Tapered Fiber Bundle for Coherent Beam Combination
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Solution Overview
Problem
High power fiber laser amplifiers face challenges in combining beams coherently to achieve a uniform phase over the beam diameter, leading to reduced beam quality and increased complexity due to the need for precise alignment of fiber arrays and external optics.
Innovation Solution
The use of a tapered fiber bundle, where the ends of fiber amplifiers are joined into a single fiber mass with an end cap, allowing for beam combining within the fiber material itself, eliminating the need for precise external alignment and maximizing the fill factor by ensuring overlap and constructive interference of fiber modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple fiber laser amplifiers are combined using external optics and fiber arrays, then the output power is increased, but the alignment complexity and device complexity increase significantly
Solution Approach 1:
The patent merges multiple fiber amplifiers into a single tapered fiber bundle where individual fiber cores are closely spaced and tapered together. This integration eliminates the need for external alignment optics by combining the functions of multiple fibers into a unified structure, thereby increasing output power while reducing alignment complexity
Solution Approach 2:
The patent implements a nested structure where multiple fiber cores are embedded within a common tapered cladding. The individual fiber modes are nested within the overall tapered fiber bundle, allowing coherent beam combination without requiring external alignment mechanisms, thus reducing device complexity while maintaining high power output
2Power
If fiber arrays are used for beam combination, then the power is increased, but the fill factor decreases due to spacing requirements
Solution Approach 1:
The patent applies local quality by creating regions of high field overlap between adjacent fiber cores in the tapered bundle. The modal fields are engineered to concentrate energy in specific regions where constructive interference occurs, maximizing the fill factor locally while maintaining overall beam coherence and high combined power
3Reliability
If external optics are used for coherent beam combination, then the beam quality can be maintained, but the system compactness is reduced
Solution Approach 1:
The patent extracts the beam combination function from external optical components and integrates it directly into the fiber bundle structure itself. The tapered fiber bundle performs coherent combination through its internal modal interference patterns, eliminating the need for separate external optics and thereby improving system compactness while maintaining beam quality
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 approach enhances beam quality by increasing the fill factor and power efficiency, allowing for higher power output with reduced losses and improved compactness, as the tapered fiber bundle integrates multiple beams into a single aperture with minimal external optics, thereby focusing the combined beam to a smaller diffraction-limited spot.
Implementation Method 1
allowing for beam combining within the fiber material itself, eliminating the need for precise external alignment and maximizing the fill factor by ensuring overlap and constructive interference of fiber modes
Data Source
AI summary
A fiber laser amplifier system including a plurality of master oscillators each generating a signal beam at a different wavelength. A splitter is provided for each master oscillator that splits the signal beam into a plurality of fiber beams where a separate fiber beam is sent to a fiber amplifier. A tapered fiber bundle couples the output ends the fiber amplifiers for each wavelength group into a combined fiber providing a combined output beam, where a separate combined output beam is provided for the wavelength for each master oscillator. An end cap is optically coupled to an output end of each of the tapered fiber bundles to expand the combined output beam. A spectral beam combination grating receives the combined beams from the tapered fiber bundles at different angles and outputs an output beam of all of the combined beams as a single beam being directed in the same direction.