Volume Grating Layered Production via Coherence Control
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Solution Overview
Problem
Existing methods for generating volume gratings in large-area recording media are limited in creating multiple thin layers with different angular and wavelength selectivity, and achieving precise control over diffraction efficiency and apodisation profiles, especially in thick media with surface irregularities.
Innovation Solution
A method involving the interference of two coherent light wave fronts at a presettable depth and angle within a photosensitive recording medium, allowing for depth-specific control of refractive index modulation and interference contrast, enabling the generation of volume gratings with varied apodisation profiles and selectivity, while accommodating surface irregularities by burying the grating or using immersion techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple film-type DOEs are stacked to generate three-dimensional image sensation, then the light-beam-influencing capability is improved, but the total thickness of the layer stack increases
Solution Approach 1:
The patent combines multiple volume gratings into a single continuous recording medium, creating a multi-layer grating stack where different grating layers are generated at different depths within the same medium. This merging approach maintains the light-beam-influencing capability of multiple DOEs while reducing the total thickness compared to stacked film structures.
Solution Approach 2:
The patent transitions from two-dimensional surface gratings to three-dimensional volume gratings within a continuous medium. By utilizing the depth dimension (z-direction) of the recording medium, multiple gratings can be embedded at different depths, effectively stacking functional layers without increasing the physical thickness of separate components.
2Ease of manufacture
If individual films are joined to create layer stacks, then flexibility in assembly is improved, but positioning accuracy between layers deteriorates due to shrinkage and misalignment
Solution Approach 1:
The patent eliminates the need to join individual films by generating all grating layers within a single continuous recording medium. This unified structure prevents positioning errors, shrinkage, and misalignment that occur when multiple separate films are assembled together, while maintaining manufacturing flexibility through various exposure methods.
Solution Approach 2:
The patent segments the recording medium into multiple functional layers at different depths, each containing specific grating structures. This segmentation allows different grating functions to be created at different z-positions within the continuous medium, achieving layer-specific functionality without physical separation and joining of films.
3Reliability
If volume gratings are recorded in thick recording media, then the capability to generate multiple gratings in layers is improved, but control over interference contrast and apodisation profiles deteriorates
Solution Approach 1:
The patent applies local quality by using depth-selective exposure methods that allow different regions (depths) of the recording medium to receive different exposure conditions. This enables precise control of interference contrast and apodisation profiles at each grating layer position, even within thick media, by adjusting exposure parameters locally at each depth level.
Solution Approach 2:
The patent utilizes parameter changes in the exposure process, such as varying exposure wavelength, exposure intensity, and exposure duration at different depths, to achieve precise control over interference contrast and apodisation profiles. By dynamically adjusting these parameters during the recording process, high manufacturing precision is maintained throughout the thick recording medium.
4Ease of manufacture
If surface gratings are used, then the manufacturing process is simplified, but the ability to influence light direction in a wavelength-specific manner deteriorates
Solution Approach 1:
The patent transitions from two-dimensional surface gratings to three-dimensional volume gratings embedded within the recording medium. This dimensional change enables wavelength-specific diffraction control because the volumetric structure provides better angular and wavelength selectivity, while the manufacturing process remains relatively simple through direct optical exposure methods.
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
Enables the generation of volume gratings with presettable angular and wavelength selectivity, suppressing side peaks and allowing for dynamic control of diffraction efficiency, suitable for large-area holographic displays and solar panels, while maintaining high precision and flexibility.
Implementation Method 1
Each volume grating is generated in the recording medium by at least two wave fronts WF1, WF2 of coherent light which are capable of generating interference
Implementation Method 2
The recording medium has at least one photosensitive layer which is sensitised for a presettable wavelength of the exposure light
Implementation Method 3
the depth z and the thickness of the refractive index and/or transparency modulation of a volume grating VG in the recording medium AZM is influenced by depth-specific control of the spatial and/or temporal degree of coherence F of the interfering wave fronts WF1, WF2
Implementation Method 4
These elements, which are typically provided in the form of transparent films with presettable thickness, influence the light beams which strike them coming from an image-generating device, such as a large-area light modulator (SLM), through diffraction effects
Data Source
AI summary
The layered generation of at least one volume grating in a recording medium by way of exposure, the recording medium having at least one photosensitive layer which is sensitized for a presettable wavelength of the exposure light. Each volume grating is generated in the recording medium by at least two wave fronts of coherent light capable of generating interference, the wave fronts being superposed in the recording medium at a presettable depth, at a presettable angle and with a presettable interference contrast. The depth and the thickness of the refractive index modulation and/or transparency modulation of a volume grating in the recording medium is controlled by depth-specific control of the spatial and/or temporal degree of coherence of the interfering wave fronts in the direction of light propagation.