2018 Vol. 47, No. 8
column
- Invited column-‘Ultra-fast fiber laser technology (I)’
- Laser technology and application
- Laser radar technology
- Infrared technology and application
- Optical design and simulation
- Photoelectric measurement
- Optical communication and optical sensing
- Spectrum detection and analysis
- Information acquisition and identification
2018, 47(8): 803001.
doi: 10.3788/IRLA201847.0803001
New research method and laser performance had been achieved in ultrafast fiber lasers when computing technique was introduced in. In this paper, the research progress on ultrafast fiber lasers based on computing technique was briefly summarized and analyzed, the enabling property of computing technique for ultrafast fiber lasers was revealed. The further combination of ultrafast fiber laser and computing technique may open a new avenue for research and application.
2018, 47(8): 803002.
doi: 10.3788/IRLA201847.0803002
Ultrafast fiber lasers have become the ideal candidate for ultrafast light source and been applied in practice. Due to the small beam diameter and the long interaction distance between light and fibers, the nonlinear effect is unavoidable. Before the appearance of multiple pulses resulted from the excessive nonlinear effect, the phenomenon of period doubling bifurcation(PDB) can be observed in ultrafast fiber lasers under appropriate operation conditions. The PDB refers to the recurrence of pulse parameters at the rate of times of cavity transmission time. The PDB is the intrinsic features of nonlinear systems. It is universal among different nonlinear systems. The latest research progress of the PDB in ultrafast fiber lasers was summarized. The characteristics of the PDB in different dispersion regimes were analyzed. In addition, the features of the PDB of vector solitons, and that of multiple pulses were discussed.
2018, 47(8): 803003.
doi: 10.3788/IRLA201847.0803003
Pulsed fiber lasers have raised extensive attentions for their great application prospects in material processing and fabrication, optical communications, biomedical fields and research of nonlinearity. Saturable absorbers(SA) are used to obtain pulsed laser, two-dimensional materials have unique optical and electrical properties, which have many applications in the fields of optical and optoelectronic devices. In particular, they are widely used in pulsed fiber lasers, due to the features including saturable absorption, simple preparation process, easy integration with optical fiber systems, wide operating wavelength. This article reviews the pulsed fiber laser applications based on the integration of two-dimensional materials and optical fibers, and dicusses the external field controls of such pulsed fiber lasers.
2018, 47(8): 803004.
doi: 10.3788/IRLA201847.0803004
High power all-fiber mid-infrared(MIR) supercontinuum(SC) light sources have attracted much attention for their wide applications in fundamental research, environments, medicine, and national defense security. Currently, such SC light sources are mainly based on fluoride glass fibers. While the relative low damage threshold and poor chemical durability of the fluoride glass fibers influenced their applications in practical high power MIR SC light sources. For further improving the performances of the MIR SC light sources and developing practical high power MIR SC light source, a fluorotellurite glass(TeO2-BaF2-Y2O3, TBY) with good thermal and chemical stabilities was developed, and fluorotellurite glass fibers was fabricated based on it. By using the fluorotellurite glass fibers as the nonlinear media, coherent SC generation from 1.4-4 m and broadband SC generation from 0.4-5.14 m were obtained in our experiments. Moreover, SC light source with an average power of 10 W was also obtained, and the spectral range covered 947-3 934 nm.
2018, 47(8): 803005.
doi: 10.3788/IRLA201847.0803005
Ultra-short pulse lasers at 1.0 m waveband have important applications in many fields such as laser processing, optical precision measurement, biomedicine etc. However, because the Yb-doped fiber laser operates in the all-normal dispersion regime, the pulse width of the laser output is usually large. Because the microfiber could provide anomalous dispersion at 1.0 m waveband by changing its size, in order to achieve ultra-short pulse the microfiber was employed as dispersion compensation device to compress the Yb-doped fiber laser pulse. In this work, the diameter and length of taper waist of the home-made microfiber were 3 m and 5 cm, respectively. The pulse width of the Yb-doped fiber laser was 37.6 ps, while it was compressed to be 8.5 ps by the microfiber. These results offer a more simple and inexpensive method for pulse compression.
2018, 47(8): 803006.
doi: 10.3788/IRLA201847.0803006
The mode-locking mechanism of an all-polarization-maintaining fiber laser based on a nonlinear polarization loop mirror was demonstrated. Instead of a fiber coupler in the traditional nonlinear amplifying loop mirror based mode-locked fiber laser, a polarization beam splitter (PBS) was implied in the nonlinear polarization loop mirror. The combination of the PBS, non-reciprocal components and a piece of gain fiber acted as the core elements in nonlinear polarization loop mirror to achieve stable mode-locking in an all-polarization-maintaining fiber laser. A passively mode-locked erbium-doped fiber laser based on this mode-locking mechanism was also presented. The laser directly emited an optical pulse train of 141 fs duration (75 MHz) with 30 mW total output power. The laser had bidirectional outputs, and the power from two outputs was adjustable by adjusting the waveplate in the cavity. Moreover, the environment stability of the free-running laser was characterized, yielding an average output power fluctuation of 0.05% in 1 h and the relative repetition rate stability of 2.010-8 in 1 s. The configuration enables self-start mode-locking, generating optical pulse trains with high environmental stability, high repetition rate and short pulse duration and fully meets the requirements of ultra-short pulse laser sources in femtosecond based ranging, laser machining, spectroscopy and other applications in spaceflight technologies.
2018, 47(8): 803007.
doi: 10.3788/IRLA201847.0803007
A passively harmonic mode-locked erbium-doped fiber laser was built up based on nonlinear polarization rotation(NPR) technique with switchable repetition rates. A 45 tilted fiber grating(45TFG) integrated in the cavity was considered as an ideal polarizer, which was combined with two polarization controllers to realize NPR mechanism. Under fixed pump power of 673 mW, a group of harmonic mode-locked pulses from 1st to 37th could be obtained only through adjusting the two polarization controllers carefully. The laser can produce stable pulses with the maximum repetition rate of 783 MHz which corresponds to 37th harmonic order, and the sidemode suppression ratio (SSR) of 37th harmonic mode is 41 dB. High repetition rate and stable pulses can be used in applications, such as modern optical communication system and optical sensors.
2018, 47(8): 803008.
doi: 10.3788/IRLA201847.0803008
As optical solitons propagate along the fiber, stable bound state solitons can be formed due to complex nonlinear interactions, and phase variation of bound state solitons reveals abundant dynamics in the nonlinear system. Based on the Ginzburg-Landau equation governing the evolution of solitons along the fiber, the dynamics of soliton phase variation induced by the system parameters was numerically studied. It was found that there exist different bound state solitons, and initial conditions finally converge to bound state solitons with different phase difference. The results also indicate that the change of pump strength influences the pulse separation of solution as well as phase difference of bound state, which is of importance for in-depth understanding of the underlying nonlinear interaction mechanism.
2018, 47(8): 803009.
doi: 10.3788/IRLA201847.0803009
The Q-switched mode-locking(QML) rectangular pulses in the L-band erbium-doped passively mode-locked fiber laser based on nonlinear polarization rotation technique was researched experimentally. The Q-switched envelope of this type of pulses contained the rectangular pulse with fundamental repetition rate,which was confirmed as noise-like pulse by an autocorrelator. A 250 m long section of single mode fiber was inserted into the cavity to ensure the noise-like rectangular pulses easy to be obtained. By carefully adjusting polarization controllers and pump power in the cavity, both the continuous-wave mode-locking noise-like rectangular pulses with fundamental repetition rate of 778.21 kHz and the QML noise-like rectangular pulses with tunable repetition rate from 3.81 kHz to 9.01 kHz and the highest energy of Q-switched pulse envelop 1.06 J were achieved. The research results further reveal the fundamental physics of noise-like pulses and QML operation in the passively mode-locked fiber lasers.
2018, 47(8): 803010.
doi: 10.3788/IRLA201847.0803010
With the rapid development of high power ultrafast fiber lasers, divided-pulse amplification (DPA) technology has attracted extensive concerns. DPA can be implemented through birefringent crystals or freespace delay lines. By combining with the techniques of chirped pulse amplification, spatial beam splitting and photonic crystal fiber amplification, DPA can be applied to coherent beam combining and nonlinear compression in order to increase both the pulse energy and peak power of ultrafast fiber lasers. The research progress of DPA in ultrafast fiber lasers was reviewed. Different system structures of DPA in the applications of coherent beam combining were analyzed. The optimization and further development of DPA was also prospected.
2018, 47(8): 803011.
doi: 10.3788/IRLA201847.0803011
With the rapid development of modern digital manufacturing technology, in the field of industrial product measurement, the measurement of the geometric dimensions of objects need some requirements, such as non-contact, high-precision, multiple sizes, high-volume, etc. The existing measurement technologies cannot meet these requirements. In order to achieve multiple sizes, high-efficiency, rapid, and non-contact precise measurement, fiber-coupled lasers with the advantages of good beam quality, ultra-fine line width, high precision, good monochromaticity, small size, convenient using, no adjustment, maintenance-free and high stability were used to develop a precision non-contact measurment system based on fiber lasers. A high-precision measurement method based on fiber-coupled lasers was proposed, which mainly included object imaging based on fiber-optic line laser, bilateral filtering and extraction of laser line, mathematical relationship establishment of measurement model, geometric parameter calibration, data conversion and 3D reconstruction and other key technologies. The fiber laser continuously emitted laser line to the object, adopted a high-resolution camera, and photographed the laser line image of the object through two imaging techniques of illumination/non-illumination to acquire 2D plane size and height information of the object. The laser line image was filtered and corrected, the laser line was quickly extracted, the geometric parameters were calibrated and the coordinate transformation was performed, and then the processing data was processed to obtain the measurement value of the measurement parts of the object. A large number of object measurements and comparative experiments were carried out to verify the validity and accuracy of the measurement system and measurement method. The measurement accuracy can reach micron level. It provides an efficient method and measurement equipment for the three-dimensional high-precision non-contact measurement of industrial products.
2018, 47(8): 806001.
doi: 10.3788/IRLA201847.0806001
Because of its simple structure, high precision ranging and good anti-interference ability, the laser fuze system with geometric intercepting ranging has a larger requirement in low-cost ammunition, as well as the ranging of the point of explosion and accuracy are all closely related to the system parameter design. In order to meet the requirements for the design of the parameters of the laser geometry intercepting ranging system, the geometric intercepting interval echo power model was established and the influence of the change of these parameters on the distance of work was analyzed, and the relation between work distance and system parameter was revealed. Then the value domain of parameter meeting these conditions was calculated. Through comparson and analysis, the optimal parameters of the system in theory obtained were d=63 mm, r=35 mrad, t=10 mrad, r=0.5 rad, t=0.45 rad. The experiment platform of the laser ranging simulation was designed to verify design results. Then the experimental results were consistent with theory. So it indicates that the design parameters can meet the system requirements. This research can provide reference to the laser geometry intercepting ranging system's parameters.
2018, 47(8): 806002.
doi: 10.3788/IRLA201847.0806002
In order to understand the phenomenon of plasma hot core evolution in air deposited by nanosecond-pulsed laser energy, a high-resolution schlieren system was set up by using two cameras with different resolution. The experimental results obtained from schlieren system showed a good illustration of the initial moment of laser energy deposition, and then the law of the two key parameters of pulse energy and lens focal length on the evolution of laser-induced plasma hot core were studied. The experimental results show that the higher the energy of laser deposition, the larger the size of the plasma hot core, but there may be saturation of the laser energy deposition. In addition, the higher the laser energy and the shorter the focal length of lens, the later the external air penetrates the plasma core after laser energy deposition, which means the plasma core can maintain a steady state of high temperature and low density for a long time, and provides sufficient reaction time for the relevant research on plasma active flow control from the laser energy.
2018, 47(8): 806003.
doi: 10.3788/IRLA201847.0806003
There has been no effective method for detecting the element segregation of large metallic material samples so far. In this research, the newly emerging laser-induced breakdown spectroscopy (LIBS) was applied to quantitatively analyze the segregation of Si, Mn and Ti in pig iron simultaneously. The spectra lines of Si (288.16 nm), Mn (293.31 nm) and Ti (334.94 nm) were selected as the quantitative analysis spectral lines, while lines of Fe (263.58 nm, 441.51 nm, 370.79 nm) were chosen as the internal calibration lines to reduce the influence of matrix effect. The fitting correlation coefficients (R2) were 0.991 7, 0.990 3, 0.991 2, respectively, which proved the ability of LIBS in measuring the concentration of Si, Mn and Ti correctly and simultaneously. A pig iron sample from blast furnace was cut into two round iron samples, whose surface were analyzed with the help of spatial-resolved LIBS subsequently. The element maps revealed the segregation locations of Si, Mn and Ti. The maximum positive and negative segregation degree of three alloy elements was also calculated based on the analysis results of LIBS. The work in this study demonstrates the capability of LIBS for detecting the segregation of alloy elements in pig iron simultaneously. It also reveals the segregation law of alloy elements in pig iron, which is meaningful for the understanding of alloy elements transfer and distribution during solidification process.
2018, 47(8): 806004.
doi: 10.3788/IRLA201847.0806004
For the requirement of non-scanning 3D imaging lidar using the wavelength from 900-1 700 nm, a 6464 linear-mode avalanche photodiode focal plane array(LM-APD-FPA) was proposed, which was composed of InGaAs/InP avalanche photodiode array and CMOS read-out circuitry(ASIC). The working mode of this device was time-of-flight(TOF). APD converted the laser pulse into pulse current which was amplified and thresholded by read-out circuitry, then the laser detection was realized after the comparison of the threshold value, the laser pulse flight time of every pixel was obtained and being converted to binary codes for serial output. Testing results show that the minimal detectable power of 6464 LM-APD-FPA is 400 nW, time resolution is 1 ns. This device is used in lidar system and realizes non-scanning single-pulse laser 3D imaging, indicating that the linear-mode laser focal plane array is useful in the field of laser 3D imaging.
2018, 47(8): 806005.
doi: 10.3788/IRLA201847.0806005
Lives of MS1 and MS2 are 10 years, they are first high orbit navigation satellites of China. In order to improve orbit accuracy and realize the precise positioning of satellites, the two satellites were equipped with laser retro-reflectors. For the optical design of laser retro-reflector, the far-field diffraction of physical and optical properties should be considered besides the design theory of geometrical optics. Taking the test satellite reflector as an example, based on the corner reflector optical far field diffraction energy distribution theory, the reflector size was optimized by using the maximum radar cross section method, the laser retro-reflector aberration was compensated by the angle compensation method, the optical parameters, such as the reflector surface machining accuracy, surface reflection characteristics, cutting mode were optimizated and analyzed, and environment adaptability problems, for example, the high level mechanical environment, 330℃ high temperature, alternating 10 years life space radiation, were solved through the rational design of the mechanical structure and materials. Optical test results show that the parameters are reasonable, can realize the far field energy maximization in predetermined observation area, at the same time, observation data on orbit shows that the reflector works properly, ranging accuracy, range of indicators meet the expected design and the theory is in according with practice, this provideds certain reference and guiding for the design of similar laser reflector in the future.
2018, 47(8): 806006.
doi: 10.3788/IRLA201847.0806006
In order to solve the problem that laser 3D projection is unable to finish tasks with high precision, real-time and intelligent compensation positioning, a new method and accuracy analysis of intelligent laser 3D projection system based on laser tracking technology was proposed. Firstly, the mathematical model of the laser 3D projection system was established. Secondly, the laser 3D projection system was calibrated, and the coordinate system of the components was calibrated by using the datum points of the projection receiving component to complete the calibration of the intelligent 3D projection system. Finally, the model of intelligent laser 3D projection accuracy was established. Results of simulation showed that the middle part of projection area of laser 3D projector had the best accuracy. The projection point error of the projection surface caused by accuracy of the laser tracking measuring equipment was much smaller than the projection point error caused by the projector. The experiments results showed that the projection shape of the intelligent laser 3D projection system developed at the projection distance of 3 meters to 4 meters position accuracy could be better than 0.3 mm. Compared with the conventional laser projector, this system solved the problem that the large-size projection receiving part is unable to install the cooperation target in a large amount and the target reflex head and calibration tool were not needed in the follow-up work. The calibration process was omitted. When the projection system or the measured components moved or drifted, the intelligent recognition, solution, compensation for the relative displacement were completed to ensure accurate real-time projection to the correct location and greatly improved the integration, projection accuracy and positioning efficiency of the projection and positioning system.
2018, 47(8): 806007.
doi: 10.3788/IRLA201847.0806007
With today's increase in large parts manufacturing and assembly requirements, the demand for precision manufacturing and assembly of such products are constantly improved. High-precision measurement and control has become an important factor restricting the development of high-ranking manufacturing. A three-dimensional coordinate measurement system based on laser tracking and absolute length measurement was developed. The system consisted of four absolute laser trackers and a host computer. The ADM module in the absolute laser tracker provided the distance from the target point to four basis points. And the three-dimensional coordinate value of the target point was calculated by the multilateral method. The system overcame the shortcomings of the laser tracking interferometer and can widen the application range of the measuring system. Simultaneously, in order to improve the accuracy of the self-calibration algorithm, a distance-dependent residual model was proposed and studied. The feasibility and accuracy of the self-calibration algorithm were illustrated by experiments. After the calibration of the system parameters was completed efficiently, the precision of the measurement system was tested. The experimental results show that the system has a measurement error of less than 20 m in a large space of 20 m and the measurement uncertainty is 12.3 m. Compared with a single absolute laser tracker system, the accuracy of the system has greatly improved. The system realizes on-line, high-efficient and accurate three-dimensional coordinate measurement in the industry scene.
2018, 47(8): 830001.
doi: 10.3788/IRLA201847.0830001
In order to solve the problem that LIDAR data segmentation algorithm cannot adapt to the environmental characteristics and determine the threshold continuously and accurately, an adaptive LIDAR data segmentation algorithm based on environmental features was proposed. According to the data characteristics of the two-dimensional lidar and the geometric characteristics of the indoor environment, the virtual environment line was fitted with the adjacent point of the laser radar data. The intersection of the virtual environment line and the adjacent laser scanning ray was taken as the reference point to determine the adaptive threshold pre-segmentation of radar data. In view of the defects in the data pre segmentation results completed by the above method, a method for judging pseudo breakpoints after data pre segmentation was proposed, and the algorithm was optimized. The algorithm was compared and analyzed with piecewise threshold segmentation algorithm and linear equation threshold segmentation algorithm. The LIDAR data segmentation algorithm adapting to environmental characteristics achieves a successful segmentation rate of 98% for the experimental data, and has better environment adaptability and higher segmentation accuracy.
2018, 47(8): 830002.
doi: 10.3788/IRLA201847.0830002
The main function of powered lower limb prosthesis is to help the amputees to achieve independent and comfortable walking. In order to make the powered lower limb prosthesis coordinate with the user, it is necessary to recognize the motion intention of the user. By knowing the environment information in front of the user, and taking it as a prior knowledge of motion intention recognition, the recognition accuracy of motion intention will be improved. In order to provide environment information in advance for the powered lower limb prosthesis, a wearable terrain recognition system was designed. The 2D lidar installed in the waist were used to collect the terrain data in front, then extract linear feature of the collected data using agglomerative hierarchical clustering algorithm, finally the terrain was recognized using finite automaton. In the experiment, four terrains were tested, including level ground to up/down stair and up/down slope. Results show that the recognition accuracy of the system to four terrains reaches to 95.8%, and it can obtain the information of terrain parameter including angle of slope, number of steps, stair height and stair depth which can't be obtained from the traditional motion intention recognition methods. It proves that the system is effective and feasible for powered lower limb prosthesis.
2018, 47(8): 830003.
doi: 10.3788/IRLA201847.0830003
Application of 2 m laser in lidar systems, remote sensing, requires more accurate wavelength. Based on the analysis of the quasi-three-level side pumped Tm:YAG laser system, the oscillating conditions of this laser were predicted from the point of pump threshold with taking into account reabsorption loss. The model accurately predictes that the laser central wavelength is switchable in the range of 2.0-2.1 m by means of different laser parameters, such as crystal temperature, the crystal length, the transmission of the output coupler.
2018, 47(8): 830004.
doi: 10.3788/IRLA201847.0830004
The emitted laser is a single frequency source in the traditional coherent detection, and this system can be used in the field of objects measuring and tracking. But in the typical ladar system abroad, it can be used in Range-Doppler(R-D) imaging through the mode-locked pulse burst combined with coherent receiving method. Therefore, the numerical simulation of R-D imaging based on the mode-locked laser pulse burst was analyzed. Firstly, the numerical model of the mode-locked pulse burst was built up. Secondly, the unfolded frequency spectral of the laser pulse was given and the matched filter of the echo signal was designed through the spinned-target model. At last, the FFT and IFFT were adopted in the processing while the R-D image can be obtained with different rotating angular speed. On the other hand, the SNR can be enhanced with many frame accumulations based on the R-D image output. From the simulation analysis of R-D imaging, the fingerprint image of the spinned-target with a macro-pulse(including many micro pulses) was obtained, it is very important in the target discrimination of the ballistic missile defense.
2018, 47(8): 804001.
doi: 10.3788/IRLA201847.0804001
The key technology of space target detection was studied during daytime, including analysis of atmospheric transmittance, sky background radiation measurement, detection ability calculation. Infrared K band spectrum was applied to the 1.23 m large aperture telescope to verify the key theoreties. Experiment shows that after optimization the limit detection of infrared optoelectronic system is 10.38 magnitude at 30 pitching angle and the detection ability increases 24.9% than before optimization. This research has a positive significance for mid-high orbit satellite detection throughout the day.
2018, 47(8): 804002.
doi: 10.3788/IRLA201847.0804002
The grid structure with welded hollow spherical joints has been widely used in industrial buildings with suspending cranes. The alternating and reciprocating action of the suspending crane causes fatigue failure to welded hollow spherical joints. During the fatigue test, temperature of the surface of welded hollow spherical joint was detected by infrared thermal imager. The higher temperature rise area was located at the weld toe of the sphere in the welded parts. This area corresponded to the final fatigue failure position. During the test, the location of the temperature rise area at the weld toe was almost constant. When the fatigue crack penetrated the wall thickness of the sphere, the position of the temperature rise area changed. The experimental results show that the temperature rise of the surface of the joint can be recorded in real time by infrared thermal imager. By analyzing the temperature rise in those area, the location of fatigue fracture can be predicted without any visible cracks. The fatigue life of the joints when the crack penetrates the wall of the sphere corresponds to the change of the position of the temperature rise area at weld toe.
2018, 47(8): 804003.
doi: 10.3788/IRLA201847.0804003
A method of far-field super-resolution infrared microscopy was presented by using vibrational sum-frequency generation(VSFG) and donut-beam illumination. To achieve this, one Gaussian-shaped visible beam and one donut-shaped visible beam with different wavelengths were combined with an infrared beam coaxially to excite the sample. When the frequency of the infrared light was as the same as the resonant frequency of the molecules, the molecules absorbed the energy of the infrared photon and were excited to the vibrational excited state. The photons in the donut-shaped and the Gaussian-shaped visible beams both interacted with the excited molecules, and generated useful and useless SFG signal respectively. Simulations based on the vectorial field of the three beams and rate equations demonstrated that, when the visible intensity was improved to a certain level, the SFG signal tended to be saturated, then the donut-shaped visible photons and the Gaussian-shaped photons competed with each other. By increasing the photon flux density of the donut-shaped visible light to be larger than the saturated value, and reducing the photon flux density of the Gaussian-shaped visible light, the useful SFG signal in the donut-shaped area was surpressed effectively, which means the effective PSF was shrinked. With an objective which has a small numerical aperture (NA) 0.6, a simulated resolution as high as 56 nm was obtained.
2018, 47(8): 804004.
doi: 10.3788/IRLA201847.0804004
Ground-based measurement is a principal method to obtain the infrared radiation characteristics of spatial target. The measuring result contains significant deviation caused by the atmosphere's influence. The deviation can be reduced by using atmospheric synchronous correction system, which is composed of atmospheric optical parameters measurement equipment and radiation transfer software. However, due to the restriction of typical atmosphere models and precision of measured parameters, the corrected measurement accuracy is also greater than 20%. A radiation measurement method based on infrared standard star was proposed by using standard star which view pitch angle approximated to spatial target's as a reference source, which could obtain precisely the transmittance of optical path from measurement system to spatial target, and the transmittance accuracy affected by water vapor, ozone and observation elevation were analyzed. The experiment of measuring the infrared stars was carried out. The radiation error of the target measured by this method is 4.65%, which is better than the classic method's 14.57%. The result shows that the proposed method can provide an effective way for acquisition of infrared radiation characteristics of spatial target.
2018, 47(8): 804005.
doi: 10.3788/IRLA201847.0804005
Aiming at requirement of automation target recognition, a new target detection method of laser and infrared fusion was studied. Firstly, the infrared target detection method based on direction saliency was introduced, and the advantages and disadvantages of the algorithm were analyzed. A laser and infrared fusion target detection algorithm was proposed. The distance information measured by lidar was incorporated into the infrared target detection algorithm based on directional saliency, which greatly improved the precision of the target detection algorithm. The simulation experiment shows that this method solves the problems of poor adaptability and robustness of single source infrared target detection algorithm, and greatly improves the detection rate of the target.
2018, 47(8): 818001.
doi: 10.3788/IRLA201847.0818001
An optical system of a portable non-mydriatic fundus camera was designed. This design realized the highly clear imaging with three million pixels. Based on the physiological and optical characteristics of the human eye, the Gullstrand-Le Grand eye model was introduced to simulate the human eye with normal diopter. The Schematic eye model was used to examine the influence of the ametropia eye on imaging system. In the imaging system, the eye-piece objective lens were firstly used to converge the light emitted through the pupil reflected from the retina of the human eye, then it was imaged to the CCD receiver by the imaging objective lens. In case of the stray lights caused by the cornea, the illuminating system with an annular aperture and coaxial illumination was specially designed. The result shows that the field of view of this system is 30 degrees, the resolution is more than 120 lp/mm, the field curve value is less than 0.12 mm, the distortion value is only -1.2%, the chromatic aberration of all fields of view is within the Airy disk. It comes to a conclusion that this fundus camera has strong focusing abilities for accommodation, and adapts to different eyes from -10 D to +10 D. All the optical components of the optical systems are common spherical glasses, which are easy to manufacture and can reduce the production costs effectively.
2018, 47(8): 818002.
doi: 10.3788/IRLA201847.0818002
In order to align large sparse aperture telescope, the application of screw theory for assembling by the serial robot arm was investigated. Firstly, the basic principle of the serial robot arm alignment for large sparse aperture telescope was analyzed by screw theory. Secondly, based on the screw theory and geometric relation, the principle of the sparse aperture telescope assembling was analyzed and the error analysis was carried out. After that, the feasibility of the installation of point source microscope(PSM) on serial robot arm was analyzed and tested. It was proved that PSM on robot arm was similar to the case in laboratory environment for image stability. In the end, the application of serial robot arm combined with PSM in the large sparse aperture telescope alignment was analyzed.
2018, 47(8): 818003.
doi: 10.3788/IRLA201847.0818003
The simulation of the imaging system is very important to the demonstration, design and performance forecast of the optical remote sensing detector. As the remote sensing object, characterization and modelling of the scene will affect the simulation results directly. Aiming at the crucial geometry, spectrum and radiance characters, a digital scene modelling method based on the optical field theory was proposed. Using the plenoptic function comprised of geometrical coordinates, direction, spectrum and intensity, irradiance field onto the scene surface was modelled including the direct solar radiance, skylight radiance and reflected background radiance. With directional reflectance character of the surface, radiance field leaving the scene surface was also modelled. A simple small 3D scene was created to validate these models. The proposed method will provide digital scene model with multiple characters for the imaging system simulation and the new-style detector development.
2018, 47(8): 818004.
doi: 10.3788/IRLA201847.0818004
Aiming at the extremely high optical path stability requirements of the spatial gravitational wave telescope in the order of picometer, the main mirror components in the system were optimized. Zerodur was chosen as the material of the primary mirror, the support structure was Invar. Firstly, through the optimization of the parameters of the mirror analysis, while ensuring the accuracy of the surface, the mirror light weight rate reached 72%. Then a biaxial joint Bipod flexible mirror support structure was designed, using the side of the three-point support form. In order to ensure the effective support stiffness and unloading effect, the mathematical model of the mechanism was established, and its size parameters were optimized based on Matlab. Finally, the modal analysis and vibration test of the primary mirror components were optimized, and the on-orbit analysis and wavefront quality calculation were completed. The results show that the first-order natural frequency of the primary mirror component is 373 Hz, and the relative error of the test result is 3.5%. The main mirror accuracy is 8.9 nm(RMS); wavefront accuracy is /5(=1 064 nm). The analysis results show that the reflector assembly meets the design requirements.
2018, 47(8): 818005.
doi: 10.3788/IRLA201847.0818005
Optimization of detection conditions is defined as maximizing the amount of heat generated in crack area, in order to perform better in the Eddy Current Pulsed Thermography(ECPT). Aiming at standardizing the method of optimization in ECPT, and a single metal plate specimen with a specific crack was taken as the investigated subject. Response signal increased with the excitation time and excitation intensity, and it had a tendency to enhance first and then weaken with the increase of lift-off distance analyzed by results of simulation and experiment. A multivariate nonlinear regression model was proposed to estimate response signal under specific detection conditions, and the quantitative relation between response signal and different detection conditions was determined. Finally, the Particle Swarm Optimization(PSO) algorithm was introduced to optimize the detection conditions, and the distribution of response signal and Probability of Detection(POD) with different detection conditions were drawn. The research results provide theoretical guidance for optimization of detection conditions in ECPT.
2018, 47(8): 818006.
doi: 10.3788/IRLA201847.0818006
The deep ultraviolet lithography projection lens is the core component of the photolithography machine. However, whether the spatial distribution of the polarization state of the illumination field or the polarization aberration of the photolithography projection lens will change the compact focusing characteristic of the beam, which can not be neglected in the imaging quality. Based on the 3D Jones matrix, the polarization aberration functions were extended to the 3D space, and the evaluation method of polarization aberration for 3D coherent light field was established. The 3D polarization aberrations of the deep ultraviolet lithography projection objective, which was a typical polarization-sensitive optical system, were analyzed. And its physical significance was expounded in detail. It is found that the distributions of the 3D polarization functions in exit pupil are closely related to its own optical parameters, such as field of view, coatings and structural parameters. The effects of coatings and polarization effect on the imaging quality of lithography projection lens were discussed. And the relationships between the polarization distributions of the illuminated beam and the wavefront aberration of the optical system were further studied. The results show that the additional phase introduced by coatings leads to a significant decrease of the image quality for lithography projection lens, and the illumination by the radially vector beam can improve the image quality.
2018, 47(8): 818007.
doi: 10.3788/IRLA201847.0818007
The cube corner reflectors (CCR) have the depolarization effect, which will affect the efficiency of the adjust-free solid state laser, and can also be applied to the beam combination. Both of them require accurate polarization characteristics. The Mueller matrices of 6 transmission light paths of the cube corner were deduced by using analytic geometry and ray tracing. To improve the experiment, a scheme of dynamic detection of Stokes parameter was designed to get high precision data. The error rate is 4.470% and is within a reasonable range. This study have meaning for eliminating the depolarization effect of cube corner, improving the performance of laser and improving the efficiency of beam combination.
2018, 47(8): 818008.
doi: 10.3788/IRLA201847.0818008
Aiming at the precision requirement of machining and assembling for the SM system of the large-aperture grounded telescope, a design method for the structure of SM system based on topology optimization was presented. Based on the variable density idea of topology optimization, the ground structure was restricted to be the Spider and Serrurie trusses, the target was that the deformation along the expected direction was minimized, and the last appearance and dimension were described by whether the material was deleted from the ground structure or not. Firstly, the relative density was taken as design variable, and then by using 1st modal and deformation in gravity direction for the Spider and deformation along the X and Y axis for the truss as a design restraint, a topology optimization model was established. Secondly, on the basis of concept structure obtained by topology optimization, it was iterated and optimized by using Workbench. Finally, the optimized parameter was set, and the static and dynamic stiffness was analyzed and optimized using the finite element method. It shows that the 1st modal in the 4 m telescope SM system is 22.7 Hz, and the deviation in the direction of the gravity is -0.173 mm and -0.195 mm when the optical axis is parallel and vertical to the gravity direction, and the lightweight ratio exceeds 30% for the Spider and Serrurier truss, respectively. The results demonstrate the validity of the proposed approach properly.
2018, 47(8): 817001.
doi: 10.3788/IRLA201847.0817001
In the spin exchange relaxation free (SERF) atomic magnetometer, it is necessary to detect an extreme small optical rotation angle. Among various methods for detecting the rotation angle, the polarization modulation technique based on a photoelastic modulator (PEM) is preferred because it features lower noise and better stability at long-time scales. However, the output signal of the photoelastic modulator contains much noise and high-order harmonics, which seriously affects the performance of the atomic magnetometer. The principle of polarization modulation technique based on photoelastic modulator and the characteristics of the detected signal were analyzed. And a dual channel digital lock-in amplifier to detect the weak signal from the atomic magnetometer was proposed. This method simplified the lock-in algorithm, reduced the complexity of the circuit and accurately detected the amplitudes of the first harmonic and the second harmonic. Theoretical analysis and simulation results show that the detection system works well and detects weak signals accurately, and the simulation error is less than 0.1%.
2018, 47(8): 817002.
doi: 10.3788/IRLA201847.0817002
Photocathode detection system of X-ray streak camera was developed for the rapid calibration and detection of the cathode in laser inertia confinement fusion. Through the design of the trinity streak tube, the optimization of electronic optical system of the streak tube, the preparation of vacuum chamber and control system, the system was installed, integrated and tested, and the photocathode detection system was developed. A static test platform for the cathode system was set up and static characteristics were calibrated. The test results show that the excursion ratio of the three slits is 2.8% in the direction of the slit, 6.6% in the direction perpendicular to the slit, and the average magnification is 1.29 with the error in the range of 0.8%, edge spatial resolution better than 10 lp/mm. The newly developed system of X-ray streak camera photocathode detection can be used for the diagnostic study of laser fusion.
2018, 47(8): 817003.
doi: 10.3788/IRLA201847.0817003
The video satellite uses the agile attitude performance to stare imaging for ground achieving the dynamic monitoring of the target. In order to eliminate the non-uniformity of sequence images acquired by the video satellite sensor, which was caused by the response difference of the detection element. To obtain the clear image and the accurate radiation information, relative radiometric calibration was needed for video satellite sensors. Because of the different imaging mechanism between video satellite and push-broom satellite, on-orbit radiometric calibration methods based on the statistics were not suitable for video satellite. The uniform scene on-orbit relative radiometric calibration method to video satellite was proposed, through staring imaging for three typical uniform scenes including cloud, ocean and desert respectively to calculate relative radiometric calibration coefficients. Among them, the processing of desert scene had achieved better relative radiometric calibration coefficients, which was used for correcting single frame image of Jilin-1 video satellite. The method could effectively repair the image defects, and the non-uniformity of the image was reduced from 3.7% to 1.2%.
2018, 47(8): 817004.
doi: 10.3788/IRLA201847.0817004
Nuclear Magnetic Resonance Atomic Gyroscope has attracted an extensive attention due to its high precision, compact size and less cost at home and abroad. Among numerous techniques for obtaining the detection target, the balanced polarimetry technique is a more general method which monitors the rotation of the polarization plane of the probe beam. Due to miniaturization installation, the size effect is obvious. So there is an inevitable azimuth deviation between optical elements that leads to a bias of the weak optical signal, which extremely restricts the extraction and amplification. For the purpose of improving the detection performance, the differential detection principle of the laser polarization was analysed and a circuit method was proposed which could automatic eliminate the photodiode current bias based on the proportional-integral (P-I) feedback loop. A low-noise and high-gain preamplifier for silicon photodiode was presented. Finally, combined with the NMRG prototype system, the simulation analyses and experimental results were given, which verified the validity of this method.
2018, 47(8): 817005.
doi: 10.3788/IRLA201847.0817005
In order to evaluate the measurement performance of laser scanning confocal microscope (LSCM) accurately, one measurement approach for checking LSCM was presented. Firstly, based on the imaging principle, the technical characteristics of LSCM, especially the vertical resolution and lateral resolution were analyzed in theory; then main parameters of the measurement characteristics were summarized, and the corresponding performance testing menthod were proposed. Such as the amplification and the lateral optical resolution of the LSCM were tested with the nanometer and sub micronmeter line spacing grid standard plates; the axial optical resolution and the axial positioning characteristics of the LSCM were tested with the nanometer height steps; the performances of the sample stage were tested with the laser interferometer. The experimental results show that this method can meet the current performance requirements of LSCM.
2018, 47(8): 817006.
doi: 10.3788/IRLA201847.0817006
An optimized angle decomposition method based on Jacobi matrix was analyzed, considering the effect of rotational angular velocity for humanoid vision system. Firstly, the two-stages four-degrees' coordinate was established, and the system model based on this coordinate was built. Secondly, considering the rotational angular velocity of eyes and neck, a target tracking mathematical model of angle decomposition, considering various rotation angular velocities, was built based on Jacobi matrix. Lastly, through experiments, the influence of rotation angular velocity in each degrees of freedom on rotation angle decomposition under the condition of optimization was studied. After that the optimized angle decomposition model based on the system mentioned above has been settled. By experimental data, within a given range, the ratio of decomposed eyes and neck rotation angle is equal to the ratio of rotational angular velocity of eyes and neck. And compared with split method, the method described in this article has remarkable advantages on time efficiency.
2018, 47(8): 817007.
doi: 10.3788/IRLA201847.0817007
A positioning method of digital zenith camera was proposed to solve the problem that the traditional positioning method required precise leveling of the instrument, the data fitting model parameter was inaccurate and the positioning iterative process was complicated. The calculation formula of CCD image coordinates in the horizontal state was derived. CCD image coordinates of the horizontal state were obtained by using the CCD image coordinates under rough leveling and the output value of the inclinometer, and the star tangent plane coordinates under rough leveling were analyzed, the analysis results showed that the star tangent plane coordinates which needn't be correct could be used to establish data fitting model. The parameters of the data fitting model were calculated by the robust estimation, which restrained the influence of rough error on the parameters and improved the accuracy of the data fitting model. In the end, positioning iterative process was optimized by solving the simultaneous equations of data fitting model to gain the CCD image coordinates of rotating axis, eliminating the inverse transformation of data fitting model and taking the average of the plane coordinates, which improved the efficiency and ensured the positioning accuracy. The experimental results showed that the positioning precision of positioning method under rough leveling is basically the same as the positioning method under fine leveling state. The accuracy of the positioning longitude under rough leveling is 0.306, the accuracy of the latitude is 0.292. Positioning accuracy satisfies the positioning requirement of digital zenith camera.
2018, 47(8): 817008.
doi: 10.3788/IRLA201847.0817008
Aiming at the problem that it's difficult for traditional Canny edge detection operator to extract the lane line features robust in real-time in complex scenes of a large amount of traffic information, an improved method for the optimal direction interval quick detection based on Gabor filter was proposed. First, the panoramic image was expanded into a rectangular image by the concentric circle approximation expansion method. Then the expanded image was processed by Gabor filter with different phases, thus obtaining the direction interval which had the highest clarity of the lane line quickly. In the process of edge detection with Canny operator, only the edge points in the optimal interval were used for non-maximum suppression and further processing. Finally, the algorithm was tested on 500 real images for videos, and the recognition rate could be better than 94.2%. The results show that the proposed method is robust for complex environment and has strong feasibility, which can effectively improve the real-time performance and stability of lane departure warning system.
2018, 47(8): 817009.
doi: 10.3788/IRLA201847.0817009
In order to reduce the influence of disturbances on the stabilized platform of seeker, an improved double integral sliding mode controller(DISMC) based on extended state observer(ESO) was proposed in this paper. Firstly, the second order extended state observer was used to estimate the unknown disturbances of the system. Secondly, a double integral sliding mode controller was adopted to achieve low steady-state error tracking; meanwhile, the improved power reaching law was adopted to reduce the chatting magnitude. Finally, the performances of tracking and disturbance rejection rate were carried out on the stabilized platform of seeker. The results showed that compared with the traditional PI controller based on disturbance observer(PI-DOB), when the system tracked the trapezoidal wave at 3()/s, response time of LOS rate was reduced by 48 ms, and the standard deviation of tracking error was reduced by 0.013 1 ()/s with the proposed controller. Meanwhile, the turntable generated a periodic motion with sin(t), 3sin(5t) and 7sin(2t) respectively to simulate the motion of the carrier, the disturbance rejection rates were increased by 2.91%, 0.45%, 0.7% respectively. In conclusion, the DISMC-ESO has better performance in dynamic response and disturbance rejecting for stabilized platform of seeker.
2018, 47(8): 817010.
doi: 10.3788/IRLA201847.0817010
When the space-to-ground optical remote sensing system with a segmented primary worked, the alignment degeneracies of secondary mirror relative to the primary mirror would have an impact on the image quality, which should be detected and corrected online. When there was no center segmented-mirror in the segmented primary mirror, the traditional sensitivity matrix inversion method would not be used to calculate the alignment degeneracies of secondary mirror. It proposed a method to calculate the misalignment of the secondary mirror by using the multi-field wavefront sensing information. Based on ZEMAX, it established a space-to-ground remote sensing system with 36 segmented primary mirror, in which there was no center mirror. For the optical system with special aberration characteristics, it built a mathematical model to obtain the misalignment of secondary mirror by means of the field-dependent wavefront aberration which can be got by multi-field wavefront sensing. The simulation results showed that when the wavefront sensing error is 1/40(=632.8 nm), the detection accuracy of the misalignment of secondary mirror on X,Y-translation and X,Y-tilt reached 30 nm and 15 respectively; the detection range of the misalignment of secondary mirror on X,Y-translation and X,Y-tilt are 0-1.5 mm and 0-0.03 respectively. And a lot of simulations based on the real space optical remote system were done to prove the feasibility of the proposed method.
2018, 47(8): 822001.
doi: 10.3788/IRLA201847.0822001
Visible light communication has a double function of illumination and communication, so it is needed to consider the light source layout and communication reliability issues. In order to ensure the international lighting standard, in the constant of the total LED lamp beads, firstly, the layout of the light source was analyzed, the illumination distribution and uniformity of the three and four array layouts under the same power consumption were numerically calculated. Secondly, in order to improve the effectiveness and reliability of multi-array visible-light communication system, MIMO technology was applied to VLC, and STBC coding was used to calculate the reliability of multi-array layout. The results show that the uniformity of illumination of the four arrays is 20.9% higher than that of the three arrays under the same power consumption. When the bit error rate is 10-4, the error performance of 41 system is improved by about 2 dB compared with the 31 system, the error performance of the 42 and 32 systems are increased by 6 dB and 5 dB compared with the 41 and 31 systems.
2018, 47(8): 822002.
doi: 10.3788/IRLA201847.0822002
A highly sensitive long period fiber grating(LPG) temperature sensor was designed and demonstrated. Cladding of the LPG was etched and encapsulated in metal to maintain constant strain, then was sealed in a test tube containing polyamic acid(PAA), which had a relatively large thermo-optic coefficient as a temperature-sensitive material. The resonance wavelength shifted with temperature for different PAA refractive index values and different LPG cladding diameters were measured and discussed. The results show that the sensitivity of the LPG temperature sensor becomes higher when the refractive index of PAA becomes larger for a certain LPG of determined diameter. Additionally the sensitivity of the LPG temperature sensor becomes higher when the cladding diameter of the LPG decreases for a determined refractive index of PAA. A sensitivity of 1.26 nm/℃ was achieved for this improved LPG temperature sensor, ten times greater than that of the sensor made of common LPG and 100 times greater than that made of common fiber Bragg grating (FBG). This new sensor exhibits good linearity of 99.80% at temperatures of 2-35℃, which improves its potential application for biomedical measurement and ocean detection, where the temperature range of interest is close to room temperature.
2018, 47(8): 823001.
doi: 10.3788/IRLA201847.0823001
An green algae area estimation algorithm for hyperspectral image based on linear mixed model was proposed. According to the obtained endmembers and the original image, the abundance map of the green algae terminal was calculated by the fully constrained least squares algorithm, and the abundance map of green algae was regarded as the area estimation result directly. The algorithm can effectively overcome the problem of inaccurate estimation of the estimated area of green algae due to the lack of resolution of hyperspectral image, and realize the estimation of green algae area at sub-pixel level. Based on the Geostationary Ocean Color Imager (GOCI) 8 bands image unfolding experiment on June 29, 2013, the estimated coverage of green algae was 321 km2, which was close to that of HJ-1B satellite. Compared with NDVI and other traditional algorithms, the proposed method has obvious advantages. Traditional methods usually present higher estimation results, because they could only justify whether a pixel includes green algae or not. The proposed method may provide a new way of thinking and technology for early warning and monitoring of green algae, and has a high application value.
2018, 47(8): 823002.
doi: 10.3788/IRLA201847.0823002
In order to test and analyze the physical evidence of plastic beverage bottles, 57 samples of plastic beverage bottles were inspected by Fourier transform infrared spectrometer(FTIR), X-ray fluorescence spectrometer (XRF) and thickness meter, and analyzed and treated by means of cluster analysis. Firstly, the main components of plastic beverage bottles were tested by infrared spectroscopy. According to the different components of the samples, they can be divided into polyethylene (PE) and polyethylene terephthalate (PET). Secondly, the main filler calcium carbonate in the sample can be determined by X-ray fluorescence spectrometry, and the samples can be distinguished according to the content of Ca elements. Finally, the thickness of plastic beverage bottle sample can be measured by thickness meter. According to the color, specification, composition, Ca content and sample thickness of the samples, the samples can be distinguished by the cluster analysis method. The experimental results show that the method is simple, fast, accurate, reliable and non-destructive, and can be used to distinguish and inspect plastic beverage bottles.
2018, 47(8): 826001.
doi: 10.3788/IRLA201847.0826001
In view of the poor real-time performance and high cost of haze detection methods, a method based on contrast and image energy was proposed to detect the haze. Firstly, the images taken by the CMOS camera were preprocessed. The image has some slight swing because the camera has been disturbed by the external environment, so the images were registered. Secondly, in the critical region of the image, two contrast vectors of contrast and image energy were obtained. Thirdly, the contrast, image energy and ambient humidity were taken as input, and the real-time PM10 concentration measured by the laser particle counter was used as the output. The relational model between input and output was constructed by training support vector regression(SVR). Finally, the PM10 concentration of the image was calculated using the model. The PM10 concentration detected by this method was compared with that measured by laser particle counter. The average relative error was less than 10% and MSE was 0.006 2, which indicates that the fitting degree between the predicted value and the true value is good and the accuracy of the model was high. On this basis, increasing the training samples can improve the model accuracy. Moreover, the method can establish the corresponding relation model for different environment to be tested, which has strong flexibility.
2018, 47(8): 826002.
doi: 10.3788/IRLA201847.0826002
In order to increase the accuracy and robustness of phase unwrapping, a novel stair phase unwrapping algorithm was proposed. This algorithm combined the gray and phase coding to unwrap the phase. The algorithm based on gray can project different gray intensities to determine different levels. However, when the period was small, there was little difference between intensities which will generate phase errors. Phase unwrapping based on phase had great robustness but it occupied the computation. Compared with traditional method, the creative point of this method was that it designed two encoding methods for phase unwrapping. The first type of pattern was based on grey information that separated the global modulation grating. The second type of pattern was based on phase coding. The experimental results show that the algorithm can determine the level of the wrapped phase accurately and the 3D information can be obtained quickly.
2018, 47(8): 826003.
doi: 10.3788/IRLA201847.0826003
With continuous development of the security industry and people's growing demands for cameras, it was urgent to have the panoramic image with a larger field of view. As a result, kinds of splicing algorithms and splicing applications have come into being. Although the existing software algorithms have been able to achieve good results, but the problems of supplement light distribution in image splicing are still outstanding. Considering the situations above, the problems of inconsistency of illumination or light intensity in Light Emitting Diode(LED) were studied. The design idea of the Total Internal Reflection(TIR) lens was used for the secondary light distribution design, which made the illumination or light intensity of the light spot from LED uniform after splicing, and the simulation was done at the same time. The simulation results show that it could avoid too bright or too dim trace after the light spot splicing, and the splicing effect would be better. It could meet the requirement of the camera working around the clock.
2018, 47(8): 826004.
doi: 10.3788/IRLA201847.0826004
Accurate classification of missile by the missile image (or in flight state) taken through the satellite equipment, which achieve the timely and effective defense, is one of the hot spot in the military field at home and abroad. Because the missile in the war state has masked color, and the missile shape differences are not significant, it is difficult to classify the missile type based on the low level features. Aiming at these problems, a new algorithm was presented based on Sparse Auto-Encoder (SAE) combining the high level visual feature and low level feature extraction. In order to improve classification accuracy, transfer learning was introduced, with the help of the STL-10 sample database local features, the global features of small sample missile target image can be extracted through the local features by the convolution neural network (CNN) of pooling layer, and then transmitted into the Softmax regression model to realize classification of missiles. Experiments show that compared with the traditional low level vision features and SAE high level vision feature classification algorithm, the SAE fusion feature classification algorithm has higher accuracy and robustness. In addition, in order to avoid classification performance reduce even failure under the lack of training for new type missile target object, the new algorithm induces transfer learning to extract local feature, experimental result proves the feasibility and accuracy of the algorithm.
2018, 47(8): 826005.
doi: 10.3788/IRLA201847.0826005
When using the method of kernel principal component analysis(KPCA) to extract feature of target in radar target recognition, the HRRP characteristic is ignored. A translation invariant features-central moments was extracted as feature vector, KPCA was used to reduce the dimensionality; The BP neural network was easy to fall into local minimum, the genetic algorithm(GA) was used to optimize the BP network node weights and threshold. The experimental results based on the measured radar data show that the translation invariant KPCA feature extraction method achieve the combination of translation invariant and descending dimension, and the BP neural network optimized by GA improves the stability of classifier and improves the defect of falling into local minimum easily.
