When branch points are present in laser beam wavefront during the propagation in turbulence, the adaptive-optics system for atmosphere turbulence compensation will be degraded greatly. The number of branch points was computed by four-dimensional code. By choosing different phase screen number, grid size and grid step, the variation of branch point number with turbulence strength in distorted optical fields was emulated. The result indicates that branch points cannot be detected in the region of weak turbulence. In the intermediate region between the weak and the strong turbulences, the branch points begin to appear, and the number of branch points grows rapidly at the outset of this region, almost linearly. When the turbulence strength continues growing, the rapid growth of the branch point number is replaced by a slower but nonlinear increase. In the end, the branch point number reaches a saturation state. In addition, the branch point number and its evolvement are different in different propagation conditions.

With high efficiency and high detection precision, the airborne lidar has become an important means to monitor marine environment. Based on the research background of monitoring red tide by airborne blue lidar, a new method of achieving the growth information of red tide alga is proposed, by detecting the concentration of chlorophyll. By this concept, based on analysis of the optical properties of several important ocean objects and bio-optical algorithm, a model is proposed based on airborne lidar detecting backward scattering signals. Simulation proves that the method can monitor the concentration of chlorophyll effectively. It provides a method for red tide detection based on the airborne lidar.

A miniature extrinsic Fabry-Pérot interferometer (EFPI) sensor based on photonic crystal fiber with very low temperature sensitivity is fused by using a simple welding method, which can effectively reduce the cross sensitivity between strain and temperature. And the transmission loss of the HCPCF is very low that allows the cavity length to be as long as several centimeters with good visibility. That makes the sensors may find its application in quasi-distributed sensing.

A novel 10 Gbit/s all-optical packet clock extraction is proposed, which comprises a Fabry-Pérot (F-P) filter and a semiconductor optical amplifier (SOA). Low finesse Fabry-Pérot filter was used to directly extract the packet clock from the data packet which ensures that the clock locks fast and vanishes quickly. The clock, amplitude modulated as a result of low-Q filter, then goes into SOA to reduce the low-frequency amplitude noise. The effect of the SOA's SGM on the locking and unlocking time of the packet clock is theoretically analyzed. Instantaneous 10.075 GHz clock extraction experimentally with the establishing time of about 8 codes periods, vanishing time of about 22 codes period and time jitter of 2.35 ps is demostrated.

A negative dispersion photonic crystal fiber (PCF) with dual core and composite lattice is proposed. The cladding is composed of two different air holes based on pure silica, and the inner core is formed with high effective index material doped with germanium. In order to realize negative dispersion, a ring of air holes in the cladding is removed. Using the finite difference frequency domain algorithm, the negative dispersion properties is analyzed. Results show that broadband negative dispersion with different levels can be achieved by optimizing air-hole pitch and two air-hole diameters. Broadband negative dispersion with full width at half maximum exceeding 200 nm is realized at 1.55 μm wavelength when the radius of the inner core, the air-hole pitch, the diameter of the larger hole and the diameter of the smaller hole is 0.95 μm, 2.15 μm, 1.9 μm, 1.1 μm respectively. To decrease the fabrication difficulty, air holes of more than 1 μm and hexagonal lattice are adopted. So this fiber can be used for broadband dispersion compensation in wavelength-division multiplexing optical fiber communication systems.

An asymmetric optical interleaver (AOI) based on G-T etalon type is proposed. In principle, by adjusting two waveplate parameters and the etalon reflectance, asymmetric interleavers with any spectral bandwidth ratio can be constructed. Simulation on the output of asymmetric optical interleavers with spectral bandwidth ratio of 1∶3 and 1∶7 are presented. The analysis on how to determine the parameters of the two waveplates, the reflectance of the Gires-Tournois etalon and their matching are given. A device with spectral bandwidth ratio of 1∶3 and 1∶7 is designed and fabricated, the output of 1∶3 device is 0.38 nm and 1.15 nm at 3 dB and the output of 1∶7 device is 0.191 nm and 1.331 nm at 3 dB. Experimental results (spectral bandwidth ratio) are in good agreement with the design.

Wireless networks based on radio over fiber (ROF) technologies have been proposed as a promising solution to meet the future demand on broadband, interactive and multimedia services over wireless media. However, millimeter-wave band signals suffer from the dispersion problem in fiber, and the structure of base station is complex. A full-duplex 60 GHz band ROF system employing a 60 GHz electroabsorption transceiver (EAT) together with a dual-lightwave technique is reported. By realizing single- and dual-wavelength modulation in downlink and uplink respectively, a base station with detection, modulation and frequency up/down-conversion functions which acts as a electroabsorption transceiver/mixer is obtained. Simultaneously, its chromatic dispersion is small and base station structure is simple.

Brillouin optical time-domain reflectometer (BOTDR) can perform distributed strain measurement along an optical fiber. Its highest spatial resolution is limited to 1 m because of the restricted probe pulse width. Because the time to accomplish one single sampling by BOTDR cannot be neglected compared to probe optical pulse width, a novel multi-Lorentz fitting method based on equivalent optical pulse (EOP) is proposed to improve its spatial resolution. In this method, the equivalent optical pulse is obtained by integrating the probe optical pulse over the time to accomplish one single sampling by BOTDR and the backscattered Brillouin signal (BBS) received by BOTDR is decomposed into sub-BBSs according to the shape of equivalent optical pulse. Then the backscattered Brillouin signal is fitted by multi-Lorentz function to obtain central frequency of each sub-BBS. The strain in the length corresponding to each sub-backscattered Brillouin signal can be obtained by use of the dependence of Brillouin frequency shift on strain. It is experimentally demonstrated that the spatial resolution for strain measurement with BOTDR is improved to 0.05m by the proposed method.

To develop computer generated holographic video (CGHV) technology utilizing the digital micromirror device (DMD), the holographic coding methods have been investigated. Basis on digital micromirror device physical microstructure, two dimensional discrete micromirror pixels, blazed diffraction gratings of rotated mirrors and its pulse width modulation working principle are discussed. The following factors have been considered, namely, digital micromirror device's resolution, mirror size, pitch, rotating angle, incident angles of reference wave and diffracting conditions, etc. In order to match the hologram to the spatial light modulating properties of digital micromirror device and fulfill the requirements of computer generated holographic video, the sampling method on interference plane, phase compensation technique and no-bias binary hologram coding method are put forward. The experimental results show that the methods have adjusted the diffractive direction of object wave, the diffraction energy concentrated on object wave, improved the quality of reconstruction, increased the utilization ratio of diffraction energy, and improved the efficiency of holographic code.

Compared with traditional optical microscopy, digital holographic microscopy can be used to measure phase information of samples. Therefore it allows quantitative detection and effective observation of transparent biological samples such as living cells. But the field curvature caused by the microscopic imaging in the hologram recording process will affect phase distribution of the reconstructed image. In order to correct the field curvature, a phase-subtraction method is presented. Recording two holograms before and after inserting the sample, unwrapping the numerical reconstructed images of the two holograms solely and subtracting them each other, the corrected phase distribution of the sample image will be obtained. As examples, some cicada wing and epidermal cells of garlic are measured by using digital holographic microscopy and the field curvature is corrected by numerical-correction method and phase-subtraction method, respectively. It is shown that the phase-subtraction method is more credible and convenient to get three-dimensional phase information and more effective to correct the field curvature than current numerical-correction method in digital holographic microscopy.

A novel multi-view video coding scheme with low complexity is proposed for wireless video sensor array based on motion-vector extrapolation at central node of network. It is noted that communication among cameras is difficult for implementation in dense video sensor array, and the encoder embedded in the camera is unable to accomplish complex encoding process due to the limitation of computational capability and power consumption. Therefore, motion-vector extrapolation is utilized to move the motion estimation out of the encoder to the central node of network, so that the complexity of motion estimation at the encoder is reduced to 0.3% compared with the traditional exhaustive block matching algorithm, and the power consumption at the encoder of the sensor array is also reduced. Experimental results show that the proposed method outperforms H.264 intra-frame coding more than 4 dB and approaches to H.264 inter-frame coding, and it also performs better than Wyner-Ziv coding schemes.

Based on the characteristics of hyperspectral images, three-dimensional set partitioned embedded zero-block coding (3D SPEZBC) algorithm for hyperspectral image compression is proposed. This algorithm adopts three-dimensional wavelet-packet transform to decorrelate hyperspectral image spectrally and spatially, and uses the quadtree partitioning method based on zero-block coding to process each of the two-dimensional subbands, and the context-based adaptive arithmetic coding scheme to further improve the coding performance. Experimental results show that the 3D SPEZBC algorithm has the same rate-distortion performances of three-dimensional embedded zero block coding (3D EZBC) algorithm, obviously outperforms three-dimensional set partitioned embedded block (3D SPECK) algorithm, three-dimensional set partitioning in hierarchical trees(3D SPIHT) algorithm and (AT-3D SPIHT) algorithm, and is slightly better than JPEG2000 multi-component (JPEG2000-MC) algorithm at different bit rate in the compression performances. Moreover, the 3D SPEZBC algorithm not only provides excellent rate-distortion performance, but also can save considerable memory requirement in comparison with the 3D EZBC algorithm.

In order to make the fused multispectral (Ms) images keep the spectrum of the original multispectral images as much as possible and improve the spatial resolution effectively, a novel algorithm for remote sensing image fusion based on the nonsubsampled contourlet transform (NSCT) is proposed. Firstly, the panchromatic (Pan) image is decomposed by the NSCT to obtain the detail information of the Pan image. Secondly, the low frequency subband coefficients of the NSCT are substituted by the band to be fused of the resampled multispectral image and the bandpass directional coefficients of the NSCT are locally adjusted by employing an injection model, in which some physical characteristics of imaging systems are included, and then the NSCT coefficients of the fused multispectral image are attained. Lastly, the fused multispectral image with high spatial resolution is obtained by performing the inverse NSCT on the attained coefficients. Several sets of IKONOS images have been merged by the proposed algorithm. The experimental results demonstrate that the proposed approach outperforms the other traditional methods in the spectral information preservation and in the spatial resolution improvement.

To carry out the precise measurement of large-scale complex workpieces, accurately calibration of the stereo vision coordinate system has becoming more and more important. This paper presents a flexible and valid method for calibrating stereo vision coordinate system, which overcomes the complexity and difficulty of the traditional calibration methods. By moving the optical reference bar over the measurement volume, there are three horizontal infrared LEDs and three vertical infrared LEDs with known length which are as feature points, the two cameras capture the images of the feature points. Then, the relative orientation and position of two cameras can be quickly determined with epipolar constraint of the stereo camera through linear algorithm and Levenberg-Marquardt (LM) iteration method. The scale factor of the translation between the two cameras can be calculated by the distance between the two extremity feature points of the optical reference bar. By automatically controlling the light intensity and optimizing the exposure time, the feature points can get uniform intensity and obtain higher signal-to-noise ratio at different position, so the calibration accuracy is improved. The experimental results prove that the proposed calibration method is flexible, valid, and can obtain high calibration accuracy. The maximum error of the large-scale three-dimensional measurement system is 0.18 mm.

The characteristics and technical requirement of a sunphotometer radiometric calibration system, including field and laboratory instruments, has been set up by the international cooperation for high-precision radiometric calibration on the sunphotometer in Aerosol Robotic Network (AERONET). Comparing the calibration results with foreign advanced calibration systems in the same sunphotometer, the accuracy of the proposed system is very high and it is able to calibrate the sunphotometer in AERONET.

Signal aliasing is one of puzzling questions of a practical fiber-optic hydrophone system based on phase generated carrier (PGC) modulation-demodulation. The physical mechanism of signal aliasing is analyzed theoretically and simulated by computer. The results show that increasing the modulation frequency and lowering the sensitivity of the fiber-optic hydrophone cannot effectively resolve the signal aliasing induced by high-frequency interfering signal. A novel acoustic low-pass filtering scheme is proposed based on the principle of acoustic low-pass filters. A simple fiber-optic hydrophone with an acoustic low-pass filter is designed and fabricated. The acoustic pressure phase sensitivity is measured in a standard standing-wave duct. The experimental results show that the fiber-optic hydrophone has fine characteristics of acoustic low-pass filtering, and can restrain the high-frequency interfering signal strongly. The low-frequency acoustic sensitivity is about -140 dB (0 dB=1 rad/μPa), the attenuation of high frequency is bigger than 20dB. The scheme is very simple and economical, can be used to eliminate the signal aliasing in a practical phase generated carrier modulation-demodulation system effectively.

The CCD noise from imaging process brings error to the results of optical measurement, so that noise suppression is a key to improve measurement accuracy. The characteristic of dark current noise and random noise is analyzed, and noise calibration and suppression techniques to each component are proposed respectively. The influence of CCD noise on optical measurement tasks, such as edge location and phase extraction of structural-light phase-shift method, is investigated. Simulation and experimental results show that the edge location accuracy is greatly improved by means of CCD noise calibration and suppression. Therefore, the validity and necessity of the proposed method is well confirmed.

In order to measure the retardation of phase retarders accurately, a new method is presented, the errors influencing test results are studied by Müller matrix theory. The measurement setup is composed of polarizing prism, normal quarter-wave plate, analyzing prism, lock-in amplifier and microprocessor. The best Fourier coefficients of the signal are obtained by the least squares method. By the band-limited functions of the lock-in amplifier, the signal-to-noise ratio is improved. A high-accuracy step motor is used to control the rotation angle by the feedback loop system. The theoretical analysis of error proves that the absolute error is less than 0.29°. The retardation of a normal quarter-wave quartz plate is measured with repetitive error less than 0.40°.

In order to design and make multimode interference (MMI) couplers, the imaging positions must be located accurately. The implicit finite difference beam propagation method (BPM) in three-dimensional alternate directions is used for the analysis of strongly guided and weakly guided multimode interference couplers. The length of multimode waveguide, the positions of input guides and output guides are determined precisely. The equivalent width Weq and the beat length Lc of two lowest modes of multimode waveguide are obtained first by the numeric modeling of a symmetric interference MMI, and then these parameters together with BPM are used for the device design. The imaging positions showed the close results between BPM and the predictions of the mode propagation analysis (MPA) theory,however, Weq and Lc were obtained by the BPM, MPA theory will not give any result without these parameters. The three dimensional (3D) waveguides are not treated as 2D waveguides by means of effective index method (EI), therefore, this method can be used directly to 3D waveguides. As a kind of numerical method, some normal approximations are not introduced as MPA theory, so it will ensure the precision of calculation and can afford reference for practical MMI device design.

K9 glass film was used as protection coating in order to avoid the surface corrosion of erbium-doped phosphate glass during ion-exchange processing for optical waveguide fabrication. The fluorescent spectrums and fluorescent lifetimes of erbium ions in samples were measured and analyzed. The fluorescent spectrums were not changed after being coated by K9 glass film with different thickness, while the fluorescent lifetimes were reduced by 0.2 ms compared with the raw erbium-doped phosphate glass. The surface morphology was observed by means of microscope and the optical characteristics of planar waveguide were measured with prism-coupling technique. The effect of thickness of K9 glass film on the waveguide fabrication was investigated and the optimal thickness was found to be 60～80 nm. It would provide a good experimental base for further fabrication of active glass optical waveguide devices.

A novel method to stretch light pulses is proposed by using the free-space coupling technique, with which the ultrashort laser pulses can excite ultrahigh-order modes in the symmetrical metal-cladding optical waveguide with sub-millimeter scale. Because of high group-velocity dispersion of the ultra-high order modes' characteristic, the light pulses can be greatly stretched after propagation in the waveguide for a short distance. An analytical expression for Gaussian beam is found and it shows 1 ps light pulses can be stretched 1000 times after propagation in the waveguide for 1.26 mm.

An in-line distributed optical fiber sensor array based on Sagnac interferometer is developed, and it is used to monitor and locate leakage for the fluid-filled (or gas-filled) pipelines in real-time. The advantage of the sensor is that it can mcrease monitoring distance by using two sensing fibers. The representation of phase change for optic signal caused by leakage is formulated; the monitor principle and the leakage source location method for the detection system are analyzed. The experiment is carried out at 3.990 km and 4.024 km from Faraday rotator mirror 1 and Faraday rotator mirror 2, respectively. The results verify that the system can realize leakage detection and locate leakage source accurately, and the error is less than 1.05%.

The characteristic of polarization chaos laser and coherence of semiconductor optical amplifier (SOA)-based fiber ring laser are investigated. By detecting the power and degree of polarization (DOP) output of the laser in laboratory, the process from amplified spontaneous emission (ASE) to stimulated emission of radiation, and to polarization chaos laser output is evolved. The coherence of chaotic light is verified employing Mach-Zehnder interferometer, and only the zero-order coherence is observed. Adjusting the optical-path difference of two arms, power output of the interferometer is measured, and visibility of interference streak is computed accordingly. The coherence time of 40 ps is got, which is basically consistent with the time of 43 ps computed by optical spectrum of chaotic laser. It is measured that the chaotic laser's coherence is independent of current of SOA. The superiority of chaotic laser's coherence in resolution and sensitivity is indicated when it is applied in the field of low coherence optical source detection.

The linear and nonlinear optical properties of three porphyrin compounds with different substituents, meso-tetra (p-hydroxyphenyl) porphyrin ［T(4-HP)P］, meso-tetra (p-esterphenyl) porphyrin ［T(4-EP)P］ and meso-tetra (p-bromophenyl) porphyrin ［T(4-BrP)P］ have been investigated by using absorption spectroscopy, fluorescence spectroscopy and picosecond Z-scan technique. The optical properties of the three compounds were discussed on the basis of π-electron conjugated structures and resonant/non-resonant enhancement. The experimental results showed that the absorption and fluorescent emission bands of T(4-HP)P substituted by stronger donating electron group shift towards lower photon energy, in comparison of T(4-EP)P substituted by weaker donating electron group and T(4-BrP)P substituted by accepting electron group. All the three compounds had positive third-order nonlinear susceptibilities χ(3). With the resonant excitation at 532 nm, the third-order nonlinear susceptibility χ(3) of T(4-HP)P showed a maximum of 6.81×10-10 esu, which is two orders of magnitude larger than that of T(4-BrP)P.

The near-stoichiometric LiNbO3 (SLN) single crystals doped Ni2+ in 0.5％ molar fraction in the raw compositions were grown by the Bridgman method under the conditions of taking K2O as flux and at a big temperature gradient for solid-liquid interface. The absorption spectrum of Ni2+ doped crystal was measured. The 381 nm, 733 nm and 1280 nm, which are ascribed to spin allowed 3A2g(F)→3T1g(P), 3A2g(F)→3T1g(F), 3A2g(F)→3T2g(F) transitions of Ni2+ ions in octahedral co-ordination, and 430 nm and 840 nm, which are attributed to spin forbidden 3A2g(F)→1T2g(D) and 3A2g(F)→1E(D) transitions, were observed. The molar fraction ratio of x(Li+)/x(Nb5+) was estimated from the absorption edge of the crystal to be 0.981. The crystal field strength of Ni2+ doped in SLN crystal, Dq=781 cm-1, the Racah parameter B=1096 cm-1 and C=4353 cm-1 were calculated from the absorption spectrum and crystal splitting theory. The emission spectra of crystal in the visible region were investigated under various light excitation, and the emission bands at 500～630 nm, 800～850 nm were observed and ascribed to the d-d transition 1T2g(D)→3A2g(F), 1T2g(D)→3T2g(F) of Ni2+ in octahedral sites, respectively.

InGaN blue MQW LEDs, grown by metal-organic vapor deposition (MOCVD) on Si (111) substrate, were successfully bonded and transferred onto new substrates Cu and Si. Then, the vertical structure LED chips based on these two kind substrates are made. In the following experiment, the properties of two different GaN LED chips have been tested and researched before the chips were scribed. Current-accelerating aging experiments under 1 A current applied on these chips have been carried out. The results indicate that the chips with Cu substrate are saturated at higher current, having better luminous output efficiency, moreover, its working voltage waved less with driving current, and its power declined less during aging experiments. All these mean that the reliability of chips on Cu substrate is much better. This suggests that the LEDs on Cu substrate have great potential for the application on the high-power LED devices.

The light-path bending phenomenon in filling-factor graded wavelike two-dimensional (2D) photonic crystals (PC) is due to the gradual modifications of the band structure and iso-frequency surface. Because of the band structure difference between TM and TE mode, the light-path bending phenomenon is polarization dependent, which is suitable for the polarization splitter in the normalized frequency a/λ region from 0.29～0.33. In the U-shaped bending waveguide of TM mode, the position of the emergent light is very sensitive to the incident wavelength and incident angle. The simulations with finite-difference time-domain (FDTD) method show that the sensitivities are 0.38 μm/10 nm and 0.29 μm/(°), respectively. The plane-parallel resonant cavity is built up in theory with the U-shaped bending waveguide for TM mode. The beam splitting and convergence effect are also discussed for the structure composed of filling-factor graded wave-like 2D-PC and one-dimensional multilayer thin films. This kind structure has the potential application in the plane-parallel resonant cavity.

Based on noncollinear optical parametric amplification in periodically poled lithium niobate (PPLN) which is realized by quasi-phase matching (QPM) technology, we consider the possibility of semi-noncollinear phase matching method between collinear and noncollinear geometry. With this configuration and geometry of all vectors in periodically poled lithium niobate, phase matching curves can be obtained. A sure grating period can always be found to satisfy the broad bandwidth optical parametric amplification (OPA) at fixed wavelengths of pump and signal from the phase matching curves. By tilting periodically poled lithium niobate-crystal's parallel grating a sure angle and keeping a sure temperature, numerical simulation with proper parameter shows broad bandwidth OPA at signal wavelengths of 800 nm and 1064 nm can be achieved.

A new theoretical model is presented to investigate the amplification of strong ultrashort optical pulses in semiconductor optical amplifiers, while taking free-carrier absorption, stimulated emission, two-photon absorption, spectral hole burning and ultrafast nonlinear refraction into account. Based on this model, the pulsed four-wave mixing model is developed to further simulate the optical sampling based on four-wave mixing theory in semiconductor optical amplifiers. The influences of free-carrier absorption and two-photon absorption on sampling characteristics are emphasized. The simulation results are in agreement with reported experimental results.

The optical assessment of head-mounted projection displays in visual space was further consummated. An eye model which was closer to the actual situation was used to simulate the human eye in order to give a detailed assessment of the projection lens. A further guidance on the design of projection lens from the imaging results of eye model was also carried on. The results showed modulation transfer function both on the zero and full field of view was good; on zero field of view, the minimum angular resolution of human eye was 1′, and on full field of view, the acuity determined by single-pixel of micro-display was achieved, so the system could completely satisfy the usability in head-mounted projective displays. Maximal distortion was less than 5%, and lateral color was unable to affect the angular resolution of human eye.

The effect of optical current transformer (OCT) output voltage for linear birefringence is analyzed, it's incompleteness problem of the examination of output light's information in the difference divided by addition detection system is pointed out, linear birefringence in bulk-glass optical current sensing head cannot be examined separately by the difference divided by addition examination system, it's proved and concluded theoretically by Jones matrix. Bringing forward the elliptical-polarization detection system of OCT, the formula to explain the relationship among the thermal induced linear birefringence, Faraday rotation angle, output elliptically polarized light's ellipticity and obliquity are deduced which are based on the elliptically polarized light parameter formula. The elliptically polarization examination system's completeness for the examination of output light's information is proved, and the thermal induced linear birefringence and electrical current intensity can be tested in the same time. The output of the 3-state detection, horizontal, vertical and 45° 3 polarization state testing are brought forward for ensuring being in real time. Linear birefringence's effect is conquered and electrical current intensity can be tested in real time, the thermal-induced linear birefringence's effect on optical current transformer is solved theoretically.

A novel technique to produce the self-imaging Talbot effect, nearly non-diffracting bottle beams which were interfered by the two Bessel beams generated from the axicons was proposed. The dynamic interaction in two interfering Bessel beams with the same angular frequency and the size control of the bottle beams were analyzed in detail. The light intensity distribution of the superimposed optical field along the propagation distance and the intensity evolution of the bottle beams in a complete period were simulated numerically. The expressions for the bottle beam number generated by the interfering Bessel beams and the non-diffracting distance of the bottle beams were given.

The theoretical formulas of Gaussian beam describe its propagation characteristics on the whole, but they don not give any description of the propagation of photons within the beam. Based on Gaussian beam's characteristic of hyperboloid with one sheet, a new photon propagation model for Gaussian beam was built. The model takes the Gaussian beam as a hyperboloid consisting of myriads of co-axis hyperboloids of one sheet, and the propagation direction of a photon is chosen equiprobably between the two generatrices of the hyperboloid that goes through the photon's initial emission point. With this model and by use of tracing the propagations of lots of photons through an optical system, the parameters of Gaussian beam were obtained, i.e. geometric configuration, light intensity distribution, photons' optical path length distribution and their propagation directions. The computation result for a practical aspheric optical system has fully proved that the method can be used to simulate the propagation characteristics of Gaussian beam allsidedly and accurately with high numerical computation efficiency.

Starting from the propagation theory of partially coherent light, the spectrum of twisted Gaussian Schell-model beams in the far field are studied. It is shown that, spectral shifts and spectral switches of twisted Gaussian Schell-model beams may also take place in the far field. Comparing with the aberration-free Gaussian Schell-model beams case, spectral shifts and spectral switches depend on spatial coherence, truncation parameter and bandwidth of the source, but the twist factor also affects them. Numerical calculation results are given to illustrate how the twist factor affects the spectral shifts and switches.

Modern applicaiton of sub-micrometer-period gratings often requires the grating profile to be rectangular with steep sidewalls. By comparing cross sections of gratings made by reactive ion-beam etching in two etchers equipped with different types of ion-beam sources, we find that the divergence of ion-beam strongly influences the sidewall steepness of sub-micrometer-period gratings fabricated by using reactive ion-beam etching. All conditions being equal, a smaller divergence angle renderes higher sidewall steepness. The divergence angle of the two-grid Kaufman ion-beam source that is widely used in China at present is typically larger than 13°, limiting the attainable sidewall angle of gratings in etched fused silica to be only 77°, unless a special measure is taken. Using such an ion-beam source, we experimented with three etching methods (rotation-tilt method, alternate-tilt method and metallic-mask recoating method), and increased the sidewall angle of sub-micrometer-period fused silica gratings to 86°, 86° and 82°, respectively. Two mechanisms by which the ion-beam divergence affects the sidewall steepness are considered: the shrinkage rate of the mask's sidewalls and the difference between the ion fluxes at the bottom and the top of the grooves. The roles of these two mechanisms in the three etching methods are also explained.

Using density matrix equation, the absorption of the probing field in N-type four-level atomic system with three coupling laser-fields under introducing laser field linewidth is calculated. The results indicate that the coupling-field linewidth abates the atomic coherence in four-level system, which enhances absorption to absorption inhibition and inhibits absorption to absorption enhancement.The coupling-field linewidth leads to decoherence. The results also indicate that the controlling-field linewidth abates the atomic coherence in four-level system, reduces absorption and enhances light transparency in electromagnetically induced transparency. The increase of controlling-field linewidth enhances absorption of the both sides absorption of the spectral line centre in electromagnetically induced absorption, while abates the absorption enhancement of the spectral line centre. So the electromagnetically induced absorption in four-level system switchs to the electromagnetically induced transparency.

The color prediction of the halftone print with a spectral reflectance model is a subject that draws closes attention in the field of quality control and equipment check. On the approximation that the ink is non-scattering and its refractive index is nearly equal to papers, we propose a spectral reflectance color prediction model for recto-verso halftone images by making use of the theory of the light propagation in paper with long- and short-distance model and net structure of multiple reflection in the recto-verso halftone images. Then the new model is demonstrated to be correct through the theoretical analyse is. The new model provides the prediction of the color of recto-verso halftone images and a theoretical method for the development of the non-line checking instrument.