Pupil Expander Light Guide with Inclined Mirrors
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Solution Overview
Problem
Conventional display systems for Head-Up Displays (HUDs) face limitations such as a restricted instantaneous field of observation due to the eye's distance from the pupil, complexity, cost, and bulkiness, as well as limited field of view and color quality, which hinder their application in aeronautical and other fields.
Innovation Solution
A display device with a light guide comprising a plane mirror and a semi-reflecting plate, where the optical axis is inclined, allowing light to propagate and be extracted through successive reflections and transmissions, simplifying production and enhancing pupil expansion without the need for complex optical components like diffractive gratings or micro-prisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional display systems with collimating lenses and semi-reflective plates are used, then the system structure is simple, but the instantaneous field of view is limited due to the eye's distance from the pupil
Solution Approach 1:
The patent introduces a light guide with inclined mirrors that expands the exit pupil in a new spatial dimension, allowing the observer's eye to be positioned closer to the system while maintaining a large instantaneous field of view. The inclined mirrors create multiple reflected images of the display that appear to originate from an expanded virtual pupil location.
Solution Approach 2:
The light guide acts as an intermediary component between the collimating lens and the observer's eye. It contains inclined mirrors that reflect and redirect light beams, creating the effect of an expanded exit pupil without requiring the eye to be at a specific distance from the optical components.
2Ease of operation
If optical relays and off-axis optical mixers are used to expand the field of view, then the instantaneous field of view is improved, but the system becomes complex, expensive, and bulky
Solution Approach 1:
The patent combines the light guide function with the exit pupil expansion function into a single integrated component. The light guide contains inclined mirrors that simultaneously guide light from the display and expand the virtual pupil, eliminating the need for separate optical relays and off-axis optical mixers.
Solution Approach 2:
The light guide serves multiple functions: it guides light from the collimating lens, expands the exit pupil through inclined mirrors, and positions the virtual image at the appropriate location. This multi-functional design replaces several specialized components with a single versatile element.
3Ease of operation
If diffractive gratings or micro-prisms are used in the light guide, then pupil expansion is achieved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent uses simple inclined mirrors with standard reflective coatings instead of complex diffractive gratings or micro-prism arrays. These mirrors can be manufactured using conventional techniques and are easier to align and manufacture, reducing both cost and manufacturing complexity while achieving the same pupil expansion effect.
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 solution provides a more compact, cost-effective, and easily installable HUD system with improved field of view and color quality, enabling broader applications including aeronautical use while maintaining high luminance and contrast.
Implementation Method 1
the light beams from the optical assembly propagating inside the light guide by successive reflections on the plane mirror and the semi-reflective plate
Implementation Method 2
the transmission of the light beams from the optical assembly to the outside of the light guide being done by successive transmissions through the semi-reflective plate
Data Source
Figure 1~2
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Figure 6~7
AI summary
The technical field of the invention is that of display devices comprising an optical assembly including a display (1), an optical system forming an image of this display at infinity, and a light guide with pupil expansion in two spatial directions. The guide according to the invention comprises three plane mirrors (41, 42, 43) and two semi-reflective plates (44, 45), the optical axis of this optical assembly being inclined with respect to the surface of the first plane mirror (41) at an angle other than zero and strictly less than 90 degrees, the light beams from the optical assembly propagating inside the light guide by successive reflections on the plane mirrors and the semi-reflective plates, the transmission of the light beams from the optical assembly to the outside of the light guide occurring by successive transmissions through the second semi-reflective plate (45).