The influence of weather can deteriorate the performance of free-space optical communication system. Based on the Mie theory and two kinds of raindrop spectral models, the laser attenuation induced by rain with different raining rates is calculated. The laser attenuation due to visibility is calculated using Kim model and AlNaboulsi model. The performances of free-space optical communications in rain and fog weather are studied. The relation between the bit error rate and the transmission range, as well as that between the bit error rate and the transmission power, is analyzed in different raining rates and rain or fog weather condition. The results show that raining rate influences the transmission ranges, and the attenuation induced by fog is much bigger than rain, which leads to a shorter transmission range. To guarantee the normal work of the system, the transmission power can be appropriately increased.

Intensity data acquired by terrestrial laser scanner contains physical and chemical information of objects. The mechanism by which the intensity data are produced is the key point to the analysis and application of intensity data. The working characteristics of terrestrial laser scanners are analyzed, hypotheses are proposed, and the calculating formulation of intensity data is simplified. The conclusion is drawn that reflectivity, incidence angle and range are the three main variables affecting the intensity data mostly. Based on a vertical surface, the distances between adjoined scanning points and influence of angular step width are analyzed and a formulation is proposed to measure a nonuniform distribution of scanning point. By simulating the intensity data of the vertical surfaces, the proposed formulation about intensity data is verified and the influence of the three variables is analyzed.

There is a fluctuation of symbols which results in error performance degradation if some errors occur in digital pulse interval modulation (DPIM) train. To address this issue, we present a novel demodulation scheme for DPIM. The decoding method is firstly proposed, and then the packet error rate is derived and compared with decoding using the optimal threshold method. Numerical simulation shows that the proposed method saves approximately 1.5 dBm average signal power than that of threshold method with different modulation levels when the packet error rate is 10-6 and information of packet n is 24 bit, but the improvement of error performance will degrade with the increase of n. Requiring no redundant information bits, the proposed method can effectively improve the error performance for DPIM, and can help to design wireless optical communication systems on modulation.

The refractive index sensing principle of tilted fiber Bragg grating (TFBG) and tilted fiber Bragg grating with surface plasmon resonance (SPR-TFBG) is provided. The transmission spectrum and reflection spectrum of TFBG with 8\O tilt angle and 1550 nm central wavelength are given. After that, refractive index sensing experiments are carried out using bare and gold deposited TFBG, respectively. The results prove that the deposited gold layer improves the refractive index sensitivity dramatically.

Based on the Mach-Zehnder (M-Z) interference principle of distributed optical fiber vibration sensor monitoring system, we propose an event recognition method for the vibration of fiber optic cable. This method solves the problem that the common fiber optic vibration sensor monitoring system does not have the pattern recognition intelligence analysis function. Through the analysis of the vibration events, the event recognition model is established. A lot of experimental data are used to classify the vibration events. Through the comparison of the vibration and these events, the vibration event recognition can be realized.

There are some minute peaked particles on the surface of semiconductor substrate during production. Sizes of the particles are usually several microns. If the height of any particle exceeds a standard value, there will be many defect wares during snagging and buffing when processed on the assembly-line. All that could affect the producing efficiency. It is desired to give test simultaneously on the height of single or several sparsely distributed non-spherical particles. We aim at offering a method to measure the height of minute particles. We also introduce a system of measuring small particle′s height on the basis of microscopic projection and successfully measure single randomly shaped minute particle with height around 100 μm.

The angle between signal light and local light is an important factor affecting the heterodyne detection. Even a small angle will lead the intermediate frequency signal to be weak. It is pointed out that the amplitude of the intermediate frequency signal can be regarded as the Fourier transform of the distribution function of quantum efficiency of detector. Based on that, a method using array detector in which the gain of unit is adjustable is proposed. One can form an effective quantum efficiency function matching the spatial mismatch angle by adjusting the gain magnification coefficient, which can enhance the intermediate frequency signal intensity. According to the method, high-speed scanning detection can be realized by a programmable controller.

The properties of the output signal of heterodyne laser Doppler vibrometer (HLDV) under random noise disturbance are studied by means of wavelet transform. Considering the principle of HLDV and the influence of white noise in this system, the modulus maximum and the coefficient correlation algorithms are analyzed and improved. Also, based on the theory of the threshold enhancement, a new threshold function is proposed and used to analyze the effects of multi-scale method on the reconstruction of the oriental signal and improvement of signal-to-noise ratio (SNR). The results show that the improved modulus maximum, coefficient correlation and threshold enhancement algorithms present much more excellent performances in extracting the vibration parameters of the micro-vibration targets.

One-dimensional dimension binary-code phase modulator (1D-BPM) for speckle reduction in laser display system is designed based on Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) and microelectromechnical system (MEMS) microfabrication technology. Mathematical model of 1D-BPM is built up, and the relationship between phase shift and electrical field applied by electrodes is deduced. Electrode configuration is investigated by simulation with finite element analysis. We find that the phase distribution across the gap between two electrodes depends not only on the electric field applied by electrodes, but also on the electrodes′ configuration when their dimensions are on the submicron order. Electrodes corner effect is the significant factors for device design and optimization.

On the basis of the spectral information, a theoretical model is developed to treat the short pulse laser generated from an active continuous wave (CW) injected ring cavity with Yb3+:YAG amplifier. Starting from rate equation, the equation describing the short pulse laser is obtained. As a computable model, it takes into account the pump absorption saturation and the laser reabsorption. By this model, the short pulse laser properties under different cases are analyzed. The results show that in order to achieve the good pulse laser, the seeding frequency and intensity as well as the amplifier length should be optimized.

In order to study the influence mechanism of laser shot peening (LSP) on the fatigue properties of wrought magnesium alloy ZK60 with high intensity, which can adapt the need of structural parts under alternate stress, the surface modification of ZK60 by LSP and the tensile fatigue test are carried out. The results show that the beneficial residual compressive stress is obtained and hardening effect is produced on the strengthening region by LSP. The profile curve fluctuation in the microscopic region of plastic deformation is less than that in magnesium matrix. With the increment of peening number, the strengthening effect of LSP can be enhanced. The average fatigue life of specimen with center hole increases from 78023 cycles to 125641 cycles after 3 LSP modifications, showing the gain of 61%. The compressive residual stress induced by LSP changes the position of fatigue crack initiation, and delays the fatigue growth rate, but it has less effect on the fast fracture area. LSP technology provides a new method for anti-fatigue manufacture of magnesium alloy.

The directed infrared projecting device based on mid-infrared laser has become more important because the mid-infrared (3～5 μm) detectors have been widely applied in the military field. The beam pointing stability is the key parameter for such application. The beam pointing measurement is conducted for an optical parameter oscillation (OPO) mid-infrared laser. The mid-infrared imaging system, image edge extraction algorithm and threshold algorithm are adopted to obtain the pointing data of this mid-infrared laser. The experimental results show that the maximum pointing error is 1.1 mrad and the average is 0.3 mrad at room temperature. The main reason is that the temperature control system for laser diode (LD) is not perfect and it may be improved further. The measurement results can provide references for the investigation, beam shaping, pointing measurement and stability techniques of mid-infrared lasers.

A 355 nm ultraviolet laser with hydrothermal KTP is demonstrated. A high power ultraviolet laser with high beam quality at 355 nm is obtained by internally frequency tripling of a diode side-pumped acousto-optic (AO) Q-switched Nd:YAG laser. Type II phase-matched hydrothermal KTP and LBO crystals are used for the second harmonic generation and the third harmonic generation, severally. Using the V-shaped resonator cavity, under the pump power of 93.09 W, 4.133 W average output power at 355 nm is obtained at 4.9 kHz, corresponding to the pump-to-ultraviolet conversion efficiency of 4.44%.

Trichromatic manipulation of dispersion switching, enhancement of Kerr nonlinearity and population inversion are analyzed in a three-level Λ atomic system. It is shown that, due to the interference among multiple two-photon channels, the Kerr nonlinearity is enhanced in multiple transparent windows and the frequency band corresponding to population inversion becomes wider. On the other hand, the sum of the relative phases of the sideband components of the trichromatic field plays a crucial role in the response of the medium. As the sum phase is adjusted from 0 to π, dispersion is switched from normal to anomalous in multiple frequency regimes, which corresponds to the switching from subluminal to superluminal light propagation. With the sum phase changing from 0 to π, the Kerr nonlinearity is enhanced in other different frequency regimes, and the frequency band of population inversion is further widened. The influence mechanism of the sum phase is also analyzed.

The influence of initial plasma temperature on the proton generation under Compton scattering is studied by using the model of multi-photon nonlinear Compton scattering and two-dimensional particle-in-cell (PIC) simulation, and the results are numerically simulated. The results show that the amounts of produced proton have an even noteworthy increase along with the increase of the initial plasma temperature than that before the Compton scattering, the energy spectrum curves of the protons before and after the target tend to be smooth, and the differences in the number of accelerated protons are decreased. When the incident laser intensity is increased, the relative extents of the proton number increasing are clearly decreased along with the increase of the initial plasma temperature. When the incident laser intensity is decreased, the energy spectrum curves of the protons still have clear differences with the increase of the initial plasma temperature, and the number and speed of protons are clearly increased.

Aiming at correcting static aberrations of telescope for quantum communication and improving the energy concentration of receiving signal light, the method of static aberration correction based on stochastic parallel gradient descent (SPGD) algorithm is proposed. Unlike the conventional adaptive optics systems, the SPGD algorithm does not require the wavefront sensor, and can effectively reduce the complexity of system. An adaptive optics aberration correction test-bed is set up with a 64-element deformable mirror (DM) and a CCD detector. The static wavefront aberrations of a 700 mm telescope is compensated, and the far-field diameter is improved to 30 μm from the original value of 58 μm. The feasibility of SPGD algorithm used to correct static wavefront aberrations of telescope is demonstrated.

A solar concentrating system is designed to solve the nonuniform illumination distribution problem of the flares through traditional concentrating systems with line focus. This concentrator system consists of curved cylindrical Fresnel lens array and a planar waveguide. A general formula of curved Fresnel with line focus and the design formula of the V-groove of the waveguide are presented. The system is in a small volume, with the total height less than 40 mm. Through orthogonal test and optical simulation, structure parameters of the system are optimized. Meanwhile, the influences of the machining error of the curved line focus Fresnel lenses and the installation error of the waveguide are discussed. It turns out that the optical efficiency of the optimized system with a lighting area of 500 mm×200 mm in the condition of 50× geometric concentration is about 75% and the illumination uniformity is above 88%. Simultaneously the optical efficiency is over 50% within ±7° declination angle of the incident light. Different concentration can be reached by splicing and it is proved by simulation that the optical efficiency is above 50% and the uniformity is more than 85% within 160× concentration.

Glass microsphere resonators have ultrahigh quality factor and small mode volume. These characteristics make them have a subject of enormous interest in areas as diverse as low-threshold microsphere lasers, microamplifiers, nonlinear optics, cavity quantum electrodynamics and high sensitive sensor. The research of glass microspheres is reviewed in terms of the preparation method, laser output, coupling method and sensor application. Their development prospects are also discussed.

Large-mode field fiber can decrease the power density of fiber core and increase the threshold of nonlinear effect, which is the best candidate for high-power fiber lasers. However, an increase in fiber core size will lead to the multimode running and decrease of beam quality. The latest progress of high-order mode-suppression technology is introduced. The development trends of mode suppression technology are prospected.

Orbital angular momentum is a quantum state of the photon. The beam with orbital angular momentum has a wide application in optical communication and other fields and has become a hot spot of research at home and abroad. Orbital angular momentum became an important option of physics of quantum information carriers in free space, which will bring important influence in quantum communication field. This paper introduces what orbital angular momentum is and how to produce it. Two kinds of classical quantum cryptography communication solution based on phase and polarization coding are listed briefly in order to compare them with the proposed communication solution, which is the photon orbital angular momentum cryptography communication scheme. We put forward to it for example, and mainly represent its application and prospect.

The working principle leads long period fiber grating (LPFG) more sensitive than fiber Bragg grating (FBG) in sensing areas such as temperature, strain, concentration, bending etc.. LPFG has great potential in the field of sensors. Compared with FBG sensing signal, the signal interrogation of LPFG needs further research to satisfy the LPFG sensing application. The signal interrogation techniques of LPFG are reviewed and analyzed. The methods of using edge-filter, Fabry-Perot (F-P) cavity and arrayed waveguide grating (AWG) to interrogate LPFG sensing signal are analyzed and compared particularly. The approach to interrogate multiplexed sensors based on LPFG is introduced. Summary and expectation of demodulation technique development trend are presented.

Based on patterned sapphire substrate (PSS) technique, threading dislocations density (TD) in GaN epilayer can be reduced and the internal quantum efficiency (IQE) as well as light extraction efficiency (LEE) of light emitting diode (LED) can be improved. Highly efficient LED based on GaN can be grown on patterned sapphire substrate. A review of PSS technique is given based on published papers, including the development of PSS technique, its fabrication and pattern structure, process of GaN epilayer growth and performance improvement of LED on PSS. IQE and LEE can both be improved by PSS, but it is unknown that improvement from IQE or LEE achieved by PSS is essential. The mechanism of improvement of IQE and LEE is not very clear, while arguments about the mechanism proposed by published papers are given. The effects of different PSS structures and sizes on the quality of GaN and performance of LED are not well investigated yet.

Confocal microscopy is an important imaging technique for micro structure, and it is widely used in micro-nano three-dimensional (3D) topographic measurement due to its high precision, high resolution and ease of use to realize 3D image reconstruction. In recent years, parallel confocal microscopy has attracted extensive attention of the worldwide experts. This technology substitutes a single point scanning pattern for synchronously multiple-beam parallel detection, greatly improving the 3D testing speed. The basic principle and the worldwide research progress of parallel confocal microscopy are reviewed and the author′s research in the field is briefly introduced. Introduction to seven categories is presented according to the parallel detection methods of parallel confocal microscopy, and the advantages and disadvantages of each type are pointed out. Finally, the existing technical difficulties are summarized and the development trend is analyzed to provide technical reference for further research in China.

Yb-doped fiber lasers operating near 980 nm have exhibited great potential to replace laser diodes as high-brightness pump source for erbium or ytterbium-doped fiber lasers. We review the current status of fiber lasers operating near 980 nm employing different types of gain fiber, including single-mode single-clad Yb-doped fiber, conventional double-clad Yb-doped fiber, jacketed air-clad (JAC) Yb-doped fiber and ultra-large-core Yb-doped photonic crystal fiber. Also the problems existing in 980 nm fiber lasers are mentioned. In the end we speculate the approaches for future development.

In space radiation environment, optical fiber can experience great attenuation additionally, which can bring many disadvantages for its application in radiation environment. In order to guarantee the performance of optical fiber in radioation environment, much attention should be paid for research on radiation induced attenuation (RIA) for optical fibers. Starting from the interaction mechanism between radiation and optical fiber, we explain the formation process of color centers, which are the primary reason for the RIA of optical fiber. More information about annealing of color centers is also mentioned. Then a detailed analysis of influence of related factors on RIA for optical fibers, such as radiation conditions, parameters of optical fiber and light waves characteristic, is given. A summary of the RIA models for optical fibers and a brief introduction to the application of the radiation-induced attenuation effects are also shown.

In order to realize the fast and nondestructive detection, the cashmere and wool near infrared spectroscopy database is created which includes the data of 228 groups of cashmere and wool from various districts, and it is applied to the qualitative detection of cashmere and wool. First the process of database creation in the cashmere and wool detection based on near infrared spectroscopy is introduced. Then on the base of the near-infrared spectroscopy original data preprocessing of cashmere and wool, the principal components of the data are analyzed, and 12 kinds of principal components are chosen. The detection model of cashmere and wool with radial basis function (RBF) fuzzy neural network is build. The comparative analysis experiments with PCA-MD modeling demonstrate that the method combining near infrared spectroscopy database, principal components analysis (PCA) and improved RBF fuzzy neural network is an effective and nondestructive detection method for cashmere and wool, and it can rapidly build high-accuracy detection models of cashmere and wool fiber.

Laser ablation emission spectra of graphite/potassium nitrate under pulse laser irradiation with wavelength of 1064 nm are analyzed to investigate the chemical reaction processes during laser ignition. Testing results indicate that ablation spectra possess the characteristics of line spectra, and wavelengths of spectra range mainly from 300 to 600 nm. Ablation spectra mainly consist of atomic spectrum and ionic spectrum of N, O, C and K. When the laser energy density is 46.7 J/cm2, NⅡ385.61 nm spectrum is the strongest while OⅡ441.70 nm spectrum is the weakest. The ablation products combusted in gas phase.

The characteristics of thermal electron emission of the metal films ablated by multi-pulse femtosecond laser are investigated using the two-temperature model (TTM) coupled with the Richardson-Dushman equation. In the numerical simulation, the variations of reflectivity and absorption of metal films with the change of the number of femtosecond laser pulses and pulse spacing are considered and the dynamic numerical simulation is achieved. It is found that, with the change of femtosecond laser pulse number and pulse spacing, the reflectivity and absorption coefficient of metal films would be raised and the absorptivity would be decreased. And the change of the parameters would have a significant influence on the thermal electron emission and the temperature field of metal films. Meanwhile, with the depth raising, the influence would be diminished.