Solving the frequency of Doppler signal is the foundation for speed measurement of high-speed moving target. When measuring speed of the moving projectile by extremum, the extreme value point carries instantaneous frequency information of the Doppler signal. So it is very important to find the location of extreme value point when estimating the frequency of projectile echo signal accurately. The measurement precision of traditional extremum method is more restricted. A method of quadratic curve fitting is proposed to deal with the noise of echo signal, all the extreme value points are found out according to the principle of quadratic function, and invalid extreme value points produced by the piecewise fitting method are eliminated. Through the analysis of actually measured projectile echo signal, the accuracy for determining the position of extreme value point is improved and foundation for high precision measurement of moving targets is laid.

Based on micro operations on nanoscale materials, a locally enhanced evanescent field theory is proposed, in which the evanescent field is produced from coupling of optical fiber probe and atomic force microscope (AFM) probe. According to the principle of near-field optics, the Fourier transform is used to deduce the evanescent field generation mechanism, and the factors affecting its strength are dicussed. In order to get the force strong enough to capture the nanoscale objects, based on the metal surface plasma resonance principle, composite optical fiber probe and AFM probe solution is used to make the propagated wave and evanescent wave converge at the conical AFM probe tip and form enhanced electromagnetic wave. The operations such as capture of nanoscale objects and movement indicate that the theory can be used in the field of microcosmic science frontier.

Pointing errors can reduce the number of received signals. The influence of pointing errors on intersatellite optical communication systems is decreased by selecting an optimum laser beam divergence angle for optimizing link reliability in the presence of pointing errors. Given that bias errors are part of pointing errors, an analytic expression of link reliability is obtained in the absence of bias errors. By maximizing link reliability, an analytic expression of the optimum beam divergence angle can be obtained. Bias errors are considered in maximizing link reliability. The numerical results and analytic approximation of the optimum ratio of beam divergence angle to pointing errors for a desired bit rate are obtained. With the application of the designed optimum divergence angle for intersatellite optical communication systems, good system performance can be achieved even in the presence of pointing errors.

In order to solve the problems of lower power efficiency and bad packet error rate in reverse differential pulse position modulation scheme for wireless optical communication, a new hybrid modulation scheme called the reverse differential pulse position width modulation (RDPPWM) is proposed, based on reverse differential pulse position modulation (RDPPM) and reverse pulse width modulation (RPWM). The symbol structure, average transmission power and bandwidth requirement of RDPPWM and its packet rate error in additive white Gaussian noise (AWGN) channel are presented and compared with on-off keying (OOK), RDPPM and RPWM. The stimulation results show that RDPPWM has advantages in power efficiency and channel capacity, and it can decrease bandwidth requirement and doesn′t need symbol synchronization. The packet error rate of RDPPWM can drop to 2.6×10-12 while that of RDPPM is 2.2×10-8 when the same signal power is -28 dBm. Therefore, these considerations make RDPPWM a favorable candidate to select as the modulation scheme in wireless optical communication.

There is a demand for simultaneous measurement of static absolute signal and dynamic relative signal with optical fiber sensor in many situations, which requires the sensing system has both large dynamic range and high accuracy. White light extrinsic Fabry- Perot interferometric (EFPI) sensor system based on fast light spectrum acquisition is utilized to meet the requirement of large dynamic range and absolute measurement,which can also response dynamic signal rapidly. Zoom-FFT algorithm is applied in cavity length demodulation of sensors to improve the demodulation accuracy, and the experiment shows that the accuracy reaches 4 nm. Zoom-FFT algorithm can satisfy the demand for demodulation speed of dynamic measurement because of its low computation cost. The experiment is conducted to calibrate the sensor in liquid level between 0~30 cm, which shows that the response of the sensor has a desirable linearity to the static pressure, and the liquid level resolution reaches 0.13 mm. One sensor is able to measure liquid level depth and sound simultaneously with the difference between the frequencies of them at the same time. And the proposed system is proved to possess the potential application in simultaneously absolute measurement of static signal and relative measurement of dynamic signal.

An optical voltage sensor is constructed by applying the non-balance fiber Michelson interferometer (MI)-piezoelectric ceramics（PZT）system to alternating voltage. Applying a tunable F-P optical filter to demodulate the output optical intensity variation of MI, which due to the transfer of the piezoelectric deformation, the measured alternating voltage can be obtained. The experimental results show that the sensor has good linear response to the alternating voltage. At the same time, the influence of positioning accuracy of tunable fiber F-P filter and extinction ratio of MI on system detection accuracy are investigated.

In order to solve the field unification problem of aperture division of multi-angle polarimetric radiometer, and ensure the polarization measurement accuracy. A division of aperture optical path base on reflective telescope is proposed, then select two mirror beam expander program, calculate the initial structure parameters and optimize the system. The polarization effect of the new telescope system with silver mirror and the original telescope system with lens coated with λ/4 MgF2 are simulated and analyzed. The simulation results show that the new telescope system with silver film mirror has 0.258% of the maximum polarization effect at a shortest wavelength of 410 nm, lower than 0.1% at the other bands. It is better than the original system, or quite. The new telescope system can ensure the unity of the field of view of all bands and meet the condition of low polarization effect, and can replace the original transmission telescope system, and a polarization detection method based on the new telescope system is proposed. Finally, the advantages of the new detection method are summarized, and the flaws and countermeasures are pointed out, the application is also analyzed.

A dual-wavelength on-axis phase-shifting digital holographic microscopy system based on color CMOS is proposed. Phase variations during the apoptosis process of human jurkat cells (human peripheral blood T cell leukemia) are quantitatively measured and analyzed without complex phase unwrapping algorithm. Using laser with wavelengths of 632.8 nm and 532 nm, color holograms at three states during the apoptosis process of jurkat cells in vitro are then recorded experimentally. Phase of the cells is reconstructed based on the extracted phase information at each wavelength. The experimental results are consistent with the results obtained by other methods. Moreover, the proposed method described here has wide measurement range and it is simple and accurate. The results indicate that dual-wavelength digital holography is a useful tool for research and application of cell phase.

For the problem that the feature extraction speed of palm vein recognition mothed based on local directional pattern (LDP) is slowly, a palm vein recognition method based on improved LDP is proposed. On the basis of keeping the Kirsch template of original LDP algorithm, the proposed method can code the edge response symbols in eight directions directly, which avoids sorting and reduces the time of feature extraction. It is called fast local directional pattern (FLDP). The proposed approach is tested on the palm vein datebases of Hong Kong Polytechnic University and the self-built palm vein datebases, the palm vein image is divided into some distributed blocks evenly, where the feature vectors of each sub block are obtained by FLDP algorithm and then the total characteristic fusion model is obtained, the chi-square distance is used for matching identification. Experimental results show that the proposed algorithm execution time is 17.75 ms and 19.98 ms respectively, whose performance obviously surpasses other typical algorithms, at the same time, the recognition rate can reach 99.8916% and 99.3665% . The proposed method has practical application value.

Established wavelength calibrating equipment has been used for precise length calibrating service of measurement devices of laser interferometers and laser trackers for many users. In term of beat frequency for laser wavelength calibrating its measurement value can be traced to the source as length wavelength standard. The wavelength calibrating equipment consists of reference laser, detected laser, optical elements of combined beam, photoelectric detector, wide band amplifier, spectrum analyzer, frequency counter and computer data acquisition system. Influence factors of improving the accuracy of detection are analyzed. Time sampling diagrams of results of beat frequency experiment are given. The basis of judging of relationship between wavelength, frequency and characteristic of frequency stability is also analyzed.

Spectral-domain optical coherence tomography (OCT) is used for the inner defect detection of the optical thin film with high accuracy. It is theoretical analyzed and experimentally validated. The two-dimensional (2-D) cross-sectional images of the optical thin film with single layer and multi-layer structure are obtained respectively. Based on the 2-D cross-sectional images, the defect in the film can be observed clearly, and the position of the defect in film can be located. It is demonstrated that spectral-domain OCT is an effective method for defect detection of the optical film.

The non-cooperative object using satellite laser ranging (SLR) is in developing period and the orbit predictions are not precise enough. The effective data are not enough to determine a precise orbit. Therefore, it is proposed that precise orbit determination of non-cooperative objects can be achieved by combining the SLR range data with optical observation data. The results of the experiment using single station SLR data of Ajisai and Jason-1 satellite prove that the precision of combined orbit determination increases one order of magnitude than the optical orbit determination, and then the orbit prediction with high precision for non-cooperative objects can be achieved. The result has significant value for promoting the laser range of non-cooperative objects to reach a well conventional operation state.

In order to make up for the disadvantages of traditional CCD method and monitor particle′s position quickly and high precisely, back-focal-plane (BFP) method is used to detect the particle′s position in an optical trap. The basic principle of BFP method for position detection is explained, then the experimental system is built and the target that detect the particle′s position quickly and high precisely is achieved. The experimental result shows that the detection accuracy reaches 80 nm and the response frequency reaches 800 Hz，so it can be used to detect the micro particle′s position in an optical trap.

Doppler frequency shift measurement is widely used in electronic warfare and radar system. Measurement in electric domain suffers from narrow range and weak electro-magnetic interference resistance. This paper proposes and experimentally demonstrates an optics-assisted Doppler frequency shift measurement approach, which employs dual-parallel Mach-Zehnder modulator for double sideband carrier modulation, band pass filtering and low-frequency photoelectric conversion in optical domain, then analyses the low-frequency spectrum in electric domain, showing an effectively solution to the disadvantages of measurement in electric domain. Experimental results shows a measurement at 7~40 GHz microwave/millimeter wave of 1 kHz~10 MHz Doppler frequency shift with measurement error of ±46 Hz.

In order to study the effect of photodetector reverse bias voltage on visibility measurement, a photodetector was used to detect the stable pulse beam, the reverse bias voltage of the photodetector was changed, and the response time and root mean square (RMS) of the output signal were read with the oscilloscope observing photodetector output signal waveform. The results show that the drift of the reverse bias voltage causes the photodetector response time changing, and RMS of the photodetector output signal is affected. The drift can affect the uncertainty of visibility measurement. When choosing photodetector in the designing of visibility meter, the influence of the reverse bias voltage should be considered, and the reverse bias voltage must be stable.

To specify the large aperture flat mirror, the discrete Fourier transform (DFT) is discussed in the processing for the slope data achieved from the pentaprism. The basic mathematic principle is processed to analysis the advance of DFT in processing the slope data. Then, the Zernike polynomials and power spectral density method are involved to evaluate the spatial domain and spatial frequency domain property of the method involved in this paper. For the large reflecting mirror, the algorithm is verified to make sure that it is enough to specify the low order mirror figure.

A high power, single-frequency, narrow linewidth fiber laser based on an active double-ring cavity under optical injection is proposed. The laser produces power of 36 dBm, signal-to-noise ratio (SNR) of 40 dB and linewidith of 7.1 kHz. The wavelength and power are stable within several hours of observing time. The allfiber double-ring cavity consists of two sub-ring cavities: the main-ring cavity is gain-controlled through adjustment of the pump power and the intracavity feedback ratio, however, the sub-ring cavity is injected by a master laser whose power and wavelength are tunable. To achieve single-frequency lasing, the intracavity gain and oscillation mode′s frequency of double-ring cavity should be matched with the optical power and frequency of the master laser, respectively. This frequency locking condition is achieved by adjusting the pump power and variable optical coupler. The single-longitudinal-mode selection regime is analyzed by a semi-classical multimode oscillation theory. Simulation results are in good accordance with the experimental results. This fiber laser can be useful in current coherent communication systems and distributed optical fiber sensors.

In order to obtain stable polarization laser, asymmetrical current injection into rectangle-shape vertical cavity surface emitting laser (ACIR-VCSEL) with oxidation aperture dimension of 70 μm × 10 μm is studied and manufactured. Room temperature (RT) continuous-wave (CW) light-current-voltage characteristics of a VCSEL described above are tested. Slope efficiency is 0.483 W/A with differential series resistance of 23.5 W. The orthogonal polarization suppression ratio is more than 5 over the whole range of operating current. The maximum power polarization ratio is 14 at current of 15 mA. Ring current injection into rectangular VCSEL (RCIR-VCSEL) with the same oxidation aperture dimensions of ACIR-VCSEL is also studied as a comparison. In the same test conditions, the slope efficiency is 0.568 W/A with differential series resistance of 18.1 W. The minimum orthogonal polarization suppression ratio is more than 2.6 over the whole range of operating current and the maximum power polarization ratio is 9. For ACIR-VCSEL, although the slope efficiency is a little decrease and the differential series resistance increases, the maximum polarization ratio effectively increases and more stable polarization is achieved.

A intra-cavity tripe frequency 355 nm ultraviolet laser with high power and high efficiency is reported. Type-II phase matching is used both in second harmonic generation and third harmonic generation. Polarization states of harmonic lasers are selected to improve the conversion efficiency from the fundamental laser at 1064 nm to the third harmonic laser at 355 nm. A simple linear resonance cavity is composed of a laser diode side-pumped Nd∶YAG module, two acousto-optic Q-switches, two LBO crystals separately as a second harmonic generator and a third harmonic generator. A maximum output power at 355 nm of 51.5 W is obtained at repetition rate of 10 kHz under the optical pump power of 623 W. The corresponding pulse width is 36.5 ns at 355 nm, the optical-optical effiency is more than 8% . The measured beam quality factor in x and y-directions are M 2x =10.89, M 2y =12.32, respectively.

Continuous laser lap welding process test is conducted on 304 stainless steel sheet, and effects of process parameters on weld shape and weld properties are studied. The results show that surface width, back width and lap shear stress of the weld increase with the increasing of laser power and decrease with the increasing of welding speed. On the premise of good weld formation, change of defocusing distance has smaller influence on weld quality. One side welding with back formation is realized when the gap is within 0.6 mm. The microstructure is fine equiaxed crystal in weld center and small columnar crystal in the junction of weld metal and the parent material, and the heat affected zone is not obvious.

The generation of high energetic proton beams and propagation characteristics in laser-plasma interaction is simulated by two-dimensional relativistic electromagnetic particle-in-cell simulation code (2D-PIC). The results show that the density gradient scale length thickness is crucial to the proton energy spectrum. The quasi- static electric field becomes stronger as increasing the density gradient scale length, which results in the enhancement of the maximum proton energy. Density gradient scale length affects high- energy proton beam emitted from thin target by certain constraints. The collimation and the beam divergence of the accelerated protons are expected to strongly depend on the spatial coupling between the laser pulse and the target plasma.

Under the introduction of background of demand pertaining to laser marking of three- dimensional (3D) freeform surface of product, laser texturing of mold cavity and laser direct structuring (LDS) of 3D- MID component, the principle of 3D freeform surface laser machining based on the 5-axes CNC system composed by both 3D laser galvanometer scanners and 2-axes CNC rotation table has been presented, the key technologies of texture mapping of two dimensional (2D) vector texture, the whole texture segmentation and 5- axes CNC machining, have been described. The experiments assure that the key technologies of the device is reliable, its machining quality is excellent. The device can laser mark and laser direct structure freeform surface in mass production efficiently, and can laser etch and texture mold cavity with accurate and fine performance.

Forward looking infrared target recognition is key technology in precision-guided weapon. In practical application, it is likely to cause wrong matching because of discrepancy of scale and angle between template and real images. In order to solve problem mentioned above, A forward looking infrared target recognition algorithm based on edge′s affine invariant coordinate. Establishing coordinate system based on regional centroids of curvic edge. Coordinates of edge points is affine invariant in the established coordinate system. Taking the set of edge points′ coordinates as edge descriptor and similarity of edge is measured by average hausdorff distance. Wrong matchings are excluded with the help of relative locations among edges and forwarding looking infrared target robust recognition is implemented. Compared with two recognition algorithms based on gray template and edge template, recognition rate and robustness of proposed algorithm are all improved through three videos.

In the three-dimensional measurement based on the linear structured light projection, the extraction precision of light stripe center affects the ultimate measurement accuracy of system directly. Aiming at the problem of broken line defect which exists in stripe center acquired from current light stripe center extraction algorithms, an proposed approach based on curve fitting of the linear structured light stripe center sub- pixel extraction is proposed. The praposed approach uses the erosion thinning method to get the stripe′s basic skeleton. The normal direction of each point on the skeleton line is computed by using the average squared gray gradient. The initial light stripe central points are obtained by weighted barycenter method. Sectional cubic polynomial curve fitting method is used to achieve smooth light stripe central positions in sub-pixel. The experimental results show that method can improve the broken line defect and the accuracy of light stripe center extraction.

In order to enhance the laser efficiency of dye-doped cholesteric liquid crystals, cholesteric liquid crystal is switched on and off by electric field and then treated by doing rubbing on the surface. The results show that the laser efficiency can be enhanced after the rubbing treatment no matter the thickness of cholesteric liquid crystal sample is thin or thick. Moreover, the laser efficiency in a thicker sample is increased more obviously. The reason is that, before rubbing treatment, liquid crystal molecules deviate from the ideal alignment direction. As a result, more or less defects are formed inside the samples, which induce light scattering and reduce its laser efficiency. More defects can be formed in a thicker sample, therefore, the optical loss induced by the light scattering is larger. Consequently, the laser efficiency in a thicker sample is decreased more compared with the ideal state. After the treatment, the alignment of cholesteric liquid crystal molecules is more or less improved and the optical loss caused by light scattering is reduced. The samples′ quality is improved and the optical loss is reduced more significantly for a thicker sample. Thus, the laser efficiency is enhanced, more significantly in a thicker sample after the treatment.

Recently, it is becoming a research hotspot to improve photocatalytic activity of TiO2. The first row transition metal Cu and Cr are selected to be co-doped rutile TiO2. The effect micromechanism of electronic properties and optical properties of Cu-Cr co-doped rutile TiO2 are discussed by using the plane wave pseudopotential method based on the density functional theory. The results show that there are five new impurity levels formed in band gap of Cu-Cr co-doped TiO2. In which, one of impurity levels on valence band maximum is mainly contribution of 3d orbit of Cu, and another four metastable impurity levels are formed by interaction of 3d orbit of Cr and 2p orbit of O. Cu-Cr co-doped TiO2 is beneficial to decrease the transition energy of electron and largely improve photocatalytic activity of TiO2. The optical properties of Cu-Cr co-doped TiO2 is also improved, which has a red shift in visible region. And the reflectivity of TiO2 is increased. The visible light absorption ability and reflection ability of Cu-Cr co-doped TiO2 is more stable compared with these of Cu doped and Cr doped TiO2.

A so-called double-pyramid waveguide network composed of one-dimensional optical waveguide segments is constructed and the properties of photonic band gap (PBG) and photonic attenuation by means of network equation, generalized Floquet-Bloch theorem, and generalized eigenfunction method are investigated. It is found that huge absolute PBGs and extreme strong photonic attenuation can be generated by this interesting optical waveguide network, which includes high density of triangular fundamental loops. When each pair of nearest-neighbor nodes in the network are connected by two waveguide segments with the length ratio of 2∶1, the ratio of the absolute PBG Δω to the midgap frequency ΔωC arrives at 154% . The average photonic attenuation of the largest PBG resulted from this two-segment-connected network with 8 unit cells is stronger than 10-21 (which is equivalent to -210 dB). This interesting optical waveguide network may be useful for the designing of optical devices with large PBG and strong attenuation.

Potential induced degradation (PID) can lead to a great attenuation in crystalline silicon solar cells module′s power and bring limitation on the large-scale application of solar cells module. The power attenuation problem of module made of different plasma enhanced chemical vapor deposition (PECVD) coating processed polycrystalline silicon solar cells is analyzed experimentally. The results show that compared with the module of standard process polycrystalline silicon solar cells (the refractive index is 2.06), the module made of preventing PID processed polycrystalline silicon solar cells (the refractive index is 2.16) suffers a power attenuation of 1.65% only, which is within the attenuation range of 5%, and has certain abilities of resistance to high pressure, high temperature and humid environment. According to the analysis, under the condition of the certain thickness of optical film, making polycrystalline silicon solar cells module with high refractive index SiNx film can better prevent the happening of the PID phenomenon.

Best matching temperature is obtained when the fundamental laser is of normal incidence in periodically poled crystal. The in-depth analysis of second harmonic nonlinear conversion efficiency uses periodically poled crystal MgO∶sPPLT as the research object, and combines the Sellmeier equation and the polar period with temperature thermal expansion relationship. When the fundamental laser tilt is incident, the equivalent polar period becomes larger, and the best matching temperature is reduced. Acceptable temperature and wavelength bandwidth can be obtained conveniently by using the normalized frequency doubling efficiency curves for the given length of frequency doubling crystal. The crystal length becomes longer, and the acceptable temperature and wavelength bandwidth become narrower. As long as the Sellmeier equation and polar period with temperature thermal expansion relationship are known, the method used in this study can be extended to other periodically poled crystals. These conclusions are useful for other periodically poled crystals and guiding continuous wave fiber laser external cavity frequency doubling.

In traditional design of an optical system, optical design and mechanical design is relatively independent. It′s difficult for a mechanical designer to know which structure is suitable for an optical system, and even harder to optimize the mechanical structure. The mechanical sensitivity is utilized to build the relationship between the caused error of the mechanical structure which includes manufacture and assemble and the quality of the optical system, and it′s easy to see how the mechanical manufacture and assemble errors affect the displace-ment, tilt and space errors and then affect the optical system quality. Mechanical designers use the mechanical sensitivity table of different mechanical structure to decide which is the best, and optimize the opto-mechanical structure.

In order to study the influence of optical surface residual on the optical image system, a kind of method dividing spatial frequency based on the exit pupil phase of the optical system is proposed and the analytical expression of modulate transfer function which is influenced by mid-spatial frequency (MSF) errors is provided. The feature spatial resolution of the image whose modulate transfer function (MTF) is influenced by MSF is obtained. By comparing the influence of low-spatial frequency (LSF) errors and MSF errors, it is concluded that there is a sudden drop of MTF on the point of feature frequency under the influence of MSF.

An active deformable lens with small coupling error is designed to meet the requirement of astigmatism compensation because of non-uniformed illumination in lithographic objective lens. The capability of the active deformable lens is studied. The finite element model is established. Based on the finite element model, adjustment ability, rigid movement error, natural frequency and maximum stress of the active deformable lens are analyzed. Analytic results indicate that the active deformable lens is able to regulate root mean square (RMS) 837 nm astigmatism compensation Z5 with 50 N drive force. The high order aberration only is RMS 1.124 nm. The rigid movement error of translation and rotation are 0.49, 0.52, 0.13 nm, 2.21, 1.73，1.10 ms, the first order natural frequency is 2555 Hz, and the maximum stress of lens is 0.852 Mpa. The active deformable lens satisfies the requirement of astigmatism compensate in lithographic objective lens.

In order to improve focal spot quality in inertial confinement fusion (ICF) system, beam smoothing technology is required so as to meet the strict requirements of target surface irradiated. Continuous phase plate (CPP) can control the shape of focal spot easily and has high diffraction efficiency. In practical optical system, beam smoothing results can be influenced since a variety of factors can cause distorted wavefront of laser beam. The relationship between the full spectrum of distorted wavefront and optical field in the far field is given, and it is obtained that the relationship between 86% focal spot size and the ratio of peak valley value of low frequency distorted wavefront and surface shape of CPP. Meanwhile, the relationship between 86% focal spot size and root-mean-square gradient value of low frequency distorted wavefront is also shown. According to the relationship, the range of controlling distorted wavefront can be found.

An electrically controlled double wavelength tunable filter based on lithium niobate (LN) is designed. Double wavelength of orthogonal polarization filter is achieved by etching Bragg grating on the Ti-diffusion LN waveguide, which supports transverse electric (TE) mode and transverse magnetic (TM) mode. The refractive index distribution and therefore the Bragg wavelength can be fast tuned by using electro-optic effect in LN. The performance of waveguide grating filter is analyzed and results show that the grating with 1/2 etching duty cycle and less than 15°etching angle has the best filter characteristic. The reflectivity and bandwidth increase with the etching depth increasing. Double wavelength filter achieves 15.6 pm/V sensitivity for TE mode, 5.5 pm/V sensitivity for TM mode by adding the transverse electric field on waveguide grating.

In order to study the influence of a left- handed material slab on the spot of sinh- Gaussian beams, the analytical expression of the spot is derived based on the generalized Huygens- Fresnel diffraction integral. Based on the expressions, the spot is calculated. The results show that when sinh- Gaussian beams propagates through left-handed material slabs, the focus position of spot size is the beam waist position which is influenced by the refractive index of left- handed material slabs, and waist width has nothing to do with the material of index of refraction; And it is similar that spot size of internal left-handed material slab and spot size of the phase space which are with eccentricity parameters changing rules is found. This study can be helpful to application of the light field manipulation.

In fiber-based quantum key distribution systems, the photons polarization fluctuation can lead to a decrease of the key generation rate. A method for polarization controlling, based on the genetic algorithm and the numerical control polarization controller is introduced. It is shown that the system could be quickly optimized and the polarization of signal beam has been locked in long term at the single-photons level. In our phase-modulated quantum key distribution system, the average photon number is less than 0.1 photon per pulse. After transmitted through 25 km single mode optical fiber, the polarization state of signal beam is realized to optimum value and keep the stable transmission for a long time, and the final key rate is up to 1.5 kp/s.

As an important part of the urban ecosystem, urban vegetation creats huge ecological benefit, so reasonable classification of urban vegetation is in favor of urban construction and planning. Based on the typical vegetation classification of Changchun, it is found that the observation time, detection angle and band are the main factors affecting the brightness temperature of vegetation. The result shows that the brightness temperature of vegetations measured in different time periods is significantly different, so it can distinguish among different vegetations easily, especially at noon, it is the most conducive to identify the four vegetation types. The brightness temperature measured under different detection angles is also evidently different, and it can also achieve the effect of distinguishing among typical vegetations, especially the brightness temperature obtained under the 0° detection angle is the most favorable to the vegetation classification; but there is only subtle difference between brightness temperature of four channels, the brightness temperature obtained in different band ranges is difficult to distinguish among typical vegetations. The results can be used to provide important basis for the identification and classification of vegetation types.

The space optical communications have gone through decades of development, evolving two generations of optical communication terminals, and accomplishing several on-orbit experiments. The overall development history of space optical communications is summarized, the development progress of Europe, Japan and the USA is introduced in detail, and then some of the typical terminals and experiments are stressed, as well as the key technologies. The development status in China is briefly introduced. The development trends of space optical communication are analyzed, and the technical challenges are pointed out.

In the big data and cloud computing era, with the challenges of optical networks increase, the next generation optical networks technology for cloud computing has attracted more and more attention. The issue of optical networks supporting cloud computing is regarded as a starting point. The biggest challenge of the optical network for cloud computing is summarized that optical networks resources and IT resources can be jointly and efficiently scheduled on customers′ demand. The latest research progresses are introduced mainly from the optical switching and transmission technology, optical networks routing technology, new generation optical networks management and control architecture and virtualization technology of optical networks. Finally, the future direction of development for the next generation optical networks technology for cloud computing is analyzed.

Silicon-organic hybrid (SOH) platform combined with silicon-on-insulator (SOI) waveguides and the functional organic nonlinear materials opens a route to highly-speed ultra-compact electro-optic devices. Recently, bandwidth of frequency responses of modulators based on SOH is up to 100 GHz, and enabled operation is up to 112 Gbit/s with an energy consumption of 640 fJ/bit. Main SOH electro-optic modulators, such as the Mach-Zehnder interferometer (MZI) modulator, in-phase/quadrature-phase (IQ) modulator and mcroring-resonator modulator, are introduced. Meanwhile, the design principle, characteristics and research status of the modulators are illustrated.

This paper reviews frequency resolved optical gating (FROG) femtosecond pulse width measurement technology. Based on analyzing the principles of FROG, the change and development of measurement technology in theory as the main line, the research status and development direction of different structures of FROG measurement are introduced according to three different transient responses of nonlinear effect, which are third-order nonlinear effect, second-order nonlinear effect and cross-phase modulation (XPM) effect. And the characteristics of three types of branch technology are analyzed comprehensively. Comparing different structures of FROG measurement in detail, their strengths and weaknesses and prospects are obtained. It provides research mentality and references for FROG femtosecond pulse width measurement technology.

The interaction of ultra-short high power lasers with gas targets is an important way to produce high power terahertz (THz) sources. Based on the model of ionization currents, the THz radiation generation is considered by use of two color lasers at 0.8 mm wavelength and its half-harmonic 1.6 mm co-propagating in a gas target. The influences of the types of gases, the laser amplitudes and the relative phase difference between the two laser pulses on the ionization currents are discussed. Compared with the case with 0.8 mm laser and its second harmonic, the THz radiation amplitude is enhanced twice under the same incident laser amplitude. The effect of the angle between the two laser polarizations is also studied. When the two polarizations are perpendicular to each other, the ionization current direction is along the polarization direction of the half-harmonic laser, even though its amplitude is much lower than that of the fundamental laser.

For the demand of spectral purity detecting in high-energy narrow-line width laser system, a method of spectral purity analysis by measuring the spectral energy distribution is reported and experimentally studied. The spectral purity analysis device is mainly composed of echelle grating, moveable blade, sensitive power meter,etc. The output spectrum of excimer laser system with a compound cavity is analysed by using this device. The experimental results show that the spectral purity detection can be achieved by accurately measuring the energy ratio of the spectral components. The spectral purity analysis device has the advantages of compact structure, low cost and high accuracy, which has important application in the building process of high-energy narrow-linewidth laser system.

Fourier transform infrared spectroscopy (FTIR) technology combined with chemometric analysis is applied to identify different varieties of Chinese roses. The infrared spectra of Chinese rose samples are similar on the whole, which are mainly composed of vibration absorption bands such as phenolic, lipid, glycosides, flavonoids, polysaccharides. The second derivative spectra of Chinese rose samples are different in the range of 1800~700 cm- 1, the second derivative spectra in the range of 1800~700 cm- 1 are selected to perform correlation analysis, principal component analysis (PCA) and hierarchical cluster analysis (HCA). The PCA and HCA results show that all Chinese rose samples are classified correctly. It is demonstrated that FTIR technology combined with chemometric analysis method can be as a possible method for identifying different Chinese rose varieties.

In order to make better use of laser induced breakdown spectroscopy (LIBS) in the liquid steel composition monitoring, a model of support vector machine based on radial basis function (RBF) kernel function is established by using particle swarm optimized support vector machine. In order to reduce the interference of instrument and environment, integral intensity of spectral line and Fe normalization is used. The experimental data is subjected to principal component analysis to carry out quantitative analysis of the concentration of Mn element in molten steel, it is obtained that the mean square error (MSE) is 0.599% , the relative standard deviation (RSD) is 8.26%, the correlation coefficient is 0.997. The results show that the particle swarm optimized support vector machine regression method can be used to analyze LIBS of liquid steel composition, its analytical performance is improved compared with traditional calibration methods.

A rapid method with thin layer chromatography (TLC) combined with surface enhanced Raman spectroscopy (SERS) for detection of the chemical drugs illegally added into compound product of Eucommiae capsule is developed. Chemical drugs added in simulation of positive drugs are separated by TLC initially, using toluene-ethyl acetate-ethanol-strong aqua (12∶3∶3∶0.2) as the mobile phase, and then the SERS method is used to analyze the separated chemical drug spots. The characteristic peaks of Raman spectra of the chemical drugs added into the compound product of Eucommiae capsule obtained by TLC-SERS method are nearly consistent with the reference substance. This TLC- SERS method can be used for detection of chemical drugs illegally added into compound anti-hypertensive Chinese patent medicine quickly, accurately and sensitively.

To improve the analytical precision of laser-induced breakdown spectroscopy (LIBS), a modified internal standard approach is studied based on the correlation of analytical lines and reference lines. The approach is investigated in detail by principle analysis and numerical calculation firstly, then experimental verification is carried out using the analytical lines of Co I 350.23 nm and Cr I 427.48 nm from the micro-alloy steel standard samples. The results show that, to improve the analytical precision of LIBS, it must meet the necessary conditions that the correlation coefficient of analytical line and reference line γ >0.5, the noise proportional factor b>0.5, and γb > 0.5 . The precision enhancement factor R increases with the increasing of γ , but increases first then decrease with b. When the fluctuation of analytical lines is greater than that of reference lines, the degree of precision improvement decrease gradually.

The concept of selectable imaging spectrum is proposed. It is an selectable imaging spectroscopy detection technology, namely, detecting the spectrum of the region of interest (ROI) selected through the whole observation of images, rather than the traditional imaging spectroscopy technology which passively measures all the pixels spectrum. Then an selectable imaging spectrometer based on beam- splitter- cube is designed to detect the spectrum information of 192 pixel diameter and located in the circular center area of the image. The performance test result shows that the spectral range of this system is 380~850 nm, the spectral resolution is 1.5 nm , lens focal length is 70~300 mm and the highest spatial resolution reaches 2.4 mm. Under natural outdoor conditions, correlation coefficient to the original spectrum is over 0.992. The proposed system with a high potential for application supplies a novel and effective method for spectral detection, it has the advantages of simple structure, non-contact, long distance and real-time detecting capability.

A new amorphous silicon film solar cell structure is designed, where the antireflective coating consists of double layer gratings. The Si film is etched into the array of Fresnel zone plate (nonperiodic grating) structure to focus light to the amorphous silicon film and amount of Si can be saved. The indum tin otide (ITO) film on Si is etched into a subwavelength and nonperiodic grating array. The designed double grating antireflective film can reduce refraction and increase the broadband transmission of light. The intensity distribution of reflection and transmission fields are simulated by using the finite difference time domain (FDTD) method. The simulation results show that, compared with the conventional amorphous silicon film solar cell without grating antireflective film, the absorptivity of light and the short-circuit photocurrent density can be improved by 19.9% and 19.9%, respectively. These results are better than results of the reported solar cell with an antireflective film of double layer periodic gratings and a metal grating back electrode.