VeCSEL Intracavity Transverse Filtering for OAM Control
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Solution Overview
Problem
Existing methods for generating helical wave-front beams, such as vortex beams, face challenges in maintaining spatial coherence and efficiency due to inherent imperfections in optics and complex alignment procedures, and struggle to control the sign and charge of Orbital Angular Momentum (OAM) in laser devices.
Innovation Solution
A Vertical External Cavity Surface Emitting Laser (VeCSEL) device with a gain region and a plano-concave optical cavity, incorporating a center-discoidal and annular transverse filtering area to control the phase and intensity profiles, allowing for the selection of rotary-symmetrical transverse modes that carry OAM with controlled charge and sign, without the need for additional optics or complex alignments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If external mode-transforming optics are used to generate vortex beams, then helical wave-front can be produced, but spatial coherence deteriorates and conversion efficiency decreases
Solution Approach 1:
The patent extracts the vortex mode selection function from external optics and places it directly inside the laser cavity through transverse filtering means. This eliminates the need for separate beam transformation optics that deteriorate spatial coherence, while maintaining the ability to generate helical wave-fronts with preserved coherence properties.
Solution Approach 2:
The patent implements preliminary action by pre-selecting the desired rotary-symmetrical transverse mode within the laser cavity before the beam exits. The transverse filtering means are positioned to filter modes intracavity, ensuring that only the desired vortex mode with controlled OAM is amplified and emitted, rather than transforming a conventional beam afterward.
2Reliability
If intracavity elements are used for direct vortex beam generation, then spatial coherence is maintained, but alignment complexity increases and device sophistication rises
Solution Approach 1:
The patent applies local quality by implementing transverse filtering only in specific regions of the laser cavity where it is most effective. The filtering means are positioned at locations that maximize mode selection while minimizing interference with the overall cavity alignment, thereby maintaining spatial coherence without requiring sophisticated global alignment procedures.
Solution Approach 2:
The transverse filtering means serve multiple functions simultaneously: they select the desired vortex mode, control the OAM charge and sign, and maintain spatial coherence. This multi-functionality reduces the need for separate alignment-sensitive components, thereby decreasing overall device complexity while preserving coherence.
3Device complexity
If conventional laser cavities are used, then simple structure is maintained, but control over OAM charge and sign is lost
Solution Approach 1:
The patent introduces an intermediary transverse filtering means within the laser cavity that acts as a mediator between the simple cavity structure and the desired OAM control. This filtering element enables precise control over the charge and sign of the Orbital Angular Momentum by selectively transmitting specific rotary-symmetrical transverse modes, while the cavity itself remains relatively simple in design.
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 direct, high-coherence, high-power generation of vortex modes with controlled OAM, improving beam quality and stability while reducing fabrication costs and complexity.
Implementation Method 1
a gain region located between one first end defined by a first mirror and a second end defined by an exit region... means for pumping the gain region so as to generate the optical wave
Implementation Method 2
a second mirror, arranged so as to form with the first mirror an optical cavity including the gain region... selecting at least one rotary-symmetrical transverse mode of the optical wave
Data Source
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Figure 6~7
AI summary
A laser device (250) for generating a helical-shaped optical wave and comprising: (i) a gain region (203) located between one first end defined by a first mirror (202) and a second end defined by an exit region, (ii) a second mirror (206) arranged so as to form with the first mirror (202) an optical cavity including the gain region (203) and a gap (207) between the exit region and the second mirror (206), (iii) means for pumping the gain region (203) so as to generate the optical wave, wherein the laser device (250) further comprises at least one mean for shaping the light intensity and/or phase profiles of the optical wave and arranged for selecting at least one rotary-symmetrical transverse mode of the optical wave, said rotary-symmetrical transverse mode being chosen between those with a radial index equal to zero and with an azimuthal index being an integer with a module higher or equal to 1.