Optical Waveguide Pupil Expansion for Ghosting Reduction
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Solution Overview
Problem
Optical waveguides in near-eye displays suffer from non-uniform brightness and ghosting due to light passing through the same reflective surface multiple times at beam-splitting surfaces, leading to manufacturing costs and inefficiencies.
Innovation Solution
An optical waveguide device with a waveguide element and pupil-expanding coupling element, featuring beam-splitting surfaces with increased tilt angles and P-light-transmissive/S-light-reflective films, ensuring light penetrates each surface only once, improving brightness uniformity and reducing ghosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discrete beam-splitting surfaces with tilt angles of 23° to 26° are used in traditional geometric array optical waveguides, then light coupling is achieved, but non-uniform brightness occurs at spliced positions and ghosting is generated due to multiple reflections
Solution Approach 1:
The patent changes the tilt angle parameter of the beam-splitting surface from the traditional 23°-26° range to a new range of 45°-60°. This parameter change fundamentally alters the light path geometry, ensuring that light passes through each beam-splitting surface only once, thereby eliminating multiple reflections that cause ghosting and brightness non-uniformity at spliced positions
Solution Approach 2:
The patent inverts the traditional optical path design by using a larger tilt angle that causes light to reflect off the beam-splitting surface first and then exit through the waveguide surface, rather than the conventional approach. This inversion of the light interaction sequence with the beam-splitting surface prevents multiple passes through the same surface, eliminating the root cause of brightness non-uniformity and ghosting
2Reliability
If multiple films or thick substrates are attached to optimize brightness uniformity in traditional waveguides, then some brightness improvement is achieved, but manufacturing cost increases significantly
Solution Approach 1:
The patent achieves brightness uniformity optimization by changing the tilt angle parameter of the beam-splitting surface to 45°-60°, which fundamentally alters the light interaction mechanism. This single parameter change eliminates the need for multiple additional films or thick substrates, thereby achieving the brightness uniformity goal while avoiding the associated manufacturing cost increases
Solution Approach 2:
The patent extracts and eliminates the need for additional optimization layers (multiple films or thick substrates) by fundamentally changing the beam-splitting surface angle. The core brightness uniformity problem is solved at the source through the angle modification, making the extraction of unnecessary components and the reduction of manufacturing complexity
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 solution effectively enhances brightness uniformity and reduces ghosting while maintaining a compact design, improving light emission efficiency without increasing the waveguide's volume.
Implementation Method 1
a first P-light-transmissive and S-light-reflective film or a first semi-transmissive and semi-reflective film is disposed on the triangular prism reflective surface
Implementation Method 2
a total reflection film is disposed on the oblique quadrangular prism reflective surface
Implementation Method 3
each of the multiple first beam-splitting slopes forms an angle α along a stacking direction, 32°≤the angle α
Data Source
AI summary
Provided are an optical waveguide device and a near-eye display device. The optical waveguide device includes a waveguide element and a pupil-expanding coupling element. The waveguide element includes at least a waveguide substrate and a longitudinal pupil-expanding beam-splitting surface array, where the longitudinal pupil-expanding beam-splitting surface array of the waveguide element is disposed at an angle of 32°≤α<40°. The pupil-expanding coupling element is disposed at an end of the waveguide substrate and includes a triangular prism, a free-surface oblique quadrangular prism and a free-surface triangular prism. A first P-light-transmissive and S-light reflective film or a first semi-transmissve and semi-reflective film is disposed on a triangular prism reflective surface. A total reflection film is disposed on an oblique quadrangular prism reflective surface. A second P-light-transmissive and S-light-reflective film or a second semi-transmissive and semi-reflective film is disposed on a triangular prism plane.