Compact Head-Mounted Display Waveguide for Wide FOV
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Solution Overview
Problem
Conventional compact optical systems for head-mounted displays (HMDs) face challenges with large eye-motion-box (EMB) limitations, sensitivity to eye movements, and impracticality due to bulkiness and low field-of-view (FOV), which hinder effective image viewing, especially in mobile applications like cellular phones.
Innovation Solution
An optical device with a light-transmitting substrate featuring two major surfaces, a coupling-in element, a first flat reflecting surface for total internal reflection, a second flat reflecting surface for coupling out light, and a redirecting optical element, utilizing different refractive indices and dynamic partially reflecting surfaces to enhance FOV and EMB, allowing for improved image quality and mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional free-space optical module is used to increase field-of-view (FOV), then the FOV is improved, but the system becomes larger, heavier and bulkier
Solution Approach 1:
The patent combines the imaging lens and combiner into a single optical module that is integrated directly onto the display. This merging eliminates the need for separate free-space optical components, thereby reducing system size and weight while maintaining or improving field-of-view performance through the waveguide-based optical path
Solution Approach 2:
The optical module is nested within or directly attached to the display structure, with the waveguide substrate serving as both the optical element and structural component. This nesting approach allows the optical system to be embedded within the display housing, significantly reducing overall system bulk and weight compared to conventional external optical modules
2Volume of moving object
If compact optical solutions are implemented to reduce system size, then the system becomes more compact, but the eye-motion-box (EMB) becomes very small and the system becomes sensitive to eye movements
Solution Approach 1:
The patent utilizes the third dimension by implementing a waveguide-based optical path that extends light propagation through the thickness of the substrate rather than relying solely on lateral spacing. This vertical dimension allows for a compact footprint while maintaining a larger effective eye-motion-box, as the optical path length is determined by the waveguide thickness and internal reflection geometry rather than lateral component spacing
Solution Approach 2:
The patent changes the refractive index parameter by using a waveguide substrate with specific refractive index properties that enable total internal reflection. This parameter change allows for precise control of light propagation angles and paths, creating a larger eye-motion-box that is more tolerant of eye movements while maintaining compact overall dimensions
3Length of moving object
If the optical system is made compact for mobile applications, then mobility is improved, but image viewing quality deteriorates due to poor display quality
Solution Approach 1:
The patent replaces conventional free-space optical mechanisms with a waveguide-based optical system that uses total internal reflection and controlled light coupling. This substitution eliminates the need for precise mechanical alignment of multiple optical components, as the waveguide structure provides inherent optical path stability. The result is a compact device that maintains high image viewing quality through robust optical coupling rather than mechanical precision
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
The solution provides a compact display system with a wide FOV and large EMB, enabling high-quality image viewing with large eye movements, suitable for HMDs and mobile devices, overcoming the limitations of existing technologies.
Implementation Method 1
a first flat reflecting surface located between the two major surfaces of the light-transmitting substrate for reflecting the coupled-in light waves to effect total internal reflection from the major surfaces of the substrate
Implementation Method 2
a second flat reflecting surface having at least one active side located between the two major surfaces of the light-transmitting substrate for coupling light waves out of the substrate
Data Source
AI summary
There is provided an optical device, including a light-transmitting substrate having at least two parallel major surfaces, edges and an output aperture, an optical element for coupling light waves into the substrate to effect total internal reflection, a plurality of redirecting elements positioned outside of the substrate comprising at least two spaced-apart redirecting elements having a selectable laterally displaceable reflection-transmission ratio, and at least one reflecting surface having at least one active side located between the two major surfaces of the light-transmitting substrate for coupling light waves out of the substrate, wherein light waves trapped inside the substrate are coupled out from the substrate through the output aperture substantially inclined in relation to the normal to the substrate major surfaces, and are reflected from the redirecting elements into a viewer's eye, and wherein at least one of the redirecting elements is lateral displaceable in relation to another redirecting element.