2015 Vol. 44, No. 5
2015, 44(5): 1397-1401.
The performance of the optical parametric oscillator was reported, which was based on the non-critical phase matching of the arsenic acid potassium titanium oxide (RTP) crystal. The intra-cavity RTP-OPO system was driven by the LD end pumped Nd:YAP laser. The output characteristics of the signal light were compared at the different pulse repetition rates of the acousto-optic Q-switcher. The 1.65 m eye-safety laser was obtained when the incident diode pump power of 13.1 W and the pulse repetition frequency of 20 kHz, the maximum average output power was up to 1.1 W and which was achieved with the conversion efficiency of 8.4%. The shortest pulse width of 4.4 ns and the highest peak power of 30.8 kW were obtained when the pulse repetition rate was 5 kHz. The results show that the RTP crystal with the OPO frequency conversion system is a new way to get 1.6 m wavelength laser.
2015, 44(5): 1402-1407.
Compared with laser weak optical feedback, laser strong optical feedback can obtain nano-scale resolution without any electric subdivision. However, it is hard to stabilize the laser frequency owing to the strong feedback level high, which may insults in mode transformation or polarization flipping. A novel technology of dynamic modulation frequency stabilization method was presented. The key technologies and algorithms of zero point and reset compensation were studied systematically. Experimental results show that the uniform modulation and equal amplitude fringes are obtained. The frequency stabilization problem of strong optical feedback system is resolved successfully by using the dynamic modulation frequency stabilization technology. The result plays an important role in developing high accuracy displacement measurement system with strong optical feedback.
2015, 44(5): 1408-1413.
Thermal blooming is one of the most important nonlinear effects on high energy laser propagation in the atmosphere. By using the four-dimensional codes, adaptive optics systems based on stochastic parallel gradient descent (SPGD) optimization were proposed for compensating thermal blooming of high energy solid pulse laser, and the compensation effects compared with the conventional adaptive optical system. The results show that when the repetition frequency equal to 10 Hz, the pulse peak power is 500 kW, the conventional adaptive optical system is better for compensation. But when the repetition frequency of increases or the pulse peak power is increased, SPGD adaptive optical system is better than conventional adaptive optical system.
2015, 44(5): 1414-1419.
Recently, the wind field in the altitude range 25-60 km is still poorly monitored in real time, therefore the 60 km mobile Rayleigh wind lidar based on a Fabry-Perot etalon was developed for wind measurement. The overall structure of this lidar system was described in detail. The design of the subsystems of this lidar was indroduced elaborately. In order to improve the accuracy of wind measurement, experiment was designed to calibrate the transmission curves of FPI, and the calibration method was presented. The transmission curves of FPI were calibrated experimentally, and the standard deviations for parameters of FPI are less than 0.06 in the calibrated experiments. The developed lidar has observed the wind of 15-60 km altitudes over Delingha, and wind velocity and direction profiles were obtained. Observations of lidar were compared with the rawinsondes', and the compared result show good agreement between both measurements. Measure error was calculated, wind velocity and direction errors of the measurements are less than 4 m/s and 6 respectively when it is lower than 40 km. They are less than 8 m/s and 18 when it is higher than 40 km. Wind observations demonstrate that the lidar has the expected good performances.
2015, 44(5): 1420-1425.
In order to solve the problems of intermediate frequency(IF) distortion and acoustic performance deficiencies during the use of polymer polyester sound film, a novel laser modification technology on polymer sound film was proposed to improve the function and characteristics of sound film in sound device. Continuous semiconductor laser with the fixed-wavelength of 975 nm was applied to irradiate the surface of sound film with different laser power. Based on the assurance of the sound film surface integrity, different effects of laser irradiation on modification of sound film were obtained. The results show that after laser irradiation, the surface of sound film is intact without breakage or deformation. The surface roughness of the sample decreases, which is benefit for raising the consistency and uniformity of sound film during the vibration process. The sound film distortion, the resonant frequency and other acoustic properties are improved, moreover, the sound quality of the product is significantly improved. Results obtained in the experiment are of great significance to quickly and efficiently enhance the market competitiveness of the sound devices using polymer polyester sound film.
2015, 44(5): 1426-1431.
Laser scanner, an important component of airborne LiDAR system, consists of several functional modules, and these function and module design methods were completely introduced in details. In order to reduce the weight and size of laser scanner, a novel four-size prism was proposed as the scanning component, the relationship of detecting distance and optical aperture was discussed, furthermore, the optical module was designed based on the parameter of detector. As the light source, a fiber laser had been applied to reduce the cubage, power and weight of the scanner, and then a collimator was designed for beam shaping. The results of the performance tests revealed that the scanner accuracy was 5 mm in 16 m range testing, and in 293 m range testing, the accuracy was 18 mm. The laser scanner was used in flight perform experiments as a part of airborne LiDAR system, the results from different flight altitudes were presented at the end.
2015, 44(5): 1432-1437.
532 nm laser imaging radar can be easily interfered by the sunlight in the imaging process and then it reduces the image SNR. The 532 nm streak tube laser radar was used to carry on the imaging experiment of the multiple scene(groups of buildings) respectively in the day time and night, and the histogram statistics method was used to analyze the distribution of pixel values of laser intensity image and laser range image in the day time and night of the same scene, then the effect of sunlight on the laser imaging properties was analyzed. The experiment results show that the sunlight can increase the brightness and the background/target contrast ratio of laser intensity image, at the same time it can also increase the sky background noise of the range image; and the laser range image has high signal-to-noise ratio at night, but target intensity image contrat ratio is poor.
2015, 44(5): 1438-1443.
To estimate the jamming effect of high repetition laser on laser seeker's decoding effectively, two quantized model were adopted, which were concerning to code distinguishing stage and code locking stage respectively. During simulation, the research emphasis was put on the effect of laser frequency on the laser seeker which adopted anti-interference technology. The simulating results show that the jamming effect is affected by laser frequency, coding pattern, sampling period, the width of time-gate, and so on. And the jamming effect during code distinguishing stage is better than code locking stage, but both stages could be jammed successfully when the frequency become higher than a certain value.
2015, 44(5): 1444-1449.
For micro-satellites in orbit, Single Event Latchup(SEL) is one of the most destructive single event effects. The SEL results in damage to the device, even failure to the mission. Firstly, the mechanism of SEL was described as well as the existing anti-SEL technology. Protective measures for SEL were put forward. An restorable anti-SEL power interface protection circuit was proposed for protection to the device in the satellite from SEL and overcurrent. By use of the pulse laser technology, a chip with experience in space was tested and analyzed. Experimental results show that the circuit can accurately detect the occurrence of SEL and remove the SEL effect, to ensure the system is stable and reliable.
2015, 44(5): 1450-1455.
When the ship sails on the sea, a wake of several kilometers length and long continuous time will appear behind the ship. The bases for detecting ship through the infrared characterization of wake are provided by the apparent feathers of ship wake. Visible simulation of wake was achieved from the characterization of ship wake. An infrared imaging model of ship wake was established based on Cook-Torrance model. The infrared imaging characterization under different detecting conditions was obtained with ray tracing method, considering the environment influence of solar radiation, sky background radiation and atmospheric transmission comprehensively. Results indicate that, sea surface is integrally dark and ship wake is apparent at low elevation angle while the sea surface bright and ship wake weak at high elevation angle; the imaging characterization of Kelvin wake is weakly affected by air temperature, and turbulent wake is a dark band at low elevation angle and air temperature but a bright band at high air temperature; Kelvin wake will be eventually unrecognizable with increasing sea surface wind velocity, then the turbulent wake is the only ship wake characterization that can be recognized.
2015, 44(5): 1456-1461.
Sonic infrared imaging is a new kind of hybrid nondestructive testing method. Research on heating characteristics of defect region is propitious to the optimization of testing scheme. Experimental results show that temperature rising of crack region measured at the excitation side is higher than that at the excitation opposite side; however, the heating rate of crack contact surface is stable in the mass. Based on the phenomenon of crack heating under intensive ultrasonic pulse, a finite element model of experimental setup was established and a thermal-stress analysis was performed by an explicit finite element method. In the finite element model, a piezoelectric-force analogy method was employed to simulate inverse piezoelectric effect in the ultrasonic excitation system, and dynamic relaxation was introduced into the simulation in order to cover the effect of engagement force on the initial state of specimen. During the FEM simulation, the crack frictional heating excited by ultrasonic pulse was calculated, and temperature distribution in space and time domain was described. The relationship between friction heating, friction force and relative velocity at contact surface was revealed. Simulated results reveal the engagement force between horn and testing plate makes the heating position in crack surface shift to the excitation side.
2015, 44(5): 1462-1466.
Optical pulse signals of two different wavelengths in the infrared regime were generated in atomic Rb vapor by nonlinear optical frequency mixing using optical pulses generated in a Ti:sapphire laser. The effects of Rb number density, pump laser intensity, and the chirp of laser pulses on the competition characteristics of the two signals were investigated. The results show that the two signals are mainly generated from two coupled parametric six-wave mixings processes, and the signals vary with Rb number density, pump laser intensity and the chirp of pump laser pulses. The competition between the two signals is dominantly governed by phase matching conditions which are closely related to Rb number density, but scarcely related to pump laser intensity and the chirp of pump laser pulses.
2015, 44(5): 1467-1471.
Chalcogenide glasses are excellent achromatic and athermalized infrared materials. They are the ideal candidate for key optical components in infrared optical systems. In this paper, chalcogenide glasses were used to achieve athermalization of the medium-wave infrared optical system. Firstly, the effect of temperature variation on infrared optical systems was introduced. Secondly, some aspects of properties for common chalcogenide glasses were analyzed and the advantages of chalcogenide glasses were summarized. Finally, an athermal medium-wave infrared optical system working in the manner of secondary imaging was designed. The most common aluminum alloy material was used as house material. Design results show that the image quality of the optical system is excellent in the temperature range of 0-100 ℃. High-performance medium-wave infrared optical systems can be achieved by using chalcogenide glasses with a low-cost.
2015, 44(5): 1472-1476.
Chalcogenide glasses is an ideal infrared transmitting optical material, were widely applied in the area of infrared thermal imaging which requires chalcogenide glasses not only have properties advantages for example larger transmission and better homogeneity and larger size, but also have processing characteristic with large volume and low cost. The key to effective satisfied above mentioned requirements is glass's melting technology. The vaccum melting technology in sealed ampoule and vacuum/atmosphere melting technology in crucible and their equipments were introduced. Specially a new chalcogenide glass melting method was mentioned and explained, which was a second melting protected with atmosphere, the influences on transmitting diagram and internal optical character and homogeneity melted with atmosphere protective were analyzed in detail. Glass's transmission was closed to those melted in sealed ampoule, in addition the internal optical character and homogeneity were improved via second melting protected with nitrogen atmosphere which purity is 99.999%.
2015, 44(5): 1477-1484.
Quantitative identification algorithm of defect or defect boundary is the key theoretical basis for the development of quantitative nondestructive testing and evaluation. For the geometry identification of inner pipe boundary (i.e. geometry-varied boundary due to defects), most methods developed up to now are not precise for the identification of irregular-shaped inner boundary. In this paper the steady-state identification problem was solved, with different inner boundary geometries and different test piece shapes, based on finite element method and conjugate gradient method by associating ANSYS software with MATLAB. A series of effecting factors, such as the initial boundary geometry guess, temperature measurement error and number of measurement points at the inspection boundary, number of discrete points of the boundary to be identified, and the thermal conductivity of the test piece, were studied systematically on the effect on the identification result. Numerical experiments certified the effectiveness of the method and proved the method to be very precise and time saving.
2015, 44(5): 1485-1490.
The geometrical optics method(GOM) and Lorenz-Mie method were used to study the scattering properties of spherical particles at the wavelength of 0.55 m, and the accuracy of the two methods were analyzed. The impacts of particle size parameter and the imaginary part of the refractive index on the forward scattering phase function of spherical particles were investigated. The results show that the scattering properties of spherical particles calculated by GOM and Mie are very close when the particle size parameter is greater than 60. When the particle size parameter is less than 1 000, the relationship of the forward scattering phase function with the particle size parameter can be described with a quadratic formula, and the results of GOM and Mie are identical with the increase of the particle size parameters, they gradually lose their quadratic relationships. When the particle size parameter is larger than 10 000, the GOM result is larger than that of Mie's result. For a particle size parameter, the forward scattering phase function firstly increases and then decreases with the imaginary part of refractive index.
2015, 44(5): 1491-1495.
Based on the diffraction optical theory, the intensity distribution in the vicinity of the focus of circular Fresnel zone plate formed by Bessel-Gauss beam was studied. Hollow beams were obtained near focus under the illumination of high order Bessel-Gauss beam, the width and the length of central hollow depended on the order of the beam and the number of plate zones. In general, the size of the dark hollow increased with increasing beam order, the length of the dark hollow decreased with increasing number of FZP. Needle beam and bottle beam can be produced under the illumination of zero order Bessel-Gauss beam. These beams with special intensity distribution may have potential applications in laser processing and trapping particles.
2015, 44(5): 1496-1499.
Aimed to the feature for long after work distance of double Gauss long focus optical system,double reflection mirrors was designed to refraction ray, the camera's size was shortened, with saved space and reduced quality. System's image had not change by analyzing reflex action matrix calculation after jionting two pieces of reflection mirror. The precision thread trim mechanism was designed for adjusted the pitch and azimuth angle of reflection mirror, then fixed. A image demacrating tool was designed that combing with corss line and radiation shape, and a adjustable observation tool with multiple microscope combination, efficiency was improved. A method combine with coarse and precision was planned out to demarcate focus, finally the image plane calibration was finished. This method has been proven was feasible in the practical work.
2015, 44(5): 1500-1505.
In order to improve the measurement precision of infrared zero momentum, specific to the problem that the image positioning accuracy caused by camera pose changing was not high, an adaptive correction algorithm of CCD camera pose small angle changing was proposed. Through the theoretical analysis, a mathematical model of the CCD camera pose calculation was established and a camera pose calculation formula was deduced. According to the infrared sight aiming baseline variation detection system, specific to the three kinds of camera pose, a contrast experiment that aiming baseline coordinate was measured in the reference coordinate system was completed. The results show that the calculating precision is 0.01 mil or less. and camera pose adaptive correction algorithm can decrease the error of the infrared sights zero momentum measurement caused by camera tilt, which provided a new method of camera position adaptive compensation for enhancing zero momentum measurement precision.
2015, 44(5): 1506-1511.
Image blur dues to the relative motion with the target in the camera exposure time, it would be worse while the ratio of speed and height(or speed and distance) increased. At present, the optical image motion compensation method bases mainly on the reflective element. In order to overcome the disadvantages of complicated image rotation corrected mechanism, difficult position location and optical vibration occurred by the swing scanning, a new method based on rotating double optical wedge was proposed, the dynamic working matrix was built, the emergent light vector's trajectory was analyzed and simulated. According to the actual image motion compensation demand, the double optical wedge designing result and controlling method were presented. Through analysis and simulation, the results show that this method has significant advantages such as compact structure, easy controlling method, stable motion state, high compensation capacity, etc. It has very important practical value for the occasions of the greater ratio of speed and height (or speed and distance).
2015, 44(5): 1512-1517.
The rectangular mirror supporting structure was designed and optimized for reducing the weight of the aerial optical remote sensor and minishing the shape error of the mirror, which was working in the bad aerial environment. First, the supporting point number of the ligntweighted mirror was calculated and the point position was optimized. Secondly, the flexible hinge was designed and optimized in the supporting structure in terms of the thermal deformation, which was indeced by the different expansion coefficients between the mirror and the back supporting structure. Finally, the surface shape was analyzed, the RMS was 20.3 nm, less than the design requirements, 1/30(=632.8 nm), the model was analyzed and tested, the first-order natural frequence was 138 Hz and 162 Hz. The results indicate that the designed structure is resonnable and feasible.
2015, 44(5): 1518-1525.
In accordance with a three mirror off-axis freeform square aperture system, orthogonal Zernike polynomial in square area was created to analyze wavefront and receive aberration parameter. During computer-aided alignment, by collecting interferograms of several fields of optical system by means of autocollimating interferometry, aberrations could be obtained from those interferograms. Furthermore, the sensitivity matrix related to the incorrect parameters derived from optical design software and these parameters of orthogonal polynomials in square area were used to determine the incorrect parameter. The results show that the averaging RMS value of the system is 0.164 1 waves(632.8 nm) and the averaging MTF value of the system is 0.453 4 after iterations, which proves it is right, and it can be used in off-axis freeform reflected system with other types of aperture.
2015, 44(5): 1526-1533.
For long-focus TMA space camera that connect to satellite platform horizontally, the connecting interface temperature difference between satellite platform and space camera is generated due to the alternation of ground test and in-orbit condition, leading to the line-of-sight drift of the space camera which effects imaging quality. In order to solve this problem, the optimized connection method that applying flexible connector, rigid connector and releasable connector cooperatively was proposed. The space camera was flexibly and statically determinate installed on satellite platform in orbit, and the connection stiffness was enhanced by two additional releasable connectors in launching stage so that the fundamental frequency was ensured. The optimized connection method was verified by finite element method, the secondary mirror angular deviation caused by satellite platform temperature decreasing 15 ℃ was 9.62(the span of installation locations was 1.2 m), which satisfied the optical tolerance. In launching stage, the fundamental frequency of space camera in X, Y, Z directions was 120 Hz, 120 Hz, and 110 Hz, there was no significant decreasing compared with rigid connection. The alternative experiment of platform temperature ascending 15 ℃ was performed via experiment fixture, the test result was consistent with the simulation, the maximum relative error of secondary mirror angular deviation between measurement and simulation was 9%. The results show that the problem of line-of-sight drift caused by satellite platform and space camera temperature difference is solved by optimized connection method, and in-orbit environment adaptability of camera is improved.
2015, 44(5): 1534-1538.
Based on Z-scan technique, the nonlinear absorption and nonlinear refraction characteristics of ZnS crystal were researched in the case of wavelength of 532 nm picosecond laser pulses and wavelength of 800 nm femtosecond laser pulses. Experimental results are as follows. The absorption of ZnS crystal is two-photon absorption and the nonlinear absorption coefficient is 5.310-11 m/W in the case of wavelength of 532 nm picosecond laser pulses. The absorption of ZnS crystal is three-photon absorption and the nonlinear absorption coefficient is 0.5910-21 m2/W2 in the case of wavelength of 800 nm femtosecond laser pulses. Under the effect of 532 nm picosecond laser pulses, the nonlinear refractive index sign of ZnS crystal is negative and the change of nonlinear index of refraction generated by free carrier is the dominant factor. But under the effect of 800 nm femtosecond laser pulses, the nonlinear refractive index sign of ZnS crystal is positive and dominant factor is the change of nonlinear index of refraction generated by bound electron.
The temperature variation law and mechanism of commercial Flash memory devices applied in space electronic products were analyzed. The temperature cycling test and high temperature step stress test of highly scaled Flash memories K9G08UD series of Samsung were carried out at the temperature -35-+105 ℃ to evaluate the feasibility of its space application. The results show that the page programming time and block erasing time of this series of memory changes with the temperature. The page programming time increase by 15% from -35 ℃ to 105 ℃. Block erasing time increase by 72% from normal temperature to -35 ℃. Block erasing time increase by 10% from normal temperature to 105 ℃. The experiment shows K9G08UD series memory can work at -35-+105 ℃. Under such environmental temperature condition, the Flash can be read, programmed and erased. No new bad block occurrs. The page program times increase with the temperature increasing and still less than the maximum page program time. In low temperature, the erase times increase dramatically. So in space application enough time should be given for erase operation.
2015, 44(5): 1544-1548.
The HfO2/SiO2 and Ta2O5/SiO2 chirped mirrors with different electric field distribution were fabricated by electron beam evaporation with good damage characteristics and stress features. The laser-induced damage test of samples was performed by laser pulses with duration 350fs, center wavelength 1 030 nm. The results show that the material characteristics and electric field distribution are the key factors which can influence the damage threshold. Ta2O5/SiO2 chirped mirror, which has much wider GDD bandwidth and has the same damage threshold as HfO2/SiO2 chirped mirror can be fabricated by reducing the peak intensity of field in the film stack. This phenomenon was illustrated by the theoretical model of conduction band electron density while the breakdown mechanism of chirped mirrors was explained and damage morphologies of samples were analyzed.
2015, 44(5): 1549-1553.
Because of the unique quantum effect, quantum dots(QDs) have attracted wide attention in various fields for many years. In order to study the nonlinear optical properties of ternary CdxPb1-xSe QDs, a convenient synthesis method of high-quality QDs was developed, on the basis of which the nonlinear optical properties of the QDs were studied using Z-scan technique under 532 nm laser radiation. The results indicate that the high-quality CdxPb1-xSe QDs with uniform size and highly crystalline nature are successfully achieved by a improved one-pot synthesis method with the synthesized N-oleoylmorpholine used as solvent, and that the nonlinear absorption coefficient and nonlinear refractive index of Cd0.5Pb0.5Se were 1.0110-9m/W and -1.110-10 esu, respectively, showing much more remarkable optical nonlinearity compared with binary CdSe QDs. Thus, the ternary CdxPb1-xSe QDs should be of potential in laser protection and photoelectric switch, etc.
2015, 44(5): 1554-1557.
The directional coupling of long-ranging channel plasmon polariton in the V-groove plasmonic waveguides covered with ultra thin metal film was studied. By calculating the modes' distributions, confinement factors and propagation lengths of the odd and even modes in different waveguide distances were acquired. The relationship between coupling length and maximum crosstalk with different waveguide distances were calculated. It is found that the coupling length is smaller than the propagation lengths of any mode in small waveguide distance, and the coupling length becomes larger and the maximum crosstalk becomes smaller as the waveguide distance increases. The investigation of the directional coupling in the V-groove plasmonic waveguides with ultra thin metal film is important to its applications in the photonic integrated circuits.
2015, 44(5): 1558-1563.
Currently in the electronic image motion compensation method based on TDI, charge packets were transferred to conduct step during the exposure, which made the electric purse move and there is a large non-synchronized effect between the image motion. This reduced the compensation effect. In order to increase the compensation effect, effects of the charge packets discretion on the compensation effect in the image motion compensation method based on TDI was analyzed, and an improved electronic image motion compensation method was proposed, which reduced greatly the asynchronous effect between the electric purse and image motion. The modulation of the two methods were compared, which theoretically proved the enhancing role of the compensation effect. The drive timing chart of the improved type of electronic image motion compensation method was advanced. The two methods were verified by imitating different image motion compensation experiment indoor.The image modulation mean of improved electronic image motion compensation method is 47/96, more than the traditional image motion compensation method which is 1/3. The image sharpness of improved electronic image motion compensation method which is 0.550 2, more than traditional image motion compensation method which is 0.475 3. It was shown that the improved electronic image motion compensation method is better than traditional image motion compensation method.
2015, 44(5): 1564-1568.
Diffraction beam deflection peak position of the acousto-optic device is proportional to the input signal frequency. It is the basic theory for acousto-optic spectrum analyzer frequency measurement. But the non-linear effects in diffraction causes diffraction peak deflection error. To get better measurement results, the diffraction intensity data should be processed to reduce the frequency of measurement variance. After the digital features of CCD background noise were analyzed, the background noise mathematical average had been taken as the threshold when denoising the data of diffraction intensity. According to the principle of least square method, fitting the diffraction intensity data by Gaussian function, the correlation coefficient is 0.997 6. Under the existing optical experimental platform, the measure variance is 542.5 kHz2 while the frequency was estimated by the diffraction peak position; the measure variance is 31.8 kHz2 while the frequency was estimated by the middle value of Gaussian fitting function. It provides theoretical support for reducing the frequency measurement variance of acousto-optic spectrum analyzer.
2015, 44(5): 1569-1573.
Atmospheric turbulence is one of the inevitable influence factor of resolution of optical imaging system. In order to research the effect of inner scale, outer scale, turbulent contour lines and height on resolution of optical imaging system, the optical resolution of optical imaging system considering inner and outer scale of slant atmospheric turbulence was derived, according to the optical imaging system integral resolution theory and modified Von Karman turbulence spectrum. ITU-R atmospheric turbulence structure constant model changing with height was used in numerical calculation. The results show that the effect of inner scale of turbulence on optical resolution is much less than that of outer scale of turbulence; the changes of inner scale will limit the effect of outer scale of turbulence on optical resolution; in slant transmission, turbulent contour lines has more influence than the effect of outer scale of turbulence; atmospheric structure constant near the ground will affect the optical resolution of optical imaging system mainly in the low height; the wind speed will be the major influence factor when the height beyond 5 000 m.
2015, 44(5): 1574-1578.
A novel approach to PM fiber length error measuring of IFOG's Sagnac interferometer was proposed according to the FOG manufacturing process. Basing on the state four square wave mechanism, the measurement of fiber length error was conversed into the measurement of peak pulses in the detector's response signal. Meanwhile, fine measurement of the peak pulse was accomplished by modulation frequency multiplying technique. A fiber length error measuring system was developed on the basis of this approach, which achieved the measuring precision of 0.2 m(2 000 m fiber). The experimental results show that a higher precision and a faster measuring speed than original methods, which can increase the efficiency of FOG's engineering assembly.
2015, 44(5): 1579-1586.
The research status of systematic calibration was analyzed, and an inertial navigation system error model was established. Additionally considering the influences of quadratic term error coefficient of the accelerometer triad and the inner lever arm parameters to the system, a systematic calibration method was proposed based on 36-dimension Kalman filter. An appropriate calibration path was designed and a Kalman filtering model was established. Simulation and experiment results indicate that the accuracy of the estimated biases is better than 0.001()/h and 9 g for the laser gyroscopes and the accelerometers respectively, the accuracy of estimated scale factor errors is better than 3 ppm and 2 ppm respectively, the accuracy of estimated installation error angle is better than 1 and 3 respectively, the accuracy of estimated quadratic term error coefficient is better than 410-10 s2/m, and the accuracy of estimated inner lever arm parameters is better than 3 mm. Therefore, this method satisfies the demands of high precision inertial navigation system calibration.
2015, 44(5): 1587-1592.
A low cost and low power consumption optical receiver differential transimpedance preamplifier for 10 Gb/s high-speed optical communications application was presented. The preamplifier includes a tranimpedance amplifier(TIA), limiting amplifier(LA), and output buffer, the weak photo-current was amplified by the preamplifier to a differential voltage swing of 400 mVpp. The preamplifier was designed in 0.18 m CMOS technology. The receiver preamplifier circuit is with a transimpedance gain of up to 92 dB and -3 dB bandwidth of 7.9 GHz, which accommodates a photodiode capacitor of 250 fF. The noise simulation result shows that the average input-referred noise current spectral density is 23 pA/up to 8 GHz. The power dissipation of transimpedance amplifier, limiting amplifier and output buffer respectively drain is 28 mW, 80 mW, and 40 mW from the 1.8 V supply respectively. The chip size is 800 m1 700 m.
2015, 44(5): 1593-1597.
For optical coherent M-ary phase-shift-keying (M-PSK) system, the frequency offset algorithm based on differential phase or FFT maximization which was widely used is difficult to achieve MHz estimation error when the data length is short, which is difficult for the following carrier phase estimation to recover the data. To meet the needs of high accuracy and real-time performance for frequency offset estimation in the M-PSK system, a frequency estimator based on fast Fourier transform and multiple signal classification (MUSIC) was proposed and investigated. For the first time, MUSIC algorithm was used in this area. The proposed algorithm is accurate especially when the data length is short. The principle and flowchart were proposed to illustrate the algorithm. Numerical simulations of 20-Gbaud QPSK coherent systems were carried out to demonstrate this algorithm.
2015, 44(5): 1598-1604.
A new full-duplex radio over fiber link model was proposed in this paper. For the down link, two mach-zehnders modulator cascaded were employed to generate sextupling-frequency millimeter wave; the single side-band modulation was used to overcome the walk-off effect, thereby the transmission distance was effectively improved. In the meanwhile, the first order sideband was employed as the carrier of uplink baseband signal and thus the requirement of additional laser source was eliminated. Furthermore, self-homodyning demodulation method was adopted to avoid the need of local oscillator, thereby the cost of system was reduced. Numerical result shows that the proposed full-deplex model can produce 60 GHz millimeter wave by only using 10 GHz modulated signal. The transmission distance for down link can reach 250 km and that for the up link is more than 300 km.
2015, 44(5): 1605-1609.
The errors of star sensor contain temporal error (TE), high spatial frequency error (HSFE) and low spatial frequency error (LSFE). The test methods of the TE, HSFE and LSFE for very high precision star sensor were presented in this paper. The errors of star locations obtained from star image were calculated with the high precision single star simulator. Then the statistics result of TE for the star sensor was calculated with the errors of star locations. The energy change in micro-stepping acquisition of the different star locations from the star image was tested with high precision turntable and single star simulator. The test result of HSFE was calculated with the energy change. The X direction errors and Y direction errors of the star image were calculated with two axis turntable. Then the LSFE was calculated with X direction errors and Y direction errors. Finally, the star sensor for satellite control system was tested with the test method presented in the paper. The results show the method is availability. And the method is used for the acceptance test of principle prototype of star sensor.
2015, 44(5): 1610-1615.
The coordinates on the CCD image plane is regarded as star sensor's input signals. The accuracy of the inputs is affected by the inherent errors of the optical system and the CCD installation error. The method of star sensor's calibration and leading building was based on star reference frame, and it didn't depend on large expensive equipment such as swivel table and star simulator. Based on the precise celestial equator coordinates of the star observing, this method had solved the problem of the CCD installation error and made it to be a part of the optical system calibration. In a word, it is a simple and efficient method about calibration and leading building. Above all, experimental results and analysis show that the method is able to achieve the high accuracy to arc second scale.
2015, 44(5): 1616-1622.
By using mixing of monocular vision and laser rangefinder, a closed-form method for relative pose parameters of spacecraft was proposed. Firstly, by using quaternion measurement algorithm, the closed-form method for relative parameters of spacecraft were obtained utilizing five feature optical points and monocular vision, and they were corrected. Secondly, the above 6D pose parameters and 1D distance that obtained by laser rangefinder were fused, so as to correct the 6D pose parameters further. Finally, the solution was validated by using mathematical simulation, and simulation results show that the algorithm guarantees the pose parameters estimation accuracy under the condition of large errors caused by camera calibration and feature optical points extraction and matching. The simulation results also illustrate that the solution can satisfy the demand for the accuracy of relative parameters between spacecrafts and the real-time computation.
2015, 44(5): 1623-1627.
The theodolite which works on a vehicle has measurement error caused by the deformation of vehicle platform. Two methods that the single error accumulation method and the comprehensive coordinate transformation method to compensate the error were deduced. First, the basic principle of the two methods was analyzed, taking into account the limitations of the different correction methods. Then a practical example with a vehicle platform containing large deformation derivation was built. The measurement error were summarized in two correction methods were compared. The results show that the correct error of the single error accumulation method has several points within large error in whole work scope of the theodolite, caused the error about 5 larger than the comprehensive coordinate transform method. Therefore the comprehensive coordinate transformation method must be used to obtain high-precision measurements.
2015, 44(5): 1628-1632.
Depth measurement is an important problem in computer vision field. Firstly, a new grid pattern was designed and a sequence coding and decoding algorithm for the pattern was proposed. Secondly, a linear fitting algorithm of system parameters for constructing the linear relationship between the object depth and the pixel shift was proposed, and the lens distortion was rectified. Thirdly, depth information of object was obtained based on this linear relationship. Moreover, 3D reconstruction was implemented based on Delaunay triangulation algorithm. Finally, the regularity of the error curves was utilized to correct the system errors and the measurement accuracy was improved. The experimental results show that the accuracy of depth measurement is related to the step length of moving object.
2015, 44(5): 1633-1637.
MRED with a low precision usually can be detected by a subjective way which is based on the human eye observation before. In order to improve the measurement accuracy, a new objective way based on the theory of Barten module was built, which was one model of Contrast Sensitivity Functions(CSF). Four-bar target pattern was received by color imaging system. After a series of processing such as color space conversion, Fourier transform and CSF processing, the chromatic aberration on the CIELAB color space was calculated when the chromatic aberration of the test pattern reached the threshold value determined by CSF. Both of the two results tested by the subjective and objective way on different spatial frequencies of the four-bar target were recorded and compared. The results show that the value got by the subjective measurement method is consistent with that of the objective. That means the subjective measurement method based on human visual model in this paper is desirable.
2015, 44(5): 1638-1642.
The design of four spectrum imaging of a single sensor spectro-imaging system was presented. The prism was placed before lens set, departure at different direction of the objective radiation across prism, the separate spectro-image was formed at different place of focal plane. The F number of the spectro-imaging system whose working wavebands are 8.2-8.6 m, 9.4-9.8 m, 10.6-11.2 m and 11.2-12.2 m is 4, the focal length is 55 cm and the aperture diameter is 50 mm. The spot diagram diameter is less than 40 m. Vignetting was introduced to solve the superimposition between different spectrum. The aberration characteristic and the blur circle diameter distribution of the system was analyzed. The analysis results showed that the system had a good image quality and met with spectro-imaging requirements.
2015, 44(5): 1643-1646.
As a novel type Fourier transform imaging spectrometry, large aperture static imaging spectrometry has come forth in recent years, which has many advantages such as high throughput, multi-channeland so on. However, if there are certain registration error on the detector array and interferogram, it will have a greater impact on the restoring spectrum, and even affect the final application of the instrument. To solve this problem, according to the imaging prinple analysis of LASIS, a detector registration error calibration method was given, after verification, this method can well solve the problem of the detector registration error, and the accuracy of recovered spectrum was evidently improved. This study has important guiding significance for the development of large aperture static imaging spectrometer.
2015, 44(5): 1647-1653.
In order to study the effect of temperature on airborne imaging spectrometer optical performance, the characteristics of the instrument under temperature load onboard were analyzed, the mechanism and manifestations of temperature load were described, the thermal performance of the spectrometer was studied. Firstly, the characteristics of the temperature load under airborne was analyzed. Secondly, the least squares method and coordinate transformation method were taken as the theoretical basis for the preparation of the surface error and rigid displacement solver, combined with the finite element method to calculate the deformation and rigid body displacement of the mirror of the optical systems at a temperature load. Finally, a ray tracing was used to solve the mirror line position change due to displacement of the rigid body displacement, study its spectral drift, and calculate the effect of the rigid body displacement on the modulation transfer function(MTF). The results show that within the range 10 ℃, line drift is less than 1/3 of the required accuracy of spectral calibration, no further spectral calibration and correction is needed.
2015, 44(5): 1654-1659.
According to the optical scattering theory and the orbital dynamics, mathematical model of equivalent magnitude of space object was established with Bidirectional Reflectance Distribution Function (BRDF) by region classification, grid division and vector coordinates transformation. Combining with the noise resources in space-based imaging detection of space object, mathematical model of Signal-to-Noise Ratio(SNR) was put forward. On the basis of the structure, material, background and orbit parameters of the object and the orbit and performance parameters of the detector, equivalent magnitude and SNR of the Space-Based Infrared System(SBIRS) were calculated. It shows there is about three magnitudes difference in equivalent magnitude during the observation time, which leads to the correlated variation of SNR. The simulation results illustrate the validity of modeling method. The dynamic analysis of SNR for space-based imaging detection of space object is achieved.
2015, 44(5): 1660-1665.
Perceptual contrast between the target and background is one of the main influencing factors of visible and infrared gray fusion image quality. Existing contrast metrics have not put enough consideration for the human visual system. An simple and effective target-background perceptual contrast metric was proposed combined with the human luminance masking effect based on the form of Weber contrast model. The simulated image and the observer evaluation scores of real scene gray fusion images were used to test the proposed model. Experimental results show that the proposed target-background perceptual contrast metric provides better predictions than five other existing contrast metrics. It is more closely matched to human perceptual evaluation and can efficiently implement the objective evaluation of target-background perceptual contrast for gray fusion images.
2015, 44(5): 1666-1672.
The imaging systems are affected by various interferences, causing image blur and noise. In order to solve the problem, a new blind restoration method was proposed to recover the images using knowledge of sharp images. Firstly, the statistics of gradient magnitude values of sharp images were analyzed, and the images were divided into two parts, the highly textured region and the flat region. Fitting the probability distribution functions, the priors of sharp images were obtained, and the constraint was injected which the probability distribution of the flat region was little affected by blur kernel, aiming to avoid the image ringing. Then, the image noise model was established and divided into two parts, the Gauss noise and random noise, with propose of keeping off outliers caused by the over-saturated pixels. Finally, the maximum posterior probability was utilized to construct cost function, and emploied the expectation-maximization algorithm and iterative shrinkage algorithm were emploied to solve the cost function to recover image. The experiments show that it archive in recovering much image details, sharpening edges and avoid artifacts.
2015, 44(5): 1673-1679.
Becauce of interruption contained in a Lidar echo signal, mode mixing is often generated when using EMD (Empirical Mode Decomposition) to denoise such a signal. It lead to that it can't remove the noise from useful signal easily, and make the denoising effect so worse. In order to solve this problem, a combinational algorithm was presented which combine the morphological filtering and EMD together. Firstly, an adaptive multi-scale morphological filter was used to dispose the signal and remove the interruption, as a preliminary treatment, then used EMD for denoising. At last, a simulated signal denoising experiment and a real Lidar echo signal denoising experiment were done, the results showed that SNR increased by 8.89 dB and RMSE reduced by 0.051 4 compared with using EMD to denoise directly in the former experiment, the mean-SNR after 6 km increased by 3.356 4 dB in the later. This combinational algorithm can restrain mode mixing effectively, and has a better denoising effect and application prospects.
