2016 Vol. 45, No. 4
column
- Review
- Invited paper
- Adaptive optics
- Terahertz technology and application
- Advanced optical imaging technology
- Infrared technology and application
- Laser technology and application
- Photoelectric measurement
- Optical design and simulation
- Photoelectric devices and microsystem
- Advanced optical material
- Optical communication and optical sensing
- Spectrum detection and analysis
- Scene information processing
With the increase of human exploration of space activities, space debris detection is particularly important. In this paper, the space debris hazard and detection significance were firstly introduced. Then, the main difficulties and the development trend of space debris detection were analyzed. On this basis, combined with space debris detection difficulties, a new scheme of detection for space debris and information transmission was proposed, which integrated laser ranging, spectral polarization imaging, laser communication features. And the key technology to decompose and feasibility analysis were made, which may provide a new way of thinking for space debris detection.
2016, 45(4): 402001.
doi: 10.3788/IRLA201645.0402001
In this paper, by investigating the terahertz(THz) waveforms emitted from different lengths of filaments via THz time-domain spectroscopy system(THz-TDS), superluminal propagation of THz wave during filamentation was observed. It implies that the refractive index of the THz wave is smaller than the unity within the filament region, and thus the THz pulse may propagate inside the filament. This hypothesis is supported by further numerical simulation, which demonstrates THz eigenmode inside the plasma filament.
2016, 45(4): 402002.
doi: 10.3788/IRLA201645.0402002
Liquid crystal wavefront corrector (LCWFC) is one of the most attractive wavefront correction devices for adaptive optics system. The main disadvantages for conventional nematic LCWFC are polarization dependence and narrow working waveband. A polarized beam splitter (PBS) based open loop optical design and an optimized energy splitting method was used to overcome these problems respectively. The results indicate that the open loop configuration is suitable for LCWFC and the novel energy splitting method can significantly improve the detection capability of the liquid crystal adaptive optics system.
Wavefront aberration characterization and correction in laser beam propagating over saline water and sand was investigated in this paper. An experimental setup was built for wavefront aberration measurement and correction by an adaptive optics(AO) system. Based on the input-output data of the AO system, a model was established for the AO system and a closed-loop controller was built. Experimental results show that the laser beam propagating over sands surfers more severe wavefront aberration by the turbulence. After closed-loop AO correction, the variance of the spots displacement in the wavefront sensor is reduced by 28% forsaline water and 10% for sands. By doing this research, the feasibility of using close-loop AO systemsfor wavefront aberration correction in marine environment is investigated.
2016, 45(4): 432002.
doi: 10.3788/IRLA201645.0432002
The Arctic probability distribution of cloud phase, cirrus clouds top temperature, cirrus clouds top height, cirrus clouds optical thickness and effective radius in summer were presented based on Moderate resolution Imaging Spectrometer(MODIS) cloud product data(MOD06) of 2011-2014 in July, and the relationship between effective radius and cirrus clouds top height was discussed. Results show that in summer the occurrence frequencies of cirrus clouds become higher while the occurrence frequencies of water clouds become lower in the Arctic. Cirrus clouds top temperatures mainly distribute in the 230-272 K(that is -43℃ to -5℃). The cirrus clouds top height distribute from 2 to 8 km, and has a highest occurrence frequency in the range of 4.5-6 km. The cirrus clouds optical thickness is less than 10. The cirrus clouds effective radius distribute from 5-40 m and most probable appear in the range of 10-20 m. The relationship of cirrus clouds effective radius and cirrus clouds top height has a positive correlation in the Arctic, while in mid-latitude this relationship is opposite. The higher the cirrus clouds top height,the greater the cirrus clouds effective radius is. In the Arctic, with the increase of the latitude, the cirrus clouds occurrence frequency, cirrus clouds top height, cirrus clouds effective radius and cirrus clouds optical thickness increase, while the cirrus clouds temperature decreases.
2016, 45(4): 432003.
doi: 10.3788/IRLA201645.0432003
Optical axis jitters, which arise from different factors such as wind shaking and structural oscillations of optical platforms, have a significant deleterious impact on the performance of adaptive optics systems. When conventional integrators are utilized to reject such high frequency and narrow band disturbance, the benefits are quite small; even worse, the system may fail to operate normally due to the amplification of jitters. On the basis of observed data, its frequency characteristics were analyzed. With the help of the Smith predictor, one effective and stable technique to design a controller was proposed on account of the peak frequency and bandwidth of the jitter. The relationship between controller parameters and filtering features were discussed, and the robustness of the controller against changing parameters of the control object was investigated. Results show that the variance of one axis aberrations caused by optical axis jitters can be reduced by about 60% as a result of exploiting novel controllers, which compensates the deficiency of conventional controllers.
2016, 45(4): 425001.
doi: 10.3788/IRLA201645.0425001
To use the non-linear GaAs photoconductive semiconductor switch (PCSS) with avalanche effect for terahertz generation, it is important to quench the photo-activated carrier domain (PACD) transporting in the semiconductor. In this work, a basic setup for quenching the non-linear GaAs PCSS was proposed which consists of two laser beams. The second laser beam was delayed about 100 ps for quenching the PACD after the first beam. In the experiments, the PCSS with 12 mm electrode gap can be biased up to 32 kV with 0.9 kA switching current. Good reproducibility of waveforms about 230 times at 20 kV is achieved with 14mm PCSS when trigger laser is orders of magnitude of tens milli-joules. Results show the process of infrared quenching non-linear mode could be operating repeatedly, which paves the way for future research of high power terahertz generation at high repetition rate.
2016, 45(4): 425002.
doi: 10.3788/IRLA201645.0425002
THz wave lies in the region between the microwave and infrared range in the electromagnetic spectrum. There are unique advantages for THz wave in the space research and application field. THz remote sensing instruments can provide a new perspective for the exploration of the earth's atmosphere. As a result, THz technology has a good prospection the field of atmospheric science. The main applications of THz technology in the field of atmospheric sounding were introduced. The current research status of THz atmospheric observation instruments at home and abroad were summarized. By comparison and analysis of key parameters of each instrument, the development trend and the development prospect of THz instruments for atmospheric observation were summarized. Meanwhile, the suggestions for developing THz atmospheric remote sensing technology were presented.
2016, 45(4): 425003.
doi: 10.3788/IRLA201645.0425003
An exploration on heavy metal Pb2+ detection method was presented based on Terahertz(THz) Spectroscopy, which is rapid and maybe portable and low cost for future in-field applications. THz is a brand new and safe technology with many unique features. It showed feasibility for heavy metal detections in soil according to former experiments. A series of experiment were carried out in this study. Soil samples with predefined concentration levels of Pb2+ ions were carefully prepared. Pressed-slice method was used for the spectra measurement and sample making parameters were determined. The absorption spectra were collected with a THz spectroscopic system in Capital Normal University. Multivariate statistical methods were studied and used to analyze the collected data and establish predication model for Pb2+ concentrations. Calibration and prediction models were established based on Partial-least-square(PLS) and Interval Partial-least-square(i-PLS) methods using the full THz spectrum and the selected THz wavebands respectively. The results show that the optimized models are able to predict soil heavy metal Pb2+ content with a correlation coefficient of 0.81. The method of using THz technology for soil heavy metal Pb2+ detection is feasible. With the detection results, it can be found the heavy metal Pb2+ pollution spatial distribution information of the soil in-field and get the pollution map. Specific measures shall be taken based on the pollution map to manage the soil to improve the farmland productivity. This study will provide a reference for heavy metals pollution detection solutions for precision farming and sustainable agriculture development.
2016, 45(4): 425004.
doi: 10.3788/IRLA201645.0425004
Dielectric metamaterials based on high-impedance silicon were designed for controlling the amplitude and phase of the terahertz waves. Here, the basic unit cells of the dielectric metamaterials are subwavelength silicon pillars, they have lower loss and thus have higher efficiency compared with the metal based metamaterials. As different silicon pillars with different geometric parameters and orientation angles will have different transmission amplitude and phase when the terahertz wave passes through them, nearly arbitrary spatial amplitude and phase distributions can be achieved by designing the geometric parameters and orientation angles of the silicon pillars at different positions, which allows to fully control the shape of the transmitted terahertz wavefront. In experiment, three different meta-gratings were designed using the silicon based structures in which the diffractive orders and their numbers can be arbitrarily controlled. Such dielectric metamaterials are very easy to design and fabricate, making them very promising in developing low-loss terahertz functional devices.
2016, 45(4): 424001.
doi: 10.3788/IRLA201645.0424001
Frequency-domain photoacoustic imaging is a new imaging modality, which uses the output amplitude information periodically modulated by a continuous-wave laser as a light source to stimulate biological tissues and to produce photoacoustic signals processed at frequency-domain and used to image the tissues. Firstly, the principles, developments and research status of photoacoustic imaging and frequency-domain photoacoustic imaging were introduced, and then the specific test methods and basic reconstruction algorithms of the frequency-domain photoacoustic imaging filed were described. In order to make up for time domain photoacoustic imaging with high costs, great harmful, poor portability and so on shortcomings, two imaging modalities were proposed and two complete experimental system structure diagrams were exhibited, showing different features and developing directions of photoacoustic imaging with respect to the traditional domain-photoacoustic imaging. At last, the outlook of the frequency-domain photoacoustic imaging was made to provide some references and guidance for our research and development about photoacoustic imaging.
2016, 45(4): 424002.
doi: 10.3788/IRLA201645.0424002
According to some specific problems of conventional star simulator including the less simulation parameters, low accuracy and big difficulty of star simulation technology, by creatively introducing the LED luminous technology into the design of star simulator, a development scheme of novel star simulator based on the LED luminous technology was proposed. Combining with design results of collimating optical system, the overall mechanical structure of star simulator was designed in detail, to ensure that the designed simulator having characteristics of the largest possible weakening of temperature change, vibration and other external factors in the simulation environment. Control technology of star position accuracy, star brightness, star roundness, emitting uniformity of star light was researched and analyzed. Analysis and test results show that the designed star simulator owing the properties of angular distance precision between stars less than 3, a variety simulation of 5 continuous magnitudes, at the same time to meet multi-parameter simulation requirement about the star roundness, luminous uniformity and luminescence spectra. The proposed design method can provide a feasible technical solution for the development of higher level of star simulator.
2016, 45(4): 424003.
doi: 10.3788/IRLA201645.0424003
The theory that light can transmit information in a unique way has been proved by the experiment and theory of correlated imaging. In this paper, the principles of correlated imaging were discussed in semi-classical interpretations. In the view of pseudo-thermal light field, photoelectric detection and correlated computation, the imaging process was analyzed. Field of view, spatial resolution and contrast of the system were given. On this basis, the traditional linear correlation algorithm was improved to make the ghost image a mean square convergence unbiased estimation of the object transmission function. The corresponding computational ghost imaging experiment measurement indicates that under the same number, especially less than the Nyquist frequency, the PSNR is significantly improved and background noise is effectively suppressed compared with the traditional algorithm.
The infrared detector module is the key device of target detection and imaging system and it's spatial resolution directly affects imaging quality of detection system. When evaluating the spatial resolution of detector modules, researchers usually adopt modulation transfer function(MTF), which optical crosstalk is the crucial factor to impact MTF. A set of infrared micron-spot test system was introduced whose optical dispersion diameter can achieve to 30 m in order to test the line spread functions(LSF) of detectors with different structures to acquire optical crosstalk data. The results show that the profile of overlap electric region is photosensitive, which is the main factor to cause widening LSF, secondary peak and so on. The results provide reference for optical crosstalk design of infrared detector modules.
2016, 45(4): 404002.
doi: 10.3788/IRLA201645.0404002
To realize the quantitative measurement of space target infrared radiation, infrared radiation measurement system must be calibrated in advance. Based on the deficiencies of conventional calibration method for large aperture infrared radiation measurement system, through analysis of calibration and measurement working principle of space object infrared radiation measurement system, a new calibration method was proposed which combined inner blackbody calibration and astronomical star calibration. Respond relation between matching mirror and detector was deduced when using inner blackbody as standard radiation source. Besides, calibration relation between infrared star radiation and transmittance of large-aperture primary mirror system was also deduced when using infrared star as standard radiation source. Then response relation of infrared measurement system was also advanced. The experiments show that the curve slope accuracy of new method is within 4% compared with traditional full-aperture blackbody calibration method. This new method reduces manufacture difficulty of calibration system, has advantages of easy operation, high efficiency of calibration etc.
2016, 45(4): 404003.
doi: 10.3788/IRLA201645.0404003
Under sampling leads to aliasing effect which have seriously effect on the image quality for infrared focal plane arrays. According to the imaging processing of staring system, sampling process of detector was analyzed in the time domain to study aliasing effect on image quality using a quantitative method in the frequency domain. Simulation experiment on aliasing phenomenon of periodic and aperiodic objects based on the reason of aliasing effect was completed. Simulation experiment show that aliasing distortion phenomenon will be exist in periodic objects, but there will be zigzag stripe in aperiodic objects. It can be concluded that aliasing distortion is small in low frequency and noise tends to mask the target pattern, but aliasing distortion is serious in high frequency where aliasing is dominant, this has a certain reference value for eliminating the influence of aliasing confusion and system parameter design.
2016, 45(4): 404004.
doi: 10.3788/IRLA201645.0404004
The IR simulation technology of irregular objects, such as smoke, dust, cloud, flame and so on, is one of the key technologies and difficulties of real-time IR image generation. Take the IR simulation of smoke for example, first, the shape of the smoke was modeled based on the Navier-Stokes equation, the method of initialization and boundary processing was also provided. Then, the infrared model of the smoke which take into account the smoke's own radiation and the sun's radiation was built based on the gray body radiation model and the light projection algorithm. Last, the smoke IR simulation based on the physical model was implemented using the CUDA parallel computing tool, and the IR smoke was successfully embedded into the IR scene based on Vega, also, the effects of the IR smoke based on the physical model and the Vega particle system were contrasted. The results indicate that the smoke IR simulation based on the physical model can meet the requirements of real-time, and has the advantages of strong sense of reality and good controllability.
2016, 45(4): 406001.
doi: 10.3788/IRLA201645.0406001
A novel emitting system of fiber-array 3D laser imaging using off-axis three-mirror system was proposed. High-power laser was split to certain number of beams by fiber splitting and output with fiber-array. The off-axis three-mirror was designed as normal telescope system, and its focus length was the divergence angle divided by the core diameter of the fiber, while the F number in image space was determined by the Numerical Aperture(NA) of the fiber. The total field of view was the focus length divided by the length of the fiber-array. The fiber-array was set on the focus plane of the off-axis three-mirror system, and rays were traced in the opposite way of design. The example system realized divergence angle as 20 rad of 51 fiber beams, and it showed that the divergence angle of every fiber beam satisfied the target value well and the footprint between the neighbouring beams has good uniformity on the target surface. Besides, this emitting system was suitable for any number of laser beams within the total design field of view.
2016, 45(4): 406002.
doi: 10.3788/IRLA201645.0406002
Laser Doppler Velocimetry(LDV) is able to measure the velocity of vehicle accurately for high precision navigation in the area of aerospace. The key of the measurement is to detect the Doppler signal successfully, so weak Doppler signal detection is one of the most important technologies due to the presence of noise. An adaptive signal detection algorithm in frequency domain was proposed. Noise was leached from useful signal by band stop filter and the adaptive threshold could be obtained according to the statistical properties of the left noise. Comparisons of simulation and experiments with the fixed threshold algorithm were taken, and the results show that the frequency domain adaptive threshold detection is an effective method to improve the performance of LDV. Under the condition of keeping the low Constant False Alarm Rate (CFAR), the Doppler signal can be completely detected when the Signal-to-Noise Ratio(SNR) is higher than -9 dB, and it is insensitive to the intense of noise, simple and applicable in many area.
Airborne LiDAR point cloud data filtering is the most important step in the workflow of LiDAR data postprocessing. Based on the characteristics of Triangular Irregular Networks(TIN) and curved fitting filtering methods, a from rough to fine idea was proposed for LiDAR point cloud data filtering. In this method, strict threshold TIN was used for rough classification with a priority of type II error and more reliable initial ground points were obtained, then the seed points were selected with the priori information which was rough classification result, next Total Least Squares(TLS) algorithm was introduced to fit block terrain, and self-adaption threshold was set to deal with different area more flexibly, ultimately more refined region model was obtained. ISPRS test data and Niagara data were used for experiments, and classic filtering method and traditional curved fitting filtering method were selected for comparison. Experimental results prove that, the proposed method is practical as the filtering results are more reliable than traditional moving curved fitting filtering method, and has strong adaptability to various terrains.
2016, 45(4): 406004.
doi: 10.3788/IRLA201645.0406004
Three Raman pulses are usually adopted to make cold atomic beams to split, reflect and recombine when doing cold atom interferomertry experiments. The stability of Raman laser power is as important as frequency, because it causes the Rabi ratio to change with it. When the Rabi ratio changes, the final phase difference between the two separated atom beams changes as well. It is a great disturbance for interferomertry signal stability and also the signal to noise ratio. The effect is more than acceptable when it comes to atom interferometer used as high precision acceleration measurements. Keeping laser power stable can improve phase noise a great deal. Thus a digital control system was designed for higher laser power stability using an acousto-optical modulator(AOM) as a controller, and the feedbacks from the AOM were applied to compensate the power variation outside the cavity of a laser. After realizing the identification with the AOM and a simulation model for it based on the identification results, an PID controller was programmed in the Labview language. Experimental results show that the the laser power instability can be reduced from 0.19% to 1.67% with the method under the measurement time of 1 h. And it works really well for the cold atom interferometer system.
Annular sub-aperture stitching interferometry technology can test steep conformal aspheric surfaces with low cost and high efficiency without auxiliary null optics. The effective splicing algorithm was established based on simultaneous least-squares method and Zernike polynomial fitting. Firstly, the basic principle of the algorithm of the annular sub-aperture stitching was studied. Secondly, the mathematical formulas of the sub-aperture effective area were derived and the parameters of the sub-aperture effective area were calculated and optimized. Finally, the reasonable mathematical model was established. The detection method of annular sub-aperture stitching high steepness aspheric has been tested through on experimental verification. As a result, the surface map of the full aperture after stitching was consistent to the input surface map, the difference of PV error and RMS error between them is 0.015 1 and 0.004 7( is 632.8 nm); the PV and RMS of residual error of full aperture phase distribution is 0.043 5 and 0.005 2. The results conclude that this splicing model and algorithm were accurate and feasible.
2016, 45(4): 417002.
doi: 10.3788/IRLA201645.0417002
The accuracy of position sensitive detector(PSD) is mainly affected by the non-linearity, interference and the installation tilt error, and the measurable range is limited by the size of the detector. Based on the analysis of the influencing mechanism of the non-linearity, the interference and the installation tilt error, a speckle tracking system was introduced to remove the influence by local fitting and real-time calibration according to the linear relationship between the actual value and the measured value. Al2O3/PEN sample was used to experimentally verify the designed spot tracking system platform. The results show that the linear correlation coefficient maintains in a range of 10.001 5, the linearity standard error is reduced to 0.3 m/40 mm, the maximum error is less than 16 m/40 mm and the measurable range can be increased to the stroke of the module, 200 mm in this work. This method is effective, flexible and practical for position detection applications especially under feeble light condition and for large measuring range.
2016, 45(4): 417003.
doi: 10.3788/IRLA201645.0417003
The adaptive filtering algorithm based on recursive least square algorithm was applied to a laser Doppler vibrometer and the corresponding weak vibration measuring devices were built up. Compared with Chebyshev low-pass filtering algorithm, simulation and experimental results show that this adaptive filtering algorithm can suppress the random Gaussian white noise and restore the original signal; the RLS algorithm can effectively filter out noise from the vibration signal, and restore the low-frequency 20 Hz signal drowned out in the noise; the RLS algorithm also can filter out noise from voice leading voice to being pure and enhance speech signal. The above verifies the feasibility of this algorithm in the heterodyne vibration measurement. The algorithm is simple and easy to use, fast and has strong convergence. In the aspect of filtering random noise, the RLS algorithm is more effective than low-pass filter.
2016, 45(4): 417004.
doi: 10.3788/IRLA201645.0417004
The atmospheric carbon dioxide(CO2) is a greenhouse gas which plays a dominant role in climate changes and also in some other fields. The remote sensing system for vertical profiles of atmospheric CO2 was based on non-dispersive infrared gas detection technology, which can transmit data by wireless. The modulated infrared radiation source and dual-channel detector were employed in the system which take advantage of ultra-low consumption MCU to realize automatic control and acquisition. The method of deducting the fluctuation and background noise of signal was proposed, which made the relative error at 0.29% of the detection. And the time-sharing operation mode was adopted to resolve electromagnetic interference(EMI) from high frequency transmitter of radio sounding to the operational amplifier of the CO2 detection. The digital radio sounding of widely used in meteorology and CO2 detection were integrated highly. The comparison analysis between self-made CO2 remote sensing system and LI-COR LI7500 were carried out, preliminary results show that the variation trends of atmospheric CO2 have good consistency from the two detection systems; the correlation coefficient was 0.89 from 24 hours data. It can be indicated that the self-made system has good constancy and accuracy. The self-made system offers another choice to exploit to measure the vertical profiles of atmospheric CO2.
2016, 45(4): 418001.
doi: 10.3788/IRLA201645.0418001
A LED flat panel light without light guide plate was designed to solve the disadvantages of low luminous efficiency and the high cost of Light Guide Plate(LGP) in edge-lighting LED flat panel light. The beam launched from the LED arrays was converged by the compound parabolic reflective cup(CPC) and was gazed on light emitting panel. In this way, the uniform luminous can be obtained on light emitting panel. Then, Taguchi method was used to design the experiment and analyzed the factors that affected maximum and uniformity of illumination by the software of Tracepro simultaneously. Furthermore, the influence of quality was studied by the theory of ANOVA to optimize structural parameters. Finally, the LED flat panel light without light guide plate after optimizing was designed with the illumination uniformity of 95.87% and the maximum illumination of 39 870 lx. These results show that the flat panel light that designed has achieved the general or even better effects of LED flat lights. It can also largely reduce the production cost of LED flat panel lights owing to the design of removing LGP. Besides, the applying of Taguchi method greatly simplified the design processes.
2016, 45(4): 418002.
doi: 10.3788/IRLA201645.0418002
A minitype optical system used in stereo camera was designed based on civilian low cost stereo imaging requirement, the optical system aimed to achieve 50 m ground sampling distance at 250 km orbit altitude. This optical system can both achieve stereo imaging function and large format array imaging function combined with a CMOS. The system has a focal length of 32 mm, a field of view of 66, an F-number of 6.8 and a working wavelength range of 450-750 nm. The optical system consists of two parts of optical configurations-retrofocus lens and apochromatic microscope. The system design value of MTF achieves 0.49@78 lp/mm, distortion value less than 0.1%, the relative illumination of marginal field of view achieves 0.83, principal ray incoming angle in image plane of marginal field less than 15. The testing result after optical mounting centering alignment shows that the MTF of each field of view all achieve 0.4@80 lp/mm,which meets the static MTF requirement in laboratory. This optical system has better performances in imaging width and distortion value compared with other international famous stereo cameras.
2016, 45(4): 418003.
doi: 10.3788/IRLA201645.0418003
To the problem that off-axis three-mirror optical system has narrow field and complicating initial structure solving process, a method by using optical transfer matrix to solve initial structure was proposed, the focus length and rear cut-off distance of three-mirror system was deduced, then an initial structure parameter of three-mirror system with aperture stop on secondary mirror was given. High order aspheric surface was used to increase system design variance, and making off-axial optimization design to coaxial system based on optical design software ZEMAX, finally got an off-axis three-mirror optical system with wide rectangle field of view 172, focus length of 1 440 mm, F number of 4.8. The system has three high order aspheric optical elements, it can satisfy the requirement of high resolution and large field, the MTF is more than 0.6 at 50 lp/mm, approaches to the diffraction limitation. The designed result shows that the system can be used in space of imaging system with Timed Delay and Integrated Charge-couple Device(TDI-CCD), can expand the ground coverage of system obviously, and achieves high information retrieval efficiency.
2016, 45(4): 418004.
doi: 10.3788/IRLA201645.0418004
Field-of-view(FOV) is the key performance indicator to evaluate a head-mounted display (HMD) in areas such as virtual reality. In order to overcome the difficulties of a sharp increase of optical system aberrations with the increased FOV, a wide FOV HMD optical system with double freeform surfaces was proposed. First, the principles of the double ellipsoid HMD which could achieve large FOV and low distortion were analyzed, and the reason of the aberration correction limitations of the double ellipsoid HMD was pointed out. Then wide FOV HMD optical system with double freeform mirrors was proposed. Two free-form mirrors were used by the new optical system which were symmetrical in vertical direction and asymmetrical in horizontal direction to correct off-axis aberrations brought by increasing FOV. The FOV of the new optical system was 106.3(H)80(V). The maximum relative distortion is 6.97%. The exit pupil diameter was 8 mm and the eye clearance distance was 19 mm. Through tilt outside 8 the binocular FOV was 122.3(H)80(V) and the binocular overlapped FOV was 90.3(H)80(V). The IPD is adjustable within 55-71 mm. The analysis of optical performance indicates that image quality is greatly improved, and the relative distortion and FOV can meet the application requirements of the virtual reality.
2016, 45(4): 418005.
doi: 10.3788/IRLA201645.0418005
Infrared optical systems usually work at a large temperature range due to complex environment. Method of designing three-lens athermalized infrared objective has been introduced. The location of three-lens objective stop was changed to achieve 100% cold stop efficiency. This structure was combined with athermalization model to deduce distribution of the initial focal power. Method of lens materials selection was also given. An example of infrared objective with a 88 mm focal length was designed by this principle. Its wavelength range is 3-5 m and F number is 2.0. The objective has a perfect image quality. The RMS spot diameter is less than 5 m, while the MTF reach 0.75@17 lp/mm. The focal length, focal plane and image quality keep steady at temperature range from -20℃ to +70℃ which shows the feasibility of the design method.
2016, 45(4): 420001.
doi: 10.3788/IRLA201645.0420001
Based on the RF LDMOS transistor and flange from the independent research, a power amplifier was developed for wireless communication as well as L band and S band radar system with high power and efficiency. On the basis of electric grounding and heat sinking, the input and output internal matching circuits were designed to increase the impedance of the transistor. Using the characteristics of the Doherty power amplifier for the backed off efficiency enhancement and internal matching for the invertion of impedance, a power amplifier with the performance of 398 W, 52% at peaking point and 126 W, 43% at 8 dB backed-off power average point was achieved. The optimized technique enhances the backoff efficiency of Doherty power amplifier, 16% relative increasment to common structure, and improves the radio frequency performance of the wireless communication system further.
2016, 45(4): 420002.
doi: 10.3788/IRLA201645.0420002
A broad-spectral imager integrates three detectors which include a visible multi-spectral detector, a short-wave/middle-wave infrared detector and a long-wave infrared detector, and it can provide coverage over the broadest spectral range of more than 10 spectrums in the same type of domestic remote sensors so far, which involves more complex systems and more difficult design challenges. In this paper, a design of data control and processing system of multi-detector was given to solve these challenging problems of the broad-spectral imager such as synchronization control of multi-detector, mass data storage and integrated processing, imaging parameters adjustment of detectors which include gain, stage, integral time and others on orbit, etc. Field programmable gate array(FPGA) was used as a key cell of control and processing in the system hardware; and optocoupler and low-voltage differential signal(LVDS) devices were used to transmit signals to other systems; By means of modularized conceptual design, the software was designed from top to bottom with very-high-speed integrated circuit hardware description language(VHDL); Finally, verification of the design were performed with simulation tools and hardware simulator, and the results show its correctness and effectiveness. In practical engineering application, the system has comprehensive functions, flexible interface, high reliability and expansibility.
The influence of growth temperature on the properties of aluminum nitride(AlN) films are grown by plasma enhanced atomic layer deposition(PEALD) at different deposition temperature. NH3 and trimethylaluminum(TMA) were used as precursors, 200, 500, 800, 1 000, 1 500 cycles AlN layers were deposited at 300℃, 350℃ and 370℃, the growth rate, crystallinity and surface roughness were discussed. Deposition rate and crystallization of the films increased whereas the surface roughness decreased in the growth temperature range of 300-370℃.
2016, 45(4): 422001.
doi: 10.3788/IRLA201645.0422001
As the investigation deepened, it is necessary to measure the velocity of the object in an array with large quantities of points or in a covered area, in the field of explosion and shock waves physics, intense laser, et al. The operational principle and topology of photonic Doppler velocimetry were introduced, the transformation of power in optical fiber link was computed in detail, and the maximum number of channel was analyzed for multi-channel photonic Doppler velocimetry. According to the analysis, a 8-channel photonic Doppler velocimetry which can measuring 8 targets' velocity simultaneously, is assembled on the basis of the optical Doppler effects, and the velocity of the explosively driven metal plate was tested by the proposed velocimetry. The experimental results show that the velocities of the steel flyer plates and the lead granules are measured well, with the poor receiving efficiency. The research results will provide a valuable reference for the practical application of the velocimetry to measure a large number of targets' velocity simultaneously.
2016, 45(4): 422002.
doi: 10.3788/IRLA201645.0422002
Technique of residual cladding pump light detection in active fiber was researched, which was used in assembling the fiber laser system. With this technology, a fiber probe was used to detect the pump light leaking from the cladding with fiber's coating on and stripping. It's found that there was a linear relationship between leaking light power and pump light power, and the proportionality factor was measured. Therefore, it does not need to cut and fuse the active fiber for many times to get the best length of active fiber, and it can save the measuring period and experiment expense a lot. Two types of fiber probes were used, one was taper fiber probe and the other was ramp plane fiber probe. The testing results of low light using these two fiber probes were given, and it's found that taper fiber probe is better than ramp plane fiber probe. In order to check the accuracy of fiber probe, a laser test has been done. By testing the power change before and after cutting off optic fiber, and by testing the power via fiber probe at the same position as the cut off point, it proves that fiber probe can well predict the residual pump light.
2016, 45(4): 422003.
doi: 10.3788/IRLA201645.0422003
Wave-front coding is a classical computational imaging technique and famous for its capability in extending the depth of focus(DOF) of incoherent imaging system. In fact, besides the DOF extension, this technique has the potentials in realizing super-resolution imaging, which is rare to be investigated in existing literatures. On the one hand, the introduction of phase mask makes defocus invariance of optical transfer function(OTF) possible and the dramatic decrease of modulus of OTF alleviates the aliasing effect owned by most digital imaging systems. In this case, a better image data suitable for super-resolution imaging could be provided. On the other hand, the prominent expansion of point spread function(PSF) allows us to obtain the real sampled PSF corresponding to any specific pitch size in a digital way using the ideal continuous optical PSF whose sampling interval could be considered as unlimitedly small. Therefore, based on these two characteristics, an amplification based single image super-resolution reconstruction algorithm was especially designed for wave-front coded imaging system and an experimental prototype camera has been fabricated to verify the effectiveness of the algorithm. The results demonstrate that the extended DOF which is more than 20 times original DOF has been obtained and at least 3X super-resolution reconstruction effect could be achieved. Besides that, the quality of reconstructed image approaches the diffraction limited level.
2016, 45(4): 422004.
doi: 10.3788/IRLA201645.0422004
It is considered that optical fiber channels modeled by the stochastic nonlinear Schrodinger equation and operating at zero dispersion. The statistic characteristic of optical fiber channel with noise was analyzed. In order to find the capacity of the dispersionless optical fiber channel, one first needs to statistically model the communication channel. The Schrodinger equation added noise was modeled. The stochastic differential equations(SDEs) in polar coordinates were built by using It formula. The Fokker-Planck equation of SDEs were presented and the probability density function(PDF) was given. As a result of the Kerr nonlinearity and its interaction with amplified spontaneous emission noise, the amplitude and phase channels correlate with each other and the statistics of the received signal are non-Gaussian.
2016, 45(4): 423001.
doi: 10.3788/IRLA201645.0423001
The infrared spectrum of mixed gas got in the battlefield and complex environment results in overlapping and stagger of the primary and secondary peaks, so its feature extraction of qualitative recognition is particularly important. The infrared spectral data collected from a variety of chemical warfare agents and organic gases are high-dimensional data. Centralizing before reducing dimension was used for feature extraction to capture the essence of more information it contained. Since the infrared spectrum of the mixed gas was non-linear and non-Gaussian signal, this method regarded non-Gaussian as independence measure to separate each component as independent component. In order to meet real-time requirements, its iterative process was optimized based on the traditional fast independent component analysis(FastICA) algorithm and extreme learning machine(ELM) model was applied to quantitative analysis. Experiment results show that the iterations of optimized method reduces compared with the traditional method and mean square error of quantitative analysis is E=2.392 610-4 and regression coefficient is R=0.999. And the optimized method improves the isolated efficiency of separating pure substances spectra from mixture substances without affecting the separate accuracy.
2016, 45(4): 423002.
doi: 10.3788/IRLA201645.0423002
To extend the durability of timber, some research have been done on the timber factors' analysis and expression. Jujube timber, Northeast China ash timber, poplar timber are chosen as the samples, to measure the carbon-nitrogen content of the timbers and the lignin, analyze the ratio of carbon-nitrogen content as well; and to measure the lignin content, lignin density, water soluble lignin density, the extract content of soluble in benzene, alcohol solution and total extract density, compare the FTIR of timber and lignin, research the ratio of guaiacyl and syringyl. Results indicated that the air dry density of Jujube, the best durability timber, is 0.93 g/cm3, and as the FTIR of Jujube timber is 1 633 cm-1, during the stretching vibration of the carbonyl(C=O), there is wave crest existence. The value of G/S is 0.975, the nitrogen content of Jujube timber is 0.274% and nitrogen content of Jujube lignin is 0.444%, these values are the minimum compared with those of the other two timber samples. The carbon-nitrogen content ratio of Jujube timber and of Jujube lignin is respectively 180 and 135, the density of Jujube lignin is 184.39.7 mg/cm3, the total extract density is 88.13.5 mg/cm3, compared with Northeast China ash timber, poplar timber, these numerical values are the maximum.
2016, 45(4): 428001.
doi: 10.3788/IRLA201645.0428001
To resolve the data processing problem of point cloud for optical surface in general interface of optical-mechanical integrated simulation, the surface data processing method based on point cloud boundary detection was presented. First, the surface data preprocessing method in integrated simulation was discussed and effect of boundary detection in surface preprocessing data was also referred. Then, boundary detection algorithm referring to several techniques was researched including the data organization of point cloud, the small tangential plane fitting algorithm of the K-nearest neighbor node and the judgment of boundary node. Based on the research of point cloud boundary detection algorithm, the primary data structure and the program realization was discussed and by the extraction of demonstrated surface point cloud, the algorithm of boundary detection was proved to be right and effective. The algorithm of boundary detection provides the new technical reference for data process of optical surface.
2016, 45(4): 428002.
doi: 10.3788/IRLA201645.0428002
Inspired by the fact that a rigid body has consistent transformation for its individual part, a novel target tracking algorithm based on high-dimension data clustering is proposed. The proposed measure is proved to be available in object tracking mathematically. Thus, it is called the High-Dimension Data Clustering(HDDC) tracker. The frameworks of proposed method are as follows. First, Harris detector is utilized to extract the corners both in the template and the tracking region. Second, these feature points are grouped via their position information separately. Third, affine matrixes between the template and the tracking region are calculated among their respective feature groups. At last, high-dimension data clustering is carried out to measure these matrixes, and the feature points corresponding with the similar matrixes that are tracked targets. Extensive experimental results demonstrate that HDDC is efficient on measuring affine deformed objects and outperforms some state-of-the-art discriminative tracking methods.
2016, 45(4): 428003.
doi: 10.3788/IRLA201645.0428003
In order to improve the security and reliability of the image in the information exchange, a new method was put forwards that laser speckle and Henon mapping were mixed and applied to the image encryption in this paper. Laser speckle image gray distribution was random, it could be scanned for difference random sequences by using the SCAN language. A sequence generated by this sequence with Henon mapping that sum modulo form a new sequence. Using the new sequence to made bit-wise exclusive or implement encryption with original images to be encrypted. The results showed that the method has a good encryption effect, strong key sensitivity and weak correlation of adjacent pixels, could against the statistical attack.
2016, 45(4): 428004.
doi: 10.3788/IRLA201645.0428004
Traditional gradient optical flow has large motion estimation deviation with real value, thus cannot be directly applied to image stabilization system. In order to improve traditional gradient optical flow, a pyramid multi-resolution coarse-to-fine search strategy was incorporated into this algorithm. Firstly, computing area affine transform parameters were selected as the final transform parameters. Then, in the compensation period, error control propagation method was selected to obtain long term stabilized sequence. The experiment results show the improved method can detect severe complex jitter, and can achieve the rotating precision less than 0.09, translation precision less than 0.07, scaling precision less than 0.02, the compensation sequences' average PSNR raised 2.36 dB.
