Exit Pupil Expander Diffractive Zones Non-Diffractive Zones
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional exit pupil expanders in diffractive display technology cause image brightness and uniformity losses, as well as color imbalance due to grating-related disturbances, limiting the performance of waveguide displays in personal displays like HMDs and HUDs.
Innovation Solution
Incorporating a combination of diffractive and non-diffractive zones in the exit pupil expander (EPE) region of waveguide displays, optimized through numerical methods to enhance geometric complexity and efficiency, allowing for improved light distribution and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional EPE gratings are used to expand the exit pupil, then the viewable area is extended laterally, but image brightness and uniformity are reduced due to grating losses and disturbances
Solution Approach 1:
The EPE grating is segmented into multiple zones with different grating orientations. By dividing the EPE into distinct grating regions, each zone can be optimized for specific light redirection paths, reducing overall losses and improving image brightness while maintaining lateral expansion capability.
Solution Approach 2:
Different regions of the EPE are assigned different grating line orientations and densities tailored to local optical requirements. This local optimization minimizes diffraction losses in critical areas while maintaining the overall exit pupil expansion function, thereby improving image brightness and uniformity.
2Area of stationary object
If conventional EPE gratings are used to expand the exit pupil, then the viewable area is extended laterally, but color balance is degraded due to grating-related disturbances
Solution Approach 1:
The EPE is divided into multiple grating zones with different orientations, allowing each zone to handle specific wavelength ranges or light paths separately. This segmentation reduces chromatic dispersion and grating-related color disturbances, improving color balance while maintaining lateral viewable area expansion.
Solution Approach 2:
The grating zones are designed with asymmetric orientations relative to the waveguide geometry, optimizing the diffraction angles for different wavelengths. This asymmetric design compensates for grating-induced color imbalances and improves overall color accuracy in the expanded viewable area.
3Ease of manufacture
If simple geometrical calculations are used to design EPE shape, then the design process is simplified, but the performance in terms of color balance and efficiency is suboptimal
Solution Approach 1:
The EPE design transitions from static geometric calculations to dynamic numerical optimization. By using computational methods that can adaptively optimize grating parameters, the design achieves superior optical efficiency and color balance while maintaining reasonable design complexity through automated optimization algorithms.
Solution Approach 2:
The design process incorporates numerical optimization that systematically varies multiple grating parameters (orientations, densities, zone boundaries) to maximize optical efficiency and color balance. This parameter optimization approach delivers significantly improved performance compared to simple geometric calculations.
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 significantly enhances image brightness, uniformity, and color balance, enabling more compact form factors and larger field of view capabilities for wearable displays while reducing image imperfections.
Implementation Method 1
light is directed from a projector to an in-coupling grating, which diffracts the incoming light into the waveguide, where it propagates via total internal reflections towards an out-coupling grating via an EPE grating to extend the viewable area of the display laterally
Implementation Method 2
where it propagates via total internal reflections towards an out-coupling grating
Implementation Method 3
non-diffractive zones (non-grating zones) between at least some of the diffractive zones... at which no diffraction, but only total internal reflection from a surface of the waveguide takes place
Data Source
Figure 1
Figure 2A~2B
AI summary
There is provided an exit pupil expander (EPE) for use in a diffractive display, the EPE comprising a plurality of diffractive zones on a waveguide and a plurality of non-diffractive zones between at least some of the diffractive zones.