Waveguide Air Gap and Index-Matching for LED Light Coupling
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Solution Overview
Problem
Conventional LED-based illumination devices face challenges in achieving high coupling efficiency while maintaining mechanical stability, as the geometric dimensions of waveguides are larger than LED dies, leading to increased contact areas that absorb light rather than reflect it through total internal reflection (TIR), resulting in efficiency losses.
Innovation Solution
The solution involves encapsulating the LED die within the waveguide material or index-matching materials, creating an air gap between the waveguide and the LED sub-assembly to facilitate TIR, minimizing contact areas and reducing in-coupling losses by using discrete attachment points and index-matching materials with refractive indices between those of the LED and waveguide, thereby optimizing light extraction and confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the LED die is embedded within the waveguide to increase coupling efficiency, then light coupling efficiency is improved, but mechanical stability deteriorates due to the large geometric dimensions difference between waveguide and LED die
Solution Approach 1:
The patent introduces an index-matching material as an intermediary substance between the LED die and waveguide. This material has a refractive index intermediate between the LED die and waveguide materials, enabling optical coupling while allowing mechanical support structures to be positioned without disrupting light propagation. The intermediary material fills the gap between optical and mechanical requirements.
Solution Approach 2:
The patent segments the waveguide structure into distinct regions: an input region where the LED die is positioned and embedded in index-matching material, and an output region where light exits. This segmentation allows the LED sub-assembly to be positioned at the edge of the waveguide without blocking the main light propagation path, thereby maintaining both mechanical stability and optical efficiency.
2Strength
If the contact area between waveguide and LED sub-assembly is increased to improve mechanical connection, then mechanical strength is improved, but light absorption increases and total internal reflection is disrupted
Solution Approach 1:
The patent applies local quality by creating a localized index-matching material region at the LED die interface, while maintaining air gaps or low-index material regions in the broader contact area between the waveguide and LED sub-assembly. This allows mechanical connection strength to be achieved through localized adhesive bonding without compromising the overall optical performance and TIR conditions across the waveguide interface.
3Productivity
If index-matching material is used to optimize light coupling, then input coupling efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The patent merges the index-matching material application with the existing LED die mounting process. The index-matching material is applied as part of the standard die-attachment procedure, combining two functions (mechanical bonding and optical coupling optimization) into a single integrated process step, thereby minimizing additional manufacturing complexity while achieving improved coupling efficiency.
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 approach enhances mechanical stability and input coupling efficiency by minimizing non-TIR regions and reducing light absorption, allowing for more efficient light propagation within the waveguide while maintaining mechanical integrity.
Implementation Method 1
light from the LED 105 is coupled in to an input region 130 of the waveguide 120 via an input coupling element 135. The light then propagates toward an output region 140 by means of total internal reflection (TIR) off of the top and bottom faces of the waveguide 120.
Implementation Method 2
using discrete attachment points and index-matching materials with refractive indices between those of the LED and waveguide, thereby optimizing light extraction and confinement
Data Source
AI summary
In various embodiments, an illumination apparatus includes an air gap between a sub-assembly and a waveguide attached thereto at a plurality of discrete attachment points, as well as a bare-die light-emitting diode encapsulated by the waveguide.