Research On Diffractive Optical Elements Applied In Novel Display Technologies

In recent years,in order to fulfill people's higher demand in display,such as three-dimensional display,larger color gamut and the ability to overlap on the real environment,a variety of novel display technologies flourish.However,the development of them is limited by the performance of some key devices.Thus,the study of these key devices is of great importance.Diffractive optical element(DOE)has been popular among the optics community for its advantages such as special optical character,large design freedom,high energy efficiency,small volume,light weight and so on.It has been widely used in multiple fields.In display filed,many researches have been done on designing those key elements using diffractive optical elements.However,their performance have not meet the requirements of these system so far.Therefore,based on our predecessors,we have further studied the diffractive optical elements applied in novel display technologies,including beam shaper in laser projection display,directional diffuser in light-field display and coupler in optical see-through head-mount display.First,we conduct the research on beam shaper in laser projection display.The code used to simulate the performance of the DOE is firstly built.Based on this,the design of DOE applied as beam shaper in laser projection display using geometrical transformation(GT)and iterative Fourier transformation algorithm(EFTA)are conducted.The result Root Mean Square Error(RMSE)of the output beam is 23.97%and 26.15%respectively.In order to improve the intensity uniformity,an algorithm composed of GT,IFTA and particle swarm optimization(PSO)is proposed.The result RMSE using this algorithm is 11.42%,far better than the former ones.Second,the research on directional diffuser in light-filed display is conducted.Based on the former chapter,we believe designing directional diffuser with DOE is a promising way.In order the fulfill the functionality of the directional diffuser,which includes enlarging the divergence angle of multi-color beam accurately,making the intensity distribution of the multi-color diffused beam be uniform subject to angles and identical,an improved PSO algorithm is proposed.Pre-optimized initial structures and adaptive weight strategy are employed in the algorithm to achieve better and identical shaping performance for multiple colors.Accordingly,a DOE for shaping light from green and blue LEDs has been designed and fabricated.Both experiment and numerical simulations have been conducted and the results agree well with each other.15.66%RMSE and 0.22%RMSE difference are achieved from the simulation and similar result is obtained in the experiment.Third,the study on coupler in optical see-through head-mount display is conducted.In order to solve the trade-off problem between field and light efficiency,the design of space-variant volume holographic grating is proposed.Based on this,the design of the high efficient waveguide display is proposed.The local period and the slant angle of the SVHG vary along its tangential direction,changing angular selectivity curve of the local gratings,which makes light coupled out with high efficiency at target areas only.As a result,the FOV is enlarged without using the multiplexing scheme,achieving high efficiency and large FOV at the same time.Experiment shows that the proposed display can achieve 31.9%system efficiency for broadband light source and 52.3%for coherent light source,20° FOV,as well as high brightness uniformity.We believe that this design can be widely applied in various fields which adopt augmented reality technologies in the future.At the last of the paper,the potential improvements are discussed and the direction of the future researches is shown.