Diffractive Optical Member Buffer Layer Stress Management
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Solution Overview
Problem
In virtual image display devices, the use of a dielectric film around a hologram element to prevent moisture intrusion can cause stress due to the curing and contraction of the adhesive layer, leading to changes in the diffraction characteristics of the hologram element, which affects image formation.
Innovation Solution
A diffractive optical member is designed with a buffer layer made of a low elastic modulus resin around the hologram element to absorb stress from the adhesive layer, and dielectric films between the hologram element and substrates to prevent moisture intrusion, while an adhesive layer adheres the buffer and dielectric films to each other.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a dielectric film is disposed around the hologram element via an adhesive layer to prevent moisture intrusion, then moisture protection is improved, but stress is applied to the hologram element causing diffraction characteristic changes
Solution Approach 1:
A buffer layer is introduced as an intermediary between the adhesive layer and the dielectric film surrounding the hologram element. This buffer layer absorbs the stress generated when the adhesive layer cures and contracts, preventing the stress from being transmitted to the hologram element. Meanwhile, the dielectric film maintains its moisture barrier function, thus resolving the contradiction between moisture protection and diffraction characteristic stability.
2Ease of manufacture
If an adhesive layer is used to attach the dielectric film to the hologram element, then assembly is simplified, but stress and contraction during curing affect the hologram element
Solution Approach 1:
The buffer layer is positioned beforehand around the hologram element to cushion and absorb the stress that will be generated when the adhesive layer cures and contracts. This prior cushioning prevents stress transmission to the hologram element, allowing the use of adhesive layers for simplified assembly without compromising hologram element stability.
3Device complexity
If the dielectric film is directly attached to the hologram element, then the structure is simplified, but stress from adhesive curing changes the diffraction state
Solution Approach 1:
The buffer layer serves as a mediator between the dielectric film and the hologram element. While this adds one additional layer to the structure, it prevents stress transmission that would otherwise change the diffraction state of the hologram element. The increase in structural complexity is minimal compared to the significant improvement in maintaining diffraction efficiency.
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 maintains the desired diffraction state of the hologram element, preventing adverse effects from stress and moisture, thereby ensuring favorable image formation in virtual image display devices.
Implementation Method 1
a buffer layer that is formed around the hologram element so as to buffer a stress applied to the hologram element from outside of the hologram element
Implementation Method 2
an adhesive layer that makes the buffer layer and the dielectric film adhere to each other
Implementation Method 3
a dielectric film that is provided between the hologram element and the substrate
Data Source
AI summary
A diffractive optical member includes: a hologram element, a substrate that supports the hologram element, a dielectric film that is provided between the hologram element and the substrate, a buffer layer that is formed around the hologram element so as to buffer a stress applied to the hologram element from outside of the hologram element, and an adhesive layer that makes the buffer layer and the dielectric film adhere to each other.