Broadband Diffractive Imaging Of Photon Sieves Based On Wavefront Coding

Diffractive optical elements(DOEs)have increasingly shown a promising type of optical imaging components in modern optical systems,such as ultra-large space telescope primaries,THz optics for tomographic imaging,X-ray or EUV lithography that are difficult,or even impossible,with conventional glass-based refractive optics,because of their unique characteristics of compact size,light weight,and high degree of design flexibility.However,DOEs suffer from large chromatic aberration and on-axis imaging limitation due to the strict constrain conditions imposed by optical diffraction and interference,and therefore,DOEs can work only at a single designed wavelength and at near-zero field-of-view,which significantly limits the applications of DOEs,especially in optical imaging.Photon sieves is a newly developed diffractive focusing element in recent years.To achieve broadband achromatic and wide field-of-view imaging of a photon sieves,we proposed and demonstrated a broadband and wide field-of-view diffractive imaging technology of the photon sieves based on wavefront coding.The proposed methodology of wavefront coding in a diffractive photon sieves breaks the limit of inherent wavelength-dependence in DOEs,suppresses off-axis aberrations and opens up new possibilities for manipulating wavefront phase and achieving new applications or new functionalities of DOEs.The main content and innovative results are as follows:1.We proposed and demonstrated a broadband diffractive imaging technology of the photon sieves based on wavefront coding,in which a designed separated bulk aspheric phase element is placed in front of a conventional photon sieves(CPS)to form separated wavefront coding photon sieves system(SWFCPSS).SWFCPSS reduces the sensitivity of point spread function(PSF)and modulation transfer function(MTF)to incident wavelength.Through the use of the ambiguity function and the stationary-phase method,the cubic wavefront coding for a broadband achromatic SWFCPSS imaging are readily found with a cubic coding parameter?directly correlated to the operation bandwidth.The SWFCPSS(?=20?)imaging is demonstrated and compared with that of a CPS of the same numerical aperture(diameter:50mm and focal length:500mm).Both theoretical simulation and experimental results show that the working bandwidth of the SWFCPSS reaches 14nm compared with 0.32nm in CPS,which represents that an extension of imaging bandwidth of the proposed system is at least 44 times that of the conventional one.It should be noted that the demonstrated method works generally for all types of DOEs(e.g.,Fresnel zone plate,Fresnel lens)because of the same physical mechanism.The proposed method opens a new direction of extending the applications of DOEs to work in a broadband wavelength range in a generalized way2.A broadband wavefront coded photon sieves(WFCPS)is proposed and demonstrated,in which the pinhole pattern in a photon sieves is wavefront coded and generates equal focusing power for a wide range of operating wavelength in a single thin-film element without any auxiliary elements.Wide field-of-view imaging can also be obtained with WFCPS.The demonstration of the proposed WFCPS(?=30?)imaging is performed and compared with that of a CPS of the same aperture(50mm)and focal length(500mm).Results show that the working bandwidth of the WFCPS reaches 28nm within a wide field-of-view ranging from-4~o to 4~o compared with 0.32nm bandwidth and field-of-view from-0.5~o to 0.5~o of the CPS.Both theoretical simulation and experimental results show that broadband and wide field-of-view imaging can be obtained with a WFCPS.Further demonstration of the achromatic imaging with a bandwidth of 300nm(in whole visible region from 400nm to 700nm)is also performed with a WFCPS integrated with a refractive element.3.Thin-film diffractive primary lens can extend the aperture size,reduce the volume and achieve high resolution,so DOEs are hot research orientation and important research contents in space telescope.However,DOEs suffer from large chromatic aberration in space telescope imaging.Combining broadband achromatic characteristic of the WFCPS and Schupmann chromatic aberration correction approach,a broadband diffractive space telescope system is designed with WFCPS primary lens(aperture:500mm),covering the bandwidth of 200nm(from 450nm to 650nm)in visible spectrum region.The dissertation presents a design method for the space telescope system with WFCPS primary lens,which plays an important role in diffractive space imaging technologyThe theoretical thoughts,design methods,experiments and conclusions achieved in this dissertation can be the new perspective and scientific evidence of DOEs(e.g.,Photon sieves,Fresnel zone plate and Fresnel lens)applied in optical imaging.