Laser Speckle Reduction via Optical Path Length Adjustment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for reducing speckles in laser light projections, such as those using polarized light and switchable Bragg gratings, face challenges in accurately combining split light due to sensitivity in incident angle, leading to diminished effectiveness.
Innovation Solution
The use of an optical path length adjuster with OC-type polarizing diffraction gratings and a reflective or refractive member to create an optical path length difference and adjust the angle of incidence, ensuring accurate combination of split laser light components, thereby reducing speckles effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a PBS is used to split and combine light, then the speckle reduction effect is achieved by overlaying two patterns of speckles, but the deviation in incident angle greatly affects the reflected angle, making it difficult to combine light accurately
Solution Approach 1:
A retroreflector is introduced as an intermediary component in the optical path. The retroreflector receives the s-polarized light component and reflects it back through the PBS, ensuring that the light returns along the same path it originally traveled. This intermediary device compensates for angle deviations by inherently correcting the reflection angle, allowing accurate recombination of light components even when incident angles vary.
Solution Approach 2:
Instead of using a conventional mirror that reflects light at an equal but opposite angle, the patent employs a retroreflector that inverts the reflection principle by returning light along its incident path regardless of the angle. This inversion of the traditional reflection approach allows the system to maintain accurate light combination despite variations in incident angle, directly addressing the technical contradiction.
2Object-affected harmful factors
If the optical path length difference is increased to reduce speckles effectively, then the coherent length requirement is met, but the device complexity increases with additional optical components
Solution Approach 1:
The patent combines multiple functions into the retroreflector component. This single element simultaneously serves to: (1) reflect the s-polarized light back through the PBS, (2) maintain the optical path length difference greater than the coherent length, and (3) correct angle deviations. By merging these functions into one component rather than using separate elements, the system achieves effective speckle reduction while minimizing the increase in device complexity.
Solution Approach 2:
The retroreflector is designed as a multi-functional component that performs multiple critical roles in the optical system. It acts as both a beam splitter alternative and an angle correction device, while also establishing the necessary optical path length difference. This multi-functionality reduces the overall number of components needed compared to traditional speckle reduction systems that would require separate elements for each function.
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 achieves high-accuracy reduction of speckles by ensuring an optical path length difference equal to or larger than the coherent length, resulting in improved image quality by overlaying circularly polarized light with perpendicular polarization directions.
Implementation Method 1
a first polarization convertible diffraction device which splits laser light emitted from a light source into a plurality of components of the laser light
Implementation Method 2
a first polarization convertible diffraction device which splits laser light emitted from a light source into a plurality of components of the laser light
Implementation Method 3
a reflective member arranged between the first and second polarization convertible diffraction devices, and reflecting at least one of the plurality of components of the laser light
Implementation Method 4
a refractive member arranged between the first and second polarization convertible diffraction devices, and refracting at least one of the plurality of components of the laser light
Implementation Method 5
a second polarization convertible diffraction device which combines together the plurality of components of the laser light into combined laser light
Implementation Method 6
a second polarization convertible diffraction device which combines together the plurality of components of the laser light into combined laser light
Data Source
Figure 1
Figure 2
Figure 3~8
AI summary
An electronic appliance has a first polarization convertible diffraction device which splits laser light emitted from a light source into a plurality of components of the laser light; a second polarization convertible diffraction device which combines together the plurality of components of the laser light into combined laser light; an optical path length adjuster which adjusts the optical path length difference between the plurality of components of the laser light along the path between the first and second polarization convertible diffraction devices; and an angle-of-incidence adjuster which adjusts, to predetermined angles, the angles of incidence at which the plurality of components of the laser light are respectively incident on the second polarization convertible diffraction device.