2017 Vol. 46, No. 1
2017, 46(1): 102001.
doi: 10.3788/IRLA201746.0102001
The thermal infrared spectrum is a very useful band for earth-observation hyperspectral remote sensing. Due to the limitation of technology, the hyperspectral imaging system of thermal infrared spectrum in domestic space photoelectric system is not very common, but it has developed quickly and made great progressunder the support of national related department in recent years. Based on the airborne thermal infrared hyperspectral im ager' developing during the Twelfth Five-Year Plan period, the signal flow model of the system was established in this paper. The background radiation of the system was modelled and simulated, the dark current of the infrared focal plane component was analyzed and measured, and on this basis the factors affecting the detection sensitivity of the system were analyzed, the design rules of the cryogenic optical 100 K for the cryogenic temperature was presented. After the completion of the airborne thermal infrared hyperspectral imager, the comparison between the actual detection sensitivity and the simulation results was carried out. The results show that the system has good compliance and has accumulated important data for the further development of thermal infrared hyperspectral imaging technology.
2017, 46(1): 102002.
doi: 10.3788/IRLA201746.0102002
The performances and advancements of the two optical payloads, produced by Beijing Institute of Space Mechanics and Electricity, onboard GF-5 satellite were introduced in the paper. The atmosphere environment high-resolution infrared Fourier transform spectrometer had high-resolution, high sun tracking accuracy and high spectral calibration accuracy. Visual and infrared multispectral sensor had high spectral resolution, wide spectral range and high radiometric calibration accuracy. Compared with other similar optical payloads, they were advanced both here and abroad which greatly improved the ability of high-precision observation of China. Key parameters, system composition, key technology, advancements and test results were introdued. At the end of this paper, development direction and enlightenment of follow-up spectrometer were pointed out.
2017, 46(1): 102003.
doi: 10.3788/IRLA201746.0102003
The state and trend of digital cooled infrared focal plane array detector assembly in USA,Israel and France were presented. According to the work mode of digital Read Out Integrated Circuit(ROIC),recent research results on digital cooled infrared focal plane array detector assembly in USA,Israel and France were introduced. By the concept of SWaP, some kinds of small pixel, HOT performance, digital output, million pixels mid-wave infrared focal plane array assembly were developed in Israel and France. At last the research result on digital cooled infrared focal plane array detector assembly in Kunming Institute of Physics was briefly introduced. The key technology of column-level ADC ROIC had been broken through, and the 640512(15, 20, 25 m pitch) column-level ADC digital cooled infrared focal plane array detector assemblies were developed. The performance measures of the digital detector in Kunming institute of physics were comparative with the digital detectors abroad.
2017, 46(1): 138001.
doi: 10.3788/IRLA201746.0138001
Compared with a given laboratory calibration, systematic shifts on the center wavelength and the Full Width at Half Maximum (FWHM) of each band of a hyperspectral sensor, will emerge as the imagery environment changes. The center wavelength shift and the FWHM variation have influence on the inversion precision of the emissivity and temperature, especially near the atmospheric absorption bands. A technical process of spectral calibration for thermal infrared hyperspectral data was proposed, which was verified through a simulation experiment with the water vapor absorption band at 11.73 m selected as the reference band. The experiment shows when the spectral resolution is 50 nm, the center wavelength shift ranges from -50 nm to 50 nm and the FWHM variation ranges from -25 nm to 25 nm, atmospheric water vapor content has the most influence on the error of the estimated wavelength shift and the FWHM variation. Meanwhile, the error distribution were also fitted using different surface functions, and the error distribution models used to estimate the errors were obtained. When the atmospheric water vapor content was high enough, the estimation error of the spectral center wavelength shift was able to reach within 1 nm. Finally, the proposed approach was applied to spectral calibration of the airborne thermal infrared hyperspectral data obtained by a push-broom hyperspectral thermal-infrared imager. The results show that the center wavelength shift of the thermal infrared hyperspectral imager is 28.4 nm and the FWHM variation of the imager is -18.5 nm.
2017, 46(1): 1136002.
doi: 10.3788/IRLA201746.0138002
In order to acquire the polarization characteristics of targets and backgrounds, a hyper-spectral polarization imaging system based on a non-collinear, acousto-optic tunable filter(AOTF) and a linear polarizer was designed in this paper. The paper began with an analysis of the equivalent relationship of the AOTF to describe the principle of polarization detection of this system. Appropriate parameters of hardware components were assigned reasonably later. Then, the hyper-spectral polarization experiment about the aluminium plate, which was coated with light green, dark green and khaki pigments, within meadow was conducted by using the imaging system proposed above. Moreover, the hyper-spectral intensity and polarization contrast characteristics of the target and natural background in the scene were deduced by processing the experiment data. The results indicate that the polarization characteristics of pigments are different from that of natural background. The detection means can be chosen reasonably to realize the effective and quick detection and recognition for targets under the mixed background at those wavelengths or wavebands with obvious polarization contrast characteristics.
2017, 46(1): 136003.
doi: 10.3788/IRLA201746.0138003
The spectrum and polarization which were often used to identify the target were important radiation characteristics of the target. The detection technology that fused spectral and polarization information and owned the advantages of both signific antly improved the ability to effectively identify the target in a complex background. It played an important role in the field of environment monitoring, military reconnaissance and atmosphere analysis. Around the problem of detecting the target spectra and polarization information, a fusing imaging method to detect hyperspectral and Stokes polarization information was researched. The methed detected polarization information with the principle of micro-polarization array modulation on the basis of the Sagnac Fourier transform imaging spectrometer. Then a model of the imaging system was designed while the spectrum recovery method and extraction mode of the polarization information were discussed. A prototype was developed and good experimental results of an actual scene objects were obtained. The research shows that besides high throughput and high spectral resolution, the advantages that four polarized fringe patterns are obtained simultaneously also achieved in this method.
2017, 46(1): 136004.
doi: 10.3788/IRLA201746.0138004
Disease stress is one of the main factors causing a reduction in wheat production and threatening food security. How to distinguish similar diseases accurately and diagnose disease severity scientifically is becoming a hot topic worldwide. The objective of this study is to discriminate powdery mildew and yellow rust of winter wheat, two common fungal diseases in the Chinese wheat-growing region. In the study, a high-resolution hyperspectral imaging system(ImSpector V10E) was utilized to capture spectral and imagery information of wheat leaves infected by two diseases. The dimensionality reduction of hyperspectral images was done by using principal component analysis(PCA), and with the density slice method, the recognition accuracy for the disease area at leaf level can be 97%. On this basis, the spectral difference of two diseases was analyzed, and 12 disease-sensitive bands were selected in the light of the second principal component(PC-2) images. The bands for powdery mildew were at 519, 643, 696, 764, 795 and 813 nm, while those for yellow rust were at 494, 630, 637, 698, 755 and 805 nm. Furthermore, a support vector machine(SVM) discriminant model was established based on selected sensitive wavebands, and its accuracy reached 92%. The results revealed that the hyperspectra combined with feature extraction of high-resolution imagery could effectively achieve discrimination of powdery mildew and yellow rust at leaf level, which will provide a theoretical foundation for developing a portable recognition device.
In the case of infrared thermography of semitransparent materials, the heat stimulation mechanism differs from that of opaque materials, and the heat absorption of a specimen depends on its optical properties and the radiation spectrum of a light source used. Based on the spectrum characteristics of semitransparent materials, a body heating mechanism and modelling were proposed. To obtain the spectrum absorptivity of the materials, the reflectivity and transmittance of the glass fiber reinforced plastics with different thicknesses were measured in a certain wavelength range. The spectrum characteristics of heating lamps were described by a color temperature model, the effect of the color temperature of a flash on the flaw detection was analyzed by using finite element method, and the relationships between the detectable information parameters(the maximum temperature difference and maximum contrast) and the flash color temperature were presented. The results show that the maximum temperature difference and maximum contrast are a nonlinear function of the color temperature, and they decrease first and then increase when the color temperature increases, so a low or high color temperature is more favorable for the inspection of semitransparent composite materials. The conclusions provide a theoretical reference for the flash infrared thermography of semitransparent composite materials.
2017, 46(1): 104002.
doi: 10.3788/IRLA201746.0104002
Limited to the high cost, low quantity and few species for the measurement of infrared spectrum of pollutant gas cloud, it is extremely important to simulate infrared spectrum with which to improve spectral identification algorithms. Traditionally, empirical probabilistic model and empirical or semi-empirical parameters were used to simulate the real-time explosion of pollutant gas cloud and furthermore simulate the infrared spectrum. A physical-based model was established, which compensated for the low accuracy of the empirical or semi-empirical models, to finely simulated the explosion of pollutant gas cloud. The mechanism of the physical-based explosion model and the way of infrared spectrum simulation based on the physical-based explosion model were studied. Finally, a comparison between the simulated infrared spectrum based on physical model, simulated infrared spectrum based on probabilistic model and the practical one was made and it got a more accurate result that improved by 14 percent at most as far as spectral residual is concerned and figured out the application scope of two models. The physical-based explosion model and the way of infrared spectrum simulation established are significant to finely simulate infrared spectrum of pollutant gas cloud and study high-quality spectral identification algorithms.
2017, 46(1): 104003.
doi: 10.3788/IRLA201746.0104003
The infrared (IR) characteristic of a turbofan engine exhaust system with lobed mixer was studied experimentally and numerically, and the results were compared with a relevant annular mixer exhaust system. The results show that, the lobed mixer can enhance the mixture of core flow and fan flow and reduce the plume temperature, making the plume IR radiation attenuated; compared with the annular mixer exhaust system, the IR radiation intensity of the lobed mixer exhaust system reduces at least 9% in the direction right behind the nozzle exit, and reduces more than 39% in the direction vertical to the axis of the nozzle exit; the axisymmetric nozzle with low emissivity and high reflectivity has negative effect on IR suppression because of its strong reflection to the radiation of the high temperature components within angles range from 40 to 70, thus, it is appropriate to increase emissivity and reduce the reflectivity of nozzle wall in order to achieve better IR suppression.
2017, 46(1): 104004.
doi: 10.3788/IRLA201746.0104004
The development of the large format polarimetric LWIR quantum well infrared FPA. The 20 m pitch, 640512 array was divided into 22 unit cells. Each pixel in the unit cell was etched a 1D lamellar grating on it, with four different orientations of 0, 90, 45 and 135, to get the polarimetric information of the incidence irradiation. Based on the QWIP FPA key technologies such as quantum well material epitaxy and chip preparation, the single-chip integration with LWIR and the polarization detection function was realized on the QWIP FPA. The 640512 polarimetric LWIR QWIP FPA assembly with noise equivalent temperature difference (NETD) better than 30 mK was obtained with the integration the FPA chip with the Dewar and the sterling cooler.
2017, 46(1): 104005.
doi: 10.3788/IRLA201746.0104005
In order to improve the high combustion temperatures of the traditional PTFE/Mg-based infrared decoy, a discrete array infrared decoy material with a low burning temperature was prepared based on an additive of red phosphorus/copper oxide(P/CuO). Thin foils were made by process and formulation designs. It may be achieved that the foils were ignited at low temperature and burn stably at low temperature. The samples were tested for their relative parameters such as burning rate and the obtained parameters were analyzed. The results show that, after red phosphorus/copper oxide thermite is added therein, the ignition temperature of the foils of 0.5 g thin foils with a dimension of 150 mm15 mm0.2 mm is decreased from 520℃ to 390℃, its burning temperature is decreased from 1 500℃ to 850℃ and they can burn stably. After the thermite added, their action duration increases from 1.2 s to 1.6 s. However the infrared radiation intensity somewhat decreases. By analyzing its performances such as ignition temperature, burning stability and radiation intensity, the performance of PTFE/Mg-based infrared decoy may be improved by adding P/CuO thermite. It is suitable for the design requirement for discrete array infrared decoy ignited by dispersing.
2017, 46(1): 104006.
doi: 10.3788/IRLA201746.0104006
In order to improve the precision of infrared systems in sand and dust storms, by using the multiple scattering theory of electromagnetic wave propagation in discrete random medium, the backscattering enhancement mechanism was analyzed for infrared wave propagating in sand and dust storms. The formula about the relation of the particle number per unit volume and atmosphere visibility was presented in sand and dust storms. From visible light to far infrared wave, the backscattering enhancement caused by multiple scattering in sand and dust storms was researched for different visibilities. The results show that the backscattering enhancement for different wavelength waves is different. The lower visibility in sand and dust storms, the stronger backscattering enhancement is. For different types of sand and dust storms, the particle size distribution is different. At a given visibility, the particle number per unit volume is larger, the backscattering enhancement are stronger. At a given particle number density, the number of the larger size particles is larger, the backscattering enhancement is stronger. Especially, the enhancement for the longer wavelength wave is more obvious. That is, the lower visibility, the larger number per unit volume, and the more the larger size particles, the backscattering and enhancement is stronger in sand and dust storms, and the effect on infrared systems is severer.
2017, 46(1): 104007.
doi: 10.3788/IRLA201746.0104007
Sonic IR imaging is one of the emerging NDT methods. The detectability of the cracks is based on its heating effect, which correlates with several excitation conditions, for example the excitation position. For the unclear effect of excitation position on crack heating, the finite element model and the experimental system was utilized to study the characteristic of crack heating under different excitation positions, and made an effective verification by using the equivalent force, equivalent velocity and equivalent heat flux. The research shows that when the excitation position is under the crack face, the crack heating will be restrained as a result of vibration synchronization for the two crack surfaces. However, as the excitation position moves both sides, the crack heating will rise first and fall later with a fluctuation, and bigger engagement force can lead it more severe. The study results clearly demonstrate the effect principle of excitation position on crack heating, which may further lay the theory basis to the optimization of test conditions in the sonic IR imaging.
2017, 46(1): 106001.
doi: 10.3788/IRLA201746.0106001
The power dependence of phase shift spectrum is very important for the optimization design of vector Brillouin optical time domain analysis (VBOTDA) system. The phase shift spectrum of stimulated Brillouin scattering (SBS) gain was analyzed by mathematical modeling; the phase shift spectrum of SBS gain in 400 m long standard single-mode fiber was measured in a pump wave power range of 5-90 mW and a Stokes wave power range of 5 W-9 mW by a heterodyne pump-Stokes system; the mechanism of Stokes wave power dependence of SBS gain phase shift was analyzed. The results indicated that the phase shift range of SBS gain had a good linear relationship with pump wave power for a fixed Stokes wave power; the pump power sensitivity of phase shift range of SBS gain decreased from 1.448 ()/mW to 1.156 ()/mW with the increase of Stokes power from 5 W to 8 mW due to pump depletion. According to the theoretical and experimental results, the optimization design of VBOTDA system based on SBS gain was discussed, which provides a basis for the development of SBS gain based VBOTDA system in the field of long distance and high precision sensing.
2017, 46(1): 106002.
doi: 10.3788/IRLA201746.0106002
In order to choose appropriate frequency stabilization method in the atom gravimeter system under construction, Doppler-free dichroic atomic vapor laser lock(Doppler-free DAVLL) and saturated absorption spectroscopy(SAS) method were implemented on Rubidium atomic vapor. Basic principle and experimental details of both frequency stabilization methods were introduced. With restructuring of optical path and applying of self-made low noise photoelectric detector as well as digital lock module, excellent error signal was obtained. For each method, two sets of locking system were built and kept locked during 3 000 s' data acquisition. A frequency fluctuation of 629 kHz when the laser is free running and of 16.2 kHz 31.4 kHz after locked by SAS and Doppler-free DAVLL were calculated respectively, corresponding to a frequency stability of 1.6410-9 in the condition of free running and 4.2110-11 8.1810-11 after locked for averaging time of 10 s. The strength and weakness of both methods were elaborated with the demand of system miniaturization. After compared with SAS, Doppler-free DAVLL isconsidered to be a promising choice for miniaturization and modularization in atom interferometry gravimeter.
2017, 46(1): 106003.
doi: 10.3788/IRLA201746.0106003
An 0.2 THz brodband unbalanced doubler multiplier was designed and realized based on four anodes in anti-series GaAs planar Schottky diodes. The Schottky diode was flip-chiped on the 75 m thick quartz. The circuit output power and efficiency was measured under the condition of small and large input power. The measured efficiency was bigger than 3% over the band of 210 GHz to 224 GHz with the input power between 10 mW to 15 mW under the condition of forward bias voltage. The peak efficiency is 7.8% at the frequency of 212 GHz. The measured efficiency was bigger than 3.6% over the band of 210 GHz to 224 GHz with the input power between 48 mW to 88 mW under the condition of self-biased. The peak efficiency is 5.7% at the frequency of 214 GHz. The biggest output power is 5.7 mW and 7.5 mW at the fixed frequency of 212 GHz when the input power is 132 mW under the condition of self-biased and reverse bias voltage of -0.8 V separately.
2017, 46(1): 106004.
doi: 10.3788/IRLA201746.0106004
The experimental phenomena and laws of the supercontinuum laser irradiating the visible light CMOS image sensor were studied. Some typical interference phenomenon was observed with the incident laser power increasing, like pixels saturation, partial saturation, local supersaturation and full screen saturation of the output image with CMOS sensor. A comparison of the similarities and differences between the 1 060 nm mode-locked fiber laser and supercontinuum on affecting the quality of CMOS imagers was described from three aspects such as effective jamming area, image correlation and image variance. It is found that the response characteristic of CMOS image sensor, the spectrum characteristic of the laser and the dispersion of the imaging optical system lead to the difference of interference effects.
Laser shock processing is a novel surface treatment technology to increase the fatigue strength of materials. Based on the characteristic of K24 nickelbased alloy simulation blades, the laser shock processing without coating (LSPwC) was carried out. Whilst the change discipline of micro-hardness and residual stress on the cross-section of K24 nickel-based alloy after different parameters of LSPwC were examined by micro-hardness tester and residual stress tester. In addition, the high cycle fatigue tests were conducted to verify the reinforcement effect. The experimental results show that particular compressive residual stress on the surface was induced by LSPwC, the largest residual stress value was -428, -595, -675 MPa with 110, 150, 160 m depth affected layer under 1, 3, 5 impacts respectively. The surface micro-hardness was increased by 29.2% with 60 m depth under one impact. The fatigue strength of simulation blades was improved from 282 MPa to 327 MPa, improved by about 16% after unequal stress impact.
2017, 46(1): 106006.
doi: 10.3788/IRLA201746.0106006
To meet reliability of rail steel flaw inspection and signal acquisition, a nondestructive testing (NDT) system based on laser ultrasonic technique(LUT) was established. The system was mainly composed of high energy pulse laser, electromagnetic ultrasonic transducer (EMAT), embedded data acquisition system and P60 rail specimens with artificial cracks. Based on analysis of Rayleigh wave detection principle, this paper focuses on impedance matching method of EMAT probe coil. Besides, working flow path and signal processing of embedded signal acquisition system were introduced. Moreover, system based LUT was used to locate the rail steel surface crack with depth no less than 0.5 mm. Finally, relationship between EMAT probe lift-off distance and signal amplitude was given.
2017, 46(1): 106007.
doi: 10.3788/IRLA201746.0106007
A pixel readout circuit was presented and designed for Geiger-mode avalanche photodiode (GM-APD) array applying to laser 3D imaging. Based on the principle of time-of-flight (TOF), the pixel readout circuit consisted of two main parts:active quenching circuit (AQC) and time-to-digital converter (TDC). The adopted TDC was a two-segment coarse-fine architecture to manage a trade-off between clock frequency and temporal resolution. Based on interpolation technique, the LFSR used for coarse counting and the delay-line type TDC used for fine counting achieved a wide dynamic range up to 18-bit together. Meanwhile the clock frequency used in those two parts were reduced to 250 MHz and 50 MHz, which are 1/20 and 1/10 of the conventional design frequency, respectively. Thus, the difficulties of design and applications were reduced significantly. The circuit was designed with SMIC 0.18 m process. The post-simulation results reveal a high precise temporal resolution of 200 ps and a responding range resolution of 3 cm, satisfying the ranging requirements of 3 km laser 3D imaging. Furthermore, the pixel circuit layout area is less than 5095 m2, and the total power consumption is 0.89 mW, having the advantages of small area and low power consumption.
2017, 46(1): 117001.
doi: 10.3788/IRLA201746.0117001
A femtosecond laser tracker achieves target tracking through detection of miss distance via a PSD. The location of reflected laser spot on PSD when tracking laser exactly points to center of the retro-reflector, named initial position of miss distance, was the benchmark of miss distance calculation. So it was important to precisely calibrate initial position of miss distance in order to achieve high accurate measurement. A calibration method for initial position of PSD based on the retro-reflector feature analysis was presented in this paper. First, the error factors that may impact miss distance calibration were analyzed, and the mathematic model was established. Then, according to the laser tracker's structure design and the geometric errors of axes, the calibration method for the initial position was simulated. Results show that the calibration error was limited below 17.8 m, which means when the retro-reflector was placed at a distance of 10 m from the tracker, the laser tracker's pointing error was limited below 1.1. These results can be helpful in further error compensation model. At last the proposed calibration method of initial position of miss distance was applied to the self-developed femtosecond laser tracker, and provides the benchmark for further dynamic measurement.
2017, 46(1): 117002.
doi: 10.3788/IRLA201746.0117002
Based on APOSOS (asia-pacific ground-based optical space observation system) project, the first 15 cm ground-based space debris photo-electric telescope manufactured by China was firstly installed abroad and obtained much observational data. The paper calculated and analyzed the observational accuracy of observational data using two accuracy estimation criterion-internal fitting accuracy and external fitting accuracy estimation, and the result of internal fitting accuracy is on 5 arc seconds; then, obtained precise orbit of satellite Lageos1, Lageos2 and Ajisai derived from precise orbit determination which made use of satellite laser ranging normal point data from International Laser Ranging Service(ILRS), and the analysis of external fitting accuracy was based on the precise orbit, the result of external fitting accuracy was around 6 arc seconds. All the results indicate that APOSOS 15 cm opto-electric telescope has relatively high observational accuracy and reaches the design specification, which can satisfy the demands for science and engineering application.
2017, 46(1): 117003.
doi: 10.3788/IRLA201746.0117003
Spatially modulated imaging polarimeter (SMIP) system is able to modulate four Stokes parameters S0-S3 in a single interferogram by using Savart plate. Through sliding reconstruction method, the entire polarization information can be demodulated from the interference fringes. In this system, the alignment errors of the half wave plate (HWP) and the analyzer has a non-ignorable impact on the measurement accuracy of the Stokes parameters. A theoretical model including these two alignment errors were presented in this paper. Based on this model and parameters of the prototype SMIP, the Stokes parameters measurement accuracy of unpolarized light, 0/90linear polarized light, 45/135linear polarized light and left/right circularly polarized light was analyzed. According to these four basic polarized lights, a method for solving Stokes parameters measurement error of incident light with any state of polarization (SOP) and degree of polarization (DOP) was given. In order to alleviate the influence of HWP and analyzer alignment errors, an optimization using condition number of measurement matrix as an objective function was given. It is shown that when the thickness of Savart plate is 23 mm, which is corresponding to the minimum condition 2.06, measurement errors induced by HWP and analyzer alignment errors can be effectively diminished.
2017, 46(1): 117004.
doi: 10.3788/IRLA201746.0117004
The on-board calibration unit is an important part of the space-borne remote sensor and used to achieve the on-board radiometric calibration and other functions. An on-board calibration unit installed on a time-modulated fourier transform spectrometer was introduced. Used the sun as the light source to illuminate the calibration diffuser, the on-board calibration unit carries out the on-board radiometric calibration of the spectrometer in the full aperture, the full optical path and the full field of view. The calibration diffuser was in the front of the optical path of the spectrometer to reflect the sunlight and the standard radiance was obtained by used the known exoatmospheric solar irradiance and the BRDF(bidirectional reflectance distribution function) of the calibration diffuser. The BRDF of the calibration diffuser needs to be measured accurately in the lab. With the whole spectrometer, using the sun simulator and the standard diffuser, the in-lab system-level BRDF test method of the calibration diffuser was introduced. While using the system-level BRDF of the calibration diffuser, the accuracy of the on-board absolute radiometric calibration was analyzed and can satisfy the requirement of 5%.
2017, 46(1): 117005.
doi: 10.3788/IRLA201746.0117005
An adaptive cubature Kalman filter algorithm based on singular value decomposition (SVD-ACKF) was proposed for orbit determination by optoelectronic theodolite when unknown or inaccurate noise statistics lead to low precision and divergence of filter. First, Sage-Husa maximum a posteriori and its improved form were used to estimate noise statistics online, and SVD instead of Cholesky decomposition in was used order to improve the stability of numerical calculation. Then, the mathematical model of orbit determination was expound, compared with the Euler method, improved Euler method was used to disperse the orbital dynamics equations with J2 perturbation. Finally, the simulation results show that improved Eular method can achieve a higher discrete precision, and SVD-ACKF algorithm can improve the accuracy and stability.
2017, 46(1): 117006.
doi: 10.3788/IRLA201746.0117006
The influence of background stray light can not be ignored in the high precision PST test. In order to improve the precision of the PST test, a high performance light trap system which can effectively suppress the background stray light was developed. The quantitative mathematical relationship between the main design parameters and the test error of PST was given based on the theory of the PST test and the theory of optical radiation transfer. The design idea of the light trap was proposed, which was fully controllable in the scattering path and greatly increased the scattering times to the imaging field of view. Through the simulation comparison experiment of some light trap models, the superiority of the design ideas and the model was verified. The result show that, when a light trap with diameter of 20 m is used for the PST test to an optical system with diameter of 2 m and size of 2.8 m3.5 m11 m, the testing error can be as small as 1.4910-10, it is reduced by about 4 orders of magnitude compared with the test system without light trap under the same experimental space, and reduced by about 2 orders of magnitude compared with the existing light trap schemes under the same experimental space. The light trap can be used to the high precision PST for the large space telescope.
2017, 46(1): 118001.
doi: 10.3788/IRLA201746.0118001
In order to obtain the optimal design of the 620 mm ground mirror assembly, the parametric model of mirror and its support system was established and the thickness of mirror, the support position and design parameters of flexible support structure were optimized based on the parametric model. Firstly, the kinematic restraint design principle of the 620 mm ground primary mirror support system was stated. Then, flexibility matrix and thermal equivalent force of flexible support was deduced from the theoretical perspective, a parametric model of mirror assembly was established to facilitate the optimization iteration, and the parametric model was compared with solid element detailed FEM model in multiple static loadcases in term of the RMS and the first six eigenvalues of the support system. The calculation error was less than 10% of the results to verify the validity of the parameters of the model. Finally, based on the theory of radial basis function approximation model, the multi-objective optimization of the parametric model was possessed in Isight environment. After obtaining the Pareto front of multi-objective optimization, the two objectives of optimal design system was weighed. The proposed optimum design method has better applicability in engineering and can provide reference for the optimization design of the same type of mirror assembly.
2017, 46(1): 120001.
doi: 10.3788/IRLA201746.0120001
A new type of distributed sensor system based on Rayleigh scattering Brillouin Optical Time Domain Analysis (RBOTDA) was proposed. This system was realized in one end access fiber, which can improve the shortcomings of two end access in conventional BOTDA. Parallel structure with two EOM were used to generate pulsed light with continuous base wave. Probe light was provided by the Rayleigh scattering of the base continuous light. This avoids the interference of a variety of Stimulated Brillouin Scattering (SBS) effect and brings the higher signal to noise ratio and longer sensing distance. The dual sideband probe scheme turns the system to be highly robust against pump pulse depletion and non-local effect. The SBS function mechanism of the system was analyzed and the feasibility of the proposed method was demonstrated experimentally. The results show that the Brillouin gain spectra fit Lorenz Curve perfectly and non-local effect is suppressed effectively. The Brillouin frequency shift is 10.867 GHz and the Brillouin linewidth is about 40.21 MHz with 50 ns pulse width on the 2.4 km optical fiber at the temperature of 25℃.
2017, 46(1): 120002.
doi: 10.3788/IRLA201746.0120002
A CMOS image sensor with coupling capacitor based AC-coupled CTIA and digital CDS was proposed. By adding a coupling capacitor to the conventional CTIA circuit, the dark current of the photodiode was reduced via controlling the bias voltage of the photodiode; Meanwhile, an off-chip digital CDS was adopted to reduce the reset noise of the pixel and the FPN by realizing the subtraction algorithm between the reset signal and pixel signal after A/D conversion off-chip. This CMOS image sensor was implemented in the 0.35 m standard CMOS technology. The pixel array was 256256, and the pixel size was 16 m16 m. The experimental results show that the dark current can be minimized by reducing the bias of the photodiode nearby zero. The temporal noise and FPN are obviously reduced after adopting the off-chip digital CDS.
2017, 46(1): 120003.
doi: 10.3788/IRLA201746.0120003
The output power of terahertz resource is a critical parameter to limit the long range application of terahertz technology. To accomplish the high efficiency terahertz multiplier, two high-efficiency 170 GHz balanced doublers were built using the two planar Schottky diodes with diverse electrical specification. The employed equal circuit diode model, based on the developed high-frequency characteristic modeling, considered the IV characteristics, the limits drift velocity saturation of carries, DC series resistance and skin effect simultaneously. From the comparison and analysis of the simulated data, the impact of diode electrical parameter on the doubler performance was discussed. Test data show that the two 170 GHz balanced doublers show 11% and 24% highest efficiency respectively, 15 mW and 25 mW output power correspondingly across a 155-178 GHz band. As shown in measured result, the employed Schottky diode modeling and balance structure is suitable option to design high efficiency terahertz multiplier.
2017, 46(1): 120004.
doi: 10.3788/IRLA201746.0120004
Aimimg at the problem of the defects on the surface of components in infrared optical systems, the scattering characteristics of optical components surface under different levels of defects were analyzed quantitatively based on Mie scattering theory. The variation of the bidirectional scattering distribution function(BSDF) on the surface of the optical component was discussed, and then a scattering model of optical components under different levels of defects was established. On this basis, a Gemini telescope was taken as an example, and the self-generated thermal radiation flux and its distribution of the system on the image plane was simulated quantitatively by using the ASAP optical analysis software for the case of the primary mirror under different levels of defects. Furthermore, according to the definition of the effective emissivity, the quantitative evaluation of the stray radiation of the system was carried out. The results indicate that the optical component under different levels of defects not only alter the stray radiation flux and its radiation distribution of the system on the image plane, but also change its effective emissivity, the effective emissivity of the system is 2.19%, 2.34%, 2.46%, 2.59%, 2.72% and 3.08% respectively when primary mirror defect levels under six cases such as 0, I-10, I-20, I-30, II and III. Thus, the stray radiation performance of the system decreases with the increasing of the level of the defects. Consequently, the levels of defects on the surface of the optical component should be strictly controlled in the practical applications.
2017, 46(1): 120005.
The crosstalk between the pixel units is the key parameter for the imaging quality of CMOS array detector. The mathematical analysis model of the electrical crosstalk was established in order to explore the influence of different light sources on the electrical crosstalk of CMOS. Furthermore, the characteristics of electrical crosstalk under the illumination of monochromatic light and broadband sources were also numerically simulated. The results show that, the electrical crosstalk increases with the increase of the wavelength of monochromatic light, as well as the spectrum bandwidth and the center wavelength of broadband sources. Moreover, the impact of broadband sources on the electrical crosstalk is greater than monochromatic light when their center wavelengths are the same. The electrical crosstalk for the monochromatic light with the radiation power of 600 W and the wavelength of 1 064 nm is about 50.611 mV, and the electrical crosstalk for broadband source with the spectrum bandwidth of 400 nm is about 50.914 mV in the same radiation power and wavelength. Consequently, the electrical crosstalk of broadband source increased by about 0.303 mV compared to the monochromatic light.
2017, 46(1): 122001.
doi: 10.3788/IRLA201746.0122001
Due to the special vehicle's narrow space, lighting layout is limited and the difficulty is increased. Based on the theoretical analysis of illumination and received optical power, both the direct and the first reflection models of illumination and received optical power were developed. In illumination demand constraint conditions, an optimal scheme of rectangular lighting layout for narrow vehicle space was proposed based on optical power evenly distribution principle. Simulation experiments proved that the optimizing rectangular layout scheme is valid as follows:the average received optical power was obtained about -0.5 dBm and the illumination range was 333.74-466.44 lx in 2 m2 m1.5 m space size, uniform illumination rate was 79.5%, which meet the international illumination standards and the actual data communication in a special vehicle.
Wavelength of Fiber Bragg Grating(FBG) changes with ambient temperature and pressure. If change of wavelength is detected, then ambient temperature and pressure can be calculated. In this paper, a highly stable Fiber Bragg Grating(FBG) wavelength demodulation system based on F-P etalon with tempe-rature control module was proposed. The theory of the FBG wavelength demodulation system was discussed and the reason of high stability was analyzed. In this system, a Fabry Perot(F-P) etalon with temperature control module was introduced for real-time wavelength calibration. Wavelengths of F-P etalon can be inquired by the specification. Wavelength of FBG can be calculated by linear interpolation. The temperature control module can ensure temperature of the etalon changes within 0.01℃, so that wavelengths of the etalon can be regarded as constant values. In the end the stability of the system was experimented by measuring wavelengths of FBG which was in a water-bath. The system was also compared with the MOI corporation optical sensing interrogator sm125 on the stability. Experimental results demonstrate that the system can achieve a long-term stability of 0.15 pm in 20 h, while sm125 was 3 pm.
2017, 46(1): 122003.
doi: 10.3788/IRLA201746.0122003
An optical logic gate is the core of optical information processing in all future optical network elements, allowing for high-speed optical packet switching, all-optical address identification, data coding, parity, and signal regeneration. A micro-ring resonator was adopted to design a new electro-optical logic gate using three asymmetric micro-rings. The analysis of coupled transfer matrix equations showed that the change in the load voltage signal resulted in a change in the refractive index. Micro-rings using the logic-switching characteristic of light intensity can achieve an optical logic gate. The computer simulation verified that the working wavelength was 1 600 nm. The high-level load voltage 50.7 V was defined as logic 1, whereas the low-level load voltage was defined as logic 0. A voltage of 0 V was obtained by six light intensity change logic operations. The response time of the entire system is 1.8 ps theoretically, and the computation speed can reach approximately 200 Gbit/s. The bistable logic analysis revealed that the micro-ring is equal to the corresponding control micro-ring at maximum resonant wavelength. No deformation occurred in the resonant wavelength and the sum of the offset. Therefore, modulation can be achieved through micro-ring resonant wavelength control.
2017, 46(1): 125001.
doi: 10.3788/IRLA201746.0125001
Terahertz imaging has wide applications such as biomedical, security check and so on. With the development of modern information technology, portable terahertz imaging devices are demanding. An imaging system based on CMOS terahertz detector was proposed. The system includes a CMOS terahertz detector, an off-chip ADC, an FPGA, a 2-D step motor, four parabolic mirrors and a terahertz source. The terahertz detector integrates an on-chip patch antenna and a source-feeding NMOS transistor as detection element, which was implemented in 180 nm standard CMOS process. The output signal of the detector was a dc voltage signal which depends on the detected terahertz radiation power proportionally. An external ADC converts the output signal of the detector into digital signal which was captured by an FPGA and then transferred to a computer to realize imaging. In order to reduce the system volume, all above elements were mounted on a set of printed circuit boards(PCBs). Clear raster-scanning transmission images can be obtained by the imaging system with continuous terahertz illumination. The image of metals in an envelope was obtained by the imaging system at 860 GHz.
2017, 46(1): 125002.
doi: 10.3788/IRLA201746.0125002
A cross-shaped multi-hole terahertz waveguide directional coupler was designed. This compact structure has a large frequency band, stable coupling value and high directivity. The terahertz waveguide directional coupler structure was simulated and optimized with professional electromagnetic simulation software high-frequency structure simulator(HFSS) based on multi-hole coupling principle. The results show that the coupling degree of the terahertz waveguide directional coupler is 7.50.8 dB, the isolation is 30 dB, that is, the directivity is higher than 20 dB, and the return loss of each port is less than -20 dB in the range of 325 GHz to 475 GHz. Through high temperature and pressure simulation of the waveguide directional coupler, negative photoresist SU-8 is considered as a suitable material for structure fabrication. The directional coupler is fabricated by micro-electro-mechanical system(MEMS) technology, at the same time, sacrifice layer technology is applied to form the waveguide cavity structure. The uniformly-spaced coupling holes on the common wall of straight waveguide and coupling waveguide can be achieved by photolithography, therefore a wider bandwidth and a good coupling flatness of the directional coupler were obtained. This method improves the accuracy of the size and position of the coupling holes, reduces the reflection loss, and thus provides a new idea for the processing of terahertz waveguide structures.
