The Study Of Nanoscale Light-guide In Head Mounted Display Technology

As an indispensable technology,the Head Mounted Display(HMD)plays an important role in various applications,such as military,education,health-care and entertainment,arisen from the unique feature of immersive display,real-time interaction and portable format.The HMD has been promoted by the rapid development of micro-display,sensor technology,multi-focus display,retinal projection display,light field display,holographic display towards lighter and thinner format,more intelligence and hominization.Nowadays,the existence of the visual fatigue is the main factor which restricts the development of the helmet mounted display technology.In this paper,a HMD technology based on diffractive optical elements has been proposed for the sake of more natural display experience by reconstructing the light field near the eyes with the pixelated nano-gratings.A super-view distribution enables the accommodation of monocular vision and reduces the visual fatigue caused by accommodation-convergence conflict.Firstly,the structure of the nano-grating is optimized by Finite-Difference Time-Domain analysis.We theoretically calculated the influence of the groove depth and the duty cycle of the nano-grating on the diffraction efficiency.The positioning accuracy of the view points is accomplished by the combination of generalized grating equation designing the cycle and orientation of the pixel nano-grating.Then,we expound the principle of the UV continuous variable space frequency lithography system and calibrate the original location in the 4F system based on the precision of this system.The field view stop is fabricated to restrict the scale of the pixel nano-grating and the nano lens is fabricated through the two-beam interference system.The principle of the effect of HMD based on binocular parallax and the super-view theory forming monocular accommodation has been analyzed by the physiological structure and characteristics of the human eyes.The phase information based on pixelated nano-grating and the amplitude information of graphic coding is combined to reconstruct the near eye light field distribution,accomplishing a natural display effect of virtual reality.In the experiment,a 3cm*3cm nano-lens creates 4 view-points with an angular separation of 1 degree.When we combine the nano-lens with the amplitude information,a focal depth over 3cm is achieved.As a result,it is verified that the monocular accommodation can providing a good scheme to reduce the visual fatigue.