Acousto-Optic Modulator for Laser Speckle Reduction
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Solution Overview
Problem
Current methods for reducing laser speckle in projection systems are inadequate, as they often result in image haze or distortion, and fail to provide quantitative performance results or discuss their impact on image sharpness.
Innovation Solution
An active diffuser system with a separation layer between transparent conductors, where a diffuser material is disposed on one or both surfaces, and an alternating voltage is applied to create a moving diffuser that reduces speckle by causing axial deformation, thereby minimizing static interference patterns and maintaining image sharpness without haze.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a moving diffuser or phase plate is used to reduce speckle, then speckle contrast is reduced, but image sharpness deteriorates and haze is introduced
Solution Approach 1:
The patent applies the dynamics principle by using an acousto-optic modulator to dynamically change the optical path length of different portions of the laser beam in a time-varying manner. This creates multiple statistically independent speckle patterns over time without requiring physical movement of diffusing elements, thereby reducing speckle contrast while preserving image sharpness and avoiding haze.
Solution Approach 2:
The patent replaces the mechanical system of moving diffusers or phase plates with an acousto-optic modulator that uses acoustic waves to modulate the optical beam. This substitution eliminates the need for mechanical movement, preventing image distortion and haze while achieving speckle reduction through time-varying optical path length modulation.
2Object-affected harmful factors
If a rotating diffuser or phase plate is placed in the beam to create random phase delays, then speckle patterns are averaged, but device complexity increases
Solution Approach 1:
The patent replaces the complex mechanical rotating diffuser or phase plate mechanism with an acousto-optic modulator. This device uses acoustic waves to create time-varying refractive index changes in a crystal, achieving phase modulation without any moving parts, thereby reducing device complexity while maintaining speckle reduction effectiveness.
Solution Approach 2:
The patent employs periodic acoustic wave modulation to create time-varying optical path length changes. The acousto-optic modulator uses periodic acoustic vibrations to modulate the optical beam, creating the necessary phase variations for speckle reduction through a simpler periodic acoustic drive rather than complex mechanical rotation.
3Object-affected harmful factors
If in-plane displacement of a diffuser is used to create independent speckle patterns, then speckle reduction is achieved, but lateral movement requirements increase device complexity
Solution Approach 1:
The patent changes the dimension of modulation from in-plane lateral displacement to temporal modulation of optical path length. Instead of moving the diffuser laterally in the x-y plane, the acousto-optic modulator modulates the optical path length in the time dimension, creating independent speckle patterns through temporal variations without requiring lateral mechanical movement.
Solution Approach 2:
The patent replaces the mechanical lateral displacement system with an acousto-optic modulator that uses acoustic waves to modulate the optical beam in place. This eliminates the need for lateral movement mechanisms while achieving the same goal of generating independent speckle patterns through time-varying optical path length changes.
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 active diffuser system effectively reduces speckle by generating multiple independent light paths, improving image clarity and sharpness while maintaining the resolution of the projection system, with the speckle reduction factor linearly related to the applied voltage.
Implementation Method 1
Applying an alternating voltage across the conductors expands and compresses the separation layer, creating a 'moving diffuser'
Implementation Method 2
the separation layer is either compressible or causes axial deformation in one of the conductors when a voltage is applied across the two conductors
Implementation Method 3
a diffuser material is disposed upon at least one of the surfaces of one of the conductors or dispersed throughout the separation layer
Data Source
AI summary
An optical modulator (12) for speckle suppression in a laser projection system includes a first planar transparent conductor (20); a second optionally transparent planar conductor (26); a diffusing element (22) disposed between the first and second conductor; and an alternating voltage applied across the first and second conductors creates in-plane movement or distortion in the diffusing element to reduce laser speckle.