Research On Visible-Near Infrared Linear Variable Filters

With the development of optical technology,the miniaturization of optical systems has attracted more and more attention.Linear filter,also known as linear variable filters（LVF）,is one of the development paths of miniaturization of spectroscopic technology.Compared with traditional beam-splitting prisms,gratings and other beam-splitting devices,LVF have the advantages of small size,high transmittance,and high integration.With the application of LVF,the spectroscopic technology has developed rapidly.Spectroscopic techniques based on linear gradient filters are used in many fields such as military detection,atmospheric monitoring,and medical analysis.Therefore,research on its preparation has very important application value.However,as a highly integrated spectral detection device,the development of the LVF at the current stage cannot be systematic,and at the same time,it has the characteristics of complex preparation process,long development cycle and high cost.In this paper,according to the use requirements of the hyperspectral camera acquisition system,the research work is carried out around the preparation of high-quality LVF.In-depth theoretical analysis and experimental research are carried out on the deposition theory of thin films,the film system design of LVF,the preparation technology and the test of thin film characteristics.The transmittance of the prepared LVF in the cut-off area is less than 4%,the peak transmittance of different wavelengths are all greater than 80%,and the spectral range of500nm～800nm can be changed in the length of 40mm.Firstly,the emission characteristics of electron beam thermal evaporation sources are systematically studied,and the emission characteristics of point sources and surface sources are analyzed by using cosine characteristics.Using Mathcad15 to perform programming simulation to establish the relationship between the correction baffle and the relative film thickness,through only a few experiments,the Ta₂O₅ and Si O₂ double baffles of the LVF were designed and optimized,and the single-layer film thickness changed linearly film.Secondly,starting from the basic theory of thin film,according to the calculation of the characteristic matrix of the thin film,the influencing factors of the bandwidth and out-of-band cutoff of the narrow-band filter film system and the interference cut-off filter film system are analyzed.Combined with the smaller passband of the LVF,a wide cut-off region two characteristics,the design of the LVF film system used in the hyperspectral camera acquisition system is carried out.Finally,the preparation of the LVF was carried out with Leybold coating equipment.According to the test theoretical model of the tiny light spot,the test equipment for the linear gradient filter was improved,which effectively improved the accuracy of the spectral measurement of the linear filter.The optical and non-optical properties were tested and analyzed.The test data show that:in the working range of 500nm～800nm,the transmittance of the cut-off area of the LVF is less than 4%,and the peak transmittance of different wavelengths is greater than 80%.The error caused by the spectral curve of the LVF analyze and discuss.It provides a new method and new idea for the preparation process of linear progressive filter.