Great attention has been received in recent years for the applications of visible-blind and solar-blind photodetectors, such as flame sensing, secure space-to-space communications, and missile plume detection. Due to the direct wide band gap, GaN is an excellent choice for optoelectronic devices in the visible and the ultraviolet (UV) portion of the spectrum. The p-i-n structure is an attractive candidate for an UV photodetector because of its high responsivity, low dark current and the facility in integration. The p-i-n structured GaN photodetectors have been fabricated on sapphire substrates by metalorganic chemical vapor deposition (MOCVD) in this paper. Furthermore, the carrier density of p-type GaN layer can be enhanced by thermal treatment in N2 ambience, which results in reducing dark current. The dark current of the device is only about 65 pA at 1 V bias. The maximum responsivity of the device is 0.92 A/W at 361 nm under 1 V bias.

Linear regression theory is introduced to analyze the process of photoacoustic image and the algorithm of multi-wavelength component concentration distribution is constructed. Computer simulation and biological tissue sample experiment are carried out to prove that the algorithm can make photoacoustic image reflect more biological tissue information. During the experiment, all parameters are kept as constant except the wavelength of exciting pulsed laser. The result shows that the information reflected by photoacoustic image of single wavelength matches well with the absorption of mixture component at excited wavelength. Photoacoustic image of single length cannot fully indicate the distributions of each component when the component absorptions are quite different. Based on this, the distribution information of image components changes and matches well with real sample after being treated by the algorithm.

The influence of an applied water film on bone hard tissue ablation by pulsed CO2 laser is evaluated. Fresh bovine shank bone in vitro used in the experiment is put on a PC-controlled motorized linear drive stage and is moved repeatedly with the speed of 12 mm/s through focused beam of laser. In each sample, two cuts are produced, one with water film and the other with not. The wavelength of pulsed CO2 laser is 10.64 μm, the pulse repetition rate is 60 Hz, the energy density is 18～84 J/cm2, the beam diameter is about 400 μm and the water film tickness is 0.4 mm. The scanning number is five. The surface morphology and microstructure of ablation grooves are examined by steroscopic microscope and scanning electron microscope (SEM) respectively. The crater depth is measured with optical coherence tomography (OCT). It shows that water film can not only reduce carbonization and thermal damage, clean the ablation groove, but also augment ablation rate at the radiant exposure of 50 and 70 J/cm2.

To investigate the feasibility of in vivo effect assessment monitoring by functional near infrared spectroscopy (FNIRS) during laser induced interstitial thermotherapy (LITT) in real time, the reduced scattering coefficient during LITT therapy by different laser powers and heating time on Fresh pork liver in vitro and the subcutaneous implanted rat liver cancers by FNIRS system are recorded in vivo. The reduced scattering coefficient (s）which gets through the FNIRS increases during LITT, it increases quickly at beginning, and gradually reaches the stable state. s rises faster when the laser power is greater. There is the same changing trends of s of different tissues, but there is difference between the curve shapes. The system of FNIRS can be used to assess the therapy effect during laser induced interstitial thermotherapy in vivo, and s can be used as a new effect assessment factor. By monitoring the changes of s can effectively guide clinical therapy.

An advanced model of underwater laser range-gated imaging system is proposed in order to improve the shortcoming of present modeling methods in shoot-receive scheduling and instruments characteristic. One-dimensional (1D) rectangular signal is selected as the target, whose output signal to noise ratio (SNR) is used to evaluate the system performance. The time-domain broadening of pulse underwater and noise characteristic of intensified charge coupled device (ICCD) is integrated into the proposed model to improve the shortcoming of present models. The validity of the proposed model is validated through comparison of the simulation and the accquired images by the underwater laser range-gated imaging system. Finally the range-gated technology detects the target with middle and small size effectively with the system in different water qualities and maximum detecting distances, which shows that discovering, identifying and recognizing distances of the ranged-gated technology are at 9, 7.5 and 7 attenuation lengths respectively.

Laser imaging tracking system is a potential way of tracking dark target in distance especially in space, but target image under the illumination of laser is modulated by the laser speckle and it will affect the identification and orient precision of target. Analysis of the statistical characteristic of laser imaging is given, then a combined numerical filter that utilize gray level linear transformation, median filtering and Lee filtering acting on the original image in turn is provided to reduce the image noise. The results indicate that the noise coefficient reduces from 0.67 to 0.22, and edge-preserving degree is up to 0.96, respectively, and it makes a necessary basis for the followed image processing.

As one of the most important techniques in optical tweezers, two-dimensional array optical tweezers have the widespread applications in nanofabrication and biochip manufacturing. Diffractive optical element is the key device to design array optical tweezers. Combined theoretical simulations using pseudo-random phases encoding through Gerchberg-Saxton (G-S) algorithm with experimental measurements, we find that obvious background noise appears when the regular output distribution is array points. A double amplitude filter is adopted to effectively suppress the background noise and impove the quality of diffraction images. These findings are helpful for designing array optical tweezers in the near future.

For the rapid manufacturing of thin-wall parts, the process experiments of selective laser melting (SLM) have been carried out on Dimetal-280 system. The influence factors such as laser power, scanning speed, powder preparing setting, defocus length and powder layer thickness are experimented and analyzed, then a group of optimal process parameters have been gotten. In the experiment, a variable cross-section thin-wall part with density of 96.95% has been produced. The result shows that the metallurgical bonding layer by layer is excellent in the thin-wall part when investigated in scanning electron microscope; It is shown that the minimum absolute error in the wall thickness of manufacturing parts using the SLM equipment is about 20 μm. The top and bottom thickness of the SLM part wall are 101.3 and 142.0 μm, respectively, and the differences between designed and SLM part are 21.3 and 22.0 μm, respectively, which are identical with the minimum absolute error. Tensile strength test shows that the tensile strength is 465~625 MPa, yield strength is 390~515 MPa, and elongation is 23%~48%.

With excellent beam quality, high wall-plug efficiency, low maintenance costs, long lifetime of pump diodes, flexible beam delivery and compact size, the new fiber lasers are very attractive for welding and cutting various kinds of materials in industrial applications since the short wavelength laser beams can be absorbed by almost all metals and alloys. Fiber laser- metal inert gas (MIG) hybrid welding is carried out onto TC4 alloy. The effects of laser-leading (LL) and arc-leading (AL) welding direction on top bead appearance, cross section, penetration depth, width and reinforcement of welds are investigated. The results show that the fiber laser-MIG hybrid welding in LL welding direction leads to better top bead appearance, wider weld width and shallower penetration depth, than those in AL welding direction. The weld direction has little influence on the reinforcement of the welds.

Microstructure and mechanical performances of samples prepared by direct laser metal sintering (DLMS) technique with FGH95 superalloy were discussed. The experiment parameters that effected on the microstructure, the density and the micro-hardness of sample were analyzed systematically. Two kinds of crystal morphology appeared in the microstructure, one was equiaxial structure and the other was the dendrite structure. Size and number of these two kinds of crystal morphology varied with different parameters. The equiaxial structure has been trended to the dendrite structure and the density and micro-hardness of sample have been increased with the larger laser power, the slower scanning speed or the smaller scanning spacing in a certain range. In this certain range of parameters, a set of parameters, such as laser power of 900 W, scanning speed of 0.8 m/min, scanning spacing of 0.6 mm and thickness of 0.9 mm, have been achieved to fabricate an ideal sample that is provided with smooth sintering surface, fine crystal, higher micro-hardness and less micro-defect. The micro-hardness of the sample can reach 477 HV.

In order to reduce thermal stress and crack of clad layer in laser cladding process, a method through changing power density distribution of laser beam was presented. A thermal-mechanical coupling finite element model of laser cladding by using uniform shape and convex shape laser spot was established. The results show that laser cladding with uniform shape spot has a typical character of quick heating and cooling rate as the conventional laser manufacturing. However, laser cladding with convex shape beam could preheat and slow cooling rate of sample to some extent, and reduce the temperature gradient between the clad area and non-clad zone. In addition, the thermal stress of clad layer with convex shape laser beam is lower than the uniform shape laser spot dose, so it can effectively reduce crack of the clad layer.

The temperature fields of powder laser sintering have a direct influence on optimization of process parameters and sintering quality. From three-dimensional heat transfer of point source, three-dimensional analytical model of non-steady-state temperature field for scanning laser sintering was established. With the moving Gauss area heat source, effective thermal conductivity of nylon powder with temperature changed was calculated. The expression of thermal diffusivity and laser energy was obtained. Finally, by simulation and theory of temperature field, validity of the model and parameter fitting was verified.

248 nm discharge-pumped KrF excimer laser is importantly used in microelectronics and medicine. For most applications, maximal output efficiency and energy are very important parameters of a laser. A KrF excimer laser with high efficiency is developed. For obtaining the maximal output efficiency and energy and achieving the stationary discharge of the KrF excimer laser, a new switching power supply, compact electrodes the optimization of storage/discharge capacity, and gas mixture are used to develop a small-type high-efficency discharge-pumped KrF excimer laser. The effect of switching power supply on the charge/discharge characteristic and the effect of gas mixture on the output efficiency and energy of the laser are studied. Compared with the previous product, the property of the laser is improved considerably. The repetition rate of the laser is 1~80 Hz, the maximal efficiency is about 2.5% and the maximal output energy is up to 380 mJ. The pulse to pulse stability is about 1.8% with discharge voltage above 25 kV.

Research on the beam quality of high-power bottom-emitting laser-diode from the M2 factor, the far field divergence angle, near field and far-field intensity distribution is done. Analysis of different device parameters on the beam quality is also made. Vertical cavity surface emitting laser (VCSEL) array with a novel arrangement is designed. By the modulation of the aperture size and the centre spacing of the units, high power density up to 1 kW/cm2 and good beam property of Gaussian far-field distribution at 4 A injecting current are obtained. Compared with the single device and the 4×4 two-dimensional array with the same total lasing area, the novel array is better in the property of lasing spectra and far-field distribution, etc.

Different from the light distribution along the propagation direction in optical thin-film induced by nanosecond pulse or continuous wave, the one irradiated by femtosecond laser pulse is an unsteady process, and can not be solved directly by characteristic matrix of coatings. The model is setup by means of multiple-beam interferometry in time domain, and simulated with the parameters of ZnS material after that. The result reveals that, to single layer reflecting film, the reflectance is proportional to the pulse width, and equals ultimately to what illuminated by continuous wave. Furthermore, under the same pulse width, the reflectance decreases with the increase of the film thickness. The distinction of light intensity distribution induced by ultrashort laser pulse and continuous wave is obviously, as well as the increase of the film thickness. In detail, the curve of intensity distribution in the film irradiated by continuous wave flunctuates with the fixed amplitude. However, it grows up gradually under the ultrashort laser pulse.

In order to obtain pulse width of hundred femtoseconds in optical parametric chirped pulse amplification system, the spectrum of the seed pulse is shaped to compensate gain narrowing, gain saturation and self phase modulation. A new arbitrary spectral shaping method for chirped seed pulse can be achieved with pump pulse time shaping in optical parametric amplification. Compared with the spectral shaping method for chirped seed pulse before optical parametric amplification, the new method will not bring the spectral phase modulation, and the procedure of spectral shaping and energy amplifying will go on in the same time. The results from numerical simulation indicate that the two methods require the same stability for input pump and seed pulse. To insure the amplified signal energy stability is better than ±5% after parametric coupling, the peak intensity change of pump pulse must be controlled less than ±1%, and the peak intensity stability of seed pulse can be controlled in the range of ±3%.

The all-fiber and all-solidified technique was installed to the front end of the next generation high power laser system. Appropriate control to the polarization was required to maintain the stabilization of the fiber system. In order to maintain low repetition narrow band pulses′ polarization stabilization, a novel active control technique applied to single mode fiber laser system which worked with low repetition narrow band pulses was proposed. A root-mean-square of 1% and a peak to valley ratio of 7% stability were achieved, when the pulse polarization stabilizer based on this novel technique was used to 1.5 ns pulses at repetition above 100 Hz. The new polarization stabilizer was applied to fiber front end of the second generation high power laser system. The performance index was better than national ignition facility (NIF), and this technique could be used to control the polarization of the narrow-band and low-repetition system actively.

Power coupling efficiency of beam uplink propagation is a critical factor of the relay mirror system. By optimizing the optical phase at the launching telescope, the intensity distribution at the receiving telescope can be shaped and power coupling efficiency of the two-telescope system can be improved. Model of the two-telescope system is established, results of the 0.1～0.5 m two-telescope system with 10 km and 30 km propagation distance are calculated. The results show that the power coupling efficiency can be significantly improved.

In high average power laser system, electro-optic switches encounter both limitation of aperture and thermo-effects. Plasma-electrodes technology is adopted to scale the switch to large aperture, and thin KD*P is used as electro-optic crystal to reduce absorption of the laser. Based on analyzing themo-effects, a mean of end-face conduction-cooling the KD*P is arised, and optimum design is done. Numerical simulation results show that, by adopting one piece of sapphire to cool two pieces of KD*P, the required switch-voltage could be reducd to 27 kV. For 35 W/cm2 average power density laser, the maximum depolarization in the end-face conduction-cooled switch, which has a 40 mm×40 mm aperture, is 0.22%, and the peak to valley(PV) value is 0.60 λ. These perturbations are acceptable to meet the design requirements.

To improve heat-sink performance of the high-power solid-state laser, the refrigeration-spray cooling system was designed by combining the refrigeration cycle and the spray cooling system, and R600a was used as the coolant. The effects of heat flux, evaporation pressure, and nozzle inlet pressure on the heat transfer performance were analyzed by experiment. The heat-sink surface temperature could be kept below 60 ℃ at 123 W/cm2 heat flux. The heat transfer coefficient was obtained up to 25000 W/(m2·K) when the nozzle inlet pressure and the evaporation pressure were 350 and 185 kPa, respectively. And standard deviation of the surface temperature was only 2.5 ℃ when the heat flux was 130 W/cm2. The above results show that the system can get a lower surface temperature, more uniform surface temperature distribution and higher heat transfer coefficient, which can meet the heat removal demand for high-power solid-state lasers.

A simulation of performance of thermal management with variable doping gain medium in active mirror configuration of laser diode pump solid-state laser is reported. The parameters of temperature, temperature gradient, stress, strain and optical distortion for a conventional amplifying medium and several variable doping media for different doping distributions, in active mirror configuration amplifier with pumping in the front surface and cooling in the back are simulated and compared. The calculation indicates a positive result that the variable doping media can ameliorate the problem of heating and cooling in different surfaces in active mirror configuration, and can elevate the thermal, optical and mechanical performances for laser diode pump solid-state laser (DPSSL) system. The simulation results prove the feasibility for ameliorating thermal management performances in DPSSL by variable doping media.

Based on the theory of Gaussian-Schell model source and Collins diffraction integral formula, the sufficient condition for invariant polarization of stochastic electromagnetic beams through astigmatic optical systems is derived. Both analytical and simulated results indicate that, when the astigmatic coefficient of optical systems is large enough and it satisfies certain restrictive condition with source parameters, degree of polarization of beams will keep invariant in propagation. As a result, the propagating degree of polarization is as the same as its initial value in the source plane. This sufficient condition is sole, and it is independent of optical systems′ elements and propagation distance, etc. The results may provide potential merits and applications in polarization imaging and detecting in optical systems.

In order to obtain yttrium aluminum garnet (YAG) transparent ceramics, YAG nano-powders were synthesized by co-precipitation method, and then sintered by wide-band laser after dry press forming. The YAG powders and the ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results indicate that pure phase of YAG nano-powders are obtained by calcining the precursor at 1100 ℃ for 2 h, and the YAG powders are nearly spherical and the average size of the particle is about 50 nm. YAG transparent ceramics with relative density of 99% were obtained by wide-band laser sintering, and the maximal transmittance was 32% in the visible light range.

Superhydrophobic poly (vinylidene fluoride) is rapidly prepared by KrF excimer laser irradiation at room temperature in ten seconds. The results show that the water contact angle on modified surfaces can be increased from 53° to approximately 170°. The morphologies and chemical construction of the modified layer before and after excimer laser irradiation are analyzed with atomic force micrograph(AFM) and X-ray photoelectron spectrometry(XPS). It is observed that a well 3D net-like microstructure is formed gradually on modified area, and the groups of C-CF2 and C-F become the subject of modified layer instead of CH2 and CF2. It is concluded that the effect of surface roughness increased and surface energy reduced together contribute to the observed superhydrophobic property of modified poly (vinylidene fluoride).

Nd-doped phosphate glass photonic crystal fiber (PCF) with a 25 μm diameter core was prepared by the stack-and-draw method. Amplified spontaneous emission (ASE) spectra of the PCF were investigated by end pumping. The result showed that PCF has stronger peak at 1060 nm and dramatically weakened peaks at 900 nm and 1330 nm, while linewidth of the peak at 1060 nm gets narrower slightly than linewidth of glass rod. The single mode operation was obtained at 1060 nm with a measured loss of 9.1 dB/m. The potential advantages of application in the area of fiber laser were discussed.

The main source of fusion splicing loss between photonics crystal fibers (PCFs) and conventional fibers is from the mismatching of mode field diameters (MFDs) of fibers. We proposed a method to realize low loss splicing between small core diameter PCFs and conventional fibers. Using a fusion taper rig, we controlled hole collapse accurately to enlarge the MFDs of PCFs. As a result, the splicing loss of conventional fiber and PCF with quite mismatch MFDs can be decreased. Using this method a 0.2 dB splicing loss between a PCF with 3.94 μm MFD and a conventional fiber with 10.4 μm MFD was obtained experimentally.

A simple method to deposit silver thin films and microstructures onto glass substrates by visible laser irradiation has been investigated. Under laser irradiation on a glass sample cell filled with a mixed solution of sodium citrate and silver nitrate, a bright silver thin film can be produced on the surface of the glass in contact with the solution at the irradiated region. The growth rate of silver films is influenced by laser power density, laser wavelength, irradiation time, reactant concentration, etc. X-ray diffraction, atomic force microscopy and Raman spectrometer are used to investigate the characteristics, surface morphology and Raman activity of silver films. The prepared silver films exhibit excellent surface-enhanced Raman scattering activity. Furthermore, the silver relief gratings with period from several micrometers to several hundred nanometers are achieved on the surface of the glass by two-beam interference method.

Indium tin oxide (ITO) thin films are deposited on glass substrates at 190 ℃ by direct current (DC) magnetron method. The photoluminescence properties of ITO thin films are investigated by using fluorescence spectrophotometer. With the photon excitation wavelength of 250 nm at room temperature, ITO films show a strong broad blue emission and a weak red emission centered at around 467 and 751 nm, respectively. The blue and red emissions of ITO films are related with the energy level formed by oxygen vacancies and indium vacancies in forbidden band. Oxygen vacancies results in a donor energy level at 1.2 eV below the bottom of the conduction band. Meanwhile, an acceptor energy level resulted by indium vacancies at 1.65 eV above the top of the valence band is observed.

Laser-induced damage test of the sample is performed in a femtosecond laser system with duration 80 fs, centre wavelength of 2 μm. A wavelength separation multilayer of Ta2O5/SiO2（HT at 1.064 μm & HR at 2.128 μm）serves as the target, which is prepared by ion beam sputtering (IBS) on infrared glass. Meanwhile, damage morphologies of the sample are observed by Leica optical microscopy and scanning electron microscope (SEM). The laser-induced damage thresholds (LIDT) of the sample is calculated through the relation between damage area and laser fluence. It is found that damage morphology of the sample is layered, clear edges are easily seen around the damage spot, and the damage crater has no obvious sign of heat diffusion and conductance which means the femtosecond LIDT is closely related to intrinsic characteristics of materials. A theoretical model based on conduction band electrons is applied to discuss the phenomenon. Combining with electric field distribution and band-gap of materials we consider that the damage of the sample under 2 μm femtosecond laser pulse irradiation will first occur in the narrow band-gap material at the interface between high-index and low-index layers.

A composite optical waveguide (COWG) based on polarimetric interferometer was developed. The COWG is a single-mode glass waveguide which overlaid with a tapered high-index layer such as TiO2 and Ta2O5. It can cause the spatial separation in the film-covered region of the zero-order transverse electric (TE0) and magnetic (TM0) modes that transmit along the same path in the glass waveguide, making the evanescent field with the TE0 mode much stronger than that with the TM0 mode. By using the COWG polarimetric interferometer combined with a novel prism-chamber assembly and a polarization-controllable photodetector, the model OWG-01 biochemical analyzer was developed, which is highly sensitive, reliable and convenient. Test results indicate that the response of the analyzer to refractive index of liquid reveal has a very weak thermo-optical effect on the COWG chip, and the main measurement error comes from the temperature variation of refractive index of the liquid sample.

Pattern measurement accuracy is mainly depended on polarization analyzers array perpendicular error. Based on a developed four-channel time division multiplexing skylight polarization measuring system, a polarization perpendicular error model is proposed. Effects of error on the measurement accuracy are analyzed theoretically and investigated experimentally. The results show that when the polarization perpendicular error is reduced, the measurement accuracy of skylight polarization patterns and system positioning accuracy are improved greatly. When the error exists and cannot be eliminated, the adjustment of initial angles of polarization analyzers can improve dramatically the measurement accuracy of the system.

Relative time delay of the optical device under test (DUT) is measured by optical low coherence interferometry by measuring the phase change of a broadband light after passing through it. The interference patterns of broadband light are recorded and analyzed using Fourier transform (FT) to calculate the phase change of the broadband light in frequency domain. The polynomial fitting algorithm is used to smooth the calculated phase curve. The derivation of phase delay curve versus frequency is the measured time delay. Measurement error of time delay comes from the intensity noise and pure phase noise of interference patterns. Theoretical analysis and simulation calculations show that the time delay error is directly proportional to phase error, and the phase error due to intensity noise is directly proportional to the noise too and it can be eliminated by polynomial fitting algorithm. Experimental results show that the instability of the phase characteristic of the DUT is mainly due to temperature variation, which is also the main source of measurement error. The relative time delay of a section of photonic crystal fiber (PCF) about 19 m from 1540 to 1560 nm is measured and the best precision reaches sub-picoseconds.

A new measuring method of transverse mode configuration in a laser beam is presented. It is based on the spatial relative intensity distribution of laser field. The simulation indicates that the measuring method is feasible. An experiment is also conducted to measure transverse mode configuration for a Q-switched laser diode pumped solid state laser (DPL). Without cavity parameters, the transverse mode proportion is figured out with these testing data by using this new measuring method. Based on this measured transverse mode proportion, the laser beam is also reconstructed theoretically, and it agrees well with the spatial transmission of the laser beam for measuring.

Inversion of the size distribution of fire smoke particles is an ill-conditioning problem, and it tends to lose global optimal solutions on account of being trapped into local minimum. Under spherical model, the inversion of monodisperse systems and lognormal distribution systems have been performed by simulated annealing algorithm which has a powerful ability in global searching. Before that, the interference of random noise on the angular distribution of Mueller matrixs in the light scattering of fire smoke particles has been analyzed in detail. Errors of inversional results are less than 0.3% when signal mixed with 3% stochastic noise. Then, the optical equivalent radius of smoke particle clusters with different fractal dimensions could be calculated when the program is used to fit the scattering light of the clusters. Furthermore, it has an approximatively linear relationship with radius of gyration of the clusters.

Ladar and CCD camera have the excellent ability of capturing 3D information of objects, and they are widely used in 3D modeling. The major problem of the fusion of ladar data and CCD camera data is the coordinates calibration between them. In consideration of the traits of ladar and CCD camera, a special 3D calibration object is designed, and an improved coordinates calibration method is proposed, which fits a plane by using principal components analysis and can highly improve the calibration precision. The improved coordinates calibration method is applied on the 3D reconstruction and texture mapping. Experiment results show that our algorithm gives good result in texture mapping.

In order to accurately identify the size and material of contaminants about the wafers and optical elements, the scattering model about two kinds of slightly non-spherical particles on wafer is established by the Bobbert and Vileger (BV) theorem. The scattering process is analyed and the scattering coefficients are derived through expansion vector spherical harmonic function. The figure about the differential scattering cross setion (DSCS) of a non-spherical particle is calculated, which is compared with that from extended Mie. The results are coincidence, which proves the validity of the method. The effect of different material non-spherical particle deformations is reviewed by the calculation. The result shows that the effect of the dielectric is smaller than that of the metal. Therefore, the material of the defect and the shape can be extracted by calculating the DSCS.

The temporal and spectral characteristics of output pulse for an optical pulse cleaner under the input pulses with initial chirps and different shapes were analyzed, by solving the coupling mode equations, which ignored coherent coupling part and neglected chromatic dispersion of the fiber. It was concluded that, the Gauss pulse′s temporal shape was narrowed seriously after the pulse cleaner, and the initial chirps and the energy transmittance were independent of the initial chirps, but the output spectrum were quite different with the initial chirps. When the temporal shape of the input pulse was square, the output pulse′s temporal shape and the spectral shape were both changed slightly but the energy transmittance was highly enhanced.

The nonlinear parameter of photonic crystal fiber (PCF) with triangular lattice structure is studied by using the empirical relations and the effective-index model of PCF. More simple empirical relations are summed up, the problems of requiring large computational resources and time in full-vector analysis are resolved by using the empirical relations, and the effective index of the fundamental guided mode and space-filling mode in the triangular air-hole lattice are calculated with it. With the effective-index model of PCF, the PCF with triangular lattice structure is replaced by an equivalent conventional fiber, an effective core area of a PCF of simple expressions is obtained, in which the fiber numerical aperture is used as an association point of the two models. Based on the simple formula, the nonlinear parameter of photonic crystal fibers with different structural/material parameters are fully discussed, and several conclusions coincide with the actual material nonlinearity(the known conclusions) are expressed.

Chromatic dispersion is a major factor affecting system performance in 160 Gb/s 100 km optical time-division multiplexing (OTDM) communication systems. To reduce the resulting signal waveform distorted, theoretical analysis and research are done, which is verified by the corresponding experiments. Hybrid dispersion compensation is adopted in the transmission link. Chromatic dispersion and chromatic dispersion slope are compensated accurately. The optimized chromatic dispersion map of the transmission link and working power of the various points are optimized. So nonlinear effects are suppressed effectively. The whole system performance is improved by high precision dispersion management. The fiber length is adjusted to the order of 10 m with 500 GHz optical sampling oscilloscope, and the experimental results are observed accurately. Neither the forward error correction technology nor the compensation of polarization mode dispersion(PMD) is used. 100.25 km stable error-free (bit error rate is smaller than 10^{-12}) transmission of 160 Gb/s OTDM signal is achieved through high-precision chromatic dispersion management.

The fiber Bragg grating (FBG) sensor network which is used to monitor the external load position information of a certain aircraft wing box is researched in this paper. The forecast precision influence of the disabled sensor number to the external load position information is researched; Optical switch is introduced to overcome the shortcoming of the traditional FBG sensor network topology low reliability, proposing a higher reliabile network topology, and the reliability of the two types FBG network topologys are researched. The results indicate that the reliability of the new sensor network is superior to the traditional one obviously. The reliability of the two types network topologys is dependent on the failure rate of the single sensor. When the single component failure rate change between 0.001 and 0.01, if the acceptable position forecast error of the external load is less than 5 mm, the failure rate of the new sensor network is reduced to 50% of the traditional one; if the acceptable position forecast error of the external load is less than 10 mm, the failure rate of the new sensor network is reduced to 12.5% of the traditional one at least.

Based on the theory of one-dimensional photonic crystal (1DPC), a flat-top polarization filter composed of cascaded thin-film glass cavities is proposed. A detailed design example is also given. The value of transmittance of P polarized light at transmittance window is higher than 99.6% and the maximum value of transmittance of S polarized light is about 0.1%. The center-frequency of transmittance windows for P polarized light accords with the ITU standard. On this basis, the influence of structural parameters of each reflecting film (including glass cavity) and incident angle on spectral performance such as rectangle degree, duty cycle and frequency spacing are investigated systematically. The proposed filter structure not only is very simple and easy to accomplish but also has high transmittance for P polarized light and good cut-off characteristic for S polarized light. It will have some applications in wavelength division multiplexing systems.

A time-interweaved sampling scheme for analog-to-digital (A/D) conversion based on mode-locked-pulse and high-speed optical switch is proposed. The radio frequency (RF) signal is sampled by high repetition rate ultra-short mode-locked pulse, and then demuxed by high-speed optical switch, which can convert the high frequency sampled signal to multi-channel lower frequency signal. So we can use electronic A/D conversion to quantize and code. The frequency of signal demuxed by optical switch can change easily if the frequency of the optical switch is changed. This scheme is very flexible, and only one mode-locked-laser is required. The scheme is demonstrated using a mode-locked-pulse with repetition frequency of 10 GHz and a 1.25 GHz high-speed switch. Using the experimental data, a better in-time signal is recovered and the spectra is obtained. The signal-to-noise of this scheme is 32.02 dB, equivalent to effective number of bits of 5.03 bit.

Based on optical wave space-time duality theory, time lens and principle of optical pulse transmission in dispersive media are studied. A method have been proposed using pulses′ spectral envelope to transmit optical signals. With the fact that pulses′ spectral envelope will keep unchanged when propagating in dispersive medias, at the transmitter, an all-optical inverse Fourier transformation device based on time lens is used to transform the spectral envelope into time-domain, and a new transmitting symbol is obtained. An corresponding Fourier transformation device will be placed to recover original signals at the receiver. The transmission system presented can eliminate the chromatic dispersion, polarization mode dispersion (PMD), timing jitter and other liner distortions. Detailed implementations of optical Fourier transformation and inverse Fourier transformation are given. Besides, a 10 Gb/s-200 km optical transmission experiment without any dispersion compensations or pre-chirp verifies our transmission scheme, which offers a new method in high-speed optical communications.

Theoretical and experimental research of gas sensing technique is one of the focus in modern fiber sensing area. Wavelength modulation and active intra-cavity methods are two effective ways which increase the sensitivity obviously. Combined with these two methods, an intra-cavity gas sensing system based on wavelength modulation technique (WMT) is established. The relationship between the second-harmonic component of gas absorption spectra and concentration is investigated. And then the optimized parameters of the system are obtained theoretically and experimentally. The second-harmonic components of several gas absorption spectra can be detected. And the average algorithm is used to increase the sensitivity further. The sensitivity of acetylene can be less than 7.5×10-5. With fiber Bragg grating (FBG) as wavelength reference, the wavelength-voltage relationship model of the system can be established. This model can be used to detect the absorption wavelength of different gases. When the system is used to measure acetylene, the maximum absolute error of the detected absorption wavelength is less than 0.445 nm.

By numerically solving the generalized nonlinear Schrdinger equation, mid-infrared supercontinuum generation in two cascaded fibers has been analyzed. The simulation results show that the spectrum has been greatly broadened in the high nonlinear SF57 photonic crystal fiber(PCF) with two zero dispersion wavelenghs by self-phase modulation, stimulated Raman scattering and dispersive waves amplification. Spectrally smooth, highly broadband mid-infrared supercontinuum in a short piece of SF57-PCF is presented here. The spectral range extends from 1800 to 3500 nm with the 3 dB spectral power density. It is found that the long wavelength edge of supercontinuum is further broadened with the increase of the peak pump power.

THz Array imaging has wide application foreground because of the high imaging speed and large detection area. The design of optical path has great effect on image quality. The THz real imaging system is constructed by use of the SIFIR-50 THz laser as imaging illuminant and Pyrocam Ⅲ thermal imager as array detector. The system has been improved using a series of off-axis parabolic reflectors and polyethylene lens. Imaging experiments on the object of water mark, hollowed-out metal board and resolution board have been made and clear images are obtained. By comparing with original imaging results, it is validated that the imaging quality is well improved. By analyzing the imaging results, resolution of the imaging system can be evaluated and reaches up to 0.6 mm.