Coherent Light Source Speckle Reduction via Optical Mixing
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Solution Overview
Problem
The degradation of uniformity in projected light due to speckle when using coherent light sources, such as semiconductor lasers, in projectors, which affects image quality and illumination efficiency.
Innovation Solution
A coherent light source apparatus with a first optical system forming a second light emission region, a light deflection section that continuously changes the direction of rays, and a light mixing section downstream to mix components of angles and positions of rays, creating a third light emission region conjugate to the exit pupil of the first optical system, thereby reducing speckle visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a coherent light source (semiconductor laser) is used in a projector, then illumination efficiency and brightness are improved, but speckle patterns appear causing degradation of uniformity in projected light
Solution Approach 1:
The patent segments the coherent light beam into multiple sub-beams using a diffuser or microlens array. Each sub-beam maintains coherence but has slightly different spatial characteristics. When these segmented beams are recombined at the projection target, the speckle patterns from individual sub-beams interfere destructively, reducing overall speckle visibility while preserving illumination efficiency.
Solution Approach 2:
The patent employs a nested structure where a light mixing section (containing diffusers or microlens arrays) is integrated within the optical path between the coherent light source and the projection lens. This nested configuration allows the speckle-reducing elements to be embedded without significantly increasing the overall system size, maintaining compactness while achieving uniformity improvement.
2Ease of operation
If a light mixing section is added to reduce speckle, then uniformity of projected light is improved, but device complexity increases
Solution Approach 1:
The patent designs the light mixing section to serve multiple functions simultaneously: it diffuses the coherent light to reduce speckle, maintains beam collimation for efficient projection, and preserves the optical conjugate relationships required for proper image formation. This multi-functionality reduces the need for separate components, thereby limiting the increase in device complexity.
Solution Approach 2:
The patent introduces a light mixing section as an intermediary element between the coherent light source and the projection lens. This intermediary contains diffusers or microlens arrays that mediate the light propagation, breaking up speckle patterns while maintaining the overall optical pathway. The intermediary approach allows speckle reduction without requiring fundamental redesign of the entire optical system.
3Ease of operation
If the third light emission region is formed conjugate to the exit pupil of the first optical system, then speckle visibility is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent adjusts optical parameters (focal lengths, distances, magnifications) to establish conjugate relationships between the first light emission region, the light mixing section, and the third light emission region with the exit pupil. By carefully selecting and tuning these parameters, the system achieves speckle reduction through proper optical conjugacy while maintaining feasible manufacturing tolerances for the optical components.
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 effectively suppresses the degradation of uniformity in projected light, making the speckle pattern finer and more difficult to view, thereby improving image quality and illumination efficiency.
Implementation Method 1
a light mixing section provided downstream of the second optical system, and configured to mix components of angles and positions of rays incident on an incident end of the light mixing means
Implementation Method 2
a light deflection section configured to deflect a bundle of rays in vicinity of the second light emission region, the bundle of rays being related to formation of the second light emission region
Implementation Method 3
a first optical system configured to project light derived from a first light emission region to form a second light emission region
Implementation Method 4
The second optical system is configured to form, in distance, an image conjugate to the first light emission region, and form, at the incident end, a third light emission region substantially conjugate to an exit pupil of the first optical system
Data Source
AI summary
Provided are a coherent light source apparatus and a projector. A first light emission region is formed on basis of a coherent light source; a first optical system projects light derived from a first light emission region to form a second light emission region; a light deflection section deflects a bundle of rays in vicinity of the second light emission region; a second optical system downstream of the light deflection section; and a light mixing section downstream of the second optical system that mixes components of angles and positions of rays incident on an incident end. The second optical system forms an image conjugate to the first light emission region and a third light emission region substantially conjugate to an exit pupil of the first optical system. The light deflection section continues to cause a direction in which the bundle of rays is deflected to be continuously changed.