Cemented Optical System with Thin Adhesive Layers for Short Focal Length
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Solution Overview
Problem
Existing optical systems for image display apparatuses, such as head mount displays (HMDs), face challenges in achieving a compact design with wide viewing angles and high optical performance while minimizing image quality deterioration due to factors like birefringence and unevenness in adhesive layers.
Innovation Solution
The optical system integrates a transmissive reflective surface, polarization separation surface, and polarizing element with a lens using a resin material, adhered via adhesive layers that satisfy specific refractive index and thickness inequalities, forming a cemented structure to reduce thickness and enhance optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If adhesive layers are used to cement the optical unit and lens, then the optical system can be assembled, but image quality deteriorates due to birefringence and unevenness in the adhesive layer
Solution Approach 1:
The patent applies parameter changes by precisely controlling the refractive index and thickness of the adhesive layer. By selecting an adhesive layer with a refractive index within a specific range and controlling its thickness to satisfy defined inequalities, the patent minimizes birefringence and unevenness effects, thereby reducing image quality deterioration while maintaining assembly feasibility.
2Strength
If the optical system uses multiple adhesive layers, then components can be firmly joined, but the focal length increases and optical performance decreases
Solution Approach 1:
The patent minimizes the total thickness of adhesive layers by precisely controlling each layer's thickness parameter to satisfy defined inequalities. This parameter optimization reduces the cumulative thickness that would otherwise increase focal length, while still providing sufficient joint strength for assembling the optical unit and lens.
3Strength
If the adhesive layer thickness is increased, then better bonding is achieved, but optical performance deteriorates due to increased birefringence
Solution Approach 1:
The patent resolves this contradiction by optimizing the adhesive layer thickness parameter within a specific range defined by inequalities. This optimized thickness provides sufficient bonding strength while minimizing the path length for light through the adhesive, thereby reducing birefringence effects and maintaining optical performance.
Solution Approach 2:
The patent applies local quality by selecting adhesive materials with specific local properties (refractive index within a defined range) and controlling the thickness locally to satisfy inequalities. This ensures that the adhesive layer provides adequate bonding in specific regions while minimizing optical degradation effects.
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 achieves a reduced focal length, wide viewing angle, and improved image contrast by minimizing the impact of adhesive layers on optical performance, resulting in a lightweight and high-quality image display.
Implementation Method 1
N1 is a refractive index of the lens for d-line, and N2 is a refractive index of the first adhesive layer for the d-line
Implementation Method 2
minimizing the impact of adhesive layers on optical performance
Implementation Method 3
an optical system that folds an optical path by using polarization
Implementation Method 4
a lens including a resin material
Data Source
AI summary
An optical system is configured to guide light from a display element to an observation side, and includes a transmissive reflective surface, a polarization separation surface, a polarizing element, and a lens including a resin material. The transmissive reflective surface or the polarization separation surface and the polarizing element are integrated with each other to form an optical unit. The optical unit and the lens are cemented to each other via a first adhesive layer. The light transmits through the first adhesive layer a plurality of times. Predetermined inequalities are satisfied.