Stationary Rectangular Chamber for Laser Coherence Reduction
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Solution Overview
Problem
Laser beams used for image projection often suffer from high coherence, leading to speckle artifacts that degrade image quality, and existing solutions using moving components are prone to mechanical wear and increase the etendue of the beam.
Innovation Solution
A stationary rectangular chamber with reflective walls and a beam splitter is used to reduce laser beam coherence by creating additional modes through a closed light path, which does not increase the etendue and avoids mechanical failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If moving components are used in the optical path to reduce laser beam coherence, then speckle is reduced, but mechanical wear and failure occur
Solution Approach 1:
The patent replaces moving mechanical components with a stationary rectangular chamber containing fixed reflective surfaces. The chamber uses stationary mirrors arranged to create multiple internal reflections of the laser beam, generating additional spatial modes without any moving parts. This substitution eliminates mechanical wear and failure while achieving speckle reduction through modal diversity.
2Object-affected harmful factors
If moving components are used in the optical path to reduce laser beam coherence, then speckle is reduced, but the etendue of the laser beam increases
Solution Approach 1:
The rectangular chamber introduces multiple spatial dimensions through its three-dimensional geometry. The beam undergoes reflections off multiple surfaces oriented at different angles, creating spatial mode diversity in multiple dimensions simultaneously. This approach increases the number of modes without requiring lateral expansion of the beam footprint, thereby avoiding etendue increase.
3Object-affected harmful factors
If the light path length is increased to generate additional modes, then coherence is reduced, but the chamber size increases
Solution Approach 1:
The patent segments the light path into multiple discrete reflection segments within the rectangular chamber. Instead of using a single long optical path, the beam undergoes multiple shorter reflection segments off different chamber surfaces. Each segment contributes to mode generation, and the cumulative effect achieves the required coherence reduction while keeping the overall chamber volume compact.
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 effectively reduces laser beam coherence and speckle, maintaining image quality without the drawbacks of moving components, with modest intensity losses and increased rotational homogeneity of the output beam.
Implementation Method 1
The fourth wall is configured to transmit a portion of the laser beam into the chamber to form an input laser beam
Implementation Method 2
The first wall is configured to reflect the input laser beam onto the second wall. The second wall is configured to reflect the input laser beam onto the third wall; and the third wall is configured to reflect the input laser beam onto the fourth wall
Implementation Method 3
When the length of the light path is greater than or equal to the coherence length of the laser beam, the chamber can generate additional modes and thereby reduce the coherence of the laser beam
Implementation Method 4
If two or more of the four optical components (i.e. the three reflective walls and the beam splitter) are tilted in relation to one another about at least two axes, the apparatus can also rotate the laser beam about its axis of propagation
Data Source
AI summary
There is provided an an apparatus for reducing coherence of a laser beam, which apparatus comprises a rectangular chamber having a first, second, and third walls each comprising a reflective inner surface, and a fourth wall comprising a beam splitter. The fourth wall is configured to transmit a portion of the laser beam into the chamber to form an input beam incident upon the first wall. The first wall is configured to reflect the input beam onto the second wall, which is configured to reflect the input beam onto the third wall, which is configured to reflect the input beam onto the fourth wall. The fourth wall is configured to reflect a portion of the input beam to form a further input beam incident upon the first wall and to transmit another portion of the input beam out of the chamber to form an output laser beam.