Multi-Wavelength VCSEL Array Speckle Reduction
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Solution Overview
Problem
Existing illumination systems using coherent light sources, such as lasers, suffer from speckle noise, which degrades image quality and limits spatial detail resolution, and current de-speckling techniques often compromise system efficiency, cost, reliability, and power consumption.
Innovation Solution
A VCSEL array with varying emission wavelengths is employed to reduce speckle noise, using techniques like single-chip spectral interleaving and structural variations in VCSELs to produce low-contrast speckle patterns, thereby maintaining imaging capabilities without system efficiency losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a single-wavelength VCSEL array is used, then the system achieves high output power and low beam divergence, but high-contrast speckle patterns are formed that degrade image quality
Solution Approach 1:
The VCSEL array is segmented into multiple wavelength groups, where each group operates at a different wavelength. This segmentation of the wavelength spectrum causes the speckle patterns from different wavelength groups to be uncorrelated, and when combined, they average out to reduce overall speckle contrast while maintaining high output power.
Solution Approach 2:
The invention changes the wavelength parameter across different VCSEL groups in the array. By tuning VCSELs to operate at multiple discrete wavelengths rather than a single wavelength, the speckle patterns become wavelength-dependent and uncorrelated between groups, reducing the overall speckle contrast in the combined illumination.
2Object-affected harmful factors
If current de-speckling techniques such as vibrating diffusers are used, then speckle noise is reduced, but additional artifacts are introduced that reduce image quality
Solution Approach 1:
The invention converts the harmful effect of coherent speckle patterns into a beneficial effect by utilizing wavelength diversity. The same coherent light property that creates speckle is leveraged across multiple wavelengths to create uncorrelated speckle patterns that average out, transforming the harmful coherence into a useful speckle-reduction mechanism without introducing mechanical artifacts.
3Ease of manufacture
If VCSELs with uniform wavelength are used in the array, then manufacturing is simplified, but the speckle patterns from individual VCSELs combine to form high-contrast speckle
Solution Approach 1:
The invention applies local quality by assigning different wavelength characteristics to different spatial groups of VCSELs within the array. While each VCSEL group maintains uniform wavelength within its group for ease of manufacture, the local wavelength parameter varies between groups, creating the necessary diversity to reduce speckle contrast in the combined output.
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 VCSEL array with diverse emission wavelengths effectively reduces speckle noise, improving image clarity and maintaining system efficiency, making it suitable for applications like night-vision and industrial illumination without introducing additional artifacts.
Implementation Method 1
Speckle (or speckle noise) may exist when one or more coherent light sources, such as laser light sources, are used in an illumination system. Speckle is typically randomized interference and a characteristic of coherent imaging.
Implementation Method 2
Laser light is inherently narrow band and gives rise to the perception of fully-saturated colors and unfortunately, narrow band light incident on random surfaces introduces an unacceptable image artifact known as 'speckle.'
Data Source
AI summary
Embodiments of the invention describe an illuminator having a light source to originate an illumination beam, wherein the light source further comprises a set of vertical-cavity surface emitting lasers (VCSELs), including a first VCSEL having a first laser emission wavelength, and a second VCSEL having a second laser emission wavelength different than the first laser emission wavelength. Thus, by varying laser emission wavelengths of VCSELs in a VCSEL array, embodiments of the invention produce low-contrast speckle, and do not limit the imaging capabilities of the host illumination system. In some embodiments of the invention, vertical external cavity surface emitting lasers (VECSELs) are utilized to produce the above described varying laser emission wavelengths.