Fiber Coupled Diode Laser Power Scaling via Fast Axis Beam Optimization
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Solution Overview
Problem
Conventional multi-emitter laser diode systems face limitations in scaling power and brightness due to large emitter fast axis numerical apertures, which restrict the number of emitters that can be stacked along the fast axis without increasing the fast axis image size and numerical aperture, thereby limiting the coupled power into an optical fiber.
Innovation Solution
The approach involves using thinner gain regions and higher fast axis numerical apertures to couple power from more emitters into a beam delivery fiber, achieved by selecting suitable fast axis dimensions and epitaxial waveguide designs, and employing fast axis collimators, afocal telescopes, and objective lenses to maintain constant beam parameter product and increase emitter count without altering the fast axis spacing or optical design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If more emitters are stacked along the fast axis to increase power, then the fast axis numerical aperture increases, but the coupled power into the fiber does not increase further
Solution Approach 1:
The patent changes the fast axis beam dimension parameter by using thinner gain regions (e.g., 3-5 μm) to reduce the emitted beam size. This parameter change allows increasing the number of stacked emitters while maintaining the same fast axis numerical aperture and beam parameter product at the fiber aperture, thereby increasing coupled power without worsening the NA constraint
Solution Approach 2:
The patent addresses the limitation in the fast axis direction by transitioning to another dimension - stacking emitters along the slow axis direction. This dimensional transition allows power scaling without increasing the fast axis numerical aperture, as the additional emitters are arranged in a different spatial configuration that does not worsen the fast axis beam parameters at the fiber
2Quantity of substance
If the number of stacked emitters is increased for power scaling, then the emitter count increases, but the fast axis image size and NA remain unchanged only with optimized beam dimensions
Solution Approach 1:
The patent applies parameter changes by precisely controlling the gain region thickness (e.g., 3-5 μm) to achieve the desired fast axis beam dimension. This precise parameter control enables stacking more emitters while maintaining constant fast axis image size and NA at the fiber, resolving the contradiction between increasing emitter count and maintaining beam quality
Solution Approach 2:
The patent replaces mechanical adjustment methods with optimized epitaxial waveguide designs that inherently provide the desired beam dimensions. By using thinner gain regions in the waveguide structure, the system achieves precise beam control without requiring complex mechanical adjustment mechanisms, enabling higher emitter counts with maintained manufacturing precision
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 method allows for higher beam powers and brightness scaling by enabling more emitters to be stacked along the fast axis while maintaining constant fast axis image size and numerical aperture, thereby increasing fiber-coupled power without requiring changes to the fast axis spacing or optical alignment.
Implementation Method 1
laser diodes with a predetermined spacing with respect to a stacking axis, each laser diode having an emission region defining a fast axis and a slow axis that produces an emitted beam
Implementation Method 2
Fast axis collimators (FACs) are associated with each of the laser diodes, each of the fast axis collimators having a common focal length. Emission regions of each of the laser diodes are coupled to a respective fast axis collimator so as to produce respective beams that are collimated along the fast axes
Implementation Method 3
An afocal telescope (also referred to as a fast axis telescope or FAT) is situated to receive the fast axis collimated beams from the fast axis collimators and produce a fast axis beam spacing based on the predetermined spacing and a magnification M associated with the afocal telescope
Implementation Method 4
An objective lens receives the fast axis collimated beams from the afocal telescope and delivers a combined beam to a core of an optical fiber
Data Source
AI summary
A number of beams that can be coupled into an optical fiber can be increased using emitted beams having greater divergence, thus providing increased beam power. Alternatively, with a fixed number of emitters, total optical power can be maintained with fewer beams in an output beam with a smaller numerical aperture.