Eyeglass Display Diffraction Element Wavelength Matching
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Solution Overview
Problem
Existing eyeglass display devices face challenges in reducing size and thickness while maintaining even light intensity distribution due to the use of diffraction optical elements, which deflect light in varying angles, leading to uneven image intensity across the display surface.
Innovation Solution
The display device incorporates a diffraction optical element that deflects light by different angles depending on the position on the display surface, with light emitting diodes having varying center wavelengths to maintain diffraction efficiency across different angles of view, ensuring even intensity distribution by shifting the wavelength peak accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a diffraction optical element is used to largely change the light advance direction for reducing device size and thickness, then the device size and thickness are reduced, but the light intensity distribution on the display surface becomes uneven
Solution Approach 1:
The patent applies local quality by making the diffraction optical element have position-dependent properties. Specifically, the diffraction pattern is designed so that the diffraction angle varies depending on the incident position, with larger diffraction angles for light incident at positions corresponding to peripheral display areas and smaller diffraction angles for central areas. This local variation in diffraction characteristics compensates for the intensity non-uniformity caused by the compact light guide design.
Solution Approach 2:
The patent changes the diffraction parameter (diffraction angle) as a function of position. By designing the diffraction optical element with a diffraction pattern where the diffraction angle varies with incident position, the system dynamically adjusts the light direction based on where the light enters the element. This parameter change enables uniform light intensity distribution across the display surface while maintaining the reduced device size and thickness.
2Reliability
If the diffraction optical element deflects light to satisfy Bragg's condition, then the light is efficiently diffracted, but the main wavelength of diffracted light differs depending on the angle of incident light causing wavelength deviation
Solution Approach 1:
The patent addresses wavelength consistency by making the diffraction optical element's characteristics position-dependent. The diffraction pattern is designed so that each region of the element is optimized for the specific incident angle from that region, ensuring that Bragg's condition is satisfied locally across the entire element. This maintains high diffraction efficiency while accommodating the range of incident angles without significant wavelength deviation.
3Volume of moving object
If light is guided by repeating total reflection inside the light-guiding unit, then the light can be transmitted through the compact structure, but the device requires large light advance direction changes increasing complexity
Solution Approach 1:
The patent extracts the light direction-changing function from the light guide structure itself and transfers it to a separate diffraction optical element. Instead of relying solely on complex internal reflections within the light guide to achieve large direction changes, the system uses a dedicated diffraction element that performs the angle conversion function. This separation simplifies the overall light guidance structure while maintaining compact device size.
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 effectively suppresses intensity fluctuations in the image light as the angle of view changes, maintaining brightness across the display surface and preventing the image from appearing darker near the periphery.
Implementation Method 1
a diffraction optical element configured to deflect the image light in the optical system
Implementation Method 2
light emitting diodes having varying center wavelengths to maintain diffraction efficiency across different angles of view
Implementation Method 3
incident light is guided by repeating total reflection inside the light-guiding unit
Data Source
AI summary
An image in a predetermined hue is displayed at a display surface, and is emitted as image light. The image light is guided to a display position by an optical system, and is deflected by a diffraction optical element. The emitted image light includes light emitted from a first position of the display surface and light emitted from a second position of the display surface. A deflection angle at which the light emitted from the first position is diffracted by the diffraction optical element is larger than a deflection angle at which the light emitted from the second position is diffracted by the diffraction optical element. Of the image light in a wavelength range expressing the hue, a wavelength peak of the light emitted from the first position is present on a long wavelength side with respect to a wavelength peak of the light emitted from the second position.