Multispectral And Large Bandwidth Achromatic Imaging With A Single Diffractive Photon Sieve

As a new focusing imaging optical element based on the theory of light diffraction,photon sieves play a more and more important role in modern optical system.Photon sieve is a typical diffractive optical element(DOE),which is evolved from traditional Fresnel zone plate(FZP).FZP is constituted by a series of concentric absorbing and transmitting annular zones while photon sieve uses a great number of non-overlapping pinholes of different sizes to replace the clear zones.Photon sieve is superior to a counterpart FZP in that no extra support structure is required and higher resolution capability can be achieved due to effective suppression of sidelobes.However,as a typical DOE,photon sieves can work only at a designed single wavelength with near zero bandwidth due to the nature of strong wavelength dependence in DOEs.When working at multiple wavelengths or a wide spectral source,photon sieves will suffer from large chromatic aberration,which greatly limits its applications in optical image.Conventional photon sieves cannot be used in multispectral and large bandwidth imaging.In this thesis,a novel photon sieve that can image achromatically and simultaneously at multiple wavelengths with wide spectral bandwidth is proposed and demonstrated experimentally.The multispectral achromatic imaging with a single diffractive photon sieve is implemented with harmonic diffraction and wavefront coding,in which harmonic diffraction makes different diffracted orders of multiple harmonic wavelengths on a common focus while wavefront coding through coded distribution of the pinholes expands bandwidth of diffracted imaging.The detailed contents of the thesis include:(1)A generalized theoretical model that is suitable for any wavelength band is reviewed and set up,the diffractive field distribution at the focal plane is given,which forms the theoretical basis for optical design of photon sieves.(2)Analyses on the features of harmonic diffraction and wavefront coding are given.The characteristics of axial aberration(focal depth extension)of using wavefront coding in an image system and the behavior of focusing of different diffracted orders of multiple harmonic wavelengths in the harmonic diffraction are investigated,which forms the theoretical mechanism for the proposed multispectral and large bandwidth achromatic imaging.(3)Based on the above theories,a detailed multispectral and large bandwidth photon sieve is designed,in which four wavelength bands from 429.5-445.5 nm,491-509 nm,572.3-594.3 nm and 686-714 nm in the visible wavelength range with design parameters of aperture diameter 50 mm,focal length 500 mm,design wavelength 700 nm,and wavefront coding 30? are obtained,and the optical imaging performance of the photon sieve is simulated and analyzed using MATLAB.(4)Experimental verification of the designed multispectral photon sieve is conducted which include fabrication of the designed photon sieve,set up of the imaging system and the imaging experiments.The experimental results agree well with the design specifications.