Phased Laser Array Beam Control via Phase Diversity
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Solution Overview
Problem
Existing laser radar systems face challenges in anisoplanatic imaging and beam control over an extended field of view due to atmospheric turbulence, which distorts optical wavefronts and limits the useable aperture of telescopes, particularly when targeting extended objects like missiles or aircraft, and are hindered by backscatter issues in coherent detection techniques.
Innovation Solution
The implementation of incoherent detection techniques using forward-model image reconstruction and tomographic estimation of three-dimensional atmospheric turbulence, combined with phase diversity and aperture partitioning, allows for high-quality anisoplanatic imaging and beam control without the need for additional apertures or heterodyne sensing, effectively overcoming backscatter and maintaining aimpoint selection and phase control across the full aperture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If adaptive optics is used to correct wavefront distortions, then image quality is improved, but the system complexity increases significantly when dealing with extended regions consisting of multiple isoplanatic patches
Solution Approach 1:
The patent divides the extended field of view into multiple isoplanatic patches, each with its own wavefront correction. By segmenting the correction task across multiple independent adaptive optics channels rather than attempting to correct the entire extended region with a single complex system, the patent achieves high-quality imaging across multiple patches while managing system complexity through modular architecture
Solution Approach 2:
The patent extracts wavefront information from the temporal dimension by analyzing sequences of images over time. Instead of requiring simultaneous multi-dimensional spatial measurements that would increase hardware complexity, the system uses temporal evolution of atmospheric turbulence to infer wavefront characteristics across multiple isoplanatic patches
2Measurement precision
If coherent detection techniques are used to measure complex field amplitudes, then beam control precision is improved, but backscatter from the target interferes with the returned signal
Solution Approach 1:
The patent uses periodic modulation of the laser frequency and employs pulsed laser operation with time-gated detection. By modulating the laser frequency periodically and detecting returns only during specific time windows, the system distinguishes between the modulated laser signal and unmodulated backscatter, enabling precise beam control while rejecting backscatter interference
Solution Approach 2:
The patent employs frequency modulation of the laser and detects returns at different frequency components. By changing the color (frequency) of the laser light periodically and using heterodyne detection to separate different frequency components, the system achieves precise beam control while filtering out backscatter that does not carry the modulation signature
3Weight of stationary object
If a single large power laser source is used, then system size is reduced, but the system degrades more severely with laser faults compared to phased array architecture
Solution Approach 1:
The patent divides the laser system into multiple independent laser channels arranged in a phased array, where each channel contributes a portion of the total power. This segmentation allows the system to maintain reliability through graceful degradation - if one or more laser channels fail, the remaining channels continue to operate and can be phased to the target, albeit with reduced total power rather than complete system failure
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 high-resolution aimpoint selection and phase control, reconstructing detailed images of extended objects and reducing backscatter, while operating in strong-turbulence conditions without additional complexity, thus improving the precision and effectiveness of laser beam projection.
Implementation Method 1
a phase modulator for modulating a phase of the laser beamlet output by the laser
Implementation Method 2
a polarizing beam splitter arranged such that a laser beamlet output by the laser will impinge on the polarizing beam splitter
Implementation Method 3
a diverging lens arranged such that laser light transmitted through the polarizing beam splitter will impinge on the diverging lens, wherein the diverging lens is displaceable in three mutually orthogonal directions
Implementation Method 4
a primary lenslet arranged such that laser light transmitted through the diverging lens will impinge on the primary lenslet and laser light transmitted through the primary lenslet will impinge on the beam director
Implementation Method 5
a focal plane array arranged such that light that passed through the diverging lens and then impinged on the polarizing beam splitter will impinge on the focal plane array
Data Source
AI summary
Systems and methods that combine forward-model image reconstruction techniques with tomographic estimation of three-dimensional atmospheric turbulence to enable high-quality anisoplanatic imaging and beam control through the atmosphere over an extended field of view using a phased laser array. The system projects laser energy onto specific locations of extended objects in various geometries, overcomes atmospheric anisoplanatism and backscatter; estimates phase across the full aperture, and reconstructs the target object in great detail to enable high-resolution aimpoint selection and maintenance. Aimpoint maintenance is performed by sequentially analyzing a passive image and a laser spot in rapid succession, in each subaperture at high signal-to-noise ratio. As a further improvement, backscatter issues from the projected laser beam are eliminated by cycling the laser and/or sequentially lasing on different wavelengths within the laser gain bandwidth.