Touch Sensing LCD With Low Birefringence and Circular Polarization
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Solution Overview
Problem
Liquid crystal displays (LCDs) with high birefringence materials in their optical stack cause rainbow-like artifacts when viewed at different angles, especially when the viewer is wearing linear polarizing objects like sunglasses, due to changes in polarization state and luminance variations across the field of view.
Innovation Solution
A touch sensing LCD is designed with a stack of layers that have controlled or low birefringence, and a retardance layer is added to circularly polarize the output light, converting linearly polarized light into circularly polarized light to minimize artifacts across various viewing angles and through linear polarizing objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high birefringence materials are used in the optical stack, then touch sensing properties are improved, but rainbow-like artifacts appear when viewed at different angles
Solution Approach 1:
The patent changes the birefringence parameter of the touch sensing layer from high to low values. Specifically, it uses materials with birefringence less than 0.05, preferably less than 0.03, to eliminate rainbow artifacts while maintaining touch sensing functionality. This parameter change resolves the contradiction by prioritizing visual quality over maximum touch sensitivity.
Solution Approach 2:
The patent employs composite material structures including multiple layers with different optical properties. The optical stack comprises a polarizer, liquid crystal layer, and touch sensing layer with controlled birefringence characteristics. This composite approach allows optimization of both touch sensing and visual display properties by combining materials with complementary characteristics.
2Device complexity
If linear polarized light is used in the display output, then display simplicity is maintained, but artifacts appear when viewed through linear polarizing objects like sunglasses
Solution Approach 1:
The patent changes the polarization state parameter from linear to circular polarization. By using a circular polarizer instead of a linear polarizer in the optical stack, the display eliminates artifacts when viewed through linear polarizing objects like sunglasses. This parameter change in polarization type resolves the contradiction between simplicity and artifact reduction.
3Illumination intensity
If birefringent materials are used in the optical stack, then optical filtering is improved, but luminance variation and coloration occur across the field of view
Solution Approach 1:
The patent changes the birefringence parameter from high to low values in the touch sensing layer. By selecting materials with birefringence less than 0.05, the patent maintains optical filtering efficiency while eliminating luminance variation and coloration artifacts across the display field of view.
Solution Approach 2:
The patent applies local quality control by optimizing the birefringence characteristics specifically in the touch sensing layer while maintaining other layer properties. This localized optimization ensures uniform luminance and color across the display without compromising overall optical performance.
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 combination of low birefringence and circularly polarized output light reduces visible artifacts, allowing the LCD to be viewed from multiple angles with minimal distortion, even through linear polarizing media like sunglasses, enhancing display quality and usability.
Implementation Method 1
The final layers of the output of the touch sensing liquid crystal display circularly polarize the output light
Implementation Method 2
light transmitted through a partially or fully birefringent layer may undergo a phase delay between orthogonal components of a linearly polarized input state such that the light exiting the layer may experience a change in the polarization state
Data Source
AI summary
A touch sensing liquid crystal display is made with a stack of layers that has controlled or low birefringence. The final layers of the output of the touch sensing liquid crystal display circularly polarize the output light. The combination of low birefringence and circularly polarized output light provides a touch sensing LCD that can be viewed from many angles with low visible artifacts, even through linear polarizing objects, such as sunglasses.