Ultra-dense LED Array Half Cavity Sidewalls
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Solution Overview
Problem
Ultra-dense LED arrays for applications like contact lens-based femtoprojectors face challenges in achieving higher resolution and extraction efficiency due to small pixel sizes and tight projection optics, which result in stray light issues.
Innovation Solution
The use of a half cavity and sloped, straight reflective sidewalls in the LED array design redistributes light emission to improve power distribution and increase the amount of light collected by the projection optics, with the half cavity formed by a reflector and a thinner p-layer and thicker n-layer, and sidewalls that redirect light through total internal reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel sizes are reduced to achieve higher resolution in ultra-dense LED arrays, then resolution is improved, but extraction efficiency deteriorates due to small pixel sizes and tight projection optics
Solution Approach 1:
The patent introduces a half cavity structure extending in the vertical dimension below the active region, transforming the light extraction problem from a two-dimensional surface issue to a three-dimensional volumetric solution. This vertical dimension allows light to be extracted through the bottom reflector and redirected upward, bypassing the limitations of small pixel aperture areas.
Solution Approach 2:
The patent employs a bottom reflector as an intermediary element that redirects light generated in the active region. The reflector acts as a mediator that captures light attempting to escape downward and redirects it upward through the half cavity, effectively increasing the extraction efficiency without requiring larger pixel areas.
2Measurement precision
If pixel sizes are reduced to achieve higher resolution, then resolution is improved, but stray light increases due to tight projection optics
Solution Approach 1:
By extending the light extraction path into the vertical dimension through the half cavity, the patent separates the light extraction function from the lateral pixel boundaries. This dimensional extension allows for better control of light directions and reduces stray light that would otherwise escape laterally from small pixels.
Solution Approach 2:
The bottom reflector serves as an intermediary that controls and redirects light paths, preventing stray light from escaping in unwanted directions. By mediating the light extraction process, the reflector ensures that light is directed primarily toward the intended optical collection paths rather than becoming stray light.
3Ease of manufacture
If conventional LED structures are used with discrete red, green, and blue emitting LEDs, then color emission is achieved, but pixel pitch remains large at 25 um
Solution Approach 1:
The patent merges multiple LED structures into a single integrated pixel unit with a shared bottom reflector and half cavity. Instead of treating red, green, and blue LEDs as separate discrete components requiring individual extraction paths, they are combined into a unified structure where the half cavity serves all color channels, reducing the overall pixel pitch.
Solution Approach 2:
The bottom reflector and half cavity structure serve as universal components that function for all color LEDs within a pixel. This multi-functional design eliminates the need for separate extraction structures for each color, enabling tighter pixel packing while maintaining effective light extraction for all wavelengths.
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 enhances the extraction efficiency and reduces stray light by concentrating light into specific lobes that align with the collection angle of the projection optics, improving the overall performance of ultra-dense LED arrays.
Implementation Method 1
sidewalls that redirect light through total internal reflection
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.