According to the technical requirements of the laser and far infrared common-window imaging system, a wavelength separation coating was developed, which aimed to separate the laser and far infrared light through a common window, that is, 1 064 nm laser reflected, 8~14 μm far infrared light transmitted. By analyzing the microstructure of the films, the refractive index changes of the films before and after moisture absorption were studied. The structure of the films was optimized by combining the optical film theory. On the basis of studying the stress of the film, the film thickness was optimized and the film firmness was improved. The average transmittance of the wavelength separation coating in the bands of 8~12 μm、12~14 μm are 97.1%, 90.1% and the reflectivity of 1 064 nm is 99.71%. The separation coating can meet the technical requirements of the imaging system for a long time in various military outdoor environments.
In this paper, the SiCx thin films with silicon quantum dots were prepared by RF and pulse magnetron co-sputtering and rapid thermal annealing. The films were characterized by grazing incidence X-ray diffraction, Raman spectroscopy, UV/VIS/NIR spectrophotometer and transmission electron microscopy. The effects of pulse sputtering power on the number, size and crystallization rate of silicon quantum dots in the films and the optical bandgap of the films were investigated. The results show that with the increasing of sputtering power from 70 W to 100 W, the number of silicon quantum dots increased; the size increased to 5.33 nm; the crystallization rate increased to 68.67%; the optical band gap reduced to 1.62 eV. When the sputtering power increased further to 110 W, the number of silicon quantum dots reduced; the size reduced to 5.12 nm; the crystallization rate of thin film reduced to 55.13%; the optical band gap increased to 2.23 eV. In this experiment, the optimized sputtering power was 100 W.
Based on push broom linear TDI-CCD imaging system, the principle of charge storage and signal transfer process was studied. According to the mechanism of saturation and crosstalk phenomenon induced by different continuous laser conditions, the crosstalk effects model was established. The modeling and simulation process for secondary spot was included. With an optical ray tracing model, the irradiant distribution of the imaging result was simulated when continuous laser jamming the satellite-borne infrared camera. Some general quality factors on imaging results were selected to qualitatively evaluate output images with given laser irradiant angles. The research indicates that the laser jamming result is different as the laser incident angle changes. At the given condition of 1.064 μm off-axis laser, when the laser incident angle differs from 2.86° to 2.89°, the secondary spot appears; When the laser power density is increased by 1~4 times, the percent of the crosstalk areas after laser jamming raises to some extent.
The analytical expression of the relationship between interference fringe spacing of target pattern and light time distribution of optical target reflection was derived by using the related knowledge of physical optics, Collins diffraction integral formula and the hard edge aperture complex Gauss function decomposition method. The quantitative relationship between interference field fringe spacing, optical aperture size and target reflected light time distribution of envelope peak number, peak to peak spacing and peak to peak ratio was discussed from the aspect of principle analysis, simulation and experimental. The results show that when the fringe spacing is about the size of the target aperture, the peak number of reflected light time distribution envelope is from single peak to multi peaks, and the peak to peak spacing and peak to peak ratio curves appear a maximum value. The estimation results of the aperture parameters can be deduced according to the change rule of parameters mentioned above, its accuracy is affected by the fringe spacing adjustable range.
The effect of the two-color laser wavelength on intense terahertz generation was studied based on the transient photocurrent model. Theoretical calculation proves that the terahertz signal will increase with the increase of laser wavelength, and this trend will not vary with the variation of the pulse intensity, the pulse duration, the laser phase and the intensity ratio of the two-color laser. The distribution of terahertz spectrum will not change with the variation of the laser wavelength. Furthermore, the influence of laser wavelength on terahertz generation is analyzed, and the physical mechanism of this effect is explained by the free electron density and the drift current density.
A separated guided-mode resonance filter was presented, which is consisted of a grating layer and two planar dielectric waveguide layers partitioned by an air gap. The optical responses of the grating under different parameters are analyzed by time domain finite difference method. The research shows that the resonance wavelength of the grating can be tuned by varying the height of air gap when the TM polarization incident wave is applied.Furthermore, the resonance wavelengths almost vary in a linear relation respect to the height of air gap. A narrow linewidth characteristic can be obtained by applying a shallow grating. The simulation results show that the wavelength can be tuned from 1 515 to 1 558 nm with the FWHM less than 0.6 nm.
In order to solve the problem that the rencent design method can only fit the small divergence angle situation, a novel method is prensented for disigning the beam laser splitter with large angle based on the Rayleigh-Sommerfeld Integral. In the design, firstly the target intensity distribution is modified with coordinate transformation and intensity adjustment, then the modified Gerchberg-Saxton algorithm is adopted to optimize the phase distribution of the beam laser splitter. Our method and original method are used to design the 5×5 splitter with 40°×40° diffraction angle. The simulation and experiment result shows that original method shows significant pillow distortion and uneven intensity distribution. In contrast, the sub beams of the splitter designed by our method are well-proportioned and the intensity distribution is even.
Developing super-resolution scanning and reconstruction method on the existing hardware can improve imaging performance and saving the cost to upgrade hardware. In this paper, a super-resolution scanning mode based on sub-pixel scanning is designed and a series of low-resolution images of the sample is acquired through modulating the position of the sample. Then, the point spread function derived by processing the edge spread function is employed to the image restoration of the low-resolution image series. Finally, super-resolution reconstruction algorithm based on POCS is used to reconstruct super-resolution images. The experiments conducted on the high-resolution X-ray microscope equipped with a 10 times optical lens coupling detector show that the contrast-to-noise ratio increases about 20%, the spatial resolution has been improved about 0.2 μ m (about 15%), the detail resolution can exceed the limits of pixel size of the detector and more details are seen than low-resolution images. The experiment's results illustrate that the super-resolution technique has great potential in improving the spatial resolution of the high-resolution X-ray microscope.
In order to get a more precise 3-D reconstruction, a peak detection method based on Gaussian fitting of trust region has been proposed in this work. Gaussian modeling is performed on the returned wave of single time channel of each frame, then the modeling result which can effectively reduce the noise interference and possesses a unique peak could be taken as the new returned waveform, lastly extracting its feature data by peak detection. The experimental data of aerial target is for verifying this method. This work concludes that the peak detection method based on Gaussian fitting reduces the extraction error of the feature data to less than 10%; ultilizing this method to extract the feature data and reconstruct the target makes it possible to realize the spatial resolution with a minimum 30 cm in the depth direction, and improve the 3-D imaging accuracy of the Streak tube imaging lidar concurrently.
A sky brightness photometer with a side-baffled structure, which adopts multibaffles to suppress diffracted stray light layer-by-layer in the inner field of view, is proposed. In addition, specially designed upper baffles block both scattered and diffracted stray light in the outer field of view. A mathematical model is established to simulate the baffles, and calculated results show that the field of view of the photometer can be designed to be 3.5~10 solar radii by optimizing the geometric parameters of the baffles. The stray light in the full field of view can be suppressed effectively to less than 10-8 of the mean solar brightness. Compared with the High Altitude Observatory, which has a sky brightness monitor with a field of view of 4~8 solar radii and a stray light level of 10-7 of the mean solar brightness, the proposed photometer expands the observable field of view and improves the stray light suppression level by over an order of magnitude.
Flash X-ray diffraction imaging system based on flash X-ray generator (TD-450S of Scandiflash AB) and imaging plate was designed to measure microscopic response in shock wave compression studies. Due to intense Bremsstrahlung radiation, continuous X-ray generator and HPGe detector were used to regulate diffraction optical path. Diffraction signal of LiF single crystal was recorded using flash X-ray tube with molybdenum as the anode material under ambient conditions and shocked state. Results show that flash X-ray diffraction imaging system described here is useful for examining structural changes in shock compression experiments and temporal resolution is 25 ns.
This paper has proposed ultra-lightweight design and optimization for a primary mirror of a space camera with Φ210 mm aperture to improve surface quality and reduce its launching cost. Three-point support on mirror back is selected as the support method and the locations of the supports are carefully studied. Through the topology optimization, the mass distribution of the back of the mirror and the distribution of the removable part are obtained. The initial structure of mirror is light weighted on its back applying triangular hole light-weighting method. Multiple-object optimization which combines mass and surface figure error along X-axis(detection direction) as optimization object under constraint of surface figure error along Z-axis(machine direction) is carried out on the initial structure of mirror. Finally, a mirror with RMS(Root Mean Square) as lowas 0.18 m with X-axis straight down and 2.38 mm with Z-axis straight down is achieved. The mirror weights 0.568 kg, surface density of it is as low as 16.9 kg/m2. And the primary frequency of X,Y,Z are more than 500 Hz. Through the FEM analysis and vibration test, verify the good mechanical properties of the mirror structure. The results show that the optimal design method of this paper is reasonable for the lightweight mirror.
A novel lenticular screen of double-sided grating applied in low-crosstalk naked-eye 3D display is designed. Linear concave free-form gratings, with their number of grating lines equal to the number of horizontal sub-pixel on the screen display panel, are fabricated into the incident surface of the lenticular screen, and convex free-form slanted gratings are fabricated into the opposite surface. Design formulas for grating free-form surface and grating parameters are deduced based on the principles of naked-eye 3D display and geometrical optics. The grating parameters are calculated using MATLAB and grating model is established by modeling software Solidworks. The results show that the image crosstalk in 6-view naked-eye 3D displays, using double-sided lenticular screen, is 0.068% at the best viewing angle by selecting optimal parameters, which is lower than a conventional one by 2 orders of magnitude. The image crosstalk remains basically unchanged within the range of the viewing distance of 2 000 mm~3 000 mm.
A photonic method for instantaneous microwave frequency measurement based on stimulated Brillouin scattering was proposed. The unknown radio frequency signal is modulated by intensity modulator and then it is considered as pump light. The signals generated by vector network analyzer are modulated by phase modulator and then they are considered as sweeping signal light. When the phase matching condition is satisfied between pump light and sweeping signal light, the stimulated Brillouin scattering occurs and the conversion from phase modulation to intensity modulation selectively is achieved. The frequency of unknown radio frequency signal is ultimately measured. Experimental results demonstrate that the measurement ranges from 0.5 GHz to 27 GHz and the maximum measurement error is less than 20 MHz.
The coherent superposition of incoming linearly polarized light and radially polarized light can generate the three-dimensional (3D) polarization optical field at the focal spot of a high NA microscopic objective. In addition, arbitrary 3D polarization orientation of focusing optical field can be obtained by adjusting the intensity ratio between two incoming beams and rotating the polarization orientation of the incoming linearly polarized light. Based on the vectorial diffraction theory, a simulation model was developed to theoretically verify the feasibility of the proposed control method of 3D polarization, and to evaluate the 3D polarization optical field generated from this control method. After experimental test on the basis of theoretical analysis and building the practical optical setup, the feasibility of the method was confirmed. It was also disclosed that this method and the corresponding optical path is simpler and easier to implement compared with other existing 3D polarization control methods.
A polarization converter that uses metasurfaces composed of cross deformable structure is proposed. Ultrawideband 90° polarization rotation is obtained in the reflective mode. Reflectance of the cross-polarized wave is above -0.2 dB while co-polarization wave is blow -12 dB in range of 8.4-20.7 GHz. The cross-polarized reflectance is greater than -0.03 dB at the resonant frequency points, and the co-polarized reflectance reaches -60 dB. That is, almost complete cross-polarization conversion be achieved at the resonance frequency points. The relative bandwidth is 84.5% with average orthogonal polarization conversion ratio (PCR) of 96.7%. In addition, the metasurface polarization converter is fabricated on FT5880 substrate. The experimental results show that the cross-polarized reflectance is greater than -1 dB in the operating frequency band and the co-polarized reflectivity is less than -10 dB. The experimental results are in good agreement with the simulation results, which verifies that the metasurface can realize the cross-polarization conversion of the linearly polarized electromagnetic wave in the ultra-wide frequency band. The ultrawideband conversion metasurface has the advantages of high conversion efficiency and simple geometric structure. The similar model can be extended to terahertz or even visible light.
The spectral reflectance of reduced graphene oxide and graphene oxide from near UV to near infrared was tested, and its complex refractive index was calculated by Kramers-Kronig relation. Then the relative errors were analyzed by inversely deducing reflectance and spectral analysis. Finally, absorption and extinction efficiency were calculated by T-matrix method in order to analyzing its extinction and absorption properties. The results show that the error between inversely deduced reflectance and the measured one are at 10-6, and its spectral absorption characteristics are coincided with the image part of complex refractive index. The absorption and extinction ability of reduced graphene oxide is strong in visible and NIR, but weak in UV. The absorption and extinction ability of graphene oxide is strong in UV and visible, but weaker rapidly in NIR. Therefore, reduced graphene oxide and graphene oxide both can be used as wide-band photoelectric absorption or extinction material, but the performance of reduced graphene oxide in near UV and graphene oxide in NIR need to be improved.
The effect of environmental factors on Secondary Organic Aerosol (SOA) formed from hydroxyl radical (OH·) initiated photooxidation of isoprene were investigated by using a home-made smog chamber. The size distribution of SOA particles from the above reaction were measured using Aerodynamic Particle Sizer spectrometer (APS). The effect of radiation time, reactant concentration, and CH3 ONO concentration on SOA formation from isoprene were evaluated by performing photooxidation experiments under varying conditions. Experimental results showed that aerodynamic diameter for SOA detected in isoprene photo-oxidation experiments was predominantly in 0.4 mm~1.4 mm, which were in the form of fine particles with diameters less than 2.5 μm. These fine particulate matters are more easily deposit in the lung of the human being, and do great harm to the health. This paper also highlighted that both the number and mass concentration of SOA particles were increasing with the prolonging of the radiation time, the increasing of light intensity, and the increasing of the reactant concentrations. The results could provide useful information to infer possible emission sources of atmospheric particles in future field measurement.
Based on laser induced bioluminescence technique, ultraviolet 355 nm and 266 nm laser were used as excitation light source respectively to construct a model of biological aerosol fluorescence radar monitoring system. The effects of different excitation bands, ozone absorption and solar background light on lidar fluorescence detection are comprehensively considered. The system performance is numerically simulated and analyzed. The simulation results show that the system with the laser excitation of 266 nm band, is strongly affected by the surface ozone, so the effective detection range at daytime is very limited. When the system signal-to-noise ratio is 10 (SNR=10), ozone concentration 50 ppb, the maximum detection range is about 300 m. While at the night time conditions, the detection range is about 450 m. For the excitation of 355 nm, ozone has little effects on the detection performance of the system, its detectable range up to 750 m at night. Solar background light effects on 355nm quite large at the field of view 0.5 mrad, where the effective detection range is about 330 m. In order to reduce the influence of daytime background light, the field of view of the telescope was compressed to 0.3 mrad, and the filter with 50 nm bandwidth was used. The detection range can be up to 480 m at this case. In the conclusions, the excitation of 355 nm band should better be used in night time measurement, while excitation band of 266 nm can well inhibit the effects of solar background light, so as to realize the effective detection of biological aerosols during the day.
In order to enhance the Signal-to-Noise Ratio (SNR) of Differential Column Image Motion lidar (DCIM lidar) detetion, a hybid denoising method which combines Ensemble Empirical Mode Decomposition (EEMD) and singular value decomposition(SVD) is proposed.The multilayer mode components are obtained from EEMD firstly. The difference of cross-correlation coefficients among these mode components is then utilized to determine the main noises which should be removed. The residual noises contained in mode components are identified by SVD and then the useful signal is extracted. Both the EEMD-SVD and EEMD methods are used to denoise the simulation signals and measured DCIM lidar signals. When the standard deviation of simulated noises is between 0.05 and 0.2, the signal-to-noise ratio(SNR) of retrieved turbulence profile with EEMD-SVD denoising is increased by 2.718 7 dB to 6.921 5 dB and the SNR of corresponding EEMD method is increased by 0.168 4 dB to 3.555 4 dB compared with the retrieved profile without denoising. Turbulence profiles retrieved from the undenoised and denoised DCIM lidar measurements and radio-sounding balloons are also compared at two typical time periods. It is found that the maximum SNR of turbulence profiles can separately be increased by 2.526 5 dB and 2.155 6 dB for EEMD-SVD and EEMD method compared with undenoising retrieval profile. The results indicate that the noise reduction effect of EEMD-SVD is superior than EEMD,which it is able to identify and reduce the noises more effectively.The SNR of original signal is greatly improved through EEMD-SVD method, thereby the retrieved atmospheric turbulence profile is achieved more accurately.
In order to realize multi-point current monitoring on power line, a multipoint all-fiber current sensor was described on the principle of time-division multiplexing using ordinary silica fibers and a fiber loop. The multi-channel sensor system was used to share a set of light source, detection equipment and digital signal processing system, which can improve the utilization rate while saving cost. In experiment, a dual-channel fiber current sensor structure was used to measure the current at the same time in the two different points. The direct current of a measurement point ranged from 0 A~600 A and the direct current of another survey points ranged from 0 A~1 500 A. The experimental data is fitted with linear fitting. The results show that the suitable cycle number K is 8 and the current sensitivity of K=8 was approximately 3 to 4 times as high as when K=2. The dual-channel fiber current sensor had good linear responses for both channels between the output signal ΔP and the current I. The channels are independently affected by the current, they require separate calibration.
In order to study the effect of particle radius、particle concentration and charge number of charged dust in dusty plasmas on the performance of quantum communication, according to the Mie scattering theory, the light scattering cross section of single charged dust particle was obtained. Based on particle concentration, the extinction cross section of particles was calculated, the mathematical model of the link attenuation was established, and the relationship between the characteristics of charged particles and quantum entanglement was proposed. Aimed at the depolarization channel, when the number of charged particles adsorbed by a dust particle is 50, the quantitative relation among the dust particle radius and the particle concentration, the channel capacity and the quantum bit error rate was given. The simulation results show that when the transmission distance of quantum signal is 10km, particle concentration increases from 1×1010 m-3 to 10×1010 m-3, the channel capacity decreases from 0.672 6 to 0.107 5; the dust particle radius increases from 0.1 μm to 10 μm, the quantum bit error rate increases from 1.334×10-3 to 5.309×10-3. It can be seen that the radius and concentration of charged dust particles in the plasmas have a significant influence on the performance of free space quantum communication. Therefore, in order to ensure the reliability of quantum communication, the various parameters of the communication system should be adjusted according to the conditions of the detected plasmas environment.
In the long-range Modulating Retro-Reflector (MRR) communication system, the retro-reflective signal is weak and difficult to be detected. In this manuscript, a novel detection mode of MRR communication based on speckle technology is proposed, which can detect small fluctuation of the light from the modulator. The novel detection mode is simple, modular, inexpensive and suitable for low speed MRR communication. System design as well as the detection principle is descripted. The experiment part was completed the transmission of 1.3 kHz digital signal on 60m distance and analog voice transmission on 330 m distance.
In order to improve indoor localization accuracy and realize three dimensional positioning, a high precision three dimensional positioning system for visible light communication based on ant colony algorithm is proposed. This system adopts Code Division Multiple Access (CDMA) modulation technology and solves the inter symbol interference between multiple signal sources in visible light communication. In the system, the ID information related to the geographical position of LED signal sourses are loaded directly to the LED drive circuit through direct spread spectrum modulation. After the optical signal is amplified, filtered and sampled, the ID information and the intensity attenuation information can be recovered according to the orthogonality of the spread spectrum code in the Code division multiple access modulation technology. After calculation, the signal intensity attenuation factors are obtained from different LEDs and the global searching property of ant colony algorithm is used to determine the optimum location point. The error correction factor is introduced and the parallel search of ant colony algorithm is used to correct the deviation of the intensity attenuation factors.The simulation results show that the positioning accuracy of the algorithm are 2 cm, 4 cm, 8 cm respectively when the condition of signal-to-noise ratio are 30 dB, 20 dB and 10 dB. When the computation accuracy is higher than 45 cm, the searching efficiency of the ant colony algorithm is higher than that of the ergodic method. After correcting the attenuation factor of light intensity, 100% of test points can reach the positioning accuracy of 5 cm under the signal-to-noise ratio condition of 10 dB. The experimental results show that under the condition of 20 dB signal-to-noise ratio, the positioning error of 92.59% of test points is 8 cm and 96.29% of the test points have three dimensional localization error of less than 10 cm. The maximum localization error is 11.30 cm. After error correction, 96.2% of the test points achieve the precision of 3 cm and 61.6% of the test points achieve the precision of 2 cm. The algorithm reduces the computation of the optimal localization solution and achieves high-precision positioning.
A scheme of microwave photonic radar architecture based on mutual optical fiber dispersion was proposed, including generation and compression of wideband linear frequency modulation signal. Linear frequency modulation was generated at the transmitting end by using the mutual dispersion fiber. At the receiving end, the radar echo was modulated by the Mach-Zehnder modulator onto the pre-chirped optical signal, and that was further dispersed in the optical dispersion fiber. Finally, the pulse compression signal of the target echo can be obtained at the detector end. The linear frequency modulation signal can be directly compressed by the proposed technique in the optical domain without digital signal processing during pulse compression process, and the pulse compression ratio could be further programmable. The numerical simulations and experimental results showed that the proposed scheme can effectively perform the pulse compression of the LFM in the optical domain. A linear frequency modulation signal with temporal width of 1.2 ns, bandwidth of 3.2 GHz in the C-band was generated by the experiment, and that was compressed to 0.09 ns through the mutual dispersion fiber. The pulse compression ratio is up to 13.3.
In order to extract human action features effectively under the panoramic view, we propose a novel PMK algorithm with adaptive partitioning based on the original shape context feature matching algorithm.First we combine optical imaging principle with the projection characteristics of human body under the panoramic view, and utilize the second moment to correct the principal axes direction of human contour. Then do the uniform sampling with the edge points, and extract the shape context feature at each sample point. In the process of matching sampling points, through the analysis of the distribution characteristics of sampling points in the high dimensional feature space, we introduce adaptive partitioning to Pyramid Match Kernel (PMK) algorithm to improve the convergence strategy. According to the range of data points at each dimension, the improved algorithm can adjust convergence coefficient the data adaptively, thus achieving the consistent convergence speed of the points set at each dimension. Finally we perform an experiment on fall indoor detection to verify the reliability of the proposed algorithm, and the K-means clustering algorithm is used for classification,the recognition rate can reach 92.9%. The results show that the improved feature extraction algorithm can provide the guarantee for the stability of the intelligent monitoring system.
Considering that infrared polarization and intensity image contain common information and their own unique information, a method of image fusion based on Dual-Tree Complex Wavelet Transform and sparse representation was proposed. Firstly, the high and low frequency components of source images wereobtained by using Dual-Tree Complex Wavelet Transform, and the high frequency components werecombined by absolute maximum method. Secondly, a joint matrix was constructed by low frequency components, and a redundant dictionarywas acquired by using K-singular value decomposition to train the matrix. Based on the dictionary, the sparse coefficient of low frequency component was calculated, and the common information and unique information werejudged by the location of non-zero value of the sparse coefficient,and two kinds of information was merged by proper fusion rules. Finally, the fusion image was obtained by performing inverse Dual-Tree Complex Wavelet Transform on the fused high and low frequency components. The experimental results show that the proposed fusion method can highlight the common information of source images and keep their own unique information, and the fusion image own higher contrast and clearer details.
Two channels of photon arrivals are applied to construct fiber pseudo-random depth acquisition photon counting system. In order to find the method to diminish the depth error, Gauss function is used to model laser echo pulse. By calculating the probability density function,the time walk effect is introduced and the Cramer-Rao lower boundary is modeled. The theory model proves that with the growing signal energy, the depth error decreases sharply firstly and then rises and the longer code length can bring smaller depth error. From the theoretical part, using the cumulative distribution function to generate photon arrivals and simulate the pseudo-random depth acquisition photon counting system, Monte Carlo simulation results are larger than the numerical modelling,which agree with Cramer-Rao lower boundary. 17 experimental tests also converge to the presented boundary model in this paper. It has been proven that fluctuation of the number of detected photon counts in the laser echo pulse caused by different target reflection leads to the depth drift of Correlation Function on pseudo-random depth acquisition photon detection process. Finally, numerical fitting function is used to determine the relationship between the depth error and the photon counting ratio. Depth error is calibrated by substituting the measured photon counting ratio into numerical fitting function. The corrected depth RMSE is decreased to 1 cm.