Virtual Image Display Grating Layout for Uniform Luminance
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Solution Overview
Problem
Existing virtual image display apparatuses using light guide plates with diffraction elements suffer from uneven luminance between the left and right sides of the angle of view, leading to significant differences in luminance due to varying diffraction angles and light paths.
Innovation Solution
The apparatus employs a first and second optical member with overlapping emission diffraction gratings and pupil enlargement gratings, ensuring that the optical paths and luminance are balanced by adjusting the diffraction grating pitches and angles to overlap and emit image light towards a common exit pupil, thereby reducing luminance differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a light guide plate with diffraction elements is used to achieve a thinner optical system, then the optical system thickness is reduced, but uneven luminance occurs between the left and right sides of the angle of view
Solution Approach 1:
The optical system is divided into multiple optical members (first optical member with first diffraction element, second optical member with second diffraction element, etc.), each handling different angular regions. This segmentation allows independent optimization of each member's diffraction characteristics to achieve uniform luminance across the entire angle of view while maintaining a compact overall structure.
Solution Approach 2:
Different diffraction elements are designed with locally optimized properties - each diffraction element has specific diffraction angles and efficiencies tailored to its assigned angular region. This local quality optimization ensures that luminance is uniformly distributed across different viewing angles while keeping the optical system thin.
2Adaptability or versatility
If the angle of view is divided into sides using multiple input and output coupling elements, then the angle of view coverage is improved, but luminance difference between left and right regions increases
Solution Approach 1:
Multiple optical members are combined in an integrated optical system where their diffraction patterns are coordinated to work together. The first, second, and third optical members handle different angular segments, and their combined effect produces uniform luminance across the entire angle of view, avoiding the luminance imbalance that would occur with separate independent elements.
Solution Approach 2:
The diffraction parameters (grating pitch, diffraction angle, efficiency) are carefully adjusted for each optical member to compensate for the inherent luminance differences. By changing these parameters appropriately, the system achieves uniform luminance distribution while covering a wide angle of view through multiple coupled elements.
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
This configuration suppresses uneven luminance by ensuring consistent luminance across the entire angle of view, providing a seamless and uniform virtual image display experience.
Implementation Method 1
a first incident diffraction grating on which the first image light from the first display element is incident; a first emission diffraction grating having a first region that emits the first image light toward a position where an exit pupil is formed; and a first pupil enlargement grating diffracting the first image light from the first incident diffraction grating toward the first emission diffraction grating
Data Source
AI summary
In a virtual image display apparatus, as viewed from an exit pupil, a first emission diffraction grating and a second emission diffraction grating overlap, and a region, of the first emission diffraction grating, emitting first image light is different from a region, of the second emission diffraction grating, emitting second image light. As a result, an optical path from the first display element to the first emission diffraction grating can be prevented from being largely different from an optical path from a second display element to the second emission diffraction grating. Thus, unevenness in luminance in a virtual image displayed due to an increased difference in luminance between the first image light emitted from the first emission diffraction grating and the second image light emitted from the second emission diffraction grating can be suppressed.