Beam Shaper Array Tiles for High Fill Factor Fiber Lasers
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Solution Overview
Problem
Fiber laser amplifier systems face challenges in combining beams to achieve a uniform phase over the beam diameter, leading to clipping losses and reduced fill factor, which affects the ability to focus the beam to a small spot effectively, especially in applications like directed energy weapons.
Innovation Solution
A spectrally combined fiber laser amplifier system with a beam shaper assembly that includes spaced apart tiled beam shaper arrays, converting round Gaussian beams to high fill factor beams while minimizing clipping losses, using beam shaper arrays to alter the spatial phase distribution and intensity profile of the beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple fiber laser amplifiers are combined to increase output power, then the power of the laser amplifier is improved, but the beam quality deteriorates due to non-uniform phase distribution across the beam diameter
Solution Approach 1:
The system divides the beam combining function into separate spectral combining and spatial phase correction stages. Multiple fiber amplifiers are spectrally combined using diffraction gratings, while a dedicated beam shaper array with tiled beam shaper cells corrects the phase distribution independently, allowing power scaling without compromising beam quality
Solution Approach 2:
A beam shaper array acts as an intermediary element between the spectrally combined beams and the final output. This array includes tiled beam shaper cells that introduce appropriate phase delays to equalize the phase across the entire beam diameter, thereby restoring beam quality while maintaining the high power output from multiple amplifiers
2Quantity of substance
If beam shaper arrays are used to convert round Gaussian beams to high fill factor beams, then the fill factor is improved, but clipping losses increase due to beam expansion
Solution Approach 1:
The beam shaper cells use diffractive optical elements to transform the beam profile from a round Gaussian distribution to a square flat-top profile. This dimensional transformation in the spatial domain increases the fill factor by efficiently packing the beam energy into a larger aperture area while the diffractive nature of the transformation minimizes energy loss through controlled diffraction patterns rather than hard clipping
Solution Approach 2:
The beam shaper cells modify the intensity distribution parameter of the beam by converting the Gaussian intensity profile to a uniform flat-top profile. This parameter change allows the beam to better fill the aperture without the exponential tails of the Gaussian profile causing clipping losses, thereby increasing fill factor while preserving energy
3Adaptability or versatility
If phased array approach is used for beam combining, then beam steering capability and atmospheric compensation are improved, but device complexity increases due to phase control requirements
Solution Approach 1:
The system merges spectral beam combining with coherent beam combining in a unified phased array architecture. The beam shaper array simultaneously performs spectral combination through diffraction gratings and phase control through tiled beam shaper cells, combining multiple functions into a single integrated system that reduces overall complexity compared to separate systems
Solution Approach 2:
The beam shaper array elements serve multiple functions: they act as diffraction gratings for spectral combination, as phase modulators for coherent beam combining and electronic steering, and as beam profilers for optimizing fill factor. This multi-functionality reduces the number of separate components needed, thereby reducing device complexity while maintaining enhanced adaptability
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 system achieves a nearly 100% fill factor with uniform intensity and phase across the emitting aperture, enabling high-speed beam steering and compensation for atmospheric aberrations, improving beam quality and focusing capabilities.
Implementation Method 1
beam shaper arrays that alter the spatial phase distribution and intensity profile of the beams
Implementation Method 2
each convert a round Gaussian or other low fill factor beam to a high fill factor beam
Implementation Method 3
multiple lasers of different wavelengths are combined on a diffraction grating or other dispersive optic into a single beam
Implementation Method 4
multiple mutually coherent lasers are locked in phase with one another and combined into a single beam either by overlapping in the near field using a beam splitter
Implementation Method 5
phased array pistons can be actuated at GHz-class speeds using commercially fiber-coupled waveguide electro-optic modulators
Data Source
Figure 1
Figure 2~3
Figure 4A~4D
AI summary
A spectral beam combining (SBC) fiber laser amplifier system including a beam shaper array assembly and a beam source that provides a plurality of beams having a low fill factor profile. The assembly includes an input beam shaper array having a plurality of input cells positioned adjacent to each other that are shaped to cause the beams to expand as they propagates away from the input array to be converted from the low fill factor profile to a high fill factor profile and be tapered to a lower value at a perimeter of each input array cell. The assembly further includes an output beam shaper array having a plurality of output cells positioned adjacent to each other that are shaped to cause the beams to stop expanding so that the output array provides a plurality of adjacent beams with minimal overlap and a minimal gap between the beams.