VCSEL Angular-Selective Feedback for Stable Ring Profiles
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Solution Overview
Problem
Large area vertical cavity surface emitting lasers (VCSELs) tend to emit laser radiation in distinct angles sensitive to temperature and current changes, making it challenging to achieve stable and desired intensity distributions, such as ring or top-hat shapes, which are necessary for material processing and medical applications.
Innovation Solution
A laser device comprising a large area VCSEL with an angular-selective optical feedback element, where the reflectivity of the outcoupling mirror and feedback element are designed to provide higher feedback for laser radiation emitted at angles greater than 0 degrees than on-axis radiation, allowing for point-symmetric intensity distributions and achieving a product of reflectivities greater than 98%, thereby stabilizing the emission across a wide range of currents and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If large area VCSEL is used to achieve higher output power, then output power is improved, but emission angle stability deteriorates due to sensitivity to temperature and current changes
Solution Approach 1:
The patent applies optical feedback by directing a portion of the laser radiation back into the laser cavity through a feedback mirror. This feedback mechanism stabilizes the emission characteristics by compensating for changes in detuning caused by temperature and current variations, thereby maintaining stable emission angles while operating at high power levels with large active areas.
Solution Approach 2:
The patent changes the operating parameters of the VCSEL by operating it in a detuned regime where the cavity resonance is deliberately offset from the gain peak. This parameter change, combined with optical feedback, stabilizes the emission against further parameter drifts due to temperature and current changes, enabling stable high-power operation.
2Shape
If beam homogenizers are used to achieve desired intensity distributions, then intensity distribution is improved, but device complexity and alignment difficulty increase
Solution Approach 1:
The patent extracts the beam shaping function from separate external optical components (beam homogenizers) and integrates it directly into the laser cavity through the feedback mirror. The feedback mirror is positioned and oriented to provide different feedback for different angular emissions, thereby shaping the intensity distribution (e.g., ring profiles) within the laser device itself, eliminating the need for external beam homogenizing optics.
3Shape
If beam homogenizers are used to shape laser beam, then intensity distribution is improved, but alignment precision requirements increase
Solution Approach 1:
The patent extracts the beam shaping function from separate external optical components (beam homogenizers) and integrates it directly into the laser cavity through the feedback mirror. The feedback mirror is positioned and oriented to provide different feedback for different angular emissions, thereby shaping the intensity distribution (e.g., ring profiles) within the laser device itself, eliminating the need for external beam homogenizing optics.
4Shape
If ring shaped intensity profile is generated using beam homogenizers, then desired beam shape is achieved, but power loss increases
Solution Approach 1:
The patent uses optical feedback to selectively enhance specific angular emission modes that correspond to the desired ring-shaped intensity profile. By providing positive feedback for the desired modes and suppressing others, the system achieves the target intensity distribution without the significant power losses associated with traditional beam homogenizers that absorb or scatter unwanted light.
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 enables the stabilization of laser emission in desired angular distributions, particularly ring-shaped profiles, with high stability and adaptability, allowing for efficient material processing and medical applications by maintaining consistent beam profiles across varying conditions.
Implementation Method 1
at least one optical feedback element providing an angular-selective feedback for laser radiation emitted from said laser
Implementation Method 2
the reflectivity of the outcoupling mirror and feedback element are designed to provide higher feedback
Data Source
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AI summary
The present invention relates to a laser device comprising at least one large area VCSEL (101) and at least one optical feedback element (201, 301) providing an angular-selective feedback for laser radiation emitted from the laser. The angular-selective feedback is higher for at least one portion of laser radiation emitted at angles ? > 0 to the optical axis (601) of the laser than for laser radiation emitted on said optical axis (601). The invention also refers to a method of stabilizing a laser emission of a large area VCSEL in a desired angular distribution (501, 502). With the proposed device and method, the intensity distribution of a large area VCSEL can be stabilized in a desired shape, for example a ring shape.