Design And Analysis Of Fresnel Lenses Used In Infrared Imaging

With the continuous improvement of processing technology, optical functional elements are highly demanded and their sizes tend to miniaturization. Diffraction-optics has made a rapid development in recent years, and Fresnel lenses have the advantage of small size, light weight with wide potential applications, especially in infrared detection and infrared laser rangefinders.Based on previous work, research on the infrared binary Fresnel lenses including the design and algorithms for binary diffractive surfaces, and the analysis of the impact of the errors of main parameters on the diffractive efficiency have been studied in this thesis.Firstly, the fundamental theories such as the scalar diffraction theory and the vector diffraction theory for the design of DOE (diffraction optics element) have been investigated. The algorithms based on the scalar diffraction theory and the design method under the sub-wavelength condition has also been studied.Secondly, the relationship between the diffractive efficiency and the main parameters of the micro-structures of binary Fresnel lenses has been studied. The simulation has been done using the MATLAB software.Thirdly, based on the theoretical study, the design results of binary Fresnel lenses with 3mm and 30mm diameters under the 1064nm working wavelength,100mm focal length and 0.3° field angle have been obtained. The analysis results have shown that the diffractive efficiency could be 93.36% at 3mm diameter and 90.13% at 30mm diameter, and the sizes of defocused spots also meet the requirement.Fourthly, the results also show that, for the change of the wavelength of light, the diffractive efficiency could be changed much greater when the incident light wavelength become shorter than longer, and for the depth errors of steps, the tolerance of the depth error of each step could be up to 5% with little impact on the diffractive efficiency.