The entanglement dynamics of two atoms in the one-photon and two-photon Jaynes-Cummings models are studied by employing the concurrence and linear entropy. The effect of the initial entanglement degree of two atoms and the initial state of the cavity field on the time evolution of concurrence is analyzed. The results show that the phenomenon of sudden death of entanglement between two atoms happens when the field is initially in the state |11〉. The length of the death time interval is dependent on the initial entanglement degree of two atoms. Moreover, it is found that the atom and the field are entangled in the overall time evolution process.

To accurately obtain the three-dimension (3D) velocities fields of the rotating flow fields, digital holography particle image velocimetry (DHPIV) is presented. A new method, namely the integrated gray-level gradient, is used to locate the focal plane of the particle and to extract the 3D particle′s coordinate. The 3D cross-correlation pairing algorithm is applied for the pairing of particles. The rotating flow fields′ 3D visual velocities fields, corresponded to the theoretical modeling, are obtained by DHPIV based on the integrated gray-level gradient method and the three-dimension cross-correlation pairing algorithm. The experimental results demonstrate that this technology can be applied for measurement of the rotating flow fields effectively.

Ladar range image is closely relative to the physical structure property of object surface, and reflects essential characteristics of objects, thus it has received considerable attention in object recognition field. Image moments are significant methods for object recognition. The low order moments of Hu moment invariants and affine moment invariants are combined to describe the features of three-dimensional objects, and back-propagation (BP) neural network is applied to recognize objects on different azimuth angles. When the view angle is constant, the case that training 10 objects and sampling from 3 to 19 per object, under different carrier-to-noise rates (CNRs), is analyzed about the correct rate of recognition for the Hu moment invariants, the affine moment invariants and the combination of both. The theoretical and experimental analyses prove that using the combination of the Hu moment invariants and the affine moment invariants as features to classify objects can achieve better recognition performance than only using either the Hu moment invariants or the affine moment invariants.

With the development of laser technology, laser imaging radar gradually possesses vast application in complicated battlefield of modern warfare. At present automatic target recognition technology for laser imaging radar is a hot problem at home and abroad. Target recognition algorithm based on combination moments for laser imaging radar is put forward. Combination moments feature including lower-order Zernike moments, Hu moments and central moments is extracted from range image of laser imaging radar target, this feature is not sensitive to range image noise. Radial base function (RBF) neural network is used to recognize three kinds of ground targets. Experimental result shows that comparing this algorithm with using Zernike moments and Hu moments feature to recognize targets, the average recognition rate of three kinds of ground targets of laser imaging radar is raised by 1.0% and 3.7% separately under high carrier-to-noise ratio (CNR) (20 dB); the average recognition rate is raised by 11.8% and 42.5% separately under low CNR (10 dB); when CNR is higher than 17 dB, the average recognition rate of this algorithm is 100%. Therefore this algorithm gains good recognition effect.

The commercial pure titanium sheet TA2 is continually mould-free laser shock deformed by means of a Ndglass Q-switched laser setup with 1064 nm wavelength and 20 ns short pulse. The microstructure characteristics of the deformed sheet on whole section are analyzed with the thermo-field emission scanning electron microscope (SEM) and transmission electronic microscope (TEM) respectively. Three main microstructure characteristics are observed based on the stress state in deformed zone. The first is the near nanometer micro-twin gate in the compression strain region, which is thought to be a product composed of high density of stacking faults in the same direction. Due to the inter-actions between neonatal microstructures and the induced third type of internal stress, high density of dislocation networks and/or dislocation cells formed in laser shocked substrate. The second is the inverse-transformed martensite, which is induced by partial shear deformation in the compression zone of laser shock deformed sheet. The third is the local stratified cluster slips along the cleavage direction, induced by the ultra high energy and ultra-high strain rate of laser shock, in the tensile deformed region owing to the increasing of deformation resistance of highly constrained hcp crystalline material. The above-mentioned phenomena can be attributed to the confinement conditions and deformation mode of micro-zone upon laser shock forming, and will result in microscopically inhomogeneous of microstructures and hardness in the deformed section. Therefore, repeated shocking is not conductive to the uniformity of deformation of titanium sheet.

Finite element method (FEM) models are established to perform transient thermo-elastic-plastic FEM analysis on stress and deformation of single-pass multilayer with and without substrate pre-deformation during laser solid forming (LSF). Simulation results show that substrate with pre-deformation can affect the distribution and size of stress and deformation in formed parts which can effectively alleviate the warpage of substrate. The point with initial tensile stress on the bottom surface of substrate has a smaller residual stress than that of the substrate without pre-deformed. The middle position of the interface between the substrate and the cladding layer also has a smaller residual stress than that of the substrate without pre-deformation. In both models, the positions of maximum residual compressive stress are different. Both sides of cladding layers deform badly compared with the middle location. The first cladding layer has the largest effect on substrate deformation; the deformation of the substrate gradually reduces as the cladding process proceeds. The longitudinal displacement change rate of the substrate constantly reduces and eventually tends to stable. Appropriate pre-deformation of the substrate before LSF can effectively control deformation of the substrate and improve stress distribution of the part.

A central composite rotatable experimental design is used to plan the experiment of laser transmission welding of polymers. Response surface methodology (RSM) is employed to establish the mathematical models of relations between the welding process parameters and the weld strength as well as weld seam width, and then the desirability function coupled with genetic algorithm is used to carry out the multi-objective optimization of the weld strength, weld width and weld cost. It demonstrates that the predicted results of the optimization are in good agreement with the experimental results, so this study provides an effective direction to enhance the weld quality and minimize the weld cost.

The mechanical properties of laser solid forming (LSF) of Ti-Al-V ternary system titanium alloys from blended elemental powders are investigated. The relationship between the composition and the hardness of LSF Ti-xAl-yV(x≤10, y≤25) is obtained based on the hardness test and the neural network model optimization. The room temperature tensile properties of some typical LSF Ti-xAl-yV alloys are obtained, and the scale factor K of the tensile strength to the microhardness is obtained between 2.86 to 3.00, and thus the tensile strength prediction for LSF Ti-xAl-yV can be realized. The test results show that the room temperature tensile properties of laser deposited Ti-4Al-3V、Ti-5Al-3V、Ti-4Al-4V、Ti-5Al-4V and Ti-3Al-6V have reached the wrought standard of Ti-6Al-4V.

A laser diode (LD) end-pumped RTP electro-optic (E-O) Q-switched adhesive-free bond composite crystal laser TEM00 operating at repetition rate of 150 kHz is reported. Details are compared on performance of high repetition rates E-O Q-switched composite NdYVO4 and NdGdVO4 lasers. The experimental results reveal that under small and medium pump powers, the composite NdYVO4 crystal, compared with the composite NdGdVO4 crystal, has more capability to obtain higher peak power and shorter pulse width output through high repetition rates E-O Q-switched operation, for its larger stimulated emission cross-section and moderate upper-state lifetime. Compared with composite NdYVO4 crystal, composite NdGdVO4 crystal with excellent thermal performance under high pump power is more suitable to be the laser gain medium for high repetition rates E-O Q-switched operation.

A XeCl excimer laser system used for treatment of vitiligo is developed. A push-pull pulsed switching power supply is designed for pulsed discharge of excimer lasers. The dependence of laser output energy on repetition rate, discharge voltage and gas lifetime is studied. The pulse-to-pulse stability is measured. Based on a feed-back control system, the discharge voltage is adjusted automatically to achieve laser operation at a preset energy level. The laser beam is transmitted through a liquid-core optical fiber to achieve a homogeneity of laser spot for treatment. The transmissivity of the 308 nm excimer laser in liquid-core optical fiber is about 70%. The repetition rate of the laser is 1~200 Hz. The discharge voltage can be adjusted from 18~25 kV. The pulse to pulse energy stability is less than 4%. The diameter of effective spot is 22 mm while the pulse output energy density is 2~3 mJ/cm2.

A passively mode-locked erbium-doped fiber soliton laser based on graphene saturable absorber is reported. At a pump power of 370.4 mW, the pulse width is about 1.32 ps and the pulse repetition rate is 3.16 MHz with average output power of 1.07 mW, which corresponds to single pulse energy of 0.338 nJ. Moreover, the central wavelength can be tuned between 1556.72 nm and 1558.76 nm. The simulation based on Ginzburg-Landau equation is consistent with the experimental results.

The external cavity laser diode array (LDA) with volume Bragg grating (VBG) recorded in photo-thermo-refractive (PTR) glass as wavelength selected element is studied experimentally. The influence of fast-axis-collimation on coupling efficiency is studied. Experimental results indicate that the wavelength of the LDA is locked and the line-width is narrowed sharply under the effect of VBG external cavity. The influence of VBG reflectivity on spectral characteristics and efficiency of external cavity LDA is studied mainly. Experimental results show that the increase of VBG reflectivity can inhibit the intra-cavity mode effective and enhance the contrast of spectrum and narrow the line-width. Using the VBG with a reflectivity of 30%, an output power of 24.8 W is obtained with the linewidth down to 0.18 nm, which corresponds to the efficiency of 82.6% compared with the output power in free-running LDA.

A novel all-fiber ultra-long ring cavity erbium-doped fiber laser is reported. The laser consists of only single mode fiber (SMF) components except the nonlinear polarization rotation (NPR) parts which are utilized to achieve self-starting passively mode-locking. The total length of the ring cavity amounts to 4.046 km, which is achieved by incorporating a 4 km SMF. In experiment, the laser generates stable mode-locked pulses with a 50.92 kHz fundamental repetition rate. The maximum average power of output pulses is 2.73 mW, which corresponds to a single pulse energy of 53.61 nJ.

A dual-wavelength passively mode-locked Yb-doped fiber laser (YDFL) based on the interaction of graphene and fiber-taper evanescent field is reported. Using optical evanescent-light deposition technique, graphene-polymer nanocomposites in aqueous suspension are coated onto taper waist region. The graphene-based tapered-fiber as a saturable absorber has the advantages of flexibility, all-fiber configuration, and high optical damage threshold. Based on the saturable absorption of this graphene-based component and the cavity-birefringent filtering characteristics, the stable dual-wavelength mode-locked operation is obtained, by properly adjusting the polarization state of the laser cavity. The two mode-locked wavelengths of YDFL are 1034.77 nm and 1038.85 nm, and the mode-locked repetition rate is 1.09 MHz at the second harmonic frequency, and the intracavity pulse energy can reach 35 nJ.

On the basis of the development of the model of transient state spectral absorption coefficient and ultrafast carrier dynamics, a theoretical model is established, which can describe the transient bleaching mechanism induced by femtosecond laser, so as to investigate the characteristics of the transient bleaching of direct bandgap semiconductor. The results indicate that femtosecond laser can not only induce the corresponding spectral bleaching but bleach the spectrum ranging from the exciting wavelength to the semiconductor′s long wavelength cutoff as well, and the effect becomes more obviously with the increase of laser wavelength and even results in negative absorption phenomena at the bottom of band.

A novel method to calculate the thermal focal length of corner-pumped slab lasers is proposed. Traditional methods generally use uniform distribution or exponential decay distribution to characterize the heat distribution, and the difference between calculation results and the experimental value is not small which is against the further cavity design. Tracepro software is used to trace the pump light in the medium so as to get the accurate heat distribution within the gain medium, and then the temperature distribution and thermal focal length is calculated. The calculation results of this method are according with experiments much better than those of the traditional. This method is of general applicability, and is especially suitable for lasers with novel pump ways and special shape gain media.

High-pulse-energy semiconductor saturable absorber mirror mode-locked 2.0 μm thulium-doped ultrafast all-fiber laser is reported. Stable mode-locked pulse train occurred at 1.8 W incident pump power and the pulse repetition rate is 14.3 MHz in a ring cavity configuration. Increasing the incident pump power to 3.8 W, the maximum output power is 59 mW, corresponding to the maximum single pulse energy of 4.1 nJ. The pulse width is measured to be 2.2 ps, the center wavelength and the spectral bandwidth are 2015 nm and 2.9 nm respectively.

A tunable multiwavelength Brillouin-erbium fiber laser is demonstrated. With the mirror constructed by the optical circulator and the ring-cavity, a bidirectional feedback structure is constituted to reduce the Brillouin threshold. This fiber laser provides a tuning range of 65 nm from 1513 nm to 1578 nm. At the Brillouin pump power of 15 dBm (32 mW) and the 980 nm pump power of 23 dBm (200 mW), 11 output channels with 0.08 nm channel spacing are achieved.

A laser diode with the central wavelength of 888 nm is used as the pump source to mitigate the thermal load in the pumping progress. Through the optimization of the ring cavity, the mode size in the Nd:YVO4 crystal is enlarged, and the astigmatism of the cavity is minished. A figure "8" shaped ring cavity is employed to enforce the single-frequency operation. As a result, a stable, high-power, single-frequency green laser (M2<1.1) of 21.5 W is obtained with the optical-optical conversion efficiency of 31.9%, and power stability of ±1% for 8 h.

A multi-wavelength fiber laser with phased-shifted fiber grating (PSG) is proposed. The phase-shifted fiber grating with two phase shift points is used as the wavelength selection device which is formed by inserting two phase shift points in the Bragg grating. Under 980 nm laser diode (LD) pumped, stable triple-wavelength can be obtained by adjusting the polarization controller (PC) at the room temperature. The triple-wavelength output power fluctuation is less than 0.6 dB within 25 min. Further more, the temperature tunability of the wavelength of the fiber laser is investigated. The output wavelength can be tuned with the temperature changing from 25 ℃ to 85 ℃. Due to the stable multiwavelength output, the fiber laser can be used in the multiwavelength interference measurement and optical communication systems.

In order to solve the problems in mode hopping detection for single-frequency fiber lasers, a method is put forward based on the dynamic phase changes in an unbalanced Michelson fiber-optic interferometer. Steep frequency changes in mode hopping process are transformed to steep phase changes in the working point of the interferometer, and the changes are obtained accurately by tracking simultaneously both the sine and cosine functions of the working point in time domain. Various mode hops in an ultra-narrow linewidth erbium-doped fiber ring laser, including occasional hops and thermally-induced serial hops the moment the laser is switched on, have been detected successfully with this method. The results show that this method has a high testing sensitivity, and makes real-time and apparent criterions for identifying mode hops. Besides, possible frequency drift between two serial mode hops can also be measured by use of this method, which plays an effective role in evaluating the lasing mode stabilities of single-frequency fiber lasers.

Transmissivity of one-dimensional sine function photonic crystals is studied, and the characteristic of light transmission is analyzed. There are some important results: for one-dimensional sine function photonic crystals, the electric field can be increased or decreased at the defect layer, which depends on the refractive index of the defect layer; when the position of the defect layer is closer to the front side, the impact is larger on the distribution of electric field behind the defect layer. These results are important for the design and application of photonic crystals.

PVP/［Y(NO3)3+Al(NO3)3+Eu(NO3)3］ composite nanofibers are prepared via electrospinning, and YAlO3:Eu3+ nanofibers are fabricated by calcination of the prepared composite fibers. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectroscopy. Pure phase YAlO3:Eu3+ nanofibers are obtained by calcination of the relevant composite fibers at 1200 ℃ for 2 h and YAlO3:Eu3+ nanofibers belong to orthorhombic system with space group Pnma. The diameters of fibers analyzed by Shapiro-Wilk method obey normal distribution under the confidence of level 95%. The surfaces of as-prepared composite fibers are smooth with a good aspect ratio, dispersion and uniform size. The diameters of PVP/［Y(NO3)3+Al(NO3)3+Eu(NO3)3］ fibers and YAlO3:Eu3+ nanofibers are (152.9±26.0)nm and (106.7±20.2)nm, respectively. Fluorescence spectra analysis manifests that YAlO3:Eu3+ nanofibers emit the predominant emission peaks at 590 nm and 609 nm under the excitation of 234 nm ultraviolet ray, attributed to the transitions of 5D0→7F1 and 5D0→7F2 energy levels of Eu3+, respectively. The doping concentrations of Eu3+ have no effect on the shape and wavelength of the emission spectra of YAlO3:Eu3+, and the luminescent intensity reaches a maximum at about 5% of Eu3+.

The effect of CO2 laser irradiation on the dielectric properties of PZT-4 ceramic is investigated. After laser irradiation, dielectric permittivity and dielectric loss of the ceramic decrease 5% and 60%, respectively, and the coercivity increases. The mechanism of the changes are analysed by Raman scattering, scanning electron microscope (SEM), X-ray diffraction (XRD) and the annealing process. It is shown that the microstructure changes of the irradiated sample mainly account for the dielectric properties. The CO2 laser irradiation could induce the tension stress, leading to the larger lattice parameter and the deviation of B site ion from the center of oxygen octahedron. The distortion of the oxygen octahedron results in the less activation of electric domains. Therefore, the polarization switching of the electric domains become more difficult, exhibiting the properties of "hard". This suggests that the laser irradiation may offer a new approach for the fabrication of lead zirconate titanate (PZT) based "hard martial" in several seconds without any ions addition.

The CNx films are deposited on monocrystalline silicon substrates by pulsed laser deposition (PLD) technique with different laser fluxes and CNx coating as the target. The morphology，composition and microstructure of the films are characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) respectively. The tribological behavior is investigated using a ball-on-disk tribometer in atmosphere (RH=48%~54%). The results show that an introduction of iterative PLD technique can improve the nitrogen content of the CNx films remarkably. With the increase of laser flux from 5 J/cm2 to 10 J/cm2, the percentage of N-sp2C bonding increases and the nitrogen atom fraction of the CNx film increases from 23.8% to 29.9%. A decreased percentage of N-sp3C and sp3C-C bonding of the CNx film are observed and the wear rate of CNx film increases from 2.1×10-15 m3/(N·m) to 9.0×10-15 m3/(N·m). The friction coefficient of the films ranges from 0.15 to 0.23. Compared with the others, the film deposited at laser flux 5 J/cm2 exhibites an optimal tribological performance.

The key performance of super-resolution optical disk storage technique is mainly determined by the mask material. In this work, the super resolution pits on the optical disk are dynamically read out with indium thin film as a functional mask layer. Thin films with different thicknesses are deposited by direct current magnetron sputtering method, the thickness changes with time of the In thin films are measured by profilometer and the different surface morphologies are observed by atomic force microscopy. In thin film in the pre-engraved super-resolution optical disk with pit size of 390 nm is created to form the In mask super-resolution optical disk. The readout is tested by the optical disk dynamic tester, and the largest carrier to noise ratio (CNR) of 26 dB is obtained. To explore the internal mechanism of this super-resolution readout ability, the optical constant under different temperatures is studied by variable temperature ellipsometer. The reflectivity and absorption coefficiency are also obtained. The experimental results indicate that the mechanism of the super-resolution readout with In thin film as mask can be explained by the model of aperture-type super-resolution.

Pinpointing hole center is crucial for machining shaft hole of large-scale workpiece. In order to improve the precision and efficiency of workpiece machined, an approximation hole center positioning method is proposed by rotating laser displacement sensor without angular coordinate. Laser displacement sensor is installed on the rotatable spindle, and the rotatable spindle is placed randomly at a different position around hole center. Spindle is moved along two directions respectively, which are mutually perpendicular and both perpendicular to spindle on machine tool, resceltin in the alteration of sensor data. With the application of the approximant positioning method of hole center, relative coordinate of hole center to machine tool can be obtained quickly and accurately, which could accurately guide the subsequent machining. The experimental results show that this method can be used to improve the accuracy and efficiency of hole center positioning.

The phase-shifting Jamin shearing interferometer is very fit for measurement of diffraction-limited wavefront. To improve the performance of existing phase-shifting Jamin shearing interferometers with two polarizers, a phase-shifting Jamin shearing interferometer based on polarization combination is proposed. In the interferometer, the beam to be measured is reflected by two surfaces of the Jamin plate to form two interfering beams. They are polarized and combined to form a polarization phase-shifting interferogram. The interferometer keeps up the optical configuration and improves fringe visibility. Two kinds of phase-shifting Jamin doube-shearing interferometers before and after improvement are built for experiments. Results show that the usefulness of the interferometer is verified.

On the Basis of the long-baseline laser interferometer, an online stability monitoring technique is studied for nanoscale displacement and vibration measurement. A laser interferometer with 22 m arm is built to measure displacement and vibration. Based on phase generated carrier (PGC) demodulation technique, an indication signal with known frequency and fixed amplitude is added. Working condition monitoring of laser interferometer, measurement of environmental changes and fluctuation indication can be realized by the variation of the amplitude of indication signal. Experimental results show that online condition monitoring of the laser interferometer can be achieved by adding a known indication signal. This method can carry out online stability monitoring of laser interferometer without extra hardware load, which can simplify the debugging process of interferometer and improve the running efficiency.

Optical manipulation based on surface plasmon excitation has recently attracted significant interest for its low energy consumption and simple installation. Surface plasmon field is excited with Kretschmann prism coupling scheme and effective trapping of 10.8 μm diameter polystyrene beads is realized. By modulating the incident laser pattern with a micro-aperture array, microparticles are massively dynamic patterned on a homogeneous gold thin film. A 20 mW He-Ne laser is used in the experiment as the light source. The applied power intensity is tens of times weaker than that of laser tweezers. Owing to its advantages such as low cost, flexible manipulation ability and low power consumption, the trapping method can be used to the manipulation of living cells and DNAs in medical treatments.

Micro fiber polarization filter is one of micro basic components for optical communication and sensors system. Theoretical analysis based on super mode theory shows that polarizing effect in coupling component of two contacted micro fibers can be achieved when the fibers′ coupling length and diameters are chose suitably, which means unpolarized light can be changed into polarized light after it is through the coupling micro fiber component. Theoretical analysis and design give the geometric parameters for the polarizing effect. Experiments are made to investigate the relationship between degree of polarization (DOP) of the output light and coupling length when two micro fibers are lined parallel to couple. Micro fiber polarization filers based on evanescent field are manufactured. Experiments show that the (DOP) of the output light within the wavelength band of 1545~1560 nm in the micro fiber polarization filers are higher than 90% when the unpolarized light is input, which means the light is polarized. The linear polarization extinction ratio (LPER) of output light at some wavelengths with the band are higher than 24 dB, while output lights at another wavelengths are elliptical or circular polarized light. It means that output lights are polarized according to their wavelengths. The micro component can construct the band-pass wavelength fiber when it is used with an optical polarizer.

Bit error rate (BER) is a key indicator of asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM). The number of subcarriers is an important factor of the indicator. By theoretical deduction and simulation, the impact of subcarriers′ number on the BER of ACO-OFDM transmitted in standard single-mode fiber (SSMF) with optical single-sideband (OSSB) modulation is analyzed. Theoretical analysis shows that, when the total transmission rate is constant, changing the number of subcarriers from 128 to 16384, the total bandwidth required changes no more than 0.775%. And based on this, further theoretical analysis and simulation illustrate that, with different transmission rates of ACO-OFDM system, there always exists the optimal number of subcarriers resulting the lowest BER, and the optimal number increases with higher transmission rate.

High-reflectivity fiber Bragg grating (FBG) is successfully inscribed on the 20/400 μm large-mode-area double-clad fiber (LMA-DCF) by the phase-mask method, and the relevant technical requirements and difficulty of the inscription technology are analyzed. Considering the possibility of existence of the high-order mode in LMA-DCF, the mode characteristics are theoretically simulated by altering the relative displacement between the fiber core of SMF and LMA-DCF. The grating reflection spectra of different relative displacements are experimentally measured and the corresponding light spots are obtained. Besides, the frequently-used measuring methods of spectrum of LMA-DCF Bragg grating are compared and their respective characteristics are analyzed. Research results will provide theoretical and experimental basis for the application of LMA-DCF in high-power laser systems.

Polarization properties of gratings become a research hotspot of fiber Bragg grating based sensors. A new pressure measurement method based on the first normalized Stokes parameter s1 is analyzed. The relationship between s1 parameter and linear birefringence is studied and the causal model of s1 parameter, linear birefringence and pressure is given. The effects on s1 parameter of incident angles of linearly polarized light are researched. The results show that the base value and linearity of s1 parameter are affected by the incident angles of linearly polarized light. A real-time pressure measurement system with fiber Bragg gratings and in-line polarimeter is set up. The curves of s1 parameter with different pressure values are measured and the feasibility of the theory is proved.

For suppressing pedestal and cross-correlation noises in receiver, optical thresholder plays an important role in multiple-user optical code-division multiple access (OCDMA) system. Nonlinear optical loop mirror (NOLM) is an effective method to implement optical thresholder. The threshold characteristic is experimentally demonstrated and analyzed. The method of analyzing threshold by changing duty cycle of pump light is proposed, and the power at threshold point is 3.75 W for the pump duty cycle of 1/25. The relationship between output signal and wavelength spacing between signal and pump is discussed, and the optimal wavelength spacing is 5.8 nm at the threshold point. Experimental results show that when the duty cycle D=1/25, the pulse can be suppressed by 114.47 ps. The noise suppression result is given through eye diagram analysis of a receiver thresholder system built for the experiments.

A fiber-optic perimeter security system based on Mach-Zehnder (M-Z) interferometer is designed. Modified phase detection of double-fiber M-Z interferometer is proposed in getting signal in combination with correlation algorithm. The usage of correlation algorithm in location is introduced in detail. The simulation verifies the feasibility of this method. If the same signals with different time delays are analyzed using correlation algorithm, the accurate time difference can be obtained by the location of the maximum. The system′s location accuracy is directly related to the sampling rate. When the sampling rate is set as 20 MHz, a theoretical location accuracy of 10.22 m is obtained. A new method of processing piecewise signal is presented, which can reduce the computational complexity on the base of high positioning accuracy brought by the high sampling rate. The computation speed is increased about 8 times.

A novel all-optical ultrawideband (UWB) signal generation scheme is proposed based on injection locking of Fabry-Perot laser diode (FP-LD). By injection locking the FP-LD with one wavelength signal light and two continuous probe light, multi-wavelength conversion is realized with two wavelength inverted signals output and one wavelength non-inverted signal output. After propagating through the fiber with a proper dispersion, time delay between different wavelengths output is introduced and the UWB signal pulse is generated. UWB signal is then obtained after the photo-detection. The operational principle of the proposed scheme is analyzed. Experimental investigation is carried out on the waveform and frequency spectrum characteristics of the UWB pulse. Differential UWB signals generation based on injecting 1.25 Gb/s non-veturn-to-zero (NRZ) signals to the FP-LD is then demonstrated. The experimental results show that the minimum full-width at half-maximum (FWHM) of the pulse is 83.3 ps, and the 10 dB spectral width is about 4.6 GHz with the fractional bandwidth of 107%.

Affecting factors for detection accuracy of four-quadrant detector are studied. The effection of facula size, facula centroid position, calculation formula, the noise of detector and amplifier is analyzed in theory, then the effection of these factors is verified by means of calculation and simulation. In the end, a method is proved to be correct by experiment. The research results show that using the appropriate optical system and signal detection circuit, high-precision error detection based on the four-quadrant centroid algorithm is realized.

A novel dual-core photonic crystal fiber (PCF) for broadband polarization-insensitive coupler with elliptical central hole is proposed. The impacts of its structural parameters on coupling characteristics are investigated in detail using full-vector finite element method. Optimizing fiber structure parameters, dual-core PCF is obtained and meets the application requirements of easy to fabricate, free to splice and low splice loss. Then an improved dual-core PCF is proposed for reducing the difficulty of fabrication. The coupler based on this fiber is obtained with the coupling ratio stabilized at (50±1)% and the coupling ratio difference between x polarization and y polarization less than 0.2% in wavelength range of 1.26~1.625 μm.

A scheme for fast temperature measurement based on distributed Brillouin optical fiber sensor is proposed. The Brillouin scattering signal is detected by the high speed pulse RF detector based on the principle of heterodyne coherent detection, with which the measuring time can be decreased. Moreover, the noise of the Brillouin scattering signal is decreased by combining cumulative average technology with wavelet transform technology. Thus the de-noised signal is demodulated for temperature measurement within large distance. The experimental results make it clear that a temperature measurement error of less than 3 ℃ and a measuring time of less than 3 s can be achieved at a distance of 24.8 km.

Based on vectorial diffraction theory, the intensity distribution of radially polarized beam (RPB) at focal point is calculated. In the focusing process of the RPB, the size of focus spot is mainly decided by the light at the verge of field. According to this characteristic, a continuous phase filter function with the tangent of the field angle as independent variable is designed. A group of optimized phase filter parameters is acquired by non linear rules algorithms, targeting on a smaller focal spot and constrained by several Strehl ratios. The results show that the focused RPB through the proposed a phase filter, a shaper focus could be obtained with the same Strehl ratio.

For the requirement of large area graphic exposure of digital projection photolithography, a graphic matching method is proposed based on grayscale mask modulation, which includes graphic segment, mask design, sub-graphic grayscale modulation and sub-graphic exposure. Before graphic inscription, the exposure graphics are segmented into many sub-graphics of size 1024 pixel×768 pixel, then every sub-graphic is multiplied by corresponding mask for the realization of exposure graphics′ pretreatment. Feasible edge grayscale masks are designed according to the principle of digital micromirror device (DMD) modulation for grayscale graphic. The basic method of graphic segment and principle of masks design are given in this paper. The computer simulation experiment shows the process of graphics matching. The results show that matching problems in large area graphic inscription can be solved properly using this method. Besides, the quality of graphic inscription using this method is effectively improved.

Two important beam combining errors, piston errors and tilt errors are studied. Supposing, both piston errors and tilt errors obey normal distribution with zero-mean but leaving standard deviations to be determined, according to Strehl ratio, the permitted maximal standard deviations of piston errors and tilt errors are calculated based on iterative algorithm, respectively. Relations between the permitted maximal standard deviations of the two beam combining errors and obscuration ratios and numbers of sub-telescopes are revealed. The permitted maximal standard deviations of piston errors have no relationship with obscuration ratios of the sub-telescopes; but they decrease slowly within a narrow range of 0.11λ～0.08λ as the numbers of sub-telescopes increase. In the case of known pupils size, the permitted maximal standard deviations of tilt errors decrease as the obscuration ratios of sub-telescopes increase, while they have no significant correlations with the numbers of sub-telescopes.

Using solid powder directly, an approach to acquire the fluorescence polarization is demonstrated by combining solid surface fluorimetry and fluorescence polarization, and the fluorescence polarization properties of vitamin B2 are researched with this method. The results show that the degree of fluorescence polarization of vitamin B2 solid powder is dependent on the incident angle of the exciting light, and is independent of the relative compactness when it is greater than 0.6667. The degree of polarization hits 0.4178 while the incident angle is 45°. It is 1.42 times of that the detected result from the aqueous solution. The degree of fluorescence polarization of the vitamin B2 solid sample keeps steadily in error band under constant illumination for 6 h.