Dual Waveguide Structure for Head-Up Display Pupil Expansion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Head-up displays face challenges in achieving a large exit pupil size while maintaining uniform light distribution and preserving far-field image quality, due to limitations in waveguide design that affect pupil replication and color rendition across the visible spectrum.
Innovation Solution
A dual waveguide structure is employed, where a main waveguide with a low refractive index is combined with a secondary waveguide of higher refractive index, utilizing a semi-reflecting surface and a diffractive grating to achieve pupil replication in two dimensions, ensuring light is trapped within the waveguide while maintaining ray direction alignment and correcting for color-dependent variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single waveguide is used to propagate light, then the device structure is simple, but the exit pupil size is limited and uniform light distribution across the eye box cannot be achieved
Solution Approach 1:
The waveguide system is divided into multiple separate waveguides (first waveguide and second waveguide), each contributing to different portions of the exit pupil. This segmentation allows the system to achieve a larger combined exit pupil area while maintaining manageable individual waveguide structures that can be independently optimized and manufactured.
Solution Approach 2:
The patent extends the waveguide system from a single-plane configuration to a multi-plane or three-dimensional arrangement by stacking or positioning multiple waveguides at different locations. This dimensional expansion enables the exit pupil to be enlarged in areas where a single waveguide would be insufficient, while keeping each individual waveguide component compact.
2Area of stationary object
If multiple waveguides are used to expand exit pupil size, then the exit pupil area increases, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent employs waveguides with substantially identical structures and optical properties, ensuring uniform light propagation characteristics across all waveguides. This homogeneity simplifies the manufacturing process by allowing mass production of identical components, reduces assembly complexity through standardized interfaces, and ensures consistent optical performance across the entire exit pupil area.
3Stability of the object's composition
If waveguides are used to propagate light, then light is trapped within the waveguide, but color-dependent variations in ray angles cause non-uniform color distribution across the eye box
Solution Approach 1:
The patent assigns different optical characteristics to different waveguides based on their specific functions. Certain waveguides are optimized for specific wavelength ranges or propagation angles, allowing each waveguide to handle light with locally optimized properties. This local quality approach corrects color-dependent variations by ensuring that each portion of the spectrum is properly managed by the most suitable waveguide.
Solution Approach 2:
The patent varies key optical parameters such as refractive index, waveguide geometry, and coupling angles across different waveguides to compensate for color-dependent variations. By adjusting these parameters, the system maintains uniform color distribution across the eye box while preserving efficient light trapping and propagation in each waveguide.
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 allows for a compact waveguide design that expands the exit pupil size without degrading image quality, providing a uniform near-field distribution and preserving the far-field image, thus enhancing the usability and image clarity of head-up displays.
Implementation Method 1
utilizing a semi-reflecting surface and a diffractive grating to achieve pupil replication in two dimensions, ensuring light is trapped within the waveguide
Implementation Method 2
utilizing a semi-reflecting surface and a diffractive grating to achieve pupil replication in two dimensions, ensuring light is trapped within the waveguide while maintaining ray direction alignment and correcting for color-dependent variations
Implementation Method 3
Waveguide 10 is a piece of glass or other optically transmissive material with parallel faces which traps a light beam within the waveguide. Waveguides utilising refracting and reflecting surfaces to inject the light beam into the waveguide, to propagate it within the waveguide, and/or to project it out from the waveguide
Implementation Method 4
A first waveguide (304) has a first interface (309) with a second waveguide (308). The first waveguide (304) is formed from a material with a first refractive index and the second waveguide (308) is formed from a material with a second refractive index, wherein the second refractive index is higher than the first refractive index
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
An optical waveguide device for use in a head up display. The waveguide device provides pupil expansion in two dimensions. The waveguide device comprise a primary waveguide and a secondary waveguide, the secondary waveguide being positioned on a face of the primary waveguide. The secondary waveguide has a diffraction grating on a face opposite to the face which contacts the primary waveguide. The diffraction grating diffracts light into more than diffraction order. Rays diffracted into a non-zero order are trapped in the secondary waveguide by total internal reflection.