Laser Projector Image Plane Modal Vibration Speckle Reduction
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Solution Overview
Problem
Projectors using laser light sources suffer from speckle, which is not effectively mitigated by existing methods such as vibrating large and complex projection screens or optical elements, as these solutions do not sufficiently reduce speckle to an imperceptible level for viewers.
Innovation Solution
A laser projector with a surface at the image plane, configured to transmit and reflect images, and at least three asymmetrically positioned actuators that generate moving surface waves at non-integer multiples of each other's frequencies to minimize standing nodes and randomize light paths, thereby reducing speckle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a diffuser is oscillated by up to four actuators, then speckle reduction is achieved, but the system complexity and cost increase
Solution Approach 1:
The patent employs asymmetric positioning of three actuators on the diffuser surface, where the actuators are located at non-symmetric positions relative to the diffuser center. This asymmetric configuration prevents the formation of standing waves and nodes, effectively reducing speckle while using fewer actuators than symmetric configurations would require
Solution Approach 2:
The patent utilizes mechanical vibration of the diffuser surface through piezoelectric actuators that generate surface waves at specific frequencies (e.g., 200 Hz, 400 Hz, 600 Hz). The vibration causes the diffuser surface to dynamically change, randomizing light paths and reducing speckle visibility without requiring the diffuser to be physically moved or replaced
2Object-affected harmful factors
If optical elements are vibrated in rigid-body mode, then some speckle mitigation is achieved, but speckle remains visible to viewers
Solution Approach 1:
The patent applies mechanical vibration to the diffuser surface at frequencies that generate surface waves rather than rigid-body motion. The vibration frequencies (e.g., 200 Hz, 400 Hz, 600 Hz) are specifically selected to create standing wave patterns that are then disrupted by asymmetric actuator positioning, ensuring effective speckle reduction
Solution Approach 2:
The patent creates localized surface waves at specific positions on the diffuser where actuators are placed, rather than uniform rigid-body vibration. The surface waves are confined to specific regions and propagate across the diffuser surface, creating localized variations in light path that effectively reduce speckle
Data Source
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AI summary
A projector with image plane modal vibration for speckle reduction is provided. The projector includes: a laser light source; a light modulator; and optics that convey light from the laser to the modulator and project modulated light from the modulator, the optics comprising an image plane. The projector further includes: a surface comprising at least a first region located at the image plane, the first region being at least as large as an image formed at the image plane, the first region configured to one or more of transmit and reflect the image; and at least three actuators, positions of interaction of the actuators with the surface are asymmetric relative to the surface, the actuators configured to generate respective moving surface waves in the first region at respective frequencies, the respective frequencies comprising non-integer multiples of each other.