Photonic Backlight Device Speckle Reduction
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Solution Overview
Problem
Existing display architectures using coherent light sources face challenges such as speckle interference, crosstalk between pixels, and difficulty in controlling the angular cone of light emission, especially at high pixels per inch (PPI) densities.
Innovation Solution
A high-performance backlight device incorporating photonic integrated circuits and a spatial modulator, featuring a light assembly with de-speckling mechanisms, a multi-mode slab waveguide for light expansion, and an out-coupling assembly with gratings to focus light onto pixels, thereby mitigating speckle and improving light efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If coherent light sources (lasers) are used to provide high brightness, then illumination intensity is improved, but speckle interference and image non-uniformity occur
Solution Approach 1:
The patent segments the coherent light beam into multiple independent waveguides (e.g., 2x2 or 3x3 arrays), where each waveguide carries a portion of the total light. By dividing the single coherent source into multiple spatially separated coherent beams, the interference patterns from each waveguide do not perfectly overlap, thereby reducing speckle visibility while maintaining high brightness through additive light output.
Solution Approach 2:
The patent changes the spatial parameters of light propagation by transitioning from a single-mode waveguide to a multi-mode slab waveguide structure. This parameter change in waveguide mode distribution alters the interference characteristics of the coherent light, reducing speckle formation while preserving the high brightness advantage of laser sources.
2Manufacturing precision
If small pitch (high PPI) is achieved to increase resolution, then manufacturing precision is improved, but crosstalk between neighboring pixels and waveguides increases
Solution Approach 1:
The patent transitions from two-dimensional planar waveguide arrays to a three-dimensional slab waveguide structure with controlled light confinement in the vertical dimension. By adding the vertical confinement dimension through total internal reflection at angled interfaces, the system achieves better spatial isolation between adjacent waveguides at high PPI, reducing crosstalk while maintaining manufacturability.
3Manufacturing precision
If small pitch (high PPI) is achieved to increase resolution, then manufacturing precision is improved, but control of angular cone of light emission becomes difficult
Solution Approach 1:
The patent designs the slab waveguide structure with uniform refractive index distribution and symmetric boundary conditions, creating equipotential optical paths for light propagation. This equipotential design ensures that light from each pixel position is emitted with consistent angular characteristics, making angular cone control predictable and uniform across the entire high-PPI display surface.
4Ease of operation
If single-mode waveguide is used to achieve good angular spectrum control, then orientation control is improved, but light efficiency decreases due to alignment difficulties
Solution Approach 1:
The patent segments the light path into multiple independent single-mode waveguides arranged in arrays, where each waveguide maintains good angular spectrum control for its specific pixel position. By segmenting rather than using a single large waveguide, the system preserves orientation control benefits while reducing alignment sensitivity through distributed, modular waveguide structures that are more tolerant to manufacturing variations.
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 reduces speckle interference, minimizes crosstalk, and achieves uniform angular output, enabling high-resolution displays with improved image quality and efficiency.
Implementation Method 1
a multi-mode slab waveguide configured to in-couple the conditioned light and expand the in-coupled conditioned light in two dimensions
Implementation Method 2
The out-coupling assembly may include one or more gratings that are configured to out-couple light from the slab expansion region
Data Source
AI summary
Embodiments of the present disclosure relate to a high performance backlight device with photonic integrated circuits. The backlight device includes a light source assembly, a multi-mode slab waveguide, and an out-coupling assembly. The light source assembly includes one or more light sources that generate light in accordance with emission instructions, and a de-speckling mechanism that conditions the generated light to mitigate speckle. The multi-mode slab waveguide in-couples the conditioned light and expands the in-coupled conditioned light in two dimensions to form a homogenous area of conditioned light within a region of the multi-mode slab waveguide. The out-coupling assembly out-couples the conditioned light from the region in a direction normal to the two dimensions, wherein a light modulation layer forms an image from the out-coupled conditioned light.