Design Of Infrared Dual-Band Athermal Optical System

Owing to the rapid development of the infrared detectors, infrared optical system design is alsoin progressing. Monochrome detector can only receive single band signal, in order to obtain theDual-band infrared optical system, in the1970s, double color detector was developed successfullybased on Material of HgCdTe, so the infrared dual-band systems get more applicationsin variousfields of military and civilian. Due to the effects of temperature to the infrared materials is muchlarger than ordinary visible materials, and infrared system usually work in changing temperatures,especially in the field environment, therefore, athermalisation is introduced to eliminate the influenceof temperature in optical systems.The temperature effect on the influence of the infrared imaging quality is discussed in this paper，analysis is made concerning temperature effect on three factors: refractive index of optical elements,curvature radius and center thickness of optical elements, and the space distance between opticalelements, and their relation to temperature variation are as well discussed, finally we found thechanging refractive index of optical elements make the biggest contribution to the image quality.Athermalisation is introduced to eliminate the influence of temperature in optical systems, and theadvantage and the disadvantage of the three athermalisations used currently are compared. The theoryabout the achromatism and athermalism is discussed in detail.In this paper, we design a touched multilens system and a separated multilens system in theinfrared dual-band based on the projective athermal chart and give the corresponding analysis. Adesign example with large relative aperture of infrared dual-band athermal optical system is givenbased on the unique athermal and achromatic characteristics of single-layer HDOE. To improve thediffraction efficiency, the Double-layer HODE structure is investigated using the Matlab softwareprogramming and simulation,and the diffraction efficiency of single-layer HDOE and double-layerHDOE was giving respectively, the result of simulation shows that the diffraction efficiency isimproved, and increase the transmission of the infrared system, finally, a design example is given baseon double-layer HDOE, the results show that the modulation transfer function is approached to thediffraction limit under the study temperature, the image quality is good, it is clarified HDOE has theability of the achromatism and athermalism.