Light-Guide Optical Element with Angled Partially-Reflective Surfaces
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional light-guide optical elements (LOEs) in head-up displays face challenges in achieving uniform image output due to non-uniform reflectivity across partially-reflecting surfaces, particularly at varying angles of incidence, leading to brightness inconsistencies and 'ghost' images.
Innovation Solution
The optical system employs a light-guide optical element with obliquely angled reflector surfaces that have high reflectivity above 60 degrees and partial reflectivity below 35 degrees, allowing for varying reflectivity between successive surfaces to compensate for intensity decreases and prevent ghost images, with reflector surfaces inclined at 20°-26° to the major surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If partially-reflecting surfaces are used to couple out image illumination, then the optical aperture is multiplied, but the reflectivity must be precisely controlled as a function of incident angle which is difficult to achieve in practice
Solution Approach 1:
The patent applies different reflectivity characteristics to different regions of the same optical surface. Specifically, the optical surface has a first region with first reflectivity characteristics and a second region with second reflectivity characteristics, allowing each region to be optimized for its specific function without requiring precise angular-dependent control across the entire surface.
Solution Approach 2:
The optical surface is divided into multiple discrete regions with different reflectivity properties. This segmentation allows independent optimization of each region's reflectivity for its specific incident angle range, simplifying manufacturing compared to achieving continuous angular-dependent reflectivity control.
2Object-affected harmful factors
If the facet is made transparent (zero reflection) for rays at certain angles, then ghost images are prevented, but this requirement becomes increasingly difficult to fulfill as angles of incidence get larger
Solution Approach 1:
Different regions of the optical surface are assigned different reflectivity characteristics appropriate for their specific incident angle ranges. Regions receiving larger incident angles can have higher reflectivity without generating ghosts, while regions receiving smaller angles maintain low reflectivity to prevent ghosting.
3Illumination intensity
If high transmission (near complete transmission) is achieved at certain angle ranges, then image illumination brightness is maintained, but this conflicts with the need for partial reflection at other angles
Solution Approach 1:
The optical surface is divided into regions with different reflectivity characteristics matched to the incident angle ranges they receive. This allows each region to optimize for its specific angular range, maintaining brightness where needed while enabling partial reflection elsewhere.
Solution Approach 2:
By segmenting the optical surface into multiple regions with different reflectivity properties, the system can simultaneously achieve high transmission in some regions and partial reflection in others, resolving the conflict between maintaining brightness and enabling angular-dependent reflection.
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 configuration ensures high reflectivity for steeper angles, maintaining image intensity and preventing ghost images, while allowing partial transmission at shallower angles, resulting in a uniform and continuous image output with reduced energy loss.
Implementation Method 1
at least one of the reflector surfaces is configured to have high reflectivity for angles of incidence above 60 degrees to the normal and partial reflectivity for angles of incidence less than 35 degrees to the normal
Implementation Method 2
employ light-guide optical elements (LOEs) having a pair of parallel major external surfaces to convey a collimated image which propagates within the LOE by internal reflection
Data Source
AI summary
An optical system includes a light-guide optical element (LOE) (100) having a pair of parallel major external surfaces (102, 104) and a set of mutually-parallel reflector surfaces (106a, 106b, 106c) obliquely angled within the LOE. At least one of the reflector surfaces has high reflectivity for angles of incidence above 60 degrees to the normal and partial reflectivity for angles of incidence less than 35 degrees to the normal.