Harmonic Diffractive Optical Elements In The Dual-band Infrared Optical System

In infrared optical system, the design of diffractive optical elements and processinghas been very mature. Ordinary Diffractive Optical Element (DOE) has unique negativedispersion and negative differential thermal. Using this feature, we can designachromatic and athermal optical system. But every coin has two sides, it is also due tothe large dispersion, DOE could not used very well in a wide wave band optical system.DOE must match the refractive element to meet the needs of achromatism which makesthe structure of the optical system complex, the size and weight of the optical systemincreased.In response to the above problems of DOE, Harmonic Diffractive Optical Element(HDOE) has been used in a dual band infrared optical system design, which reduce thesize and weight of optical system, simplify the structure of the optical system, andreduce the difficulty of processing. Meanwhile, Application of HDOE solved theproblem of the large dispersion of the DOE on the wide-band and low diffractionefficiency in theoretically. This paper first introduces the research status of HDOE anddual-band infrared optical system. Then, it deduced the phase, imaging characteristics,and the diffraction efficiency characteristics of HDOE in theory. On the basis of thistheory, we give the dual-band IR optical system design principles and specificimplementation steps. In accordance to the guidance of the steps, add a HDOE to athree-lens IR Optical System. Based on the characteristics of HDOE, MWIR4mat+5order diffraction and LWIR10mat+2order diffraction imaging at the sameplace. The addition of harmonic diffractive surfaces increases the minimum processingline width of the diffraction plane and its processing depth of micro-structure, simplifythe process under the premise of the imaging quality meets the system requirements.