Omnidirectional Reflector for LED Efficiency
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Solution Overview
Problem
Conventional reflectors, such as distributed Bragg reflectors, are not omnidirectional, leading to reduced efficiency in reflecting light emitted by light-emitting diodes (LEDs) across a range of incident angles, particularly when used with light-absorbing substrates like silicon, resulting in less than 10% reflection efficiency.
Innovation Solution
An omnidirectional reflector system is created by incorporating a reflective layer and a two-dimensional photonic crystal layer over a substrate, with the photonic crystal layer reflecting light in two dimensions while allowing it to travel unreflected in a third dimension, thereby collimating and increasing the efficiency of light reflection across various angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a distributed Bragg reflector (DBR) is used to reflect light from the LED, then light direction control is improved, but reflection efficiency drops when the angle of incidence increases relative to normal to the surface
Solution Approach 1:
The patent transitions from conventional planar reflectors to a three-dimensional photonic crystal structure. The photonic crystal layer features periodic variations in refractive index in three dimensions, creating omnidirectional reflection properties that maintain high reflection efficiency across all angles of incidence, thereby resolving the angle-dependent efficiency loss of DBRs.
Solution Approach 2:
The invention combines multiple materials with different refractive indices to form the photonic crystal structure. This composite approach creates a periodic optical structure that exploits interference effects to achieve omnidirectional reflection, overcoming the limitations of single-material DBR structures.
2Ease of manufacture
If a conventional reflector is used with a light-absorbing substrate like silicon, then device integration is simplified, but less than 10% of light is reflected due to substrate absorption
Solution Approach 1:
The photonic crystal layer acts as an intermediary structure between the LED and the substrate. This intermediate photonic structure manipulates light propagation before it reaches the absorbing substrate, creating omnidirectional reflection that prevents light from entering the substrate at angles where absorption would occur, thereby maintaining high reflection efficiency while preserving substrate integration.
3Device complexity
If the LED emits light in all directions without a reflector, then light generation is simple, but only a small portion of total light is received in the desired direction
Solution Approach 1:
By implementing a three-dimensional photonic crystal structure, the patent achieves omnidirectional reflection that captures light emitted in all directions and redirects it toward the desired output direction. This 3D structural approach efficiently collects light from all angles without requiring complex multi-component optical systems.
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
The omnidirectional reflector enhances the overall efficiency of light reflection, directing more light in the desired direction and reducing loss due to absorption by the substrate, thereby improving the performance of LEDs.
Implementation Method 1
A two-dimensional photonic crystal layer is located over the reflective layer, and an LED is located over the photonic crystal layer
Implementation Method 2
the photonic crystal layer reflecting light in two dimensions while allowing it to travel unreflected in a third dimension
Implementation Method 3
reflectors have been formed as part of the LED in order to direct the light in a desired direction and away from any light-absorbing substrates
Implementation Method 4
A light-emitting diode (LED) is generally formed of a first contact layer, an active layer, and a second contact layer that form a diode that will generate light when it is forward-biased
Data Source
AI summary
A system and method for manufacturing an LED is provided. A preferred embodiment includes a substrate with a distributed Bragg reflector formed over the substrate. A photonic crystal layer is formed over the distributed Bragg reflector to collimate the light that impinges upon the distributed Bragg reflector, thereby increasing the efficiency of the distributed Bragg reflector. A first contact layer, an active layer, and a second contact layer are preferably either formed over the photonic crystal layer or alternatively attached to the photonic crystal layer.