Research Of Low Angle Effect Bandpass Filter For Iris Recognition

With the continuous development of image recognition technology,people have higher and higher requirements for the use of iris recognition systems,so the requirements of iris recognition systems for their core optical components,filters,are becoming more and more strict.According to the requirements of iris recognition system,this paper develops a lowangle effect bandpass filter with large angle and small offset.After studying the characteristics of a variety of thin film materials,a-Si:H,Si3N4 and SiO2 were respectively selected as high,medium and low refractive index materials.Through theoretical calculations,software simulations,and test analysis,it is found that the higher the refractive index of the spacer material in the cavity layer,the higher the equivalent refractive index of the cavity layer,and the better the low-angle effect of the thin film.Therefore,the use of a-Si:H and Si3N4 material pairs The cavity layer is designed and a a-Si:H material is used as the spacer layer.Plasma-assisted intermediate-frequency twin-target reactive magnetron sputtering equipment is used to deposit thin films,the ratio of Si and H in a-Si:H materials is adjusted by changing the amount of H2 gas following,which increases the refractive index of a-Si:H films,and this also increases the equivalent refractive index of the cavity layer.The technological parameters of a-Si:H material were determined.The processes of Si3N4 and SiO2 were also optimized through experiments,and the optical constants of the three materials were accurately fitted by means of the dispersion model.Utilizing the strong anti-interference imaging capability of near-infrared light in the 950 nm band range,with 950 nm as the center wavelength,according to the technical indicators of the iris recognition filter,combined with the optical film theory,and using the doublesided split principle to realize the front and rear surface films Department design.Calculate the deposition time of each film layer in the design of the film system,and then import it into the computer ACS program that controls the operation of the experimental equipment.Use the film material to optimize the obtained process parameters,complete the preparation of the front and rear surface filter films,and perform spectrometry on the developed samples test.The developed filter has a passband transmittance of more than 93% and an offset of 19.2 nm when light is incident at 0～38°.By modifying the protective layer process,the problem of peeling off the film during the boiling test was solved.The samples were tested for firmness,high and low temperature,and the samples did not fall off or crack.All the data can meet the technical indicators of the iris recognition bandpass filter.