2012 Vol. 41, No. 1
2012, 41(1): 1-6.
The new development of infrared scene projection technology which emerged in recent years
were summarized in this paper. Some new typical methods were introduced, for example VLSI-
membrane-mirror-light-modulator scene projection technology, mid-wave infrared light emitting diodes
for using in infrared scene projection, infrared liquid crystal light valve based on polymer/liquid crystal,
a new electron beam-addressed reflective spatial light modulator and projection system for HWIL scene
generation, an improved CMOS-compatible bulk-silicon-micromachined microemitter for dynamic
infrared scene projector, single-layer SiGe infrared wide-band microemitter arrays by MEMS
technology, and so on. At last, the development trends of the infrared scene projection techniques was
analyzed.
2012, 41(1): 7-9.
Infrared (IR) photo detectors based on InAs/GaSb type II superlattice have developed quickly in recent years. Many groups show great interest in InAs/GaSb superlattice detector for its superiors as high quantum efficient, high working temperature, high uniformity and low dark current densities. The growth of mid-wavelength infrared InAs/GaSb superlattice on GaSb substrates by molecular beam epitaxy (MBE) was studied. The growth temperature and the interface structures to obtain high quality material were optimized. The InAs/GaSb superlattice layers were characterized by atomic force microscope(AFM) and high resolution X-ray diffraction(XRD). Finally, highly lattice matched mid-infrared InAs/GaSb superlattice material was achieved. The FWHM of the 0th satellite peak of X-ray scanning curve is 28.8 arcsec. The p-i-n single IR photodiode based on InAs/GaSb superlattice has current responsivity of 0.48 A/W and blackbody detectivity of 4.541010 cmHz1/2W, and peak detectivity of 1.751011 cmHz1/2W at 77 K.
2012, 41(1): 10-14.
Aircraft plume is a kind of high temperature and high pressure gas, which will lead to strong radiation energy into the space and have a great influence on aircraft stealthy performance. To compute the infrared radiation signature of plume, firstly based on the Navier-Stokes equation and other governing equations, the characteristics of the whole flow field were calculated under the division of flow field, including the temperature, pressure and composition of each gas. Then, the band model parameters of the gases contained in the plume, such as spectral line absorption coefficient, interval density and half width, were computed by using both the Collided-broaden effects and the Doppler-broaden effects of the spectrum. Finally, by use of the Curtis-Godson approximation of non-uniform gas, the infrared radiation intensity of a rocket plume from the wavelength of 2 to 5 m was computed, and the results of simulation validate the correctness of this method.
2012, 41(1): 15-19.
Infrared scene simulation systems based on computers are limited in input and output interface, which induces the weakness in real-time response and extendibility. The demonstration platform of real-time close-looped infrared scene simulation system based on embedded hardware was described. The parallel-calculation and multi-pipeline technology of this system were introduced. It combined several chips together to enhance its real-time calculation capability. The single-task environment enabled the simulation system to response real-time, which made the close-looped simulation possible. A self-design real-time rendering engine especially for infrared application was adopted to enhance the simulation precision. The realization and optimization process of this system were described, and the experimental result was given. The running time was controlled within 25 ms/frame with frame frequency of imaging system of 40 frame/s. All the results prove that it can reache design requirement.
2012, 41(1): 20-24.
A hardware approach based on looking-up table was proposed to implement image fusion by transferring natural daylight colors to multi-band images in the l space, and consequently a long-distance infrared and low light level (LLL)/visible fusion imaging system was developed. An LLL camera and a CCD fusing with an infrared thermal imager in the night and day respectively, which ensured the system to keep 24-hour fusion imaging. The colors in the resulting colorized multiband night-time images closely resemble the colors in the daytime color reference image and object colors remain good color constancy. Two fields of view were designed, which satisfied the need of searching in the big field of view and tracking in the little field of view. A laser rangefinder was embedded in this system to satisfy the need of measuring distance. Preliminary field trials demonstrate the potential of the system for applications like surveillance, navigation and target detection.
2012, 41(1): 25-29.
It has important theoretical significance and application value to study the real-time simulation technology of infrared sea background. Considering the conditions of existing computer software and hardware，a sea background infrared real-time simulation method was presented, which introduced a variety of optimization techniques, and achieved a higher frame rate of the sea background infrared real-time simulation. The 2D FFT technique was used to fast compute the geometric model data of sea, and the Geomipmap technology was introduced to optimize the organization of sea geometry model data. To accelerate the infrared radiation computing, the GPU was used. In order to improve the real-time rendering speed, pregenerated off-line data technique and view point based rendering technique were proposed. The result shows that the rendering speed of infrared sea created by the method can achieve 300 frame/s, meets the requirement of real-time simulation, and reserves more computing resource for other simulation parts of simulation system.
2012, 41(1): 30-36.
MMW radar/IR compound guidance technology has become a hot research content of compound guidance field. Starting from the characteristic of MMW radar/IR composite seeker system, the federated filter(FF), structured with 2-levels, was used to set up a distribute information fusion algorithm of radar/IR composite seeker in this paper. In order to solve the problems that the extended Kalman filter algorithm had linearization errors and the glint noise of radar sensor was not a Gauss noise, the particle filter algorithm(PF) was used to design radar local filter; in order to solve the problem that the IR sensor couldnt measure the distance between missile and target, the pseudo-linear Kalman filter (PLKF) algorithm was used to design IR local filter; and after that, the main filter was responsible for data fusion and data reset to local filters. Simulations results demonstrate the effectiveness of this mode and show that this information fusion algorithm improves the tracking precision and the stability of radar/IR compound seeker system.
2012, 41(1): 37-42.
The technology about detection, reconnaissance, and guidance of IR imaging occupies an important position in modern war. In order to quantitatively evaluate the obscuring effect of smoke agent and smoke equipment to IR imaging system, the test process and calculation method of some characteristic parameters were discussed in detail. Both the mass extinction coefficient() and the total obscuring capability(TOP) were characteristic parameters to evaluate the obscuring performance of smoke. And their comparatively accurate test results could be got in the smoke chamber where distribution of smoke particles was easily uniform. So the smoke agent could be selected on the basis of the mass extinction coefficient and the total obscuring capability. Nevertheless, in the field experiment, the motion state of smoke particles was strongly affected by meteorological factors. Then it was very difficult for and TOP to be directly measured. So the obscuring efficiency of smoke agent and smoke equipment to IR imaging system had best be quantitatively characterized by other parameters, such as the transmissivity and the effective obscuring time.
2012, 41(1): 43-48.
SNR is a crucial parameter of the detector. In this paper, it was mainly concentrated on the analysis on the relationship between the integration time and the SNR of the domestic 640512 MWIR cooled detector. Based on the theory of the fact that the integration time is corresponding to the signal and the noise, a lot of work was done which focused on these two aspects in the separate way when the detector was working under the normal condition. A large number of experimental data was analyzed which demonstrated the increasing relationship between the detectors output signal and the noise signal while the integration time was changed. The experimental and the theoretical analyzed results both concluded the impact of the integration time to the SNR. Finally, the most optimal integration time was submitted.
2012, 41(1): 49-52.
The high-repetition 3-5 m mid-infrared laser has gain a lot of attention for its potential applications in civil and military. However, there are many technical difficulties to generate this band laser and it is invisible. Therefore, there are rarely such reports about methods of near- and far-field measurements for the lasers. In this article, the near-field measuring for the parameters of laser was conducted at first. Then, the absolute and relative energy density distribution were obtained by the point detector sampling. At last, the infrared imaging system was used to record the image of laser spot received in a far-field screen in the distance of 180 m. The relative energy density distribution could also be simulated by theory of Fresnel diffraction integral of circular aperture. The theoretical and experimental results show that the wavelength of this laser is about 3.9 m with the properties of high average power, high repetition and stability about 10%. The far-field theoretical results show that the energy density distribution is quasi-Gaussian distribution and agrees well with the average energy density of 6.367nJ/cm2,which is smaller than the evaluation of empirical formula by the factor of 1.3. This work will definitely be helpful to measure the parameters of pulsed high-repetition mid-infrared laser and judge the disturbing threshold for the detectors in more far distance.
2012, 41(1): 53-57.
A tunable multi-wavelength erbium-doped fiber laser with up to 17 wavelengths was proposed. The intensity-dependent inhomogeneous loss induced by nonlinear polarization rotation (NPR) was applied to mitigate the mode competition caused by the homogeneous gain medium of erbium-doped fiber. Therefore, stable multi-wavelength output was generated at room temperature. In this experiment, a polarization-maintaining fiber(PMF) with a polarization-dependent isolator was used to form an equivalent Lyot birefringent fiber filter. The wavelength spacing could be altered by selecting proper length of the birefringent fiber. In the meantime, the fine tuning of wavelength could be achieved through adjusting polarization controllers(PC). A 10 m length of PMF was inserted into the laser cavity, which resulted in 17 wavelengths output with 0.35 nm wavelength spacing. In addition, a 4 nm tuning range was realized through PCs fine tuning. Three different coupling ratio couplers were used. And the laser was output from the small ratio port. The maximum numbers of the output wavelengths were 13, 14 and 17 with 7 dB,10 dB and 13 dB fluctuation for 50:50, 30:70 and 10:90 couplers, respectively. Besides, the corresponding maximum output power were 0 dBm、-3 dBm and -7 dBm. The results indicate that the output wavelength number is reduced, wavelength spectrum becomes smoother and output power is higher while the output rate of the output coupler is increasing.
2012, 41(1): 58-62.
By using partially coherent combining technique, beam combining of a 22 all-fiber laser array was experimentally studied. The laser array consisted of two incoherent laser groups. Each group contained two all-fiber lasers which were phase-locked by using direct mode mutual injection method through a fiber Bragg grating with proper reflectivity. The four laser beams were arranged symmetrically. And they were placed as close as possible by using a four-right-angle prism. In the experiment, two groups of clear interfere strips with maximum visibility of about 43% and 38% were observed, respectively. The whole laser array finally generates 925 W output power when the total pump power was 1 624 W. The beam-quality value BQ of the combined beam emitting from the laser array was 1.95 when the fill factor of the laser array was 0.54. This fiber laser combining array was constructed by all-fiber components, thereby was monolithic with stable performance. During the long time of high power operation, the monolithic fiber laser array works with excellent stability, no thermal distortion and damage are observed.
2012, 41(1): 63-68.
Evanescent coupled fiber laser array was described and studied. Array modes were derived by applying the static eigenmode/supermode theory. The stability of output power, the array scalability and the array mode were analyzed by numerically studying the dynamical characteristics of the laser array system. The array modes based on the above two methods were compared and analyzed. The results show that the output power level and the power stability are directly affected by the phase locking property and the relative phase errors respectively. With the increase of laser elements, the total output power of the array increases nonlinearly. By tracking the phases of array elements and examining the laser array property in both near and far fields, the evidence that at least 37 fibers can be coherently combined, is given. With the increase of fiber elements, the power differences between central element and its neighbors become smaller gradually.
An (AB)N(BA)N typed one-dimensional photonic crystal was constructed from electric single-negative material A and magnetic single-negative material B, and the simulated result from transfer matrix method shows that there appears a tunneling mode in the band gap. The tunneling mode exhibits the characteristics that it moves toward short-wavelength direction and its FWHM becomes narrow with increasing of the incident angle . The greater the incidence angle is, the more obvious these change will be. When the geometric thickness of the medium layer is increased, the mode moves linearly toward long-wavelength direction. When either the permittivity A of medium A or the permeability B of medium B is increased, the mode moves non-linearly toward long-wavelength direction. In addition, a larger A or a smaller B will result in a narrower FWHM of the mode. However, the transmittance of the mode remains 1 all the time when changing those parameters above.
2012, 41(1): 73-78.
Based on the fact that interferometric correlation term of femtosecond pulse contains the phase and frequency information, the magnitude information of chirp of femtosecond laser pulse can be obtained by measuring the magnitude and shape of two visual spectra component with surging frequency ?棕?子 and 2?棕?子 inside the autocorrelation second harmony interferometric stripe, and the area and shape of envelope of second interferometric autocorrelation function. Otherwise, through the derivative modified spectrum of autointerferometric correlation(D-MOSAIC) derived from a conventional second order interferometric autocorrelation trace, whose peak and value correspond to the positive and negative chirp, the sine function factor of the determinant chirp direction was obtained. Futhermore, chirp direction of ultrashort laser pulses could be determined. Thus, the chirp characteristics of femtosecond pulse laser could be detected through second order autointerferometric correlation using measurement system meeting basic condition of optics interference.
2012, 41(1): 79-84.
As an important issue in the area of underwater laser imaging, how to completely analyze the detection capability of the range-gated underwater laser imaging system, was introduced in this paper. For the purpose of evaluation, according to the imaging mechanism, the analysis of target and background radiation was reported, along with the analysis of backscattering of seawater, the characteristic of range-gated and the performance of laser transmitter and receiver. Then, the detection sensitivity model of the range-gated underwater laser imaging system was established based on the beam spread function(BSF). This model could be applied in practice as the ratio between seawater scattering coefficient and attenuation coefficient ranges from 0 to 1. In addition, simulations were done to analyze the beam divergence, the optical system aperture, the gate width of intensified CCD camera and other factors that influence the imaging systems detection capability. The results show that the maximal detection depth of such a system can be achieved when gate width equals to laser pulse width. Thus, this work can provide a theoretical basis for designing the underwater laser imaging system and optimizing the system parameters.
2012, 41(1): 85-88.
Range-gated technology, which plays a very important role in the three-dimensional imaging laser radar, is one of simple and effective method to solve the underwater low light level imaging and inhibit backscattering. The principle and application areas of range-gating technology were outlined in this article. Then, according to the demand for real-time imaging, a real-time range-gated imaging system was presented. This system could complete range-gated imaging and solve the target distance just with an imaging picture. By use of the centroid method, the detail of detection range was derived from the imaging system, and the relations between range accuracy and target distance, slice number, signal to noise ratio(SNR) were analyzed. The results of simulation analysis show that the system distance accuracy is greatly influenced by the SNR of the imaging system, and it can achieve better than 0.2 m range accuracy with the SNR greater than 2 000.
2012, 41(1): 89-95.
To improve the slant visibility measuring accuracy of Mie scattering lidar, a combination algorithm for return signals processing was proposed. Firstly, the adaptive algorithm based on empirical mode decomposition (EMD) was applied to improve the SNR of return signals by removing the high frequency noise. Secondly, the iteration algorithm based on fixed point principle was used to invert extinction coefficient. Using this algorithm, the mean extinction coefficient could be calculated without the accuracy boundary value. Additionally, the accurate boundary value was obtained, via which the extinction coefficient distributing could be achieved. Numerical simulations show that the output SNR of EMD algorithm increases 4.67 dB compared with five point three times smoothing denoising algorithm; the relative error of mean extinction coefficient inverted by fixed point iteration algorithm is 31.50% smaller than the value obtained by the least square fitting algorithm for the estimation of the extinction coefficient boundary value. Furthermore, only 3 to 5 iterations are required. Therefore, the combination algorithm is effective.
2012, 41(1): 96-100.
The principle of scannerless LiDAR was introduced. The developed one-dimensional scannerless LiDAR system based on linear APD was described. Linear array APD and infrared pulsed nanosecond laser were employed as detector and probe light source respectively. By using the time-of-flight pulsed laser rangefinding technique, the one-dimensional scannerless distance image of the target could be obtained. Parallel multi-channel pre-amplifiers were implemented and high-speed relays were used to switch between channels, by which, the isolation of channels were improved effectively. Several groups of one-dimensional distance imaging experiments were carried out. The results illustrate that the resolutions of multi-channel distance imaging are better than 10 cm and the average standard deviation for channels is approximate to 8.6 cm. The design in this system provides the basis on developing the two-dimensional scannerless LiDAR by APD planar array.
2012, 41(1): 101-106.
Temperature control is an effective way to realize the total internal cavity diode-pumped Nd:YAG microchip laser. How to provide effective means of temperature control for Nd:YAG microchip laser was studied. The temperature control accuracy needed was within the fluctuation range of
0.09 ℃. Based on this designed goal, the design process of each key link was presented. By means of frequency domain analysis, the characteristics of the temperature control system was analyzed and adjusted. By theoretical calculation, the system was remolded into an optimal model for second-order system and the theoretical analysis was verifiedby experiments. The temperature control system was designed for the total internal cavity diode-pumped Nd:YAG microchip laser, which guaranteed the temperature of the microchip can be set arbitrarily between 18 ℃ and 38 ℃ within the fluctuation range of 0.05 ℃ under normal condition (around 26℃). The system can also guarantees the temperature of the microchip can be set at 24 ℃, within the fluctuation range of 0.05 ℃, under arbitrarily temperature condition between 18 ℃ and 27 ℃.
2012, 41(1): 107-111.
The principle of Doppler wind lidar based on Mie backscattering was introduced. The wind lidar was composed of transmitting system, receiving system, transceiving system and controlling system. The most important of these systems is receiving system which was usd for a frequency discriminator. The parameters of Fabry-perot etalon were designed while the wind measures error was least and the mechanical technics can be realized. The structure of Mie Doppler wind lidar receiver was designed. The transmittance of etalon was measured and the parameters of etalon were fitted by Pseudo-Voigt function. The difference between the measured etalons parameters and designed parameters was lower than 5%. This receiver be used for the wind lidar system and the horizon wind velocity and direction were obtained. The result of wind profile measured by the system is in accordance with the wind profile measured by Airda16000 approximately.
2012, 41(1): 112-115.
Solar energy is one of the leading energy in the future, and researches about solar cells are becoming hot spots gradually. Its properties under energetic particles irradiations have been widely characterized, but there is few about its laser-induced damage. So its necessary to study the laser-induced damage of solar cells. Behaviors of monocrystalline silicon solar cells under 532 nm 20 ns and 300 ps pulse laser irradiations were studied. Damage mechanism of monocrystalline silicon solar cells under the irradiations of ultrashort pulse laser was analyzed. When the single pulse energy was fixed, the relation among damage effect, pulse width and repetition frequency was described. The differences of damage mechanism between different types of laser were compared. Through the analysis, the principal factor of solar cells damage was pointed out, and the damage of solar cells induced by laser irradiation mainly relied on the thermal effect.
2012, 41(1): 116-118.
The THz radiation generated by the vacuum electron device is often the ring-based or linac-based source. The generation of relativistic, sub-picosecond electron pulses allows the direct production of high-power, coherent THz radiation by passing the electron beam through an undulator. This provides a reliable and easily tunable powerful source of THz radiation for scientific applications. In this paper, the generation and observation of coherent THz undulator radiation from a femtosecond accelerator facility was reported. The accelerator facility consisted of an S-band thermionic cathode RF-gun, an alpha magnet and a SLAC-type accelerating tube, which could provide the electron bunches with energy of 20-30 MeV and bunch length of 100-300 fs. The undulator was an Apple-II type undulator, which could operate in various linear, elliptical or circular modes when the two rows at one diagonal moved along the longitudinal direction. To measure the frequency spectrum of the THz radiation, a modified Michelson interferometer was employed. The experiment setups were described and experiment results were given.
2012, 41(1): 119-123.
Optical remote sensing instruments including IR detection channels are always the major payloads of meteorological satellites. Radiant coolers are used for cooling the IR detectors and its aft optics to the desired temperatures, aboard on Chinese polar orbit meteorological satellites and geostationary orbit meteorological satellites. Depending on the requirements of optical instruments and satellites on the radiant coolers, the different style coolers such as W style, O style, L style, G style and octahedron-cone style in the past 30 years were studied, and the flight performance of the radiant coolers on FY-1A to FY-1D, FY-3A/ 3B, FY-2A to FY-2E meteorological satellites were presented. The lowest temperature of radiant cooler on FY-3 satellite was about 85 K and had 120 mW at 100 K. The concerned technologies needed for long-life operational meteorological satellites were discussed and its application results were also given. The possible application of passive cooling technology in future was discussed.
All-optical switching based on nonlinear polarization rotation(NPR) effect in semiconductor optical amplifier(SOA) has a fast speed and is also integrated together easily. The optical switching operation can be achieved by the different currents of injecting SOA. The performance of this optical switching is also influenced by the input power and the electric current. In this paper, theoretical analysis of the relationship between NPR effect and control current was proposed. Experiments results of polarization rotation with different optical power injected were provided. The optical splitting ratio and extinction ratio were important factors of optical switching. The results show that with the increase of input power the splitting ratio was also increased which could effectively improve the capability of optical switching. In the experiments, an optical switching with high optical splitting ratio and extinction ratio of 30 dB is realized when optical power injected is 5 dBm.
2012, 41(1): 129-132.
In order to satisfy the requirements of infrared detector that can penetrate in 1.064 m and 3-5 m double wave bands, be reflected in 1.2-2.8 m wave band, work in the harsh environmental condition and have high stability and reliability etc, the reasonable design of the coating was discussed. The reasonable coating design method that based on the design theory of film and used TFC software of coating design was chosen to optimize thin films structure. Infrared multi-wave bands filter film was deposited on sapphire crystal substrates by using the electron beam vacuum evaporation and the ion auxiliary deposition technology. Moreover, the optical, physical, chemical and mechanical characteristics of the film material were studied and analyzed. The multi-wave bands filter film was made successfully by means of continuous experiment and optimization of technical parameters. The film was tested and analyzed and the result satisfied the basis use requirements of the infrared detector.
2012, 41(1): 133-138.
The high-contrast 1D and 2D periodic microstructures of photonic lattice were formed in a photorefractive crystal by using the coplanar multiple-beam interference method. The distribution regularities and influence factor of periodic microstructures by interference of the coplanar of two or more beams intersecting at a photorefractive crystal were investigated experimentally and theoretically. The universal mathematical model of coplanar multiple-beam interference was established on the base principle of interference optics, and the light intensity distribution with n(n=1, 2, 3, 4, 5, 6) beams interference was simulated by computer. In the experiment, the coplanar multiple-beam interference was used to fabricate interference pattern and generate photonic lattice. The results show that it is quite consistent with the simulation results. The effect of various factors on characteristic in coherent system was further discussed. Interference pattern formed by coplanar multiple-beam laser was used to illuminate ferroelectrics lithium niobate crystal, then microstructure of photonic lattice was fabricated in the crystal due to holographic recording.
2012, 41(1): 139-143.
Microcosmic defects influence the optical properties and mechanical properties of CVDZnS effectively. In this article, the deposition technique was introduced and experiment methods such as SEM, TEM and metalloscopy were adopted to study the microcosmic defects such as unique large grain, columnar grain, micro-cracks, micro-poles and impurity. The microstructures of these defects were observed, at the same time the formation cause of these defects was analyzed. The main reason of the growth of unique large grain in CVDZnS was the high deposition rate. High reaction concentration, shield effect on substrate and Zn/H2S1 formed columnar grain which made the structure of CVDZnS loose. The lower deposition temperature increased growth stress in CVDZnS, brought bowing, made the grain blending and produced lots of micro-cracks in crystal. Micro-poles and impurity were made by high reaction concentration in local deposition chamber. So it is necessary to improve the gas flow in deposition chamber to make the concentration uniformly.
2012, 41(1): 144-148.
Using the filtered cathodic vacuum arc(FCVA) deposition technique with a process of changing substrate bias, a stable thick multilayer ta-C film was prepared. The multilayer films with a good adhesion consisted of alternating sp2-rich sublayers Ai and sp3-rich sublayers Bi(i=1,2,3). The sublayers thickness ratio dAi/dBi was about 1.0, and the total thickness of the multilayer film was about 1 m. The calculated compressive stress of sublayers by the Stoney formula revealed an alternating wave change. After anealling at 500 ℃ in vacuum, the Raman spectra suggested the multilayer film had a non-changed sp3-rich microstructure. The nanoindentation measurement showed an increasing hardness and Youngs modulus of the multilayer film after annealing. The nanoscratch test showed the favourable scratch resistance and adhesive properties of multilayer film. The results indicate that the multilayer ta-C film has some excellent mechanical properties and thermal stability. The multilayer film is proper for the optical protective coatings for aeronautics and space applications.
2012, 41(1): 149-154.
In the optical system, the apertures of most of target detecting systems on the ground are large (500 mm) which are the on-axis optical systems, and the wide field of view and broad waveband become the most urgent problem to be solved. The catadioptric optical system with small aperture refractive corrector group was designed, which eliminated those aberrations brought by large relative aperture, wide field of view and broad waveband. The primary mirror was aspheric surface and easy to be fabricated. An example which optimized and evaluated with optical design software ZAMAX, and the practical result of observation for star were given finally. The aperture of this practical system was Ф750 mm, whose relative aperture was 1:1.32, the field of view was 4 and the waveband was from 500 nm to 800 nm, the practical capacity of detecting was above 15 Mv. The simple construction consists of several kinds of regular glass, and the imaging quality is very excellent.
2012, 41(1): 155-159.
The principle of optical rotation due to the transfer of spin angular momentum from light to particles was discussed by analyzing the interaction between beam of light and birefringent crystal particles. The optical rotation of birefringent crystal particles was realized by using the equipment of the optical tweezers in experiment. For increasing the rotation frequency of crystal particles, the relation between rotation frequency of crystal particles and radius was analyzed in the experiment and theory research. The relation curve between calcium carbonate and silicon dioxide particles rotation frequency and radius was simulated with MATLAB, and the result showed that the rotation frequency was inversely proportional to the cube of radius, in addition, the experimental data was in agreement with the theoretical simulation. Rotation frequency was measured in experiment with the same laser power, the result showed the maximum frequency of calcium carbonate was 15.1 Hz, and the maximum frequency of silicon dioxide particles was 11.4 Hz. The rationality of the experiment was testified compared with theoretical analysis. The conclusion can be used to the choice of crystal particles and the optimization control of rotation frequency in actual application.
2012, 41(1): 160-166.
In order to characterize wavefront aberration behavior of misaligned reflective optical systems over the entire image plane, thereby realize effective alignment to reflective optical systems, the third order coma and third order astigmatism of several reflective optical systems with tilt and decentration were studied. Firstly, the vector form of the third order wavefront aberration of misaligned optical system was deduced. Then, the distribution characteristics of third order coma and third order astigmatism of misaligned classical Cassegrain systems, Ritchey-Chrtien systems and three mirror astigmatism systems in the image plane were analyzed. Finally, the alignment of two mirror and three mirror optical systems was briefly discussed. Moreover, Zernike polynominals were used to fit wavefront aberrations of grid sampling points in the view of field. Third order coma and third order astigmatism were separated and displayed over the whole field of view. Theorectical analysis and practical fitting results were similar, which shows that conclusions are correct.
2012, 41(1): 167-172.
Imaging spectrometer requires its optical system have high spatial resolution and spectral resolution over wide field of view and waveband range. A design method for unobstructed, off-axis, reflective optical system was proposed. When pupil and field of view were off-axis properly, obstructing between mirrors was avoided based on the three-mirror anastigmatic. According to the parameters, the unobstructed, off-axis three-mirror anastigmatic systems were designed, when the aperture stop was in front of primary mirror, or on the secondary mirror or focal point of third mirror. The optical system has a spectral region from 1.0 m to 2.5 m, focal length of 1 600 mm, relative aperture of f/5, field of view of angle of 6.861.48. Their imaging qualities reach the diffraction limit and meet the requirements of the imaging spectrometers optical system，which has wide field of view and large relative aperture.
2012, 41(1): 173-177.
According to the working characteristics of equatorial telescope, the supports scheme on 700 mm primary mirror were designed. The finite element model of the system was established by the software MSC. Patran. The surface deformation under gravity was analyzed in different load cases. The curves of surface deformation errors PV and RMS were plotted. As a result, the surface deformation is influenced mostly by angle , and it decreases when the angle rises. The effect of the radial support is better than the axial support. The surface deformation errors can satisfy the precision requirements. When the system is perpendicular, the test result of RMS is 28.48 nm by Zygo interferometer, which shows that the surface shape with the supports is close to the test state. It validates that the finite element model is accurate.
2012, 41(1): 178-183.
One method for athermalized infrared telephoto objective design was proposed. First, by synthesizing the formulated athermal model for the multiple-lens optical system with telephoto objective model, the optical power distribution equations were established. Thus, the initial optical power distribution among lens could be resolved with consideration of the telephoto ratio requirement and lens material constraint. Then, a final routine computer-aid modification procedure would help to correct the optical systems aberrations. This systematic design method was straightforward and applicable. As practical examples, a mid wavelength infrared optical system and a long wavelength infrared optical system were designed with ZEMAX software. With the focal length equal to 100 mm and F number equal to 2.0 for both systems, the telephoto ratio reached 0.8. When environment temperature varies from -40 ℃ to 60 ℃, the image preserves high quality and modulation transfer function (MTF) still approaches diffraction limit. The result of the implemented design agrees well with the method predictions.
2012, 41(1): 184-189.
The research on the mechanism of moving mirrors based on Michelson interferometer is one of the technical difficulties in the whole research process of Fourier-transform spectrometer, in which case flexible mechanism is considered as a critical component of moving mirror. On the basis of parallelogram flexible mechanism, a kind of complexity design was conducted and a novel flexible mechanism was created. In addition, the principle of its mechanism was analyzed by simulation softwares such as finite element analysis software Patran and Nastran. The corresponding results were compared with those from traditional theoretical calculation of parallel double rod mechanism. The final results show that this novel flexible mechanism can not only decrease its vertical coupling displacement of the moving mirror to 1.4 percent of its original amount, but also be capable of reducing the dimension of freedom (DOF) of the moving mirror to one dimension effectively, which provides valuable conclusion for the coming researchers.
2012, 41(1): 190-195.
The number of pixels scanned in star image can be large with conventional star tracking algorithm under large maneuvering of the vehicle. The feasibility of irrelevant star within threshold scan windows is increased. And the number of calculating angular separation between two stars is increased. This results in the decreasing of the update rate of star sensor. Therefore, the feasibility of error stars from star image is increased. Above all, an autonomous star tracking algorithm with high angle velocity was presented in this paper. Firstly, the next frame potential attitude was estimated according to previous attitudes. Secondly, the next frame ideal star centriodings of stars in FOV was calculated according to the potential attitude. Finally, all the real star centriodings would be obtained within the threshold scan windows of the ideal star centriodings. This algorithm can not only improve update rate of star sensor, but also avoid fault star pattern recognition. At last, the algorithm was tested by simulation and night sky experiment. The algorithm will be applied star sensor of satellite GNC.
2012, 41(1): 196-199.
Along with the expansion of application demand, the new generation of guiding system must be able to obtain rich information in the detection process, including angle and distance information. Therefore, laser ranging technology becomes a hot spot in the field of guiding field. In order to provide the simulation experimental conditions for laser ranging technology, a lot of works on laser echo simulation were done. In this paper, the development of the echo simulation system was described, which had the characteristic of angle and distance measurement for the laser ranging system. This system was named as laser echo simulator. The simulator could give the proper echo signal with a corresponding delay after receiving the trigger signal from the detection system. The echo characteristic and delay control capacity were analyzed. The hardware-in-the-loop system design was presented to verify the performance of laser ranging system. The experimental results indicate the feasibility of the system.
2012, 41(1): 200-204.
In order to detect the quality of the substrate and coated optical elements effectively, the first-order vector perturbation microfacet polarized light scattering model was established by microfacet theory and the polarized bidirectional reflectance distribution function was derived. The influence of incident angle, degree of roughness about substrate and the thickness of film to the polarized bidirectional reflectance distribution function was simulated and analyzed numerically. And the relationships among PBRDFPP, scattering angle and azimuth angle were talked about. The results show that the polarized bidirectional reflectance distribution function is inversed to incident angle, correlation length, root-mean-square height, and the thickness of film. PBRDFPP depends on incident angle, scattering angle and azimuth angle strongly. The position of Brewsters angle decreases with the increase of incident angle.
2012, 41(1): 205-210.
The polarization characteristics and their changes reflect the status of the targets. In this work，the concept and the feasibility of using the polarization detection to characterize space targets were discussed. Then the performance of a polarimetric device applied for space targets detection was introduced. Meanwhile, the results of polarimetric observation on space targets were given and the characteristic of scaled models which were similar to the actual targets were measured, respectively. By comparing the two results, it is demonstrated that the trends of the both polarization characteristics fit well with each other. Therefore, the validity of the polarimetric observation on space targets is confirmed. The polarization characteristics of space targets is revealed, for example, the degree of polarization will increase from 5% at midnight to 23.8% before dawn. Especially, the attitude of the solar panels plays a vital role in affecting the polarization characteristics of the satellites. It is indicated that the polarimetric observation is an innovative method applied for space targets detection and identification.
2012, 41(1): 211-217.
To depress the guidance message noise of air-to-surface semi-strapdown imaging seeker, the control loop model of stability tracking was established, the transform characteristic of various error and output was derived. The power spectrum response of main noise was obtained. Then, the weighted angular rate of line of sight was gained. In order to verify the validity of the weighted angular rate of line of sight, the simulation were completed in the guidance loop. The results show that the weighted method can effectively compressed the noise measurement information of seeker. The semi-strapdown TV seeker was achieved with semi-physical way, the double closed-loop was completed in TV seeker to make disturbance isolation and track the target. The methods for extracting guided information through weighted angular rate of line of sight and direct extraction methods were compared. The experimental results show that the weighted extraction method of line of sight angular rate noise variance is 0.098 ()/s, which is lower than the direct synthesis of noise of 46%. The weighted method can improve the problem of large semi-strapdown sight angular rate noise.
2012, 41(1): 218-222.
The hyper-ectral imaging with polarization is an emerging cross-echnology. It has been the key topic to explore the technology in the aerospace, civil and other areas at home and abroad. In particular, imaging spectrometer based on acousto-ptic tunable filter (AOTF) has many advantages compared with the traditional imaging spectrometers both in running mechanisms and in the design of instrument. By studying the principle of AOTF, the working process of AOTF polarization spectral imaging instrument which was used in the experiment was analyzed, the data acquisition system matching with the instrument was made and the system design process based on LabVIEW platform was discussed in detail. At the same time, the LabVIEW program design diagram of each module was given. The function of system was verified through actual scene test. The final result shows that the system can complete the image data collection efficiently and reliably, as well as controlling the hardware of the instrument correctly. In a way, it is of research and practical value for the system.
2012, 41(1): 223-228.
In the second phase of Chinas lunar exploration program, an actual landing on the lunar surface will be included, and so greater flexibility with regard to landing locations is one of the many improvements planned. An optimized algorithm based on the Monte Carlo method was proposed to calculate the probability of safe landing under various specified conditions on a large number of different terrains generated in simulation experiments. Topography simulation was based on the actual characteristics of the lunar surface topography and statistical distribution of lunar craters and rocks. The algorithm depended on the lander attitude information and landing plane envelope model. Engine control, attitude control and dynamic property were not considered in simulation experiments. Only under same lander profiles in one group tests, the experimental results were reasonable. The landing territory , lander profile and safety parameters were simulated on computer by this method. It could be applied to bothground simulation experiments and real-ime analyzing possibility of landing safety during soft landing on the lunar surface. These improvements in the descent and landing are essential to the development of a lunar outpost, and also for increasing the number of potentially accessible lunar sortie locations.
2012, 41(1): 229-233.
In some space project, a specific CCD sensor has been used to design a set of space imaging CCD camera system, and the image frame rate is higher than the standard frame rate of CCD sensor. Signal to noise ratio should be decreased by simple overclocking readout the CCD. Firstly, a variety of reasons which could affect the imaging signal to noise ratio of CCD camera under the space conditions were analyzed, it had been found that readout noise was the most important reason. So the regional frequency doubling readout methods was introduced and used to improve the output frame rate of CCD camera. Namely, four times the pixel clock was used to readout part of CCD pixels in the horizontal and vertical directions. Finally, the SNR of image signal by regional frequency doubling readout CCD and overclocking readout CCD was compared. Test result shows that the former image has higher SNR.
2012, 41(1): 234-238.
An image mosaic method of object straight edge nodes was proposed by the unique transformation relation between the image sequences of one aerial reconnaissance CCD camera. In that scheme, overlap area of images were first segmented into smaller sub-mages independently, and Canny edge detection operator was employed to extract the edge information from each single area, then straight edges from the obtained edge information were also derived by Hough transform. Moreover, a strategy of area expanding and selection was proposed to extract the straight edge nodes, and it was applied to keep the segment area containing an effective object. Finally, image registration was finished according to the obtained straight edge nodes, and seamless mosaic image could be achieved by bilinear interpolation method. The actual mosaic results are also presented to verify the effectives of the proposed image mosaic approach.
2012, 41(1): 239-247.
Shape is a kind of important feature to detect or recognize objects in computer vision. However, some disadvantages still exist in many methods based on shape feature at present, such as having no abundant information, easily affected by the default and distortion of edge, or having no local property. Especially, it is very difficult to detect object correctly under some complicated environments. In order to overcome these defects, a kind of shape feature extracted by using the chord-tangent transformation and corresponding algorithm of target detection was presented in this paper, which was obtained according to the finite edge point. This geometric feature had the invariant character of translation, rotation and scale. Some important parameters about movement including the location of object could be obtained through this method, even under some complicated environments. However,because the edge extraction is usually affected by the quality of image, contrast between the object and background and quantized error, the precision can be decreased. Therefore, some gray information was added to the feature in order to improve the algorithm. Finally, experimental results indicate the effectivity of the algorithm. The matching rate between the object and model can be extended to more than 90% after improving.
In order to solve the problem that using classical mutual information measure in infrared and visible images registration may suffer from local extremum, and large amount of calculation by using classical gradient normalized mutual information measure, an improved gradient normalized mutual information measure based on classical gradient and mutual information was proposed, which counted mutual information of gradient image directly to combine image gradient information with gray information effectively. Compared with classical gradient normalized mutual information measure, the new measure could improve registration precision and reduce computation cost. During the optimization of parameters, for the defect of sinking into local extremum for classic particle swarm optimization algorithm, the improved particle swarm optimization algorithm was proposed, which included chaos optimization idea and hybridization idea in genetic algorithm. The improved particle swarm optimization algorithm can restrain local extremum and accelerate convergence. Experimental results demonstrate that this new algorithm can achieve high registration efficiency.
2012, 41(1): 255-260.
In the process of target tracking with complex background, changes in the target brightness and contrast easily lead to instability or failure of target tracking. To deal with such problem, a new correlation tracking approach was presented which was robust to the variation of brightness. Taking advantage of the merit of phase congruency that was insensitive to the variation of image brightness, the phase congruency was calculated firstly from the original image, and then the traditional MAD (Minimum Absolute Difference) correlation tracking approach was used to track the target. Experimental results show that the proposed algorithm is considerably adaptive to the variation of image brightness. It can successfully solve the problem of the tracking point excursion and even the failure of tracking which the traditional tracking methods is unable to deal with when the image brightness changes.
2012, 41(1): 261-266.
A method of getting tile image groups of airport before damage from Microsoft Virtual Earth image database was proposed. The storage structure of these images in remote database was analyzed 半by using quadtree data structure. High-resolution image of airport before damage was developed by organizing these images together. After this, image projection method, especially the method of longitude and latitude registration was studied under WEB mercator projection. So geographical coordinate can be projected to local image pixel coordinate. The depth and visible diameter of craters caused by kinetic projectile on concrete runway were simulated with classical Bernards Formulas on Depth of Projectile Penetration in Rock. Finally the simulation software was designed with 2D image generated technology. With position and other property of the crater, the virtual damaged airport image was derived by superposing the simulated crater images on the image of airport before damage.
2012, 41(1): 267-272.
As the biological vision features shows superior performance on object classification, a multiclass and multiview object detection approach based on sparse biological vision features was adopted. Firstly, the standard model of biological vision was improved with the technique of sparse features, which improved the separability of object effectively. Then, the object detector based on sparse biological vision features was designed with the technique of sliding window, and the detection task was completed via local neighborhood suppression algorithm. At last, the multiclass and multiview object detection task was accomplished through building object dictionary and designing several object detectors in the scene. The experimental results show that the proposed approach exhibits a robust performance.
