Holographic Display Speckle Reduction via Dynamic Diffusion
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Solution Overview
Problem
Display apparatus using holography with coherent light beams suffer from speckle noise due to constructive or destructive interference, leading to uneven luminance and reduced image quality, as conventional methods to eliminate speckle affect the spatial light information.
Innovation Solution
Incorporating a light-diffusing element with an actuator that changes the diffusion angle of the three-dimensional image beam, either through rotation or vibration, and a liquid crystal element with a controller to adjust the arrangement of liquid crystal molecules, allowing for dynamic diffusing patterns to improve uniformity without altering the spatial light information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent light beams are used for holographic display, then three-dimensional image formation is achieved, but speckle noise is generated leading to uneven luminance
Solution Approach 1:
The patent introduces a light-diffusing element with an actuator that dynamically changes the diffusion angle of the coherent light beam. By making the diffusion angle variable rather than fixed, the system can adjust the speckle distribution over time while maintaining the three-dimensional image formation capability, thus resolving the contradiction between image accuracy and speckle noise.
Solution Approach 2:
The actuator is driven at a specific driving frequency to periodically change the diffusion angle of the light-diffusing element. This periodic modulation causes the speckle pattern to change over time, and when combined with the persistence of vision effect, the human eye perceives an averaged uniform luminance rather than the instantaneous speckle patterns, thereby eliminating speckle noise while preserving 3D image quality.
2Object-affected harmful factors
If a vibration mirror is arranged in front of the coherent light source to homogenize light beams, then speckle is eliminated, but spatial light information is altered affecting hologram formation
Solution Approach 1:
Instead of placing the diffusing element directly in the coherent light beam path before hologram formation (which would alter spatial light information), the patent positions the light-diffusing element on the intermediate imaging surface where the three-dimensional image beam is already formed. This intermediary positioning allows speckle elimination without interfering with the hologram formation process, as the spatial light information has already been encoded by this point.
Solution Approach 2:
The patent applies the light-diffusing element after the three-dimensional image beam has been formed by the display unit, rather than before. This preliminary action sequence ensures that the spatial light information is first properly encoded by the display unit, and then the speckle is eliminated by the light-diffusing element, avoiding any interference with hologram formation.
3Illumination intensity
If the diffusion angle is changed to eliminate speckle, then luminance uniformity is improved, but image quality may be affected
Solution Approach 1:
The actuator modulates the diffusion angle at a driving frequency that creates periodic changes in the speckle pattern. When this modulation frequency is appropriate, the human visual system integrates these rapid changes over time due to persistence of vision, perceiving a uniform luminance distribution without noticing the individual speckle patterns, thus maintaining image quality while achieving luminance uniformity.
Solution Approach 2:
The patent changes the diffusion angle parameter dynamically through the actuator rather than using a fixed diffusion angle. By controlling the diffusion angle to vary within an appropriate range at a controlled frequency, the system optimizes both luminance uniformity and image quality, avoiding the trade-off that would exist with a static diffusion angle setting.
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 achieves a uniform luminance and enhanced image quality by adjusting the speckle distribution over time, improving user visual perception while maintaining the recorded spatial light information.
Implementation Method 1
the display unit is configured to form a three-dimensional image beam based on interference of the coherent light beams
Implementation Method 2
a diffusion angle of the three-dimensional image beam is sequentially changed by passing through the light-diffusing element
Implementation Method 3
the controller controls an arrangement state of liquid crystal molecules of the liquid crystal element to be sequentially changed
Data Source
AI summary
A display apparatus includes a coherent light source, a display unit, a light-diffusing element, and at least one optical element. The coherent light source is configured to provide coherent light beams. The display unit is configured to form a three-dimensional image beam based on interference of the coherent light beams, wherein the three-dimensional image beam is imaged on an intermediate imaging surface after passing through the display unit. The light-diffusing element is located on the intermediate imaging surface, wherein a diffusion angle of the three-dimensional image beam is sequentially changed by passing through the light-diffusing element. The at least one optical element is located on a transmission path of the three-dimensional image beam from the light-diffusing element, and is configured to project the three-dimensional image light beam passing through the display unit out of the display apparatus to display a three-dimensional image.