Ultra-dense LED Array with Half Cavities and Reflective Sidewalls
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Solution Overview
Problem
Ultra-dense LED arrays for femtoprojectors face challenges in achieving high resolution and efficient light extraction due to small pixel sizes and tight projection optics, leading to issues with stray light and low extraction efficiency.
Innovation Solution
The use of a half cavity and sloped, straight reflective sidewalls in the LED array design redistributes light to improve power distribution, with the half cavity formed by a reflector and a thinner p-layer and thicker n-layer, and angled sidewalls that reflect light into the collection angle of the projection optics, reducing stray light and enhancing extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel sizes are reduced to achieve high resolution in femtoprojector, then resolution is improved, but light extraction efficiency deteriorates
Solution Approach 1:
The patent introduces a vertical dimension by creating a half-cavity structure extending downward from the LED active region, and adds reflective sidewalls at angled orientations. This transforms the traditionally planar light extraction into a three-dimensional configuration, allowing light to be redirected from small horizontal pixel areas into the collection angle of projection optics through vertical and angular pathways.
Solution Approach 2:
The patent introduces reflective sidewalls as intermediary structures between the LED active region and the projection optics. These sidewalls act as mediators that intercept light emitted at various angles and redirect it into the collection angle, effectively coupling light from ultra-dense pixels into the optical system without requiring larger pixel areas.
2Measurement precision
If pixel density is increased to achieve high resolution, then resolution is improved, but stray light increases
Solution Approach 1:
The reflective sidewalls serve as intermediary structures that actively manage light direction. By positioning these reflective surfaces at specific angles, the patent redirects light that would otherwise become stray light into the collection angle of the projection optics, thereby reducing harmful stray light while maintaining ultra-dense pixel configurations.
Solution Approach 2:
The half-cavity structure extending vertically downward provides an additional dimension for light management. This vertical space allows reflective sidewalls to intercept and redirect light from multiple angles, converting potentially harmful stray light into useful light directed toward the projection optics.
3Volume of moving object
If projection optics size is reduced to fit in contact lens, then device size is improved, but collection angle decreases
Solution Approach 1:
The patent compensates for the limited collection angle of miniaturized optics by introducing vertical light management through the half-cavity structure. Light is redirected from the LED active region through vertical and angular pathways created by reflective sidewalls, effectively increasing the range of light angles that can be captured by the small projection optics.
Solution Approach 2:
The reflective sidewalls act as intermediary elements that expand the effective collection angle. By strategically positioning these reflective surfaces, the patent redirects light emitted at various angles into the limited collection angle of the miniaturized projection optics, effectively decoupling the collection angle limitation from the physical size of the optics.
4Measurement precision
If ultra-dense LED array is formed with small pixel sizes, then resolution is improved, but manufacturing complexity increases
Solution Approach 1:
The patent segments the light management function into distinct structural elements: the half-cavity extending downward from each pixel and the reflective sidewalls positioned at angled orientations. This segmentation allows each element to be optimized independently while working together to achieve high resolution and efficient light extraction in ultra-dense arrays.
Solution Approach 2:
The reflective sidewalls serve multiple functions simultaneously: they redirect light into the collection angle, reduce stray light, and can be integrated into the pixel fabrication process. This multi-functionality reduces overall device complexity by combining several light management functions into a single structural element.
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 design significantly increases the extraction efficiency of light into the projection optics, improving the resolution and reducing stray light, while also simplifying the fabrication process by creating high aspect ratio structures that are challenging to produce.
Implementation Method 1
sloped, straight reflective sidewalls... angled sidewalls that reflect light into the collection angle of the projection optics
Implementation Method 2
the half cavity and sloped, straight reflective sidewalls redistribute the light to improve the power distribution
Data Source
AI summary
In one approach, an LED array uses a combination of a half cavity and straight reflective sidewalls to improve the power distribution so that more light falls within the collection angle of the projection optics. From the bottom upwards, the LEDs in the array include a reflector, a thinner p-layer and a thicker n-layer. An active region (such as quantum wells) between the p-layer and the p-layer generates light. Without additional structures, the generated light would have an isotropic distribution and not much of the light would fall within the collection angle of the projection optics. However, the bottom reflector and p-layer form a half cavity for the light emitted from the active region. This alters the angular power distribution. Straight reflective sidewalls extending from the active region upwards into the n-layer further reflect light from the altered power distribution into the collection angle of the projection optics.