Variable-Focus Lens Speckle Reduction in Laser Projection
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Solution Overview
Problem
Image projection devices using laser beams suffer from speckle noise, which degrades image quality, especially when the projection surface is positioned farther from the beam waist, leading to increased speckle contrast and reduced resolution.
Innovation Solution
An image projection device equipped with a variable-focus lens, scanning means, and control means that measures the distance to the projection surface and adjusts the focal length to position the beam waist deeper than the projection surface, ensuring the surface is scanned by convergent light to minimize speckle noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the projection surface is positioned farther from the beam waist, then the beam radius on the projection surface increases, but speckle contrast increases and image resolution deteriorates
Solution Approach 1:
The patent employs a variable-focus lens that can dynamically adjust its focal length to maintain optimal beam waist positioning on the projection surface regardless of distance variations. This dynamic adjustment capability allows the system to adapt to different projection distances while maintaining consistent beam radius and speckle characteristics, thereby resolving the contradiction between beam size and image resolution.
Solution Approach 2:
The invention changes the optical parameters (focal length) of the lens system to control the beam waist position. By adjusting the focal length parameter, the system can ensure the beam waist is formed at the projection surface even when projection distance varies, thus maintaining both adequate beam radius and low speckle contrast for high image resolution.
2Device complexity
If a fixed-focus lens is used, then the device structure is simple, but the beam waist position cannot be adjusted when projection distance changes, causing speckle noise
Solution Approach 1:
The patent transitions from a static fixed-focus lens to a dynamic variable-focus lens system. This allows the focal length to be adjusted in real-time based on projection distance, ensuring the beam waist remains positioned on the projection surface. This dynamic capability effectively eliminates speckle noise while maintaining reasonable device complexity through automated control mechanisms.
Solution Approach 2:
The system incorporates feedback control where the projection distance is measured and used to determine the appropriate focal length setting. This feedback mechanism automatically adjusts the lens focal length to maintain optimal beam waist positioning, thereby eliminating speckle noise without requiring complex manual intervention or overly complicated device architecture.
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 reliably reduces speckle noise and maintains high image resolution regardless of the projection surface's position, achieving a speckle contrast reduction and improved image quality.
Implementation Method 1
a variable-focus lens in which focal length can be changed; scanning means that scans the projection surface by a light beam that is condensed by the variable-focus lens
Implementation Method 2
distance measuring means that measures the distance from the variable-focus lens to the projection surface
Data Source
AI summary
An image projection device includes: a variable-focus lens (2) in which focal length can be changed; scanning means (3) that scans a projection surface (12) by means of a light beam that is condensed by the variable-focus lens (2); distance-measuring means (9) that measures the distance from the variable-focus lens (2) to the projection surface (12); and control means (4) that controls the variable-focus lens (2) such that the focal length of the variable-focus lens (2) is greater than the distance measured by means of the distance-measuring means (9).