Liquid Crystal Light Guide Element for AR Exit Pupil Expansion
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Solution Overview
Problem
In augmented reality glasses, the use of an intermediate diffraction element to expand the exit pupil leads to a decrease in light utilization efficiency, resulting in reduced image brightness.
Innovation Solution
A light guide element with an incidence diffraction element, an intermediate diffraction element, and an emission diffraction element, where the diffraction elements include a liquid crystal layer with a specific alignment pattern and pitch configuration, optimizing the light utilization efficiency by adjusting the pitch and rotation angle of the liquid crystal layers to enhance image brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If an intermediate diffraction element is disposed to expand exit pupil, then the exit pupil is expanded, but the light utilization efficiency decreases and image brightness decreases
Solution Approach 1:
The patent changes the pitch parameters of the liquid crystal layers in the diffraction elements. Specifically, it sets the pitch of the intermediate diffraction element's liquid crystal layer to be larger than that of the incidence diffraction element, and sets the pitch of the emission diffraction element's liquid crystal layer to be smaller than that of the incidence diffraction element. This parameter optimization improves light utilization efficiency while maintaining exit pupil expansion.
Solution Approach 2:
The patent introduces liquid crystal layers with controllable pitch and rotation angles into the diffraction elements. The liquid crystal layers can dynamically adjust their optical properties to optimize both exit pupil expansion and light utilization efficiency, resolving the contradiction between these two parameters.
2Area of moving object
If an intermediate diffraction element is disposed to expand exit pupil, then the exit pupil is expanded, but the brightness of the displayed image decreases
Solution Approach 1:
The patent optimizes the pitch parameters of liquid crystal layers in all three diffraction elements (incidence, intermediate, and emission). By setting specific pitch relationships (Pe > Pin and Pout < Pin), the system maintains high light utilization efficiency, which directly preserves image brightness while achieving exit pupil expansion.
Solution Approach 2:
The patent uses liquid crystal materials with specific optical properties in combination with diffraction grating structures. This composite approach allows simultaneous optimization of exit pupil expansion and light efficiency, maintaining image brightness while expanding the exit pupil.
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 effectively increases light utilization efficiency and maintains image brightness, even when an intermediate diffraction element is used to expand the exit pupil, thereby improving the overall performance of the image display apparatus.
Implementation Method 1
an incidence diffraction element, an intermediate diffraction element, and an emission diffraction element that are provided on the light guide plate
Implementation Method 2
a liquid crystal layer that is formed of a composition including a liquid crystal compound and has a liquid crystal alignment pattern in which a direction of an optical axis derived from the liquid crystal compound changes while continuously rotating
Implementation Method 3
in a cross-section of the liquid crystal layer observed with a scanning electron microscope, bright portions and dark portions derived from a liquid crystal phase are tilted with respect to a main surface of the liquid crystal layer
Data Source
AI summary
Provided are: a light guide element that includes an intermediate diffraction element to expand exit pupil such that a light utilization efficiency is high and a decrease in the brightness of an image to be displayed can be suppressed; and an image display apparatus. The light guide element includes a light guide plate, an incidence diffraction element, an intermediate diffraction element, and an emission diffraction element, in which the incidence diffraction element, the intermediate diffraction element, and the emission diffraction element include a liquid crystal layer that is formed of a composition including a liquid crystal compound and has a liquid crystal alignment pattern in which a direction of an optical axis derived from the liquid crystal compound changes while continuously rotating in at least one in-plane direction, in a cross-section of the liquid crystal layer observed with a SEM, bright portions and dark portions derived from a liquid crystal phase are tilted with respect to a main surface of the liquid crystal layer, and in a case where an interval between the bright portions or between the dark portions is represented by a ½ pitch, the pitch Pin of the incidence diffraction element and the pitch Pe of the intermediate diffraction element satisfy Pin<Pe.