Light Guide Device with Sub-Wavelength Grating for Polarization Conversion
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Solution Overview
Problem
Conventional backlight modules for LCDs suffer from low light energy utilization efficiency due to the reflection and absorption of S-polarized light, resulting in only 50% of the light being used, while the use of quarter wavelength plates and reflective polarizing beam splitters further reduce efficiency by consuming light through frequent refraction and diffusion.
Innovation Solution
A light guide device with a sub-wavelength grating and stress-induced birefringence is introduced, where the light guide substrate has orthogonal stresses and a sub-wavelength grating on the top, optimizing the phase retardation to achieve nearly 100% polarization conversion efficiency, eliminating the need for quarter wavelength plates and reflective polarizing beam splitters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional light guide plate with reflecting sheet and diffusion sheet is used, then the light guide structure is simple, but the light energy utilization efficiency is low (only 50% light is used) due to reflection and absorption of S-polarized light
Solution Approach 1:
The patent introduces a sub-wavelength grating structure on the light guide plate surface, changing the geometric parameters of the light guide system. This grating structure with specific pitch and depth parameters enables selective polarization conversion, transforming S-polarized light into P-polarized light to improve light energy utilization while maintaining manufacturing feasibility
Solution Approach 2:
The patent replaces the conventional mechanical/optical system consisting of separate reflecting sheets and diffusion sheets with an integrated light guide plate incorporating a sub-wavelength grating. This substitution eliminates the need for multiple separate components while achieving both light reflection and polarization conversion functions, thereby improving light energy utilization efficiency
2Reliability
If quarter wavelength plates and reflective polarizing beam splitters are added to improve polarization conversion, then the polarization conversion efficiency improves, but the light energy utilization efficiency decreases due to frequent refraction and diffusion consuming light
Solution Approach 1:
The patent merges the functions of polarization conversion and light guidance into a single integrated light guide plate structure with a sub-wavelength grating. This consolidation eliminates the need for separate quarter wavelength plates and reflective polarizing beam splitters, reducing the number of interfaces where light can be lost through refraction and diffusion, thereby maintaining high polarization conversion efficiency while improving overall light energy utilization
Solution Approach 2:
The patent extracts and eliminates the quarter wavelength plate and reflective polarizing beam splitter components from the conventional backlight module structure. By removing these separate components and integrating their functions directly into the light guide plate, the patent reduces light loss from frequent refraction and diffusion while maintaining effective polarization conversion
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 solution enhances light energy utilization efficiency by converting S-polarized light into P-polarized light with over 99% efficiency, improving the overall light utilization in backlight modules for LCDs, and allows for the integration of multiple wavelengths of light to illuminate the LCD panel effectively.
Implementation Method 1
Two orthogonal stresses or strains are formed in the light guide substrate, and a phase retardation due to a stresses or stains difference is defined by the equation: δ=2πCΔσL/λ=2kπ+π
Implementation Method 2
The light guide substrate has orthogonal stresses and a sub-wavelength grating on the top, optimizing the phase retardation to achieve nearly 100% polarization conversion efficiency
Implementation Method 3
The sub-wavelength grating on the top of the light guide device... achieving nearly 100% polarization conversion efficiency, eliminating the need for quarter wavelength plates and reflective polarizing beam splitters
Data Source
AI summary
A light guide device (52) includes a light guide substrate (520) and a sub-wavelength grating (527). The light guide substrate has a light input surface (521), a light output surface (522) adjacent to the light input surface (521), a bottom surface (523) opposite to the light output surface (522). In the light guide plate, stress-induced birefringence is introduced to achieve the polarization state conversion. The SWG 527 located on the light output surface includes a top layer (525) and a bottom layer (526). The SWG 527 is configured to work as a reflective polarizing beam splitter, consistent with the principle of rigorous coupled-wave theory.