Phased Laser Array Coherent Combination Power Scaling
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Solution Overview
Problem
Fiber lasers face limitations in power due to high energy density, which leads to nonlinear phenomena and damage, and existing methods for combining multiple fiber lasers struggle to achieve high power while maintaining spectral and temporal coherence, especially for lasers with broad spectral bandwidths.
Innovation Solution
The solution involves precise control of the integer multiple of wavelengths of the fiber lengths in a laser array to match the spectral and temporal properties of individual lasers, allowing for coherent combination and increasing the energy of mode-locked laser pulses, and overcoming power-handling limitations by actively controlling relative phases and lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the cross-sectional area of the fiber is increased to raise the nonlinear and damage thresholds, then the power handling capability is improved, but the fiber becomes prone to bend-induced losses and beam quality degrades
Solution Approach 1:
The invention divides a single high-power laser into multiple lower-power fiber lasers operating in parallel. Each fiber operates below the nonlinear and damage thresholds, while their outputs are coherently combined to achieve the desired high total power. This segmentation allows each fiber to maintain optimal dimensions for beam quality while the array provides the required power handling capability.
2Device complexity
If incoherent combination techniques are used to combine multiple fiber lasers, then the system complexity is reduced, but the energy density and power limitations of individual lasers remain unresolved
Solution Approach 1:
The invention merges the outputs of multiple fiber lasers through coherent combination, where the phases of individual laser beams are actively controlled to be synchronized. This allows the intensities to add constructively, achieving total power scaling proportional to the square of the number of lasers (N²), far exceeding incoherent combination limits while maintaining manageable individual laser power levels.
3Power
If actively-phased coherent beam combining is used to achieve high combined power, then the total power output is improved, but the spectral bandwidth is limited due to the need for narrow spectral widths to maintain phase coherence
Solution Approach 1:
The invention employs dynamic phase control where the phase of each laser in the array is actively adjusted in real-time to maintain coherence. This dynamic adaptation allows the system to handle broader spectral bandwidths by continuously compensating for phase variations across different wavelengths, enabling both high combined power and useful spectral bandwidth simultaneously.
4Power
If the number of fiber lasers in the array is increased to overcome power limitations, then the total power output is improved, but the challenge of maintaining phase coherence and controlling individual laser power distribution increases
Solution Approach 1:
The invention implements feedback control systems that monitor the phase and power output of each individual laser in the array. This feedback information is used to adjust the operating parameters of each laser in real-time, ensuring optimal phase coherence and balanced power distribution across all N lasers. The feedback mechanism automatically compensates for variations in laser performance, simplifying the management of large-scale arrays.
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 the generation of high-energy pulsed lasers and high-power CW lasers, increasing the energy of individual pulses by a factor near the number of lasers in the array, while maintaining beam quality and coherence, effectively overcoming the power limitations of single fiber lasers.
Implementation Method 1
The narrow sources also have a distinct disadvantage: they tend to suffer from stimulated Brillion scattering (SBS), a nonlinear phenomenon which today limits the power of the individual lasers to roughly 100 W
Implementation Method 2
Coherent combination means that, at the point of combination, the phases of the lasers are the same, or within the needs of a given application, nearly the same
Implementation Method 3
They may be combined by a series of beam-splitters or a diffractive optical element, or they may be allowed to simply diffract and combine as they propagate toward some distant target
Data Source
AI summary
Architectures for coherently combining an array of fiber-based lasers are provided. By matching their lengths to within a few integer multiples of a wavelength, the spatial and temporal properties of a single large laser are replicated, while extending the average or peak pulsed power limit.