Waveguide Grating Layers for Pupil Banding Mitigation
Solution Overview
Problem
Prior art projection displays using waveguide techniques suffer from pupil banding, a phenomenon where individual pupils of image bearing light do not overlap, leading to modulation of intensity as the observer's line of sight changes, resulting in perceived pupil banding.
Innovation Solution
The use of a waveguide with layers of materials having different refractive indices or thicknesses, where a grating element is arranged between these layers to alter the spatial periodicity of pupils, causing them to mix and overlap, thereby mitigating pupil banding. This is achieved by varying the refractive index and/or thickness of the layers to direct impinging image bearing light and provide beam splitting, ensuring that the pupils of image bearing light exiting the waveguide overlap, reducing the perception of pupil banding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a waveguide with uniform material layers is used, then the structure is simple and easy to manufacture, but pupil banding occurs due to non-overlapping pupils of image bearing light
Solution Approach 1:
The waveguide transitions from uniform material layers to layers with different refractive indices or thicknesses at specific locations. This local variation in optical properties causes beam splitting and spatial periodicity variation of pupils, making pupils overlap and eliminating pupil banding while maintaining overall structural simplicity
Solution Approach 2:
The waveguide employs composite material layers with different refractive indices or thicknesses. This composite structure creates the necessary optical path differences to vary spatial periodicity of pupils, causing them to overlap and eliminate pupil banding artifacts
2Reliability
If layers with different refractive indices or thicknesses are introduced to vary spatial periodicity of pupils, then pupil banding is mitigated, but device complexity increases
Solution Approach 1:
Rather than making the entire waveguide complex, the invention applies local variations in refractive index or thickness only where needed to achieve pupil overlap. This targeted approach mitigates pupil banding while minimizing overall device complexity
Solution Approach 2:
The invention changes optical parameters (refractive index or thickness) of specific layers to achieve the desired pupil spatial periodicity variation. This parameter adjustment approach provides a controlled method to eliminate pupil banding without substantially increasing device 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 overlapping of pupils results in a mitigation of pupil banding, providing a more stable and uniform intensity of the image as the observer's view changes, enhancing the display quality by eliminating the modulation of image intensity.
Implementation Method 1
a grating element arranged on either the first or the second layer of material and arranged to direct at least some impinging image bearing light out of the waveguide and to provide at least some beam splitting of image bearing light passing through the grating element
Implementation Method 2
a first layer of material with a first predetermined refractive index and/or first predetermined thickness, a second layer of material with a second predetermined refractive index and/or second predetermined thickness... the first predetermined refractive index and second predetermined refractive index and/or the first predetermined and second predetermined thickness are arranged to vary the spatial periodicity of pupils of image bearing light radiated from the waveguide
Implementation Method 3
Light impinging on the internal surfaces of the first plate-like waveguide 14 is greater than the critical angle for the material from which the first plate-like waveguide 14 is made. The image bearing light is constrained within the first plate-like waveguide 14 to propagate along the first plate-like waveguide 14 reflecting from each internal surface in turn
Data Source
Figure 1~2
Figure 3~10
Figure 4
AI summary
A projection display (60) includesafirstwaveguide (64) incorporating a grating structure (74) and second waveguide (66) incorporating an exit grating (84). The first and second waveguides (64, 66)are arrange to expand an image in orthogonal directions. The second waveguide (66) includes a first layer (86) with a first predetermined refractive index and/or first predetermined thickness, a second layer (88) with a second predetermined refractive index and/or second predetermined thickness. The exit grating (84) is arranged to direct at least some impinging light out of the second waveguide(66)and to provide at least some beam splitting of light passing through the exit grating (84). The first and second layers (86, 88) are arranged to abut one another such that the exit grating (84) is therebetween. The first predetermined refractive index and second predetermined refractive index and/or first predetermined thickness and second predetermined thickness are arranged to vary the spatial periodicity of pupils of image bearing light radiated from the second waveguide (66).