Distributed Pump-Dump Delivery Fiber for High-Power Laser Systems
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Solution Overview
Problem
High-power fiber lasers and amplifiers face limitations due to nonlinear optical effects such as Stimulated Brillouin Scattering, which can lead to power limitations and device failure, especially when scaling to larger sizes or lengths, and existing solutions struggle with compact packaging due to bending losses in low-numerical-aperture fibers.
Innovation Solution
A distributed pump-dump delivery fiber with a graded concentration of absorbing materials is used to absorb and dissipate pump and signal wavelengths, reducing hot spots and nonlinear effects by spreading energy dissipation over a longer length, and incorporating a double-clad structure with a transparent core and attenuating cladding to manage pump power and signal amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a large core diameter is used to reduce nonlinear optical effects, then power handling capability is improved, but numerical aperture decreases requiring lower NA to maintain beam quality
Solution Approach 1:
The fiber is divided into multiple segments with different core diameters and NA values along its length. The first segment has a larger core diameter for high power handling, while the second segment has a smaller core diameter with higher NA for maintaining beam quality. This segmentation allows each section to be optimized for its specific function without compromise.
Solution Approach 2:
Different regions of the fiber are assigned different optical properties. The first segment is designed with large core diameter and low NA for power amplification, while the second segment is designed with smaller core diameter and higher NA for beam quality control. This local differentiation of properties enables simultaneous optimization of power handling and beam quality in different locations.
2Power
If fiber length is increased to reduce nonlinear effects, then power scaling is improved, but bending losses increase making compact packaging difficult
Solution Approach 1:
The long fiber is segmented into multiple sections with different characteristics. The first segment can be made with larger core diameter to reduce nonlinear effects over its length, while the second segment is optimized for lower bending losses. This allows the system to achieve the necessary length for power scaling while minimizing the impact of bending losses through proper segment design.
Solution Approach 2:
The fiber parameters (core diameter, NA, doping concentration) are changed along the length of the fiber. The first segment uses parameters optimized for power amplification, while the second segment transitions to parameters that reduce bending sensitivity. This gradual parameter change allows the fiber to maintain performance over long lengths while enabling compact packaging with reduced bending losses.
3Power
If pump power is increased to achieve higher output power, then power output is improved, but nonlinear optical effects such as SBS increase limiting further scaling
Solution Approach 1:
The fiber amplifier is divided into segments where the first segment handles the initial power amplification with larger core diameter to keep intensity low and reduce nonlinear effects. The second segment continues power amplification with optimized parameters. This segmentation allows progressive power scaling while maintaining low intensity in each segment to suppress nonlinear optical effects like SBS.
Solution Approach 2:
Different segments of the fiber are assigned different local properties (core diameter, doping concentration, NA) to optimize power amplification while controlling nonlinear effects. The first segment has properties optimized for high power handling with reduced intensity, while subsequent segments are optimized for continued amplification. This local optimization allows high pump power to be used without triggering limiting nonlinear effects.
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 effectively reduces the risk of device failure by distributing energy dissipation and managing pump power, allowing for higher peak and average powers while maintaining good beam quality and enabling compact packaging of fiber-laser systems.
Implementation Method 1
the inner cladding is doped with an absorbing dopant that absorbs at the pump wavelength to dump pump power
Implementation Method 2
the core is surrounded by an inner cladding layer that delivers pump light... the core delivers an optical signal at a signal wavelength
Data Source
AI summary
Apparatus and method for distributed absorption of pump light over a length of delivery fiber that is, for example in some embodiments, fusion spliced to an end of a multiply clad gain fiber that has significant unused pump light at the end of the gain fiber. In some embodiments, this includes coupling a fiber amplifier to a passive-core delivery fiber that includes a distributed pump dump. In some embodiments, at an output end of the amplifying fiber there is still a significant amount of pump power. If all this pump power is dumped in one small place (e.g., at a splice between the amplifying fiber and a passive delivery fiber) a hot spot will result, leading to unreliable devices that fail (have catastrophic changes in operating performance). The present invention provides a distributed pump dump built into a delivery fiber that is passive to the signal in its core.