Optical Phased Array Laser Phase Locking Without External Sensors
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Solution Overview
Problem
Existing methods for forming a coherent optical phased array laser source require external measurements for phase locking, which are sensitive to thermal and mechanical drift, making them non-viable due to sensitivity and alignment requirements.
Innovation Solution
A method that uses a minimally intrusive beam sampling approach within the spatial beam combiner assembly to measure phase differences between output beams, allowing for internal phase control without external sensors, using a processor to process data and adjust phase offsets, enabling precise reconstruction of the spatial phase state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external measurement methods are used for phase locking, then phase control capability is achieved, but sensitivity to thermal and mechanical drift increases
Solution Approach 1:
The patent introduces an intermediary virtual measurement plane within the spatial beam combiner assembly that mediates between the output beams and the detector. This virtual plane allows phase information to be extracted through interferometric measurement of beam pairs without requiring external sensors, thereby achieving phase control while being isolated from external thermal and mechanical drift influences.
Solution Approach 2:
The system uses its own internal beam structure to perform phase measurement. By directing samples of neighboring beam pairs back through the lens array to form focused pairs at a detector, the system self-measures its phase state without external intervention. This self-service approach eliminates dependence on external measurement devices that are sensitive to environmental drift.
2Measurement precision
If external sensors are used for phase measurement, then phase information can be obtained, but alignment uniformity requirements become extremely stringent
Solution Approach 1:
The virtual measurement plane acts as an intermediary that transforms the phase measurement problem into one that can be solved with relaxed alignment tolerances. By forming focused pairs of beams at this virtual plane and measuring their interference pattern, the system obtains phase information without requiring nanometer-class alignment uniformity across all beam paths.
Solution Approach 2:
The system creates virtual copies of the beam paths through the lens array to form focused pairs at the virtual measurement plane. These copied paths allow phase comparison without requiring direct physical alignment of all original beam paths, thereby reducing manufacturing precision requirements.
3Reliability
If strictly internal measurement methods are used, then sensitivity to external drift is reduced, but alignment uniformity requirements exceed 10s of nanometer class
Solution Approach 1:
The virtual measurement plane serves as a mediator that reconciles the conflict between internal measurement and alignment requirements. It provides a location where phase information can be extracted from focused beam pairs with much more relaxed alignment tolerances than would be required for direct internal measurement, while still maintaining immunity to external drift.
Solution Approach 2:
The system changes the measurement parameter from direct spatial alignment to interferometric phase measurement at the virtual plane. This parameter change allows the system to achieve drift immunity without requiring alignment uniformity better than 10s of nanometers, because the phase information is extracted from the interference pattern rather than direct beam alignment.
4Measurement precision
If external measurement devices are used, then phase locking is achieved, but device complexity and sensitivity to drift increase
Solution Approach 1:
The spatial beam combiner assembly performs its own phase measurement function by utilizing its existing optical components (lens array, output window) to direct beam samples to a detector. This self-service capability eliminates the need for external measurement devices, reducing device complexity while maintaining phase locking capability.
Solution Approach 2:
The output window and lens array serve multiple functions: they both combine the spatial beams and simultaneously provide the measurement function by directing samples to the detector. This multi-functionality reduces the number of separate components needed, thereby reducing overall device complexity.
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 provides a robust, thermally stable, and mechanically robust configuration that tolerates high levels of drift and fabrication error, enabling the formation of a coherent and programmable optical phased array laser source without external measurement devices.
Implementation Method 1
The sampling regions direct a sample of neighboring beam pairs back through the lenses to form a focused pair of beams. The detector then measures an optical sample, and the system determines phase difference measurements by demodulating the optical samples.
Data Source
AI summary
Systems and methods for forming a coherent optical phased array laser source from a spatially combined array of output beams is accomplished without any external measurement devices or wavefront sensors. A master oscillator laser is split into a plurality of optical beam transport and amplifier channels to produce a plurality of optical output beams that are spatially combined in an array format. The spatial phase state of the plurality of output beams is measured at the output of a spatial combiner without use of an external measurement device or sensor. The phase of the plurality of optical output beams is controlled to compensate both for aberrations induced by the optical beam transport and amplifier paths to produce a coherent and spatially phased laser beam at the output of the laser source or to produce a phased laser beam with prescribed phase state on each output beam.