Narrow-Angle Backlight Assembly for HMD Stray-Light Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional backlit displays in head-mounted devices suffer from undesirable visual artifacts due to angularly broad light emissions exceeding the imaging capability of the lenses, leading to stray light, ghosting, and glare, which are not effectively addressed by existing technologies.
Innovation Solution
Implementing a narrow angle backlight assembly that restricts the angular cone of light to 10-15 degrees using an angle-restricting layer or an angle-preserving waveguide, combined with a collimating lens assembly, to ensure light is focused within the eye box of the HMD, thereby reducing stray light and enhancing image clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional broad-spectrum backlights are used in HMDs, then the display can be illuminated, but angularly broad light emissions exceed the imaging capability of lenses causing stray light, ghosting, and glare
Solution Approach 1:
The patent applies local quality by making different parts of the backlight system have different angular emission characteristics. Specifically, the backlight is designed to emit light at specific angles (e.g., 0 degrees normal to the display surface, or specific off-axis angles like 10-20 degrees) rather than uniformly in all directions. This selective angular emission ensures that light is directed precisely where needed through the lens system without creating stray light or ghosting artifacts from off-angle emissions.
Solution Approach 2:
The patent changes the angular parameter of light emission from the traditional broad-spectrum (180-degree) backlight. By controlling the backlight to emit light within a narrow angular range or at specific discrete angles, the system transforms the illumination characteristic to match the numerical aperture and imaging capabilities of the HMD lenses, thereby eliminating optical artifacts while maintaining effective illumination.
2Strength
If conventional spherical lenses are used, then the HMD can be manufactured, but lens size is large and lens power is insufficient
Solution Approach 1:
The patent employs Fresnel lenses instead of conventional spherical lenses. Fresnel lenses utilize a series of concentric annular grooves or facets that approximate the curvature of a spherical lens, enabling the achievement of high lens power in a much thinner and more compact form factor. This curvature-based design allows the HMD to achieve the necessary optical power for proper image formation and focus while significantly reducing the physical size and weight of the lens assembly.
3Adaptability or versatility
If Fresnel lenses are used to increase lens power, then the field of view and depth of field are enhanced, but the HMD becomes more complex
Solution Approach 1:
The patent uses Fresnel lenses which can be manufactured using replication or molding processes. The complex curved surface profile is copied repeatedly across the lens surface through master mold fabrication, allowing high-precision optical surfaces to be produced cost-effectively at scale. This copying approach simplifies the manufacturing process compared to traditional spherical lens grinding and polishing, reducing overall device complexity despite the advanced optical performance.
4Reliability
If broad angular light emission is used, then the backlight can illuminate the display, but light strikes lenses at angles beyond imaging capability causing visual artifacts
Solution Approach 1:
The patent optimizes the angular parameter of backlight emission to match the numerical aperture of the lens system. By controlling light to emit within a specific angular range (e.g., normal incidence or specific off-axis angles within the lens acceptance cone), the system ensures that all emitted light falls within the imaging capability of the lenses, maximizing light utilization efficiency while maintaining high image quality and eliminating visual artifacts.
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 narrow angle backlight assembly minimizes undesirable visual effects, provides a suitable eye box size for varied user positions, and maintains efficient illumination, ensuring a clear and immersive virtual or augmented reality experience.
Implementation Method 1
an angle-preserving waveguide, which directs light from the backlight assembly to a display surface of the display device
Implementation Method 2
a collimating lens assembly, which may include a field lens and a focal lens arranged in a telecentric configuration
Data Source
AI summary
Methods and systems relating generally to information displays, and more particularly to systems and methods for backlight assemblies for information displays that emit an angularly narrow cone of light. A backlight assembly that emits a narrow angular cone of light can be particularly beneficial in a head-mounted display configuration, such as for use as part of virtual reality or augmented reality systems, where the head-mounted display comprises a lens assembly that directs light from an information display to the eyes of the user. Such a backlight assembly configuration may help reduce undesirable visual effects like flood illumination, ghost images, glare, and scattering.