Optical Fiber Dithering for Speckle Reduction in Coherent Imaging
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Solution Overview
Problem
Imaging systems using coherent light sources suffer from speckle patterns due to the high coherence of the light, resulting in grainy images, which are not easily accommodated by the human eye and reduce image quality.
Innovation Solution
The method involves coupling a coherent optical source into a multimode optical fiber, modulating the fiber's position using a ditherer, and refracting the beam through a lens to a microlens diffuser, which is then projected onto a spatial modulator to reduce speckle contrast by altering the power distribution among modes and interfering patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a coherent light source is used to improve resolution and brightness, then image brightness and resolution are improved, but speckle patterns appear causing grainy images
Solution Approach 1:
The patent applies dynamics by modulating the position of the optical fiber at a frequency above the human eye's integration bandwidth. This dynamic modulation causes the speckle pattern to change over time, and since the eye cannot integrate these rapid changes, the perceived speckle contrast is reduced while maintaining high brightness from the coherent light source.
Solution Approach 2:
The patent employs mechanical vibration by physically modulating the position of the optical fiber using a ditherer or similar actuator. This mechanical vibration alters the spatial distribution of light modes in the fiber, which changes the speckle pattern dynamically, thereby reducing the visibility of grainy patterns while preserving image brightness.
2Measurement precision
If coherent light is used to improve picture quality, then resolution is improved, but grainy patterns reduce viewer satisfaction
Solution Approach 1:
The patent uses dynamics to resolve this contradiction by rapidly modulating the optical fiber position at frequencies above human visual integration. This creates a time-varying speckle pattern that the eye perceives as smoothed out, allowing high-resolution imaging with coherent light while eliminating the grainy appearance that would otherwise reduce viewer satisfaction.
Solution Approach 2:
The patent introduces an intermediary element (the modulated optical fiber) between the coherent light source and the image formation process. By modulating the fiber position, it acts as a mediator that transforms the static, high-contrast speckle pattern into a dynamic pattern that averages out perceptually, thus preserving resolution while improving picture quality.
3Illumination intensity
If laser light is used to provide better picture quality, then brightness is improved, but speckle contrast creates noticeable patterns
Solution Approach 1:
The patent applies dynamics by implementing temporal modulation of the optical fiber position at frequencies above the human eye's integration bandwidth. This dynamic approach maintains the high brightness of laser light while transforming the static speckle pattern into a time-varying pattern that perceives as smooth, thereby improving perceived image smoothness without sacrificing brightness.
Solution Approach 2:
The patent employs periodic action through sinusoidal or other periodic modulation of the optical fiber position. This periodic modulation continuously varies the speckle pattern at a frequency that prevents human visual integration, creating a smooth perceived image while maintaining the high brightness advantage of laser illumination.
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 approach significantly reduces speckle contrast, improving image quality by making the image appear more continuous and increasing detail density, particularly beneficial for head-up and head-mounted displays.
Implementation Method 1
coupling a source beam received from a coherent optical source into a multimode optical fiber
Implementation Method 2
the interference between the light waves interferes constructively and destructively thus forming a pattern of bright and dark fringes
Implementation Method 3
A position of at least a portion of the fiber may be modulated using a ditherer
Implementation Method 4
The source beam may be refracted in a lens after it is decoupled from the optical fiber
Implementation Method 5
a microlens diffuser, which is then projected onto a spatial modulator
Data Source
AI summary
A method and system for reducing speckle in an image produced from a coherent source of radiation is provided. The method includes coupling a source beam received from a coherent optical source into an optical fiber. A position of at least a portion of the fiber may be modulated using a ditherer. The source beam may be refracted by a lens after it is decoupled from the optical fiber, such that the source beam is aimed at a microlens diffuser. In accordance with a particular embodiment, the source beam may be projected from the microlens diffuser onto a spatial modulator. The spatial modulator may be positioned to project the source beam via an imaging lens, to a target.