Integrated DOE-SBC Grating for High-Power Beam Combining
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Solution Overview
Problem
Current fiber laser amplifier systems face limitations in combining beams coherently and spectrally due to bandwidth and phasing errors, restricting the output power and beam quality, especially when trying to focus the combined beam to a small spot.
Innovation Solution
An integrated diffractive optical element (DOE) and spectral beam combination (SBC) grating are fabricated in a single step, allowing for both coherent and incoherent beam combination by forming periodic structures in a top layer, reducing fabrication complexity and improving optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple fiber lasers are used to amplify and combine seed beams to generate higher powers, then the output power of the laser amplifier is increased, but the beam quality deteriorates due to phase non-uniformity across the beam diameter
Solution Approach 1:
The patent combines multiple fiber laser beams into a single coherent output beam using a diffractive optical element that enforces uniform phase across the combined beam diameter. The DOE merges N input beams with different phases into one beam with uniform phase distribution, enabling both high power and good beam quality.
Solution Approach 2:
The patent changes the phase parameter of individual fiber beams by adjusting the optical path length for each beam. By controlling the phase of each input beam relative to others, the system achieves coherent combination while maintaining beam quality. The DOE then processes these phase-adjusted beams to produce a uniform phase output.
2Productivity
If a diffractive optical element is used to combine coherent beams, then beam combination efficiency is improved, but the number of beams that can be coherently combined is limited due to bandwidth and phasing errors
Solution Approach 1:
The patent extends the beam combination capability from a single wavelength to multiple wavelengths by adding spectral beam combination gratings to the DOE. This dimensional extension allows the system to handle more beams by utilizing different wavelength dimensions, thereby increasing the total number of combinable beams beyond what a single-wavelength DOE can achieve.
3Adaptability or versatility
If separate DOE and SBC grating are used for hybrid coherent and spectral beam combination, then both coherent and incoherent beam combining are achieved, but the device complexity increases
Solution Approach 1:
The patent merges the DOE and SBC grating into a single integrated optical element. The DOE portion handles coherent beam combination while the SBC grating portion handles spectral beam combination, both within one device. This integration reduces the number of separate optical components while maintaining the dual functionality for combining both coherent and incoherent beams.
4Manufacturing precision
If multiple fabrication steps are used to create integrated DOE and SBC grating, then fabrication accuracy is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent incorporates the DOE periodic structure into the master mask before the grating fabrication process begins. This preliminary inclusion allows the DOE pattern to be transferred simultaneously with the SBC grating lines during a single lithography and etching cycle, achieving both structures with high precision without requiring separate fabrication steps.
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 the beam quality and output power of fiber laser amplifiers by enabling more precise and efficient beam combination, focusing the combined beam to a nearly diffraction-limited spot with reduced fabrication steps and improved accuracy.
Implementation Method 1
The DOE has a periodic structure formed into the element so that when the individual amplified beams each having a slightly different angular direction are redirected by the periodic structure all of the beams diffract from the DOE in the same direction
Implementation Method 2
the coherently combined beams are directed to a spectral beam combination (SBC) grating at slightly different angles that diffracts the beams in the same direction as a single combined beam of multiple wavelengths
Data Source
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AI summary
An integrated optical device that combines a diffractive optical element (DOE) to provide beam combining for coherent beams and a spectral beam combination (SBC) grating to provide beam combining for incoherent beams. The device includes a planar substrate and a reflective coating deposited on the substrate. A top dielectric layer is deposited on the reflective coating and a photoresist layer is deposited on the top dielectric layer. A periodic structure is formed into the top dielectric layer in a first direction that defines the DOE and a periodic grating having grooves is formed into the top dielectric layer in a second direction substantially orthogonal to the first direction that defines the SBC grating where the periodic structure includes periodic modulations along the length of the grooves that are orthogonal to a channel-to-channel periodicity of the periodic grating.