Helmet-mounted Display Design Based On Free-form Surface

The helmet mounted display(HMD)technology originated from the military needs of the early 20 th century.With the continuous development of science and technology,it gradually evolved into a new display technology that integrates modern science such as optics,signal processing,computer science and precision machinery.As a part of life and work,these supplements have been widely used in education and training,medical care and entertainment,and the demand in the remaining areas is still increasing.Under this background,this paper carried out research work,completed the design of a variety of HMD optical systems,it also proposed a new structure for a dual-focal plane HMD optical system based on a free-form surface.Based on a large amount of literature research,the article first studies the development and application of HMD in the military and civilian fields and application of freeform surfaces in domestic and foreign respectively.It looks forward to the development trend and describes the background and significance of the subject.Subsequently,the vector aberration and its distribution characteristics in off-axis optical system were analyzed,combined with human eye characteristics and different application requirements,and the performance parameters such as field of view,exit pupil and distortion of HMD optical system were analyzed.Then,combining the parameter analysis and application requirements,the design of the helmet mounted display optical system was carried out:(1)Helmet mounted display optical systems with two different structures: free-form prism and off-axis synthesizer structure are designed respectively.The XY polynomial and Zernike polynomial are studied in detail,and when designing the structural system of the off-axis synthesizer,two optical systems are designed using the aspheric surface and free-form surface characterizing the shape of the combiner to compare.Among them the MTF has been improved greatly,the distortion and RMS spot radius have also been controlled well compared the free-form surface system with the aspheric surface.(2)Proposes and designs a new structure that can realize a dual-focal plane display of the HMD.This design uses a prism as the main structure,and selects two surfaces as freeform surface,one of them is a freeform polyhedron structure composed of two different characterization functions,which greatly increases the freedom of design.The design example shows that the optical system of this dual-focal-plane HMD has a field angle of 17°×16°,the diameter of the exit pupil is 8mm,the distance of the exit pupil is 18.25 mm,the working wavelength is 486?656nm,and the focal lengths are 95.2mm and 35.2mm respectively.This structure adopts with a single image generation unit,a single prism and two mirrors,which solves the traditional design problem of the multifocal HMD with complicated structure and large volume.(3)At the end of the article,the comprehensive performance comparison of the three structural design schemes is summarized,the advantages and disadvantages of each structure are summarized.The tolerance analysis of the processing and assembly of the dual-focal-plane HMD optical system was carried out.The results prove the feasibility and correctness of the design.