The factors affecting the resolution of varied line-space grating angular displacement sensor are analyzed. The calculation formula of the sensor resolution is deduced, in addition, the relation between the parameters and the method of improving the resolution are discussed. Besides, it is theoretically analyzed and verified that the diffraction order has influence on the resolution. The relationship between the resolution and the grating space of the varied line-space grating angular displacement sensor is proved, as well as simulated and verified. Theoretical guidance and calculation method are thereby provided for the design and optimization of the varied line-space grating angular displacement sensor.

The four-quadrant photoelectric inspection model is studied on the basis of the second atmospheric channel modulator for enhancing the four-quadrant photoelectric inspection adaptability of the atmospheric channel. Firstly, the conversion relations of natural resolution and division precision are discussed from error theory perspectives for the analysis of the axis detection system. Afterwards，through the analysis of restricted constraint condition of four-quadrant photoelectric inspection system in atmospheric channel, it is found that the signal-to-noise ratio (SNR) of the beacon light and axis offset are two main technical parameters affecting the electro-optical inspection system. Then a concept is presented that enhancing natural resolution optical-axis detection system can lower the sensitivity of the whole system to the atmospheric channel. Finally, the division precision of axis detection is found to be gravely affected by the atmospheric channel. Axis detection can still provide precision for wireless laser communication if the natural resolution of four-quadrant photoelectric inspection is enhanced.

LEDs are not only used as lighting devices, but also as transmitters for communication systems. In this paper, the electronic guide system based on outdoor lighting LED mobile optical communication is designed. The lighting LED driver, modulation code, the channel characteristics of outdoor lighting LED and the trajectory recognition of light receiving navigator and voice broadcast are analyzed in theory. The relationship among pulse modulation LED, optical transmission and light flashing is discussed, and the visualizing electronic guide map is established in this embedded environment. The optical receiving system provides mobile track-oriented services for tours by picture, text and sound, and makes self-service electronic guide features be realized at the set area. Experimental results show that the system can make normal scenic lighting, get the position information transmission by using light radiation region attractions, and display and broadcast the corresponding information of the attractions simultaneously. The system can reliably realize the visual navigation of the moving path of optical receiver target. It has good utility and spread profit and shows a great advantage in the short-range wireless optical communication.

This paper mainly studies the bias control performance for multiple bias voltages of 16-quadrature amplitude modulation 16-QAM optical transmitter based on IQ optical modulator. The cooperative control of two Mach-Zehnder modulators′ (MZMs′) bias voltages and Mach-Zehnder interferometer′s (MZI′s) bias voltage is analyzed theoretically. Multiple extreme values of the average output optical power as the monitoring signal of feedback control for two MZMs′ bias voltages are also studied by numerical simulation. The results show that the average optical power of 16-QAM optical transmitter is the extreme value when MZMs′ bias voltages are biased at the null transmission points. This conclusion is unaffected by MZI′s bias voltage, and there does not exist the risk of trapping in local extremum if the amplitude of the driver signal is controlled in the proper range.

By simulating the reflection and refraction of single-ray at each interface of double-layer dielectric sphere, the force exerting on the dielectric sphere by a single ray is analyzed, and the force exerting on the sphere by the total Gaussian laser beam is calculated. The axial force is calculated when the refractive index of inner layer of double-layer sphere is 1.0 and 1.9, respectively, and then the influence of the refractive index of inner layer on optical tweezers trapping force is analyzed. As shown by the calculation results, the influence of different refractive indices and radii of inner layer on trapping force is notable. As the refractive index of inner layer is smaller than that of the outer layer, the stability of optical trapping is improved, but the spatial scale of trapping is reduced. And the performance of optical trapping is reduced as the refractive index of inner layer is larger than that of the outer layer. Analysis conclusion of the force trapping double-layer sphere provides reliable theoretical basis for this kind of sphere used as an optical handle.

Images captured from optical holograms printed on goods, documents, personal identity cards, etc. would be distorted due to the imaging quality of the optical system and the influence of shooting conditions. A distortion correction method for the captured optical holograms is proposed. Firstly, an image pre-processing technique is used to extract the target hologram and the boundary of the target hologram is determined. Then four vertexes and midpoint positions of the hologram and the corresponding ideal points can be sought automatically. The holograms with projection distortion and nonlinear distortion are corrected by using different polynomial models. Compared with the other methods, the proposed one is simpler and faster, as it does not need the high-precision calibrating module and deals with an object′s hologram only in calibrating and recognizing process. The experiments show that the corrected holograms can be recognized clearly. The proposed method has the advantages of high efficiency, fast speed and high-recognition rate.

In traditional Gabor in-line holography, direct passing reference wave and diffracted object wave overlap in space, thus it is unable to realize phase-shifting interferometry. A method to realize Gabor in-line phase-shifting digital holography is presented. Based on the characteristic that different spatial frequency components are separate in the spatial frequency domain, a spatial light modulator is placed in the spatial spectrum plane of the 4f system to introduce phase-shift to the zero-frequency component of spatial frequency spectrum, and the corresponding phase-shifting algorithm is utilized to obtain the reconstructed image. Theoretical analysis and experimental results show that the proposed method can improve the quality of reconstructed image while retaining the original advantages of conventional Gabor in-line holography at the same time.

We studied the intensity distribution of single soliton at the focal plane in tight focusing system. The soliton is an analytical solution of differential nonlinear Schrdinger equation (DNLSE) with non-vanishing boundary condition. Bright and dark solitons are considered for different soliton parameters and different numerical apertures of the tight focusing system. The simulation result shows that the focusing property of dark soliton has a good periodicity with the soliton parameter, the bright soliton has a better focusing property than the dark soliton, and the focal spot of the soliton will shift by changing the soliton parameter, which provides a possible application in optical guiding.

Due to the characteristics of small size and light weight of unmanned aerial vehicles (UAVs), wind has great influence on UAV flight, and images photographed by UAV suffer large distortion. Therefore, it has practical significance to correct the distortions before image matching. We focus on extracting the edge contour based on Canny operator and obtain the large number of surface features contour using Hough transform theory. Then step approximation is used to obtain inverse solution model of the real image pixel coordinates, which is used to correct the results. Meanwhile, on the foundation of parallel and perpendicular terrain contour lines, the correction methods of quadrilateral connection and parallel lines constraint are proposed. It is found through experiments that the achieved results are satisfactory.

Zero order waveplates and achromatic waveplates are biplate compensators. The misalignment angle between the axes of the two waveplates affects the phase modulation of the designed compensator. A method for measuring the misalignment angle of the optical axes is reported. The method is based on a straight-through rotating-compensator system. The measurement can be implemented without the knowledge of the relative azimuthal angle between the polarizer and analyzer. The influence of the misalignment angle on the ellipsometric measurement is analyzed. The principle and mathematical expressions are given. The validation of this method is demonstrated by the simulation of measurement process. This method is valuable for inspecting and hence for improving the accuracy of biplate compensator in manufacturing.

Fourier transform profilometry (FTP) is a kind of active technology by projecting a grating on object surface to measure the three-dimensional (3D) shape. It requires only one structured fringe pattern to analyze the entire range of the measurement system. Based on the subtraction of the distortion grating phases of the object surface and the reference surface, FTP can measure the height distribution. But in divergent light path the coordinate of the height is only an approximation, so that in precise measurements we need theoretical correction. We analyzed the cause of the height measurement error introduced by the coordinate confusion, and made the first order correction. In experiment, we used bi-color fringe technology, in combination with the Matlab software, to and successfully carried out a quantitative analysis of the error.

Laser butt welding of 7075-T6 aluminum alloy is carried out by Nd:YAG laser, and the welding sample quality is measured by ultrasonic fault detector. The ultrasonic echo data are gathered and analyzed by experiential waveform analysis, and different typical echo data are collected at different processing paramenters of laser butt welding. The relation between echo feature and processing parameters of laser butt welding is also obtained. The research results show that processing parameters of laser butt welding including laser voltage, laser defocusing amount and welding speed are very important to the welding quality. The optimum processing parameters can be obtained by analyzing the ultrasonic echo data. The research provides a new method to measure the quality of welding seam.

The laser-diode-array (LDA) pumped Yb:YAG thin-disc 1030 nm laser is demonstrated. The Yb:YAG crystal doped with 10% Yb atomic fraction is 420 μm in thickness and 11 mm in diameter. It is mounted onto the micro-channel copper heat sink by Cr/Au/In. The four-pass optical coupling system is well designed with two spherical imaging mirrors (diameter 26 mm, radius of curvature 50 mm). With 32.4 W pump power, the maximum output power of 13.55 W at 1030 nm is obtained. The optical-optical conversion efficiency is 41.8%.

Recently, improving the visible-light utilization ratio by the metal and non-metallic impurities co-doped TiO2 semiconductor is a research focus. The band structure, density of states, partial density of states and optical properties of Mn-doped, N-doped and Mn-N co-doped anatase TiO2 are studied by plane-wave supersoft pseudopotential method based on the density functional theory. Contrasting Mn, N, Mn-N doped anatase TiO2, the results show that N single doped TiO2 effectively makes the band gap decrease from 3.2 eV to 2.83 eV and a Mn single doping results in three impurity levels in the band gap, which reduces the electron transition energy from the valence band to conduction band. While Mn-N co-doped anatase TiO2 crystals lead the Fermi level to move to the conduction band, simultaneously forming impurity level in the valence band top and reducing the band gap. The electronic transition energy is about 2.1 eV (wavelength is 590 nm) from impurity levels to the conduction band, which exactly corresponds to the absorption peak in the absorption spectrum. This will more effectively improve the utilization of the visible light.

We introduce a design method of the 1.57 μm eye-safe laser range-finder′s optical system. It utilizes the PW method according to the primary aberration theory of thin lens system to determine the initial structure of the range-finder′s optical system. A symmetric structure of range-finder′s optical system is designed by the Zemax software. After optimization, the symmetric optical system not only has the simple structure, convenient processing and assembly and low cost, but also satisfies the requirements of the performance of the range-finder′s emitting and receiving parts.

The athermalization method for dual-wavelength infrared optical system is introduced. An athermalized dual-wavelength infrared dual-view optical system is designed. The optical system adopts the passive optical athermalization technology and a re-imaging system. A passive optical athermalization design of dual-wavelength infrared optical system is presented by using three common materials Ge, ZnS and ZnSe and two aspherical surfaces. The results show that the optical system working in the 3.7～4.8 μm and 7.7～10.3 μm wavelength bands has a compact structure and can meet the requirement of 100% cold shield efficiency. The imaging performance of dual-wavelength infrared optical system is very well in the temperature range from -60 ℃ to 70 ℃. The correctness and feasibility of the design method are proved.

An athermalization design of switchable dual-field-of-view optical systems for 8～12 μm wavelength band using infrared focal-plane array (FPA) is presented. In order to switch the field-of-view (FOV), two different optical configurations are explored and compared. The first scheme is based on the axial motion of a lens group and the second is based on a rotate-in motion of two widely separated lens groups. It is found that the rotate-in scheme achieves better performance than the step-zoom scheme, but the optical passive athermalization misfits this scheme. The step-zoom scheme is easy to use the optical passive athermalization to achieve lighter weight and smaller volume, and the performance is well for small zoom ratio. Aspheric surfaces are utilized to control aberrations and reduce the total lens cost. The results show that the optical system in the 7.7～9.7 μm wavelength band has a compact structure and can achieve 100% cold shield efficiency. The final optical designs along with their modulation transfer function (MTF) are presented, showing excellent imaging performance in dual FOVs at the temperature range between -60 ℃ and 70 ℃.

Off-axis three-mirror system has the advantages of good imaging quality of vision, large field, compact structure and no central obscuration, so it is increasingly used as the structure of the space telescope. According to the requirement of optical parameters of the optical system design, an off-axis three-mirror telescope system is designed. It has a spectral region from 0.4 μm to 0.8 μm, a focal length of 4000 mm, a relative aperture of 1/10 and a angle of vision of 2.08°. For the designed optical system, the imaging quality is good, at the spatial frequency of 62.5 lp/mm, the modulation transfer function (MTF) value of each field of vision is greater than 0.5, and the imaging quality is close to the diffraction limit. The design result satisfies the requirement. Meanwhile, the effects of mismatch of the primary mirror, the secondary mirror and the tertiary mirror on the MTF of the system, and it is found that mismatch of the secondary mirror shows the greatest influence. This may provide reference for the assemble work of system.

The combination of photonic crystal technology and terahertz technology has provided a new idea to design the terahertz-wave modulator. A terahertz-wave modulator based on self-collimation effect and Fabry-Pérot (F-P) cavity is presented. It is made by filling 5CB liquid crystal into the air holes of the photonic crystal which is designed with special structures. The transmission characteristics of the THz wave, including time-domain response, frequency-domain response and energy distributions of the steady state, are studied with the finite-difference time-domain method (FDTD). The modulator, with a modulation rate of about 10 kHz, an insertion loss of about 0.308 dB, and a tuning range of 0.308～34.32 dB, has a small size. It can be designed according to the demand of the working wavelength and can be easily integrated. Wide operating wavelength range is the greatest advantage of this modulator. It is an ideal terahertz-wave modulator.

Detailed derivation is conducted to solve the Bloch wave solutions of the electromagnetic wave theory of two-dimensional photonic crystal and periodic media. The theoretical basis for the existence of the band gap in the photonic crystal is given. We measured the concentration of fructose solution in a two-dimensional triangular lattice photonic crystal using plane-wave expansion method. To get the numerical simulation of photonic band diagram for analysis, we take advantage of the large permittivity of silicon and fructose solution. The results show that the photonic band gap (PBG) of TE mode distinctly broadens with the difference of the concentration of the fructose solution but there is no PBG in TM mode, when fructose solution is used as the dielectric material in the air hole. The results of this study and the proposed method may play a guiding role in clinical applications for helping hyperglycemia patients.

This paper introduces the principle of four-quadrant detector and the various factors influencing its detection sensitivity. The influence of dead zone on detection sensitivity is analyzed in detail. The deviation of spot is simulated with Matlab software. The experimental system, including the circuit part and optical part, is designed. Light intensity of each quadrant of the detector is detected by the circuit part. When the width of the dead zone is 0.1 mm, the deviation of spot is measured for the light spot radii of 0.6 mm and 0.4 mm, respectively. The experimental and theoretical results show that the detection sensitivity increases with the size ratio of dead zone to spot increasing.

The design of a polarization beam splitter(PBS) is presented according to different band gaps with different photonic crystals. The splitting properties of the PBS are numerically simulated and analyzed by using the finite-difference time-domain method and the plane wave expansion method. It is shown that a highly efficient splitting for TE mode and TM mode can be achieved. The transmission probability is above 92% for both TE mode and TM mode while the incident wave is Gaussian and the wavelength range is 1.5～1.58 μm. Especially the transmission probability can reach 95.5% for TE mode and 99% for TM mode the 1.55 μm Gaussian incidence. Meanwhile, its size is only 10 μm×11.5 μm. The PBS makes a promising candidate in the future integrated optical circuit.

The defect-mode property of ten-fold photonic quasicrystal (PQC) is investigated, and the changes of light path when introducing different defects are observed. The transmission spectra of ten-fold PQC are calculated by using finite-difference time-domain (FDTD) method. By changing the crystal structure and introducing the point and line defects, the defect-mode characteristics are investigated, leading to the design of good micro-cavity and waveguide structures. In TE mode, the transmission spectra with defect modes are observed and quality (Q) factors are calculated to optimize the micro-cavity structure.It has the biggest Q factor when the central dielectric cylinder is removed. Furthermore, we design different waveguide structures and explore the field distribution. Different waveguide structure can be used to control different light path and choose different incident light frequency.

The phase velocity and the group velocity of focused pulsed light beams are studied in the vicinity of the focus of an aberration-free lens analytically and numerically. The phase anomaly caused by the diffraction leading to superluminal pulsed beam propagation is illustrated. The effect of the small shift in position between the geometrical focus and the beam waist of the focused beam on the group velocity and the phase velocity is given.

Fiber Bragg grating (FBG)-based accelerometer has been a research focus in the fields such as civil, electromechanical and aerospace. The principle and mechanical model of FBG-based accelerometer are introduced briefly. The latest development of FBG accelerometers with different structures and principles is emphasized. According to different operating frequency ranges, the present situation of the development of FBG accelerometer with low and high resonant frequencies is expounded respectively. Particularly, this paper illustrates the accelerometer capable of acceleration measurement in multiple dimensions simultaneously. And the further outlook of FBG accelerometer is prospected.

Final optics assembly (FOA) is one of the most important parts in high-power laser facilities. The FOA primary functions include frequency conversion, focusing, wavelength separation and diagnostic beam sampling, which can be realized through optimized FOA optical and structural design. Such a design can meet the basic requirements of high-power laser facilities for different experiments. However, laser-induced damage of final optics and several nonlinear effects resulting from high intensity ultraviolet (UV) laser pulses are major concern during FOA design, construction and operation. This paper reviews the development process of FOA in high power laser facilities, analyzes the core consideration, and discusses the main solution in FOA design.

In recent years, as a novel mid-infrared photonic crystal fiber (PCF), chalcogenide glass PCFs have attracted much attention. We summarize the properties of chalcogenide glass PCF and its research progress, especially the nonlinear optical effect and its applications. The methods to improve and measure the nonlinear coefficient are also introduced. Finally, the development prospects are disscussed.

X-ray microscope has the property of providing high resolution. However, it should employ phase contrast for imaging materials consisting of light elements, such as biological samples, because the signal obtained from the penetrating X-rays is very weak and as a result the image contrast is extremely low with increasing photon energy and decreasing object size. Several phase contract methods for high-resolution X-ray microscope, including Zernike phase contrast mode, differential interference mode and off-axis holographic mode, are reviewed. Basic principles and main research progresses of these phase contrast microscopic techniques are presented, and their advantages and disadvantages are compared, in an attempt to show potential advantages as well as main challenges of X-ray phase contrast microscopic imaging techniques in detecting internal structures of biological samples.

A tunable single-frequency optical parametric oscillator (OPO) based on quasi-phase-matching is an ideal coherent light source with, high efficiency, good coherence, wide tunable spectral range and reliable and stable performance. It is widely used in laser interference measurement, laser differential absorption radar, spectral analysis, optoelectronic countermeasure, laser medicine etc. Due to the wide optical parametric gain and high power pump, most OPOs are often operated in multiple longitudinal modes, and a variety of methods are needed to achieve single-frequency operation. These methods include frequency selection method (such as injection-seed, grating and Fabry-Pérot etalon) and the operation characteristics of the OPO system itself (pump threshold ratio, thermal self-locking effect and thermal waveguide effect). This paper analyzes the realization of tunable single-frequency OPO.