Variable Height Sub-Pixels for HMD Chromatic Aberration
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Solution Overview
Problem
Conventional head-mounted displays (HMDs) suffer from optical distortions such as chromatic aberration and field curvature due to pixels being on a single planar surface, which affects the quality of the content presented to the user.
Innovation Solution
The HMD system incorporates sub-pixels mounted on microbumps of varying heights to mitigate longitudinal chromatic aberration and field curvature, with the substrate being micromachined or deposited with additive layers to achieve specific thicknesses for optimal optical performance, and template layers to compensate for stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If pixels are arranged on a planar surface in conventional HMDs, then the manufacturing process is simple, but optical distortion (chromatic aberration, field curvature) occurs
Solution Approach 1:
The patent transitions from a two-dimensional planar pixel arrangement to a three-dimensional configuration where pixels are positioned at different heights (z-axis) above the substrate. Specifically, blue pixels are positioned at a first height, green pixels at a second height, and red pixels at a third height, creating vertical layering that corrects chromatic aberration by aligning different wavelength pixels at optimal focal distances.
Solution Approach 2:
Different regions of the pixel array are given different vertical positions based on their wavelength characteristics. Each color sub-pixel (red, green, blue) is locally positioned at a specific height optimized for its wavelength, rather than all pixels being at the same plane. This localized positioning correction addresses the optical distortion specific to each wavelength band.
2Object-affected harmful factors
If sub-pixels are mounted at different heights to correct chromatic aberration, then optical quality improves, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into the pixel mounting structure: the microbumps serve simultaneously as electrical interconnects and as height-positioning elements. By integrating the positioning function into the existing bump structure rather than adding separate positioning mechanisms, the solution achieves chromatic aberration correction without proportionally increasing device complexity.
Solution Approach 2:
The patent modifies the z-position parameter of pixels based on their wavelength characteristics. Blue pixels are positioned at a first height, green at a second height, and red at a third height, creating a systematic parameter variation that corrects chromatic aberration. This parameter-based organization provides a structured approach that manages complexity through regularity.
3Object-affected harmful factors
If substrate thickness is varied to mitigate chromatic aberration, then manufacturing precision requirements increase, but optical performance improves
Solution Approach 1:
The patent performs preliminary positioning of pixels at different heights during the manufacturing process itself, using microbumps formed on the substrate before final assembly. This preliminary action establishes the correct z-positions early in manufacturing, avoiding the need for complex post-processing adjustments and reducing the precision burden on later manufacturing steps.
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A head-mounted display (HMD) presents viewable media to a user. The HMD includes a light source and an optical block. The light source includes a first sub-pixel mounted on a first set of microbumps at a first height from a substrate and emits light within a first optical band, and a second sub-pixel mounted on a second set of microbumps at a second height from the substrate that is different from the first height, and emits light over a second optical band that is different than the first optical band. The optical block receives the image light from the light source, and directs the image light to an eyebox, wherein the first height and the second height mitigates longitudinal chromatic aberration and field curvature in the optical block.