussian pulse resulting from the mismatch between the initial nonlinear negative chirp and the nonlinear positive chirp that induced by self-phase modulation can give rise to the spectrum splitting and residual sidelobes, which degenerates the quality of spectral compression. Phase compensation by external dual cosinoidal phase modulation can effectively reduce the residual sidelobes in the spectrum and extend the distance of spectral compression, so that the quality of the spectrum compression can be enhanced. And the amplitudes and frequencies of the dual cosinoidal phase modulation originate from the nonlinear phaseshift analysis for the pulse. Also, the quality of spectrum compression in a wide range of the initial stretching factor can be optimized.

A Fourier transform imaging spectrometer (FTIS) of medium and long wave infrared bispectrum spatiotemporal joint modulation based on static interference system is presented, and the front telephoto system and post-imaging system are designed. According to the theory of aberration, the initial structure of the reflective front telephoto system is calculated by adding the constraint. The large-scale astigmatism and coma aberration caused by the tilt beam splitter and compensation plate in the system are corrected through the optimization of the optical design software. The modulation transfer function (MTF) of the front telephoto system is close to the diffraction limit in the range of the medium wave and long wave bispectrums. The transmission structure is adopted in the two post-imaging systems of the spectrometer. The results of spot diagram show that the root mean square (RMS) values of the imaging spots of the post-imaging systems are less than 7.0 μm in the bispectrum range. The overall optical system is made up of the front telephoto system and the post-imaging system, whose field of view is 1.5°, medium wave channel F number is 4 and long wave channel F number is 2. In bispectrum range, the spot diagram RMS value of the overall system is less than 10.7 μm, and the MTF of the overall system is more than 0.5 at the detector’s characteristic frequency of 17 lp/mm. The overall system has a good imaging effect.

The unidirectional transmission of light waves based on photonic crystal heterostructures is of great significance in all-optical networks and optical signal processing. Based on the total reflection principle, two kinds of triangular lattice photonic crystal waveguide heterostructures are designed by using silica and germanium materials. The finite difference time domain method is used to analyze the unidirectional transmission performance in a broad bandwidth. The structure is further optimized by changing the waveguide width at the forward exiting end. The results show that in the heterostructure one, the forward transmittance of TE mode wave is higher than 0.8 in the wavelength range from 1458 nm to 1517 nm, and the transmission contrast is higher than 0.9 with unidirectional transmission. In heterostructure two, the forward transmittance of TM mode is higher than 0.8 in the wavelength range from 1498 nm to 1689 nm, and the transmission contrast is close to 1 with unidirectional transmission.

Metamaterials with I-shaped metal structure units have abnormal electromagnetic properties. The finite difference time domain (FDTD) method is used to simulate the I-shaped metamaterials. It is found that there are three special reflected modes in symmetric I-shaped structure. When the symmetry of the structure is broken and the slit length increases, a new mode appears, respectively, and five specific reflection modes are in the structure. Theoretical model is developed and physical causes of formation of the five reflection modes are analyzed combing near field distribution. It is believed that different position resonance couplings of surface plasmons in the I-shaped metal structure units lead to the five specific reflection modes. When the symmetry of the structure is broken, new resonant mode appears. When the slit length increases, high order resonance mode appears.

On the basis of the assumption of local thermodynamic equilibrium and isothermal spheres, the continuum emission (recombination radiation and bremsstrahlung) and line emission of argon plasmas are investigated. Net emission coefficients are calculated for the argon plasmas in the wavelength ranges of the entire, vacuum ultraviolet and non-vacuum ultraviolet spectra at 0.1 MPa and the temperature range from 5000 K to 25000 K with different sphere radii of Rp. Special attention is paid to analyze the contribution of the vacuum ultraviolet to the entire emission and the influence of various radiative mechanisms on vacuum ultraviolet. The results show that for Rp=0 mm (without self-absorption), the contribution of the vacuum ultraviolet is greater than 94.8%, with the line emission dominant in the radiation. For Rp=1 mm, the contribution decreases due to the strong absorption of the vacuum ultraviolet, accompanied by the improved influence of atomic continuum. Nevertheless, the contribution is still greater than 80% at temperature above 17000 K. Our calculation results are proved to be correct by comparing with the previous calculated and experimental results.

Aiming at the fact that the asymmetric channel is not considered in the traditional quantum key distribution (QKD) protocol, the performance parameters of measurement-device-independent QKD protocol for the asymmetric channel with heralded single-photon sources are investigated. The relationships between the mean-photon numbers, the unilateral transmission efficiency, the key generation rate and the channel transmission loss in the protocol are analyzed. The performances of measurement-device-independent QKD protocols with the heralded single-photon sources for symmetric and asymmetric channels are compared. The simulation results show that, as the channel transmission loss increases, the key generation rate and the safe transmission distance decrease gradually, but the performance for the asymmetric channel is still higher than that for the symmetric channel.

Load identification plays an important role in structural health monitoring. A method to identify load for a cantilever beam based on dynamic strain measurement by FBG (fiber Bragg grating) sensors is presented to facilitate the control over the system during structural health monitoring. The algorithm is based on Kalman filter, using the strain measured by FBG sensors as observed signal, and the gain matrix, the residual innovation sequences and covariance matrix generated by Kalman filter to estimate the load in real time through least squares algorithm. The proposed load identification method based on FBG sensors is a recursive method, which means that recent measurement value and previous estimated value need to be kept in storage. This will save considerable memory and greatly decreases the system burden. The proposed method is based on Kalman filter, and this can be helpful for system control by using optimal control theory after identifying load. To prove the effectiveness of the proposed method, numerical simulations and experiments of the beam structures are employed and the results show that the method has good stability and real-time capability.

An approach for measuring three-dimensional (3D) volume scattering function (VSF) of suspended particles in water is proposed, in which one can simultaneously obtain the VSFs of several scattering planes in the hemisphere space by using the detection method of parabolic mirrors combining with sensors. The 3D VSF measuring device is constructed. With the standard polystyrene particles with diameters of 57-954 nm as samples, the VSFs of the suspended particles in water are obtained, which are in multiple scattering planes corresponding to azimuthal angles of 0°-180°. The detectable scattering angle is in the range of 18°-160°. The experimental results agree with the simulated ones, which verifies the feasibility to detect the VSFs of suspended particles with diameter less than 1 μm in water by this device.

To study the polarization properties of rough surfaces, we build a polarized bidirectional reflectance distribution function model based on the micro-facet theory by considering both the diffuse reflection and mirror reflection of micro-facet. By decomposing and changing the form of Mueller matrix, based on polarized bi-directional reflectance distribution function, we get three sub-matrixes and corresponding expressions which characterize the dichroism, phase delay, and depolarization of rough surfaces. We calculate the polarization properties of typical rough surfaces, and analyze the impact of incidence angle, azimuth angle, and roughness on polarization properties of rough surfaces. The results show that, the dichroism of rough surfaces has the maximum in the range of incident angle, and increases with increase of azimuth angle. The phase delay has the maximum in the range of azimuth angle, and decreases with increase of incident angle. The depolarization has the minimum in the range of incident angle, and decreases with increase of azimuth angle. The roughness has little impact on these factors except for depolarization.

With M-shell X-ray radiation from plasma produced by nanosecond high power laser irradiating on high atomic number targets, the experimental study on Si K-edge X-ray absorption near-edge structure (XANES) is carried out with an elliptic cylinder crystal spectrometer. By describing the experiment setup in detail, and analyzing the principle of elliptic cylinder crystal spectrometer, the position-energy dispersion relation of the spectrometer is obtained, and the laser plasma X-ray spectra from six targets of Au, Lu, Yb, Dy, Ta, and Co are compared. The results show that by comparing the laser plasma X-ray spectra from six targets of Au, Lu, Yb, Dy, Ta and Co, we find that the M-shell radiations from Lu, Yb, and Dy are more brilliant than the others in the vicinity of Si K-edge (1839 eV), and the corresponding signal to noise of XANES is much better. The XANES obtained from experiment and calculation by FEFF9.0 software are in good agreement with each other, indicating that the static experimental result of single shot is reliable.

The framing converter is an important two-dimensional spatial resolution diagnostic device in the inertial confinement fusion experiment. In order to study the imaging performance of pulse-dilation framing converter using short magnetic focusing, the spatial resolution and imaging surface are simulated by the electron motion trajectory and imaging distribution of the converter, and the aberration theory is used for analysis. The result shows that the spherical aberration and field curvature of short magnetic focused system are the main reasons for the loss of spatial resolution, the spherical aberration of the single/double lenses tube are 0.229 and 0.07, the field curvature are 0.021 and 0.009, respectively. The smaller spherical aberration and field curvature are, the better imaging performance of the tube is.