Tapered Fiber Bundle for High Power Erbium Laser Pump Coupling
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Solution Overview
Problem
High-power fiber lasers employing 'eye-safe' wavelengths, such as Erbium-doped fibers, face challenges in achieving efficient power transfer due to lower peak absorption cross-sections compared to Ytterbium-doped fibers, leading to increased nonlinear effects and reduced laser efficiency, limiting their scalability to kilowatt power levels.
Innovation Solution
The use of a tapered fiber bundle with smaller-diameter fibers optically coupled to larger-diameter fibers, allowing for a lower taper ratio and increased number of input fibers, which enhances pump power coupling into an output fiber while maintaining efficient power transfer and minimizing divergence angle limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a longer fiber is used to absorb all pump light due to lower peak absorption cross-section of Erbium, then pump light absorption is improved, but nonlinear effects increase and laser efficiency decreases
Solution Approach 1:
The patent divides the single long Erbium-doped fiber into multiple shorter fiber segments coupled in series through pump combiners. Each segment absorbs a portion of the pump light, achieving complete absorption without requiring an excessively long single fiber. This segmentation reduces nonlinear effects and maintains laser efficiency while still absorbing all pump light.
2Use of energy by moving object
If doping concentration is increased to improve pump absorption, then pump light absorption is improved, but clustering and concentration quenching effects occur which reduce laser efficiency
Solution Approach 1:
The patent uses multiple shorter fiber segments instead of a single long fiber with high doping concentration. This allows maintaining lower doping concentrations in each segment, avoiding clustering and concentration quenching effects, while achieving complete pump absorption through the series arrangement of multiple segments.
3Power
If a tapered fiber bundle with large taper ratio is used to combine multiple pump beams, then pump power is increased, but divergence angle increases beyond acceptance angle of gain fiber
Solution Approach 1:
The patent divides the pump combining process into multiple stages using series-coupled pump combiners. Each combiner handles a smaller taper ratio and combines fewer beams, keeping divergence angles within acceptance angles. The cumulative effect of multiple combiners achieves high total pump power while maintaining coupling efficiency at each stage.
Solution Approach 2:
The patent introduces intermediate optical elements (pump combiners and transition fibers) between the pump sources and the final gain fiber. These intermediaries progressively combine and transform the pump beams, managing divergence angles and enabling efficient coupling through multiple stages rather than a single large-taper-ratio combiner.
4Loss of energy
If core and overall diameters of pump combiner fibers are matched to pump lasers to minimize splice losses, then splice efficiency is improved, but taper ratio must be increased to combine multiple beams
Solution Approach 1:
The patent divides the pump combining into multiple stages, each handling a smaller number of fibers with more manageable taper ratios. This segmentation allows maintaining better diameter matching at each splice point while achieving the overall goal of combining many pump beams through the series arrangement of multiple combiners.
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 enables higher pump power transfer and reduced waste heat, allowing Erbium fiber lasers to handle kilowatt power levels with improved efficiency and reduced parasitic lasing, making them suitable for long-wavelength, eye-safe directed energy applications.
Implementation Method 1
A tapered fiber bundle includes a set of bundled fibers at a near end and an output at a distal end, the near end of the tapered fiber bundle configured to collect the pump optical beam from the input fibers and to provide the pump beam to the output fiber
Implementation Method 2
output fiber device including an output fiber and configured to transform a pump optical signal having an intermediate wavelength into the output optical beam, the output fiber having a cross-sectional area value Aout and a numerical aperture value NAout
Implementation Method 3
the input fibers having respective cores for carrying the pump optical beam and having respective first cross-sectional core areas
Data Source
AI summary
A tapered fiber bundle device couples optical power from an optical power source into an output fiber. The tapered fiber bundle device includes a tapered fiber bundle including a set of bundled fibers having a near end and a distal end. The near end of the tapered fiber bundle is configured to collect the optical power from the optical power source. Each fiber k in the set of bundled fibers has a first cross-sectional area Ak(1) at the near end and a second cross-sectional area Ak(2) at the distal end such that Ak(2) is substantially smaller than Ak(1). Each fiber also has a substantially uniform core and a substantially uniform numerical aperture value NAin. A cross-sectional area of the set of bundled fibers at the distal end has a cross-sectional area value Adist substantially equal to Aout.