Holographic Optical Element Fringe Prevention via Stack Bending Control
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Solution Overview
Problem
The production of large area holographic optical elements is hindered by the occurrence of fringes, which reduce the quality and diffraction efficiency of the elements due to asymmetric heating and subsequent bending of the recording stack during the irradiation process.
Innovation Solution
Adjusting parameters such as the ratio of lateral dimensions to thickness, coefficient of thermal expansion, fill factor, and exposure time to ensure the maximum bending deviation does not exceed a threshold, thereby preventing fringe formation in the holographic optical elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the recording stack is irradiated by a recording beam for a predefined exposure time, then a holographic optical element with desired pattern is generated, but fringes appear as dark and bright rings reducing the quality and diffraction efficiency
Solution Approach 1:
The patent applies preliminary anti-action by pre-bending the recording stack in the opposite direction of the expected thermal bending before irradiation. This counter-bending compensates for the asymmetric thermal expansion that would otherwise cause fringe formation, allowing large area holographic optical elements to be produced without fringes while maintaining high manufacturing precision
Solution Approach 2:
The patent employs parameter changes by adjusting the initial curvature radius of the recording stack and the exposure time based on the lateral dimensions and thickness of the stack. These parameter modifications optimize the thermal distribution during irradiation, preventing the asymmetric heating that leads to fringe formation while ensuring complete hologram recording
2Area of stationary object
If large area holographic optical elements are produced, then the application requirements are met, but fringe formation becomes more severe reducing diffraction efficiency
Solution Approach 1:
The patent uses preliminary anti-action by pre-bending large area recording stacks before irradiation to counteract the asymmetric thermal expansion that occurs during exposure. This approach enables the production of large area holographic optical elements without the fringe formation that would otherwise severely reduce diffraction efficiency
Solution Approach 2:
The patent applies preliminary action by calculating and setting the initial curvature radius and exposure time before irradiation based on the specific lateral dimensions and thickness of the recording stack. This preliminary configuration ensures uniform thermal distribution during the actual irradiation process, maintaining high diffraction efficiency in large area elements
3Manufacturing precision
If the recording stack parameters are optimized to prevent bending, then fringe formation is reduced, but the exposure time or other parameters must be precisely controlled
Solution Approach 1:
The patent employs parameter changes by establishing specific relationships between the initial curvature radius, exposure time, lateral dimensions, and thickness of the recording stack. These parameter optimizations enable bending deviation control while providing clear guidance for parameter selection, reducing the practical complexity of implementation
Solution Approach 2:
The patent applies feedback by using the known lateral dimensions and thickness of the recording stack to calculate the appropriate initial curvature radius and exposure time. This feedback-based parameter selection ensures optimal bending control for each specific recording stack configuration without requiring complex real-time adjustments
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 method effectively reduces the risk of fringe occurrence, allowing for the production of high-quality holographic optical elements without fringes, enhancing their diffraction efficiency and overall performance.
Implementation Method 1
the recording element can be irradiated by at least one recording beam for a predefined exposure time for generating the holographic optical element
Implementation Method 2
asymmetric heating and subsequent bending of the recording stack during the irradiation process
Data Source
Figure 1
Figure 2a~2b
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AI summary
The invention relates to a method for producing a holographic optical element by providing a recording stack comprising at least one recording element (402) laminated on at least one supporting element (409), irradiating at least a part of the recording stack with at least one recording beam in an irradiating step, wherein during the irradiating step, the recording stack bends, providing a bending deviation threshold for the recording stack, and adjusting at least one first process parameter such that an expected maximum bending deviation of the recording stack does not exceed the bending deviation threshold, wherein the at least one first process parameter influences the bending behaviour of the recording stack during the irradiating step.