The Study On The Middle Infrared Hybrid Objective Lens And Its Diffractive Microstructure

In recent years,the design of hybrid refractive diffractive optical systems has made considerable progress,and the refractive diffractive hybrid optical systems are becoming more and more widely used.Comparing to the traditional refraction optical system,the refractive diffractive optical system has more compact structure,lighter weight and shorter length.Moreover,the dispersion effect of optical system can also be improved with the addition of diffractive optical elements.It has a wide range of realistic and potential applications in telescopes,space optical remote sensing instruments,medical imaging,infrared night vision and other fields.At present,many studies at home and abroad concentrate on the processing methods of diffractive optical elements,including single point diamond turning,photolithography,ion beam etching,nanoimprint and other main methods.The images generated by photolithography have high transverse(X,Y direction)accuracy.High precision steps can be formed in the longitudinal direction(Z direction)by optical coating,thus forming a high precision diffraction structure.This is the basic technical path of this paper.In this paper,based on the application requirements of the hybrid diffractive optical system,by analyzing and calculating the parameters required by the objective,a medium infrared diffractive compound mirror,with a working band of 3.7~4.8,a focal length of 64 mm and a F number of 1.6,has been designed.The diffraction microstructures is fabricated by photolithography and thin film deposition.The total weight and total length of the system are reduced by about 40% comparing to the fully refracted objective lenses with the same performance.The imaging quality and tolerance are analyzed,which provides technical reference for the processing error of objective lens.Three lenses of the lens are made.The diffraction microstructures of the 9 rings with 16 steps are fabricated on a planar silicon lens by means of photolithography and thin film deposition.The microstructure and transmittance of the diffractive microstructures are tested.The cause of the error is analyzed and some solutions are given accordingly.The diffractive optical element with a working band of 3.7~4.8 micron m can meet the requirements of the performance.Finally,aiming at the problems encountered in the research process and the deficiencies found in the research,the solutions and future research directions are proposed.The research in this paper is conducive to the design and fabrication of the mid infrared diffractive elements,and provides a new reference for the development of the mid infrared diffractive refractive objective.