Waveguide Coupling Using Top Mirror for Thin Illumination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing thin, planar illumination systems face inefficiencies in coupling light sources to waveguides, with coupling efficiencies limited to around 85% due to the side-emitting LED design, leading to light loss and increased complexity and cost when trying to achieve higher efficiencies.
Innovation Solution
Embedding an LED within a waveguide and using a specular mirror to reflect light back into the waveguide, allowing for total internal reflection and improving coupling efficiency, while using standard LED and waveguide shapes to reduce complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a side-emitting LED design is used to couple light to a waveguide, then the coupling efficiency can approach 85% when the waveguide thickness is larger than the LED width, but the waveguide thickness cannot be reduced below the LED width and light loss increases
Solution Approach 1:
The patent inverts the conventional side-emitting LED configuration by using a top-emitting LED positioned below the waveguide. Instead of coupling light from the side, the LED emits light upward through the waveguide bottom, with a mirror beneath the LED reflecting light back into the waveguide. This inversion enables thin waveguide designs (t≤d) while maintaining high coupling efficiency and reducing light loss.
Solution Approach 2:
The patent introduces a mirror as an intermediary element positioned beneath the LED. The mirror reflects light that would otherwise be lost downward back into the waveguide, effectively mediating the light coupling process. This intermediary component enables the system to achieve high coupling efficiency with thin waveguides by recovering and redirecting light paths.
2Loss of energy
If specially engineered LED and waveguide structures are used to increase coupling efficiency, then coupling efficiency can be improved, but the system complexity and cost increase
Solution Approach 1:
The patent changes the emission direction parameter of the LED from side-emitting to top-emitting configuration, and positions the LED below the waveguide rather than on the side. This parameter change enables standard, inexpensive LED components to achieve high coupling efficiency with thin waveguides, eliminating the need for specially engineered complex structures while maintaining superior performance.
3Length of stationary object
If the waveguide thickness is reduced to achieve thinner illumination systems, then the profile is lowered, but the coupling efficiency decreases and more light is lost
Solution Approach 1:
By inverting the LED placement from side-mounted to bottom-mounted with upward emission, the patent enables thin waveguide designs to maintain high coupling efficiency. The mirror beneath the LED captures and redirects light that would otherwise escape, allowing the waveguide thickness to be reduced below the LED width without significant light loss.
Solution Approach 2:
The mirror acts as an intermediary that recovers light paths in thin waveguide configurations. By reflecting light back into the waveguide from below, the mirror compensates for the reduced thickness, maintaining high coupling efficiency even when the waveguide is thinner than the LED width.
4Ease of manufacture
If top-emitting LEDs are used instead of side-emitting LEDs, then inexpensive high-power LED chips can be used, but light coupling to the waveguide is less efficient without additional structures
Solution Approach 1:
The mirror serves as an intermediary that enables standard top-emitting LEDs to achieve high coupling efficiency. By positioning the mirror beneath the LED to reflect light upward into the waveguide, the system maintains simplicity and low cost while achieving superior light coupling performance without requiring specially engineered LED structures.
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 enables coupling efficiencies greater than 85% even when the waveguide thickness is equal to or less than the LED width, using inexpensive top-emitting LEDs and reducing light absorption, thus providing efficient light in-coupling to thin waveguides.
Implementation Method 1
A first portion of the emitted light propagates through the waveguide because its emission angle (with respect to the waveguide's upper surface) results in total internal reflection (TIR) of the first portion
Implementation Method 2
A top mirror is disposed above the discrete light source. The top mirror reflects light away from a top surface of the sub-assembly module and into a confined mode of the waveguide
Data Source
AI summary
In various embodiments, an illumination structure includes a discrete light source disposed proximate a bottom surface of a waveguide. A top mirror may be disposed above the discrete light source to convert modes of light emitted from the discrete light source into trapped modes, thereby increasing the coupling efficiency of the illumination structure.