2019 Vol. 48, No. 8
2019, 48(8): 827001.
doi: 10.3788/IRLA201948.0827001
Mantis shrimp eyes have a powerful vision system with multi-spectrum and polarization detection capabilities. Bionic studies were carried out based on the microvilli arrays structure of mantis shrimp eyes. For the problems of energy utilization and the spatial resolution in the polarization detection, the structure of micro-villi array of bionic mantis shrimp eyes was studied. The structure of aperture array photonic crystal was studied to realize the integration of polarization filtering and spectral filtering. According to the spectral filtering and absorbing characteristics of the microvilli array, the bionic structure based on the nano wire grids was researched on, which can absorb spectrum and polarization at the same time. Based on the microstructure with orthogonal microvilli of rhabdom in mantis shrimp eyes, the orthogonal nano wire grids was used as the basis of the bionic structure to realize the unit pixel bidirectional polarization absorption.
2019, 48(8): 805001.
doi: 10.3788/IRLA201948.0805001
In order to improve the beam quality of output beam in high power laser system, a method to detect defocus by using three spot sizes was presented, the spot sizes at three positions in the axial direction of the beam on the CCD detector was detected using the method, the defocusing amount of the beam can be calculated by the size relationship among the spots, and then closed-loop correction was performed according to the defocusing amount. In the experiment, the defocusing amount of the beam was compensated by adjusting the shaping system, so that the defocusing amount of the beam was corrected from (4.90.2) mm to (0.30.1) mm. The experimental results show that the method is simple in structure, and can measure strong laser convergence and divergence caused by various factors. The study provides reliable criteria for defocusing compensation, and a method to solve the problem of beam divergence caused by strong laser thermal effect.
2019, 48(8): 805002.
doi: 10.3788/IRLA201948.0805002
The conventional laser cladding forming process generally uses equal line-width scanning, which can difficultly realize a continuously variable width deposition. A blade model with variable wall thickness was designed. The inside-beam powder feeding nozzle was applied for the variable laser spot deposition. A deposition height control system was used to measure the actual height of each segment. PI-controllers with scanning speed as the control input were designed to guarantee equal deposition heights in different widths. A segmented deposition height control strategy was developed to realize continuous variable width deposition of the variable wall thickness twisted blade. The structure was formed based on methods of continuously varying focus distance and closed-loop control. The test results indicate that the wall thickness varied uniformly from 2.52 mm to 6.18 mm, and the largest error was -0.58 mm. The heights of the segments were in accordance with the largest error of -0.22 mm. The micro-structure in different wall thickness positions were compact and uniform.
2019, 48(8): 805003.
doi: 10.3788/IRLA201948.0805003
Aming at the dynamic pressure sensor calibration, the pressure can not be accurately traced, a method of measuring refractive index of water medium by laser interferometry was used for sinusoidal pressure calibration. The pressure chamber was filled with water medium and generated dynamic pressure. Taking the periodic sinusoidal pressure as an example, the dynamic pressure of the medium was obtained by measuring the change of refractive index of the water under the sinusoidal pressure by laser interference. In order to measure sinusoidal pressure accurately, a mathematical model was established and verified by experiments. A special demodulation system was developed to measure sinusoidal pressure accurately through hardware and software cooperation. Through static and dynamic experiments, the mathematical model of pressure measurement based on laser interferometry was validated. It is feasible to measure dynamic pressure by laser interferometry, and the value of dynamic pressure can be traced back to such basic quantities as time and length.
2019, 48(8): 805004.
doi: 10.3788/IRLA201948.0805004
Laser space debris removal has been the hot research topic around the world. Impulse coupling introduced by high-energy pulsed laser acted on debris is the bedrock and key to achieve debris removal. To study the impulse coupling effects, the aluminium alloy-ball-hanged single pendulum movement were recorded, pushed by ns-pulsed and ms-pulsed laser respectively, with high speed camera. By analyzing the impulse coupling generation theory, difference of the impulse coupling coefficient and the variety rate between the two mode lasers was summarized. Especially, a conclusion was drew that ms-pulsed laser could produce much more unit area impulse coupling than ns-pulsed laser, available for space debris removal. Moreover, compound ms-pulsed laser with ns-pulsed laser could increase the coupling efficiency and obtain higher impulse coupling. The study in this paper indicates a new idea for laser space debris removal, which have strong directive meaning.
2019, 48(8): 805005.
doi: 10.3788/IRLA201948.0805005
The influences of the focal length and the focal position on the damage probability and the damage morphology near the front and the rear surfaces of K9 glass were studied by using the millisecond laser damage test platform. Results show that, the melting process is dominant when the laser is focused at the front surface. While the stress induced damage is dominant when the focal plane is at the rear surface, and the damage size is obviously larger than that of the front surface. A two-dimensional thermal stress model was established to calculate the temperature field and the thermal stress field. Results show that the radial stress and the hoop stress are the main factors leading to the stress damage. The laser supported combustion wave induced by the laser irradiation at the front surface can enhance the energy coupling efficiency, which is one of the main reasons for the melting process at the front surface. Moreover, for the shorter focal length, the damage probability decreases rapidly with the increase of the distance between the focal plane and the sample surface. While for the longer focal length, the front and the rear surfaces can be damaged simultaneously when the laser is focused at the front surface, which can be attributed to the focal depth of lens.
2019, 48(8): 805006.
doi: 10.3788/IRLA201948.0805006
The gas isotope abundance can be detected by laser absorption spectroscopy method. As the absorption coefficient of the absorption line of the gas to be measured can be affected by the temperature of the gas to be measured, the temperature of gas will directly affect the accuracy and stability of the gas isotope detection system. A high-precision multi-pass gas cell temperature control system was designed and developed in this paper. In hardware, a high-accuracy PT1000 platinum resistance temperature acquisition circuit and a polyimide electrothermal film heating device were used to form a complete closed-loop temperature control structure. In software, Ziegier-Nichols' engineering setting method was used to complete the three coefficient settings of P, I, and D. Aiming at the problem that a large amount of overshoot caused by the complex structure and slow response of the controlled object, the integral separation PID control algorithm was used to make the temperature control fast and without overshoot. The system was used for temperature control experiments, experimental results show that the temperature control range was 18-42℃, the temperature control precision is 0.08℃, and the stabilization time is 15 s. This multi-pass gas cell temperature control system has the advantages of high precision and fast response and no overshoot, which provides reliable guarantee for laser gas isotope detection.
2019, 48(8): 805007.
doi: 10.3788/IRLA201948.0805007
Laser radar is an important technical way for high-accuracy detection, tracking and monitoring space-based target in the distance. Compared to the traditional imaging system, the range-resolved laser radar system has the advantages of simple structure and small atmospheric effect. At home and abroad the relative research institutes have done much work about this technology. The status and trend of two kinds of laser radar, which were called high resolution echoes detecting laser radar and reflective tomography imaging laser radar respectively, was introduced. The developments of the theoretical algorithms, modeling simulation, experimental verification and actual application were summarized and compared with each other. The technical characteristics of these two kinds of laser radar were analyzed, and the prospect of developments was expected.
2019, 48(8): 805008.
doi: 10.3788/IRLA201948.0805008
On the ground-to-air link wireless optical communication link, the cloud layer is one of the main factors affecting the scattering characteristics of laser transmission. The cloud layer is mainly composed of water droplets, ice water or other mixed core-shell ice crystals. In this paper, a 2, 8 and 39 spherical core-shell structure agglomerated ice crystal sub-models were established considering the crystal nucleus and intermediate mixed layer structure, and the influence of crystal nucleus size on the ice extinction, absorption and scattering coefficients of ideal agglomerated core-shell structure was analyzed. By comparing the refractive index of the uniform mixed layer, the scattering intensity of the three kinds of multi-spheroidal ice crystals with pure ice crystals, ideal core shell and core shell considering the intermediate mixed layer was compared with the scattering angle. The numerical results show that the ideal core-shell structure and the core-shell structure of the intermediate mixed layer have great influence on the scattering characteristics of ice crystal particles. Under the same conditions, there are significant differences in the extinction, absorption and scattering coefficients of ice crystal grains in three different agglomerated core-shell structures. The results of this study are more accurate in the study of the scattering characteristics of ice crystal particles, which lays a theoretical foundation for the transmission analysis of wireless optical signals in random distributed ice clouds.
2019, 48(8): 805009.
doi: 10.3788/IRLA201948.0805009
In order to make the fiber laser operate in two different states simultaneously, the erbium-doped fiber laser with both nonlinear polarization rotation (NPR) technique and carbon nanotube saturable absorber (CNT-SA) was fabricated in this experiment. The intra-cavity birefringence-induced comb filter based on NPR effect was employed to realize the dual-wavelength operation, and the Q-switched and Q-switched mode-locking pulses could be achieved by utilizing the NPR technique and the CNT-SA together. Therefore, the coexistence of Q-switched and Q-switched mode-locking pulses could be obtained in the fiber laser by finely adjusting the cavity parameters. After filtering each wavelength, it was found that the lasing line at 1531.23 nm corresponded to the Q-switched pulse with repetition rate of 45.62 kHz, while the lasing line at 1557.18 nm corresponded to the Q-switched mode locking pulse. The Q-switched envelope repetition rate and pulse repetition rate of the Q-switched mode locking pulses are 45.62 kHz and 18.18 MHz, respectively. The experimental results would enhance the operation flexibility of fiber laser, and further expand its application in related fields.
2019, 48(8): 805010.
doi: 10.3788/IRLA201948.0805010
To solve the problem that the power density of laser beam attenuated along the propagation direction, which was caused by large beam divergence angle (14-46) of semiconductor laser diode, a beam shaping optical system to improve power density was proposed. An X type planoconvex cylindrical lens and a Y type planoconvex cylindrical lens were selected to collimate the laser beam. Then, a pair of planoconvex spherical lenses were applied to improve the parallelism. Finally, a single planoconvex spherical lens focused the laser beam to a spot with high power density. The lenses were chosen and optimized through Light Tools simulation. A real beam shaping optical system was mounted and built. Test results show that 67% laser power is converged into a cycle with diameter of 1 mm, and the power density is over 30 W/cm2.
2019, 48(8): 805011.
doi: 10.3788/IRLA201948.0805011
Based on the Doppler broadening principle of absorption spectrum, the gas temperature measurement experiments of the optical cavity and the diffuser section were carried out on the D2/NF3 combustion-driven HBr chemical laser using the tunable diode laser absorption spectroscopy (TDLAS) technique. In order to effectively measure the TDLAS absorption spectrum, the R2 line of the HF molecular (2-0) vibrational band with a large absorption coefficient in the main gas flow was selected. In the experiment, a distributed feedback (DFB) diode laser with a center wavelength of 1 273 nm was used to build a HBr chemical laser gas temperature measurement system based on direct absorption TDLAS technique. By fitting the Voigt line shape to the absorption line of the HF molecule, the Doppler broadening width was obtained, and the gas temperatures of the optical cavity and the diffusing section were given. In the time domain frequency domain conversion, an F-P etalon with a free spectral range (FSR) of 1.5 GHz was used for frequency calibration. Experimental measurement results show that the temperature of the optical cavity is about 280 K and the temperature of the diffusing section is about 400 K. The ratio of collision broadening and Doppler broadening during the experiment is less than 0.1, indicating that the Doppler broadening is dominant, and the gas temperature of the optical cavity and the diffusing section can be conveniently monitored by the broadening of the HF absorption spectrum.
2019, 48(8): 803001.
doi: 10.3788/IRLA201948.0803001
The internal background radiation of the infrared spectrometer has a significant effect which will seriously reduce the resolution and signal-to-noise ratio of the optical system in the long-wave infrared band(8-12 m). In this paper, the TracePro optical analysis software was used to analyze the background radiation of the cross asymmetric Czerny-Turner (C-T) type planar waveguide infrared spectrometer, including the surface emissivity of the mechanical components and the influence of the surface temperature of the optical elements on the background radiation. The stray light coefficient was introduced as the evaluation indicator, and the actual measurement was carried out before and after the background radiation suppression of the spectrometer system in the high and low temperature box. The experimental results show that the stray light coefficient of the spectrometer system can reach less than 5% under the normal temperature (298 K) after the background radiation suppression measures are taken.
2019, 48(8): 803002.
doi: 10.3788/IRLA201948.0803002
Rotor airfoil design is the foundation of helicopter rotor design, and accurate calculation of aerodynamic characteristics is the key to the design of practical engineering airfoil. In the aerodynamic characteristics design process of airfoil, the infrared imaging non-contact measurement transition test technology was used to test the free transition position of OA309 rotor airfoil in a large ?3.2 m low-speed wind tunnel, and the influence of free transition position and free transition on aerodynamic force was calculated using the Michel model. By comparing the calculation and test results of OA309 rotor airfoil, it can be seen that the transition positions captured in the calculation are basically consistent with the test results. The joint application of infrared imaging non-contact measurement transition technology and Michel model improves the calculation accuracy of rotor airfoil resistance and lays a foundation for multi-objective airfoil design.
2019, 48(8): 803003.
doi: 10.3788/IRLA201948.0803003
The design of a double-band infrared detector stacked structure microlens array was introduced, which was modeled from the angle of actual light and optimized by using the principle of optical non-imaging theory, taking into account the requirement of microlens processing linewidth. According to the diffraction efficiency of the microlens, the calculation method of the factors affecting duty cycle was analyzed and explained in detail. The design method was novel and unique, which was based on the actual incident light. The method was verified to be feasible by coupling the processed microlens with the detector. Some inspiration is given to the designer of microlens arrays, which can be used in the design of microlens arrays for other multi-layer detectors.
Estimation of time series dynamic thermal radiation of terrain surface is the core section in IR scene simulation. Calculating land surface thermal radiance by heat-transfer Finite Difference Method(FDM) is a physically rigorous method. However, it is limited to the uncertainty of boundary conditions of the difference equation, therefore the method is not widely used in IR scene simulation. A simulation method of time series dynamic thermal radiation of terrain surface based on environmental parameters(illumination, temperature, humidity, etc) was proposed. In this method a closed-loop iterative process was designed according to the variable regulation of geological thermal environment. It could automatically correct the initial temperature profile and bottom boundary thermal radiance, which solved the problem of uncertainty of boundary conditions, and the algorithm accuracy and adaptability were promoted. The outfield experimental results indicate that the absolute error of temperature is less than 2 K, and the relative error of equivalent blackbody radiance is less than 3%. Compared with previous methods, the precision of this method has been improved obviously. The method provides the fundamental module for IR scene simulation. In addition, this method was used to simulate the temporal changes of the thermal radiation distribution on the surface in mountain area, showing its preliminary application effect in infrared scene simulation.
2019, 48(8): 813001.
doi: 10.3788/IRLA201948.0813001
The onboard airglow imaging interferometer can obtain the spatial distribution and temporal evolution information of the global atmospheric wind by using the limb-viewing mode, which makes it a research hotspot in the field of international satellite remote sensing. The O3 radiation source based Michelson onboard imaging interferometer can detect the atmospheric wind field in the stratosphere region through all-day. But there is more complex wind uncertainty because of working in the infrared band. Therefore, on the basis of limb-viewing forward simulation, the instrumental thermal background signal was studied, the measurement noise was analyzed, the atmospheric wind error caused by the measurement noise of atmospheric signal and the instrument thermal background noise was given, and error profile of line-of-sight wind was obtained by apparent quantities simulation and signal-to-noise ratio analysis. The uncertainty analysis shows that the O3 radiation source based Michelson imaging interferometer can detect atmospheric wind in the range of 15-45 km onboard through all-day, and the inversion accuracy is better than 1-2 m/s. This research provides important theoretical guidance for atmospheric wind measurement based on infrared radiation source. At the same time, it has great engineering significance and practical value for the development of infrared Michelson imaging interferometer.
2019, 48(8): 813002.
doi: 10.3788/IRLA201948.0813002
As a small and low-cost photosensor, the photodiode can be used as low-precision sun sensor alternatively for at least three photodiodes combined, to measure the full sun vector. To obtain the sun vector anywhere providing the continus 360 filed-of-view, it was difficult to choose the number and design the layout of the multiple photodiodes. This paper discretized the 360 field of view as equal surface areas firstly, and transformed the infinite sensor layout optimization problem into a finite combinatorial optimization(nondeterministic polynomial time). Then, the combinatorial optimization problem was solved by establishing the multi-objective optimization function considering the coverage and uniformity and combining the quantum genetic algorithm. The experiment gave the layout effect for the various number and the different field of view of photodiodes, and provided theoretical basis for the optimization of the layout of multiple photodiodes. The experimental results show that the 12-14 photodiodes selected can achieve layout with no coverage and uniform risk nearly.
2019, 48(8): 813003.
doi: 10.3788/IRLA201948.0813003
A method of detecting reconstructed wavefront was introduced based on Hartmann principle sub-aperture slope scanning to solve image quality evaluation for large aperture optical system at different elevation angles. The method does not need the same size caliber standard mirror. The information of wavefront can be obtained by scanning. The optical software and mathematical analysis software were used to carry out computer simulation through DDE link. The simulation optical system used Cassegrain system with primary mirror 720 mm and secondary mirror 100 mm to verify the feasibility of this method. Random error inducing and multiple scanning averaging were used to study the accuracy of reconstructed wavefront. The error included spot centroid error, sub-aperture positioning error and sub-aperture tilt error. The comparison between the simulation results and the results of optical software was given, and the physical models of errors and reconstructed wavefront accuracy during error injection were obtained.
2019, 48(8): 813004.
doi: 10.3788/IRLA201948.0813004
The co-phasing detection technology of segmented mirror is one of the key of the segmented process and maintaining the quality of mirror. The quantitative measurement piston error is not only the chief gauge of the adjustment of segmented mirror, but also the guarantee of the segmented telescope's imaging performance and the segmented telescope's angular resolution. In order to realize the detection of lager range and high-precision of piston errors of segmented mirror, the new two-wavelengths co-phasing detection algorithm was raised in this paper. The relation between the theoretical detection range and the values of two wavelengths was got and the relation between the max value of template interval and the values of two wavelengths was got based on circular diffraction and the two wavelengths detection theory. In two wavelengths algorithm, the gap error, eccentric error and camera noise between two half circular diffraction patterns could influence the detection range and accuracy of two wavelengths algorithm, how the errors of gap, eccentric and camera noise influence the detection range and accuracy by theory and simulation were analyzed and got. And the gap error less than 0.2r, the eccentric error less than 0.2r and the Signal to Noise Ratio (SNR) of camera noise more than 30 were got, the two wavelengths detection will not cause false detection. The study on error sprovided reference for the co-phasing experiment of segmented mirror in two wavelengths algorithm.
2019, 48(8): 813005.
doi: 10.3788/IRLA201948.0813005
In order to accurately detect the content of H2S trace gas in oil field, an on-line, real-time monitoring and analysis system for trace impurity gases, such as hydrogen sulfide(H2S) in oil field associated gas was designed, which can provide basis for the improvement and formulation of associated gas recovery and utilization technology in oil fields. The system was based on Tunable Laser Diode Spectroscopy(TDLAS) and Wavelength Modulation(WMS), using a tunable distributed feedback laser (DFB), lock-in amplifier, combined with a new Herriot chamber, InGaAs detector, to achieve the simultaneous on-line monitoring of H2S trace gases in oil field associated gas. To eliminate interference of background gases CH4 and other impurities in the gas, comparative experiments of RBF and BP neural network were carried out. A variety of H2S standard gas test systems with different concentrations were provided in the analog gas mixing station. The experimental results show that the interference of strong background gas, the detection limit for H2S is 1.2 ppm, in terms of interference, compared with the classical BP neural network, RBF neural network has a strong advantage, the prediction error is less than 10-10, the system had high detection accuracy and robustness, and strong application value in the field of oil gas detection.
2019, 48(8): 813006.
doi: 10.3788/IRLA201948.0813006
In order to effectively prevent and control the serious impact of the oil spill incident on the economy and the marine environment, and aiming at the detection of small area oil spills which were not easily detected in the early stage, an original minitype offshore oil spill monitoring system combined with the characteristics of Surface Plasmon Resonance(SPR) sensing technology, such as instantaneity, high sensitivity and low sample consumption was proposed. Specifically, the optimal parameters and relative fixed positions of the components in the sensing device were determined by simulating with MATLAB on the basis of an adoptive four-layer Kretschmann prism-coupled sensing structure in a non-scanning angle modulation mode and the range of refractive index of crude oil samples. The theoretical detection sensitivity was 6.09410-5 RIU(Unit:Refractive Index). Under the guidance of the simulation results, an experimental device was set up and the experimental analysis for sucrose solutions and crude oil samples was conducted. The experimental results show that the detection sensitivity of sucrose solution is the same as theoretical simulation sensitivity, which corresponded to 9.01710-5 RIU. The experimental device is effective, and the crude oil detection result conformed to the SPR response trend. The feasibility of the system solution is verified.
2019, 48(8): 814001.
doi: 10.3788/IRLA201948.0814001
Based on a 2 m lightweight SiC primary mirror, a new type of active adjusting lateral support mechanism was designed. Firstly, the structure forms and characteristics of the commonly used lateral support mechanism were analyzed; and then the active adjusting support mechanism composed of displacement actuator, flexible hinge structure and embedded lever system was designed. Finally, the finite element analysis of the support force and the displacement of the mechanism were carried out, and the experimental platform was built to test the stiffness and the energy-saving ability of the mechanism. The experimental results show that when the supporting force is 562.55 N, the force acting on the displacement actuator in the lever structure is 97.57 N, and the stiffness and strength requirements of the displacement actuator are greatly reduced; The stroke of the displacement actuator is 0.065 mm, which is 22 times that of the supporting rod, and greatly reduces the resolution requirement of the displacement actuator; The stiffness measured by the experiment is 1 225 N/mm, which meets the design requirements. It shows that the flexible lever support system has good engineering application ability.
2019, 48(8): 814002.
doi: 10.3788/IRLA201948.0814002
High numerical aperture(NA) projection objectives with freeform surfaces are demanded for extreme ultraviolet lithography(EUVL) with high resolution. The traditional aspherical EUVL lens design is difficult to meet the need of correcting aberrations under a large NA, which often causes obscuration and destroys the imaging contrast. A design method of a high NA EUVL objective with freeform surfaces and without obscurations was proposed. Lens-form parameters were used to determine the best position to insert freeform surface, which could effectively correct aberrations and increase NA of the system without affecting the imaging performance. A set of high NA EUVL projection objective(PO) with freeform surfaces was designed by this method. Compared with the initial aspherical objective, by adding four freeform surfaces, the objective NA was increased from 0.3 to 0.35 and wavefront error RMS was reduced from 1 nm to 0.6 nm, and there was no obscuration in the entire optical path. The design results indicate that the proposed method effectively improves the design efficiency of the freeform surfaces EUVL objective. In the case of no obscuration, the system not only increases the NA, but also reduces the wavefront error, which greatly improves the overall performance of the objective.
2019, 48(8): 814003.
doi: 10.3788/IRLA201948.0814003
In order to solve the problem that there exists astigmatism during the fabrication of carbon fiber reinforced polymer(CFRP) reflective mirror, a theoretical model was established to explain the relations, and relative experiments were made to verify the model. First, from classical laminate thermal effect theory, ply angle misalignment and temperature variation during manufacturing process were considered. The corresponding formulas were deduced to demonstrate that the surface of CFRP reflective mirror existed astigmatism under thermal effect because of ply angle misalignment. Two groups of samples with respective ply sequence[0 90 45 -45]2s and[(0 90 45 -45)s]2 were manufactured and their astigmatism were measured with a Zygo long-wave infrared interferometer(=10.6 m). Experimental results indicate that average astigmatism RMS of the front group is 0.034, and average astigmatism RMS of the latter group is 0.510. It verifies that one of the main reasons causing astigmatism of CFRP reflective mirror is ply angle misalignment, and the degree of astigmatism will decrease by increasing quasi-isotropy of bending stiffness.
The measurement accuracy of spectropolarimetric imaging is severely affected by ambient temperature, voltage, and incident angle based on acousto-optic tunable filter(AOTF) and liquid crystal variable retarder(LCVR). The spectropolarimetric imaging system is more complex. However, the superachromatic wave plate has the advantage that the retardation varies very little with temperature and wavelength. According to it, a new method of full polarization hyperspectral imaging based on superachromatic wave plate and acousto-optic tunable filter was proposed. The working principle of the method was analyzed in detail. According to the slight fluctuation of retardation and the fast axis of the superachromatic 1/4 wave plate, the effect of this fluctuation on the polarization measurement was analyzed in detail. For these errors, a correction strategy was proposed. The specific principle of all the Stokes parameters images and the modified measurement verification experiment were performed for 633 nm waveband. The experiment result shows that the measurement error of the polarization degree of the system is less than 1% in the band of 450-950 nm, and the measurement deviation of the polarization orientation is less than 1.8. The experimental results show that the new technology principle is correct and the correcting strategy is feasible. This research can provide new theory and implementation scheme for high-precision, high-resolution, full-polarization imaging technology under complex conditions.
2019, 48(8): 814005.
doi: 10.3788/IRLA201948.0814005
A dual concave gratings imaging spectrometer with excellent imaging ability in near infrared waveband has been presented. The main aberrations as astigmatism and coma have been analyzed existing in this tandem gratings system. By calculating, the best imaging conditions, the optimal arrangements of gratings and adding cylindrical lens, were obtained. The advanced Wadsworth mounting could eliminate coma and astigmatism in the wide waveband and realize the high imaging quality. It could also realize the high spectral resolution with low ruling density gratings. A designed example presented excellent optical performances, the spectral sampling was 0.92 nm per pixel and modulation transfer function in all fields of views were higher than 0.45 in the Nyquist frequency at 17 lp/mm over the waveband from 780 nm to 1 100 nm. The aberrations of the system were corrected and the tolerances were loose. The results analysis proves the principle of design.
2019, 48(8): 814006.
doi: 10.3788/IRLA201948.0814006
Based on the finite element analysis of hot pressing process, a new non-isothermal molding method was proposed for improving hot pressing quality of small-diameter aspherical chalcogenide glass enses and avoiding pressing defects. A heating gap was set between the upper mold core and heating plate, and the upper and lower heating plate were heated by using different temperatures to realize non-isothermal heating of the glass preform. Firstly, based on the high temperature viscoelastic constitutive and heat transfer model of chalcogenide glass, the finite element model of glass lens on hot pressing process was established by using the relevant parameters. Then, according to above FEA model, the influence of non-isothermal temperature difference on the temperature, maximum residual stress distribution and contour offset was analyzed, and the optimal temperature difference was also determined. Finally, the experiments of non-isothermal hot pressing were carried out, and the results of simulation and experiment were also compared to verify the validity of the simulation model and results. Both simulation and experimental results show that the optimal non-isothermal temperature difference is 10℃. Under this condition, the internal temperature difference of the glass preform obtained by simulation is only 2.6℃, the maximum residual stress of the pressed lens can be reduced to 3.375 MPa, and the maximum contour offsets of the formed lenses ASP1 and ASP2 are 0.562 m and 0.615 m, respectively. The actual PV values of the pressed lenses ASP1 and ASP2 are 118.2 nm and 194.0 nm, Ra values are 17.0 nm and 37.8 nm, and maximum values of contour offset are 0.583 m and 0.644 m, respectively, which meet the accuracy requirements. The simulation results show good agreement with experimental results. By using the reasonable temperature difference, the new method of non-isothermal hot pressing can effectively reduce the internal temperature difference of the glass preform and maximum residual stress of the pressed lens, avoid the defects such as adhesion and bubbles, and improve the lens precision.
2019, 48(8): 818001.
doi: 10.3788/IRLA201948.0818001
For the shortcomings of backlash shaft, friction and clearances in coarse tracking system of satellite optical communication, a scheme of using a flexible shaft to support the terminal was presented. The principle of flexible shaft in satellite optical communication was presented. Then the characteristics of flexibility in working direction and stress in thinnest incision were analyzed. According to the key point deflection, the rotation error angle expression was derived and its influence on capture probability was analyzed. Based on the research of flexible shaft characteristics, the flexible hinge was optimized by genetic algorithm. The results are as follows:the flexibility in working direction is 0.768 rad/Nm, the stress of thinnest incision is 1.768 e+8 Pa and the rotary error angle is 343 rad. Finally, the finite element method was utilized to verify the design consequences, the relative error of the three indexes was less than 3.5%, which proved that the design was reliable. This study can provide some reference for flexible shaft design in satellite optical communication terminal.
2019, 48(8): 818002.
doi: 10.3788/IRLA201948.0818002
For the deep space optical communication system based on pulse position modulation (PPM) and photon detection array, a PPM slot synchronization method that directly predicted frequency offset and initial phase offset was proposed. In this method, the arrival time of each photons was measured firstly, and in this way, it can get the offset of every photon's arrival time relative to PPM slot position and draw out the photon distribution diagram of different offsets of the half-frame forward and backward. Then, the frequency offset was evaluated by using the offset of the photon distribution between the half-frame forward and backward(i.e. the cumulative value of frequency offset in the half frame data). After correcting the data of the arrival time of photons according to the frequency estimation value, the initial phase offset can be estimated by calculating the offset between the frequency corrected photon distribution and that of the ideal synchronization. The simulation result shows, when the counting clock frequency in the receiver is equal or greater than 4 times that of the PPM slot, this method can realize PPM slot synchronization.
2019, 48(8): 818003.
doi: 10.3788/IRLA201948.0818003
A novel hydrogen sulfide gas sensor based on titanium dioxide membrane-coated coreless fiber was presented. The sensor was fabricated by two different length no-core fibers (NCFs) which were spliced both ends with single-mode fibers (SMFs) and then constructed an interferometer with the structure of SMF-NCF-SMF. Different modes can be excited in the coreless fiber when the light traveled from SMF to NCF, an interferometer based on multimode interference was formed. The titanium dioxide film was coated on the outside surface of NCF which could adsorb hydrogen sulfide gas, then the relation between gas concentration and spectral shift was obtained, and thus the detection of hydrogen sulfide gas was performed. The experimental results show that a high sensitivity of 18.93 pm/ppm and a good linear relationship are achieved in the range of 0 to 60 ppm, and the interference spectra appear red shift with the increasing concentration of hydrogen sulfide. The rising time and falling time of the sensor are about 80 s and 110 s. The sensor has the advantages of simple structure, high sensitivity and easy manufacture, and can be used in the safety monitoring field of tracing hydrogen sulfide gas.
Wavelength division multiplexers/demultiplexers and variable optical attenuators(VOAS) are key devices used in optical communication systems. In order to get their monolithic integrated chip with simple fabrication process and fast time response, and considering the possibility of it to integrate with other different optical devices, a 16-channel 200 GHz arrayed waveguide grating(AWG) multiplexer/demultiplexer was monolithically integrated with electro-absorption variable optical attenuators on a silicon-on-insulator (SOI) platform. The on-chip loss was less than 7 dB and the crosstalk was less than -22 dB. The power consumption of the electro-absorption VOA is 572.4 mW(106 mA, 5.4 V) at 20 dB attenuation. Besides, the device provides fast optical power attenuation, and in a 0-5 V square voltage, the rising/falling time of the VOA is 50.5 ns and 48 ns, respectively.
2019, 48(8): 809001.
doi: 10.3788/IRLA201948.0809001
The periodic controlled supersonic mixing layer was simulated using large eddy simulation(LES) method. Features of vortices in this flow field was revealed clearly, and the ray tracing method was employed to calculate wave front distortion of a beam passing through the controlled supersonic mixing layer. A correction method for wave front distortion was proposed based on the analysis of dynamical characteristic of vortices in the controlled flow field, and it was tested by a supersonic mixing layer periodic controlled with different frequencies. The results show that the presented correction method can reduce the amplitude of wave front distortion to 50 percent or more, and shape of the controlled vortex in mixing layer is the key factor dominating the correction effect.
2019, 48(8): 809002.
doi: 10.3788/IRLA201948.0809002
According to the hygroscopic characteristics and different forms of sea salt particles in different relative humidity conditions, the models of sea salt particles under three conditions were established:low humidity(RH=0%), medium humidity(RH=50%), high humidity(RH=95%). Influence of relative humidity and particle morphology on the scattering characteristic of sea salt was studied by discrete dipole approximation (DDA) method. Influence of relative humidity and particle morphology on the scattering and radiation characteristic of sea salt was studied by DDA method, Mie scattering theory and Discrete Ordinate Method Radiative Transfer (DISORT) method. The results show that relative humidity and particle morphology have great influence on the scattering characteristics of sea salt particles. Under medium relative humidity, the scattering and radiative transfer characteristics of the sea salt aerosol are more sensitive to particle shape. When the optical thickness is equal to 0.1, the relative difference of BRDF of spherical-cubic sea salt model can be more than 15%, the effect of relative humidity and particle morphology must be taken into account when studying the scattering and radiation transfer properties of sea salt aerosol. With the increase of optical thickness, the relative difference of BRDF decreases, when the optical thickness is greater than 1, the relative difference of BRDF is less than 5%, the equivalent sphere method can be used to simulate calculation within a certain precision range. These findings have important implications to the theory and application of atmospheric aerosol scattering and radiation transfer.
2019, 48(8): 817001.
doi: 10.3788/IRLA201948.0817001
Using transfer matrix and equivalent principle, the Tamm state on the surface of the symmetric photonic crystal was investigated in the new point of energy levels. The result shows that when the symmetric system is an infinite periodic structures for photonic crystal, there is impedance mismatch between incident medium and photonic crystal, thus the optical Tamm state on the surface doesn't exist. When the photonic crystals is truncated to finite period structure, it supports the appearance of the optical Tamm state on the surface, and the doubly degenerated energy level of TE and TM polarization appears in the energy band. In optical off-axis transmission, the optical Tamm state form the passband edge non-degenerated energy which is restricted on on the surface of photonic crystal. When the truncation parameter is matched with the high refractive index of outmost layer, it is easy to form a strong optical Tamm state. But when it is matched with the lower refractive index of outmost layer, it is difficult to realize the surface state. When the surface state of photonic crystal is excited by the ATR total reflection technique, the coupled resonance absorption can be observed. The properties of optical Tamm state on the surface of photonic crystal can provide guidance for research and design of optical waveguide or surface wave sensor.
2019, 48(8): 817002.
doi: 10.3788/IRLA201948.0817002
An experimental platform capable of continuously controlling the polarization angle of the 1 and 2 lights was constructed, and a series of all-optical poling of the silicon germanium glass sample was realized. The poling effectiveness and poled direction, which were determined by the magnitude and direction of internal electric field, correlations of which with the poling polarization state and intensity were studied. Basically the experimental results were consistent with the classic model and its derivation, but quantitative inconsistencies were found as well, including local tendency, angle size, etc, which further proved the complexity of the all-optical poling process. It was experimentally found that the effectiveness of the poling process was the best when 1 and 2 lights were polarized parallel, and the poling process was also very sensitive to the poling intensity.
2019, 48(8): 825001.
doi: 10.3788/IRLA201948.0825001
The Fresnel Incoherent Correlation Holography (FINCH) technology is an on-axis system, which needs phase-shifting technology to eliminate the conjugate image and the zero-order image. Based on the theory of FINCH imaging system, the formula of n-step phase-shifting method was derived, an experimental light path of incoherent light reflection digital holographic recording was constructed. The effect of n-step phase-shifting on the FINCH imaging system through simulation and experiment was studied. The results show that the quality of the reconstructed image cannot significantly improved by increasing phase-shifting steps; two-step phase-shifting can enhance recording speed, whose zero-order image can be suppressed by eliminating original image and wavelet decomposition. A comparison was made between the reconstructed images obtained separately by averaging hologram and hologram photographing once of three-step phase-shifting, and the result shows that the quality of the reconstructed image is getting better and better with the increase of the shots. Not only the background noise is greatly weakened, but also the intensity of the pixels becomes stronger and stronger, which provides a new way and new experimental basis to promote the development of the FINCH system.
2019, 48(8): 825002.
doi: 10.3788/IRLA201948.0825002
In order to reconstruct the 3D surface from gradient fields quickly and accurately, a new fast and accurate least squares integration algorithm was proposed. Compact finite difference scheme was introduced into optimization equation for better accuracy. Then the objective function was represented as a Sylvester function. With Hessenberg-Schur algorithm, the space and time complexity were reduced from O(N2) and O(N3) to O(N) and O(N3/2), respectively. The experiment result showed that when the 4th-order compact scheme is used, the accuracy of the new method is improved by one order higher than Higher-order Finite-difference-based Least-squares Integration(HFLI) and Global Least-Squares(GLS). While with 6th-order compact scheme, the accuracy is improved by one order higher than Spline-based Least-squares Integration(SLI). The robustness of the proposed method is weaker than that of HFLI and SLI, but better than GLS. The reconstruction speed was obviously faster than that of HFLI and SLI.
2019, 48(8): 825003.
doi: 10.3788/IRLA201948.0825003
By introducing the popular equidistant projection theory, a non-similar stereo vision was explored, and the three-dimensional (3D) location model and depth precision model were established. The correctness of proposed models was verified through carring out the 3D location experiment with a 11590 infrared stereo vision system. From the experimental results, the targets in different depths and large-airspace scene were located successfully. The depth error increases smoothly with increasing target depth, and it reached 1.32 m in the depth of 30 m. The error variation of 3D location model matched well with the results of depth precision model, and the whole error was obviously less than that of similar stereo vision model. The advantages of the proposed model is that the 3D coordinates of space target can be obtained directly without correcting the non-similar distorted images, and it contributes to enriching and improving the theory of stereo vision, and will help to spread the application of non-similar imaging theory in the fields of large-airspace situation awareness, target detection and so on.
2019, 48(8): 825004.
doi: 10.3788/IRLA201948.0825004
Although X-ray grating-based phase contrast imaging enables to obtain high image contrast of weekly absorbing substance, the imaging time is too long, due to high resolution detector. Furthermore, the imaging energy is usually about 30 keV, because of the limitation of grating manufacturing technique. In this paper, the requirement of grating manufacturing technique was relaxed sharply, thus the imaging energy was increased, based on the principle of projection imaging. In addition, fast phase contrast computed tomography (CT) imaging was realized on account of cycle-step-cycle mode, using medical CT tube source and medical detector. Experiments were carried out with tube voltage 80 kV, tube current 180 mA and 80 s exposure time to substance on the imaging system at National Synchrotron Radiation Laboratory. Last, how to improve the density resolution of the imaging system was discussed.
2019, 48(8): 819001.
doi: 10.3788/IRLA201948.0819001
Homocysteine is a sulfur-containing amino acid, which is an important intermediate product produced during the metabolism of methionine and cysteine. High concentration of homocysteine in human blood or urine will significantly increase the risk of cardiovascular disease, alzheimer's disease, bone fracture and other diseases. Based on terahertz time domain spectroscopy (THz-TDS), a method of concentration, enrichment and drying was proposed for the detection of homocysteine in liquid state. The THz absorption spectra of homocysteine at different concentrations were measured effectively. Compared with the results of Raman spectroscopy, the accuracy of terahertz detection was three times higher than that of Raman spectroscopy. The results were of great significance for the accurate and rapid diagnosis of homocysteine-related diseases in clinical medicine.
2019, 48(8): 826001.
doi: 10.3788/IRLA201948.0826001
Tilting mode imaging is a method to improve the spatial resolution of images from the sampling mode, and the imaging angle of tilting mode is closely related to the image quality. This paper was focused on the analysis of the relationship between the angle of the tilting mode and the effective resolution, aliasing, blur, and noise of the tilting mode image, and determined the best imaging angle of the tilting mode superresolution imaging. Firstly, the aliasing index, field width and effective resolution of imaging angle 1-90 were simulated and analyzed, and the resolution, aliasing, blur, and noise of the image were evaluated quantitatively by the cross-restoration method. Then, the modulation transfer function (MTF) was used to restore the tilting mode image by combining the method of the reciprocal cell, and the optimum imaging angle was finally determined to be 72. Finally, the results of the analysis were verified by practical experiments, which show that the resolution of the image is increased by about 1.41 times when the angle of tilting mode imaging is 72.
2019, 48(8): 826002.
doi: 10.3788/IRLA201948.0826002
As an essential component of the Kinect sensor, depth image always contains inevitable and unpredictable shadow noises which limit their usability in many 3D vision applications. Therefore, a shadow detection method based on fractional differential was proposed for depth image. Based on the study of Tiansi template defined by fractional differential, a non-linear stretching operator was designed and implemented. This operator can enhance the boundaries information of shadow regions significantly and accomplish the shadow detection effectively at 0.6 order. Compared with other traditional methods, the proposed method can reach up to 0.971 for F-measure, while the other methods were all less than 0.7. The experimental results indicate that the new method can detect shadow noises effectively.
