2014 Vol. 43, No. 2
2014, 43(2): 345-349.
In order to satisfy the requirement of laser interference imaging, especially Fourier telescope imaging, to generate frequency-stably high-power optical heterodyne interference mode, the concept of optical heterodyne interference laser based on the structure of MOPA was put forward and was proved by experiment. The limits of conventional method of generating optical heterodyne interference mode were pointed out and the main merits of optical heterodyne interference laser based on the structure of MOPA were presented. The possible limits of obvious effects on interference and inducing optical excursion were pointed out and were proved by experiment. The conclusion is given that the process of power amplification has no effect on interference and the line width is less than 0.1GHz by single amplification(based on real measurement of coherent length, the line width is about 30 MHz),and also that the processes of power amplification and frequency doubling has no effects on optical excursion and it is deduced that the real measurement of frequency excursion less that 10 Hz coinciding with frequency stability of AO frequency shifter was only related with frequency shifter.
2014, 43(2): 350-354.
Based on the rate equations, a numerical model of double clad Q-switched fiber laser was built, and the all fiberized high power linear polarized pulsed ytterbium-doped fiber laser was developed by using a fiberized acousto-optic Q-switched fiber laser as the seed source, a double clad ytterbium-doped fiber as the gain medium. In the pump power of 38.4 W, repetition rate of 40 kHz, pulse duration time of 30 ns, the laser delivered a linearly polarized pulsed emission output with an average power of 29.8 W. Its polarization extinction ratio was greater than 10 dB, and the beam quality factor (M2) was 1.32.
2014, 43(2): 355-359.
Laser diode pumped microchip lasers passively Q-switched by Cr4+:YAG, with high repetition rate, short pulse width and high peak power, have important applications in optical communication, lidar, remote sensing, nonlinear frequency conversion, laser micro-processing and so on. However, in these lasers, the output stability is poor and the repetition rate of output laser cannot be changed widely. This will restrict the applications of these lasers in fluorescence analysis of aerosols or ranging, space optical communication. In the experiment, output pulses with continuously tunable repetition rate from 2 kHz to 28 kHz and stable oscillation were obtained in the laser diode pumped microchip laser passively Q-switched by Cr4+:YAG. In the stability of single pulse energy from 2 kHz to 28 kHz was less than 2.50%. Stable 2.431 ns pulse at 20 kHz with single pulse energy of 17.6 J and extinction ratio of 252:1 and with amplitude instability of 4.00% and frequency instability of 2.40% was obtained. This laser diode pumped microchip laser passively Q-switched by Cr4+:YAG with wide continuously tunable repetition rate and stable oscillation will have broad application prospects.
2014, 43(2): 360-364.
In order to investigate the gain distribution characteristic of non-chain pulsed DF laser, based on the influence of collision widen and Doppler widen of spectrum on gain coefficient, the simple equations were given to calculate the gain coefficient using the variable output coupling method. Under the conditions of different output mirror transmission, utilizing the method of moving iris to scan sample, the DF laser output power of every sampling position had been measured on the cross-section of gain medium. For arbitrary sampling position, two independent gain coefficients were calculated which standard deviation was less than 3%. Average gain coefficient of DF laser was 2.594 3 m-1 and the non-output loss coefficient was 1.243 5 m-1. For gain coefficients of each sampling position, two-dimensional interpolation algorithm had been used to obtain gain distribution on the cross-section of gain medium. The calculation showed that the gain coefficients submitted to supper-Gauss-Poisson distribution which was high in the central and low in the margin. The investigation could provide a guide to design resonator and electrode structure of non-chain pulse DF laser, and provide a reference to analyze the uniformity of gas discharge of this laser.
2014, 43(2): 365-368.
Demand for optical element resistance of laser damage is higher and higher in the high power laser system. The damage characteristics and mechanism of film by pulse laser induced damage was researched. The experiments used by YAG pulsed laser for TiO2/SiO2 thin film were offered for 1-on-1 way of laser induced. The experimental results show that the impact on the optical transmittance of thin film is not big in low energy laser induced. Under the low energy laser induced, film surface structure defect is repaired. The surface structure tends to be complete, and becomes uniform and fine. Under pulsed laser induced TiO2/SiO2 thin film, when the laser energy order is smaller, the laser damage threshold of thin film increases with the increased energy, damage threshold maximum can increase 1 times. When the laser energy order is bigger, thin film damage threshold decreases with the increased energy order.
2014, 43(2): 369-374.
The spatial distribution of burning particles in the pyrotechnic flame play an important role in the ignition and spectral radiance of the pyrotechnic. The first, the local model of the burning particles was built based on the parameters of initial velocity. The second, the sharply focused images of the burning particles in pyrotechnic flame were shot by the high speed camera (HSC) photography, and then coordinate position and velocity vector were analyzed by the image processing techniques. As a result, the local model of the burning particles was corroborated and revised, thus the regulation of velocity distribution was derived. Particle image velocimetry (PIV) was used to investigate the spatial pattern and velocity of burning particles in the flame of pyrotechnics. The investigation result shows that the direction of main burning particles matches the fluid field of flame, but the contour profile of velocity exist large difference.
2014, 43(2): 375-381.
For study of the 90-type mechanically dithered ring laser gyro SINS system which is self-developed by the authors' department, this article detailed analyzed the convergence time and alignment precision of inertial alignment on static base and swing base. Theoretical analysis shows, the value of the alignment time should basis on the IMU accuracy, settings of the algorithm parameter and the disturbance situation. Through a large number of experiment, on static base, it takes 150 s for the heading angle reaches a steady state value, and then the oscillation amplitude of the roll angle and pitch angle are lower than 1.5, the heading angle oscillating is within 1'; on swing base, after 200 s, the error of the roll angle and pitch angle are lower than 7, the error of heading angle is within 1.5'. Results confirm that the inertial alignment can meet the requirement of reaching a certain attitude angle accuracy range within a short time, and can be well used in engineering applications.
2014, 43(2): 382-387.
Single-photon detectors and time-correlated single-photon counting techniques have been widely used in pulse laser ranging system and three-dimensional imaging systems. Analyzing the factors influencing detection precision will improve the performance of ranging system. In this paper, a theoretical model of single photon ranging system based on TCSPC was established and the main factors affecting the accuracy was analyzed. The main factors included laser pulse intensity and pulse width of echo signal statistics waveform and the latter depended on laser pulse width and time jitter of detector. And simulation of the detection process by Monte Carlo method was used to get the specific influence of the above factors on measurement accuracy. Finally, an experimental single photon ranging system is built in lab. The system has an accuracy of 4 mm about the target 10 m away by experiment and the accuracy verifies the simulation results under the same parameters.
2014, 43(2): 388-393.
Research of atmospheric turbulence is actually investigation of atmospheric refractive index. The atmospheric structure constant of refractive index Cn2 is an important parameter of denoting atmospheric turbulence. The atmosphere temperature, pressure and Cn2 were measured in Hefei and Beijing, using new micro-thermal meter. And the statistical character of vertical distribution of atmospheric parameter was investigated by analysis of experimental sounding data in different typical area, offering necessary data for atmospheric turbulence model. Using NOAA model, the atmospheric turbulence models in different typical area were obtained on the basis of actual upper air data. Method evidence and valuable reference will be provided for research on atmospheric turbulence model in other typical area.
2014, 43(2): 394-397.
With background of terminal guided weapon, at first, a scheme of hardware-in-the-loop simulation(HILS) was derived; and the principle of laser semi-active seeker was introduced in detail. Secondly, in the limited indoor environment, mathematical model of geometry between missile and target was established; subsequently the optical characteristics of the laser received by seeker were researched; the model of HILS in the terminal trajectory was designed for guidance and control system. In the end, seeker and gyro was introduced into the closed loop of simulation, simulations were repeated many times under two different conditions of the initial state. In conclusion, the results indicate that guidance and control system of the missile based on this seeker and gyro is achieved correctly and have the ability to hit the target precisely.
2014, 43(2): 398-403.
It is found that the black silicon fabricated by femtosecond laser in the vacuum is different from that fabricated in the gas atmosphere of SF6. To study the related optical properties of this micro-structured silicon fabricated in the vacuum, the changes of its peak height and absorptance were studied by changing the energy of laser pulse. It is found that the microstructures fabricated in the vacuum can also reach the absorptance of ~95% in the spectral range of 200-2 500 nm as that fabricated in the gas atmosphere of SF6. Finally, by annealing the black silicon fabricated in two different environments, the black silicon fabricated in the vacuum has better annealing resistance. These results are very significative for the fabrication of infrared sensor.
2014, 43(2): 404-410.
Researches on the laser deposition repair of BT20 alloy forgings having defects mis-machined or damage were investigated, the reasons of occurring defects such as gas porosities and ill bonding in the repaired zone were analyzed. And flawless samples were obtained through optimizing laser process parameters and introducing the ultrasonic vibration into laser deposition repair system. The microstructure characteristic of laser deposition repair component and distribution of main alloy elements were investigated, and the microhardness of the laser deposition layer was tested. The results indicate that there is a dense metallurgical bond between the repaired zone and the substrate with the optimized process parameters. While the gas porosities ratio of the laser deposition layer is decrease obviously through introducing the ultrasonic vibration to the repaired system. The component elements are unifomly distributed without fluctuation and segregation in the whole repaired sample. Distribution of microhardness from the substrate to the repaired zone showes an increasing trend.
2014, 43(2): 411-416.
The means of coherent Doppler has obvious advantages to obtain the target range change. Based on laser Doppler effect, designed a set of imaging Doppler lidar experimental system. Introduction all phase measurement phase treatment consideration to do time-frequency analysis for heterodyne signal, restraining spectral leakage and reducing the impact of noise on the measurement results, a high measurement accuracy signal frequency curve will be acquired. The process simulation in the simulink interactive simulation integration environment which comes with MATLAB software, to prove it can achieve higher resolution, high precision imaging for scan space. The experimental results show that the system was able to restore the surface of target feature preferably. It plays a promoting role in high-resolution and high-sensitivity imaging of the target for lidar.
2014, 43(2): 417-423.
The DMD dynamic infrared scene projector is an integral component of the hardware-in-loop IR simulation system. The time performance parameters of the projector directly affect the accuracy of images projected to the unit under test. The working principle, driving mode and working sequence of the DMD projector were introduced. The demands for time performance parameters such as modulation time, synchronization and frame frequency in the hardware-in-loop IR simulation were discussed. The testing methods of time performance parameters were put forward, and the experimental platform were set up. The time performance parameters of our projector were tested, some problems of the projector were analyzed, and some suggestions for improvement were put forward. These results would provide some reference for DMD projector design, application and performance evaluation.
2014, 43(2): 424-428.
The comparison research of infrared radiation characteristics of target and background was important for the infrared-guided and infrared stealth topics. The infrared radiation characteristics contrast between target and background on different grounds was researched in this paper. Firstly, the formula of infrared radiation characteristic of target was analyzed, then the different algorithm with different background-soil and cement was obtained. After the experiment, the transformation about the vehicle and background in different grounds was got by the temperature increase. Meanwhile, the achieved temperature of target with different emissivity in soil ground and cement ground were educed. The results also can provid the data support to target stealth in future.
2014, 43(2): 429-433.
Compared with the two-dimensional imaging technique based on spin-stabilized satellite platform of the first generation geosynchronousremote sensing satellite, the biggest advantage of the imaging technique based on three-axis stabilized platform lies in its significant improvement of imaging efficiency, shorter imaging period and simultaneous multi-payloads. In China, the second generation geostationary three-axis-stabilized platform weather satellite, FY-4, is in development. FY-4 scanning imagery radiometer adopts the imaging scheme of double-scan-mirror mechanism combined with three-mirror-anastigmat(TMA), linear array detectors and radiant cooler, achieving an imaging band from visible to very long wavelength IR. The radiometer development is faced with a combination of various task requirements, including the radiometer's harsh on-orbit temperature environment, pointing accuracy, long movement life, etc. So during the developing process, comprehensive technologies of optics, precision mechanics, long lifetime movement, motor control, space thermal control, information processing, etc. were employed to realize high precision imaging under poor temperature environment. The FY-4 satellite will be launched in 2016, which will then further enhance Chinese capacity of unexpected disaster and short-time weather forecasting.
2014, 43(2): 434-437.
Exfoliated graphite is a new kind of composite interfering materials used in electro-optical countermeasure. Exfoliated graphite with different expanding volume was prepared by two-step intercalation, in which the mixture of nitric acid and phosphoric acid and that of nitric acid and acetic acid were employed as intercalating agent step by step, and potassium permanganate was used as oxidant. The microstructure of exfoliated graphite with different expanding volume was analyzed by scanning electron microscope. The infrared screening performance of exfoliated graphite with different expanding volumes was measured by a static method. The results show that the porosity of exfoliated graphite rises with the increasing of expanding volume, the interlayers of graphite are fully opened. And the infrared screening performance enhances with the increasing of expanding volume. When the expanding volume increases from 233 mlg-1 to 450 mlg-1, the infrared screening rate rises from 66.43% to 90.77%.
2014, 43(2): 438-441.
On account of the present situation that the contrast formula can't be used to calculate target and atmospheric background contrast, the irradiance contrast formula of target and atmospheric background was deduced based on the operating principle of focal plane detector. By calculating the atmospheric background infrared radiation, comparing it with the aircraft infrared radiation data report, and analyzing the contrast, results indicate that: the effect of atmospheric background on detection must be taken into consideration. The atmospheric infrared radiation between 3-5m is very low, target in 3-5m is easier to be detected. The atmospheric infrared radiation near 10m is higher, and the target detection is more difficult. As the detection distance increases, the difference of radiance between the atmospheric path from detector to space and from detector to target decreases, and the contrast increases, which is an unneglectable factor to detection distance analysis.
2014, 43(2): 442-448.
In order to study of the influence of low emissivity infrared materials on the range and probability of detection of infrared search and track system for attack aircraft in air combat, aircraft flight process and infrared search and track system detection process model were established, the trend of the range and probability of detection with time, velocity and locus in three typical air combat process such as opposite, same and side direction were obtained. In the calculation, the influence for target spectral radiation characteristics, atmospheric transmittance, detector performance and other factors on the range and probability of detection were considered. The results show that after infrared suppression measure are taken by target aircraft, the range of detection is decreased significantly in the case of the same probability of detection, the probability of detection is decreased significantly in the case of the same distance of attack and target aircraft.
2014, 43(2): 449-453.
In recent, aerosol which is a passive jamming method has been taken seriously by the military and has been widely used in the modern super-science local war because of its obvious economic benefits and great practicability. The aerosol particles' motion equation was presented in this paper. By using the finite-difference method, the motion equation and a mathematical model of aerosol sedimentation and diffusion were given in difference expressions, and a dynamic model of aerosol sedimentation and diffusion was formulated. Method of numerical simulation of aerosol dynamic sedimentation and diffusion was presented. The consistence of the simulation experiment's result and smoke chamber experiments show that the model presented in this paper can accurately simulate the motion of aerosol, which is significant in the research of aerosol material and aerosol behavior, the dynamic simulation experiment of aerosol jamming and the performance evaluation of aerosol jamming.
2014, 43(2): 454-457.
Aiming at the severe problems of system performance degradation that was caused by the blind pixels and the nonuniformity which exists in Infrared Focal Plane Array (IRFPA), multivariate normal distribution sequence noise model of IRFPA was set up firstly, and blind-pixel was regarded as abnormity pixel for the unconformiting mold statistical distribution characteristic and it was dissociating the multivariate normal distribution ellipsoid. Then the principal component was applied to sequence pattern, and the statistical distance and bisectrix spatial angle are regard as statistical criterion of abnormity pixels detection. Finally, to test and verify the performance of the method on taken full advantage of thermal infrared imager to do sequential multiple frames of noise data collection. The algorithm was applied to actual blind pixel detection of uncooled IRFPA and the validity of the algorithm was proved by the experimental result.
2014, 43(2): 458-463.
In order to solve problem of the existing infrared calibration system as laboratory calibration and engineering calibration, a simple infrared calibration system was designed for practical applications in the fields. Its response model was established. Key parameters such as the standard radiation source were also analyzed in detail. In addition, an assistant system was designed and performed in practical measurements. A infrared radiation calibration system was bulit up and the corresponding experiment was performed. Compared with the laboratory calibration results, it was shown that the designed setup could be employed in infrared calibration and radiation measurement with attractive precision and useful simplicity.
2014, 43(2): 464-468.
The near infrared readout circuit reads avalanche signals of avalanche-photon-diode operating in the Geiger-mode. Two ps-grade programmable ECL delay chips were used to get adjustable gate pulse, control APD's dead time, quench the avalanche signals and decrease the after-pulsing. The paper detailed describes gate pulse generated block, dead time controlment block and avalanche signals readout block. A moderate delay and edge trigger flip-flop were used to read avalanche-photon-diode signals. During the whole experiments, avalanche-photon-diode worked in the temperature -55C, the gate pulse width is 10 ns, the gate frequency are 1 MHz and 10 MHz, the wavelength of laser is 1 550 nm and the single photon detector is PGA-400 InGaAs avalanche-photon-diode.
2014, 43(2): 469-473.
According to the need of controlling the slag content in the process of converter tapping, a slag detection system based on the principle of infrared temperature measurement was designed. Firstly the temperature of pouring stream was measured using the infrared temperature measurement system. The molten steel and slag were distinguished according to their infrared emissivities that had big difference in far infrared band and the real-time amount of slag contained was calculated. In different steelmaking sites(different atmospheric transmittances, different ambient temperatures, different tap temperatures, etc), the infrared emissivities of the molten steel and slag were changed, therefore a calibration method of the temperature threshold that was used to distinguish the molten steel and slag in a certain environment was proposed. A method that could quickly find the edge of the pouring stream was applied to complete the tracking of pouring stream, which could avoid the amount of slag was incapable of being calculated due to the change of converter angle(moving of pouring stream). Experimental results show that this method controls the amount of slag in the steel ladle and meet the requirement of molten steel refining.
2014, 43(2): 474-478.
The design of a liquid crystal(LC) device was presented, which could be used to measure and regulate the polarization state of the incident light by only changing the voltage amplitude of the driving signal applied over the patterned electrodes, and simulate the direction orientation distribution in the LC layer of the device. As known, the tilt angle of the LC molecular can be controlled easily. However, it always was ignored that the twist angle could also be electrically controlled. So, the LC material can be used as a variable and rotatable phase retarder, and then the polarization state was regulated after measuring the polarized incident light through the same testing architecture. The direction orientation distribution of the LC layer with the cross-shape electrodes was simulated firstly. Results show that the twist angle can be electrically controlled, and it is achievable to regulate the polarized state of incident light to any desired polarization state.
2014, 43(2): 479-482.
A dielectric structured lens formed by varying the high-refractive-index square dielectric holes was proposed. This lens can realize higher energy efficiency compared with the high-refractive-index square dielectric metal structured lens. The energy efficiency has achieved 44% by finite difference and time domain(FDTD) algorithm, and the spot size leads to the diffraction limit. Second, the dispersion characteristic of the lens was researched, it has the counter dispersion characteristic with the geometrical optics lens, so lens group make up of those dielectric structured lens and the geometrical optics lens can be used to clear dispersion. In addition, it overcomes the limitation of feature size of the large numerical aperture(NA) lens, so the large NA lens can be achieved. Four lens with the same aperture but different focus length were designed for the wavelength 10.6m. The smallest F number has reached 0.25.
2014, 43(2): 483-487.
By applying a magneto-optical semiconductor layer of which has the Voigt effect to the surface of a dual-periodical photonic crystal heterostructures doped by impure layer, the transmittance of the defect mode of this photonic crystal makes a response to the external magnetic field.The variation of dielectric constant(refractive index) of the magneto-optical semiconductor surface accompanied with the external magnetic field was studied firstly. And then, the variation of transmittance of the defect mode with a external magnetic field was explored via using transfer matrix method.The results show that under the conditions of selecting a appropriate structural parameters and material parameter, it can realize the correlation between the transmittance of defect mode and the magnetic field,and obtain the transmittance of defect mode controlled by an external magnetic field.Therefore, the photonic crystal with such structure can be applied to the magnetic switch of the narrowband filter.
2014, 43(2): 488-492.
A periodic structure of bonded GaAs wafers can be used for high power quasi-phase-matched second-harmonic generation of a CO2 laser. The fabrication of the QPM GaAs based on wafer bonding technology and interfacial properties of this crystal were studied. Hydrogen ion beam was used to remove the oxide layer on the GaAs surface to improve its optical properties. Pre-bonding process in the ultra-high vacuum reduced the microspores density of the bonding interface. Heat treatment increased the bonding force. Thus a reliable bond of the two-layer GaAs was realized. The two-layer GaAs combined into a single crystal structure without amorphous layer formed by oxide. By this bonding process a periodic polarization reversed GaAs crystal with large aperture, low loss was obtained, therefore providing a way for realizing high power frequency doubling of CO2 laser using quasi-phase-matching technology.
2014, 43(2): 493-496.
Based on theory of optical transformation, a novel rotatable and amplifying optical transformation device was proposed, and this device could be realized with metamaterials with parameters of positive refraction index. The constitutive tensors of the proposed device were derived, and then some full wave simulations of the devices based on the above constitutive tensor were performed to confirm the functionality of the proposed device. The simulations results verified that the proposed device can make the inside object rotate and enlarge. Therefore, it is expected that the proposed device will have potential applications in the electromagnetic engineering.
2014, 43(2): 497-501.
The operational principle and characteristic of incremental photoelectric angular encoder were summarized and discussed. And the reasons of reference mark excursion for incremental photoelectric angular encoder were analyzed. In order to validate reference mark excursion, a pointing function, which defined in the spherical coordinate of level mounting telescope, was expanded into series by spherical function. Then the spherical function model of pointing error was obtained. 30 stars scattered in sky space uniformly were selected to observe, through which the discrete value of 30 stars' pointing error were gained in longitude dimension and latitude dimension respectively. A new technique called external checking method, which used observing data two days ago to check intraday pointing error, was tested to validate the phenomenon of reference mark excursion. An experiment measuring pointing error before and after reference mark calibration by observing Polaris last 11 days. The results showed reference mark excursion caused pointing error of telescope becoming greater than the technical index designed. And after calibration the reference mark became fixed all night. To evaluate the effect of reference mark calibration, orbital position of a GPS satellite was measured by optoelectronic telescope. Pointing error of the telescope was gained compared with precision orbital position of GPS satellite. The results show that before reference mark calibration the mean azimuth and elevation error was 13.99, 11.50. And after calibration the mean azimuth and elevation error decreased to 5.94, -3.49 respectively. The experiment of GPS star observation showed that the reference mark calibration was available to eliminate reference mark excursion and to improve observation precision.
2014, 43(2): 502-505.
Laser gyroscope working mode is likely to hop when it works for a long time or the ambient temperature changes greatly. To change the mode of the laser gyro will bring a great impact on it's performance. Based on the analysis to the backscattering properties in the adjacent model of laser gyro, the backscattering intensity is periodic, and there is a strict correspondence between the working mode and backscattering intensity. The laser gyro mode hopping pattern is that if the model of laser gyro jumps in the same model gyro performance before and after does not change significantly, while it jumps in the adjacent model gyro's lock-in will arise and bias will jump, and gyro performance is affected greatly. According to the mode hopping law the reasonable suggestion was put forward, the above conclusions were proved by the experiment.
2014, 43(2): 506-510.
A dual-elliptical-core polarization splitter based on photonic crystal fiber was proposed. The relationship between splitter length and structure parameters was analyzed using full vectorial finite element method. The variation rules of splitter length with hole pitch, duty circle and bridge were found for the given dual-elliptical-core polarization splitter. Results suggest that if the structure pattern was set, the shorter hole pitch is and the broader the bridge is, the shorter the splitter length is. Duty circle has noticeable influence on extinction ratio, but not on splitter length. According to these rules, an ultra-short dual-elliptical-core polarization splitter was optimized. The length of the polarization splitter is as short as 0.775 mm, extinction ratio reaches up to 50 dB with the wavelength of 1 550 nm, and the bandwidth is more than 30 nm when the extinction ratio more than 20 dB, which covers the communication C band from 1 535 nm to 1 565 nm.
2014, 43(2): 511-516.
Chalcogenide glasses were possessed of some unique advantages, such as large infrared transmission window(up to 25 m), low phonon energy(lower than 350 cm-1), large glass forming region and highly nonlinear refractive coefficient n2(about 100-1 000 times than silica). With excellent optical nonlinear,calcogenide glass photonic crystal fiber had a large number of potential applications in the infrared filed. A highly nonlinear photonic crystal fiber based on Ge20Sb15Se65 chalcogenide glass was designed. Using plane-wave method(PWM), numerical analysis of its nonlinear and dispersion characteristics with different structure parameters were carried out. By optimization structural parameters, a highly nonlinear and broadband dispersion-flattened fiber was obtained. With a 3.4 m laser pumping, signal light could be effectively amplified in 3.3-3.5 m.
2014, 43(2): 517-522.
An optical system of UV limb panoramic imager was designed by using panoramic annular lens (PAL) and relay lens, the central wavelength was 360 nm, the waveband was 10 nm, the field of view was 360(70.9～73.3), the focal length was 5 mm, and the relative aperture was 1:3.3. The method of improving the uniformity of image illumination was studied against the large field of view of the optical system. Optimization and analyzsis were performed using CODE V and ZEMAX software. The design result shows that the RMS radius of disc of confusion of spot diagram is less than half of the pixel, 80% of energy is enclosed in a pixel, the MTF is 0.72@38.5 lp/mm, the f- distortion is less than 0.4%, the uniformity of image illumination is 91%. The design results satisfy the requirement of the specifications, the volume is small, and suitable to application in space atmosphere sounding. It indicates that the optical design method of UV panoramic imager is feasible, and the design method can be used in other wavebands, it is instructional for designing the panoramic imager.
2014, 43(2): 528-534.
According to the large aberration of conformal optical system caused by the large slope and eccentric, the rotation double Zernike phase plates were combined with fixed corrector based on Wossermann-Wolf equation. The aberration of optical system in different field of regard(FOR) was effectively corrected by rotating the two plates. It can both improve the image quality and make the structure more compact. An optical system with f=90 mm, diameter D=48 mm, wavelength 3.7-4.8 m, field of regard(FOR) 42, instant view angle 2.44 was designed. The results show that each field of optical transfer function is close to the diffraction limit. An optical passive athermal infrared conformal system is realized by using DOE elements. During -20-60C the merit transmitting function in each FOR is more than 0.45 at 17 lp/mm. The image quality performs well.
2014, 43(2): 541-545.
The hyperspectral imaging spectrometer is a new type of load in the modern space remote sensor. The hyperspectral imaging spectrometer optical system designed in this paper has been made up by two parts, front telescope system and imaging spectrometer system. The front telescope system and imaging spectrometer was designed respectively, then assembled and optimized. Off-axis TMA structure was used by front telescope system to increase width, improve image quality, and reduce distortion. Separated fields method was applied on front telescope system for larger swath width and better image quality. Imaging spectrometer was designed by Offner structure with grating convex second mirror. Assembled system has larger swath width, smaller volume, better image quality, higher spectral resolution, and more spectral passage. The MTF of every fields and every spectrum is higher than 0.7 at Nyquist frequency, the diffusion circle of image with 80% energy is 15 m, smaller than CCD pixel size, so the image quality reaches the technology target of system.
2014, 43(2): 546-550.
By comparing the advantages and disadvantages of two-mirror and three-mirror reflective systems,a novel unobscured two-mirror three reflective optical system was presented. In contrast with other off-axe three- reflective optical systems, the greatest advantage of this system was that it only utilized two aspherical reflectors,which saved the cost,reduced the difficulty of process. The design steps of this system were analyzed in detail. And a optical system was designed with its focus length, field of view, relative aperture, and system length are 500 mm, 10.1, F/5,125 mm respectively. Pixel size of the system was 10. Its MTF curve and spot diagram show the imaging quality approximates its diffraction limit. This approach can provide reference for the optical system design of present aerospace cameras.
2014, 43(2): 551-556.
The optical signature measurement technology plays an extremely important role in the fields such as missile penetration,optical reconnaissance and operational effect. In order to make better use of infrared radiation characteristics measuring in the optical signature measurement system, it is very necessary to make high-accuracy calibration of the signature measurement system. As requested in developing a certain model ground-based optical signature measurement system, three calibrating methods were discussed and high-accuracy indirect extended source methods were used for calibrating the system. From an overall point of view, the design of tracking and measuring system,blackbody system and large caliber off-axis collimators were explicitly introduced, so the signature measurement system embodied 1 000 mm tracking and measuring facilities,calibration oriented 50-300 ℃ cavity blackbodies as well as 1 100 mm off-axis collimators. Thus the ground-based optical signature measurement system is capable of high-accuracy radiation calibrating and high-accuracy measuring.
2014, 43(2): 557-561.
Visual simulation is useful for designing, analyzing and testing a space-telescope on the ground. Based on the coordinate transformation theory and the equal-angle projection method, visible boundary of the telescope was deduced for different orientation, and the two-dimension visual simulation was carried out using a real star catalog and the world coast line data. Reasonable results show that when the space-telescope is pointing to the high latitude area, a distortion of the round visible boundary appears in the Equidistant Cylindrical Projection style map chart. And the visible area on the earth surface is expanded when the height of the space-carrier increases. The simulation was used to imitate the celestial background in a real testing of a space-telescope outdoor. It's useful in testing and providing space environment for space-telescope on the ground.
2014, 43(2): 562-568.
As to minimize size of the measurement system of large size and ultra-long focal length lens, two mirrors are used to change light path. In this case, installation error of the two mirrors added may be a large obstacle to accurate measurement of ultra-long focal length lens. For the sake of analyzing how installation error of two mirrors infect the angle of Moir stripes on receiver, Moir stripes are understood as parallel lines which composed of point light source with certain light-path vector. This approach proposed uses the calculation formula from mirror deflection angle to the reflector unit normal vector, and the matrix form of the law of reflection, to calculate the relationship matrix from vector of incident light to vector of exit light. Based on unit normal vector of two mirrors, incident light-path vector, exit light-path vector, and analytic geometry, equation of line on which image of point light source place can be presented, so we can get the angle of Moir stripes on receiver and so is the angle error caused by installation error of the two mirrors added into light path. In addition, the angle error of Moir stripes is calculated theoretically in 49 different situations of small mirrors deflection smaller than 1 degree. The results indicate that the installation error of the two mirrors should be taken into consideration. A new method by using autocollimator to adjust the installation error of the two mirrors is proposed, installation error of the two mirrors can be controlled to lower than 1 through this method. Moir stripes angle error should be better than(10-4) order of magnitude in this situation. Experimental results show that Moir stripes angle measurement error is 0.005 degree, which fully illustrates the effect of mirrors adjustment when this system is used for the measurement of ultra-long focal length.
2014, 43(2): 569-573.
The traditional unobscured three-mirror optical system is an intrinsically rotationally symmetric optical system with an offset aperture stop, a biased input field, or both of them, so off-axis sections of rotationally symmetric aspheric parent surface are ineluctable. Using the conclusion of vector wavefront aberration theory, a new unobscured three-mirror system by tilted the rotationally symmetric aspheric mirror was presented. The design reason and step of this system was analyzed, and then a system with effective focal length of 1 000 mm, field of view of 1020 and F-number 10 was designed. The volume of system(LengthWideHeight) less than 350 mm350 mm120 mm and image qualities of the example are near diffraction limit. Compared with other unobscured three-mirror system, the most prominent advantage of this system is that using tilted rotationally symmetric aspheric mirror to achieve unobscured style, thus reducing cost of the system.
2014, 43(2): 523-527.
Three-field zoom system has advantages of simple mechanical structure, better reliability, short time of changing focal relative to other pattern zoom systems. Using 320240 resolution cooled detector with 30 m30 m pixel dimension, a middle-wave three-field optical system was designed by secondary imaging way. The system's F number is 4, FOV range is 1.4-23.8, it can realize 30 mm/100 mm/500 mm three position focal length. In designing process, the Germanium material and Silicon material were adopted to balance chromatic aberration, introducing one asphere to balance sphere aberration. The system use two mirrors reducing the axis dimension. The dimension of system better than 210 mm160 mm120 mm, it has characteristics of small dimension, simple zoom structure, good image quality etc. The modulation transfer function(MTF) is above 0.5 at spatial frequency of 17 lp/mm and energy concentration ratio is greater than 70% within the sensing element of the detector.
2014, 43(2): 535-540.
The large space remote sensing instrument has high requirements for heating and mechanical characteristics, as well as strict limitation in weight, to adapt to severe launching and working environment. Thus the mirror and supporting system is stringent in weight, rigidity and environmental flexibility. The paper analyzed, designed and demonstrated the parameters of a 620 mm remote sensing mirror and its mounting structure. The central mounting system was served to meet the light weight and rigidity requirements compared with the other mounting methods. Radical weight-reduction slot morphology was developed in accordance with equal strength principle. The partial contact stress would increase as temperature changed. A flexible material was utilized to solve the problem, which would mitigate the structure effect to optical mirror. The results show that the weight of mirror is 15 kg and mounting accessory is 3.5 kg, with the weight reduction rate of 71.2%. The first mode is 420 Hz;The profile accuracy of mirror is 0.03 RMS. The technical parameters are stable and satisfied with the optical system requirements under various tests. The primary mirror project is implemented in the space and attains the expected goal.
2014, 43(2): 574-578.
Spectral imaging and polarimetric imaging are both advanced optical detection techniques. In recent years, these two techniques appear new trend to merge into the imaging spectropolarimetry, and make the optical remote sensing tend to multi-dimensional and multi-information fusion. In 2010, two novel methods for measurement of the spectrum, polarization and imaging of scenes were originally proposed: one was pushbroom mode, the other was windowing mode. In this paper, the concept and theory of a sensor based on the windowing mode method were given. With specially aligned static birefringent retarders, different phase factors were modulated onto the Stokes vector of incidence light. After passing through a static birefringent interferometer, the spectrally dependent Stokes parameters were distributed into several separated interferogram channels. With corresponding Fourier-transform demodulation, all of the wavelength-dependent polarization, spectral and spatial imaging of objects could be completely obtained. Besides the sensor employed 2-D field of view, which meant the optical throughput was two order of magnitude higher than that of pushbroom one. The experimental demonstration of the sensor was also presented. This research gives a new way for spectropolarimetric imaging measurement, and provides theoretical and practical supports for the development of new space remote sensors.
2014, 43(2): 579-585.
The side-scan imaging of the linear push-broom hyperspectral camera could solve the problem that the remote sensing images collected from the satellite platform could not get the spectral data of building facades. The main components and the key technical specifications of linear push-broom hyperspectral remote sensing system integrated and developed by our research team were stated in this paper. According to the feature of side-scan imaging, the geometric correction model was derivated in detail, which was suitable to the linear camera side-scan imaging. The methods of geo-referenced image divided into grids and spectral resampling were presented, and the solution for data loss in the collection process was also proposed. The validity and robustness of linear image distortion correction algorithm were verified through amounts of simulation experiments. It provided reference for the application of similar products.
2014, 43(2): 586-594.
Near-ground imaging spectroscopy applied in field provides new opportunity for development of quantitative remote sensing in agriculture. It deserves concern about how to exert its data advantage of integrating image and spectra into one, particularly in analyzing the influence of background targets, such as soil, shadow on crop nutrient inversion model. In this research, imaging cubes of wheat group in the field were collected by visible/near-infrared imaging spectrometer (VNIS). A normalized spectral index was set up according to reflectance characteristics of illuminated soil, shadow soil, illuminated leaf and shadow leaf in the image. Furthermore, the index was used to extract spectra of different targets in soybean images and analyze the variation of determination coefficient R2 between normalized spectra of soybean group and chlorophyll density before and after removing background soil. The results showed that when spectra of soil and shadow leaf were removed, the sensitive bands of chlorophyll density shifted from red and near-infrared ranges (727 nm, 922 nm) to red ranges (710 nm, 711 nm), meanwhile, the overall trend was that visible ranges increased, near-infrared regions decreased and red bands had the highest determination coefficient. Therefore, it can be concluded that spectral purification based on normalized spectral index has important significance for quantitative research in agricultural remote sensing.
2014, 43(2): 595-599.
Cerium (Ce) and ytterbium (Yb) co-doped silicon oxide (SiOx: Ce, Yb) thin films were deposited by using magnetron co-sputtering technique. The down-conversion photoluminescence (PL) properties and structural evolution of the films after thermal treatments were studied. Under the excitation of a He-Cd 325 line, light emissions from the Ce3+ ions are rather weak while quite strong from the Yb3+ ions; the Yb PL intensity increases with elevating the anneal temperature, and both PL excitation and decay spectra indicate that energy transfer from Ce3+ to Yb3+ ions has taken place in the oxides. X-ray diffraction patterns show that Ce and Yb-related silicates have formed as the annealing temperature is higher than 1 000 ℃. The authors believe that the Yb PL can be enhanced greatly by forming high-luminescent Ce3+-related silicates in the oxide films, and thus increase the down-conversion efficiency.
2014, 43(2): 600-604.
Composite coatings with micro/nano scale TiN reinforcing phases were successfully fabricated by pre-nitriding+pulse laser cladding treatments on TC4 substrate surface. A comparative research on microstructures and mechanical properties were carried out between the pre-nitriding+cladding(PNC) composite coatings and the conventional laser gas nitriding(LGN) samples. The results showed that the PNC composite coatings were composed of TiN and ' martensite. With the contents of N in powder mixtures augmenting, the hardness increased gradually. Comparative analysis indicated that, the hardness properties of the PNC composite coatings were equivalent with that of LGN samples. In addition, the PNC composite coatings displayed better homogeneity of hardness along depth direction than that of the LGN samples. Based on data fitting, an empirical formula was tentatively developed to estimate the hardness of PNC coatings.
2014, 43(2): 605-609.
YMnO3 nano-powders were synthesized by microwave-assisted sol-gel method. The composition and the thermo-decomposing process of the gel were studied by means of IR spectrum and TG-DSC analysis. The phase constitutution and particle morphology of the YMnO3 powders were characterized by XRD, FSEM and TEM. The magnetic properties of YMnO3 nano-powders were also studied. The results show that, by using microwave-assisted sol-gel method, nano-sized YMnO3 powders can be synthsized under lower calcined temperature in relatively shorter time compared with the traditional sol-gel method. The YMnO3 powders prepared by the microwave-assisted method have a uniform particle size smaller than 100 nm. The magnetic hysteresis loop result shows that YMnO3 nano-powders exhibit paramagnetic characteristic at room temperature.
2014, 43(2): 610-614.
(NH4)2CO3 was added into mixed solution contained Li+, Co2+, Ni2+ and Mn2+ ions as a precipitant. The mixing precipitation precursors were prepared by one-step co-precipitation reaction. After being dried and ground, the precursors were sintered under different sintering temperatures(700-1 000 ℃) and different sintering times(6-24 h), and then LiNi1/3Co1/3Mn1/3O2 powders were obtained. The microstructures and electrochemical properties of the as-prepared powders were examined using X-ray diffraction(XRD), scanning electron microscopy(SEM), cyclic voltammetry(CV) and electrochemical impedance. The results show that the obtained LiNi1/3Co1/3Mn1/3O2 powders are pure -NaFeO2 layered structure;the powders are uniform and exhibit excellent discharge specific capacitance and lower impedance. After sintered at 900 ℃ for 12 h, the obtained LiNi1/3Co1/3Mn1/3O2 powder exhibits the optimum electrochemical performance. The specific capacitance of the LiNi1/3Co1/3Mn1/3O2 powders can reach 399.46 Fg-1 within potential range of (0-1.4) V at a scanning rate of 5 mVs-1 in 1 molL-1 Li2SO4 solution. And the powders also have the lowest impedance.
2014, 43(2): 615-619.
The equipment of Micro Unmanned Aerial Vehicle (MUAV) was limited by weight. In this paper, the coordinate solver model based on machine vision was introduced, and on this basis, the iterative approximation algorithm which was based on Digital Elevation Model (DEM) was considered to get the altitude difference between the Unmanned Aerial Vehicle (UAV) and the target in order to locating the ground target caught by the optronics pod with the airborne equipment of an MUAV autonomously. The computer simulations and the flight experimental results from program which was transplanted to the airborne devices showed that the coordinate solver model combined with the iterative approximation algorithm could calculate the position of ground target in the video stream (25fps) timely and accurate.
2014, 43(2): 620-624.
Based on the global motion of the scene caused by the movement of the camera focus, a method named MOF(Motion Of Focus) was established. As the camera moved freely, the compensation of the overall movement was needed for the strong parallax caused by the depth of field. From the perspective of the camera, analysis of the compensation was performed which emphasized on the movement relation between the moving camera and optical field, and a MOF Model was given to show the characterization of the overall movement of the scene. With the camera movement speculated by the overall movement, optical flow constraints were deduced to exclude the parallax false alarm by projective geometry from the perspective of the moving camera. At the end, experiments were performed based on actual image data. And the results compared with other algorithms show that this model is practical under the translation and rotation of camera.
2014, 43(2): 625-632.
Joint transform correlator(JTC) was applied to track the moving target in foggy weather or the other low visibility environment, to solve the low recognition ratio problem caused by low contrast and low visibility characteristic of the target and the background noise interference in this environment, a pre-processing method based on multi-wavelet enhancement was applied, it can use different methods to process the high and low frequency coefficients according to the different feathers of the decomposition coefficients on the basis of the multi-wavelet transform merits, which can make the processed image undistorted, simultaneously enhance the contrast and the target edge, and suppress the background noise. The optical correlation experiments on a large number of moving targets captured in a simulation fog environment show that this method can effectively enhance the efficiency of the moving target tracking in foggy weather environment and verify the feasibility of this algorithm.
2014, 43(2): 633-639.
Considering camouflage target polarization detection under the complicated background, basing the Chinese color system and CIE1976L*a*b* color space, the 256 gray levels table was established by LMS and l color space. A best polarized reference direction was found out by field experiments of the high polarization degree target-background contrast. Representing polarization information advantages- disadvantages and reflecting polarization detection capability strengths-weaknesses was further researched. Experimental results showed that, the?linearly polarization direction of perpendicular to the incident is a best reference direction, the polarization image of LMS space was reduced few information than its gray image in the bright illumination, but possessed the stronger ability of representing target polarization information; polarization image of l space was compared its gray image in low illumination, not only the contrast of targets and background was obviously improved, but also the detecting ability of shadowed target was stronger, the calculation results is consistent with the interpretation results of human eye.
2014, 43(2): 640-646.
In order to reduce noise and extract richer discriminant feature, the local ternary local derivative pattern operator was proposed. By determining whether the adjacent pixel gray values within a certain range, the local derivative pattern of current pixel was extended from binary to ternary, and the face feature vector was formed by sequentially connecting the uniform pattern of the space histogram of the encode. The chi-square statistic was used to calculate the sample similarity of face feature vector. The experimental results on ORL, Yale and CAS-PEAL-R1 face database show that the recognition performance of the proposed algorithm was superior to local binary pattern and local derivative pattern.
2014, 43(2): 647-653.
To solve the problem that the pure linear or nonlinear filter is difficult to obtain the optimal state estimation results of a hybrid linear/nonlinear dynamic system, a novel hybrid dynamic filter based on Kalman filter(KF) and Augmented Cubature KF(A-CKF) was proposed by utilizing the advantages that KF can obtain optimal solution for linear state and its computation cost is low. In the presented filter, the system state was decomposed into linear and nonlinear parts which were estimated by the KF and the Simplified Twice Augmented Cubature KF(STA -CKF) respectively. The simulation results of the maneuvering target tracking and the strapdown inertial navigation system nonlinear initial alignment cases show that the novel filter had similar filtering accuracy to the Rao-Blackwellized particle filter but lower computation cost. Compared with the pure STA-CKF, its accuracy and real-time performance were improved significantly.
2014, 43(2): 654-658.
Using the morphological filters for de-noising, the determination of the structuring element's size is the most important step. However, most of the determination methods depend on either the experience or a comparison with the ideal waveform for optimizing structuring element's size, the former is lack of accuracy, the latter is lack of practical significance. Aiming at these problems, the paper proposes a new method that uses a detection factor function determinate the structuring element's size.Firstly, the message of signal structuring size was obtained by the use of detection factor function.Secondly, with the derivation of the message, proper sizes of the structuring elements were acquired.Finally, the multiscale pyramid type filters was used to de-noise the signal. Through the simulation of random signal de-noising and the de-noising experiment of lidar return signals, this method demonstrated better de-noising effect. Comparing with other usual morphological filtering methods, it neither depends on experience nor the introduction of the ideal waveform. Therefore, this method has a promising future.
2014, 43(2): 659-664.
This paper presented a novel affine invariant image matching algorithm based on subspace theory. Firstly, the nonlinear geometry structure of the affine invariant feature space was explored and the affine invariant subspace image features were extracted; then the global consistent matching of shape feature was realized based on the theory that the feature matrix of target shape can be determined only by its orthogonal projection matrix; finally, the same target images were matched with affine transform through computing the subspace distance. Matching experiment results on simulated transformed real images and real images shows that the proposed algorithm exhibits higher capacity to affine transform and robust to perturbations.
2014, 43(2): 665-670.
Based on the principle of Gyrator transform, the self-imaging effect, i.e., the Talbot effect, was investigated firstly. The condition under which the Gyrator transform Talbot effect can occur was given, and the difference between the Talbot effect mentioned in this paper and the traditional Talbot effect was found the Talbot angle was not fixed, the distribution of the angles was not linear, and the fractional Gyrator transform Talbot effect could not obtain through fractionalizing the Talbot angle. Secondly, noise reduction in image processing based on Gyrator transform was also discussed in the paper. It was found that the Gyrator transform could not only reduce the hyperbolic noise efficiently, but also can reduce the-kind noise that brings hyperbolic information efficiently. At last, the shortcoming of the study and follow-up investigations were pointed out. The research in this paper can help people understand Gyrator transform deeply, also develop the self-imaging and noise reduction techniques.
