Based on the Zeeman catastrophe machine theory, the critical equation of potential function of Pearcey beams is solved. It is found that the number of roots of the critical equation determines the optical morphogenesis of Pearcey beams. This critical equation has at most three real roots, which correspond to three stable points and three diffraction lines, respectively. By choosing suitable control variables of Pearcey beams, if two of the three real roots are equal, the two corresponding diffraction lines overlap and the caustic line of Pearcey beams is formed. If three real roots are all equal, the optical cusp of Pearcey beams is formed. The study not only clarifies the mathematical mechanism of the generation of caustics and optical cusps of Pearcey beams, but also shows the caustic line equation and the position of the optical cusp.

To improve the convergence ability of a wave-front sensorless adaptive optics (AO) algorithm using a general model-based approach, an AO system simulation model based on Zernike modes is established with a 127-elements deformable mirror (DM). Using peak Strehl ratio (Sr) and the proposed fast-steady-convergence percentage as evaluation criterion, good correction capability for static distorted wave-front is verified by analyzing the impact of different perturbation coefficient, the number of Zernike modes, and slope factor on correction effect and convergence speed under different turbulence intensity. The results show that when the perturbation coefficient is less than 0.01, the system can converge steadily and increasing the number of Zernike modes can ascend Sr of the convergence while it will sacrifice some convergence speed. A modified vector slope factor is put forward, and the system correction can be improved efficiently after the first iteration. For the large distorted wavefront has strong adaptability especially.

The interference phenomenon of vortex beams and plane waves is analyzed. By using coaxial superposition interference of vortex beams, we can generate the light with binary orbital angular momentum, and apply it to the topological charge number detection of orbital angular momentum. We use fork dislocation grating to generate centrosymmetric vortex beams and then discuss the generation of light beams with binary orbital angular momentum by the interference of two vortex beams with different topological charge numbers. Numerical and experimental results show that with the change of the topological charge number value, either plus or minus, the interference image which is generated by the interference superposition of two vortex beams is also changing regularly. According to this, vortex beams can be detected. Moreover, vortex beam has important significance in information transmission and coding. Our study provides experiment basis for the reuse of vortex beams in free space communication, and provides potential for performance improvement of optical communication system.

The spatial light modulator (SLM) has narrow wavelength range and low diffraction efficiency, and limits the research of high-quality helical beams. Based on this, an effective SLM optimization method is proposed to greatly enhance the quality of helical beams produced by SLM. A laser with 650 nm wavelength is used as an example to produce the helical beams with different orbital angular momentums. The intensity distribution and diffraction efficiency of the generated helical beams are analyzed, and the experimental analysis proves the effectiveness of the proposed optimization method.

Skin cholesterol is a novel biomarker to assess the risk of atherosclerotic diseases. A system based on diffuse reflectance spectroscopy technology is designed for noninvasive and rapid detection of skin cholesterol. The feasibility of the system is validated through detecting digitonin-horseradish peroxidase copolymer solution which simulates the skin cholesterol of gradient concentration and skin cholesterol in vivo of subjects. A parameter S based on the relative diffuse reflectance increases linearly with the increasing concentration of the copolymer solution in the wavelength band from 440 nm to 550 nm (correlation coefficient r=0.992, P<0.01). After adjusting age, gender and other factors, it shows significant positive correlation between the skin cholesterol test results of subjects and the total cholesterol, low density lipoprotein cholesterol, and the correlation coefficients are 0.837 (P<0.01) and 0.778 (P<0.01), respectively. The diffuse reflectance spectroscopy is a noninvasive and convenient method for the detection of skin cholesterol, and the noninvasive detection of skin cholesterol in vivo contributes to the early detection of atherosclerotic diseases.

The parallel phase modulation (PPM) algorithm is investigated for spectral phase measurement and compensation. Detailed theoretical analysis and a numerical simulation are carried out to find how to determine the modulation frequency and reconstruct the spectral phase. A femtosecond pulse shaper is set up based on the PPM algorithm. The shaper is driven by our home-developed LabVIEW program and can be used to measure and compensate spectral phase of femtosecond pulses. The experimental results are verified with the multi-photon intra-pulse interference phase scan (MIIPS) method. Different from such existing ultrafast pulse measurement methods as MIIPS, the PPM method only needs to measure the signal intensity to determine the spectral phase quickly, and requires no spectrum measurements of nonlinear signals.

With the Yb:GdYCOB crystal end-pumped by a diode laser with an annular-shaped beam profile, the direct emission of vortex laser is realized in a laser resonant cavity. By measuring the spatial intensity distribution, beam quality factor, beam purity, and wave front phase information, it is confirmed that the laser output beam is really a highly pure vortex beam. With 3.2 W pump power, the maximum output power is 281 mW, the optical-to-optical efficiency is 8.7%, and the slope efficiency is 21.7%.

A subwavelength anti-reflective grating made from GaAs material is proposed, with optional wavelength and polarization mode and a working wavelength of 976 nm. On the basis of effective medium theory and membrane theory, the grating is initially designed. Parameters of duty cycle, ridge height and period of the grating are optimized and determined according to the rigorous coupled wave theory. Meanwhile, the influence of various parameters on the grating transmissivity is analyzed. The designed anti-reflective grating is of high transmissivity, 99.99% for TE mode and 99.86% for TM mode, respectively. In the range of 976 nm± 30 nm, the transmissivity is above 99% for both mode gratings, which meets the requirements of device application. The effect of non-rectangular shape of the grating caused by fabrication error on the transmissivity and dominant polarization mode is studied.

A terahertz single-polarization single-mode (SPSM) fiber with tunable polarization is proposed based on the index-matching coupling method. The asymmetric microstructure is designed in fiber core to split the x and y polarized core modes. The index matching liquid is filled into the air-hole of the fiber cladding, so that the x or y polarized core modes match the defect mode. The matching switch between the two polarized modes is realized by changing the refraction index of filled liquid. The results show that the x polarized mode matches when the refractive index of the liquid is 1.288. When the frequency of the incident light is higher than 0.73 THz, the polarization loss ratio of the fiber is bigger than 100, and the optical fiber operates in y-polarization mode. At the frequency of 1 THz, the polarization loss ratio reaches the maximum of 1020. The y polarized mode matches when the refractive index of the liquid is 1.338. From 0.87 THz to 0.93 THz, the polarization loss ratio of the fiber is bigger than 100, and the optical fiber operates in x-polarization mode. At the frequency of 0.9 THz, the polarization loss ratio reaches the maximum of 118. This design has realized the switch of the single fiber polarization operation mode, and has features such as broadband, tunable and easy to fabricate.

With high peak power and good beam quality, it is easy for pulsed fiber lasers to trigger nonlinear process in a nonlinear crystal, and the near-infrared laser can be transferred into the ultra-violet or mid-infrared regime. In an experiment, the homemade high power pulsed fiber laser with central wavelength of 1064 nm and pulse duration of 650 ps is used to pump KTP (potassium titanyl phosphate) crystal, and the 532 nm laser is output after second-harmonic generation (SHG). In the process, the pulse width is compressed from 650 ps to 1 ps, the peak power density of the pump laser is raised to 24.97 GW/cm2, and the SHG efficiency increases from 0.8% to 8.4%. SHG efficiency is investigated for the pump laser of different average power, pulse width and beam spot, and the possibility to achieve highly efficient SHG with an oscillator is proved.

With ICEM software, the mesh generation of the two-dimensional cross-section of the simplified gas flow channel of excimer laser is introduced. Based on realizable k-ε model and multiple reference frame (MRF) model, the simulation to the steady-state flow field of gas flowing inside laser with FLUENT software, and the velocity value and its distribution of gas flow are obtained. The simulation results indicate that there exist linear relationships between the average gas flow velocity and the rotational speed of blowers, also between the torsional moment and the square of rotational speed of blowers. The gas flow velocity distribution measured by a pitot tube is compared with the simulation results, and the consistency between them confirms the validity of the latter.

By utilizing the principle of polarization-selective grating mirrors, a 35-layer circular grating mirror, with 1000 nm period and 70 nm groove depth, has been designed and fabricated. The grating mirror is placed in a laser diode pumped Nd:YAG rod laser system as the cavity mirror. After optimizing the laser system, we get a radially polarized beam, of which the degree of radial polarization and the power are 97% and 13.4 W, respectively.

A spectral beam combination (SBC) laser with dual multi-layer dielectric (MLD) grating dispersion compensation configuration is studied theoretically and experimentally, which can combine multiple-channel fiber lasers into a common aperture beam with high beam quality and reduce the linewidth requirement of the single channel fiber laser. The analysis model of the degradation of beam quality is optimized. The influences of the laser wavelength, the dispersion of grating and the spectral structure on the output beam quality of the SBC laser are analyzed. The variation of the beam quality of the SBC system at different output power levels is also studied experimentally. The output combined beam with the maximum average output power of 9.6 kW is obtained, of which the beam quality factor M2 is 2.9 and the combination efficiency is 92.0%. By reducing the linewidth and improving the output power of each channel fiber laser or increasing the number of channels, the common aperture SBC output beam can be further scaled with higher output power and higher beam quality.

By the hybrid technique of fiber laser and variable polarity tungsten inert gas, A7N01 aluminum alloy is welded with filler wire. After optimizing process parameters, joints with good formation and without defects are obtained. The microstructure, tensile and fatigue properties of these joints are investigated, and the fatigue-fracture characteristic and fracture morphology are examined. The research results indicate that these joints are mainly composed of fine-grained zone, columnar grains, and equiaxed dendrites. The average tensile strength of these as-welded joints is 320 MPa, around 75% of that of base metals. After natural aging of 30 days, the average tensile strength increases to 369 MPa, around 83% of that of base metals. Fractures locate at the stress concentration zone of the weld toe, and the fracture shows an obvious dimple shape, which is the unique characteristic of ductile fracture. The fatigue limit of these joints is 115 MPa.

An experimental study on the laser welding of glass/stainless-steel and glass/titanium-alloy materials is conducted, and the differences in fracture morphology, sectional shape, and weld phase of welding parts are emphatically analyzed. The results indicate that, as for the glass/stainless-steel and glass/titanium-alloy materials, their welding mechanisms are similar, and the mosaic structure in the welds of glass/metal material and the adhesion substance at the interface play major roles in connecting these two kind of materials. The linear expansion coefficient of glass/titanium-alloy material is small, which is the main reason why the breaking strength of welding parts between titanium-alloy and glass is high. Chemical adhesion takes place in laser welding of glass/titanium-alloy material, which produces Ti5Si3 compound. In contrast, as for the glass/stainless-steel material, mechanical mixing occurs mainly.

The variation rule of micro-nano structures on titanium alloy surface induced by femtosecond lasers as a function of the laser energy density and pulse number is investigated, and the scanning electron microscope images of these micro-nano structures are shown. The research results indicate that the evolution of micro-nano structure on the titanium alloy surface mainly includes four phases, in the order of no-laser-induced periodic surface structure phase, classical ripple structure phase, classical and non-classical ripple structure coexisting phase, and micro-hump structure phase. Further research indicates that non-classical ripple cycle increases with the increase of laser energy density or pulse number.

By means of the technology of inside-beam powder feeding, the formation technology of double-inclined-walled parts (DIWPs) with small gapsis is investigated. By using the methods of sequentially independent accumulation path, normal layering, and non-dislocation accumulation, the DIWPs are formed. The experimental results indicate that the technology proposed can increase the forming efficiency of DIWP, save metal powder, and ensure the thickness uniformity of thin-walled parts and the gap stability of the double inclined walls. The formed parts have smooth surfaces, uniform morphology, no cracks, no holes and no other defects, and uniform microhardness distributions.

The characterization and analysis of fractures of TA2 CP-Ti tensile specimen by laser shock processing (LSP) under different temperatures are conducted, and the effect of temperature on the characteristic fracture morphology and the tensile property is investigated. The results show that the necking phenomenon of tensile fracture subjected to LSP is more obvious than that of the untreated sample, and the treated sample has a better plasticity. With the gradual increment of temperature, the fracture mode turns from the brittle fracture into mixed fracture, and finally to ductile fracture.

Silicon paste prepared by boron doped Si nanoparticles and organic carriers is used as the source. The Si wafers from the standard process of solar cells are used as the substrate. The Si paste is fully screen-printed on the preprocessed Si rear surface and dried, and then a homogenous B-doped Si cladding layer is formed by picosecond laser. During the process, B diffuses into the substrate. The structure of Si cladding layer and doping performance of B element are observed by laser scanning microscope, scanning electron microscope, and secondary ion mass spectroscopy. The results show that the Si cladding layer formed by picosecond laser is uniform and dense without cracks and voids. The highest B concentration in the cladding layer is about 3×1019 atom/cm3, and B is doped into the Si substrate for the depth of 0.5-1 μm. Cells with an average efficiency of 20.3% are fabricated on China Sunergy′s production line.

As one of the key technical solutions for nano-displacement measurement, the interferometric grating displacement measuring system has such characteristics as high precision, high resolution and small size. Because the interferent light beams come from the diffraction of gratings, the system is sensitive to gap and rotational tolerance between the optical head and scale, and is difficult to align. A symmetrical double-grating interferometric displacement measuring system, which achieves high-precision displacement measurement, is developed based on optical effect of Doppler shift and circularly polarized light interference. The system has small tolerance and simple alignment. The performance tests show that the developed system has the actual resolution of 0.8 nm, repeatability of 1.4 nm. In the movement range of 1-14.5 μm, its accuracy without correction is 15.4 nm, and the accuracy with trajectory error correction is 5.5 nm. After periodic error correction, the accuracy can be improved to about 1.4 nm.

In order to screen a high-performance detector for spatial heterodyne spectrometer, a method of detector screening and testing is proposed. Parameters of detectors which influence the spectral reconstruction of spatial heterodyne spectrometer are determined by simulations, and the screen method based on these parameters are obtained. The experiments are conducted with the designed screening and testing setup. Through processing and analyzing the experimental data, the optimal array detector is chosen from the alternate detectors. The satellite-borne detector obtained by screening and testing has already been used in the spatial heterodyne spectrometer and passed a series of test evaluations.

This paper introduces the principle of chirped femtosecond pulse interference ranging and typical time-frequency analysis methods, and the influences of these methods on the analysis of the chirped spectra interference signal are compared. The factors which can affect the results are studied, and these methods are used for processing the ranging data of chirped spectrum interference. The experiment comparison shows that the relative precisions of the time-frequency transform methods are all better than 6×10-7 in a range up to 65 m, with respect to the reference He-Ne interferometer data, which meets the high-precision processing requirements. Wherein smoothed pseudo Wigner-Ville distribution, continuous wavelet transform and smoothed Choi-Williams distribution perform better in processing chirped spectral data and get the expected results.

The temperature, H2O concentration, pressure, velocity and mass flux of supersonic gas flow are measured based on scanning wavelength-modulation spectroscopy method. The simultaneous measurement methods of multiple parameters of supersonic gas flow in uniform flow filed are studied using the harmonic signals of two H2O absorption spectral lines. The measurement results based on wavelength modulation spectrum technology can precisely reflect the gas parameters in the uniform flow field, while the actual flow field often has the boundary layers. Aiming at the approximate uniform flow field with boundary layer, the numerical simulation is carried out to study the effect of line selection and boundary layer thickness on the measurement result of core flow in flow field. The simulation results show that the measurement error increases with the boundary layer thickness, and the absorption spectral lines which are insensitive to temperature of boundary layers can effectively decrease the influence of boundary layer. The experiments of supersonic gas flow is carried out in a direct-connected scramjet test facility isolator, the results show that the measurement method based on wavelength modulation spectroscopy has high measurement accuracy in strong noise and strong vibration environments. The maximum relative deviation of predicted value and measured value for temperature, H2O concentration, pressure, velocity and mass flux are less than 8.2%, 7.2%, 2.0%, 3.1% and 6.4%, respectively.

The closed loop passive work-points control method is introduced for mixing frequency modulation of light source. The phase-shift signal is picked up from single interferometer signal by directly high frequency modulating light source, and compensated by the low frequency control signal with directly modulating light source. The problem of work-point tracking is resolved by the cooperation of high and low frequency modulation, the system is always working in the most sensitive linear region by way of passive control. The modulation characters of laser source are tested under different frequencies, and the variation tendency of work-point under open-closed loop is compared. Demodulation results of closed loop passive work-points control method and phase carrier demodulation algorithm show that the demodulation relevancy of two methods is above 99%, which proves the feasibility of the proposed method.

To compensate the image motion and improve the image quality, it is necessary to accurately detect the displacement vector between images. Based on the principle of image motion vector measurement with joint transform correlator, an improved method is proposed. To detect the edges of low altitude images, the improved self-feedback fuzzy edge detection method is presented to realize the input image preprocessing. By eliminating the 0th diffraction peak, the coordinates of relative correlation peaks are extracted with centroid method, and the high-precision detection of relative correlation peaks is achieved. The measurement accuracy and performance of proposed techniques are analyzed with simulation test and real low imaging experiments. Simulation tests show that the detection accuracy can be controlled within 0.03 pixel, when motion blur in the range of 0~10 pixel, Gaussian noise is less than 0.002 and the displacement between image in 0~20 pixel. Experimental results further show that the measurement accuracy of the proposed method reaches 0.2 pixel, and it can detect the image displacement vector of low altitude images with high accuracy and robustness.

A large work area framing image tube with magnetic lenses is designed. By theoretical analysis and analog simulation, the characteristics of spatial resolution in different off-axis positions of framing image tube with single lens and treble lenses are studied. Experiments are also conducted to verify the results. In the simulation, when the imaging demagnification is 21, the single lens structure can reach 5 lp/mm spatial resolution within 10 mm off-axis radius, while the treble lenses structure can reach 5 lp/mm spatial resolution within 30 mm off-axis radius. In the experiments, the single lens structure can reach 5 lp/mm spatial resolution within 12 mm off-axis radius, while the single lens structure can reach 5 lp/mm spatial resolution within 27 mm off-axis radius. The results show that by using the framing image tube of treble lenses structure design, its effective detection area is about 4 times as large as that of the single lens structure.

High precise frequency transfer is realized in partial Beijing-Shanghai optical fiber backbone network of 430 km using the cascaded method. The entire cascaded system is comprised of two stages with fiber links of 280 km and 150 km, respectively. To keep high symmetry and low noise, specific bi-directional Erbium-doped fiber amplifiers are used to compensate the large optical attenuation of each fiber link. When the whole system achieves stable status by optical compensation method, the stabilities of 1.02×10-13 at 1 s and 8.24×10-17at 104 s are obtained. Experimental results verify that the actual results of the cascaded system are in accord with the error theoretical ones calculated from the results of two stages.

A single-polarization (SP) directional coupler based on dual-core photonic bandgap fiber (PBF) is proposed, and the coupling properties of the coupler are studied numerically using the full vector finite element method (FEM). Results show that by appropriately adjusting the size of the holes between the cores and the refractive index of doping, the SP property can be obtained in a coupler; however, the ellipticity of the hole between two cores has no effect on the SP property, which means that the coupler has high structure parameter error tolerance; an SP directional coupler with length of 0.403 mm is obtained by optimizing the parameters. In the application of the all polarization-maintaining PBF (PM-PBF) based resonant cavities, the coupler can serve as a beam splitter and a polarizer at the same time, break the resonant condition of secondary eigenstate of polarization (ESOP) and effectively inhibit its transmission. The mode field of SP coupler with short length matches with the PM-PBF proposed in former study, which is beneficial to the establishment of an all PM-PBF resonant cavities, and therefore has great significance in reducing the thermally induced polarization crosstalk noise of resonator fiber-optic gyroscopes (RFOG) and improving the long-term stability of RFOG.

To solve the low channel estimation performance of LED communication system, a visible light communication system which combines the orthogonal frequency division multiplexing (OFDM) system with the multiple input multiple output (MIMO) technology and its adaptive channel estimation based on signal-to-noise ratio (SNR) are proposed. The critical threshold of SNR is determined when the five algorithms, i.e., least squares (LS), minimum mean square error (MMSE), least squares-discrete Fourier transform (LS-DFT), minimum mean square error-discrete Fourier transform (MMSE-DFT) and distributed compressed sensing synchronous orthogonal matching pursuit (DCS-SOMP), are analyzed. When SNR is lower than the critical threshold, the MMSE-DFT algorithm is used for the channel estimation, and when SNR is higher than the critical threshold, the DCS-SOMP algorithm is applied to the data reconstruction and the recovery of channel impulse response matrix. Simulation results show that when SNR is 1 dB~40 dB the proposed algorithm can reduce the mean square error (MSE) from 2.95 dB to 15 dB, and improve the LED communication quality.

The interferometric fiber sensor is applicable in many fields for its high sensitivity, but the polarization induced signal fading is a serious problem. We proposed an orthogonal-polarization switching method and a signal synthesis algorithm based on the phase generated carrier (PGC) scheme to solve the problem for the pulse interrogation. The principle of the method was demonstrated and an algorithm for signal synthesis was derived based on the PGC scheme. The experimental results show that the equivalent visibility is steady between 0.93 and 0.94, and the background noise of the synthesized signal is lower than that of all the four polarization channels. The method can eliminate the polarization induced low frequency phase drift as well, making the synthesis results not influenced by perturbation of polarization states. The long time measurement results demonstrate that the background noise can reach -96 dB/Hz at 1 kHz when the frequency of the PGC demodulation was 8 kHz. This result is equivalent to that of the system with the Faraday rotator mirrors. This method is applicable for solving the signal fading problem in the time division multiplexing sensor array especially for the inline interferometric fiber sensor array based on fiber Bragg gratings and the distributed sensor array.

A discrete dynamic model of fiber optical current transformer is established. The relationship between the scale factor error, phase error of the transformer and the system loop gain is theoretically investigated. It′s determined that the loop gain drift is one of the main reasons that lead to the degradation of the long-time operation accuracy of the transformer. A method for online loop gain monitoring is presented which can monitor the change of loop gain in real time. The monitoring value can be used as one of the fault monitoring points for long-time operation of the transformer. Based on it, the model correctness is verified by experiments. Results show that on the condition of ensuring the static test accuracy, the greater the system loop gain value is, the smaller the influence of loop gain fluctuation on scale factor error and phase error of the transformer will be. When the system loop gain is 0.05, the loop gain fluctuation should not exceed 10% to ensure that the transformer measurement accuracy in long-time operation is less than the required error limit.

The cross-track baseline component of the along-track interferometry processing baseline is introduced by the angle of pitch and yaw in the actual flight, and the accurate imaging of elevation fluctuation terrain is difficult to obtain under the condition of vibration. In order to realize vibration estimation in airborne synthetic aperture ladar (SAL) effectively, a kind of vibration estimation and imaging method is proposed based on interferometry processing of three detectors with orthogonal baselines, and the signal model is established and its accuracy is analyzed. This method need to make the field of view overlap, and it is realized by the characteristic of SAL non-imaging optical system. The optical system containing a wide swath ground imaging detector and three vibration estimating detectors is introduced. The impact of overlapped degree of field of view of detectors and signal-to-noise ratio on performance of vibration estimation are discussed respectively. The imaging simulation results of the elevation fluctuation terrain under platform vibration condition validate the effectiveness of the proposed method.

In conventional Brillouin optical time domain reflectometry (BOTDR), mutual restraint between the spatial resolution and the width of spontaneous Brillouin scattering spectrum can not be avoided. To solve this problem, we ameliorated the approach using double ultra-short pulses as probe light. By detecting spectral envelope, the spatial resolution of BOTDR can be extracted. This method improves the spatial resolution of the BOTDR system and meanwhile avoids the influence of Brillouin gain spectrum broadening caused by narrowing pulse on measurement accuracy. The experimental results show that with this novel BOTDR system, the temperature measurement can be realized at a 0.5 m spatial resolution, and the large broadening of the spontaneous Brillouin scattering spectrum can be avoided.