Complemented Out-Coupling Element for Uniform Waveguide Display
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Solution Overview
Problem
Existing display devices with diffractive expander systems suffer from reduced brightness and unintended image exposure due to light diffracted through unintended surfaces, leading to non-uniform intensity distribution and potential unauthorized viewing of confidential information.
Innovation Solution
A display device with a complemented out-coupling element featuring buried diffractive ridges and solid complementing regions, optimized for single-sided output and uniform intensity distribution, where the ridges and regions have different refractive indices and a slant angle between 20° to 70°, directing over 70% of guided light through the intended surface and less than 30% through the unintended surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a conventional out-coupling element diffracts light through both major surfaces of the waveguide plate, then the eye box size is increased, but the brightness of the virtual image is reduced and unintended image exposure occurs
Solution Approach 1:
The out-coupling element is designed with spatially varying diffraction properties: the first region has diffraction structures optimized for directing light through the first major surface to the intended eye box, while the second region has different diffraction structures that prevent light diffraction through the second major surface. This local differentiation allows the system to maintain large eye box coverage while preventing brightness loss and unintended exposure from light leaking through the wrong surface.
Solution Approach 2:
The out-coupling element is divided into two distinct regions with different optical functions: a first region that actively diffracts light to the intended viewing area, and a second region that suppresses unwanted diffraction. This segmentation allows independent optimization of each region's diffraction characteristics, resolving the contradiction between maximizing eye box size and maintaining image brightness by preventing harmful light paths.
2Adaptability or versatility
If light is diffracted through the second major surface of the waveguide plate, then a second eye box is formed, but confidential information may be exposed and viewer disturbance occurs
Solution Approach 1:
The out-coupling element implements directionally selective diffraction by configuring the first region to diffract light only toward the intended first eye box while the second region is configured to suppress diffraction toward any unintended viewing directions. This local quality control ensures that even though the waveguide plate has two major surfaces, only the intended viewing sector receives diffracted light, preventing confidential information exposure while maintaining controlled viewing adaptability.
3Illumination intensity
If the out-coupling element diffracts most light through the intended surface, then brightness and diffraction efficiency are improved, but uniform intensity distribution across the eye box becomes difficult to achieve
Solution Approach 1:
The first region of the out-coupling element contains diffraction structures with specifically designed parameters (grating period, depth, orientation) that are optimized to produce uniform intensity distribution across the intended eye box while maintaining high diffraction efficiency. The local quality of these diffraction structures is tuned to balance brightness maximization with uniform spatial distribution, resolving the contradiction between these two performance requirements.
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 ensures a large eye box with uniform spatial intensity distribution, reducing power consumption and preventing unintended image exposure, while maintaining high diffraction efficiency for the intended viewing sector.
Implementation Method 1
The diffractive in-coupling element DOE1 forms guided light B1 by diffracting the input light IN1 at an interface between an incident medium and the waveguide plate SUB1
Implementation Method 2
The guided light B1 propagates through the waveguide plate SUB1 by repeatedly undergoing total internal reflection at interfaces between the waveguide plate SUB1 and the incident medium
Implementation Method 3
The out-coupling element DOE3 forms output light OUT1 by diffracting guided light B1 out of the waveguide plate SUB1
Data Source
AI summary
A display device (500) includes an expander device (EPE1) to form output light (OUT1) by diffractively expanding input light (IN1) that includes input light beams (B0P1, B0P2) representing an input image (IMG0). The output light (OUT1) includes output light beams (B3P1, B3P2) representing the input image (IMG0). The expander device (EPE1) includes: a waveguide plate (SUB1), a diffractive in-coupling element (DOE1) to couple the input light (IN1) into the waveguide plate (SUB1), a diffractive out-coupling element (DOE3) to form the output light (OUT1) by diffracting guided light (B1, B2) out of the waveguide plate (SUB1). The out-coupling element (DOE3) includes buried diffractive ridges (PR1) and complementing regions (FIL2) between the ridges (PR1), the buried diffractive ridges (PR1) have a first refractive index (n1), the complementing regions (FIL2) have a second different refractive index (n2). A slant angle (θS) of the ridges (PR1) is in a range of 20° to 70°.