Dual Light Guide Plate HMD for Eye Box Expansion
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Solution Overview
Problem
Wearable head-mounted displays (HMDs) face challenges in achieving both miniaturization of the optical system and expansion of the eye box while maintaining good visibility and image quality, as existing designs either compromise on size or optical efficiency.
Innovation Solution
The use of a dual light guide plate system with parallel main surfaces and angled emission reflective surfaces to confine and redirect image light, allowing for both miniaturization of the optical system and enlargement of the eye box, while maintaining image quality and visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a pupil duplication unit and light guide plate are used to enlarge the eye box, then the eye box is enlarged, but the size of the optical system increases and optical efficiency is reduced
Solution Approach 1:
The patent utilizes the thickness dimension of the light guide plate to enable multiple internal reflections that duplicate pupil images. By arranging reflective surfaces at specific angles within the plate thickness, the system enlarges the eye box in the lateral direction while keeping the overall optical system volume compact, resolving the contradiction between eye box area and optical system volume.
Solution Approach 2:
The patent embeds multiple reflective surfaces and pupil image formations within the single light guide plate structure. The light guide plate contains nested functional elements including incident surfaces, emission reflective surfaces, and multiple total reflection interfaces, allowing compact integration of pupil duplication functionality without increasing external dimensions.
2Shape
If the long side direction of the small display is increased to match the horizontal aspect ratio, then the image aspect ratio is correct, but the width of the virtual image generation unit increases
Solution Approach 1:
The patent rotates the small display so its long side is vertical, then uses the light guide plate's thickness dimension and angled reflective surfaces to stretch the virtual image horizontally. This allows correct horizontal aspect ratio without increasing the physical width of the display or virtual image generation unit, as the horizontal expansion is achieved through optical path folding in the thickness dimension.
Solution Approach 2:
The patent employs angled and curved reflective surfaces within the light guide plate to redirect and expand the light path. The emission reflective surfaces are positioned at specific angles to diverge light rays horizontally, creating a wider virtual image from a vertically-oriented display without increasing the physical footprint of the generation unit.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables a compact HMD design that enhances the eye box size, improves image visibility, and reduces the overall size of the optical system, addressing the limitations of previous designs.
Implementation Method 1
a first light guide plate and a second light guide plate that duplicate the image light from the projection unit, in which the first light guide plate and the second light guide plate each include a set of parallel main surfaces that confine the image light by internal reflection
Implementation Method 2
the first light guide plate includes an incident surface that reflects the image light inward, and two or more emission reflective surfaces that emit the image light to the second light guide plate
Data Source
AI summary
A head mounted display displays an image in a user's view field and includes a projection unit projecting image light from an image display unit; and a first and second light guide plates that duplicate the image light from the projection unit. The first and second light guide plates each include a set of parallel main surfaces confining the image light by internal reflection. The first light guide plate includes an incident surface reflecting the image light inward, and two or more emission reflective surfaces emitting the image light to the second light guide plate. The incident and emission reflective surfaces are parallel to each other at an angle different from the main surface, and the second light guide plate includes an input unit coupling the image light from the first light guide plate inward, and an output unit emitting the image light to the user's pupil.