硫系玻璃在长波红外无热化连续变焦广角镜头设计中的应用

Application of chalcogenide glass in designing a long-wave infrared athermalized continuous zoom wide-angle lens

针对市场上现有红外广角镜头大多采用定焦结构且缺乏无热化设计的现状,根据光学变焦系统的设计原理,设计了一种有效焦距范围为10~24 mm(变倍比为2.4:1)、视场角变化范围为34°~90°、工作波段为8~12μm、F/#为2.8的无热化连续变焦广角镜头。考虑到红外镜头多用在温度变化较大的使用环境中,系统设计选用了硫系玻璃NBU-IR2(Ge_(20)Sb_(15)Se_(65))以及常规红外材料锗(Ge)和硫化锌(ZnS)制备的六片镜片,通过合理分配各个镜片的光焦度及其空气间隔等参数,在连续变焦设计的基础上实现了无热化的光学设计效果。实验结果显示,系统在-40~60℃的温度范围内均可实现品质良好的红外热成像效果,调制传递函数全视场范围内均大于0.25。系统结构较为紧凑简单、质量较轻,仅在一片硫系玻璃镜片上设计了一处非球面,可有效控制光学系统的加工成本。整体设计适用于车载夜视等应用领域。

Current commercial wide-angle infrared lenses usually adopt simple fixed-focus design structures and lack proper athermalized design.To improve the performance of current wide-angle infrared lenses,the design principle of zoom optical systems and the theorem of passive athermalization were utilized to develop an athermalized continuous zoom wide-angle infrared lens.The effective focal length of the proposed system was 10-24 mm(zoom ratio:2.4:1),the field of view(FOV)was 34°-90°,the operating wavelength was 8-12μm,and the F number was 2.8.Considering the fact that infrared lenses were widely used in environments with large temperature variations,the proposed system was designed as a combination of six lens elements,including three fabricated with the chalcogenide glass of NBU-IR2(Ge20Sb15Se65)and three fabricated with conventional infrared materials such as germanium(Ge)and zinc sulfide(ZnS).By carefully allocating optical powers among the lens elements and properly controlling their air-spacing thicknesses,athermalization was realized by the proposed system design,in addition to the performance of continuous optical zoom.Simulation results show that the proposed system can produce thermal images with a close-to-diffraction-limit performance for the temperature range of-40 to 60℃.The Modulation Transfer Functions(MTFs)of the system are higher than 0.25 for the entire FOV.The system also has a compact/light-weight structure that only includes one aspheric surface on a chalcogenide glass lens element.Modern precision molding technique can be used to fabricate aspheric surfaces on chalcogenide glasses so that the fabrication costs of the proposed system can be controlled.The overall system design is suitable for the application of vehicle night vision.