Rigorous coupled-wave analysis (RCWA) method is widely used in the critical dimension (CD) measurements and getting profile structure of two-dimensional periodic grating. In the application process, Fourier series expansion of formula for relative dielectric constant distribution in two-dimensional grating periodic unit is needed, but in the previous studies, the Fourier coefficient calculation formulas are only for several regular gratings, so the grating shape types whose diffraction analysis will be made by RCWA method are limited. To this restriction, new general Fourier coefficient calculation formulas for relative dielectric constant distribution in two-dimensional periodic grating are put forward by rectangular grid subdivision. They can be used for Fourier series expansion of relative dielectric constant distribution in arbitrarily shaped two-dimensional periodic grating and be used in RCWA method for diffraction problems.

According to the coupled-mode perturbation theory, the coupled-mode equations for spun magnetically-induced fiber Bragg gratings (SMFBG) is derived. The dependency of grating spectra on the spun-induced refractive index change is numerically analyzed by using the shooting method and the theoretical results are identical with the experimental data from literatures. The concept of magnetically-induced circular-polarization dependent loss (MCDL) is proposed for analyzing the magnetic field sensitivity of SMFBG. It is shown that the MCDL of high-speed spun (or isotropic) SMFBG possesses optimal magnetic field sensitivity; however, the appropriately low-speed spun MFBG has a larger peak MCDL, which is helpful to magnetic measurement. Compared with the polarization-dependent loss (PDL) method, the MCDL method is less dependent on linear birefringence and is more convenient for theoretical analyses.

The experiment of one-time writing long period fiber grating is performed. It not only improves the efficiency of fiber writing process, but also solves the problem of multisession mismatching. So it has important research value. From the experiment, we find that effective refractive index periodical modulation and appropriate physical deformation occur in the fiber core and cladding under appropriate pressure and radiation, and the LPFG is one-time written successfully using high-frequency CO2 laser in single-mode fiber. Experimental results show that the grating transmission spectrum features in one-time writing process are better than that in multiple writing process.

A design scheme of demodulation system based on field programmable gate array (FPGA) for fiber Bragg grating(FBG) temperature sensor is proposed. Using the principle of (direct digital synthesizer (DDS), the drive voltage of Fabry-Perot (F-P) filter is constituted by FPGA. It can achieve 10 V. Many analog-to-digital (A/D) converters are controlled by FPGA to make up the successive data acquisition module. It can get the result in real time. The comb-shaped filter is used to correct the system in time. The index of a FBG sensor is calibrated confirmed. The system is used for denodulation between 30 ℃ and 100 ℃, and electronic thermometer and spectrograph are used to get the accurate result. The different records can be compared to assess the performance of system. The mean error of temperature is 0.19129 ℃, and the minimum temperature is 0.045 ℃, with the resolution being 1 pm.

Relaxation oscillation suppression in a short-cavity single-frequency distributed Bragg reflector (DBR) Er3+/Yb3+-codoped fiber laser is demonstrated. A tailored optoelectronic feedback circuit acting on the pump driver is designed to reduce the noise peak at the relaxation oscillation frequency of 1.15 MHz by 26 dB, to a relative intensity noise (RIN) value of -121 dB/Hz and thus the RIN value is below -120 dB/Hz across the whole frequency range. The noise suppression loop is integrated into the laser diode driver module and no laser beam quality degradation is observed.

Intensity modulated atmospheric laser communication requires the uniform and flat far-field intensity distribution and intensity uniformity will be improved due to the degradation of its spatial coherence. An experimental study of a D-shaped multi-mode fiber output optical field intensity distribution characteristics is presented, compared with the output optical field intensity distribution from the laser through the cylindrical multi-mode optical fiber and not via an optical fiber. Experimental results show that using a D-shaped multi-mode fiber as the mode mixer, the output beam has a low degree of coherence and good uniformity.

In the receiving end of quantum key distribution (QKD) system based on the polarization encoded BB84 protocol, the polarization control system is very key to QKD. In order to recover and stabilize very efficiently the damaged polarization states owing to these factors including the optical fiber, environment temperature and so on, the performance of the electric polarization controller (EPC) is analyzed and rotation matrix is introduced as the Müeller matrix of the EPC. A strategy of avoiding the blind zone is put forward and the real-time polarization control algorithm is designed in the non-ideal situation. The algorithm shows that every control process uses only two degrees of freedom to transform all possible polarization states and can improve greatly the rate of the controlling. Simulation results show that this algorithm is feasible.

For the problem of the change of capillary tube induced by thermal expansion and contraction with temperature change, a new temperature compensation method applied in extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor is proposed. Temperature compensation film (copper film in this paper) is deposited on the reflective fiber within silica tube to compensate the gap change caused by temperature variation. The experimental results prove the effectiveness of this method and a linear relationship between axial length of copper film and temperature compensation length is found. In experiment, the temperature compensation coefficient of 1 mm axial length copper film reaches 0.49 nm/℃.

Based on Kogelnik′s coupled-wave theory, diffraction efficiency of reflection volume holographic grating is analyzed for several parameters. We propose a method to broaden the diffraction angular bandwidth by superposing multiplex volume holographic gratings, each of which is oriented properly. Permised on the requirement of uniform diffraction, the diffraction process in multiplex volume gratings is analyzed to acquire the offset of Bragg angle between adjacent gratings, and the uniform-diffraction bandwidth versus multiple numbers and refractive index modulation are finally obtained. Numerical results show that diffraction angular bandwidth of multiplex volume holographic gratings increases linearly with the number of multiplex gratings and refractive index modulation depth. The angular bandwidth can be broadened markedly via increasing the number of superposed gratings with appropriate refractive index modulation depth.

We present a method of measuring the transmittance and Kerr coefficients of a paraelectric crystal by digital holography. Digital holograms of the crystal with different voltage are recorded, the amplitude and phase information are extracted from numerically reconstructed image. The transmittance of crystal is measured by use of the amplitude information, and the spatial distribution of the induced refractive index change can be obtained by different phase of different voltage and the effective electro-optic coefficient is calculated by means of the refractive index change. Experiment has been carried out by examining a paraelectric phase Mn0.25%:KLTN crystal, and the research results show that the method presented in this paper is successful and feasible, which are irrelevant at the shape of crystal and the size of light source.

All computation of surface area of images in various scales is performed in the original image by conventional computing method of fractal dimension. The algorithms are inconsistent with the fact that the details of image could change when the metric scale varies, as a result, the span of the fractal dimension in the same kind of ground object is too big and goes against the image segmentation and image classification. To solve this problem, a fast interpolation algorithm based on area weight is put forward to simulate the images with various scales, which is used to calculate the fractal dimension of image. Experimental results show that the proposed method speeds up to 10 times faster and has less variance within clusters than the conventional method according to the standard Lena image. In addition, it can resist image noise well. Therefore, the proposed algorithm is applicable to image segmentation or image classfication.

A multi-image encryption scheme based on optical wavelet transform (OWT) and fractional Fourier transform (FrFT) is proposed, which enriches the multi-image encryption method. The scheme combines OWT and FrFT to make full use of multi-resolution decomposition of wavelet transform (WT). WT can focus most energy of the original images on the low-frequency parts, so the sizes of images can be reduced as far as possible without loss of image quality. The mentioned properties can not only realize the multi-image encryption, but also make sure each image is processed alone. When encryption is finished, each image will get its own independent keys. Analysis of encrypted effects is completed. Furthermore, the influence of WT type and order are analyzed, and application and analysis of independent keys are accomplished as well. Numerical simulation verifies the feasibility of the scheme and shows that the problem of insufficient capacity is solved better. The security of the method is analyzed. It can be concluded that the method expands the space of keys, which improves the security. Moreover, the application of independent keys makes the variability and flexibility of scheme increase, which means that multi-user decryption, cascade, and multi-user authentication can be achieved. A simple photoelectric mixed device to realize the scheme is proposed.

In order to obtain the phase distribution from the intensity distribution of the light field in low-light conditions, we investigate the Zernike phase retrieval based on the Gerchberg-Saxton algorithm using the fractional Fourier transform and the corresponding optical system. By studying the relationship between fractional Fourier transform and Fresnel diffraction, the Lohmann optical system is improved. How the Fresnel near-field and far-field outputs influence the high and low frequency parts of phase recovery is analyzed based on wavelet theory. The numerical results show that the algorithm has good convergence and recovery accuracy with root-mean-square error (RMSE) less than 0.15λ(λ is the wavelength). When the outputting planes are placed in the Fresnel near-field, the high-frequency part of the recovery phase is better, while when they are placed in the far-field, the low-frequency part is better.

We propose an image fusion method based on infrared and visible images. The two cameras in the optical imaging system use the same optical axis. Laplacian pyramid transform is used to fuse the infrared and visible images. Then the fused image is combined with the infrared image to obtain the pseudo-color fusion image in YUV space. Experimental results show that the proposed method based on the fusion of infrared and visible images enhances the image information and highlight the specific target in the image significantly, and can get good results at a variety of environment conditions.

Adhesive structure is widely used in optical instruments because of its simplicity, uniform stress distribution and good temperature adaptability. The back embedded adhesive structure for mirror support is analyzed theoretically. The principle for choosing adhesive is determined as choosing adhesive with low elastic modulus. The adhesive structure parameters including adhesive thickness and adhesive area are analyzed from mechanical and thermal properties. The adhesive structure′s effect on mirror position accuracy is analyzed, which includes mirror decenter and movement along optical axis.

In order to measure the radius of curvature and conic factor of an off-axis aspheric mirror, a new method to measure the conic surface with a laser tracker is proposed. The data processing procedure after spatial 3D cordinates are obtained with the laser tracker is clearly explained. An off-axis reflecting aspheric mirror is tested in the experiment and the radius of curvature and conic factor are obtained using nonlinear least square fitting method. The root mean square error (RMSE) is only 1.6 μm while the coefficient of determination is up to 0.999999954. Besides, the results of our method and the existing methods are nearly the same. Both theoretical analyses and experimental results demonstrate that this is a simple, general and easily operated method, which benefits from the fast and reliable data processing. The proposed method meets the measurement requirements of conic aspheric mirrors.

In order to achieve the detection of the structural quality for complicated products accurately and rapidly, we adopt variable step-size sampling mechanism to quickly obtain the circumferential range image sequence for the product that has a variety of structural and spatial dimensional areas to be tested on the surface. With such an image sequence, rapid detection of multiple areas to be identified can be realized in the limited orientation by using incomplete data. Firstly, projection method is used to determine the rotational step and a minimum step size is selected as the qualified product sampling step in order to ensure the integrity of the information in the standard library. Secondly, the scale invariant feature transform (SIFT) algorithm and binary search are selected to find the optimal location information of product in the standard image library. Finally, the correlation degree is calculated to discriminate defects in some areas. The experimental result shows that the variable step-size method can save an average detection time of 4.14 s in comparison with the traditional fixed-step detection in the premise of ensuring the accuracy of detection.

An edge-emitting diode laser based on the asymmetric Bragg reflection waveguide is reported, which utilizes Bragg reflectors as the n-doped waveguide. The optical field is confined in the low-index core layer through photonic bandgap (PBG) effect, resulting in large mode expansion and stable mode characteristics. The reduced overlap of the optical field and the p-doped total internal reflection (TIR) waveguide helps to increase the efficiency of the laser. The 3-μm-wide ridge lasers with uncoated facets demonstrated more than 160 mw and 400 mW power in continuous-wave and pulse operation respectively, limited by the thermal rollover. The operating wavelength of the laser is 995 nm. The device shows high threshold current characteristic temperature of 121 K. The calculated and measured far-field distributions in the vertical direction reveal that the laser operates at the PBG mode.

In order to enhance the surface wear properties of cast iron, some QT500 specimens are processed with JMG-GY-300D pulsed laser in different medium(air and water), and the microstructure, micro-hardness and frictional characterization are examined and analyzed. The experimental results showed that, after laser shock processing, a lot of dislocations and twins are found in the strengthening layer, hardness is improved significantly. The friction and wear behaviors are tested using a M200 friction and wear test apparatus under dry sliding condition. It is found that the main wear mechanism is adhesion wear, the friction and wear resistance of cast iron in water is better than in air.

With the characteristics of femtosecond laser ultrashort pulse and high peak power, cutting processing of nonmetal vascular shent is studied. Experiments show that using femtosecond laser can achieve precision machining without thermal damage. The relationship between parameters of machining non metallic stent is obtained through orthogonal experiment, and the optimum processing parameters are obtained: laser pulse frequency is 10 kHz, pulse width is 412 fs, laser power is 1.6 W, the auxiliary Ar pressure is 0.8 MPa, cutting speed is 1.2 mm/s. The processing of nonmetal material polylactic acid has the effect of tangent fine flat, cutting edge smooth, no surface carbonization residue. High quality non-metallic stent sample is obtained.

A novel optical resonator is proposed, so called unstable-stable coupling resonator, whose central portion acts as unstable resonator and edge portion acts approximately as stable resonator. Using Fox-Li method, the fundamental transverse modes of unstable-stable coupling resonator are computed. An optimization of the unstable-stable coupling resonator is given for a sealed-off CO2 laser with length of 1.2 m. Results show that output power of fundamental transverse mode can be increased about 2 times and central core output power on the focus plane can be increased about 1.5 times in comparison to stable resonators. And a design of unstable-stable coupling resonator is presented, which consists of a plat mirror, a spherical lens with aberration and a spherical mirror with aberration.

The scheme of using the all-optical 2R re-amplification, re-shaping regenerator based on nonlinear optical loop mirror to amplify and shape the differential phase-shift keying (DPSK) signals among satellites is proposed. The principle of the regenerator is deduced theoretically, the restrictive condition of amplifying and shaping a signal is given, the input and output characteristics of the power and phase of regenerator are investigated by simulation, and the effect of coupling coefficient of coupler on the power characteristic is analyzed. The result shows that the 2R regenerator can significantly promote the performance of DPSK modulation/self-heterodyne detection system and the bit error rate decreases nearly two orders of magnitude compared with that without the regenerator.

Soldering technology for quad flat pack (QFP) devices is studied using a fiber laser based on scanning galvanometer with SnAg3.0Cu0.5 solder and the relationships between tensile strength of micro-joints and laser soldering parameters are obtained. Excellent lead-free solder joints are achieved at the laser soldering parameters of 11 W, 20 mm/s or 8 W, 10 mm/s. The speed of laser soldering is improved dramatically based on scanning galvanometers. The mechanical properties of micro-joints are compared for different soldering methods, including continuous-wave (CW) fiber laser soldering, pulsed fiber laser soldering and infrared reflow soldering. The results indicate that CW fiber laser soldering can obviously improve the tensile strength of the joints with SnAg3.0Cu0.5 solder. In addition, the tensile strengths of SnAg3.0Cu0.5 solder and Sn63Pb37 solder soldered by CW fiber laser are compared. The mechanical property of SnAg3.0Cu0.5 is observed to be outstanding. The microstructure of fracture surfaces indicates that the fracture mechanism is ductility fracture. The metallographic structure of the solder joints is also investigated. It is found that the structure of soldering seam is fine and the interface is flat. The generated intermetallic compounds layer is Cu6Sn5.

In order to analyze the problem of laser quenching on the cylinder circumferential surface, we put forward an arithmetic model considering the influence of residual temperature field of quenched area on the formation of the temperature field of quenching area. A laser beam of uniform intensity is assumed in this arithmetic. Through improving the algorithm based on semi-infinite material under a moving surface heat source, an algorithm of temperature field of laser quenching on cylinder circumferential surface is implemented. And by calculating laser quenching temperature for circumferential surfaces of cylinders with different diameters, the impact of temperature field coupling on the formation of temperature field of laser quenching on the cylinder circumferential surface is analyzed. The result shows that the diameter influences the effect of the coupling of the temperature fields, and then affects the formation of laser quenching temperature field.

In order to meet the requirements of deep-sea detection, an underwater optical zoom system with large relative aperture is designed. Characteristics and design principles of underwater zoom system are analyzed. The optical system is a mechanically compensated zoom system; its image size is 8.8 mm×6.6 mm with zoom ratio of 2×. Its F-number is kept constant at 1.4 during zooming process. In its short focal length mode, its field-of-view (FOV) is 66°, while its FOV in long focal length mode is 36° and its effective focal length ranges from 5.9 mm to 11.8 mm. The zoom system employs one high-order aspheric surface and its overall length is 245 mm. The water-air interface of the zoom system is the concentric lens which is able to withstand high static pressure. For short, middle and long focal length positions, the modulation transfer function (MTF) of the system is always larger than 0.6 for in-axis field and 1.0 field at the spatial frequency of 42 lp/mm. Moreover, the maximum distortion for all zoom positions in the whole FOV is less than 5%. With compact design and high image quality, the zoom system can meet the requirements of practical application.

Thirty Meter Telescope (TMT) is a 30 m Ritchey-Chrétien optical-infrared telescope. It tertiary mirror (TMT M3) is an elliptical flat mirror with the aperture of 3.594 m×2.568 m and weight of 1.8 t. The M3 system reflects the light coming from the secondary mirror system (M2S) to the science instruments that are located on the Nasmyth platforms, and the M3 System must rotate and tilt as the telescope tilts about the elevation axis and tracks astronomical objects across the sky. The M3 support system should support the M3 mirror so that the mirror surface figure will be less than λ/5 (wavelength λ=632.5 nm) or root-mean-square (RMS) slope will be less than 1 μrad. The M3 support system includes axial support system and lateral support system. The axial support system uses 18-point whiffletree structure, and after optimization the RMS mirror surface figure achieves 118.5 nm. When the tertiary mirror surface figure error cannot meet the requirement with the support structure, correct moment is used to corrective the surface figure error.

By the example of designing freeform lens based on LED light source to achieve uniform circular spot, a new method of establishing optical device model is proposed. According to geometrical optics and non-imaging optics theory, the mathematical model of lens is derived. Numerical calculation of lens surface data is obtained by Matlab, and by TracePro programming the lens modeling is completed, then a conversation between Matlab and TracePro is created with the dynamic data exchange (DDE) protocol. In TracePro, the lens model is automatically created. The ray-tracing simulation results reveal that, the circular spot with the radius of 3 m on the target placed 5 m away is achieved by a LED Lambertian light source which has the luminous flux of 100 lm, size of 1 mm×1 mm and a viewing angle of 120°. The uniformity of illumination reaches 0.7, and the lens efficiency can reach 87%. This method can simplify the design process and save time compared with conventional methods of lens entity model, which further proves its accuracy and reliability.

Uniform and heavily Ge-doped silicon oxy-nitride film is obtained by optimized fabrication of silicon oxy-nitride film. Based on an optimal design of waveguide coupler, hydrogen loading and ultraviolet (UV) irradiation intensity, single-mode channel waveguides and waveguide couplers, made from germanium-doped silicon oxy-nitride, are fabricated by an UV irradiation from a KrF excimer laser on a planar waveguide. The maximum index increase is up to 1.03 times for heavy Ge-loading (about 20% atomic fraction) waveguide core after the UV irradiation, and the transmission loss of the UV-written channel waveguide is 0.28~0.32 dB/cm. Experimental results demonstrate that the index increase in the Ge-doped silicon oxy-nitride with UV irradiation intensity is not linear, and it can be controlled by changing the hydrogen loading pressure and time, UV intensity and Ge-loading level.

Based on parallel-aligned liquid crystal (LC) cell, which is the prototype of LC spatial light modulator, Erickson-Leslie equation is solved, and the response formula with fixed phase retardation 2π is obtained. By theoretical calculations, the curves of relationship between cell gap and response time under various voltages are plot, the existence of optimal cell gap is ensured and the curves demonstrate that both optimal cell gap and response time decrease while applied voltage increases, and the variation is decreasing gradually; the variation of response time reaches to the maximal value: shortened by 10.62% when applied voltage changes from 5 V to 10 V. The relation curves between voltage and response time of three LC cells are measured by experiments. The results demonstrate that response time is shortened while the applied voltage increases, the variation of response time is close to theoretical value when applied voltage increases from 5 V to 10 V, and when 15 V or higher voltage is applied, response time changes little. Besides, slight thicker LC cell has better response than thinner LC cell regarding with the same variation to optimal cell gap under the same voltage.

The spontaneous radiation energy of current filament in high gain GaAs photoconductive semiconductor switch (PCSS) is researched. Based on the recombination of non-equilibrium carrier of current filament in GaAs PCSS, the formula of the spontaneous radiation energy of current filament is exactly derived. The theoretical model of the spontaneous radiation of the current filaments in GaAs PCSS is established. Under the condition that the current filament reaches a steady state, the spontaneous radiation energies from the 875 nm radiation and the radiation of four peak wavelengths at one end of current filament are calculated. The maximum optical output energy from the 890 nm radiation is consistent with experimental observations, explaining reasonably the spontaneous radiation phenomena of current filament and lending support for the model′s predictions about the spontaneous radiation energies from the other wavelengths radiation. This lays the foundation for further quantificational analysis on photoionization effect of current filament.