To study the general traveling properties of polarized light in the scattering medium with the influence of multi-factors, the influence of wavelength, medium thickness, particle parameters and incident polarization state on transmission properties of polarized photons is analyzed systematically. The Monte Carlo method is adapted to track polarization state changes of each photon, and the Stokes vector and polarization information after multiple scattering are obtained through statistical analysis of the polarization curve, and the traveling rules of polarized light in scattering medium are analyzed. Simulation results show that the particles with relative larger scale parameter have smaller changes on the incident light polarization state. Linear polarization light is good at keeping the polarization state. Circular polarization light can restore the polarization state in a short time. The larger the particle radius is, the stronger the recovering ability is, and the direction of rotation of the electric vector changes during the process of transmission.

To investigate blood vessel remodeling in the process of He-Ne laser irradition on periodontium of experimental tooth movement, a He-Ne laser with weavelength of 632.8 nm and power of 20 mW is used to irradiate the periodontium of experimental tooth movement in rats. Periodontal slice is treated by cyclooxygenase-2 (COX-2) immunohistochemistry dyeing and the results are obtained by image analysis. The results show that the COX-2 expression in periodontium with forced time of 3, 5, 7 d are significantly higher in experimental side than that of control side in the pressure region. While in the tension region, the COX-2 expression in periodontium with forced time of 1, 3, 5, 7 d are significantly higher in experimental side than that of control side. The results indicate that He-Ne laser can increase COX-2 expression in periodontium during the tooth movement in rats, thus probably enhance the vascularization of tooth movement.

Color holographic display is an important goal of holographic display research. Color holographic display technology using RGB lasers is studied, and color holographic display method based on space division multiplexing is proposed. Both the size and center of holographic optoelectronic reconstruction image depend on the wavelength of RGB lasers. The method by adjusting the original sizes of the RGB components of color images and adding digital blazed grating to achieve the coincidences of the sizes and centers of RGB reconstructed images is proposed. The color holographic display system with space division multiplexing method is developed, and hologram generated by 24-bit computer is added to spatial light modulator to reconstruct the color images by the advanced physics setup. Experimental results demonstrate the feasibility of the method proposed.

A novel optical encryption system is proposed by combining the optical principle of interference and diffraction. In this system, the original image is hidden into three masks, including two phase only masks (POMs) and one amplitude only mask (AOM). The AOM is randomly generated by computer while the POMs are obtained analytically. For decryption, the diffraction field of the two POMs is first superposed by utilizing the beam splitters and then modulated by the amplitude mask. After that the wavefront propagates for a certain distance and the intensity of the complex field, which is exactly the original image, can be recorded by CCD camera. Compared with the existing interference-based method, the approach is simple and easy to be realized by optical elements. Moreover, the silhouette problem that exists in the method with two POMs can be solved in our method. At the same time, the proposal is also proved to be robust to partial key exposure attack. Simulation results are presented to verify the validity of the proposed approach.

Defect of the porosity always occurs during laser welding of 5754 aluminum alloy and has a lot of bad influence on its mechanical property. Effects of the gap between two lap welding sheets on the porosity have been studied using fiber laser to weld 5754 aluminum alloy. It is found that setting a proper gap between two sheets can provide a passage for the escape of the porosity and decrease the porosity rate. When the gap changes from 0 to 0.2 mm, because of the capillary phenomenon, the escaping passage is closed by the solidification of the liquid weld metal, and the porosity decreases little. When the gap changes from 0.30 mm to 0.75 mm, the capillary phenomenon of the liquid weld metal between the gap weakens. So this part of weld metal is close to the fusion line and keeps liquid state. Then the escaping passage is opened and the porosity decreases obviously. It is also found that as the gap increases, the shear stress increases a lot.

Femtosecond laser at 1040 nm centre wavelength with 190 fs pulse width and variable (200~5000 kHz) repetition rate has been applied to microfabricate fused silica. Threshold energy has been measured as a function of the pulse repetition rate and the scan speed. The role of thermal diffusion and heat accumulation effects in forming waveguide is demonstrated. Double-line waveguides with the optimal parameters have been written, where the guided mode is fundamental mode and nearly circular. Hexagonal microstructure waveguide with elliptical cells has been made, where the mode has a nearly Gaussian intensity profile at 1040 nm. The microstructure waveguide has a large mode area about 247.48 μm2 and single polarization propagation property with extinction ratio about 9.05. The numerical aperture of the waveguide is about 0.017.

The ablation debris around the mitigated damage site on the surface of fused silica is one of the major factors inducing the damage of optics. The debris are classified into two types based on the ablation degree. The large-beam CO2 laser passivation and the buffered hydrofluoric acid solution etching method are used to eliminate the debris according to its types. Meanwhile, the corresponding optimal condition parameters are also obtained. The results show that the two methods can effectively eliminate the debris and improve the resistance damage capability of mitigated sites.

Due to existence of chill microstructure and cracks, influence of flaw control with laser cladding NiCuFeBSi alloy and preheating are investigated. Mechanical property of alloy is estimated as well. Results show that chill microstructure width of NiCuFeBSi alloy is extremely low. With preheating temperature increasing, the chill microstructure become discontinuous. Because of the generation of chill microstructure in semi-molten zone, microhardness in this zone is highest while descending at two sides of interface. Tensile strength of alloy is higher than HT250, furthermore, tensile strength along cross direction is higher than longitudinal direction. However, tensile strength of butt samples is lowest because of heat affection. Failure type of claddings is mainly cleavage fracture mixing quasi-cleavage fracture.

Machine vision system plays an important role in improving the quality of laser robot system. A system to detect three-dimensional (3D) shallow spot defects by combining two-dimensional (2D) images with 3D point clouds is carried out, which solves the problem of 3D positioning of shallow spot defects. With gray image processing, including image enhancement in the frequency domain, region marking and region merging, the system achieves the 2D positioning of defects. In order to obtain the 3D point cloud, laser remanufacturing part surfaces are scanned with binocular stereo vision system, and the 2D defect boundaries are then converted into 3D ones to realize the positioning of defects in the point cloud. Experimental results show that the system can effectively identify shallow spot defects, which further enables high precision remanufacturing of parts.

To improve wear resistance of the surface of magnesium alloy, laser alloying of Al-Cu powders coating on AZ31B magnesium alloy is achieved by the method of replaced-powder. The composition microstructure of the coating are analyzed by X-ray diffraction (XRD) and scanning electric microscope (SEM). Surface properties of the coating are evaluated using a micro-hardness tester and a abrasion tester condition at room temperature. The results show that the Al-Cu alloying layers are well bonded with the substrate; The XRD patterns show that the alloying coating is composed of α-Mg, β-Al12Mg17 and CuMg2, and the cortent of β-Al12Mg17 is higher than that of substract. The average micro-hardness of the surface layer is significantly improved from 50 HV to 210~265 HV, 4~5 times higher compared to the AZ31B substrate and the relative wear resistance is 2.5.

In order to study the effect of laser shock processing (LSP) on the stress corrosion cracking (SCC) of welded magnesium alloy, tungsten inert-gas (TIG) welded AZ31B magnesium alloy sheets surface is processed using NdYAG laser with a wavelength of 1064 nm, a pulse width of 15 ns, a pulse energy of 4 J and a spot diameter of 3 mm. At room temperature, the SCC susceptibility of the weldment samples with and without laser treatment is assessed by three points loading method in deionized water. The microstructure of specimens by LSP and fracture surfaces are analyzed by optical microscopy (OM), transmission electron microscope (TEM) and scanning electron microscope (SEM), respectively. The results show that a nanostructured surface layer can be produced on welded AZ31B Mg alloys by using optimized laser parameters and surface nano grain size is about 35 nm. The surface residual stress is converted from tensile stress (60 MPa) to compressive stress (-125 MPa). LSP can reduce the corrosion trend of the weldment samples because corrosion potential increases by 88 mV and corrosion current decreases by 73.4% as compared to the samples without LSP. SCC appeares on samples without laser treatment after 192 h of immersion, however, no cracks is observed on samples treated by laser after 10 months, which shows that LSP can obviously improve the resistance to stress corrosion cracking of TIG welded AZ31B magnesium alloy.

A 880 nm laser diode direct upper-state pumped Nd:YVO4 thin disk laser is demonstrated. With a 0.3 mm thick Nd-doping concertration of 0.5% Nd:YVO4 disk and pump power of 39.3 W, 20.6 W output power at 1064 nm is obtained and the optical-optical efficiency exceeds 50%.

The fiber ring laser based on the semiconductor optical amplifier (SOA) is widely used for optical communications and optical fiber sensing, because it can be tuned at an ultra high speed up to Mega hertz. The steady-state model and segmentation algorithm are employed to study the amplified spontaneous emission (ASE) properties of the SOA, then two kinds of the tunable ring lasers based on SOA (SOA-TRL) are investigated with the Gaussian or Fabry-Perot (F-P) filter. The evolutions of the output spectra and the peak power are demonstrated with the round trip of the light traveling in the ring cavity, which show the lasing process from the ASE to laser. It shows that the F-P filter can improve the wavelength tuning speed because the SOA-TRL with an F-P filter can establish the laser within only a few round trips, and it could be designed for some high speed applications.

By adopting the permutation entropy (PE) analysis, a high complex optical chaos generation scheme based on a semiconductor laser (SL) with double optical feedbacks is proposed. The simulated results show that, when the delay times of two optical feedbacks are close to each other, and have a difference of about a half of the SL relaxation oscillation period, the characteristic value of PE reaches a maximum, and the most complex chaotic output can be obtained. With the increase of the strength of two optical feedbacks, the characteristic value of PE firstly experiences a rapid increasing process and then decreases gradually. Thus, the high characteristic values of PE and high complexity chaos output can be founded within a certain range of feedback strengths. Moreover, under different feedback strength settings, the characteristic value of PE for double optical feedback system is always higher than that for single optical feedback system.

Fabry-Perot cavities are used as frequency references for ultrastable optical oscillators. The deformation of cavity induced by the vibration degrades the length stability of the cavity and laser produce frequency noise. Finite element analysis (FEA) is often used to examine the deformation of the cavity at arbitrary acceleration. A general expression of the change of the cavity length induced by the displacements and tilting angles of the cavity mirrors is deduced. This expression provides the definite connection between the cavity deformation and the vibration sensitivity. Based on this method, it is analyzed that the vibration sensitivity of a horizontal optical cavity, and its sensitivity to vibration can be reduced by optimizing the mounting configurations. In addition, a compact vibration platform that is able to shake the optical cavity in three orthogonal directions is designed.

Blue laser diode pumped PrYLF solid-state green laser is reported. A 5 mm long PrYLF crystal with the doping concentration of 0.5% is used as laser gain material, pumped by a blue laser diode with emitting central wavelength at 444 nm. Continuous-wave green laser output at 522.4 nm is obtained. Input and output characteristics of the lasers are studied with different output couplers. Under an absorbed pump power of about 530 mW, the maximum output power of 90.1 mW is obtained with 1.9% transmission coupler. The slope efficiency is as high as 65.3%.

The intensity noise properties of the monolithic Nd:YAG nonplanar ring oscillator are investigated via full quantum theory. By theoretical analysis and simulation, it is obtained that the relaxation oscillation is influenced mainly by the vacuum fluctuation, dipole fluctuation and cavity loss. The influence from the pump noise and spontaneous emission noise is relatively small. Meanwhile, the optoelectronic negative feedback of intensity noise is theoretically analyzed, which can provide a theoretical basis for the design of the noise suppression circuit. Based on this theory, the noise suppression circuit is designed which has better phase advance, low noise, wide bandwidth and adequate gain. Experimentally, a satisfied noise suppression result is achieved. For the noise with a relaxation oscillation frequency of 311 kHz, the experimental result shows that the relaxation oscillation noise peak value is reduced about 39 dB, and the intensity noise level is lower than -115 dB/Hz in the entire spectrum.

A new non-planar multi-pass laser amplifier based on the two-mirror ring optical path is proposed. It has the advantages of simple structure, small size, good space symmetry, easily adjustable and more amplification times. In the cavity of the amplifier, the signal beam goes through the laser medium many times for amplification along the three-dimensional non-planar symmetric path, and the high-power amplified laser can be obtained in a small-size laser medium. Theoretical modeling and parametric analysis of the optical path in the cavity of the amplifier are done. Simulation graphs for a portion of modes of optical path are given, optical loss and power amplification are also analyzed. A basic design of a solid-state non-planar multi-pass thin-disk laser amplifier based on Yb:YAG thin disk and laser diode (LD) end-pumping is given for high-power laser amplification.

The output characteristics and coexistent stimulated Raman scattering of a multi-wavelength tunable optical parametric oscillator (OPO), which is pumped by an all-solid-state NdYVO4 laser with the 1064 nm wavelength, are investigated by quasi-phase-matching period tuning technology. An experiment using the continuous wave (CW) operation mode, single resonant optical parametric oscillator and external cavity structure is carried out based on the PPMgLN crystal. Experimental results indicate that the widely tunable near-infrared spectrum from 1435.9 to 1670.2 nm and mid-infrared spectrum from 4185.0 to 2970.4 nm are obtained. The maximum total signal and idler output power at 30.5 μm poling period is 4.29 W when pump power is 11.79 W, which corresponds to an optical-optical efficiency of 36.4%. Coexistent CW OPO and stimulated Raman scattering (SRS) are demonstrated with 28.5, 30.0 and 30.5 μm poling periods. With the loss of SRS increasing, 1.98 W of the maximum idler output power at 3451 nm is obtained, corresponding to an optical-optical efficiency of 16.8%. An extra-cavity, widely tunable, high power and continuous wave singly resonant CW-PPMgLN-OPO at the signal and idler wavelength is realized, and the coexistent Raman scattering has an important effect on the output of the idler.

Based on the time-dependent nonlinear coupled wave equations, the amplitude modulation (AM) effect of third-harmonic pulse in the frequency conversion device of broadband Ndglass is studied numerically. To suppress this AM effect of output third-harmonic generation pulse, an added narrowband Ndglass laser pulse is mixed with the broadband laser pulse in the sum-frequency process of tripling configuration. Numerical results show that the limited phase-matching bandband due to the group-velocity-mismatch effects are substantially alleviated with the assist of a narrowband pulse. As a result, for a required third-harmonic wave with 1 THz bandwidth, the defined relative modulation of pulse intensity is as large as 180% in the conventional baseline design, while it will be reduced to only 20% by using the proposed scheme.

Multilayer graphene generated by chemical vapor deposition (CVD) method is irradiated by CO2 laser in vacuum with different power densities and irradiation time. Raman spectroscopy is used to clarify the influences of laser power density and irradiation time on the structure modification. At a laser power density of 13 W/cm2, the decrease of D-band and the increase of G-band intensity are due to the reduction of defects. In contrast, the sample irradiated with higher power density shows that the D-band intensity increase dramatically caused by the laser thermal effects. Nanocrystalline graphene is formed as the defects after irradiation at higher power desities. With increasing irradiation time to 120 s, amorphous carbon is formed at the surface of graphene at a lase power density of 58 W/cm2. These results show that proper irradiation of CO2 laser can improve the charactervstics of graphene.

Optical system plays an important role in space optical communication, and optical thin-film has become the key technology of the optical components. The laser filter film is designed and fabricated aiming at four bands of laser work of 532, 808, 1064, 1550 nm, by chosing Ti3O5 and SiO2 as high and low refractive index materials. It is used the design software of film system and adopts the method of electron beam evaporation and ion assisted deposition. The transmissivity of substrate after coating film at 808 nm is better than 90%, at 532, 1064, 1550 nm, reflectance is better than 99%. It is focused on half-wave hole in 808 nm transmission area and improved the laser damage threshold of film by cleaning the substrate, reducing the absorption of the film and vacuum annealed. The laser clear filter meets the requirements of the system after a performance test and evaluation.

Based on the reflection principle of polarized light and measurement of multi-angle multi-fitting algorithm, the accurate measurements of the refractive indexes and thicknesses for the film materials are achieved. When highly collimated diode laser incidents on the interface between thin films and air, the curve of reflectivity varying with the incident angle is obtained by gradually rotating the sample or changing the incident angle of the sample surface. Multiple solutions of film thicknesses and refractive indexes can be solved by using reflectivities from the different angles in this curve based on calculation formula. Its optimal solution can be determined by fitting measuring and corresponding computational reflectivities. By multiple expanding the scope of the film parameters and then fitting them, more accurate film parameters can be found out. The refractive index and thickness of the SiO2 film are measured using this method, of which error of refractive index is less than 0.3% and thickness error is less than 0.07%.

Photon sieve is a diffractive optical element with large chromatic aberration, which is not suitable for imaging in wide spectral. The focal length of photon sieve decreases when the incident wavelength increases, while the focal length of positive refractive lens increases when the incident wavelength increases. The design applying the method of hybrid refractive-diffractive into the photon sieve achromatic is proposed. These opposite dispersive characteristics are used in this method. A plano-convex len is placed close to side of a photon sieve in order to achieve achromatic design. Then the achromatic system is designed in the visible spectrum. The analysis shows that the system is achromatic and has a certain ability of secondary spectrum correction. The relative error between focal lengths of achromatic wavelength and centre wavelength is 0.33%. The imaging spectral bandwidth is 20 nm. Compared with ordinary single photon sieve, the design broadens the imaging spectrum range. Compared with the hybrid refractive-diffractive system using zone plate, a smaller focusing spot can be achieved.

The far-field light intensity model of annular plane beam through Kolmogorov atmospheric turbulence is presented, and both the discrete sampling of CCD pixel and detection noise are considered as well. The parameters of peak Strehl ratio、encircled energy Strehl ratio and beam quality factor are taken to evaluate far-field spot quality, and the Monte Carlo method is used to analyze the influence of four kinds of threshold method on calculation results of far-field spot quality when signal noise ratio (SNR) or turbulence strength is different. The results show that accurately measurement results of far-field spot quality are premised on adequately high SNR; if the SNR and turbulence strength are fixed, the threshold method of subtracting average background voltage of CCD and reserving random noise is the better choice to obtain the higher calculation accuracy of spot quality.

In order to obtain accurate signal to noise ratio (SNR) measurement of picosecond ultrashort pulse and enlarge the range of pulse SNR measurement, a repetition frequency scanning third-order correlator is built, which considers the problem of parametric fluorescence induced by ultrashort high-power laser pulses in correlated process. Besides, the measurement technology is carried on picosecond short-pulse optical parametric chirped pulse amplification (OPCPA) pump source. The results show that the impact of parametric fluorescence on the measurement is largely eliminated by large-angle noncollinear phase matching, furthermore, by reducing the background noise the dynamic range can achieve about 107. Because of the asymmetry of cross-correlation technique, the correlator can also analyze temporal profile. The results indicate that pulse front edge is coincident with sech type curve, and pulse back edge has good agreement with Gauss type curve.

A simulation model is setup to analyze the reciprocal noises reduction and the improvement of the gyro bandwidth of the single closed-loop and double closed-loop resonator micro optic gyro (R-MOG). Simulation results show that the double closed-loop R-MOG can inhibit the reciprocal noises and enhance the output bandwidth. Furthermore, the double closed-loop R-MOG can improve the gyro linearity. Based on the work mentioned above, an experimental system of the double closed-loop R-MOG is set up. The bias stability and gyro output are tested. Experimental results show that the bias stability of the R-MOG is 0.53 °/s over an hour and the linearity of the R-MOG is 99.995% over the range of ±1000 °/s.

Influence of air dispersion on the pulse width is studied in the distance measurement of femtosecond pulsed laser. The femtosecond pulsed width variations with input femtosecond pulsed width, central wavelength and the propagation distances are given in analysis. Compensation scheme of air dispersion based on high-density transmissive grating is put forward to maintain distance measurement accuracy. Then influence on compression of femtosecond pulsed laser width by grating period and distance is also given. The method has some advantages, such as compact volume and convenient operation. It will be helpful for high-accuracy long distance measurement by using femtosecond laser.

A three-dimensional (3D) shape measurement method for confined space using an optical tube is proposed. Considering small cross-sectional area and high reflectivity, a optical tube is designed for image transmission. With the optical tube, fringe patterns can be easily projected onto internal surface from external space. The collected images transferred from interior space to external space are recorded by CCD. Accordingly, shade and occlusion caused by the limitation of measurement space are avoided and 3D shape measurement for internal surface of confined space is realized. Experimental results show feasibility and validity.

A novel optical fiber transmission system for low bending loss, large mode area and single-mode operation is proposed. The system is composed of a multi-mode photonic crystal fiber (PCF) and two single-mode PCFs. The single-mode PCFs are connected to each side of the multi-mode PCF. Numerical simulation on the mode area, the bending loss, the splicing loss and other aspects of the transmission system indicates that the system can effectively suppress the transmission of higher order modes. In addition, at the operating wavelength of 1064 nm, the multi-mode PCF has a large mode area of 1593 μm2 when it is kept straight, and exhibits a low bending loss even at a small bending radius of 10 cm. The splicing loss between the multi-mode and single-mode PCFs can be as low as 0.085 dB for the optimized PCF configurations.

A photonic approach to implement a microwave channelized receiver based on superimposed chirped fiber Bragg grating (S-CFBG) is proposed. An optical frequency comb (OFC) is generated using the first S-CFBG. Broadband microwave signal is multicast by the OFC, spectrally sliced by the second S-CFBG and channelized by optical wavelength division multiplexer (WDM) de-mux. Broadband microwave signal with frequency measurement range form 0 to 20 GHz and accuracy of 0.5 GHz is achieved by simulation. 156.25 Mbit/s non-return-to-zero (NRZ) signals, which are located at different radio frequency (RF) carrier waves, can be detected simultaneously and instantaneously without local RF source array. The bite error rate (BER) performance of receiver is researched.

According to the coupled-mode theory, different properties of reflected polarization dependent loss (RPDL) of fiber Bragg grating to temperature and lateral force are analyzed. Based on the relevant sensitivity coefficient matrix, the temperature and lateral force can be demodulated by a single fiber Bragg grating simultaneously, by which the problems induced by the cross sensitivity of temperature and lateral force can be avoided in the test progress. The experimental temperature sensitivity coefficients of left peak and right peak of RPDL are 0.0101 nm/℃ and 0.0100 nm/℃, respectively. Lateral force sensitivity coefficients achieve 0.0071 nm/N and 0.0005 nm/N, respectively. The accuracy of temperature and lateral force can reach ±1 ℃ and ±0.6 N, respectively. The key sensing component of the method has advantages of simplicity, high sensitivity and easy to be buried into interior of material tested to conduct monitoring. It provides a new method to test the changes of temperature and internal structure information.

An approach to achieving continuously tunable microwave/millimeter-wave frequency multiplication signal based on injection locked dual-wavelength difference-frequency distributed feedback (DFB) laser is proposed. Wave optical signals are nonlinearly broaden by semiconductor optical amplifier (SOA), and high-order components are generated. The sine wave optical signal is injected into two DFB laser and locked enlarge, then the continuously tunable frequency multiplication is generated. In the experiment, the injected sine wave optical signal frequency is 1.25 GHz, the continuously tunable microwave signal with any natural multiples of 1.25 GHz in the 20~40 GHz frequency range is achieved, and the highest multiplier of 32.

A new scheme about a semi-etched long-period fiber grating (LPFG) is proposed based on the excellent relation between cladding effective refractive index and cladding radius. A LPFG is divided into two sections with equal length. One section is eroded using HF acid. So the two sections can be regarded as two LPFGs with different resonant wavelengths. Spectral characteristics of this in-series LPFG are analyzed using dispersion equation of three-layer dielectric fiber. It is found that the distance between two resonant wavelengths increases with the decrease of the cladding radius, and the distance also increases with higher-order mode. At the same time, strain and temperature are measured synchronously, and the sensing precisions of strain and temperature are ±8.9 με and 1.4 ℃, respectively. Semi-etched long period fiber grating can solve the cross sensitive problems of different physical quantities effectively.

A scheme for the generation of ultra-short optical pulse, based on optical frequency comb (OFC), is proposed and demonstrated experimentally. An OFC with 29 comb lines within 1.5 dB spectral power variation is obtained by cascading intensity and phase modulators modulating a continuous wave laser. The OFC is dispersed by a segment of single mode fiber (SMF). Ultra-short optical pulses with 10 GHz repetition rate and 2.68 ps pulse width are demonstrated. The pulses are used for sampling 1~4 GHz radio frequency signals. The signal-to-noise ratio of this scheme is 33.83 dB, equivalent to effective bit number of 5.33 bit.

A remote fiber Bragg grating (FBG) sensors system based on the self-heterodyne detection and wavelength-sweeping technique is proposed and experimentally demonstrated. In this system, the heterodyne signal produced by the reflected sensing signal and the local reference beam is detected by a balanced photodetector. With frequency-shift and pulse-modulation of the acousto-optic modulator, the detection sensitivity and sensing distance are improved effectively. The system is able to detect the two multiplexed FBGs placed 171 km away, offering a signal-to-noise ratio of 33 dB without amplification. In addition, this system can scan the reflection spectra of FBGs accurately. Applying this system to remote temperature detection, the results show the typical liner behavior of both FBGs, shifting their reflected Bragg wavelengths in 11 pm/℃.

A novel fiber Bragg grating (FBG) accelerometer based on an elastic structure which consists of a stainless steel tube and a mass block is proposed. Four FBGs are fixed axially on the tube surface where produce the most large strain along the circumference of the tube with a 90° angle. Two-dimensional measurement and temperature compensation are realized through the change of two pairs of FBGs′ wavelength shift caused by vibration. Finite element analysis is used to explain the two-dimensional measurement principle and the resonant frequency of the accelerometer further. Vibration test results demonstrate that the accelerometer possess of a resonant frequency of 515 Hz, a wide linear measurement range from 15 m/s2 to 75 m/s2 and a sensitivity of 0.88 pm·m-1·s2, which is consistent with the finite element analysis results. The two-dimensional vibration test results show that the accelerometer has a good anti-interference ability.

The moving target imaging in the field of ghost imaging is researched. In order to overcome the imaging degradation caused by relative motion between imaging system and target, a method of translation compensation of light intensity distribution recorded by the reference detector is proposed so that the resolution of ghost imaging for moving target can be improved. Both theoretical and experimental results suggest that ghost imaging technique can obtain high-resolution imaging of moving target by the proposed method of translation compensation. According to the application of remote sensing, the influence of detection noise to ghost imaging for moving target is discussed based on intensity correlation linear reconstruction and nonlinear sparsity constraints reconstruction algorithms, respectively. The advantages and disadvantages of both the proposed technique and existing motion-deblurring techniques are also discussed.

Iterative closest point (ICP) algorithm is widely used in multi-view fine registration of 3D point clouds, while its accuracy and convergence to global optimization depend on initial registration position. It fails when a great difference exists to initial position of the waited registered point clouds. Coarse registration aims to provide a good initial registration position for ICP. A new coarse registration algorithm—iterative least space distribution entropy is proposed based on the space distribution of point clouds, and the concept of entropy is used for describing this distribution law according to information theory. Experiments show that the proposed algorithm can offer a good initial registration position for ICP and it owns a high efficiency and can realize registration without using ICP under precision permission.

The received waveform model for different earth surfaces is significant for altimeter system design, and the model of ocean surface is rarely researched after Tsai. According to the theory of Fresnel diffraction, the character of specular reflection and statistical regularity of the ocean surface profile, the analytic expression of detector output and the average received photons are deduced which are used for ocean altimeter and different from the results of Tsai under the condition of near-normal incidence. The simulated waveform is established for laser altimeter with microradian beam divergence and compared with the real geoscience laser altimeter system (GLAS) received signal. The energy, root mean square (RMS) width, amplitude and shape are very similar and the errors between simulated and real waveforms are all less than 6%. The parameters of received signal are related to the altimeter systems and the wind speed over the ocean surface, and taking the GLAS parameters for example, the valid ocean waveforms can be hardly got when the wind speed exceeds 12 m/s. The analysis and conclusion are important theory basis for the design of laser altimeter system and the wind speed calculation over the ocean surface.