Design Of Snapshot Multispectral Imaging System Based On Array Filtering

Snapshot multispectral imaging systems have urgent application needs in many fields such as medical research,geological exploration,pesticide residue detection,antibiotic detection,fingerprint recognition,national defense and military,and disaster warning,showing significant application potential and research value.This paper studied a snapshot multispectral imaging system based on an array filter,which can achieve multi-channel imaging and real-time acquisition of spectral information.The system has advantages such as large field of view,small volume,lightweight,simple structure,and can be carried on various platforms such as smartphones and micro drones.Based on the existing structure of a multi-aperture multispectral imaging system,a compact multispectral imaging optical system composed of a composite front-end optical element,an array aperture stop,a micro-lens array,an array filter,and an image sensor was designed and verified.The design,optimization,tolerance,and stray light analysis of the optical system were completed.A 5×5 array filter,micro-lens array,and array aperture stop were developed.A compact multispectral imaging system with 5×5(25)channels was assembled,and spectral imaging of different objects was carried out.The technical indicators of the designed system were verified,and the main research content and results are as follows:(1)The design scheme of a snapshot multispectral imaging system based on array filters was optimized.First,a suitable CMOS sensor was selected according to the application background.Then,the structure design of the micro-lens array and array filter was completed through the system principle.Finally,the relationship between system parameters was studied,and the influence of chromatic aberration was analyzed in detail based on the characteristics of aberration.The initial structural parameters and system indicators of the optical system were determined according to the analysis results.(2)The design and optimization of the compact multispectral optical system have been completed.The system was modeled using ZEMAX,and stray light analysis was performed using Trace Pro.The final system had a field of view of 20 degrees,an F/# of 0.4,a focal length of 2.58)8)8)8),a total length of 12.48)8)8)8),and a single-channel MTF greater than 0.35 at 153lp/ mm with distortion less than 0.23% in the 480～650 nm wavelength range.The tolerance range of the optical system was then determined,and the optical system structure was designed in cooperation with Solid Works.(3)The development and assembly of the optical components of the system have been achieved.Firstly,a 5×5 micro-lens array was manufactured using a single-point diamond turning machine and fast tool servo machining method.The measured sagittal height was 0.619 mm,which differed from the design result by 0.087 mm with a relative error of 14%.Secondly,a 5×5array filter was developed using ion beam-assisted electron beam thermal evaporation technology,with a spectral resolution of 7nm,peak transmittance greater than 90%,cutoff band transmittance less than 1%,and a FWHM of 5nm.Finally,the processed system optical components were cleaned,bonded,and assembled.(4)The validation of the array filter-based snapshot multispectral imaging is carried out.First,a grating monochromator was used to detect the spectral and channel number of the prototype of the snapshot multispectral system,which was then calibrated to obtain the spectral characteristics and field of view parameters of the system.Then,different objects with various shapes and colors(diamond,"F",logo,apple)were imaged using the multispectral system to validate its performance,and the field of view of the system was tested under different object distances and object heights.The results showed that although there was a peak shift between the peak response of the target objects via the multispectral system and the measured peak values by the fiber optic spectrometer,they had the same spectral trend.Additionally,the absorption peak of the apple was found to be between 550～5709)9)8)8)through multispectral imaging,and the measured field of view of the system was consistent with the design parameters.This paper designs and completes a prototype of a snapshot multispectral imaging system based on an array filter,which has the characteristics of compact structure,lightweight,low cost,and high light utilization efficiency.It lays the foundation for future applications in small platforms such as smartphones.