By using the effective medium theory, thin film theory, rigorous coupled-wave analysis, and elaborated root finding method, the spectral properties of one-dimensional subwavelength gratings are investigated by using different expressions of the effective refractive index. By using the defined error function of the spectra, the validation of other effective refractive indices is evaluated by using the rigorous refractive index in both cases of TE and TM modes. For the given grating parameters, it is shown that the second order effective refractive index and the exact effective refractive index can provide solid results in estimating the spectral properties of one-dimensional subwavelength gratings for TE mode when the normalized grating period Λ/λ is less than 0.30. For TM mode, the effective refractive indices cannot give solid estimations because more evanescent waves are excited in this case. In addition, it cannot provide solid estimations by using the effective refractive indices in calculating the spectrum as a function of the grating thickness except the second order effective refractive index and the exact effective refractive index for TE mode.

Based on the characteristic of free space optical (FSO) channel and pulse position modulation (PPM) signal, by introducing turbo product code (TPC) in PPM modulation, the hardware circuit of the TPC-PPM coded modulation stucture is accomplished. Modulation gain and the code gain are tested experimentally, and it is proved that the design proposal is feasible. The experimental result indicates that under the condition that the information speed is 155.52 Mb/s, scintillation index σ2=0.1, modulation index M=4 and bit error ratio (BER) is 10-6, compared with the on-off keying (OOK) system, the PPM modulation principle prototype possessesa modulation gain of 9.03 dB and the code gain of TPC is more than 4.2 dB. The application of this module can greatly improve the performance of FSO communication system.

Visible light communication (VLC) is introduced into home network. In order to alleviate the problem of wiring in indoor visible light communication, a novel home network system based on VLC and power line carrier communication (PLC) is designed. The general structure of home network is introduced. The hardware and software realization methods of home network gateway, white light-emitting diode (LED) driver and network appliance are described respectively. VLC and PLC can be effectively applied to home network, which greatly promotes the development and research of indoor VLC.

Compressed sensing system can reconstruct the original image from fewer measurements using the sparse priors of image. Current research in compressed sensing has devised algorithms for grayscale images, but there are few methods for color images. Since each of the color channels is highly correlated, the result of simply extending the reconstruction algorithm of grayscale images to three channels of color images is not satisfying. Aiming at improving the reconstruction quality of color images, compressed sensing of color images based on local Gaussian model in the dual-tree complex wavelet is proposed, which uses the dual-tree complex wavelet having the property of translation invariance as the sparse representation of natural images. Priors of the inter-cross correlation of three channels of color images and the local neighbor statistic distribution of the wavelet coefficients are applied in reconstruction. Experimental results show that the proposed algorithm can improve the peak signal-to-noise ratio and the visual quality.

Apple mealiness is a symptom of internal fruit disorder. Mealiness degrades the quality of apples and reduces their commercial value. Hyperspectral scattering, as a promising technique, combines the advantages of spectroscopy technology and image technology, and can make noninvasive measurement of apple mealiness. A supervised isometric feature mapping (S-Isomap) coupled with support vector machine (SVM) is proposed to detect the mealiness in the apple. S-Isomap is a nonlinear lowering dimension method classifying the dimension reduction of hyperspectral data by SVM. For the unknowned category of the test samples, BP neural network model combined with SVM is used to get the corresponding testing precision. The classification results from S-Isomap-SVM are compared with those obtained using the traditional SVM and Isomap-SVM. The results show that the accuracy of the calibration models obtained with the S-Isomap is higher than that of others.

Optical nanosurface whose RMS of roughness is at the nanoscale, is widely used in microelectronics and optical instruments. Optical nanosurface processing defects mainly contain surface damage and subsurface damage. Because of the advantage of non-destructive testing, we analyze the measurement technique of surface scattering theory and white light interferometry. Then the test samples with different processing defects are prepared from different technological conditions, and are measured by three different techniques, such as white light interferometer, atomic force microscopy and surface scattering measuring instrument. Comparison of experimental results show that white light interferometry is an effective measurement means for the measurement of surface roughness and subsurface damage with high precision, high speed and no other damage during the testing.

In order to investigate the characteristic of the flow field at the entrance of the nozzle bank in a chemical laser, a physical and numerical model which is compatible with the flow was established. The model based on experimental equipment contained two types of nozzle bank with three nozzles and four nozzles, respectively. The two-dimensional viscous conservation element and solution element (CE/SE) method was used to calculate the numerical model. The results show that the CE/SE method can simulate the flow process of the high temperature burned gas effectively. The parameters gained from the simulation accord with the experimental data as the flow reaches stable. To a single nozzle, the related parameters(such as pressure and velocity) distribution in the flow field is symmetrical, which can be extended to the nozzle bank with more nozzles.

The powerful laser sintering experiment is performed on the foundry material GH4169 of an aircraft engine blade by using FGH95 which is one of nickel-based metal powder material. By changing the technology parameters such as pump current, defocusing distance, scanning speed and scanning line spacing in the laser sintering process, the effect on the forming quality of fusion zone of the sintered specimens is studied. It has been found that the foundry material GH4169 can achieve a good metallurgical bonding with nickel-based metal powder material FGH95. When the pump current is 300 A, the defocusing distance is 8 mm, the scanning speed is 180 mm/min, the scanning line spacing is 1.0 mm, and the fusion zone in laser cladding has a better forming quality.

As to the low efficiency and low degree of sphericility with frequently impeded in atomizing process of traditional gas-atomizing nozzle, a new nozzle with laval outlet accompanied by ventilation hole and guiding pipe is designed to prepare spherical alloy powders for laser cladding. The gas velocity at the outlet of nozzle is simulated and measured by pitot tube total pressure method, and the air pressure on the nozzle centerline is tested by U-shaped water pressure gauge. After the atomization experiments, the powder achieved is analyzed by scanning electron microscoope (SEM) and Hall flowmeter. The results show that compared with the traditional nozzle, the innovative nozzle can produce supersonic flow at the outlet, the process of atomization is unimpeded, and the efficiency of atomization is improved significantly. With excellent characteristics of good liquidity and granularity distribution, the spherical powder can meet the requirement of laser cladding.

A CO2 laser-gas metal arc (GMA) hybrid welding technology is used to weld the 7.0-mm-thick high strength steel. The effects of the distance between laser and arc on the weld shape, droplet transfer characteristics, probability density distribution of arc voltages and current are investigated. When the distance between the two heat sources is less than the arc plasma radius, the cross-sections are the "cocktail glass" figurate morphology. When the distance between the laser and arc is significantly greater than or approximately the same as the arc plasma radius, the cross-section of weld indicates the "cone-shaped" figurate morphology. When the laser passes through the edge of the arc plasma, the maximum effective joint area is achieved. When the distance of the two heat sources (DLA) is 2~6 mm, probability density distribution of arc current converges toward center and the range of high current and voltage is smaller, which favors the stability of the droplet transfer and hybrid welding processes.

In order to rationally design laser resonator and develop a pulsed all-solid-state slab laser, based on the heat conduction theory, temperature and deformation field in thermal equilibrium state of laser slab side-pumped by pulsed-diode-bar were analytically investigated. Through working on characteristics analysis of laser slab side-pumped by pulsed-diode-bar, a thermal analysis model of laser slab was established. Considering that the pump light intensity of pulsed-diode-bar has super-Gaussian distribution and the laser slab with the characteristics of anisotropic thermal conduction, a general transient temperature field analytical expression of anisotropic thermal conduction laser slab by pulsed-diode-bar side-pumping was obtained by the Poisson equation. The temperature variations of NdYVO4 and NdGdVO4 slab side-pumped by single pulse and repetitive pulse were comparatively analyzed. And the deformations of pump surface of the NdYVO4 and NdGdVO4 slabs in thermal dynamic equilibrium state were quantitatively calculated. The results show that, when the transient temperature field of laser slab reaches thermal dynamic equilibrium state, the maximum and the minimum temperature rise in NdYVO4 slab are 34.8 ℃ and 32.4 ℃, but in NdGdVO4 slab the maximum and the minimum temperature rise are 30.2 ℃ and 27.0 ℃. The maximum and minimum deformations of NdYVO4 slab are 0.98 μm and 0.89 μm, but in NdYVO4 slab the maximum and minimum deformations are 0.29 μm and 0.24 μm.

Excitation spectra collected at Cr3+ red emission show an intense excitation broad band at 460 nm confirming there is energy transfer, which is responsible for one order of magnitude increase in the intensity of the red emission compared to Y3Al5O12 (Ce,CrYAG) single crystal doped with Cr alone. Ce/Cr co-doped Y3Al5O12 exhibits enriched emission spectrum in the red region due to a nonradiative energy transfer from the Ce3+(2E) level to Cr3+(4T) level.

Yttrium Aluminum Garnet (YAG) has become a favorite solid laser basis material for its significant optical, mechanical and thermal properties. It′s the key point to synthesize YAG nano-particles with well-crystallized, uniform grain, good dispersion for perfect transparent ceramic. Loosely dispersed YAG nano-particles and pure cubic crystal phase are synthesized by co-precipitation-freeze drying method，using higher purity A1(NO3)3·9H2O, Y(NO3)3·6H2O and NH4HCO3 as raw materials. The YAG nano-particles are characterized by DSC/TG, X-Ray diffractometer (XRD), scanning electron microscope (SEM) and laser granulometer, etc. After calcined at 1200 ℃, the well-crystallized YAG nano-particles are obtained with higher purity, weak agglomeration, uniform grain size and regular shape.

The effects of structure parameters of substrate on the frequency response characteristics of combination element frequency selective surface (FSS) which assembles Y element and circular aperture element are studied using the spectral domain method. Frequency response characteristics of the combination element FSS show double-band characteristic including band pass and band stop. Arm-length of Y element has a very important effect on FSS frequency response characteristic, compared with other parameters. When the arm-length is increased from 2.0 mm to 3.5 mm, the resonant frequency of band pass is drifted by 4.2 GHz and the resonant frequency of band stop is drifted by 7.0 GHz to low frequency, the transmission bandwidth of band pass is decreases by 6.6 GHz and the bandwidth of band stop increases by 4.4 GHz at -5 dB.

The time modulation is detrimental to high power laser facility and even can prevent fusion ignition, which must be eliminated or substantially suppressed at least. Time domain filtering technology is proposed to eliminate such a time modulation based on optical limiting (OL) effect. OL is a nonlinear optical process by which a material displays high transmission for low input intensity and low constant transmission at high input intensity or fluence. Characters of the main OL mechanisms are introduced. In addition, the realization methods of time domain filtering based on OL devices and the application prospect are discussed.

A tunable photonic crystal filter is proposed with parallel nematic liquid crystal as defect layer. The transmission modes while varying incident angle are discussed in detail by 4×4 matrix method. The results show that transmission modes are mainly decided by the voltage when the incident angle is smaller than 10°. In this region, the transmission modes can be tuned by voltage and different modes can be selected based on polarization sensitive performance. When the incident angle is greater than 10°, the peaks of two modes shift toward the shorter wavelength side and the change of two modes is different. So the transmission modes can be tuned and selected by varying the incident angle in the voltage region of more than 8 V. Both the tunable range and the flexibility of application are enlarged.

In order to realize the optical multi-wavelength selector which is capable of selecting multiple wavelengths with unequal wavelength interval as needed in the free spectral range (FSR) νFSR, the algorithm of finite impulse response (FIR) digital filter is transplanted to the optical filter with the Mach-Zehnder interferometer (MZI) cascaded coupler structure. The target transfer function matrix is represented by discrete Fourier transform (DFT). Using method of undetermined coefficients, the array concrete physical parameters (kth-order coupling coefficient angle θk and kth-order phase shift value of φk) which the transfer function desires are derived from the transfer matrix. This kind of multi-wavelength selector is capable of selecting single or multiple wavelength of light wave randomly as needed in FSR, and the wavelength interval is unequal. Analyzing all the array parameters and simulation figures, the selector realizes nearly 0 dB transmittance on the point of the desired wavelength and the isolation is up to 12 dB. The 3 dB bandwidth of each wavelength and minimum wavelength interval decrease with increasing the cascading order N. When νFSR 1000 GHz and N=15, the 3 dB bandwidth of each wavelength achieves 0.5 nm and the minimum wavelength interval reaches 1 nm.

The principle of the in-line Sagnac interferometer current transducer is introduced. The Sagnac fiber-optic current sensor is deeply researched, and the complete system theory model has been established. The factors which affect the measuring precision are comprehensivelly analyzed and simulated. Some rules which influence the system precision are acquired. The polarization errors of the in-line Sagnac interferometer current transducer are studied by using the Jones matrices formalism. The effects of linear and cirular birefringence in the sensing coil on measuring precison are simulated, and curves and typical error data which represent the effecting rules are theoretically acquired. The simulation result shows that the linear birefringence can be restrained by adding a larger amount of circular birefringence in the sensing fiber.

The discrete dipole approximation (DDA) method is used to study the light scattering properties of a soot cluster which adheres to a large particle with different sizes and material composition. The numerical results of the scattering intensity and the degree of linear polarization for a wide variety of complex soot aggregates in random orientation are illustrated, and the effects of the material composition and the size of the large particle on light scattering properties of complex soot aggregates are analyzed. It is shown that the material composition and the size of the large particle can strongly influence or even dominate the overall light scattering properties of the aggregates.

The surface plasmon resonance (SPR) sensing technology based on gratings is the research focus in the optical fiber sensing field in recent years. The general principle and modulation methods of SPR sensors as well as the theory on grating-coupled SPR sensors are discussed. Moreover, the research achievements are comprehensively introduced, including SPR refractive index hollow core fiber sensors assisted by a fiber Bragg grating (FBG), standard optical fiber SPR sensors employing FBG or long period grating (LPG), SPR sensors based on planar integrated waveguide gratings and corrugated metal gratings, and multi-channel grating-based SPR sensors. The typical structural parameters after optimization are also summarized. Besides, the current research status and expectations of grating-based SPR sensors are given.

As the wide application of wavelength division multiplexting (WDM), polarization division multiplexing (PDM) and high-order modulation techniques, the transmission capacity over single mode fiber is rapidly reaching its Shannon limit. The only known way to overcome this limit is space-division multiplexing (SDM), which causes a significant resurgence of research interest in the multimode fibers. The multiple-input multiple-output (MIMO) technique based on multimode fiber is a new area to answer explosive growth demand for transmission capacity. Implementations of optical MIMO, coherent optical MIMO (COMIMO) systems and highlight mode group division multiplexing (MGDM) are studied and compared. Meanwhile, some problems existing in the multimode fiber MIMO system are discussed to provide a help for further research.

With the development of multimedia services, demands of higher channel capacity, wider service coverage and broadband wireless access advance radio over fiber (ROF) technology rapidly. Meantime, some new technologies, such as coherent technology, multiband technology, multiple input multiple output (MIMO), orthogonal frequency division multiplexing (OFDM) and so on, are introduced and being optimized in ROF system. Employing such new technologies in ROF system, promises to solve the present technological bottlenecks in radio over passive optical network (RPON) and optimize the performance of the whole system. In this paper, the principles of those technologies, how they could be used in ROF system and their advantages as well as shortcomings are discussed and analyzed to provide a reference for future researchs.

Beam combination is an effective way of scaling the energy of pulse fiber laser and has attracted more and more interest in recent years. The typical methods of beam combination of pulse fiber laser are briefly introduced. The new development of beam combination of pulse fiber laser of different pulse widths (such as femtoseconds, picoseconds, nanoseconds) is presented. The characteristics of those techniques are analyzed and a review on development for this technique is made.

One of the key requirements in high-power laser drivers used for inertial confinement fusion (ICF) research that will minimize Rayleigh-Taylor instability and plasma instability is that laser irradiation on a fuel target should be highly uniform. The research of beam smoothing technology of china is described and the beam smoothing projects of high-power laser drivers are analysed.

Optical phased array is a kind of agile, rapid and accurate non-mechanical scanning technology. It has many merits such as high resolution, anti-jamming and keeping secrets. The application background of optical phased array is presented. Recent research developments of optical phased arrays are introduced, including different optical shifter based on LiNbO3, PLZT ceramics and liquid crystal. Their characteristics and applicability are discussed. And the developing prospect of the optical phased array utility are presented.