Evaluation Of Imaging Characteristics Of Micro-Nano Structured Planar Optical Elements

In recent years,optical imaging systems are developing in the direction of integration,light weight and miniaturization.Micro-nano structured planar optical elements have indispensable applications in many important fields such as civil imaging,military detection and aerospace because of their small size and light weight,and also their excellent performance of high resolution and wide wave band.Micro-nano structured planar optics manipulate the wavefront through phase mutation to achieve imaging,while conventional optics achieve imaging through phase accumulation,due to the difference in their imaging nature,the evaluation method of image quality evaluation of conventional optics cannot be fully applicable.Therefore,an exploratory study on the imaging characteristics of micro and nano structured planar optical elements is carried out with the following three main areas of research:(1)The evaluation system of imaging characteristics of planar optical elements with micronano structure is established.Based on the principle of phase modulation of micro-nano structure planar optical elements and the image quality evaluation test method,a set of micro-nano structure planar optical elements imaging characteristics evaluation system with spectral characteristics,focusing characteristics,resolution characteristics and clarity was established.First,the spectral transmittance is used to evaluate the spectral characteristics of the micro-nanostructured element;second,the focusing characteristics of the micro-nano-structured element are evaluated by using the focusing spot FWHM and the wide band focal plane position;then,the resolution characteristics of the micro-nano-structured element are evaluated by using the number of line pairs that can be resolved,and the reference-free image quality evaluation algorithm is used to evaluate the imaging clarity of the micro-nano-structured element;finally,the hierarchical analysis method is used to The weight judgment matrix is fitted according to the application scenario of imaging,and the weight coefficients are calculated to give a comprehensive evaluation function.(2)Design of a platform for evaluating the imaging characteristics of planar optical elements of micro and nano structures.According to the established evaluation system,an evaluation platform for imaging characteristics of planar optical elements of micro-nano structures is designed with a light source system,a displacement detection system and a software control system.The light source system adopts a Newtonian reflective parallel light tube composed of off-axis parabolic mirror and reflector,and realizes parallel light of different wavelengths and infinity target objects through filters and target plates;the displacement detection system adopts a four-dimensional displacement module composed of an electronically controlled twodimensional translational displacement stage and a lifting and lowering rotary stage,as well as a detection module composed of a spectrometer,a spot analyzer and a CCD,which can realize spectral,The software control system adopts the control scheme of spatial scanning,which can realize the testing of imaging characteristics and data processing and analysis of any position within the spatial range of 100×100×50mm.(3)Evaluation of Imaging Characteristics of Micro-Nano Structured Planar Optical Components.Using the evaluation platform built,the imaging characteristics of Fresnel lens and a single micro-nano structured planar optical component designed for a wavelength of 550 nm were evaluated separately.The experimental results showed that the spectral transmittance of the components in the visible light range reached 85% and 97%,which is consistent with the designed transmittance of 85% and 97%.Secondly,it was demonstrated that the focused spot FWHM,focal plane position and wavelength are related.Finally,the comprehensive evaluation value of the imaging characteristics was calculated by the comprehensive evaluation function,which was consistent with the experimental data of the various imaging characteristics of the two components,thereby verifying the feasibility of the micro-nano structured planar optical component imaging characteristic evaluation system constructed in this paper.