Diffractive Laser Combining With Side-Beam Phase Error Sensing
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Solution Overview
Problem
Existing methods for combining high-energy, high-repetition-rate, ultrafast fiber laser beams face challenges in achieving efficient and stable beam combination due to limited energy from fiber amplifiers, requiring hundreds of beams to be coherently added, and suffer from noise and complexity in phase detection and control.
Innovation Solution
A deterministic phase detection scheme that analyzes the intensity pattern of uncombined side beams at the output to sense phase errors, allowing for efficient and stable beam combination without the need for complex optical paths or high noise levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If stochastic parallel gradient descent (SPGD) is used for phase control, then the method can search for optimum phase values, but the control delay scales with the number of beams and feedback bandwidth becomes impractically low
Solution Approach 1:
The patent extracts phase information from the intensity patterns of uncombined side beams rather than using a single measured output. By analyzing the intensity distribution of multiple side beams, the system obtains phase error signals without requiring iterative search methods, thereby reducing control delay while maintaining detection accuracy.
Solution Approach 2:
The patent replaces the iterative mechanical search process of SPGD with a direct deterministic measurement approach. By using the intensity patterns of side beams to directly determine phase errors, the system eliminates the need for random dithering and iterative optimization, significantly reducing the control loop delay.
2Measurement precision
If a common reference beam is used for phase detection, then deterministic measurement is achieved, but system complexity increases requiring additional optical paths
Solution Approach 1:
The patent makes the uncombined side beams serve a dual purpose: they represent the uncombined light that would otherwise be waste, and simultaneously provide the measurement signal for phase detection. By analyzing the intensity patterns of these side beams, the system obtains phase error information without requiring additional reference beams or complex optical paths.
Solution Approach 2:
The uncombined side beams perform multiple functions: they are both the residual uncombined light from the beam combining process and the measurement signal for phase detection. This multi-functionality eliminates the need for separate reference beams and reduces overall system complexity while maintaining deterministic phase measurement capability.
3Measurement precision
If random dithering is applied to all phase inputs, then the system can search for optimum values, but noise is introduced that suffers combining efficiency and stability
Solution Approach 1:
The patent extracts deterministic phase error signals from the intensity patterns of uncombined side beams, eliminating the need for random dithering. By directly measuring the relationship between side beam intensities and phase errors, the system achieves phase optimization without introducing noise that would degrade combining efficiency and stability.
4Power
If hundreds of beams are coherently added to produce Joule-level outputs, then the required power level is achieved, but the feedback bandwidth becomes impractically low due to the large number of beams
Solution Approach 1:
The patent extracts phase error information from the intensity patterns of uncombined side beams, enabling direct determination of correction signals for all beams simultaneously. This approach avoids iterative optimization methods whose control delay scales with the number of beams, thereby maintaining high feedback bandwidth even when combining hundreds of beams to achieve Joule-level output power.
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 method achieves high efficiency (84.6%) and stability (<0.3% stability) in combining laser beams, enabling scaling to large channel counts without significant slowing of control loop response time, thus overcoming the limitations of existing technologies.
Implementation Method 1
a diffractive optical element diffracts the plurality of laser beams to generate a plurality of output beams including a central beam and a plurality of side beams
Implementation Method 2
sensing phase errors by analyzing the intensity pattern of uncombined side beams at the output
Data Source
AI summary
This disclosure provides systems, methods, and apparatus related to optical systems. In one aspect, a method includes: generating a plurality of laser beams; receiving the plurality of laser beams at the point at a diffractive optical element, the diffracting optical element diffracting the plurality of laser beams to generate a plurality of output laser beams including a central laser beam and a plurality of side laser beams; measuring a power of at least two of the plurality of output laser beams generated by the diffractive optical element; determining a phase error in laser beams of the plurality of laser beams from the power of the at least two of the plurality of output laser beams; and changing the phase N−1 laser beams of the plurality of laser beams, with N being a number of the plurality of laser beams.