Volume Holographic Element Anti-Reflective Coating
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Solution Overview
Problem
In volume holographic elements, interference fringes are generated in unintended locations due to reflection at the interface between substrates and air layers during the interference exposure process, leading to difficulties in forming appropriate diffraction grids with different refractive indexes.
Innovation Solution
A volume holographic element is designed with translucent substrates and anti-reflective layers on the surfaces opposite to the holographic material layer, preventing oblique reflection of exposure light and thus suppressing the generation of interference fringes at unintended locations, and additional layers are included to manage stress and bending caused by expansion or contraction of the holographic material layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If interference exposure is performed without anti-reflective layers, then the manufacturing process is simple, but unnecessary interference fringes are generated due to reflection at substrate-air interfaces
Solution Approach 1:
An anti-reflective layer is introduced as an intermediary between the substrate and the external environment. This layer has a refractive index intermediate between air and the substrate material, reducing reflection at the interface and preventing spurious interference fringes during exposure while maintaining manufacturing simplicity
Solution Approach 2:
The anti-reflective layer is applied in advance to the substrate before the interference exposure process. This preliminary action prevents reflection and unwanted interference fringe generation at the substrate-air interface during subsequent exposure operations
2Manufacturing precision
If anti-reflective layers are added to substrates, then interference fringe positioning accuracy is improved, but device complexity increases
Solution Approach 1:
The anti-reflective layer serves as a functional intermediary that solves the reflection problem with a single additional layer, achieving improved fringe positioning accuracy without excessive complexity increase
Solution Approach 2:
The refractive index parameter of the anti-reflective layer is specifically chosen to be intermediate between air and substrate materials, optimizing its anti-reflective function while keeping the layer structure relatively simple
3Manufacturing precision
If holographic material layer is irradiated with oblique exposure light, then diffraction grid formation is effective, but reflection at substrate surface causes interference fringes at unintended locations
Solution Approach 1:
The anti-reflective layer acts as a mediator at the substrate surface, reducing reflection of obliquely incident exposure light and preventing the generation of spurious interference fringes at unintended locations while allowing effective diffraction grid formation
Solution Approach 2:
The anti-reflective coating is applied in advance to prevent reflection-related harmful effects before oblique exposure light interacts with the substrate, enabling clean diffraction grid formation without spurious fringes
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 allows for the appropriate formation of diffraction grids with different refractive indexes, enhancing the diffraction characteristics and reducing the deterioration caused by unnecessary interference fringes and stress-related bending.
Implementation Method 1
a first translucent anti-reflective layer 7A that is laminated on the first surface 5A0 of the first translucent substrate 5A
Implementation Method 2
some of the exposure light is reflected in the interface between the first surface 5A0 of a first substrate 5A, which is a surface opposed to the holographic material layer 4, and an air layer
Implementation Method 3
interference exposure is performed in such a way that the holographic material layer 4 in an uncured state or in a semi-cured state is irradiated with object light L1 and reference light L2, which are acquired by dividing light flux emitted from a common light source, parts which have different refractive indexes are formed in the shape of stripes in the holographic material layer 4
Implementation Method 4
the holographic material layer 4 is cured in a curing process
Implementation Method 5
the holographic material layer 4 is cured in a curing process
Data Source
AI summary
In a process of manufacturing the volume holographic element, a holographic material layer is irradiated with reference light from the side of a second substrate in the oblique direction, and the holographic material layer is vertically irradiated with object light from the side of a first substrate in an interference exposure process. Since a first translucent anti-reflective layer is formed on the first surface of the first substrate, it is difficult that situation in which the reference light is reflected in the first surface in the oblique direction occurs. In addition, since a second translucent anti-reflective layer is formed on the second surface of the second substrate, it is difficult that a situation in which the object light is reflected in the second surface occurs.