2017 Vol. 38, No. 1
A reconnaissance orientating method for mast-mounted photoelectric system was described. Single gyro and a double-axis inclinometer were utilized to substitute for a tri-axis perpendicular gyro, to measure the attitude of the photoelectric equipment. Combined with the earth north orientation by inertial navigation equipment, the relative distance between object and equipment obtained by laser range finder, and the native geodetic coordinate obtained by satellite positioning, the geodetic coordinate of object could be acquired accurately by coordinate transformation.The examination results show that the system orientation accuracy can reach 0.3 mil, and the object positioning accuracy can excel 10 m(CEP).
Visible/infrared double-FOV optical system used for panoramic aerial camera is designed in this paper, aiming at improving target survelliance and recoganizing capability and meeting requirements of combat demand of troops around the clock. Focal length, relative aperture and field angle of visible optical system is 165 mm/660 mm, 1: 8.8, and 9.1°×6.8°/2.3°× 1.7° respectively, while focal length, relative aperture and viewing angle of infrared optical system is 75 mm/ 300 mm, 1:4, and 8.3°× 6.2°/2.1°× 1.6° respectively. Zooming is realized by adding telescopic system in front of the limited focal length optical system. According to pixel size of infrared device and visible light device, Nyquist frequency of infrared system and visible light system are calculated as 33 lp/mm and 91 lp/mm respectively. At 33 lp/mm, infrared optical system with large and small field of view of the MTF values are 0.35 and 0.37; while at 91 lp/mm, visible light optical system with large and small field MTF are 0.41 and 0.4. Image quality is close to diffraction limit, which shows image quality of optical system can satisfies needs of practical engineering.
In order to improve target detection ability of IR images in long range effectively, an infrared telephoto objective for 8 μm~12 μm wave-band is designed for 640 pixel×512 pixel infrared CCD detector. Effects of surrounding environmental temperature are analyzed and refractive diffractive hybrid thermal compensation is discussed. Focal length of the system is 200 mm, relative aperture is 1:2.2 and field of view is 7°. Infrared telephoto system with small volume and compact structure is designed in a large range of temperature. The system is composed of four lenses with only three materials of zinc sulfide, zinc selenide and germanium to compensate for the temperature. Image quality of the system is evaluated by ZEMAX optical design software. Results show that modulation transfer function (MTF) for each field of view at cut-off frequency of 17 lp/mm is greater than 0.4 which approaches diffraction limit. Root mean square radius of spot diagram for each field of view is close to Airy disk radius. Telephoto objective has favorable performance at working temperature of -40 ℃~+60 ℃. The system meets the requirements of technical specification.
Image quality of large aperture infrared optical system is easily suffered from ambient temperature and deadweight, which can be solved by infrared adaptive system. Infrared adaptive optical system based on Hartmann-Shack wave-front sensor is designed in this paper. Large aperture telescope engaged in dual waveband such as middle-infrared wavelength and visual wavelength is designed to have 10× collimation with optical configuration of reflective Cassegrain objective lens group and multispectral achromatic refractive eyepiece lens group. Relay infrared objective lens is designed to compensate aberration of infrared telescope. Reimaging optics is chosen in such a way to minimize objective lens while maintaining 100% cold shield efficiency. Thus MTF of dual-waveband optical system for IR adaptive system can approach diffraction limit(more than 0.5). Image quality can meet technical requirements.
Grating spectrometer is one of the most important instruments in studying solar radiation, and accuracy of its wavelength scanning mechanism determines final measurement result. Taking errors from both grating parameters and machining dimensions into consideration, this paper analyzes comprehensive accuracy of wavelength scanning mechanism which is made up of screw and swing. Based on dispersive principle of concave grating, relationships between wavelength λ and displacement of end swing along direction of screw x, swing length l, grating constant g and half angle between incident light and diffraction light δ are derived. Then derivatives of equation are obtain, and wavelength errors are calculated between 650 nm and 2 400 nm and should be no more than ±1.227 nm according to principle of errors stack. Then results are tested on prototype. Fitted curve of wavelength and error can be obtained when taking mercury lamp as light source, and can be checkeded when taking helium neon laser as light source. Results prove correctness of theorectical calculation method, and provide theory evidence in choosing components.
Aiming at solving axial scanning problem of dual photon fluorescence microscopy imaging system, fast axial scanning system based on digital micromirror device (DMD) is proposed in this paper. DMD is used for selecting optical path in this system, and lens groups with different focal lengths are placed in these optical paths to generate different changes of beam divergence angle. Then axial scanning spots with different depth are obtained after beam focused by objective lens. Axial scanning distance, scanning spot and diffraction efficiency are calculated and simulated. Results show that when scanning system adopts four modules or five modules, axial scanning distance can reach 1mm, focal length of lens in four modules and five modules is 297.3 mm and 361.47 mm respectively. Axial scanning spot varies in good linearity except marginal spot. Axial scanning frequency approaches to dozens of kilohertz. This scanning system can meet requirements of cranial nerve imaging.
Aiming at solving problem of weak small target missing during dimension reduction and fusion of hyperspectral data, hyperspectral data fusion method for weak small target is studied in this paper. Class pixel matrix is produced by similarity measures, dimension reduction projection matrix is calculated by principal component transforming class pixel matrix, and dimension reduction data is obtained by dimension reduction projection matrix projecting the original spectral data. False-color result image is produced by RGB color space transforming from reduction data. Fusion performance of improved method is verified by hyperspectral data of weak small target and underwater fish group. Experiments show that similarity classification fusion method can not only get one false color image from high dimension hyperspectral data, but also avoid missing weak small targets from background, which enhances abilities of detection and identification, and has a strong application prospects.
Underwater image suffers from distortions and blurs due to water fluctuations and underwater turbulence that restricts the development of underwater surveillance, underwater target alert in the air, maritime search severely. The realization of distortion and turbulence correction has great significance. Most recent developments for the degraded image by water fluctuations and underwater turbulence are reviewed in this paper, and four methods and typical image restoration results based on lucky patch, image registration, water-waveestimation and image degradation model are summarized accordingly. Further research directions for restoring underwater degraded image are analyzed at the end of the paper.
Aiming at solving problem of existing grating ruler measurement method with which high speed and high precision can not be taken into account, measurement principle of transformation from horizontal to vertical scale of incremental grating and corresponding image processing algorithms are proposed in order to meet the requirement of feedback displacement for high speed motion and high precision positioning of electronic manufacturing equipment. In order to improve speed of grating image acquisition and processing, a hardware testing platform based on FPGA is built. Firstly, images collected by FPGA system are filtered and binarized, then processed images are added with vertical coordinates and horizontal coordinates accordingly. In this way point displacement value is obtained by calculating smallest pixels. Experimental results show resolution of 0.029 μm and precision of 0.3 μm can be achieved by using FPGA testing system with vertical and horizontal conversion algorithms.
In practical engineering applications, contour and micro-deformation of materials and structures are essential parameters to be tested, and furthermore, usually need to be tested simultaneously. To meet this requirement, a method that combines digital speckle pattern interferometry (DSPI) and digital fringe projection (DFP) is proposed. An integrated optical setup is built by embedding a digital projector in the DSPI setup. With the new setup, surface contours and deformations can be measured simultaneously. The proposed method has the advantages of full-field, non-contact measurement, simple optical arrangement, ease of operation, high efficiency and reliability. The resolution of contour measurement is up to 10 μm, while the deformation measurement resolution is up to 30 nm.
The range finder and position shift observation based on laser interfering has been widely applied with the tendency of portability, intellection and integration. However, the present laser interfering devices for distance measurements are mostly based on Michelson interferometer. The interfering information is processed in the spatial domain. Sometimes the signal is probably influenced by the turbulence and the vibration introduced by large industrial equipment. Therefore, a kind of new measurement based on laser heterodyne interfering was proposed, which could transfer the signal process to the time domain in this article. In this system frequency-modulated laser beam was split into two interferometers. The detector received the beat signal and averaged the signal at the time domain and the computer demodulated the signal in the frequency domain. The testing results appeared as good robustness, and the testing error could be controlled within 0.01 mm.
In order to improve transmittance of microstructure narrowband filters and increase precision of microstructure unit, new fabrication method of film deposition and microstructure unit are proposed in this paper. Three different center wavelength filters are design based on concepts of Fabry-Perot principle. Three different center wavelength of narrowband filters are fabricated by combining photochemical mask separation and PECVD technology. Center wavelength of narrowband filters are λ1=480 nm、λ2=520 nm and λ3=590 nm respectively, transmittance are all above 80%, with bandwidth between 30 nm to 50 nm and an area for each microstructure unit 50×50 μm2. Transmittance is improved, while precision of microstructure unit are increased to reach micron order effectively with neat edge and clear dividing line.
Aiming at solving the problem that surface of optical plastic is easy to be scratched, will have film crack at high temperature, Ti3O5 and SiO2 are selected as high and low refractive index coating material because of its stable mechanical properties in room temperature in this paper. According to theory of thin film, TFCalc software are used to achieve film system design, and electron beam evaporation and ion beam assist deposition are used to deposit coating material Finally, new anti-water fluorine material are deposited by resistance depositing.Through selecting new material SV-55 as connecting layer, adhesion of plastic lens and film is enhanced and problem of SiO2 and plastic lens expansion coefficient mismatch is solved, which improves ability of temperature resistance of plastic lenses. Through continuous optimization of experimental parameters, reflectivity of green antireflection film is less than or equal to 1% at 400 nm~700 nm. Results show that, plastic lenses have the ability to resist friction, aging and hydrophobicity, and can be widely used.
With widely uses of aspherical optical elements, aspherical machining technology has become hot study topic. This paper presents aspheric processing method based on vibrating polishing of loose abrasive grains. Surface of aspherical optical element fully contacts with loose abrasive grains, and acting force of polishing for loose abrasive grains is provided by vibrating device. In this way, free materials is remove evenly and surface roughness is reduced Taking optical parts with size for Φ55 mm and material for ZK-10L as experiment specimen, influence on polishing effects are analyzed by vibration amplitude, the concentration of polishing liquid, and the impact of particle size and polishing time. When vibration amplitude, concentration of polishing liquid and particle size are 5 mm, 80 g/L and 1mm respectively, surface roughness of the specimen is reduced to 9.4 nm from 84.4 nm after 8h polishing, while specimen surface shape accuracy stays unchanged. In this way purpose of polishing specimen with high-accuracy surface shape is reached.
In order to study effects of micro-grinding parameters on flatness of optical fiber lens and reduce flatness error of optical fiber lens in micro-grinding, a group of orthogonal experiments of micro-grinding 30° oblique fiber lens on a single fiber with 125 μm diameter are carried out in this paper. Based on grinding forces model of micro-grinding and elastic beam deformation theory of material mechanics, effect rule of micro-grinding parameters on flatness of optical fiber lens is analyzed. Theoretical analysis and experimental results show that overhang length of optical fiber has the greatest influence on flatness of oblique optical fiber lens, while increasing overhang length of optical fiber will result in a larger flatness error of oblique optical fiber lens and appropriate micro-grinding parameters can obtain smaller flatness error of oblique optical fiber lens. Appropriate micro-grinding experiment results in 30° oblique fiber lens with flatness 3 μm.
A new algorithm based on weighting LoG operator and morphological processing was proposed to solve the remote infrared small target detection problem. Firstly, the image was processed by using weighting LoG operators with different scales, and the max characteristic image of response value was extracted. Then, the morphological process was conducted to remove the image noise, and the Otsu binarization segmentation clustering was done. Finally, the position coordinates on the image of target point were output. Experimental result shows that compared with classical filtering method, the proposed method has obvious advantages, the signal to clutter ratio (SCR) gain is 36.9, the background suppress factor (BSF) is 4.7.
Aiming at improving laser beam quality in designing high power end-pumped Nd:YAG laser, thermal lensing effect is employed to achieve high beam quality in Nd:YAG laserin this paper by placing two more Nd:YAG crystals with different doping concentrations in the resonator. Under action of pumping light, thermal lensing generated from the Nd:YAG crystal is used to shape special distribution of pump beam and fundamental mode beam. Tighter overlapping of both beams results in higher efficiency of pump power and better beam quality of laser. Experimental results show special distribution of pump beam and fundamental mode beam can be shaped by thermal lensing effectively under different pump power. Two beams are matched closely at pump power of 200 W, and M2 is improved from 14.7 to 4.1.
The demonstration effect is low in large conference center with multiple projector-screens, because there is no connection between the primary and secondary projector-screens, and the laser pointer on the primary screen could not been shown on the secondary screen. A demonstration method of laser pointer for multiple projection-screens based on camera is proposed in this paper. A connection between the primary projection and the computer screen is built by the camera, and then the point of the laser pointer on the primary projection can be transformed to the one on the computer screen. Based on this, the cursor can be moved and the secondary projection will have the same demonstration effect. The main steps include: (1) compute the homography matrix H between the primary projection and the computer screen by monochromatic projection. (2) extract the point of the laser pointer on the real-time captured image of primary projection. (3) calculate the indicating point on the computer screen base on homography matrix H and control the cursor move to there. Experiment shows that this method can calculate the position of the laser pointer on the computer screen with an error within 5 pixels and track the laser pointer on the secondary screen successfully. This method can both give an unlimited space to the demonstrator and a communication to all the audience.
In order to guide setup of fluorescence lidar detecting system practically, model system is designed based on fluorescence detection principle Taking oil pollution measurement on water as an example, this paper analyzes main parameters of launch and receiving system of fluorescence lidar detecting model system and its influence on system signal-to-noise ratio, then proper system parameters are chosen according to testing conditions. Receiving system of laser with 50 μJ single pulse energy, telescope with 0.1 mrad receiving field of view and filter with 60 nm bandwidth are adopted in lab conditions, particles with concentration 10 particles/L can be tested. Results show that this simulation of fluorescence lidar model can satisfy requirements for detecting oil pollution on water surface in laboratory.
Due to urgent requirement for high speed transmission, digital atmospheric laser communication system based on double channel dense wavelength division multiplexing (DWDM) is experimentally demonstrated. Optical carriers are provided by two lasers at 1539.76 nm and 1540.55 nm respectively, and intensity modulation is adopted. After being multiplexed and amplified, DWDM signals are transmitted through an optical antenna. Spectrums, waveforms and eye diagrams are measured at receiver after transmission in the atmosphere via 1km. Experimental results show that DWDM signals are de-multiplexed in weak turbulence, and waveforms and eye diagrams are observed clearly. The Q-factors are more than 5 when transmitting 20 Gbit/s modulated signals simultaneously.
According to the principle of evanescent wave, a humidity sensor based on optics in-fiber Mach-Zehnder interferometer was proposed by using the standard single mode fiber with two waist-enlarged bitapers, and the center of sensing arm was tapered by adiabatic flam-heated fiber tapering machine. The light propagates from the input end of the sensor, the first bitaper excites a number of higher-order modes, each mode transmits through tapered fiber and into the second bitaper, which can be coupled into the output fiber of the sensor. The change of the humidity can lead to the evanescent field of the tapered fiber changing, eventually causes the energy of the transmission spectrum energy to change. The environment humidity sensing measurement can be realized through measuring the variation of transmission spectrum energy. The experimental results show that within the humidity changing scope of 35%~85%, the energies of the transmission spectra have the same variation trend, a valley of interference spectrum near the water vapor absorption peak has the highest sensitivity of 0.157 dBm/%RH, the temperature cross-sensitivity is as low as 0.014 %RH/ ℃. This humidity sensor is advantaged by easy manufacturing, high sensitivity and immunity of temperature cross-sensitivity, it have a great application prospect.
In order to calibrate deviations of demodulation system between rising slope and falling slope of triangular wave on demodulation results of FBG waves, effective calibration method of relative position to sampling point is proposed. Two FBG waves in two scanning process of triangle wave are mapped to the corresponding original data of etalon spectrum firstly. Then positional deviation of two FBG waves which is mapped into the etalon spectrum is corrected. In this way demodulation deviation of system can be reduced. Two FBGs with different wavelength to accomplish.in experiments. Results show that the wavelength deviation of FBG1 is reduced from 12.053 pm to 0.476 pm, while wavelength deviation of FBG2 is reduced from 12.101 pm to 0.427 pm. Demodulation deviations of two FBGs are decreased respectively by 25.3 times and 28.3 times than before.