Research On Key Technologies Of Optical System Of Helmet-mounted Display

Helmet mounted display(HMD), a revolutionary new display technique which is combined with optics, microelectronics, precision mechanism, and signal processing, has important application prospects in augmented reality(AR), virtual reality(VR), military, and anti-terrorism area. Among them, the application of helmet mounted display in military not only improves combat efficiency but also represents the highest level of helmet mounted display technique.As an important part of the helmet mounted display, optical imaging system should provide the user with a clear, bright symbol or a video image which can be superimposed on the real scenery, and this is its primary task. Besides, main requirements of the optical system are wide field of view(FOV), large pupil, good image quality, small volume, light weight and small offset of gravity center, etc. Till now, helmet mounted display has made noteworthy progress, but less weight, more compact structure, and better performance of human-computer interaction are still the perpetual goal of researcher, which are also the major obstacles that HMD can be used widely. So, the main works of optical design about an HMD are seeking balance and solving the conflict with all kinds of possible technologies.Under such background, this dissertation is focused on the optical system design of HMD with sorts of new technologies and components developed in recent years, such as off-axis design, freeform optics, holographic optical waveguide technology, and diffractive optical element, etc. Moreover, the dissertation tries hard to analyze and resolve potential technical difficulties of developing helmet mounted display in advance and makes its due contribution to the development of helmet mounted display.Based on a large amount of literature, the development situation of helmet mounted display at home and abroad is studied and the background and significance about the research topic are illuminated in the dissertation. At the same time, the tendency of this kind of system is concluded. Basic parameters of optical system of helmet mounted display are analyzed and according to different usage requirements. Finally and most importantly, combined with new technologies in recent years, three totally different configurations of HMD optical systems which are freeform prism, off-axis combiner, and holographic optical waveguide are studied systematically and comprehensively. During researching on freeform prism, three common kinds of mathematical descriptions of freeform surface are analyzed, and an optical system with this kind of configuration of which the surface is described with Zernike Polynomials is designed. During researching on off-axis combiner, a new method which is helpful to design an optical system of user-defined surface is presented for optical system design. Moreover, an optical system with this kind of configuration of which the combiner is desceibed with Gaussian radial basis functions is designed, and the design results show it has properties of big field of view, large exit pupil, long exit pupil distance, and high image quality. During researching on holographic optical waveguide, this dissertation first tries to simulate this kind of optical system with optical design software on basis of principle of optical holography and recursive technique of holographic optical element(HOE).Comprehensive image quality evaluation and performance comparison of three different configurations of optical systems are carried out, and the advantages and disadvantages of each kind of configuration are summarized. Research results can forsee that the off-axis combiner with freeform surface is the most feasible scheme to design a optical system for HMD at present.