An all-solid-state coherent radiation at 488 nm by intracavity sum-frequency generation of 914 nm Nd:YVO4 laser and 1047 nm Nd:YLF4 (Nd:YLF) laser is reported. Blue laser is obtained by using a double cavity and type-I critical phase matching LiB3O5 (LBO) crystal sum-frequency mixing. With total pump power of 32.2 W (13.4 W pump power for Nd:YLF laser and 18.8 W pump power for Nd:YVO4 laser),TEM00 mode blue laser at 488 nm of 650 mW is obtained at last. The power stability in 30 minutes is better than ±2.8%. The M2 factor is 1.3.

According to LAS-CAD software,a compact laser diode (LD) dual-end-pumped acousto-optic Q-switched Nd:YVO4 laser is designed and optimized. In the experiment,an 808 nm fiber-coupled system and double concave face mirror folded cavity are adopted. The length of resonance cavity is 185 mm and the transmission of output coupler is 15%. A TEM00 mode output of 18.6 W is obtained under the condition of continuous waves (CW) at a pump power of 44 W,resulting in an optical conversion efficiency of 42.3%,and a slope efficiency of 47.8%,and M2 of 1.5. An 11.3 W of 1064 nm average power at a repetition rate of 100 kHz is generated with a 41 W LD as pump source,and an optical-to-optical conversion efficiency of 27.6% is obtained. The steady operation is achieved with pulse width of 25 ns,peak power of 4.52 kW and single pulse energy of 113 μJ at the repetition rate.

The expression for the temperature distribution in the end-pumped slab cross section was deduced and the thermal distortions in single and composite medium were analyzed. The results indicate great difference in temperature distribution and thermal distortion exists between composite and single slabs. For the single slab,positive lens caused by thermal gradient could be reduced by increasing the bounce number of the light in zigzag propagation through the slab. For the composite slab,the thermal lens may be positive or negative. Thus the thermal distortion could be reduced either by increasing the bounce number of the light in zigzag propagation through the slab or by optimizing the length of each segment at the given bounce number.

A laser diode (LD) end-pumped optical-contact composites Nd:YVO4+KTP three-wavelength laser is reported. The output laser wavelengths are 532,537 and 542 nm respectively. By adjusting the angle of the crystal,1064 nm doubling frequency,1064 and 1084 nm sum-frequency and 1084 nm doubling frequency coexist in KTP crystal. From the impact of nonlinear conversion efficiency on fundamental oscillation,the condition of 1064 nm and 1084 nm dual-wavelength oscillation was discussed and the reasons of three wavelengths power changing with pump power were studied.

A single-mode-quasi-continuous-wave 980 nm Yb-doped fiber laser is realized. An acousto-optics Q-switched Nd:YAG laser at 946 nm is used as pump source and the high Yb-doped single-mode fiber is used as gain medium. The total average power of the laser pulse is 73 mW at 980 nm when the pulse duration is 10 ns at the repetition frequency of 16 kHz. The quasi-continuous-wave 980 nm fiber laser oscillator used as seed source is amplified by another 28 cm Yb-doped fiber. As a result,the pulse with average output power of 167 mW is generated. The pulse width is 15 ns with the peak power of 700 W.

A structure of bidirectional filter to achieve single longitudinal mode for fiber laser gyro (FLG) application is demonstrated using a 0.1-nm bandwidth fiber Bragg grating (FBG) as a filter element. In filter section,the two direction lasers are kept orthogonal polarized as to keep counter-propagating mode coupling in minimum. Then a polarization beam splitter(PBS)is used to guide bidirectional laser out of filter. The insertion loss is about 3 dB and back reflection loss is more than 35 dB by test. The 1550 nm wavelength is gotten with the filter accessing to the ring cavity. Single longitudinal mode is certified for bidirectional laser output by using scanning ring resonator,which proves that the device is fit for bidirectional filtering.

The performance of a high power long-pulse ultraviolet-preionized TE CO2 laser with an active volume of 2.48 L utilizing pulser/sustainer discharge technique is investigated in detail. The laser head consists of a plano-concave resonator for non-tunable operation or a grating resonator for tunable operation. Stable volume discharge and high laser pulse energy output are obtained under various mixture pressures of 20-40 kPa and various discharge lengths of 10-50 μs. Typical laser discharge voltage/current waveforms and detailed data of laser output pulse energy and electro-optical conversion efficiency under various discharge lengths and various mixture pressures are given. The laser pulse profiles of the four main transition lines are demonstrated as operated with a grating resonator. When operated under a non-tunable resonator and 30 kPa mixture pressure,the laser generates 11.1 J pulse energy at 50.1 μs discharge length,corresponding a laser pulse power of 220 kW;1.52 kW average power at 31.6 μs discharge length and 150 Hz high repetition rate,resulting in an average pulse energy of 10.0 J and an average pulse power of over 300 kW.

The small signal gain measurement of the all gas-phase iodine laser driven by D2-NF3-DCI combustion is taken using a wavelength tunable 1315 nm diode laser gain measurement system. A small signal gain of 3×10-5 cm-1 and the profile of small signal gain along the flow direction are obtained. The positive gain indicates that a material progress has been made in the D2-NF3-DCl combustion-driven all gas-phase iodine laser,but it is still difficult to demonstrate lasing as to the magnitude of the small signal gain,a detailed parameter optimization must be done in order to improve markedly the small signal gain,and the plentiful supply of HN3 and the optimization of the supersonic mixing flow field are key factors to obtain a high small signal gain for the D2-NF3-DCl combustion-driven all gas-phase iodine laser.

Based on the theory of semi-analytical thermal analysis,the thermal effects within a laser diode (LD)-end-pumped Nd:YAG microchip crystal with back surface cooling are investigated. Through the working characteristics analysis of Nd:YAG microchip crystal that is pumped by a LD with a Gaussian distribution,a thermal model is established. The temperature field in the microchip Nd:YAG crystal is obtained by a novel solution to solve the third find heat conduction equation with Dini series,and the influence of air heat transfer coefficient on the temperature rise in the crystal is researched. Research results show that a maximum temperature rise of 70.17 ℃ and a maximum thermal distortion of 0.836 μm occur in the center of the pump face when the total pump power is 24.2 kW. These results can provide basis for the optimized design of LD-end-pumped microchip laser with back surface cooling.

In laser coherent combination,phase detection and control are most critical to master oscillator power amplifier (MOPA). Using heterodyne method,consistence of output beam phase can be ensured through real-time detection and correction of optical phase. The modulator is a liquid crystal optical phase modulator,the wavelength of the main oscillation laser is 532 nm,and the output power of laser can be adjusted continuously from 0 to 6 W. The shifted frequency of the heterodyne system is 40 MHz,and the accuracy for phase control is superior to λ/7. In the process of closed-loop control,a good signal phase correction of optical path has been achieved.

Compared with symmetrical optical system,the optical system which consists of non-spherical lens can implement some special mathematical transforms. Based on the paraxial approximation,the tapered lens are investigated by geometrical optics,and the transmission function is derived. Furthermore,the transmission functions of cone and cylinder lens are also derived. With the help of these conclusions,the optical system consisting of double cylinder lens is constructed. This setup is the basic unit to implement anamorphic fractional Fourier transform. Finally,on the basis of scalar diffraction theory,the analytical solution is obtained. Furthermore,the system parameters are studied in detail in order to satisfy the requirements for various fractional Fourier transforms.

A mobile 1064 nm Mie scattering lidar system has been developed which can measure the vertical aerosols backscatter coefficient and horizontal visibility. The configuration and specifications of the Mie scattering lidar system are presented and the designed alignment of the optical mechanic unit is described. As a mobile system,the transportation stability of the lidar system is solved and the optical transmitting and receiving axis are well aligned. Validation experiments are made in Hefei. The vertical backscatter measurement is compared with another 532 nm Mie scattering lidar and the visibility measurement is compared with Belfort 6230A visibility sensor. Both results are in good agreement which indicates the new made mobile 1064 nm Mie scattering lidar is stable and reliable.

A pump-probe setup is used for experimental study and it is found that an obvious dark-center diffraction appears at the transmission direction of probe beam when the chromium films is excited by the femtosecond pulse laser and the continuous-wave (CW) laser and when the laser power reaches a certain level. While the dark diffraction phenomenon disappears without the pump beam. This reversible diffraction phenomenon is explained by using the binary phase plate theory. It is also found that the phase change induced by the femtosecond pulse laser is larger than that by the CW laser. The experimental and theoretical results can contribute to understand the mechanism of the interaction between the chromium films and the femtosecond pulse laser and the CW laser.

A novel micro cantilever-based hydrogen sensor with fiber Bragg grating(FBG) for detection of hydrogen was developed. The deflection of microcantilever due to absorption of hydrogen was measured by the wavelength shift of FBG,then,the content of hydrogen can be inferred. The stress transfer model of the sensor is analyzed based on elasticity theory. The relationship between the Bragg wavelength shift and the saturation hydrogen content is derived,and it shows that the sensitivity of the sensor can be improved by changing the thickness ratio of palladium and silicon cantilever beam and the maximum wavelength shift is obtained as thickness ratio is 0.4. The response of the sensor to hydrogen was measured. The analytical value was close to the experimental result.

Fabrication methods of SiO2 optical microsphere cavities and tapered fibers are introduced. Using a tunable single-mode NewFocus laser (short-term linewidth of 300 kHz) with an adjustable extent of 1520-1570 nm as the excitation optical source,whispering gallery modes (WGM) of microsphere with a diameter of 150 μm are achieved through coupling a tapered fiber with waist diameter of 1.2 μm. The microsphere and the tapered fiber are all fabricated by experimental laboratory setup. Based on the microsphere cavity′s temperature distribution,binding the thermal expansion coefficient and the thermo-optical refractive index effects,resonant spectrum shift(2.5 GHz/℃)induced by the high pump power in the microcavity is analyzed. The experiments indicate that controlling the WGM pump power is an effective way to suppress microcavity thermal effects,and in this way it is easy to fulfill a stable high quality factor (Q) model. Through adjusting the tapered fiber pumping angle,higher-modes are suppressed effectively,and an ultra-narrow linewidth about 22 MHz is measured. The corresponding Q of this microsphere is 107.

By theoretically analysing white-light interferometer and the testing principle of polarization coupling (PC) in polarization maintaining fiber (PMF) based on white-light interferometer,a fiber Michelson interferometer testing system of polarization coupling in polarization maintaining fiber based on white-light interferometer is designed. Testing experiments of polarization coupling in PMF are made and a good result of 70 dB detection sensitivity is obtained. The feasibility and veracity of polarization coupling testing based on white-light fiber Michelson interferometer are validated. Finally,a small PMF coupling coefficient is tested using different light sources including super luminescent diode (SLD),amplified spontaneous emission (ASE) and erbium-doped fiber amplifier (EDFA). Then we get the measurement error of 0.36%,1.8% and 2.5% respectively,which verify the accuracy of the testing system.

In order to get the characteristics of optical field in the pigtail fiber of fiber coupled laser diode and increase the pump efficiency of fiber laser,propagation ray calculation and experiments of transmission efficiency in bending pigtail fiber are presented. In bending fiber experiments,it is found that more than 15% of output power differences are given by fiber coupled laser diode with the same nominal output power and pigtail fiber. It means optic modes need to be chosen so as to maintain the pumping efficiency and stability in pumping application. Based on the analysis of propagation ray theory,a new approach to judge the beam quality of fiber coupled laser diode by bending fiber is presented. It also can be used in detecting the fiber coupled efficiency of laser diode.

Based on holographic optical holographic imaging theory,a wavelength beam combining approach of fiber coupling lasers using off-axial holographic optical elements is proposed in this paper. This method for beam combining is easy constructed and high efficiency. This paper designs the off-axis holographic optical element (HOE),and gives the phase distribution of the element. We use the stimulation software Zemax and angular spectrum theory to calculate the combined beam divergence angle and the beam quality. The stimulation shows that for fiber lasers with wavelength at 635,808,975 nm,maximum M2 increases from 23.5 to 47.9 and the theoretical efficiency is 95%.

Based on vectorial Debye integral,the light field and intensity distribution expressions are presented when partially polarized Gaussian beams pass through a high numerical-aperture objective. Numerical calculations are taken to analyze the tightly focusing properties of partially polarized Gaussian beams with various degrees of polarization. The research results show that the total intensity distribution and each direction components of partially polarized Gaussian beams on the focal plane will change with the change of polarization. It is also found that the values of the maximal angle of the high numerical-aperture objective will influence the total intensity on the focal plane. Therefore,the intensity distribution of partially polarized Gaussian beam on the focal plane can be controlled by adjusting the polarization and the maximal angle of the high numerical-aperture objective.

Without prior intensity information in input plane,one method using random binary phase modulation and iterative algorithm is adopted to reconstruct complex wave-front in Fresnel and Fraunhofer diffraction domains,respectively. Three or more diffraction patterns in Fresnel or Fraunhofer domains with different random binary phase masks are used to successfully retrieve the complex wave-front. The differences of the methods used in Fresnel or Fraunhofer diffraction domains are finally discussed in detail.

An approach based on the correlation between two intensity distribution images of the object wave is proposed to determine the phase-shifting value in two-step phase-shifting digital holography. By changing the phase-shifting values used for reconstruction in a certain range around the nominal phase-shifting value,a series of correlation coefficients between the object intensity recorded by CCD and the same intensity reconstructed by computer are obtained. The accurate phase-shifting value will be determined when the correlation coefficient reaches its maximum. The real phase-shifting value is successfully extracted in computer simulations by this method,thereafter the approach is employed in LED-based digital holography. The quality of the reconstructed field by using the obtained value and the nominal value are compared. The feasibility of this method has been verified by both computer simulations and experiments.

A phase-contrast imaging technology with digital holographic microscope based on system calibration is present. After a theoretical analysis of the phase-contrast microscopy,results show that the phase curvature introduced by the microscope objectives can be compensated by introducing two digital phase masks located on recording plane and imaging plane respectively. Without affecting the sice of the reconstructed image,the mathematic models of the two phase masks are defined,which can be constructed by the proposed system calibration method. The calibration process includes pre-recording two reference holograms,inserting the imaging microscope objective,filtering and square fitting etc digital processing to compute the recording system parameters,constructing the required digital phase masks by the calibrated system parameters. Finally,a demonstration experiment is carried out. In the experiment a small water bead with size of no more than 0.09 mm is phase-contrast imaged with different magnification ratios. The experiment shows that the proposed method is credible and convenient.

Both holographic interferometry and shearing interferometry are important methods in optical measurement but they are developed independently. Digital hologram can reconstruct wavefront numerically,and shearing interferometry essentially is the interference of a coherent wavefront with a copy of itself “sheared” or translated by a distance,so the principle of shearing interferometry can be applied to reconstruct the wavefront of digital hologram. By shearing numerical wavefront,several pixels to obtain few wrapped shearing phase will make the phase calculation easy. Based on theoretical analyses and the least-square principle,the algorithm of constructing wavefront is presented. Simulated and experimental results show the validity and feasibility of the presented algorithm. The obtained phase approaches experimental value well and is better than the results of conventional methods.

The finite element analysis (FEA) softeware ABAQUS is applied to establish the finite element model (FEM) for one-side and both-side laser shot peening (LSP) of specimen with a central hole. User subroutine VDLOAD is used to program the loading model of shock wave pressure for both-side LSP. The influence of the hole on the peening effect is investigated,and the three-dimensional (3D) residual stress distribution of ZK60 magnesium alloy after one-side and both-side LSP is analyzed. The beneficial residual stress distribution was obtained after both-side LSP,with a stress value as two times high as that after one-side LSP on the bottom surface. The experimental results are compared with numerical simulation results and good consistency is observed.

Laser welding is a complicated process,and quantitative analysis of this process is quite difficult. A non parametric statistical method of light intensity distribution modeling,based on normalized radial basis function neural network,is proposed to predict the spatiotemporal dynamics of surface optical activity in the laser welding process. This neural network adopts Gaussian function as radial basis function. A quantitative evaluation method for light intensity distribution of modeling quality is proposed. Parameters are optimized according to this evaluation method. Comparison of predicted images and testing images exhibits a good resemblance.

With the SYSWELD finite element code,a three-dimensional finite element model has been developed to apply for analysis of overlapping laser surface melting on roller. The thermal circle and temperature rate of overlapping laser melting were investigated and the phase transformation and residual stress fields were analyzed. It is found that overlapping area becomes second melted and the boundary of overlapping area exists tempering for twice laser scanning after overlapping laser surface melting on roller. With the increase of the overlapping ratios,the width of the laser melted layer becomes smaller,while the martensite contents are independent on the overlapping ratios and exceeds 90% in the melt-hardened zone. The residual stress distributed within the melt-hardened zone is mainly of the compressive type,while there is the tensile stress in the heat-affected zone. The tensile stress cannot be eliminated by changing overlapping ratios,but the tensile stress amplitude can be reduced by choosing the proper overlapping ratios. The ideal stress distribution can be obtained by choosing 3 mm overlapping ratio under these experimental conditions. The comparisons between the calculated results with the experimental measured values show a good agreement for axis residual stresses.

Binocular stereo vision system is equipped in laser remanufacturing robot. The robot can automatically find the defect of objects to be repaired and give the best repairing path and technological parameters. Calibration is the basic and key task of vision system. Two cameras are installed in the robot terminal and calibrate the two-dimentional (2D) plane target. The right and left cameras acquire target images in different positions by changing the camera′s positions through the robot teaching pendant. Internal and external camera parameters are calculated by OpenCV programming and robot hand-eye calibration is completed by Matlab. Calibration accuracy is analyzed with the help of robot teaching pendant. The result shows that the maximum relative error is 1.08%,which meets the requirements of laser-repairing remanufacturing.

The high-frequency method may possibly disrupt operation of peripheral equipments and is harm to human body in tungsten inert gas (TIG) arc welding process,so a new method that the laser induced plasma ignites the TIG arc is presented. In this paper,a pulsed CO2 laser with pulsed width of 10 ms is used to ignite the TIG arc. A high-speed visual sensing system is established to detect the process of laser induced plasma triggering arc discharge and the shape of plasma. The experimental results show that the shape and volume of laser plasma are ones of the key factors. And only when the laser plasma contacts the tungsten rod,which therefore results in producing electron emission and forming self-maintaining discharge,the TIG arc can be ignited. Furthermore,the influence of main factors,such as shielding gas,workpiece materials,defocusing distance,and flow of shielding gas etc.,on the shape,the volume and the performance for triggering arc discharge of laser plasma are studied.

In order to improve building efficiency and ensure good accuracy and adequate mechanical properties of metal parts,a variable density rapid manufacturing process based on selective laser melting technology is proposed. Computer aided design (CAD) part model is divided into two building regions:shell region which is built by near-full-density producing method and internal region which is built by porous structure producing method. The transition condition of two producing methods are analyzed:transition between near-full-density structure and porous structure can be achieved through control of the melting depth of solid substrate by adjusting processing parameters. The experimental results of producing 316 L stainless steel parts by variable density rapid manufacturing process show that,compared to producing metal parts only using near-full-density producing method,producing efficiency is obviously increased,part weight can be reduced significantly and sufficient hardness can be obtained when using appropriate shell thickness. To larger dimension metal part made by this process,the experiments also show that the dimensional accuracy is greatly improved in addition to the above-mentioned advantages.

A numerical model based on the theory of fluid-structure interaction is developed by finite element method to simulate the laser thermo-elastic generation and propagation of interface waves at the fluid-solid interface. The propagation characteristics of leaky-Rayleigh wave,Scholte wave and lateral wave are analyzed,and the numerical solution of full wave field is obtained. Furthermore,the effect of different fluid media on the waveform of interface waves is discussed. The results show that various modes of fluid-solid interface waveform are excited simultaneously by pulsed line source,with the waveform significantly affected by the material parameters of liquid media. The numerical simulation establishes a quantitative relation between the laser parameters,the material parameters and the corresponding waveform.

To fabricate small objects with high accuracy and low cost,an integral stereolithography (SL) system has been developed,and the system consists of dynamic pattern generator,recoating system and control system. Photo-sensitive resin is solidified with image mask produced by dynamic pattern generator,and then small objects can be fabricated. Ultraviolet (UV) light intensity distribution in the imaging plane is investigated,and the relationship of UV light intensity with position in the imaging plane and gray-scale of pattern is established with least squares method. Uniformity UV light intensity distribution is obtained by controlling the gray-scale value at different positions in the imaging plane according to the relationship,and the difference between maximum and minimum value of UV light intensity is 0.4 μW/cm2. Small objects with microstructures are built with the SL system. A test part was designed,and the results of accuracy testing and statistical analysis demonstrate that the dimensions with error within ±0.06 mm are 72.22% in all testing dimensions. The notable characteristic of the novel SL system is that the new SL system can fabricate micro-structures with high-resolution at low cost.

In order to improve the fatigue strength of the blade,the Ni-based superalloy laser shock peening (LSP) parameters and method are researched. After laser shock peening on the Ni-based superalloy(K417),the surface roughness,micro-hardness,and microscopic structure are analyzed,and the parameters are determined for LSP. Then the fatigue performance is tested by means of vibration fatigue test adopting the samples with the same groove in a turbine blade. The results indicate that LSP changes the surface roughness lightly,but increases the micro hardness evidently and the depth affected by LSP is up to 0.7 mm. The breadth at half height of the X-ray diffraction peak after LSP indicates that the plastic deformation occurres in the LSP part,and the dislocation density and micro-residual stress increase,which are advantageous to the fatigue performance. The vibration fatigue tests prove that the fatigue life with LSP is 1.67 times longer than that without LSP.

In this study,Fe-Ti-V-B-C alloy coatings reinforced by ceramic particles are produced by laser cladding on the Q235 steel,the influence of ferroboron on the microstructure and property of the coatings is investigated by means of X-ray diffraction(XRD),optical microscope(OM),scanning electron microscope (SEM),micro-hardness tester and wear tester. Results show that the coatings are free from slag inclusion,exhibit high formability and good metallurgical bond with the substrate. The boron addition not only refines ceramic particles,but also changes the microstructure of the matrix of coatings from acicular ferrite to pearlite or high carbon martensite. The micro-hardness of the coatings increases while ferroboron content increases,however,when the ferroboron content is beyond mass fraction of 25%,the crack extending along longitudinal direction of the coating is found. Through the test of wear resistance,the weight loss of the coating,which contents mass fraction of 20% ferroboron,is just one tenth of that of the substrate.

The effect of laser on the frequency of metal transfer and welding current in Nd:YAG laser+P-GMA (pulsed gas metal arc) hybrid welding was studied. The results show that the addition of laser energy into P-GMAW (pulsed gas metal arc welding) process can help to increase the frequency of metal transfer at the lower welding current and decrease its frequency at higher welding current. The addition of laser energy can reduce the welding current of P-GMAW,but its effect is very weak. The analyses indicate that the laser exerts the influence on metal transfer by the vaporization of material and the interaction between laser induced plasma and arc plasma,and its effects on welding current are exerted by the interaction between laser induced plasma and arc plasma.

Laser transmission joining of dissimilar and biocompatible materials has potential application in biomedical implants and their encapsulation process. 0.1 mm thick PET films and 0.1 mm thick titanium are joint using laser transmission joining technology. The effects of main laser parameters including laser power,scanning speed on joint quality are investigated by using analysis of variance. The results show that laser transmission joining can be used to join PET films and titanium. Based on the research,laser transmission joining of PET film and titanium process window is obtained;it will be helpful for the premise of guarantee of joint quality.

Spectral phase interferometry for direct electric field reconstruction (SPIDER),as a fast and accurate technique,is usually used in spectral phase measurement of femtosecond optical pulses. The effects of pulse replicas separation on the spectral phase retrieval of femtosecond optical pulses are investigated by experiments. The results show that the difference of reconstructed pulse width (FWHM) is within 2.76% in the replicas separation range from 0.22 to 1.82 ps. This research proves that spectral phases can be precisely retrieved in a broad range of pulse replica separation,which reduces the demand of high resolution spectrometer and facilitates the optimal parameter of pulse replicas separation in experimental measurement.

We present an optical coordinate measuring method using inverse photogrammetry. It mainly consists of micro-cameras,measuring rods and liquid crystal displays (LCD). One end of measuring rod is the fixed mini-cameras,on the other side is a trigger probe,LCD shows a two-dimensional sinusoidal fringe pattern. When measuring,the probe contacts the surface of the measured object,and then the camera captures the stripes image. The coordinates of camera principal point in the world coordinate system may be determined by the phase information that the fringe pattern carries. The relationship was determined between the principle point and the coordinates of the camera probes using least square optimization method. So that,the three-dimensional coordinate of the probe can be determined. The experimental results show that the method is simple,reliable,and can carry out optical coordinate with high precision.

An idea of using multipoint layer-type laser Doppler self-velocimeter (LDV) to offer velocity for vehicle navigation system is proposed,because the accelerometer has the error term generated by overload. The principle of measuring its own velocity with laser Doppler is expounded while multipoint layer-type LDV is designed. And Doppler signal is processed with the technique of tracking filter and digital autocorrelation. The results of theory and experiment show that,multipoint layer-type LDV can solve the problem that dual-beam LDV can not measure the velocity while out of focus. Background signal and part of noise in the passband are restrained by tracking filter,and residual noise is removed by digital autocorrelator so that the signal-to-noise and sensibility of the system are raised. Comparing with global position system (GPS),the relative accuracy of the system is about 2%.

Both the absolute accuracy and repeatability of phase-shifting point diffraction interferometer (PS/PDI) are influenced by the alignment errors of interferometer,so a highly sensitive computer aided alignment method is necessary. A highly sensitive computer aided alignment method based on the spatial frequency domain characteristic of PS/PDI is developed. In the coarse alignment stage,the information provided by the discrete Fourier transform of the light field distribution on CCD is used to align the PS/PDI. In the fine alignment stage,the frequency domain contrast of fringes on CCD is used as the merit function to align the PS/PDI. Alignment experimental results show that the alignment repeatability of 0.1 μm can be achieved for an 1.5 μm diameter pinhole used in visible light PS/PDI.

A full-duplex orthogonal frequency division multiplexing-radio over fiber (OFDM-ROF) system with 40 GHz optical millimeter-wave generation by utilizing single-arm Mach-Zehnder intensity modulator and optical carrier suppression modulation in base station is proposed and experimentally investigated. In the downstream,2.5-Gb/s OFDM analog data and 20-GHz radio frequency clock are mixed and used to modulate optical carrier by driving optical intensity modulator. The signal at base station after transmission over standard single mode fiber is demodulated,received and analyzed. In the upstream,the same optical carrier is reused at base station for uplink connection of 2.5-Gb/s on-off keying data. Experimental results show that the downlink and uplink data is successfully transmitted over a 50-km single-mode fiber (SMF-28) with less than 1 and 0.5 dB power penalty,respectively.

A new modulation scheme called dual pulse-pulse interval modulation (DP-PIM) is proposed for optical wireless communication systems by resolving the problems which exist in fixed-length digital pulse interval modulation (FDPIM),pulse position modulation (PPM),and digital pulse interval modulation (DPIM). Based on given symbol structure,bandwidth requirement,average transmission power and capacity are studied. Meanwhile,the packet error rate is derived based on weak turbulence channel model. After compared with on-off keying (OOK),PPM,DPIM and FDPIM,the theoretical and simulation results show that DP-PIM has no problem such as overflow and underflow in the buffer by fixing the symbol length. DP-PIM also has built-in symbol synchronization as same as DPIM and FDPIM,meanwhile offers higher bandwidth efficiency and transmission capacity by reducing the average symbol duration for the given parameters. Hence,DP-PIM is superior in optical wireless communication systems.

The problems of spot detection and tracking in fine tracking of space laser communication systems are researched. According to the characteristics of four-quadrant detector,the spot detection and tracking system is designed by using two band amplification,digital signal processing (DSP) system,fast-steening mirror etc. The principles of composition and design are studied in detail. A testing system is set up,which can prove by experiment that when the incident power is 1.3 μW,the position resolution of 1.6 μm,angle resolution of 0.8 μrad,and subdivision of 80 in photosensitive surface can be achieved. And the tracking precision is up to 2.1 μrad in one time variance at the conditions of high signal-noise ratio. With digital signal processing used as the core in data processing and control system,this system has many advantages such as small size,convenience to modify parameters,and engineering etc.

Based on the link rule and the function principle of the banyan network,its corresponding processing matrix has been achieved to denote and illustrate the relative signal operating and controlling. In other words,the matrix computing is employed to replace the complicated control process of optical network. Furthermore,extend the results of the two-dimensional banyan network to three-dimensional space in terms of the relative mapping rule of banyan network,the performing matrix has also been attained to solve some problems such as node controlling,signal routing,etc. The simple truth is that the ability to replace the complex process of optical interconnection network using the matrix computing opens the door to a host of new and exciting opportunities including signal routing and node switch controlling. The results indicate that this method may be useful for optical switching applications,optical computing,and optical information processing.

In order to improve the performance of optical wireless communication system,a novel fixed length dual-amplitude pulse interval modulation-code division multipte access (FDAPIM-CDMA) is proposed. With the optical orthogonal codes (OOC),the bit error rate (BER) of the proposed system in chip synchronous interference and ideal chip asynchronous interference are analyzed respectively. The upper and lower bounds on BER are derived as a function of code length,code weight,number of users,and receiver threshold. The characteristics for a variety of system parameters are discussed and compared with on-off keying-code division multiple access (OOK-CDMA). Simulations show that the BER performance of the proposed system can be improved by longer code length and smaller number of users. It is effective to get the threshold level higher to improve the system performance when the code weight is larger. Moreover,both the upper and lower bounds on BER of FDAPIM-CDMA are lower than those of OOK-CDMA when the bits per symbol are not less than 6. Hence,FDAPIM-CDMA plays good performance in multi-user interference and is superior in wireless optical communications system.

The influence of IP bursty traffic on combined nonlinear effects of cross phase modulation (XPM) and four-wave mixing (FWM) in IP over WDM networks is investigated by analyzing the Poisson distributed IP traffic based on the nonlinear Schrdinger equation (NLSE). Taken combined nonlinear effects into account,at the receiver,different eye diagrams with different input light powers and different IP traffic loads are obtained. From the numerical calculation results,when the input light power per channel is bigger than 5 dBm with 40 channels of WDM networks,the effect of IP bursty traffic will distort eye diagrams drastically. Furthermore we figure out the FWM power with different IP traffic loads,different input light powers and frequency spacings. FWM power with different wavelength settings is especially emphasized. From the FWM power distribution,we could quantitatively analyze which channels cross the probe channel seriously through FWM effect.