Synthetic aperture lidar is a new ultra-high resolution optical imaging instrument, but its reception field is very narrow which is subject to the "antenna theory". In this paper, the antenna efficiency theory is used to explain the antenna theory and the method of enlarging the field of view of the synthetic aperture laser radar. Then the increase range of the field angle of the three methods is deduced by heterodyne efficiency simulation. The simulation results show that the focal plane heterodyne detection optical path of the wide-beam local oscillator beam focal plane has the ability to improve the heterodyne efficiency of the edge field of view by reducing the heterodyne efficiency of the central field of view. The focal plane heterodyne detection optical path of the array detector requires the detector whose pixel size less than 3 times Airy spot radius covers the whole field of view, which can increase the maximum 1.83N times compared to the antenna theory. The effective field of the pupil plane heterodyne detection optical path of the array detector has nothing to do with the magnification of the telescope, the pupil diameter, the size of the detector, etc., which can be increased by N times as compared with the antenna theory.
The thermal stability of optical antennas is a key parameter determining the performance of satellite optical communication links. The effects of uniform temperature changes on the performance of a Cassegrain optical antenna are discussed. In addition, a simple theoretical model is proposed to describe the defocusing distance and wavefront aberration (power) as a function of temperature. Through the theoretical model, the thermal stability can be quickly assessed in the optical design stage. The alignment data and thermal experimental results are consistent with the theoretical model.
Due to its advantageous imaging characteristic and banding flexibility, imaging fiber bundle can be used for line-plane-switching push-broom infrared imaging. How to precisely couple the fiber bundle in the optics system is the key to get excellent image for transmission. After introducing the basic system composition and structural characteristics of the infrared systems coupled with imaging fiber bundle, this article analysis the coupling efficiency and the design requirements of its relay lenses with the angle of the numerical aperture selecting in the system and cold stop matching of the refrigerant infrared detector. For an actual need, one relay coupling system has been designed with the magnification is -0.6, field of objective height is 4mm, objective numerical aperture is 0.15, which has excellent image quality and enough coupling efficiency. In the end, the push broom imaging experiment is carried out. The results show that the design meets the requirements of light energy efficiency and image quality. This design has a certain reference value for the design of the infrared fiber optical system.
For a positioning CMOS camera, we put forward a system which can measure quantitatively dispersed spot parameters and the degree of energy concentration of certain optical system. Based on this method, the detection capability of the positioning CMOS camera can be verified. The measuring method contains some key instruments, such as 550mm collimator, 0.2mm star point, turntable and a positioning CMOS camera. Firstly, the definition of dispersed spot parameters is introduced. Then, the steps of measuring dispersed spot parameters are listed. The energy center of dispersed spot is calculated using centroid algorithm, and then a bivariate-error least squares curve Gaussian fitting method is presented to fit dispersion spot energy distribution curve. Finally, the connected region shaped by the energy contour of the defocused spots is analyzed. The diameter equal to the area which is 80% of the total energy of defocused spots and the energy percentage to the 3×3 central area of the image size are both calculated. The experimental results show that 80% of the total energy of defocused spots is concentrated in the diameter of the inner circle of 15μm, and the percentage to the 3×3 pixels central area can achieve 80% and even higher. Therefore, the method meets the needs of the optical systems in positioning CMOS camera for the imaging quality control.
The use of line-plane-switching infrared fiber bundle to achieve wide field of view push-broom infrared imaging has been studied with experiment. In this technology, the linear array end of the imaging fiber bundle is used as a long-linear array infrared detector, and the plane array end of the bundle is coupled by a mature small scale Infrared Focal Plane Array (IRFPA). It can evade the difficulty of getting the long-linear array infrared detector directly, and has a signally significance to the development of internal infrared imaging technology. Based on the introduction of the composition, working principle of this novel infrared optical system, the system principle-demonstrating experiment has been accomplished. The line-plane-switching fiber bundle used in this experiment is 64×9 format plane array and 192×3 format linear array. It is made from chalcogenide glass fibers, possessing core (As40S59.5Se0.5) of 45 μm, cladding (As40S60) of 5 μm, and error of 1% in diameter. Perfect imaging results prove that this novel technology is feasibility and superiority. The analysis of the experiment makes a foundation for the subsequent further verification experiments.
A new subminiature endoscope which used for reconnaissance and diagnosis has been designed. This subminiature endoscope is designed based on imaging fiber bundle and consist of the front object lens whose aperture is only 0.5mm, imaging fiber bundle and the post coupling lens. It realized by using subminiature optical systems . The FOV(field of view) and the focal length of the front object lens are 50° and 0.59mm. And the object distance, F number and detected imaging high of the front object lens are 3mm, 6 and 0.5mm. The total number of the imaging fiber bundle are 10000 and it’s pixel cell size is 5 μm. The effective aperture of the imaging fiber bundle is 0.46mm. The post coupling lens has a reduction ratio of 1.73. It’s object distance and imaging height are 5mm and 0.8mm. The Numerical Aperture (NA) of the front object lens, imaging fiber bundle and the post coupling lens are matching will. The coupling efficiency of the imaging fiber bundle is above 93% and the system’s design result can meet the need of the limit resolution of the imaging fiber. This kind of the fiber endoscope has the peculiarity of wide FOV, fine imaging quality, compact configuration, low finished cost and etc. It is meaningful to realize the objective of miniaturization, batch-type production and high imaging quality of the endoscope.
Relay lens is an important element for infrared system coupled with imaging fiber bundle. According to the basic composition and structural characteristics of infrared system coupled with imaging fiber bundle, this paper put forward the general principle and method of its relay lens design, then a material relay lens has been designed by ZEMAX with definite performance index. It has a working spectral coverage from 3.7μm to 4.8μm, focal length of 33.5mm, magnification of -0.6, linear field of view of 12mm, objective numerical aperture of 0.15. It is objective telecentric and is adapted to the relay of infrared detector and imaging fiber bundle. The total lens has two aspheric surfaces and only four pieces of singlet. Its MTF value is 0.7@17 lp/mm, and distortion is -0.19%. After necessary tolerance analysis and structural design, this relay lens has been fabricated. The optical performances fulfill the design requirements and clear images have been got by this lens. These prove the validity and rationality of the design method. It gives a foundational guidance for such relay lens design.
Color constancy is of important for many computer vision applications, such as image classification, color object recognition, object tracking and so on. But unlike the human visual system, imaging device cannot be able to compute color constant descriptors which do not vary with the color of the illuminant, so solving color constancy problem is necessary. In the calculation of color constancy, illuminant estimation is the key. Because grey surfaces can perfectly reflect the color of the scene illumination, many methods have been proposed to identify grey surfaces to estimate the illuminant. But they either rely on the camera’s parameters, lacking universality, or work inaccurate in worse conditions. In order to solve these problems, in this paper, an iterative method is proposed. The quality of the proposed method is tested and compared to the previous color constancy methods on the Macbeth Chart and two data sets of synthetic and real images. Through MATLAB simulation, experimental pictures and quantitative data for performance evaluation were gotten. The simulated results show that the proposed algorithm is accurate and efficient in identification of the grey surfaces, even in worse condition. And it performs well in color constancy computation on both synthetic and real images.
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