Thin Film Light Pipe with Optical Coupler for LED Backlight
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Solution Overview
Problem
Existing backlight assemblies for liquid crystal displays face inefficiencies in coupling light from LEDs due to large divergence angular emittance patterns, resulting in suboptimal light distribution and lower optical efficiency.
Innovation Solution
The implementation of a non-imaging optical coupler with a concave lens and air gap, along with a thin film light pipe featuring integral diffusers and prismatic structures, efficiently directs light from LEDs into a 90-micron light pipe using total internal reflection and microgrooves, achieving uniform light distribution and high optical efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional light pipe assembly is used to couple light from LED sources, then the structure is simple, but the light coupling efficiency is low due to large divergence angular emittance patterns
Solution Approach 1:
A non-imaging optical coupler with concave lens is introduced as an intermediary component between the LED light source and the light pipe assembly. This coupler mediates the light transmission by collecting divergent light rays and redirecting them into the light pipe, significantly improving light coupling efficiency from the LED source into the thin film light pipe while managing the complexity through a dedicated optical interface component
Solution Approach 2:
The patent changes the optical parameters by implementing a concave lens with specific curvature and an air gap configuration. These parameter changes modify the light propagation characteristics, transforming the divergent light pattern from the LED into a more controlled distribution that efficiently couples into the light pipe, achieving nearly 100% coupling efficiency across the radiation plane
2Illumination intensity
If light is allowed to exit the light pipe at all angles, then more light reaches the display, but light distribution uniformity deteriorates with peripheral intensity drops
Solution Approach 1:
The patent applies local quality by implementing an air gap specifically at the periphery of the light pipe where light exits. This localized modification creates a refractive index boundary that selectively affects light at different angles and positions. The air gap causes total internal reflection for oblique rays at the periphery while allowing near-normal rays to pass through, thereby maintaining uniform light distribution across the display surface
Solution Approach 2:
The refractive index parameter is changed by introducing an air gap (n=1.0) between the light pipe material and the surrounding medium. This parameter change creates a critical angle for total internal reflection that selectively redirects oblique light rays back into the light pipe, preventing peripheral intensity drops and maintaining uniform illumination across the display
3Length of moving object
If the light pipe thickness is reduced to achieve thin film design, then the display profile is improved, but light coupling efficiency becomes more difficult to optimize
Solution Approach 1:
The patent optimizes the thickness parameter of the light pipe to approximately 90 microns, creating a thin film profile suitable for modern displays. This thickness parameter is carefully selected to balance mechanical flexibility with optical performance, allowing efficient light coupling while maintaining the desired thin form factor for the display device
Solution Approach 2:
A non-imaging optical coupler with concave lens serves as an intermediary that bridges the gap between the LED source and the thin light pipe. This coupler compensates for the reduced thickness by providing enhanced light collection and redirection capabilities, ensuring that even with the thin 90-micron light pipe, nearly 100% of the LED light is effectively coupled into the waveguide
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 enhances light coupling efficiency to nearly 100% across the radiation plane and up to 85% optical efficiency, significantly improving light distribution uniformity and reducing peripheral intensity drops, thereby enhancing display brightness.
Implementation Method 1
a light pipe that couples light from a light source such as one or more LEDs into the display using a process called total internal reflection (TIR)
Implementation Method 2
The air gap provides a significant change in the index of refraction that causes light at low angles to be reflected back into the light pipe
Data Source
AI summary
A backlight assembly is provided. The backlight assembly includes a light pipe assembly having a thickness of about 90 microns, a light source and a coupler that receives light from the light source and diffuses the received light from the light source into the first end of the light pipe assembly.