2015 Vol. 44, No. 2
2015, 44(2): 401-406.
A novel scheme was proposed to generate sextupling-frequency and octupling-frequency optical millimeter wave by using external modulator technique. Based on the nonlinear transmission characteristics of one Mach-Zehnder modulator (MZM), the third-order or fourth-order sideband could be enhanced by adjusting the bias voltage and the modulation voltage of MZM, and thus generated successfully sextupling-frequency or octupling-frequency optical millimeter wave. Walk-off effect could be prevented by only modulating the signal on one of the third-order or fourth-order sidebands. Numerical results demonstrate that the proposed scheme generate 60 GHz millimeter wave with only 10 GHz and 7.5 GHz frequency modulated signal, which greatly reduces the frequency of the modulation signal, increases the up-conversion coefficient, and reaches the transmission distance to 160 km without increasing the power penalty distinctly. Compared with other multiple frequency techniques, the proposed system has distinct advantages of simple configuration, low dispersion effect, long transmission distance due to only using one Mach-Zehnder modulator.
2015, 44(2): 407-412.
The temperature influence of each parameter in infrared detection imaging system was analyzed in the paper.Benefitting from infrared chalcogenide glasses less index temperature coefficient and catadioptric configuration excellent thermalization performance, a catadioptric MWIR detection thermalization imaging system by Code-v optical design software was presented.The working wavelength is 3.7-4.8 um,effective focal length is 109.7 mm,field of view was 6.4,F/# is 2.0 and cold shield efficiency was 100%.The design results indicate that the image quality in-40 ℃and 60 ℃have little changed, which compared with in 20 ℃.The system is compatible with staring focal plane array MWIR detector which has a format of 320256 and the pixel pitch of 30 um.
2015, 44(2): 413-418.
Using the infrared thermopile array in the system as light receiver, with miniaturization and meet the requirements of certain spectral working range and spectral resolution as the system design task, according to the theory of spectrometer and the aberration, a mid-infrared plane grating spectrometer based on the structure of Czerny-Turner was designed. A double off-axis parabolic reflector was used as the fore-optical system to reduce the size of other optical elements, the toroidal focusing mirror was adopted to correct astigmatism. The ZEMAX software was applied to design, optimize and analyze the fore-optical system, imaging system of the spectrometer. Final analysis results show that the spectrometer system working range from 8.04 um to 13.96 um, spectral resolution is better than 80 nm, F number is 2, optical size of the system is 150 mm200 mm70 mm, and satisfy the design task.
2015, 44(2): 419-427.
Infrared decoy is one of the most common interference equipment in infrared countermeasure, which intends to delude and interfere with infrared guided missile for hiding the truth and giving a false impression. The mechanisms of infrared decoy interfering with infrared guided missile were analyzed. The moving and radiation models of airborne infrared decoy were built. According to the interference shortage of airborne infrared decoy, a combat operational method of infrared decoy was obtained. The method was able to synthetically take into account many factors such as different interfered missiles, dispensing time, dispensing direction, dispensing number, dispensing interval time and fighter's elusion. The combat operational method provides a basis for fighter against infrared guided missile, so that to perform airborne infrared decoy's combat effectiveness completely and enhance fighter combat survivability.
2015, 44(2): 428-431.
In order to realize the autonomous guidance, target detection and classification/identification for extended air defence(EAD) and ballistic missile defence(BMD), a concept was presented to integrate both imaging infrared and imaging flash LADAR sensor into a compact seeker setup using the same receiver aperture and the results of optical design in this system was demonstrated. The IR sensor detected the scene, discriminated the reentry vehicle and cued the LADAR to the selected object. The LADAR sensor illuminated the selection with a high power laser pulse and the reflected light will be imaged through the receiver optics onto the focal plane. The image was then sampled in snapshot mode and 3D-information (angle-angle-distance) was generated. It used the surface of dichroitic beam splitter as a dichroic surface, to achieve a laser receiver and infrared imaging of the total diameter, saving system space. Whereafter, the way of calculating the parameters of optical system was illuminated and the results of optical design with CODE V was given out. The optical system designed in this paper can fulfil the requirement of the system scheme owing to its good quality.
2015, 44(2): 432-437.
Nitric oxide (NO) is one of the most important gas species in hypersonic vehicle's flow field, and has significant influence on infrared radiation transferring. Therefore, it's necessary to acquire an efficient algorithm to calculate NO's equivalent band width. According to HITEMP 2010, the distribution characters of spectral lines and absorption coefficients of NO in infrared spectrum 1-15 um were studied. Then an improved k-distribution model was proposed and the equivalent band width was solved by applying Gauss numerical scheme. Besides, the effects of absorption coefficient thresh on both g-k curve and equivalent band width were researched and the criteria of selecting the thresh was put forth. Experiments show that the results of the proposed algorithm agree with the ones obtained by line-by-line calculation, and the relative errors were less than 5%. When compared with the wide band k-distribution algorithm, the proposed algorithm has better computing efficiency and moreover it has better accuracy while using a proper thresh.
2015, 44(2): 438-444.
At present, linear regression model is often used to estimate typhoon inner core wind field. But the fitting effect of typhoon inner core wind speed based on linear regression was bad. Based on infrared satellite cloud image, radial basis function neural network (RBFNN) and partial differential equation(PDE) were used to build a model between typhoon inner core speed and cloud image's gray value. Firstly, typhoon's eye wall was extracted by using PDE which based on geodesic active contour model from the infrared satellite cloud image and the eye wall's space position and brightness are obtained. Then the maximum wind speed near typhoon center which was recorded by typhoon yearbook was used to build a model between typhoon inner core's speed and cloud image's gray value by RBFNN. The experimental results show that the proposed algorithm improves the fitting effect of typhoon inner core's wind speed, and the overall performance of the proposed algorithm is better than tradition method of linear regression.
2015, 44(2): 445-448.
A new jamming technology of atomized screen was studied to overcome the shortcomings of existing broad band jamming technology, such as the short acting time and the narrow jamming wave band. The theory of multiband jamming and the formula of atomized screen was introduced. The jamming effect on multiband such as visible light, laser, infrared, millimeter wave radar and centimeter wave radar has been tested. Necessary theory and experimental data were provided for the application of this technology. The experimental results show that visible light and laser could be shielded when the foam diameter of atomized screen was 2-3 mm and the thickness was 50 cm. Under the same conditions, the transmission of infrared was less than 5%, and the good screening effect was achieved on millimeter wave radar and centimeter wave radar. The high efficiency interfering time was above 20 min. The study shows that the new atomized screen was a potential wide frequency passive interfering medium.
2015, 44(2): 449-454.
The degree of polarization of backscattering laser, which is scattered from several typical targets, was measured and analyzed. Basing on the description of detection laser with Stokes vector, experimental setup of laser detection for polarization characteristics of typical targets was designed using the transceiver integration; the degree of polarization of backscattering laser of several typical targets was measured under the conditions of different angle of incidence laser, different roughness parameters and different materials of target surface; the measurement data of degree of polarization was analyzed after double Gaussian fitting on the basis of foregoing experiments, two conclusions that the degree of polarization of backscattering laser highly fits the double Gaussian function and targets with different attributes can be distinguished using the degree of polarization of backscattering laser were achieved at last.
2015, 44(2): 455-460.
Based on the rate equation model of end pumped alkali vapor laser, the characteristics of alkali vapor laser in different buffer gas environments were studied. The temperature vs output power of alkali vapor laser in different gas environments were obtained by optimizing the parameters of output coupler reflectivity and gas pressure. Results show that the optimal output power and operating temperature are improved and decreased with the increase of mixing rate in hydrocarbon DPAL respectively. And the optimal operation states of hydrocarbon DPAL can be described by its quasi two level operation curve. Moreover, the helium pressure in hydrocarbon free DPAL can be reduced largely by using 3He gas. Besides by using 3He gas, the output power can be improved for hydrocarbon free Rb-DPAL but not for hydrocarbon free K-DPAL. The simulated results have a good matching with reported experimental results, which will supply significant reference for further experimental research.
2015, 44(2): 461-465.
The wavelengths of 1 064 nm, 532 nm and 355 nm single-pulse laser were used to irradiate the polysilicon to study the interaction between different wavelengths of laser with polysilicon material systematically. The damage patterns of the polysilicon under the three laser wavelengths were studied. Experimental results shows that: with other parameters unchanged, the damage threshold decreases with the laser wavelength becomes smaller and it has linear relationship with laser wavelength; At low energy density level, the model of the interaction between the wavelength of 355nm laser and material is photochemical model based on the photochemical-photothermal common mode of action and it is light and heat model for other wavelengths; When the laser energy density is in low level, the interconnected regular hexagonal microstructure appears in the irradiated area. The center of the hexagon presents circular convex status. It is generated by nature of lateral flow fluctuations of the liquid and it has relation with the roughness of the polysilicon surface.
2015, 44(2): 466-470.
The third-order optical nonlinearities of lead and palladium naphthalocyanine compounds were studied comparatively using Z-scan technique with ns laser pulses at 532 nm. The experimental results showed that the two kinds of naphthalocyanine compounds also indicated strong nonlinear absorption (reserve saturable absorption) and nonlinear refraction(self-focusing) characteristics. Nonlinear absorption coefficient for lead and palladium naphthalocyanine compounds by theroetical fitting were 6.5410-10 m/W and 3.9010-10 m/W, reprectively. Nonlinear refractive index coefficient n2 were 1.6810-10 esu and 8.0410-11 esu, reprectively. The second-order molecular hyperpolarizabilities were 3.4410-28 esu and 2.5710-28 esu, reprectively, which were approximately about 105 order in magnitude than that of CS2(4.3210-33 esu). The experimental results show that the lead naphthalocyanine compound exhibits great optical nonlinearities than palladium naphthalocyanine compound results from the heavy metal atoms as central atom of naphthalocyanine lead compounds enhance the optical nonlinearities of naphthalocyanine compounds.
2015, 44(2): 471-476.
In the hardware-in-the-loop simulation, Laser Target Echo Simulator(LTES) is one of the most important equipment in the Laser Guidance Weapon System (LGWS). The model for the laser pulse features in time domain is a key technology in the LTES. A model of the laser pulse broadening in turbulent atmosphere was constructed. In the model, atmosphere was treated as multi-layer medium with different refractive index. The influence of medium with multi-layer for the laser pulse broadening mechanism, which is propagated in the multilayered medium, was analyzed. Then, the model of the target reflection was also constructed according to the characteristics of the target reflection. Two models were demonstrated by simulation. Moreover, the maximal pulse broadening of 10 ns was obtained when the distance of 10 km, the laser divergence angle of 1 mrad and wavelength of 1 064 nm was assumed. The result of planar target was calculated in final. This model can be applied in the real laser radar echo simulation.
2015, 44(2): 477-481.
The energy of the laser milling was input to the sample surface in the mode of local heat, which can cause the uneven and unstable of the temperature field during the laser milling. Take the laser milling on the Al2O3 ceramic materials for an example, the article set up the 3D finite element simulation model of the laser milling temperature field. The heat moving of the laser milling was simulated by the APDL language of the ANSYS software. The result of the simulation shows that the temperature of the center spot of the back track is higher than the front track with the process of the laser milling. The greatest temperature gradient located on the sample edge area in the scanning direction changes. The maximum temperature in the simulation results and literature experimental results for comparison are in good agreement.
2015, 44(2): 482-485.
In order to measure wind field of troposphere and stratosphere, a mobile Rayleigh Doppler wind lidar based on Double-edge technology was developed in Hefei, China. The detection range of the lidar is designed to cover altitudes from 10 km to 40 km with height resolution of 100m (below 20 km) and 500m (above 20 km). In the summer of 2011, wind field measurements were carried out in Urumqi (42.1N, 87.1E), the stratospheric quasi-zero wind layer, where wind velocity is almost 0 m/s, was successfully observed. Some typical results of the wind field at night were given. The quasi-zero wind layer's bottom was found stabled at about 17-18 km height. However, the thickness of the quasi-zero wind layer would increase with time until about 0-3 a.m. Beijing time, gaining its maximum, and then decrease. The maximum thickness could be more than 15 km and minimum thickness just 2-3 km according to the author's measurements. This phenomenon could be a result of change of the ultraviolet radiation's intensity emitted to the stratosphere at night. The decrease and increase of the ultraviolet radiation's intensity were different at different latitude at the same time, and that would lead to a change of temperature gradient in the stratosphere, which was pointed from lower latitudes to higher latitudes. Then the temperature gradient passes the affection to the stratosphere circulation, which was part of the quasi-zero wind layer, and eventually leads to this regular increase-decrease change.
2015, 44(2): 486-490.
In order to study the propagation and focusing properties of partially coherent sinh-Gaussian (SHG) beams through an astigmatic lens, the analytical expression of the intensity was derived based on the transmission formula of partially coherent beams, and the analytical expression of the beam width, the far-field divergence angle and the M2 factor were deduced, the intensity and the beam width were calculated and analyzed. It is found that the intensity distributions of focused partially coherent ShG beams depend on the astigmatic coefficient C6, spatial coherence parameter, decentered parameter a, Fresnel number Nw and position (x, y, z) in general. The astigmatism results in a difference between the beam widths in the x and y directions, but the M2 factor is independent of the astigmatism and decreases as the coherence increases and the decentered parameter decreases. The spatial beam shaping is achievable at the geometrical focal plane and other positions by properly varying the astigmatism and spatial coherence.
2015, 44(2): 491-496.
The temperature thermal model of crystal was built under the condition of thermal isolation of the end face and constant peripheral temperature, so as to calculate temperature field of pulse LD end-pumped Nd:YAG crystal. Based on the function of temperature of the laser crystal depending on the thermal conductivity, the thermal model of heat conduction equations were solved by methods of the secant method. The numerical values of the temperature field of the pulse LD end-pumped square cross section Nd:YAG crystal with variable thermal conductivity was obtained. Then the internal temperature field distribution was calculated under different of super-Gaussian beam with different orders and pump spot sizes. The results show that when the average output power of diode laser is 60 W, and the neodimium doped yttrium aluminum garnet with 1.0% neodymium-ion doped mass fraction, the third order super-Gaussian radius of incident light is 400 um. When the transient temperature field of Nd:YAG crystal, which size in 4 mm4 mm8 mm, reaches thermal dynamic equilibrium state, the maximum and minimum temperatures are 364K and 337K respectively. The research methods and results can also be used to analyze other time-varying thermal problems in laser systems, and will play theoretically a directional role in solving thermal problems in laser systems.
2015, 44(2): 497-502.
To accurately measure the amplitude and duration of exciting pulse for calibration of a high-g accelerometer, the measurement method of the exciting pulse was studied in this paper. Based on the analysis of the principle of Laser Doppler, a grating laser velocimeter was designed. A local mean decomposition algorithm based on polynomial fitting and Hilbert transform was put forward to process the Doppler signal with zero shift. The acceleration pulse was calculated using the above algorithm and the uncertainties of measurement of the amplitude and duration were analyzed and calculated. The expanded uncertainties verified by experiments are 3% for the amplitude and 4.8% for the duration with a coverage factor k =2. This method is effective for pulse measurement and the measurement precision met the requirements of ISO16063-13(2001).
2015, 44(2): 503-507.
There are many interference fringes and speckle on the screen of laser projection display system during to the strong coherent characteristic of laser. In order to eliminate the influence of interference fringes and speckle on image quality, temporally averaged patterns was obtained by rotating a new kind of diffuser called Engineered DiffuserTM. First, the reason of speckle formation and the theory of speckle suppression through temporally averaged patterns were introduced. Then the differences on structure and function between traditional diffuser ground glass and Engineered DiffuserTM were analyzed. Finally, the speckle suppresion experiment by rotating Engineered Diffuser in laser projection display system was established. The effect of speckle suppresion was tested by comparing other speckle suppression methods. Experimental results indicate that the speckle contrast is weakened to 3.08%. The patterns quality is good and has no interference fringes. It can satisfy the laser projection display system requirements of small volume, simple practice and so on.
2015, 44(2): 508-512.
The Al and Fe content in cement is one of the bases of classification and quality evaluation of cement. Laser-induced breakdown spectroscopy (LIBS) was used to quantitatively analyze the Al and Fe content in cement samples. According to the intensity of spectral lines and SNR,it was confirmed experimentally that the laser energy 30 mJ and delay time 1 us were the best experimental parameters for single pulse laser induced breakdown spectroscopy to detect the Al and Fe in cement. Internal standard method was used to establish the calibration curve,the correlation coefficients of Al and Fe were 0.998 and 0.997. Using cycle inversion method to detect the accuracy of quantitatively analysis,it was found that the maximum relative error of Al and Fe were 2.32% and 5.11% while the average relative error were 1.34% and 2.40%. Experimental results show that the use of laser-induced breakdown spectroscopy on quantitative analysis of Al and Fe is feasible.
2015, 44(2): 513-518.
A novel method for multi-plane imaging in digital holography was proposed. A non-conjugated quadratic distorted phase factor was used to act on the experimental recorded digital hologram and the reconstructed images at multiple planes would be obtained simultaneously by only single Fresnel diffraction. It was firstly introduced the principles for multi-plane imaging using non-conjugated quadratic distorted phase factor and the effectiveness of the proposed method was verified by experiments. It needed single digital hologram of objects at different positions and multi-plane images could be rebuilt at arbitrary reconstruction distance by selecting the suitable parameters according to this paper's theory. The root mean square error(RMSE) and peak signal to noise ratio(PSNR) were used for evaluation standard of the image quality and reconstructed images at different positions were compared. Digital focusing at multi-planes can be achieved simultaneously without the symmetric optical design on the premise and the depth of focus for the Fresnel digital holographic reconstruction images can be extended.
2015, 44(2): 519-522.
To further explore enhanced Raman scattering of surface metallic photonic crystal fiber, a model in FDTD of flat structure was built, using observed phenomenon of super-transmissive Raman scattering theory. In the photonic crystal surface of metal terahertz electromagnetic experiments, it is obtained that the greater energy of incident wave, excitation of surface plasmon resonance is more, surface metal can be achieved in the reinforcing effect which is greatly enhanced; Raman scattering effect is obvious by terahertz band, and the effect of the absorption spectrum and fluorescence effects are relatively small, which can significantly improve the sensitivity and resolution.
2015, 44(2): 523-527.
For the purpose of studying the attenuation characteristics of terahertz wave in dust atmosphere, using the Mie scattering theory, the influence of the dimension parameters of particles on the scattering efficiency factor was simulated, and the value of scattering phase function under different scattering angles, in the condition of single scattering were calcutated. Besides, the relationship between the attenuation of terahertz wave per unit distance in dust particles with certain size distribution and the visibility was simulated. In addition, the multiple scattering of terahertz wave in sand-dust condition was simulated, using Monte Carlo method. And the energy losses of terahertz wave in different visibilities and different dust types were discussed. The results show that the attenuation of terahertz wave is mainly determined by the dimension parameter, in the condition of single attenuation; and the multiple scattering must be taken into account when visibility is low. The results provide a reference point for the application of terahertz wave in those areas such as environmental monitoring, soot and wind-blown sand detection.
2015, 44(2): 528-533.
It was experimentally investigated that the laser spot size on photoconductive antenna (PCA) gap could have a great influence on terahertz (THz) generation. Moreover, the simulation on THz generation influenced by the laser power density was carried out, which was agreed well to the experiments. It is well demonstrated that the increase of laser power density on PCA gap can enhance THz generation. However, the intensity of THz radiation reached saturation while the laser power density exceeding a certain value. The laser power density increased further by focusing harder, but the THz radiation was getting weaker due to the smaller laser excited area on PCA gap.
2015, 44(2): 534-538.
The design of a hollow-core terahertz photonic crystal fiber (PCF) based on poly methylmethacrylate (PMMA) is reported in this paper. THz wave propagates inside the core large hole and the surrouding four cladding layers with small holes can confine THz wave propagation. By simulation in software COMSOL, the leakage loss of the designed PCF is found to be lower than 0.1 dB/m at 0.6 THz which is low at terahertz band. Similar to the radiation theory of metallic waveguide, the PCF can also be used as antenna to radiate energy. Its radiation characteristics are simulated. The simulated input reflection coefficient is less than-25dB and the directivity of the antenna is greater than 20dB. The half power beam width is about 13 degrees.
2015, 44(2): 539-543.
A detectable intermediate frequency current signal is generated by mixing the signal beam with the local oscillator beam in a coherent detection system. The signal beam which carries the target information is amplified and frequency shifted to allow operation at a sensitivity that approaches the shotnoise limit. To make full use of the return signal and achieve preferable performance,the mixing characteristics should be considered. Signal and local oscillator beam incident on the surface of photodetector, and the influence of fields distribution on mixing efficiency was discussed in this paper. The highest intermediate frequency current could only be achieved when the field distribution of the signal beam was completely identical with that of the local oscillator beam. For both the signal and local oscillator were Gaussian beam coherent in different conditions, such as focus offset, beam waist differecnce and beam waist mismatch, the mixing efficiency was theoretically analyzed and numerically. Numerical simulation shows that the mixing efficiency is more sensitive to the alignment of the incident signal beam than that of the local oscillator beam, the radius of the local oscillator beam waist should be equal or slightly larger than that of the signal beam, the detector radius should be double that of the local oscillator beam waist.
2015, 44(2): 544-548.
Two-dimensional coupled optics swing mirror is a core module in an infrared optical scanning system of space, which demands special requirements of high precision and decoupling movement in a servo control system. A novel decoupling strategy called coupled offset compensation and segmentation stepping method was proposed based on accurate system modeling, abundant simulating and analysis results. The proposed servo control system of optics swing mirror was mainly constructed with a DSP chip, high precision brushless resolvers and limited angle brushless torque motors, which adopted position feedback and velocity feedback by PID algorithm. The experimental results indicate that the novel decoupling strategies are correct and that the servo control system makes the swing mirror achieve high precision movement which has a good dynamic characteristics, short response time and small overshoot. The method applied to the servo control system can be widely used in the field of high-precision swing scanning control system and possesses a great application prospect.
2015, 44(2): 549-555.
In order to realize satellite sweep imaging and reduce the influence on satellite attitude during the process of load swing, a method of two same loads swing symmetrically was put forward. And the swing principle with angle in the given range was planned. Each load had angular velocities of 0.6()/s, 6()/s in roll and pitch axis. Through the dynamics and kinematics analysis of two loads swing motion, the proposal of satellite yaw axis extra moment compensated by reaction flywheel was raised. Then some satellite was used as an example to carry out simulation and analysis, the results showed that the mixed moment and angular momentum in roll and pitch axis had no impact on satellite attitude in the process of two loads swing symmetrically, respectively, an extra periodic moment existed in the yaw axis. 0.2 Nm reaction flywheel was used to compensate momentum, and the satellite attitude pointing accuracy and attitude stability achieved were within 0.032and 0.006()/s, which could guarantee higher accuracy on the surface area of sweep imaging. It was concluded that two symmetrical load body schemes could satisfy the demand of satellite sweep imaging and the design concept was feasible.
2015, 44(2): 556-560.
Compound parabolic collector (CPC) plays an important role in optical efficiency of linear Fresnel reflector (LFR) system. The CPC for LFR was studied, and its mathematical model was established by using Matlab. The method of ray tracking was used to calculate the convergence ratios of CPC with different gap, different maximum acceptance angle, and different truncation ratio. The simulation study illustrates that the CPC for LFR has the specific convergence ratio for the ray with different incident angle. There are two minimum points in the convergence ratio with the change of incident angle. And their positions only depend on maximum acceptance angle, not including truncation ratio and gap. The CPC with gap 50 mm, maximum acceptance angle 45, and truncation ration 0.75, could achieve a high concentrate ration about 80.15%. The simulation method was further verified by the experimental measurement results, and it has guiding significance for design of CPC.
2015, 44(2): 561-566.
A design of the freeform lens made by PMMA for the LED flat light applications was presented. This lens can be used to achieve the uniform illumination of the flat target of the LED flat light, which is based on the principle of freeform surface of the refraction and total reflection principle which realize redistributing the out light. A numerical method and experimental method were used in the design. The simulation results show that when the distance between the freeform lens and the flat target is 5 mm, rotation angle is 0, the distance of the freeform lens and the LED is 7 mm, the uniformity of the whole lamp is up to 96.6% with the high luminous efficiency. The experimental results show that under the action of freeform lens, the uniformity of the flat target of the LED flat light without the guide plate is 95.74%, which is similarly equal to the digital simulation.
2015, 44(2): 567-571.
Wavefront controller requires the datum from Adaptive Optical systems (AOs) based on Hartmann-Shack wavefront sensor. In order to independently design and verify the algorithms in the wavefront controller, a platform to simulate the Hartmann sensor images was designed with a combination of hardware and software. The PC monitor software which is programmed by VC2010 and MATLAB generates the Hartmann output images with different parameters according to the structure and working principle of H-S (Hartmann-Shack wavefront sensor). Meanwhile, it transfers commands and data mutually in the hardware circuit. The hardware platform based on FPGA is used to receive instructions, store data, output responding signals and images in standard Camera Link format in real-time according to the CCD timing. The verified and output results show that the simulated images conformed to the principle of H-S wavefront sensor, and the timing sequence and the speed fulfill the command.
2015, 44(2): 572-577.
To reduce the thermal design errors of high-altitude optical remote sensor and improve the efficiency of its thermal control, the thermal design parameters of high-altitude optical remote sensor were analyzed using the method of sensitivity analysis. Based on the energy conservation law, the heat balance equation of optical remote sensor was built in the high altitude environment, and the sensitivity analysis of the thermal design parameters which could influence the temperature distribution of the lens assembly was achieved. The analysis results show that heat convection, internal heat source and the thermal resistance between components have great impact on the temperature difference of lens assembly in high-altitude optical remote sensor. The test results show that the thermal design based on the sensitivity analysis results is rational and effective.
2015, 44(2): 578-582.
Off-axis three-mirror system(OTMS) has the advantage of high image quality, large field of view and non-obscuration. But drawbacks also exist, such as the alignment difficulty, cost and large optomechanical weight. In order to solve these problems, the design of a novel OTMS was necessary. In this design, the primary mirror and tertiary mirror can be integrated on a single substrate based on third-order aberration theory. An example which has a focal length of 1 200 mm,F-number of 12 and field of view of 101 was given. The mean WFE rms was /55, and the maximum WFE rms was /22. The result of this design shows that the number of alignment freedoms was reduced from 12 to 6, the weight of the mirror support assembly also can be lighter.
2015, 44(2): 583-589.
In order to realize the sunlight observation with each wavelength, aiming at the narrow spectrum test range and low spectral resolution weakness of solar radiation observation instrument, the optical system design scheme was proposed which can realize nanometer resolution based on applying spectral measurement technology. Combining with the characteristics of the sunlight and the service environment of the solar radiation observation instrument, the collecting light system was designed basing on fiber and cosine corrector. According to spectral range and spectral resolution, the spliting light system was designed with multi-channel and manometer resolution. Experimental and design results indicate that the spectral resolution precedes 20 nm and realizes the sunlight observation. It can satisfy the instrument requirements of wide spectrum and nanometer resolution.
2015, 44(2): 590-595.
A small-size satellite-borne solar spectrograph with wide spectral range was designed to monitor the Solar Spectral Irradiance (SSI) outside the atmosphere. The instrument used a modified Czerny-Turner spectral system. A beam splitter was used to split the spectral coverage into two parts: the first order spectrum ranges from 1 200 nm to 2 400 nm and the second order spectrum ranges from 600 nm to 1 200 nm. Two linear array detectors were used to get the whole spectrum at the same time for a direct-reading spectrum. The dimension of the optical system was about 80 mm55 mm20 mm. After the optimization, the tangential aberration of all the wavelengths was smaller than 6 um. The Spectral Response Function(SRF) was simulated based on the Point Spread Function(PSF) which obtained by direct integration of Huygens wavelets method. The spectral resolution is superior to 2nm from 600nm to 1200nm and 4 nm from 1 200 nm to 2 400 nm by analyzing the spectral bandwidth. The structure of the system is simple and compact with a stable performance. The instrument is applied to the measurement of SSI on the satellite.
2015, 44(2): 596-600.
The communication system which was the point of large ground-based telescope was presented, for meeting partial systems'large number, data classes'variety, data transmitting long distance and data's uneven distribution. The system was made up by up data communication system and the bottom one. By using FPGA, the maximal communication capability of system was promoted to transmit 60 paths of RS422, 32 paths of TLL, 10 paths of RS485 and 4 paths of RS232 in one time, while the connection between up and bottom system was single optical fiber. In addition, the telescope's working clock was supported by GPS, and the real-time spatial and time information was given by catching exposure signal's time and encoder data. The XILINX's Virtex-5 FPGA was designed in the heart place. The experiment results indicate that the system is valuable for large ground-based telescope.
2015, 44(2): 601-605.
The existing distance ranging systems based on the method of measuring phase do not provide information of the azimuth angle and elevation angle to achieve the target tracking, so it makes this system's application limited. In response to this phenomenon, under the conditions of not considering echo spot of non-uniformity and noise, the idea of using laser ranging system based on the receiver of four-quadrant APD to achieve tracking was proposed. Through theoretical analysis and simulation test, its result show that, the amplitude information extracted from the four quadrant signal's FFT, can calculate the azimuth angles and elevation angles; so in theory ranging system based on phase method on the conditions of not needing auxiliary equipment to provide information, can achieve automatic tracking.
2015, 44(2): 606-610.
Nearly all polarization measurement suffers from field of view (FOV) misalignment. FOV misalignment would result in discrepancy between the polarization measurement to the target and actual polarization information, named artificial polarization. Instrument and the platform (plane or satellite) movement are the main factors resulting in FOV misalignment of division of time polarization measurement. First of all, the principle of polarization measurement was discussed. The reason of FOV alignment influencing on polarimetry accuracy was described. Then the method on measurement on FOV alignment was proposed on reviewing and summarizing domestic and international current research. After that, factors on influence of FOV alignment space borne and the compensate effect were analyzed in detail.Finally, the discussion on a imaging Polarimeter was shown. Results indicate that FOV misalignment caused by satellite is decreased after compensation. Polarimetry accuracy was increased.
2015, 44(2): 611-615.
In order to achieve azimuth accurate measurement of polarizer axis in the polarization signal generating unit, a device and its working principle were introduced with the use of magneto-optical modulation, right-angled prism and autocollimator to elicit the axis azimuth, and the ordinary polarization prism problems were pointed out. A new type of polarization device was designed based on Glan-Taylor prism to solve this problem, it uses three calcite crystals with identical material composition, each side can form a Glan-Taylor prism respectively with the middle, that it can be a analyzer when it is turned 180around; the working principle of the device and installation and ways of working were described in detail, that the new component can eliminate the prism manufacture and installation errors in the work process was analyzed, it can complete polarizer axis azimuth determination. Finally, experiment results verify that the angle measurement precision of the device is 0.5, and the system has characteristics of high stability, precision and operability, and so on.
2015, 44(2): 616-619.
Stray light analysis in optical system is a key means to improve the signal to noise ratio and ensure the measurement accuracy. Based on the optical system structure and working mode of space-borne spatial heterodyne spectrometer for monitoring greenhouse gases, the outer and inner light shield was designed. With the Tracepro model, the stray light of oxygen channel (758-768 nm) in the system was simulated and evaluated, then (PST,Point Source Transmittance)of the system was calculated, PST values were less than 510-7 at the offaxial angle of 30, and the stray light coefficient was less than 4% . The obtained PST value and the stray light coefficient shows that the light baffle and other mechanisms have suppressed the stray light effectively, and the stray light suppressing level of the system satisfied the requirement of design.
2015, 44(2): 620-624.
Earth science research and application requirements have often been driven by currently available remote sensing technology. Worldview-1 is the highest-resolution commercial remote sensing satellite now operating, offering panchromatic imagery with 0.5 m resolution at nadir. An image simulation method for Worldview-1 panchromatic band was mentioned. Firstly, the visible and near infrared images obtained by low-level flight were accepted as data resources. After atmospheric correction or empirical linear method the reflectivity of ground could be deduced. Then through four steps simulation: radiative transfer, spectral band synthesis, spatial resolution simulation, modulation transfer function simulation, the panchromatic image of Worldview-1 could be evaluated. Experimentation was carried out to test the method using an airship as platform. Though similarity and texture analysis between simulated image and real Worldview-1 image, the result showed the method that simulated the interactions between parameters of objects, atmosphere and the characteristic of sensor enables one to effectively reproduce the panchromatic image of Worldview-1.
2015, 44(2): 625-631.
An ultraviolet imaging system was designed for quantitative characterization of micro-and nanostructures. A beam splitter inserted in the detection path reflected the signal from sample to a pinhole on the imaging plane. The sample was scanned to obtain the sample profile. The DUV light from apparatus was utilized to reduce the diffraction limit size and enhance resolution; and laser interferometer was used to trace the line width to international SI unit. CCD image was used to auto-focus the sample. Sequence images were captured along axial direction and the focus sharpness was determined by focus evaluation function. Algorithms were compared and wavelet algorithm for critical dimension auto-focused in used the ultraviolet measurement system. For wavelet, decomposition level, wavelet vanishing moments and other parameters for UV imaging system was determined.
2015, 44(2): 632-638.
In aerial photogrammetry, image motion blur due to aircraft forward flight and rotation is one of the error resources in image coordinate measurement, which could lead to misalignment in collinearity equation and accuracy decline in direct georeferencing. For the purpose of analysis the influence of image motion blur on direct georeferencing, the motion blur of frame imagery was modeled based on collinearity equation with consideration of both ration and translation movement. The linearity approximation equation was also derived. Analysis shows that the centroid of smear track could be used as image point in intersection only with mid-exposure time as the nominal photo exposure time to eliminate the blur problem in image measurement. Simulation result shows that maximum RMS in object space could be reduce to 0.12 mm by using the method above.
2015, 44(2): 639-646.
The scanning pentaprism system has advanta ge of simple structure, quick optical testing and providing precise measurement of low order aberrations, it is an effective method for guiding optical manufacturing of large aperture flat mirror. In order to improve the scanning pentaprism technology, this letter makes detailed analysis on the error sources include pentaprism manufacturing error, thermal effect, components'position motion, mapping error, autocollimator measurement uncertainty in the scanning pentaprism system, and derives their exact influence on the system. The analysis results show that the system's measurement uncertainty on single testing point can be about 230 nrad under current laboratory environment, and the accuracy of scanning pentaprism system is mainly limited by the measurement uncertainty of the autocollimator and the thermal effect, which providing the proceedings that should be cared for improving the system performance. This study also gives an important reference for the error analysis and precision distribution in design of the scanning pentaprism system.
2015, 44(2): 647-653.
In order to ensure the subdivision accuracy of photoelectric rotary encoder in the harsh working conditions, an error compensation method based on HHT (Hilbert-Huang Transform) was proposed. To solve the angle measurement malfunction of encoder system caused by sine vibration, a mathematical model of Moire fringe error signal was proposed according to the malfunction form of encoder mechanical system. EMD (Empirical Mode Decomposition) algorithm was used to get the intrinsic mode function of the error signal. The intrinsic mode function was demodulated and analyzed using Hilbert transform. Moire fringe signal including the malfunction characteristics was extracted. Meanwhile, the fundamental wave time domain frequency of the precise code signal was obtained based on the precise code signal square wave information of the photoelectric rotary encoder. The IMF function envelope components matching with the fundamental wave time domain frequency were extracted. A 24-bit photoelectric rotary encoder was selected as the experimental object. The experimental results show that the dynamic subdivision error peak value of the Moire fringe signal is reduced from 200to 1.54and the subdivision accuracy improved significantly.
2015, 44(2): 654-661.
In order to realize passive location to an emitter by multiple moving platforms practically, a cross location with angle-only measurements by two airborne platforms based on WGS-84 coordinate system was proposed. These rotational matrix used to transform line-of-sight from each own platform's coordinate system to common WGS-84 were derived,and then angle-only cross location was achieved as the midpoint of common perpendicular line segment of two lines on different planes. At the same time, using the 1st order Taylor expansion method, the error covariances by nonlinear transform of rotation and cross location were derived which were used to filter a number of single position estimations to improve positioning accuracy. By simulation, the main factors which affected positioning accuracy were analyzed in-depthly, and the performance of single time location and by filtering were studied contrastively. The results show the latter can improve precision obviously, and indicate the validation of the algorithm. The conclusion can guide practical application.
Through the analysis of Mapping Satellite-1's photographic principle, geometric model was established to calibrate the intersection angle of the high-resolution, multispectral camera and three-line-array nadir camera in flight. And the correlative experiments using the image data of Mapping Satellite-1 were carried out. Result proves the method's feasibility and high precision, and is close to the referenced result calibrated in laboratory on ground. Results'difference of the intersection angle of high-resolution and three-line-array nadir camera is about 1', multispectral and three-line-array nadir camera is about 5'. Meanwhile, the effect of the orbit determination error and the ground control points'precision on the camera's intersection angle is calculated and analyzed. The method is easily understood, and solves the problem that at present the intersection angle of Mapping Satellite-1's high-resolution, multispectral camera and three-line-array nadir camera is only calibrated in laboratory on ground, cannot be accurately calibrated in-flight. It plays an important role in image fusion, rectification and advanced products' producing.
2015, 44(2): 668-672.
The workspace Measuring and Positioning System (wMPS) is an indoor large-scale positioning system based on rotating laser planes. It can provide 3D coordinates with metrological accuracy, applicable in manufacturing and assembly. As a distributed positioning system, the wMPS also has problem with assigning weights to different measuring nodes. Considering the complexity of the error sources in the positioning process, a method which uses statistics to assign different weights to different nodes was proposed according to different measuring areas. To validate the efficacy, the experimental results are presented to show that the proposed approach can improve the measurement accuracy significantly.
2015, 44(2): 673-676.
Continuously tunable space optical attenuator has a wide prospect in various optoelectronic equipments. Based on the principle of Fabry-Perot interferometer, a new space optical attenuator was presented, its key component is a ZnSe crystal sheet, combined with a high accurate temperature control system, the attenuation ratio of laser beam can be tuned. The attenuation performance was measured with a Nd:YAG laser as light source. The experimental results indicate that the tuning range of the attenuator can reach 3 dB. Theoretical analysis shows that compared with thermal expansion coefficient, thermo-optic coefficient of ZnSe material plays a key role in determining the attenuator performance. In addition, by coating highly reflective dielectric film on both sides of ZnSe sheet, the tuning range can be further increased.
2015, 44(2): 677-681.
In order to realize long propagation distance and achieve subwavelength mode confinement, a dielectric-loaded hybrid surface plasmonics waveguide with a nano-hole was designed, which was based on traditional dielectric-loaded surface plasmonics waveguide.The propagation properties and mode field distributions of this novel hybrid waveguide were studied using finite-difference time-domain(FDTD) method. The results show that the structure could strongly modulate the local field enhancement. Furthermore, the nano-hole was filled with gain medium which leads to a gain enhancement, and the propagation loss could be compensated. In short, adjusting the geometrical parameters can significantly improve the confinement of the SPPs fields and reduce the losses of the waveguide. It also shows that the transmission loss is up to-13 dB/um in the case of d=44 nm. This surface plasmonics waveguide can be used for subwavelength optical confinement and applied to the field of photonic device integration and sensors.
2015, 44(2): 682-687.
The performance of optical components for fiber optic gyroscope (FOG) will degrade by ionizing damage effect and displacement damage effect in space radiation environment. Radiation effects on optical fiber, SLD optical source, and PIN-FET detector module were discussed respectively. In order to keep the performance of FOG in space, radiation protection technology was discussed from both radiation shielding and active hardening technology. Given that different optical components have different radiation sensitivity for different radiation damage mechanism, and there has a strict requirement on the weight of spacecraft payload, then the design of shielding was optimized on ionizing damage and displacement damage respectively. The active hardening technologies for every optical component were also discussed based on the analysis of radiation effects on each component.
2015, 44(2): 688-692.
Off-axis parabolic mirror has been widely used in sensor calibration, radiation measurement, infrared target simulation system and so on, because it takes many advantages such as no chromatic-aberration, common used material, broadband, no center block. The irradiance characteristic of the offaxis parabolic collimating mirror was evaluated by both theoretical analysis and simulation study. Both the expression for the irradiance distribution on the exit pupil plane of the off-axis parabolic collimator and the relations between the angle of divergence and the parameters of the collimator such as the focal length of the mirror, the aperture size of the source and the angle of off axis, were theoretically derived based on the radiation transfer model. The irradiance distribution on the exit pupil plane of the collimator was simulated by ray tracing method. The uniformity of the distribution was also analyzed. The method proposed here is useful to increase the collimation and uniformity of the off-axis parabolic mirror.
2015, 44(2): 693-698.
The application of UAV in the field of electro-optical reconnaissance is more and more widely. Desining a robust flight controller for UAV is an essential technique. A flight controller design method based on model matching and genetic algorithm optimization was proposed in this paper. A nonlinear model was used as the controlled object of this method. Compared with the classic flight controller design method, this method could access the needed controllers quickly and conveniently. A nonlinear mathematical six-degree-of-freedom model of a UAV was established, the aerodynamics, engine and environmental model were all included in this model. Using the above method, a UAV flight controller was designed. Based the finite state machine theory, the flight management model was established to design flight modes and carry out the controller switch. Finally, the six degrees of freedom nonlinear simulation was carried out to verify the effectiveness of the designed controller.
2015, 44(2): 699-704.
A newly modificated silicon (Si) avalanche photodetector (APD) desinged by standard complementary metal-oxide-semiconductor (CMOS) process was proposed in this paper. The basic structure of the Si APD which was formed by N-well/P-substrate was modificated with a deep N well below space charge area, and a independent voltage was applied on the deep N well to minish the transit time of electron hole pairs. The diffusion velocity and the drifting velocity can be improved at the same time, therefore, the 3-dB bandwidth will increase. The device parameters of CMOS APD were calculated with theoretical analysis, and the performance of the CMOS APD was optimized with SILVACO simulation, including technology simulation and device simulation. The simulation results show that when the window size of designed APD is 20 um 20 um and when biased at 16.3 V, the APD achieves avalanche gain of 20, the best responsivity of 0.47 A/W,the 3 dB bandwidth of 8.6 GHz.
2015, 44(2): 705-710.
The theoretically multiple scattering model was based on probabilistic theory and stochastically migrating theory. The relationship between transmission loss and visibility was analyzed in different communication distance in radiation fog weather with Monte Carlo simulation. The results demonstrate that there is a visibility that can makes transmission loss lower when the communication range, the elevation angle, the transmitting beam-width divergence and the field-of-view (FOV) are determined. Various parameters of schematic diagram of the atmosphere laser scattering communication geometric framework can affect transmission loss of link for non-line-of-sight atmospheric scattering communication when the communication range and the visibility are determined and an optimized link for non-line-of-sight atmospheric scattering communication was put forward through the model simulation. Laser Diode (LD) with wavelength 808 nm was chosen as the source light of simulation.
2015, 44(2): 711-714.
It is well known that channel estimation is important for overall performance of a VRVP-MQAM system. Therefore, the MMSE estimation based VRVP-MQAM scheme was studied and second order statistical characterization of the channel state information(CSI) imperfection over a Rayleigh flat-fading was derived. Then rate and power algorithms was proposed in two kinds of situations that are derived based on , the correlation coefficient between the estimated SNR and its true value. Finally, the proposed VRVP-MQAM scheme was simulated with a given Rayleigh flat fading channel. The simulation results and their comparison with an alternative rate and power algorithm which exploits an ideal CSI assumption show preliminarily that: Compared with ideal CSI(=1), the signal to noise ratio(SNR) of MMSE estimate error(=0.9) is 1 to 3 dB; When average SNR is 20 dB, the average spectral efficient(ASE) of MMSE CSI is 0.3 bps/Hz lower than that of the ideal CSI. Thus the application of VRVP-MQAM scheme will greatly improve in the future.
To solve the special issue of electrical adaptive blind equalization in wireless spatial diversity optical coherent receivers, a new blind detection algorithm of multi-value QAM signals using output-feedback-bias(OFB) type complex discrete-time continuous state(DTCS) Hopfield neural network was presented. The OFB will not change the traditional Hopfield model. The proposed OFB-DTCS Hopfield neural network can meet special requirement of the multi-valued signal detection which need enlarger the search space. The blind detection problem of multi-valued QAM signals was transformed into solving a quadratic optimization problem. How to map the cost function of this optimization problem to the energy function of OFB-DTCS Hopfield neural network was also shown. The proof, analysis and its constraints of the energy function were shown, respectively. A complex activation function to fit this special problem was discussed. Then a special connective matrix was constructed to ensure algorithm detect signals correctly. Finally, detailed simulation results and performance comparison with other algorithm were shown to demonstrate farther the effectiveness, superiority and shortage of this new algorithm.
2015, 44(2): 721-724.
Based on orthogonal frequency division multiplexing(OFDM) and wavelength division multiplexing (WDM) principle, a model of OFDM-WDM transmission system was designed. The common phase error and inter-carrier interference in OFDM system caused by the phase noise were analyzed using Wiener phase noise model. In order to suppress the phase noise, a general inter-carrier interference suppression scheme was provided based on the interleaved OFDM technology. The analytical and numerical results show that this interleaved OFDM technology effect in reducing inter-carrier interference on the performance of OFDM system, at the same time, the signal processing ability of the system.
On the basis of Mie scattering theory, simulation of circularly polarized laser beam propagating in horizontal atmosphere is designed using Monte Carlo method with the consideration of polarization character. The simulations reveal that the polarization performance at the receiving spot center is fine and better than at the edges as atmospheric visibility is 5 km and transmission distance is 11.16 km. The depolarization characteristics of left-handed circularly polarized laser beam propagating in horizontal atmosphere at the distance of 11.16 km were measured. As a result, under the conditions of atmospheric visibility is 5-10 km and Cn2 is 1.825-13 m-2/3, the rotation of left-handed circularly polarized laser beam doesn't change and the polarization performance at the receiving spot center is better than at the edges. The experiment result has the same trend as simulation result.
2015, 44(2): 731-735.
Recently, the indoor visible light wireless communications technology is emerged companied with the blooming white light-emitting diode (LED) lighting technology. In this thesis, the current visible light communication system was analyzed and aiming at the request of application in indoor visible light communication system, an avalanche photodiode (APD) detecting circuit was designed. Firstly, the work principle of the APD detecting circuit was described. Secondly, a detailed design and analysis of the system structure and their function of the circuit components was presented. Finally, a detecting circuit component of the indoor visible light wireless communications receivers was designed, and related experiment tests were tested. Experimental results show that the design is effective and feasible, the APD detecting circuit has high gain, wide bandwidth, stable temperature control and high stability etc, therefore the detecting circuit is capable of meeting the needs of indoor visible light communication systems, provides a basis for further study on indoor visible light communication systems.
2015, 44(2): 736-741.
The precise model of the fine tracking system (FTS) provides a crucial condition to study the control strategy, and find the key factors which impact the dynamic and static characteristics of FTS. The fine tracking identify system is designed in this paper which includes the fast steering mirror (FSM), the charge coupled device (CCD), the Digital to Analog Converter (DAC) and the associated electronics. Traditionally, the model of the FTS is considered as a second order model, a series of process such as the input and output data, the model class and the equivalent standards of the least square method is presented to obtain the model. In order to evaluate the performance of the least square identification method, the model is compared with the one obtained by the traditional frequency response method. The residual sum of squares between these two model outputs and the actual output are 8.20 and 89.52, respectively; while the correlation coefficients are 0.98 and 0.95, respectively. The results indicate that the model of the FTS obtained by the least squares identification method is more accurate than the one obtained by the frequency response method.
2015, 44(2): 742-746.
The influences of stimulated Brillouin scattering (SBS) on the sensing range of the phase sensitivity optical time domain reflectometry (-OTDR) was investigated and the limiting sensing range under different detection sensitivities of photodiodes was proposed. As the SBS threshold decreases along with the increasing of the fiber length, a novel scheme was presented to extend the sensing range. Circulators were employed in the scheme to divide the sensing fiber into several sections and the Rayleigh backscattering of different sections were detected by photodiodes, respectively. As a result, Stokes radiation of different sections would not affect each other such that the SBS become more difficult to build up. Therefore, the power injected into the sensing fiber increased and much longer sensing range was realized. In laboratory tests, three circulators were used to divide the sensing fiber into 3 sections, and 66.92 km sensing range was realized. The sensing range can be extend further by adding more circulators.
2015, 44(2): 747-751.
For the problem that core sensitive unit of integrated optic gyro is difficult to realize integration and high sensitivity, a program of fabricating silica wedge-resonator was proposed. Through the theoretical analysis, the ultimate resolution of the gyro caused by the photo-detector shot noise was proportional to the product of the diameter and the quality factor of the resonant cavity. Wedge cavity of 1.5 cm diameter and 22 wedge angle was produced by MEMS(micro-electromechanical systems) process; resonant cavities with different wedge angles were acquired by controlling the mask layer parameters; the relationship between mask layer parameters and wedge angles quality was discussed. Through the coupling test, the quality factor of the resonator is 2106, the theoretical sensitivity of 6 ()/h is achieved for the gyroscope based on the resonator fabricated.
2015, 44(2): 752-757.
The strip and rib waveguides based on silicon-on-insulator (SOI) microring resonator structures are investigated by the Finite Difference Time Domain (FDTD) method. The theory of microring resonators used in biosensing was explored. The effects of geometric structure dimension on biosensor sensitivity were considered and analyzed. It is demonstrated that the sensitivity of strip waveguide is much higher than that of rib waveguide, which is proved by their mode field distributions, and the sensitivity coefficients of both strip and rib waveguides have the similar trend with the increase of waveguide width. Furthermore, the strip waveguide has the highest sensitivity coefficient when the cross section is square, whereas that of rib waveguide corresponds to a not totally symmetrical geometry. The maximum sensitivity of strip waveguide is 172.3 nm/RIU when the cross section is fully symmetry.
In free space optical link systems, atmospheric turbulence is a major limiting factor. Atmospheric turbulence will result in both intensity scintillation and phase fluctuation to the laser beam. This paper is based on MZI-DPSK modulation, considered effects of intensity scintillation and phase noise caused by large-scale and small-scale turbulence to BER, and intensity scintillation is satisfy the inverse Gaussian distribution and phase fluctuation is satisfy the Gaussian distribution. We adopt the distributed antenna array receiver technology, study the performance of bits Error Ratio in free-space optical communication through the atmospheric turbulence, and derive the average BER of antenna array as a function of the phase error considering the inner scale and outer scale effects. In order to improve the BER performance, antenna receiver adopts Maximum Ratio Combining (MRC) technology. The simulation results show that the phase error has a great impact on the error rate, and the inner scale and outer scale has a negligible impact on the error rate. Using antenna reception can reduce the error rate of the system to improve the performance of the communication system and draw the best sub-antennas number of the antenna array receiver.
2015, 44(2): 764-768.
A zero-disparity adjustment method based on SIFT matching was proposed for multiview stereoscopic images using in autostereoscopic display system. First, SIFT was introduced for pixel matching between adjacent views. Then, the result of SIFT matching was filtered by saliency mask which was extracted using frequency-tuned saliency model, and the key-point of disparity control was selected. Finally, the disparity between the neighboring views was computed based on SIFT matching points, and zero-disparity adjustment was conducted based on the principle of disparity control. The disparity of selected key-point was adjusted to zero. Experimental results demonstrate that the proposed method can effectively adjust the disparity of multiview stereoscopic images and generate vivid and comfortable 3D scenes for autostereoscopic display.
2015, 44(2): 769-774.
A new subspace-based tracking algorithm is proposed to deal with rapid changes and severe occlusion of targets during target tracking. Distance invariants are used to select superior pairs of SIFT features. Affine transformation parameters of affine transformation are calculated via linear fitting using these superior pairs. PCA subspace representation of the target is calculated via quick iterations. An effective observation model is constructed to track targets by combining this representation with obtained parameters under the framework of particle filter tracking. And SIFT features and PCA subspace are updated via online learning regularly. At the end, lots of experiments are performed and it is certificated that the proposed algorithm is able to precisely track targets of which gestures and shapes vary rapidly.
2015, 44(2): 775-780.
Aiming at the problem of automatic recognition of irregular shaped and lower height plane targets under the complex background, a template matching method based on Hausdorff distance was proposed. After the forward looking template of plane target was prepared, a similarity measurement method was defined based on edge position, gradient phase and edge point significance constraints firstly. When the positions of two edge points in template and real-time image were close, the gradient phase difference was small and the edge point in real-time image was significant, the two points were matched to each other; then a kind of Phase and Confidence Restrict Hausdorff Distance(PCR-HD) template matching method was designed through the fusion of above three metrics, which achieved the exact matching of plane target contour. The processing results of measured data show that, the proposed algorithm can realize contour matching and recognition of plane target with arbitrary shape under complex ground scene, and has high location accuracy, good robustness and wide application range.
2015, 44(2): 781-785.
A natural global color mapping method matches the statistical properties of night vision imagery to those of a daylight color image. Thus the rendered night vision image appears to resemble the natural target image in terms of color appearance and the reference image is not automatically selected. However, the colored night vision image may appear unnatural if the target image's global color statistics are different from that of the night vision scene. And then target is not easy to be detected because the color of target and background is similarity. Consequently, a new local color transfer method was presented. Firstly, the infrared (IR) and low-level-light (LL) images were fused by using sparse representation. Secondly, a nonlinear diffusion filter was applied to the gray fused image. The diffused image segmented by Kernel fuzzy C-mean algorithm. Finally, the IR and LL images block were color fused by using color transfer technology in the YCbCr color space, where the Y component of the color image was replaced with the fused image, which is a gray scale image made with multi-band night vision images. Experimental result shows that the obtained image has more natural and realistic coloration compared with global coloring method.
