Coherent Beam Combining via Real-Time Holography
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Solution Overview
Problem
Current methods for combining coherent laser beams require complex and expensive adaptive optics systems with precise control for each sub-aperture, making them impractical for fieldable systems due to high complexity, size, weight, and power consumption, as well as fragile components that need constant tuning.
Innovation Solution
A system using a local-referenced interferometer generated hologram on a Spatial Light Modulator (SLM) to combine multiple coherent laser sources, which reduces the need for precise control by generating a diffraction-limited full aperture far field intensity through a real-time hologram that compensates for tip, tilt, and piston errors, and wavefront curvatures, using a single adaptive optical device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate beam control or adaptive optics is used for each laser beam, then beam combination quality is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple sub-aperture beams into a single full-aperture beam using a beam combiner, eliminating the need for separate control systems for each beam. The interferometer measures the combined beam's wavefront errors, and a single phase modulator corrects all beams simultaneously, resolving the contradiction between beam combination quality and device complexity.
Solution Approach 2:
The phase modulator positioned in the common optical path serves as a universal correction device that simultaneously corrects wavefront errors for all sub-aperture beams. This single device performs the function that would otherwise require multiple separate adaptive optics systems, reducing complexity while maintaining correction quality.
2Measurement precision
If precise piston, tip, and tilt control is implemented on each sub-aperture, then alignment accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the measurement function from multiple separate control systems and consolidates it into a single interferometer that measures the combined beam. The phase modulator then applies the necessary corrections for piston, tip, and tilt errors across all sub-apertures simultaneously, reducing alignment complexity while maintaining precision.
Solution Approach 2:
The interferometer acts as an intermediary measurement device that characterizes the combined beam's wavefront errors. This single measurement intermediary provides the information needed to correct all sub-aperture alignment errors through the phase modulator, eliminating the need for multiple separate measurement and control systems.
3Manufacturing precision
If conventional adaptive optical devices are used, then beam quality is improved, but reliability decreases due to fragility and constant tuning requirements
Solution Approach 1:
The system uses the combined beam itself as the reference for measuring wavefront errors through the interferometer. This self-referenced approach eliminates the need for external tuning and calibration, allowing the system to automatically maintain optimal performance without constant human intervention, thereby improving reliability.
Solution Approach 2:
The interferometer provides real-time feedback on the combined beam's wavefront errors, and the phase modulator applies corrective feedback to maintain diffraction-limited performance. This closed-loop feedback system automatically compensates for disturbances without requiring manual tuning, enhancing system reliability.
4Manufacturing precision
If multiple separate control systems are used for each beam, then beam combination quality is improved, but size, weight, and power consumption increase
Solution Approach 1:
The patent merges multiple separate control systems into a single integrated system where one interferometer measures the combined beam and one phase modulator corrects all sub-apertures simultaneously. This consolidation dramatically reduces the total weight of control devices while maintaining beam combination quality through shared measurement and correction resources.
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 simplifies beam combination, reduces size, weight, and power consumption, while achieving high beam quality and diffraction-limited performance by correcting phase errors in real-time, allowing for efficient and cost-effective combination of multiple coherent laser sources.
Implementation Method 1
An interferometer receives a sample of a full aperture unphased combination of the plurality of beamlets and provides interference fringes
Implementation Method 2
A spatial light modulator (SLM) receives the fringes from the interferometer and generates a hologram as a diffraction grating
Implementation Method 3
Relay optics transmit the full aperture unphased combined beamlets to the SLM and receive a diffraction corrected full aperture phased beam from the diffraction grating
Data Source
AI summary
A system for combining multiple coherent optical beams incorporates a plurality of coherent beamlets expanded to an aperture. An interferometer receives a sample of a full aperture unphased combination of the plurality of beamlets and provides interference fringes. A spatial light modulator (SLM) receives the fringes from the interferometer and generates a hologram as a diffraction grating. Relay optics transmit the full aperture unphased combined beamlets to the SLM and receive a diffraction corrected full aperture phased beam from the diffraction grating hologram for emission to the far field.