Micro-lens Array for Chief Ray Walk-off Compensation in Micro-LED Displays
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Solution Overview
Problem
Micro-LED-based display systems face challenges in efficiently coupling light from micro-LED arrays into waveguide displays due to limited field of view and exit pupil, leading to non-uniform light distribution and reduced overall efficiency.
Innovation Solution
Incorporating a micro-lens array with offset micro-lenses to redirect chief rays of light emitted by micro-LEDs, optimizing the mesa structure and reflectors to achieve high light extraction efficiency and uniformity, and using semiconductor materials like SiO2, TiO2, or polymers for the micro-lenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If micro-LED arrays are used for display systems, then high brightness and high packing density are achieved, but chief ray walk-off causes non-uniform light distribution and reduced coupling efficiency into waveguide displays
Solution Approach 1:
A micro-lens is introduced as an intermediary optical element between the micro-LED and the waveguide display. The micro-lens receives light from the micro-LED and redirects the chief rays to compensate for walk-off effects, ensuring uniform light distribution across the display while maintaining high brightness output
2Device complexity
If conventional micro-LED structures are used, then device simplicity is maintained, but light extraction efficiency is insufficient for effective coupling into waveguide displays
Solution Approach 1:
The micro-LED structure is segmented into distinct functional regions: a mesa structure for light generation, a micro-lens for optical control, and a backside reflector for light extraction enhancement. This segmentation allows each component to be optimized for its specific function while working together to achieve high overall efficiency
Solution Approach 2:
The backside reflector is positioned on the opposite side of the micro-LED from the light emission direction, utilizing the third dimension (vertical depth) to redirect light that would otherwise be lost. This dimensional approach enables light extraction from the substrate side without interfering with the forward light path
3Volume of moving object
If the field of view and exit pupil of waveguide displays are limited, then device compactness is achieved, but light coupling efficiency into the user's eyes is reduced
Solution Approach 1:
The micro-lens is designed with specific local optical properties (refractive index, curvature radius) that are optimized for redirecting chief rays within the limited field of view of the waveguide display. This localized optimization ensures that light is efficiently coupled into the user's eyes despite the compact device constraints
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
Improves light extraction efficiency and uniformity across the micro-LED array, enhancing the overall efficiency of light coupling into waveguide displays and user's eyes, with simulations showing increased external quantum efficiency and reduced chief ray walk-off.
Implementation Method 1
a micro-lens on top of the micro-LED and configured to extract light emitted by the micro-LED
Implementation Method 2
Each micro-lens in the array of micro-lenses may be configured to direct a chief ray of light emitted by a corresponding micro-LED in the array of micro-LEDs to a different respective direction
Implementation Method 3
a mesa structure including semiconductor materials and sidewalls that are vertical or inwardly tilted in a light emitting direction
Implementation Method 4
a backside reflector on a back surface of the mesa structure
Implementation Method 5
Each micro-lens in the array of micro-lenses may be configured to collimate light emitted by the corresponding micro-LED in the array of micro-LEDs
Data Source
AI summary
Techniques disclosed herein relate to micro light emitting diodes (micro-LEDs) for a display system. A display system includes an array of micro light emitting diodes (micro-LEDs), an array of output couplers optically coupled to the array of micro-LEDs and configured to extract light emitted by respective micro-LEDs in the array of micro-LEDs, a waveguide display, and display optics configured to couple the light emitted by the array of micro-LEDs and extracted by the array of output couplers into the waveguide display. Each output coupler in the array of output couplers is configured to direct a chief ray of the light emitted by a respective micro-LED in the array of micro-LEDs to a different respective direction.