基于微透镜阵列的快照式高光谱成像仪研制

Development of Snapshot Hyperspectral Imager Based on Microlens Array

推扫式光谱成像技术虽然具备较高的空间、光谱分辨率,但其推扫成像的技术特点使其牺牲了时间分辨率,无法满足对动态目标、短时过程的光谱成像,限制了高光谱成像技术的应用范围。针对该缺陷,研制了基于微透镜阵列的快照式高光谱成像仪。快照式光谱成像仪波段范围为500~700 nm,平均光谱分辨率优于10 nm。按照上述指标首先进行了快照式光谱成像仪的光学设计,然后根据光学设计结果对关键元器件进行了加工采购,并搭建了系统样机。通过对搭建的系统样机进行定标及目标物探测测试,仪器光谱成像效果良好。较传统推扫式光谱成像系统,该系统实现了快照式光谱成像,能够有效地提升高光谱成像探测效率,有助于拓展高光谱成像探测技术的应用范围。

With the development of the hyperspectral imaging technology,it has been widely used and convinced as a useful detecting tool in many areas such as medical area,food safety and mineral exploration.But most of the hyperspectral imagers used nowadays are based on push-broom spectral imaging technology,which achieve spectral imaging through moving the spectral imager by scanning structure.The time resolution is sacrificed to obtain rather good spectral and spatial resolution in this kind of spectral imaging way.And that means the dynamic target and process can not be detected by this kind of hyperspectral imagers,so the application range of this kind technology is limited largely.Due to the defects mentioned above,a snapshot hyperspectral imager based on microlens array is developed in this paper.The principle of the instrument developed is introduced in this paper.Then the imaging principle of the microlens is introduced based on geometrical optics.The signal-to-noise calculation model of the hyperspectral imaging system based on microlens is then derived according to the imaging characteristics of this kind of system.Based on these theories derived above,the optical system is designed.The detector and the microlens were first determined before the optical design job begin.The detector has 2048×2048 pixels with a pixel size of 5.5μm×5.5μm.And the microlens array is composed of 100×100 microlens.The size of each microlens is 100μm,and the focal length of the microlens is 0.5 mm.According to the microlens size and the detector size,the wavelength range of the whole system is determined as 500~700 nm.An objective lens is first designed,the F number of the objective is determined as 60 according to the calculation result,and the field of view of the objective lens is 36°.The objective lens has a telecentric feature on image side.Then the spectral imaging system is designed.The F number of the spectral imaging system is determined as 5 according to the F number of the microlens.A double amici prism is designed and used as the dispersion element in the spectral imaging system.The collimating lens and imaging lens in the spectral imaging system are symmetrical to eliminate the vertical aberration in the system and make the fabrication of the lens simpler.A simulation is taken after the design work has been finished.A prototype is set up in the laboratory according to the simulation result,and several performance verification experiments are taken to test the imaging and spectral performance of the system.The spatial and spectral calibration of the system are first taken.According to the calibration result,the monochromatic images of different bands can be extracted.To test the spectral resolution of the whole system,a mercury lamp is used to illuminate the system.And according to the test result,the spectral resolution of the system is 2.034 nm at 546.08 nm and 7.05269 nm at 696.54 nm.A special target is used to test the spatial resolution of the whole system.According to the test result,the resolution of the whole system is 2.2 mm when the object distance is 1.1 m.Then a board with different color blocks and a standard white board are used as the target and detected by the whole system.Then the reflectance curves of different color blocks are calculated,which match the reflectance curves obtained by a commercial spectrometer.The test results show that the system has a good spectral and relatively good spatial detection capability.Comparing to the traditional push-broom spectral imager,the built system can improve the detecting efficiency of the spectral imaging detection,reduce the volume of the whole hyperspectral imaging system,and expand the application range of hyperspectral imaging technology.