Design And Research Of Infrared Dual-band Ultrathin Imaging System

The infrared dual-band imaging system can obtain target information in two different bands,which has strong environmental anti-interference ability,thereby effectively improving the detection and recognition of the target.Due to the limited types of materials that can pass through the infrared dual-band at the same time,it is difficult for current infrared dual-band imaging system to balance the imaging quality and the system structure.As a result,the size of the dual-band infrared imaging system is large and cannot be applied to those situations which have strict restrictions on size and weight.Compared to conventional system structure,the annular aperture ultrathin elements are processed on the front and rear surfaces of the same substrate material,and high quality imaging is achieved by a single optical element.Based on the characteristics of the annular aperture ultrathin system,the ultrathin imaging system working in the medium-long wave infrared dual-band is designed.The band range of the system is extended by introducing a multilayer diffractive optical element.The specific content of this research is as follows:This dissertation analyzes the structural characteristics of the ultrathin annular aperture imaging system,derives the calculation method of the obscuration ratio of the initial structure of this system,and the initial structure of the medium-long wave infrared dual-band imaging system is given by this method.Based on this initial structure,a medium-long wave infrared dual-band annular aperture ultrathin imaging system is designed by adjustment of the position and focus of each mirror reasonably.The focal length is 50 mm and F number is 1.The length of the system is 24 mm,and the ratio of total length to the focal length is 0.48.At the spatial frequency of 20 lp/mm,the MTF of the medium wave infrared which ranges from 3.7 to 4.8?m is greater than 0.62,and the MTF of the long wave infrared which ranges from 7.7 to 9.5?m is greater than 0.35.Besides,The athermalization of system is realized in the temperature range of-40? to 80?,and the system is machinable.In order to further expand the wavelength range of the system,this dissertation proposes a microstructured design method of multilayer diffractive elements with regard to ultrathin imaging systems.The diffractive optical theory is applied to the medium-long wave infrared dual-band ultrathin imaging system,and an ultra-thin imaging system structure containing multilayer diffractive elements is designed.The focal length is 50 mm and F number is 1.The length of the system is 25 mm,the ratio of the total length to the focal length is 0.50.At the spatial frequency of 20 lp/mm,the MTF of the medium wave infrared which ranges from 3 to 5?m is greater than 0.60,and the MTF of the long wave infrared which ranges from 8 to 12?m is greater than 0.26.The results show that the multilayer diffractive optical element can not only correct the aberration between the medium-long wave infrared band,but also realize the thermal stability of the hybrid refractive diffractive dual-band infrared system.The study of this dissertation provides a new idea for the implementation of miniaturized infrared dual-band systems.