Design And Analysis Of Diffractive Achromat In Broadband

Diffractive lenses have the advantages including small size,light weight,and loose tolerances,which are expected to replace traditional refractive lenses in large-aperture,lightweight,and space telephoto optical systems.However,the diffractive lens caused by the diffraction mechanism has the problem of strong negative dispersion,and it is difficult to meet the needs of wide-band imaging due to the complexity of the imaging environment and the improvement of the resolution ability of the detection element.Therefore,it is currently mostly used in monochrome imaging systems or structure of Schupmann.This structure uses another diffractive lens with the opposite power to the main mirror to eliminate chromatic aberration,but the system introduces other aberrations while eliminating chromatic aberration.Besides,the bandwidth and field of view of the system are limited.Therefore,the current chromatic aberration correction of the diffractive element in the large-aperture,wide-band imaging system is more dependent on the correction of the subsequent lens or optical path.To improve the practicality of the system further,it is necessary to start with the diffractive lens itself to eliminate chromatic aberration.Aiming at the problem of serious dispersion and poor image quality when traditional diffractive lenses work in wide band,this paper proposes a design method for a monolithic partitioned achromatic diffractive lens based on RGB three bands,using scalar diffraction theory to simulate two partitions of equal width and equal area,and compare and analyze with traditional diffractive lenses.Considering the existing experimental conditions,a two-step ordinary diffractive lens and two achromatic diffractive lenses with different partitioning modes were prepared.Through the inspection and comparison of the imaging performance of the three lenses,it is proved that the design can achieve chromatic aberration correction to a certain extent,and has the potential to be applied in wide-band imaging systems.The main research contents of this article including:(1)According to the dispersion characteristics of the diffractive lens itself and the current needs in wide-band imaging applications,we design a diffractive achromats with two different partition modes,equal width and equal area,model and simulate.Comparing and analyzing the point spread function and diffraction efficiency with ordinary diffractive lenses.(2)According to the design method proposed in this paper,combined with the target parameters and the existing experimental conditions,a two-step mask corresponding to the three lenses is designed;the alignment engraving and reactive ion etching methods are successfully used on the same substrate three lens structures were prepared.(3)We Build the diffraction efficiency test light path and the imaging test light path,and perform the diffraction efficiency test,star point board test,resolution board test,and color fidelity imaging test on the three lens structures respectively.Comparing the imaging effects of two achromatic diffractive lenses with ordinary diffractive lenses,it is proved that the partitioned achromatic diffractive lens can realize chromatic aberration correction and has the ability of wide-band imaging;then we comparing and analyzing the difference in imaging effect between equal width and equal area,summarizing the relationship between the chromatic aberration correction effect of the subregional achromatic diffractive lens and the corresponding microstructure area of ? ? each band,which lays a good foundation for the design and development of the subsequent achromatic diffractive lens.