SHARC Fiber Raman Beam Combining
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Solution Overview
Problem
Current fiber lasers and amplifiers face limitations in power scalability, efficiency, beam quality, and complexity due to constraints on lasing core area and heat-sink limitations, with existing beam combining techniques struggling to achieve high-power outputs beyond 10 kW.
Innovation Solution
A method and apparatus utilizing a semi-guiding high aspect ratio core (SHARC) optical fiber with a doped core and specific refractive index profiles to enhance Raman gain and mode discrimination, combined with Stimulated Raman Scattering for efficient power conversion, allowing for high-power Raman beam combining with minimal higher-order Stokes generation and thermal loading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional beam combining techniques are used to increase power output, then power scalability is improved, but efficiency deteriorates and beam quality degrades
Solution Approach 1:
The invention segments the beam combining process into multiple wavelength channels, each processed independently through Raman amplification stages. This segmentation allows efficient wavelength-division multiplexing while maintaining high conversion efficiency at each stage, avoiding the efficiency losses associated with conventional direct beam combining methods.
Solution Approach 2:
The invention introduces a Raman amplifier as an intermediary device between the laser source and the final beam combination point. This intermediary performs wavelength conversion and power amplification in a controlled manner, achieving high efficiency (exceeding 90%) while preserving beam quality, unlike direct combining methods that suffer from efficiency degradation.
2Power
If conventional beam combining techniques are used to increase power output, then power scalability is improved, but beam quality deteriorates
Solution Approach 1:
The invention applies local quality enhancement by optimizing the Raman gain profile along the fiber length and using wavelength-specific amplification stages. Each wavelength channel maintains its beam quality characteristics through controlled Raman amplification, and the final combined beam achieves high power (exceeding 100 kW) while preserving diffraction-limited quality (M² < 1.3).
3Power
If individual fiber laser core area is increased to improve power output, then power scalability is improved, but heat-sink limitations worsen
Solution Approach 1:
The invention transitions from spatial power scaling (increasing core area) to spectral power scaling (utilizing multiple wavelength channels). By distributing power across multiple wavelengths that are sequentially amplified through Raman processes, the system achieves high total power output without increasing the thermal load on any single fiber core, thereby avoiding heat-sink limitations.
Solution Approach 2:
The invention changes the operating parameters by using wavelength conversion through Raman amplification instead of directly increasing pump power in a single wavelength. This parameter change allows the system to achieve high power output by accumulating energy across multiple wavelength channels, each operating within safe thermal limits, thus circumventing heat-sink constraints.
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 enables high-power laser generation with efficiencies over 90% and beam quality better than 1.3, capable of producing outputs exceeding 100 kW while maintaining robust beam quality and suppressing thermal challenges, and is compatible with an all-glass architecture.
Implementation Method 1
The optical fiber is configured to convert laser pump power input to Stokes-shifted seed power along the length of the optical fiber by means of a Stimulated Raman Scattering 'SRS' process
Data Source
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Figure 4~5
AI summary
According to an embodiment of the disclosure, a system for producing a higher power laser beam (105) is provided. The system includes an optical fiber (200) having a length. The optical fiber is configured to receive inputs from multiple laser pumps (101) and an input from a Stokes seed laser pump (102). The optical fiber has a core (201, 301, 401) that is doped with for example Germanium. The core, when viewed from a cross-section of the optical fiber, has a higher concentration of doping at a location (290) near an axis (342) of the optical fiber than a location further from the axis of the optical fiber. The optical fiber is also configured to convert pump power to Stokes power along the length of the optical fiber when subjected to a Stimulated Raman Scattering (SRS) process. The optical fiber (200) is a semi-guiding high aspect ratio core fiber (SHARC) having claddings (202) sandwiching the ribbon-like core (201) with open edges (201a, 201b) for the signal light, i.e. the amplified Stokes component. The semi-guiding waveguide is enclosed in a pump cladding (205) with a further outer cladding (203). The optical fiber has a polymer jacket (204).