Asymmetric Diffractive Grating for Waveguide Display Leakage
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Solution Overview
Problem
Conventional waveguide-based display devices with diffractive out-coupling gratings suffer from excessive optical leakage, particularly with TM-polarized input light, which affects energy efficiency, information security, and aesthetics in applications like head-mounted see-through displays.
Innovation Solution
A display structure featuring a waveguide with a diffractive out-coupling grating comprising a primary ridge and a secondary ridge, where the secondary ridge is parallel to the primary ridge and has a height less than the primary ridge, configured to couple light out via a second face, minimizing coupling towards the world side and enhancing efficiency for both TE- and TM-polarized input light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional thin film stacks are used to reduce out-coupling towards the world side, then out-coupling efficiency towards user's eye is improved, but optical leakage towards the world side becomes excessive
Solution Approach 1:
The patent applies asymmetry by creating an asymmetric ridge structure where the first ridge portion has a different height than the second ridge portion. This asymmetric configuration selectively directs diffracted light: the taller first ridge portion efficiently couples light towards the user's eye, while the shorter second ridge portion minimizes light coupling towards the world side, thereby resolving the contradiction between high out-coupling efficiency and reduced optical leakage.
Solution Approach 2:
The patent implements local quality by varying the height of different ridge portions within the same grating structure. The first ridge portion is designed with a specific height optimized for eye-directed out-coupling, while the second ridge portion has a reduced height specifically optimized to minimize world-side leakage. This localized differentiation allows each portion to perform its specific function optimally, simultaneously achieving high efficiency and low leakage.
2Productivity
If out-coupling grating couples light out via second face, then out-coupling efficiency is improved, but light coupling towards world side increases
Solution Approach 1:
The asymmetric ridge heights create different diffraction efficiencies for different exit directions. The first ridge portion's greater height provides strong diffraction coupling towards the user's eye, while the second ridge portion's reduced height creates weak coupling towards the world side. This asymmetric design ensures that the majority of coupled light energy is directed usefully to the user's eye, minimizing wasteful energy loss to the world side.
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 increases the out-coupling efficiency towards the user's eye while reducing coupling towards the world side, resulting in a higher eye-to-world out-coupling efficiency ratio, particularly for TM-polarized light, thereby improving energy efficiency and security in display devices.
Implementation Method 1
a waveguide comprising a first face and a second face for confining light in the waveguide by total internal reflection
Implementation Method 2
a diffractive out-coupling grating arranged on the first face. The out-coupling grating is configured to couple light out of the waveguide via the second face
Data Source
AI summary
A display structure and a display device are disclosed. The display structure includes a waveguide having a first face and a second face and an out-coupling grating arranged on the first face and configured to couple light out via the second face. The out-coupling grating includes a primary ridge having a first end facing a secondary lateral direction, a first ridge portion extending towards a primary lateral direction opposite to the secondary lateral direction from the first end, a second end facing the primary lateral direction, and a second ridge portion extending towards the secondary lateral direction from the second end. The first ridge portion has a first height, h1, and the second ridge portion has a second height, h2, less than the first height, h1.