2019 Vol. 48, No. 6
column
- Special issue-Computational optical imaging technology and application
- Infrared technology and application
- Laser technology and application
- Laser radar technology
- Optical communication and optical sensing
- Optical design and simulation
- Photoelectric device and microsystem
- Photoelectric measurement
- Information acquisition and identification
2019, 48(6): 603001.
doi: 10.3788/IRLA201948.0603001
Spectral measurement technology has been widely used in non-destructive test, geological prospecting, agriculture and many other fields, and the related technology and devices have achieved great progress in recent years. So spectral measurement technology has developed rapidly in recent years. Based on practical application requirements, the development history of spectral measurement technology was introduced comprehensively and the main spectral measurements including traditional, computational and multiplexing were summarized. The theory and implementation of computational tomography, compressive sensing, Fourier transform, Hadamard transform were introduced in detail and corresponding advantages and disadvantages were pointed out. At last, the problems that need to be solved urgently in spectral measurement technology were analyzed and summarized, and the future development of spectral measurement methods was prospected.
2019, 48(6): 603002.
doi: 10.3788/IRLA201948.0603002
Imaging at non-visible wavebands is one of the challenges in optical imaging. As a novel computational imaging technique, single-pixel imaging based on spatial light modulation is able to obtain spatial information of object via a non-spatially-resolving detector. Thus, single-pixel imaging technique is a potential approach to the challenge of imaging at non-visible wavebands. In recent years, Fourier single-pixel imaging is demonstrated to be able to offer high-quality and high-efficiency image acquisition. Since proposed in 2015, Fourier single-pixel imaging technique has been extended a series of techniques ranging from two-dimensional imaging to three-dimensional imaging, from mono-chromatic imaging to true-color imaging, from static imaging to dynamic imaging, from single-modality imaging to multi-modality imaging, and from photography to microscopy. The principle and related applications of Fourier single-pixel imaging were reviewed. Some challenging problems and prospects of the technique were also discussed.
2019, 48(6): 603003.
doi: 10.3788/IRLA201948.0603003
Unlike a digital cameras using a photodetector array to capture images, single-pixel imaging reconstructs images by sampling a scene with a series of masks and associating the knowledge of these masks with the corresponding intensity measured with a single-pixel detector. Though not performing as well as digital cameras in conventional visible imaging, single-pixel imaging has been demonstrated to be advantageous in unconventional applications, such as multi-wavelength imaging, terahertz imaging, X-ray imaging, and three-dimensional imaging. The developments and working principles of single-pixel imaging were reviewed, a mathematical interpretation was given, and the key elements were analyzed. The research works of three-dimensional single-pixel imaging and their potential applications were further reviewed and discussed.
2019, 48(6): 603004.
doi: 10.3788/IRLA201948.0603004
Single-pixel imaging aims to record the target scene information via a single element detector. For its high sensitivity and wide range of spectrum response, single-pixel imaging is attracting a lot of attentions. Based on the coded acquisition and decoded reconstruction of high dimensional optical signal, single-pixel imaging can meet the demanding requirements in some challenging cases. The research background of single-pixel imaging was firstly introduced, and its imaging principle and reconstruction algorithms were briefly described. Then, from the perspective of coding and decoding of optical information, the current researches and advanced technologies were systematically reviewed. Besides, the existing problems in single-pixel imaging, and its future extensions and potential applications were discussed.
2019, 48(6): 603005.
doi: 10.3788/IRLA201948.0603005
Light scattering is a common phenomenon in nature. How to realize high resolution imaging through turbid media is an important problem to be solved urgently in the field of optical imaging. In early studies, multiple light scattering has been regarded as a barrier in imaging through haze, cloud, biological tissue and other complex media. However, recent studies have shown that scattering is not the basic limitation of imaging:photons still contain a lot of information after multiple scattering. In order to provide insight into how new computational optical techniques can address the issues of multiple light scattering, the recent progress of scattering imaging method based on wavefront shaping, speckle correlation and deep learning was summarized. The latest research shows that, wavefront shaping technology can achieve fast optical focusing inside dynamic scattering medium with high resolution; speckle correlation method can realize non-invasive imaging by single-shot speckle pattern; deep learning is able to recover the object hidden behind the white polystyrene plate with optical thickness of 13.4.
2019, 48(6): 603006.
doi: 10.3788/IRLA201948.0603006
The underwater imaging could be severely degraded by the particles in the water due to the backscatter veiling and signal attenuation. The polarimetric image recovery method is one of the most effective way to enhance the quality of underwater imaging. Based on the polarization property, the polarimetric method can separate the target intensity from the backscattering, estimate the intensity of backscattering and medium transmittance, and then realize clear imaging. In recent years, polarimetric imaging technique has been applied to many fields more efficiently and extensively, such as underwater image restoration and target recognition, etc. As an intersection of optical imaging technique and image processing technique, the polarimetric recovery method for image restoration has aroused a wide concern and gained fruitful research results. In this paper, we mainly introduced the basic principle of underwater image restoration technique based on polarimetric imaging and the methods of polarization information processing. We also reviewed the recent advances of representative improved approaches in underwater image restoration technique based on polarimetric imaging.
2019, 48(6): 603007.
doi: 10.3788/IRLA201948.0603007
Quantitative Phase Microscopy (QPM), which combines phase imaging and optical microscopy, has been acting as a fast, non-destructive, and high-resolution methodology to measure the 3D morphology of reflective samples, as well as the inner structure or the refractive index of transparent samples. Similar to other diffraction-limited imaging systems, QPM suffers from the contradiction between spatial resolution and field of view (FOV). Therefore, how to achieve high spatial resolution in a large FOV has attracted a lot of attentions in the field of optical microscopy. In recent years, people utilized off-axis illumination, speckle illumination, structural illumination, and sub-pixel technology to synthesize a larger numerical aperture (SNA), and consequently enhanced the resolution of QPM. The resolution enhancement technologies of QPM were reviewed in this paper. The advantages and limitations of different methods were analyzed.
2019, 48(6): 603008.
doi: 10.3788/IRLA201948.0603008
As an interference imaging method, digital holography (DH) can accurately record the phase information of objects, and has the advantages of fast, non-destructive and three-dimensional imaging. It is widely used in the field of biological imaging and materials science. Like other optical imaging methods, DH also faces the problem that the resolution and the field of view(FOV) are mutually constrained, resulting in limited spatial bandwidth product(SBP). To solve this problem, researchers proposed methods such as computational illumination, computational modulation, and computational probing to extend SBP by sacrificing other degrees of freedom(such as time and polarization) of the imaging system. This paper firstly reviews the theoretical analysis of information capacity of an optical system. On this basis, we systematically summarize the high-resolution and large-FOV digital holographic imaging technology in recent years, introduce the principle and implementation of oblique illumination, structured illumination, random modulation illumination, multi-position synthetic aperture and pixel super-resolution method for resolution enhancement, and angle multiplexing method for FOV extension, and make a comparative study. The potential ways to improve resolution and expand FOV are also prospected.
2019, 48(6): 603009.
doi: 10.3788/IRLA201948.0603009
Wide field-of-view (FOV) and high-resolution is one of the goals of optical microscopy. However, limited by the optical design in traditional optical microscopes, the space bandwidth product (SBP) is generally in the order of megapixels, and thus, high-resolution and wide FOV cannot be achieved at the same time. On the other hand, complex optical systems have also made microscopes increasingly expensive, cumbersome, complex and difficult to maintain, greatly limiting their promotion and application. Lensfree on-chip microscopy is a new computational imaging technology:without the imaging lens to focus, the sample is directly attached to the imaging sensor to record the diffraction patterns and the object information can be achieved with the corresponding reconstructed method. Due to its wide FOV, high-resolution, label-free detection, low-cost, perfect portability and three-dimensional (3D) imaging, the lensfree on-chip microscope is expected to expand the boundaries of traditional microscopic imaging technology and becomes a new type of fast, point-of-care testing (POCT) tool. In this paper, a review was given to introduce the basic principles, experimental systems, reconstruction methods and applications of lens-free imaging. Finally, the changeling problems as well as future research directions were also discussed.
The technique and application developments of the deformation and displacement measurements based on the digital holography(DH, including the digital speckle interferometry) was reviewed. Because of advantages of high accuracy, non-invasive, full-field and dynamic measurement, DH became one of the most important technique for deformation and displacement measurement. In recent years, the development of DH technique was mainly in the following aspects. Firstly, deformation measurement was developed from one-dimensional measurement to multi-dimensional measurements. Especially, simultaneous deformation measurements in three dimensions was the focus of this domain. Secondly, since curved objects were common in practice. However, in-plane and out-of-plane deformation were the main concern for curved object, which needed the 3D shape information of the curved objects. Thus, for curved objects, simultaneous 3D shape and deformation measurements were studied. Thirdly, to further extend the field of view and the depth of the measurement, techniques based on long wavelength and long distance were explored. Furthermore, measurements based on DH technique progressed from engineering domain towards biomedical domain to facilitate deeper researches in biomedical domain. Meanwhile, various application improvements of deformation measurement based on DH technique were covered in this review.
2019, 48(6): 603011.
doi: 10.3788/IRLA201948.0603011
Coherent diffraction imaging(CDI) is a lensless computational imaging technique, which reconstructs the amplitude and phase of an object directly from diffraction intensity measurement by solving the phase problem using iterative algorithms. CDI can provide images at the diffraction limit resolution that is only determined by the wavelength of radiation source and the effective numerical aperture of the recorded data. Since CDI has no need for high quality imaging optics, it is suitable for short wavelength radiations such as deep ultraviolet, X-rays, and electron beam, for which imaging optics of high performance are difficult to make. Meanwhile, the past 20 years have seen rapid progress of new type of light sources (cold emission electron guns, 3rd and 4th generation synchrotron X-rays sources, and free-electron lasers), array detectors with single particle sensitivity and broad dynamic range. All those progresses greatly promote the development of CDI. At present, CDI has shown some unique advantages over traditional methods in some study of materials science and biology, and gradually becomes a mainstream technology for certain applications. This paper briefly summarized the history of CDI with a focus on ptychography and coherent modulation imaging.
2019, 48(6): 603012.
doi: 10.3788/IRLA201948.0603012
Fourier ptychographic microscopy(FPM) is a promising label-free computational imaging technique with high resolution, wide field-of-view(FOV) and quantitative phase recovery. Due to its flexible setup, promising high-contrast performance without mechanical scanning and interferometric measurements, FPM has wide applications in the digital pathology, observation and dynamic imaging of label-free cells in vitro. In this review, the principle, research status and the latest advances were introduced in several aspects of FPM such as the system calibration methods, high-throughput imaging and high-speed imaging. The current problems and future trends were also presented.
2019, 48(6): 603013.
doi: 10.3788/IRLA201948.0603013
Three-dimensional(3D) imaging has attracted more and more interest because of its wide spread applications, especially in information and life science. These techniques can be broadly divided into two types:ray-based and wavefront-based 3D imaging. Issues such as imaging quality and system complexity of these techniques limit the applications significantly, and therefore many investigations are focused on 3D imaging from depth measurements. An overview of 3D imaging from depth measurements was presented, providing a summary of the connection between the ray-based and wavefront-based 3D imaging techniques, and showed the research direction of the depth measurement based 3D imaging research.
2019, 48(6): 603014.
doi: 10.3788/IRLA201948.0603014
Differential phase contrast(DPC) is a labeled-free and non-interferometric phase imaging method based on partial coherent illumination control, which provides a fast, effective and high-resolution visualization method for unstained transparent samples. It converts invisible sample phase information into detected intensity signals through multiple asymmetric illumination modulation or asymmetric aperture modulation, thereby providing possibilities for qualitative phase contrast imaging and even quantitative phase reconstruction samples. In recent years, with the gradual deepening of research in this field, the phase transfer function(PTF) of DPC imaging was definitely deduced, and DPC has gradually advanced towards qualitative observation to quantitative research. On the other hand, owning to the full-aperture illumination control and high-efficiency phase deconvolution algorithm,DPC quantitative phase imaging can achieve the incoherent diffraction limit resolution, and obtain a low-noise, high-precision quantitative phase reconstruction result. Furthermore, drawing on the theory of three-dimensional(3D) optical transfer function, DPC has recently been extended to 3D diffraction tomography to achieve quantitative imaging of the 3D refractive index for thick samples. This paper reviews the historical development, research status and latest developments from the basic principles of DPC imaging methods, imaging systems and algorithm optimization, and discusses some key problems existing in this method and possible future research directions.
2019, 48(6): 603015.
doi: 10.3788/IRLA201948.0603015
As an important means of image processing, the edge enhancement techniques play an important role in amplitude-contrast and phase-contrast objects imaging. The vortex filtering techniques based on radial Hilbert transform have attracted much attention because it can achieve isotropic edge enhancement. However, the classical vortex filtering causes background noise and contrast reduction due to diffraction caused by central singularities and sharp edges. In recent years, many research groups have proposed new types of vortex filters for vortex filtering side lobe suppression. In addition, the isotropic and anisotropic edge enhancement techniques based on vortex filtering have also developed rapidly. In this paper, several methods for suppressing vortex side lobes were summarized in recent years, including Laguerre Gaussian amplitude modulation, Bessel-like amplitude modulation, and Airy amplitude modulation. What's more, from two aspects:scalar vortex filtering and vector vortex filtering, the isotropic and anisotropic edge enhancement methods and progress were reviewed.
2019, 48(6): 603016.
doi: 10.3788/IRLA201948.0603016
In this paper, an optical scanning imaging system based on a single cylindrical lens rotation modulation was proposed. The complete wavefront information of the sample could be iteratively reconstructed by intensity patterns of the rotational modulation of the cylindrical lens. In addition, as a key parameter of the system, rotation angles of cylindrical lens were obtained by numerical calculation method based on the Radon transform, which got rid of the requirements for high-precision rotating equipment. Both the simulation and experimental results have verified the feasibility of the method. Compared with the axial multi-distance scanning imaging system, all optical components in the imaging system remain fixed in the axial position, so the data acquisition speed is accelerated and the axial sampling rate is kept fixed. It not only simplifies the algorithm design in the light field reconstruction, but also greatly speeds up the convergence speed.
2019, 48(6): 603017.
doi: 10.3788/IRLA201948.0603017
The compressive sensing reconstruction of magnified in-line hologram was experimentally researched in this paper. It aimed at the tomographic reconstruction of magnified multilayer samples. Firstly, the compressive sensing reconstruction of in-line hologram was introduced in theory, and the realization procedure was shown, including frequency domain down-sampling mode, the flow of two-step iterative algorithms, etc. Secondly, hologram recording system in case of point-source magnification and microscope objective magnification was established, the experimental work was carried out, which took multilayer samples as an example, and tomographic reconstruction of recorded in-line hologram based on compressive sensing. In the same time, it processed back-propagation reconstruction based on traditional convolution algorithm. The experimental results show that compressive sensing tomographic reconstruction technology can realize the tomographic reconstruction of holograms obtained in two magnification modes, and have better reconstruction results than the traditional convolutional inverse diffraction reconstruction. And it shows the ability and superiority of compressive-sensing tomographic reconstruction.
2019, 48(6): 603018.
doi: 10.3788/IRLA201948.0603018
Aiming at the non-interference phase retrieval technique based on Transport of Intensity Equation (TIE), which requires that the light source be monochromatic, and the mechanical error caused by moving CCD or object in the intensity acquisition process, a dispersion phase retrieval technique suitable for the lens model was proposed. The method was based on the phase transformation characteristic of the lens imaging system, and combined the dispersion with the TIE so that different wavelengths of light were imaged at the same position after passing through the lens system, thereby obtaining the focus and defocus intensity images without mechanical movement. Then, phase information of an object was calculated from the TIE by combining the relationship between the defocus amount and the wavelength. In this simulation, the correlation coefficient between the phase recovered by this method and the original phase is 0.970 7, and the RMSE is 0.061 8. At the same time, the phase of the lens array was restored by real experiment. The error between the experimental result and the real parameter is 1.74%, which proves the correctness and effectiveness of the proposed method.
2019, 48(6): 603019.
doi: 10.3788/IRLA201948.0603019
Multi-spectral video imaging can simultaneously collect spatial, temporal and spectral information of scenes. It can be widely used in many fields such as remote sensing, agricultural monitoring, material analysis, etc. However, traditional spectrometers often depend on optical dispersion spectroscopy structure, which makes the system complex and difficult to calibrate, and it is difficult to popularize. Therefore, a miniaturized multi-sensor spectral video imaging system was built in this paper. A fast alignment method of multi-view image or video based on camera poses was proposed to realize real-time acquisition and alignment of multi-spectral video on embedded system. Through the experimental verification of complex scenes, the alignment method proposed in this paper has achieved desired results in both objective index (e.g. PSNR, SSIM) and subjective visual effects.
2019, 48(6): 604001.
doi: 10.3788/IRLA201948.0604001
In order to obtain accurate external heat fluxes of space camera with attitude change that works in the medium and high earth orbit, a method to calculate its external heat fluxes was proposed. Taking a geostationary space camera as an example, the relative position among the satellite, the sun and the earth was confirmed firstly. And then the camera's attitude was calculated according to its sun imaging mission. Finally, the instantaneous external heat fluxes on space camera were calculated based on its environmental mapping planes after changing attitude and the radiation view factors given by direct integration method. The result shows that under the same orbit condition, the total external heat fluxes of space camera with attitude change decreases dramatically by 372.5 W/m2 and 771.5 W/m2, in March equinox and December solstice respectively. The external heat fluxes on the +X direction plane where optical entrance is located increases by 2 times, and the external heat fluxes on this plane fluctuates wildly from 0 W/m2 to 1 378 W/m2. What's more, these computational results provide a good guidance for camera's thermal design, and this method can as well be applied to calculate the external heat fluxes of spacecraft with multi-dimensional attitude change.
In order to reduce the ambient temperature and the non-uniform temperature field formed by the internal heating elements, the imaging performance of the infrared thermal imager was affected. The finite element model of the infrared thermal imager was established by Proe and Ansys ICEPARK. The black anodizing and blasting treatment on the surface of the infrared lens enhanced the radiation heat transfer, and the fan was used to enhance the convection heat transfer to ensure the heat dissipation in the high temperature environment. The thermal resistance was designed for temperature rise, and the internal temperature distribution and infrared lens temperature distribution of the infrared thermal imager under different temperature environments were simulated and analyzed. The infrared thermal imager in thehigh and low temperature chamber was used to observe the target in the collimator. The image quality of the graph verified the efficiency of the temperature control design. The results show that the temperature control circuit board can control the temperature of the fan and the thermal resistance. When the ambient temperature drops to 0℃ and rises to 30℃, The temperature control system is activated to make the temperature of the infrared thermal imager optical system normal, and the imaging quality of the infrared thermal imager is ensured.
2019, 48(6): 604003.
doi: 10.3788/IRLA201948.0604003
Based on the detection mechanism of low orbit early warning satellites for the midcourse ballistic missiles, the radiation effects of various radiation sources(solar, earth, atmosphere, clouds) on targets in complex environments were considered. The irradiance generated by the background radiation sources of the three wavelength bands on the target surface was calculated, and the self-radiation and reflected radiation models of the warhead target were established. Based on the calculation results of the infrared radiation of the ballistic missile targets, combined with the diffraction effect of the early warning system, the modified model of the Synthetic Signal-to-noise Ratio(SSR) and the detection range were derived. From these two aspects, the ability of low orbit early warning satellites to detect the midcourse ballistic missiles in deep space was analyzed. The results show that the SSR effect of each radiation source on the target imaging in the complex detection environment can not be neglected. It is approximately 1.2 times that of the SSR only considering the target's own radiation. The diffraction effect of the optical system of the low orbit early warning satellites has a serious influence on the detection capability of the midcourse ballistic missiles. The ratio of the difference between the unmodified SSR and the modified SSR to the unmodified SSR in the 8-9.4 m, 9.4-10 m, and 10-14 m are 41.9%, 36.7%, and 10.4%, respectively. The detection distance changed with the observation angle, and the detection range is the largest when the detection angle is 0.
2019, 48(6): 606001.
doi: 10.3788/IRLA201948.0606001
Laser effective utilization rate is low because the gap between adjacent pixels in APD detectors used in laser 3D imaging is too large. Aiming to the question, the array beam laser 3D imaging technology was proposed. A laser beam of the laser radiation source was diffracted into sub-beams in array with a liquid crystal spatial light modulator, so that the laser beam can be divided into sub-beams corresponding to the array APD detector. The positions of the laser beam and array APD detectors were adjusted, so that the laser beam can irradiate on an object and focus on the effective array pixel of APD detector, the utilization efficiency of laser beam was improved. The composition and working principle of array beam laser 3D imaging system were introduced. The scheme to realize the array beam by using liquid crystal spatial light modulator was proposed The prototype of the array beam laser 3D imaging system was studied, and the result of laser array beam using the prototype was verified. The experimental result shows that 3D imaging range reaches 510 meters with peak power 10 kW, pulse width 8 ns, and 88 APD detector fill factor 2/3, the effect distance increases by 39.1%, compared with the laser 3D imaging system without array beam.
2019, 48(6): 606002.
doi: 10.3788/IRLA201948.0606002
Pulsed laser ranging system is widely used in laser radar, laser guidance and other fields due to its advantages of high precision, strong anti-interference ability, etc. However, the commonly used timing discrimination method has errors and restricts the improvement of dynamic ranging accuracy, which was mainly caused by the attenuation and widening of the echo pulse. A new method of timing discrimination was presented in view of this problem, which was based on the dual-channel timing discrimination method. The dual-channel timing discrimination method was composed of constant threshold timing discrimination method and peak timing discrimination method. Through the dual-channel timing discrimination method, accurate echo timing discrimination can be achieved without being affected by attenuation and broadening. By introducing the theoretical equations of the laser emission pulse, the time domain distribution model of the echo waveform was established. The experimental results show that the short ranging error can be controlled within 3 cm by adopting the dual-channel timing discrimination method, and the accuracy can be further improved by multiple measurements, which solves the bottleneck problem that the timing discrimination error restricts the dynamic ranging accuracy.
Initiative control technology based on periodic temperature excitation was used for mixing gasdynamic CO2 laser(MGDL). Through numerical simulation, influences of periodic temperature excitation on mixing characteristic of donor and assistant flows and small signal gain coefficient of mixing gasdynamic CO2 laser were studied. Investigation results indicate that compared with the case that has no periodic temperature excitation, mixing efficiency of donor and assistant flows can be enhanced and small signal gain coefficient in mixing nozzle can be improved when periodic temperature excitation with certain excitation amplitude and excitation frequency is imposed at the outlet of assistant nozzle. Excitation amplitude and excitation frequency have important effects on mixing efficiency of donor and assistant flows and small signal gain coefficient. As the excitation amplitude increases, the small signal gain coefficient first increases and then decreases. In downstream area of mixing nozzle, small signal gain coefficients under the condition of the six excitation frequencies selected by this paper are all higher than the state without periodic temperature excitation. With the increase of excitation frequency, mixing efficiency of donor and assistant flows becomes better and better; but when the excitation frequency increases up to a certain value, mixing efficiency of donor and assistant flows will not change any more.
A high stability and compact structure 488 nm light generated by intra-cavity frequency doubling in an optically pumped semiconductor disc laser was designed. In order to obtain a 488 nm laser with good beam quality and stable performance output, a semiconductor gain medium chip with 13 QWs and 808 nm/976 nm Double Band Mirror was pumped vertically by 808 nm LD on the top surface of the chip, and the chip with double diamond heat spreaders bonded on the both sides was introduced. 488 nm laser was generated by doubling frequency with I phase matched LBO crystals inserted in the cavity. 111 mW 488 nm laser with 1.3 nm spectral line width was obtained, the optical to optical efficiency was 1.2%, the beam quality of Mx2、My2 were 1.03 and 1.02 respectively, and the instability is less than 0.6% with continuously work for more than 3 h.
2019, 48(6): 606005.
doi: 10.3788/IRLA201948.0606005
Consistent with the scanning structure of airborne laser bathymetry system, aiming at the oval scanning mode of circular mirror skew axis, starting from the beam emission direction and on basis of the axial relation of scanning structure, the laser output direction vector was derived by the law of light reflection. The coordinates of laser points on the sea surface were obtained by combining the distance from the laser output location to the sea surface point. According to the law of light refraction, the coordinate calculation formula of submarine bathymetric point was derived by using the variable refractive index ray tracing algorithm, and the precise calculation model of laser incident point and submarine bathymetry point coordinate was established. According to the model positioning formula, the influence of scanning system boresight error was analyzed. Through numerical simulation, the influence of scanning boresight misalignment calibration on positioning accuracy was analyzed, which provided the basis for the processing, installation, adjustment and the integrated checking of unit device in the scanning system. The positioning formula can provide reference for accurate calculation and correction of submarine points for airborne lidar bathymetry system.
2019, 48(6): 606006.
doi: 10.3788/IRLA201948.0606006
The intracavity cascaded Raman laser output characteristics based on potassium titanyle phosphate (RbTiOPO4, RTP) crystal were reported. A diode end-pumped acousto-optic Q-switched Nd:YAG laser at 1 064 nm was adopted as the fundamental light. A 4420 mm3 in size and along x-axis cut RTP crystal was used as the Raman gain medium. The RTP Raman laser systems with X(ZZ)X and X(YY)X configurations according to the Porto notations were designed for experimental study. The relatively low Raman gain of X(YY)X geometry configuration leads to the competition of different nonlinear frequency conversion processes in the cavity, and only the corresponding optical parametric oscillation output was measured. The cascaded Raman laser output with the Raman shifts of 271 cm-1 and 687 cm-1 was successfully achieved in the X(ZZ)X configuration. The high-order Stokes lines appeared successively with the increase of incident pump power. Total average output power of 480 mW and conversion efficiency of 4.8% were obtained under an incident pump power of 10 W and a pulse repetition frequency of 15 kHz. The laser wavelength includes different order Stokes ranging from 1 000 to 1 200 nm.
2019, 48(6): 606007.
doi: 10.3788/IRLA201948.0606007
To improve the implantation stability and biological activity of the hydroxyapatite(HA) coating on the surface of medical TC4 titanium alloy, CaP bioceramic coating with different silicon contents were prepared by laser cladding method. Scanning electron microscopy(SEM) and X-ray diffractometry(XRD) were used to characterize the morphology and phase composition of the cladding layer. The results showed that the Ca2SiO4 phase was formed and the microstructure of the middle zone of the cladding layer was refined after adding SiO2(1wt.%, 3wt.%). The effects of SiO2 content on the corrosion resistance and bioactivity of the coating were investigated by electrochemical corrosion and in vitro SBF immersion experiments. Electrochemical corrosion results showed that the corrosion current density of the coating surface decreased with the increase of SiO2 content; The results of SBF soaking in vitro showed that the addition of SiO2 could accelerate the formation of bone-like apatite on the surface of the coating. When the content SiO2 was 1 wt.%, the surface of the coating-like bone apatite was uniformly distributed. Therefore, low-content SiO2 can improve the corrosion resistance and bioactivity of bioceramic coatings.
2019, 48(6): 606008.
doi: 10.3788/IRLA201948.0606008
Aiming at the frequent surface crack, volume damage and high cost of repairing materials for TC4 alloy blades, the FeCrNiB alloy and TiAlVFe were chosen for remanufacture, the surface cracks and volume damage of TC4 blade were remanufactured based on the advantages of pulsed laser forming process, the process matching was verified from the forming process, the metallographic microstructure and three-dimensional size aspects. The results show that the FeCrNiB cladding layer is composed of fine and compact equiaxed crystals, interlaced dendrite and homogeneously distributed cell crystal, while the TC4 alloy is mainly composed of interlaced acicular martensite and basketweave sstructure, both the organization of layers are in better form. The microhardness of the FeCrNiB cladding layer is 380-750 HV0.1, one time higher than the substrate. The microhardness of the TC4 cladding layer is 295-350 HV0.1, which is similar with the substrate. The dimension accuracy of the blade after remanufacture was controlled within 0.8 mm. Through the laser process optimization and performance matching analysis, the FeCrNiB alloy was suitable for local microcrack remanufacture, while the TC4 alloy was suitable for the forming of volume damage.
2019, 48(6): 630001.
doi: 10.3788/IRLA201948.0630001
The range image reconstruction algorithm of Geiger-mode APD laser radar system was studied, and a reconstruction algorithm based on pixel neighborhood kernel density estimation was designed. Starting from the system principle, the theoretical basis of the reconstruction algorithm of range image was studied with the detection probability model. According to the characteristics of the system, an improved algorithm based on pixel neighborhood kernel density estimation was proposed and its principle was analyzed. The histogram algorithm and the neighborhood kernel density estimation algorithm were verified by simulation data, and the range reconstruction accuracy rate curve was used for quantitative evaluation and comparison. The algorithm was further applied to real Geiger mode APD lidar data to reconstruct range image. The experimental results show that the reconstruction algorithm based on the statistical neighborhood kernel density estimation can effectively improve the reconstruction effect of the range image at low frame counts.
2019, 48(6): 630002.
doi: 10.3788/IRLA201948.0630002
Aiming at the problem that the current mobile robots have low accuracy for the construction of environmental maps, the calibration methods of ranging and angle measurement of LiDAR were proposed respectively. The error propagation law was used to analyze the ranging error factor of the LiDAR. It can be seen that the LiDAR ranging error was mainly caused by the echo intensity and the measuring distance, and the ranging error correction model was derived. By analyzing the error factors of LiDAR angle measurement, a triangulation calibration method was proposed for the error caused by the eccentricity of the mechanical scanning axis and the geometric rotation center, and the angle error correction model was established. The mobile robot coordinate conversion system was modified according to the LiDAR ranging and the angle correction model. The experimental results show that the standardization of the distance measurement increases the standard deviation of the longitudinal coordinate difference of the plane obstacle data by 30%-60%, which is close to the real geometric feature of the object. The angle measurement method improves the coincidence effect of the obstacle data by 30%. The accuracy of map construction of mobile robots is improved using the calibration method.
2019, 48(6): 622001.
doi: 10.3788/IRLA201948.0622001
The existing monitoring technologies of railway tracks mainly use the technologies of electrical sensing. These technologies were easy to be affected by electromagnetic fields and external environments and there were potential security risks. Therefore, the on-line monitoring technology of railway track strain based on an identity weak fiber Bragg grating(wFBG) array was used to monitor the occupancy of the track in the real-time. The sensor's structure of sensing railway strain was designed by finite element simulation and the encapsulation technology of sensors was studied. The strain signal was obtained by detecting wFBG wavelength shift to achieve highly sensitive strain measurement. The identity wFBG arrays were used to verify this sensor and system in the laboratory and field experiments. The results show that the sensor structure can achieve a smaller optical loss, and can ensure that the sensitivity of the sensor reaches 3.4 pm/, the linearity reaches 0.997 82, and the hysteresis error reaches 0.8%. The online monitoring system of railway track can meet the actual needs of railway operation and management.
2019, 48(6): 622002.
doi: 10.3788/IRLA201948.0622002
An optical generation scheme of microwave signals with multiple modulation formats based on a polarization modulator(PolM) and a Sagnac loop was proposed. The PolM was driven by a baseband coding signal to generate a polarization shift keying(PolSK) signal and the generation principle was theoretically analyzed. Two Mach-Zehnder modulators(MZM) were embedded in the Sagnac loop to modulate the PolSK signal transmitted clockwise or counterclockwise, respectively. The outputs of amplitude shift keying(ASK), frequency shift keying(FSK) and phase shift keying(PSK) microwave signals were achieved by properly adjusting the driving signals of two MZMs. In the simulation work, a 40 GHz ASK signal, a 20/40 GHz FSK signal and a 20 GHz PSK signal with a bit rate of 2 Gbit/s were produced. In addition, the broadband tunability of the bit rate and carrier frequency was verified. The system stability was improved with Sagnac ring structure. Furthermore, without changing the link configuration, the bit rate and carrier frequency for each modulation format of microwave signals can be tuned flexibly and independently by controlling the baseband coding signal and the RF driven signals of two MZMs.
2019, 48(6): 622003.
doi: 10.3788/IRLA201948.0622003
To meet the demand for monitoring the morphing wing aerodynamic shape of morphing aircraft, a flexible composite skin embedded optical fiber shape sensing method for variant aircraft was proposed. The fiber Bragg grating sensor was embedded into the thin layer of silicone rubber, then combining the silicone rubber layer with polyvinyl chloride sheet to form composite skin. The flexible skin shape sensing system was established, and the optical fiber sensing demodulation system was used to test the reflection spectrum characteristics of the fiber Bragg grating in the flexible skin under different airfoil. The morphing curvature of the flexible skin was calculated and the three-dimensional shape of the flexible skin was reconstructed. The contrast test was completed by the digital photogrammetry system. The results show that the measurement error of flexible composite skin deformation optical fiber sensing compared with digital photography is less than 4.62%, and the sensitivity of optical fiber sensing reaches 245.5 pm/m-1. The effectiveness of the embedded fiber sensing method is verified, which provides a reference for monitoring the morphing wing aerodynamic shape of the morphing aircraft.
2019, 48(6): 622004.
doi: 10.3788/IRLA201948.0622004
The biggest challenge for free space optical(FSO) communication systems is the attenuation/fluctuation of light intensity caused by influence of atmospheric turbulence in long distance communication, resulting in communication link interruption. A method to calculate the link loss due to atmospheric turbulence, based on lognormal statistics of the received power, was presented. It can be used to evaluate the system parameters in FSO communication system. The effects of different intensity turbulence were simulated, and the relationship between optical communication link loss and transmission distance at 850 nm and 1 550 nm wavelengths at receiving terminals of 2 cm and 20 cm was obtained. Then the simulated analysis results were used to design a FSO communication system with a receiving aperture of 20 cm, which could transmit HD image and video at a distance of about 2 km under strong turbulence conditions. The transmission rate of the FSO communication system was 1 Gpbs which could meet the sharpness and real-time performance of large amount of uncompressed data transmission compared with the 4 G networks.
2019, 48(6): 618001.
doi: 10.3788/IRLA201948.0618001
Panoramic annular optical system have been widely applied in various emerging field like robot sensing. This type system desire a large FOV detection capability while maintaining a small and compact size. According to above requirements a research on the panoramic annular optical system was made, and a two-channel panoramic annular optical system based on the analysis of the panoramic annular lens(PAL) was designed. The system is composed of a marginal FOV channel and a central FOV channel, which correspond to the panoramic annular optical system with entrance pupil preposition and central FOV system respectively. By rational combination, the central FOV of the system is 0-18.5, the marginal FOV of the system is 38-83. In the design process, even-ogive surface was adopted to design the certain surface of the panoramic annular lens of the marginal FOV channel, also an description of how to use the even-ogive surface in the design process was made. Finally both two channels can acquire a good image on the image plane during the working wavelength 0.486-0.656 m, the whole structure of the system is relatively compact, satisfying the demand for application.
2019, 48(6): 618002.
doi: 10.3788/IRLA201948.0618002
Infrared optical systems, facing with complex external environment, are widely used in military, aerospace, civil and other fields. The traditional method for evaluating system performance just by Optical Analysis Software should be improved, and thermal/structural/optical (TSO) integrated analysis is an effective method for synthesizing effects of multiple physical fields, which include optics, mechanics and thermology. The data conversion program between disciplines was compiled after researching Zernike polynomial fitting algorithm. The interface problem of data transmission in optical mechanical and thermal program was solved, and the thermal insensitivity optical system design was carried out using the TSO integrated analysis, as an example. The optical transfer function of infrared system under the high and low temperature environment was obtained by TSO integrated analysis, which provides a theoretical basis for the improvement of system design and performance.
2019, 48(6): 618003.
doi: 10.3788/IRLA201948.0618003
When a laser engraving machine carries out laser engraving, sometimes the laser bursting points are uneven. It is necessary to amplify and analyze the laser explosion points to better control the energy of the laser beam. A zoom microscope objective with long working distance was designed according to the observation requirements of explosion points. The explosion points inside the glass have the viewing range of 9-32 mm. The zoom range of focal length is from 6 mm to 24 mm with optical zoom mechanism. The magnification is 4-16, and the zoom ratio is 4. A 1/2-inch CCD model VA-1MG2 was adopted as the detector with pixel size 5.5 m. The optical system optimization was carried out by using Zemax. The MTF values of all fields are larger than 0.4 at cut-off frequency 91 lp/mm for each configuration. The MTF values for central field and 0.707 field approach to the diffraction limit. The RMS radius of the spot diagram is smaller than the radius of Airy disk. The image quality of the designed system meets the requirements of all technical indicators.
2019, 48(6): 620001.
doi: 10.3788/IRLA201948.0620001
As the quantitative precision of remote sensing information is higher and higher,the polarization correction factor attracts more attention. Therefore, the research on the polarization feature of remote sensors and obtaining normalized Muller elements is necessary, which play an important role in the quantitative research of remote sensing information and polarization correction. However, the polarization sensitivity cannot reflect the polarization feature, which is the comprehensive reflection of polarization response. The analytic method of normalized Muller elements was studied by Fourier series fitting, and the polarization response of remote sensors was obtained. And then the normalized Muller elements m2, m3 were calculated by the polarization response, based on Fourier series fitting. The normalized Muller elements at different Fourier orders were analyzed, and the relative deviation was better than 0.12%. Finally the test error of normalized Muller elements was analyzed, which was better than 0.96%, and the research has further application for the normalized Mueller elements of the remote sensors.
2019, 48(6): 620002.
doi: 10.3788/IRLA201948.0620002
As a new type of spatial light modulator, Digital Micromirror Device(DMD) has the advantages of high resolution, low production cost and high processing efficiency. It is very flexible to use, so the laboratory built a near infrared spectrometer based on DMD. First, the basic working principle of DMD near-infrared spectrometer was introduced. Secondly, the wavelength of spectrometer was calibrated, a method based on the correlation coefficient of the same sample absorbance curve was proposed to normalize the inter-wavelength difference, so that the inter-station difference of the wavelength was theoretically less than 0.1 nm, which meet the requirements when the model was transferred. The selection criteria of different coding templates for DMD near-infrared spectrometer were obtained by comparing the noise and signal-to-noise ratio test under strong light and weak light conditions:the scanning method was better than the Hadamard method under strong light conditions, the opposite in weak light. Finally, the actual sample gasoline and diesel were tested by the spectrometer, and the test results showed that the spectrometer performance was stable. The near-infrared spectrometer based on DMD has a detection wavelength range of 1 330 to 2 500 nm, absorbance deviation is less than 0.000 4 AU.
2019, 48(6): 617001.
doi: 10.3788/IRLA201948.0617001
Due to the complexity of calculating model for the current optical parabolic surface and to acquire the high-precision surface based on the data of finite element analysis for parabolic surface, a new high-precision algorithm of surface parameter for optical parabolic surface was proposed. Firstly, the discrete error of the optical parabolic surface was proposed, and elimination technique of discrete error was researched, which was also the crucial step for the data preprocessing of the surface parameter calculation. Secondly, the rigid body displacement and surface distortion displacement were distinguished with the data processing algorithm based on rigid body displacement. Lastly, the basic data to obtain parameter, just as the root mean square, was got using the optimal design algorithm. The algorithm realization of the high-precision parabolic surface parameter was discussed and the validity check of the algorithm was performed as well. The result of validity check demonstrated:the high-precision algorithm of parabolic surface parameter is higher, and the check error is about 6%. The precision of new algorithm can satisfy the engineering requirement, and it also provides a new technical reference for the high precision calculation of optical surface parameter under the external thermal load.
2019, 48(6): 617002.
doi: 10.3788/IRLA201948.0617002
In order to realize in-orbit measurement of the parameters of three-line array satellite-borne CCD camera, a method for measuring 6-DOF (Degree of Freedom) micro-displacement was proposed in this paper. The LED output light with high brightness was collimated and coupled to the input optical fiber. The end of the output fiber was fixed to the movable object to be measured. The fiber outputs were collimated by multiple fiber collimators ( 4) and captured by multiple area array CCD cameras ( 4) in the fixed part of the system. The 6-DOF displacement of the measured object was solved according to the position change of the light spot in the CCD image. In order to validate the model of the system and 6-DOF displacement calculation program, the proposed method was theoretically analyzed and simulated. The results show that both the maximum translational error and rotational error of the typical 4-collimation measurement system are under 10-5 m and 10-4' when the translational displacement is less than 100 m and the rotational displacement is less than 6'. And the limit errors (3) of the translational errors and rotational errors are respectively 0.9 m and 0.012' when the random quantities of -0.5-0.5 m are added to the two coordinate directions of the position of the light spot of the collimators.
2019, 48(6): 626001.
doi: 10.3788/IRLA201948.0626001
A fusion detection methodology for infrared and visible spectra was presented based on deep learning. First, a parameter transfer model for deep learning models was proposed. Then a pretraining model for infrared object detection was extracted from a visible object detection model based on deep learning and was fine-tuned on a collected infrared image dataset to obtain an infrared object detection model based on deep learning. On this basis, a decision-level fusion model for infrared and visible detection based on deep learning was established, and the model design, image registration and decision-level fusion processes were discussed in detail. Finally, an experiment comparing single-band detection and dual-band fusion detection during the daytime and nighttime was presented. Qualitatively, compared with the results of single-band detection, the confidences and bounding boxes achieved through dual-band fusion detection are superior, owing to the utility of their complementary information. Quantitatively, in the daytime, the mAP of dual-band fusion detection is 86.0% and is higher than those of infrared detection and visible detection by 9.9% and 5.3%, respectively; at nighttime, the mAP of dual-band fusion detection is 89.4% and is higher by 3.1% and 14.4%, respectively. The experimental results show that the dual-band fusion detection method proposed in this paper shows better performance and stronger robustness than the single-band object detection methods do, thus verifying the effectiveness of the proposed method.
2019, 48(6): 626002.
doi: 10.3788/IRLA201948.0626002
In order to further improve the quality of image Super-Resolution (SR) reconstruction, a SR reconstruction algorithm based on Fields of Experts (FoE) prior model was proposed for the noise problem of reconstructed image in Non-locally Centralized Sparse Representation (NCSR) algorithm. Firstly, the FoE model was used to learn the prior knowledge of the whole image from the image training data to establish the global prior model, and then the learned prior information was used to solve the optimal sparse representation coefficient in the NCSR framework. Finally, the high resolution image estimate was obtainon. The proposed algorithm updated parameters of FoE prior model while the SR reconstruction iterative operates. Therefore, the effect of image reconstruction can be effectively enhanced by selecting the appropriate prior constraints without significantly increasing the computational complexity. Compared with NCSR algorithm, the experimental results show that the proposed algorithm can obtain better peak signal to noise ratio results for both noiseless and noisy degradation images, and further improves the de-noising effect of noisy images.
2019, 48(6): 626003.
doi: 10.3788/IRLA201948.0626003
Infrared target tracking is of great significance to the research in military and civil video surveillance. Due to the special thermal-imaging mechanism, infrared targets are often with low resolution, low contrast and in the lack of textures. Aiming at the deterioration of tracking performance caused by insufficient common features of infrared targets, a novel tracking algorithm was proposed based on adaptive fusion of correlation filter responses. The algorithm explored the framework of the correlation filter with continuous convolution operators. The saliency feature was comprised to enhance the object appearance description. The center location of a target was predicted by the fused responses that were calculated from an adaptive fusion of multiple correlation responses with Hedge decision-theoretic. Additionally, the final tracking result was obtained after multi-scale estimation based on scale filters. The experimental results show that the algorithm has better performance in tracking accuracy and robustness compared with other tracking methods on the public infrared video dataset VOT-TIR2016.
2019, 48(6): 626004.
doi: 10.3788/IRLA201948.0626004
In order to solve the problem of crosstalk and limited number of viewpoints caused by aberrations and geometry in the traditional stereoscopic projection display based on cylindrical lens, a autostereoscopic projection display method based on prismatic reflective grating was proposed. The principle of 3D imaging was analyzed. The autostereoscopic projection display based on prismatic reflective grating was simulated. Compared with traditional autostereoscopic projection display based on cylindrical lens, under the condition of same horizontal video bandwidth, the illuminance of viewing field is ten times, and the crosstalk ratio is 1/5, and there is no secondary viewing zone. The prismatic reflection grating screen was made and the system was set up to carry out experiments. The feasibility of autostereoscopic projection display was verified.
