Development of a Compact Optical See-Through Head-Mounted Display with Dual Focal Planes and Spatial Multiplexing Using Freeform Prisms

The current focus of research in the near-eye display and optometry field revolves around the concept of spatial multiplexing multifocal planes. The research focus has shifted towards near-eye display optical solutions that incorporate defocus stimulation functions. Developing a compact and lightweight head-mounted display with optical transparency, absence of stray light, and spatial multiplexing dual focal planes poses a challenging endeavor. This paper presents a design methodology for a compact head-mounted display utilizing spatial multiplexing and dual focal optical transmission, with a focus on the utilization of freeform prisms. The system is comprised of four optical elements and two micro-displays. The amplification of the displayed image on the dual micro-displays is achieved through the utilization of three prisms functioning as near-eye viewing optics. Additionally, a freeform lens is employed as an auxiliary component, which is affixed to the main wedge prism. This prism serves the purpose of correcting transmission distortion and facilitating an undistorted observation of the actual scene. Both focal planes are constructed using a micro-display measuring 0.49 inches, featuring a diagonal field of view (FOV) of 36°. The optical system has an F/number of 1.915, an eye box of 10 mm × 7 mm, and an eye relief of 19 mm. Simultaneously, this article also examines the monitoring of diverse forms of stray light within the optical system, and offers pragmatic and efficacious approaches to mitigate stray light. A comprehensive analysis and assessment of the system's performance were carried out. The findings indicate that the optical see-through head-mounted display exhibits satisfactory performance that aligns with the demands of real-world applications.