Holographic Grating Alignment via Optical Mark Detection
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Solution Overview
Problem
Existing methods for assembling optical devices with holographic diffraction gratings lack a precise and simplified method for aligning the gratings, particularly when both alignment marks are formed of transparent holograms, leading to challenges in achieving accurate positioning and mutual arrangement.
Innovation Solution
The proposed method involves using alignment marks with identical interference fringes outside the interference fringe forming areas, optically detecting these marks, and aligning the holographic diffraction gratings such that the angle formed by the straight lines connecting the marks falls below a prescribed value, ensuring precise relative alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If alignment marks are formed of transparent holograms, then the optical device can maintain uniformity and avoid overlapping issues, but the alignment precision becomes difficult to achieve
Solution Approach 1:
The patent introduces a light source and imaging device as intermediaries to detect and measure the alignment marks. The light source illuminates the transparent holographic alignment marks, and the imaging device captures their positions, enabling precise measurement without direct contact or overlapping issues. This intermediary system resolves the contradiction by providing a reliable detection method for transparent marks.
Solution Approach 2:
The patent replaces mechanical alignment methods with optical detection and image processing. Instead of using mechanical fixtures or opaque markers that can be physically positioned, the system uses optical detection through imaging devices to locate and measure the positions of transparent holographic alignment marks, achieving high precision without mechanical constraints.
2Manufacturing precision
If complex alignment methods are used to ensure precise positioning, then alignment precision improves, but the assembly process becomes more complex
Solution Approach 1:
The patent segments the alignment process into distinct components: alignment marks with specific patterns, light source for illumination, imaging device for capture, and processing unit for measurement. This segmentation allows each component to be optimized independently and simplifies the overall assembly process by providing clear, modular steps for achieving precise positioning.
Solution Approach 2:
The patent uses alignment marks that contain interference fringe patterns as optical copies or representations of the actual grating structure. These patterns can be detected and measured through imaging, providing a simplified representation that enables precise positioning without requiring complex direct measurement of the grating itself.
3Stability of the object's composition
If alignment marks are placed inside the interference fringe forming area, then the alignment is more integrated, but the marks overlap and become difficult to detect
Solution Approach 1:
The patent applies local quality by creating alignment marks with specific interference fringe patterns that are distinct from the main grating pattern. These marks are positioned in regions where they can be clearly detected by the imaging device, with their local pattern characteristics enabling unambiguous identification and measurement, thus resolving the overlap issue while maintaining integration.
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 approach allows for certain and easy alignment of holographic diffraction gratings, enhancing the assembly process and resulting in improved optical device performance by ensuring accurate alignment without complex overlapping or positional errors.
Implementation Method 1
an optical device (light guide unit) 120... includes a light guide plate 121, a first diffraction grating member 130, and a second diffraction grating member 140. The first diffraction grating member 130 and the second diffraction grating member 140 are formed of holographic diffraction gratings provided to the light guide plate 121.
Implementation Method 2
a light guide plate 121... receives light displayed in the image forming device 111 and guides the light to a pupil 21 of an observer
Data Source
AI summary
In some embodiments, a head mounted display is provided, comprising a light guide, at least first and second diffraction gratings, alignment marks A1 and B1 associated with the first diffraction grating, and alignment marks A2 and B2 associated with the second diffraction grating. The first diffraction grating may be disposed on a first surface of the light guide, the first surface facing away from a light input. The second diffraction grating may be disposed on a second surface of the light guide, the second surface facing towards the light input. The second diffraction grating may be adapted to diffract at least some of the light input into the light guide, and the first diffraction grating may be adapted to diffract at least some light transmitted through the light guide back into the light guide.