Adaptive optical system testbed with karhunen-loeve polynomial based method for simulating atmospheric turbulence
Inventors
Wilcox, Christopher C. • Restaino, Sergio R. • Teare, Scott W. • Martinez, Ty
Assignees
US GOVERNMENT IN NAME OF SECRETARY OF NAVY • US Department of Navy
Publication Number
US-8725471-B2
Publication Date
2014-05-13
Expiration Date
2030-02-02
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Abstract
A system and method for simulating atmospheric turbulence for testing optical components. A time varying phase screen representing atmospheric turbulence is generated using Karhunen-Loeve polynomials and a splining technique for generating temporal functions of the noise factor for each Zernike mode. The phase screen is input to a liquid crystal spatial light modulator. A computer display allows the user to set geometric characteristics, the severity of the turbulence to be simulated, and to select between methods for generating atmospheric turbulence including Karhunen-Loeve polynomials, Zernike polynomials, and Frozen Seeing.
Core Innovation
The invention relates to a system and method for simulating atmospheric turbulence for testing optical components using a time varying phase screen generated with Karhunen-Loeve polynomials and a splining technique to produce temporal functions of noise factors for each Zernike mode. This phase screen is applied to a liquid crystal spatial light modulator (LC-SLM) to introduce simulated wavefront aberrations. The system includes a user interface allowing selection of geometric characteristics, turbulence severity, and between three methods of generating atmospheric turbulence: Karhunen-Loeve polynomials, Zernike polynomials, and Frozen Seeing.
The problem being solved arises from the difficulty and expense of realistically simulating atmospheric turbulence for calibration and testing of adaptive optics (AO) systems in laboratory settings. Previous methods using static etched glass phase screens or rotating filters are costly, computationally intensive, and limited in flexibility. The Earth's non-homogeneous and temporally varying atmosphere induces complex wavefront distortions that need to be accurately modeled for AO system characterization.
The invention addresses this by providing a computationally efficient, flexible, and dynamically adjustable optical testbed system, employing a LC-SLM controlled by software to generate time varying phase screens based on Karhunen-Loeve polynomial expansions with spline-interpolated noise factors. This allows smooth temporal evolution of turbulence simulation with controllable parameters such as the Fried parameter and aperture size, enabling high fidelity simulation of atmospheric aberrations, including secondary obscurations, for performance evaluation of optical components like telescopes.
Claims Coverage
The patent contains one independent claim addressing an optical testbed system with several inventive features concerning atmospheric turbulence simulation.
Optical testbed system with multiple turbulence simulation methods
An optical testbed system comprising a computer processor programmed to generate a time varying wavefront simulating atmospheric turbulence, which is input as a sequence of phase screens to a liquid crystal spatial light modulator. The system includes a display screen presenting selectable turbulence generation methods including Karhunen-Loeve polynomial based method, Zernike polynomial based method, and Frozen Seeing method, and a user input device to select among these methods.
Wavefront generation using Karhunen-Loeve polynomials with temporal noise functions
The Karhunen-Loeve polynomial based method generates the time varying wavefront as a weighted sum of Karhunen-Loeve polynomials combined with temporal noise functions represented by a spline fit to random numbers, with coefficients weighted based on Zernike-Kolmogorov residual errors for each mode.
Incorporation of a Fried parameter for turbulence severity control
The system's display is adapted to show the Fried parameter representing the turbulence severity, and the user input device receives and inputs a user-selected Fried parameter to control the simulation level.
Use of Frozen Seeing method via large phase screen movement
The Frozen Seeing method includes generating an initial phase screen larger than the aperture, then sequentially applying subsections of this screen to the spatial light modulator to simulate temporal turbulence effects as the phase screen moves across the aperture.
Optical configuration with LC-SLM and optional Fourier filter
The system includes a liquid crystal spatial light modulator that receives a collimated light beam, modulates the wavefront according to the generated phase screen, and outputs the aberrated beam to an optical component under test. For LC-SLMs with 0 to π phase range, an optically arranged Fourier filter between the modulator and component extends phase modulation to a full 0 to 2π range.
User-selectable addition of secondary obscuration to phase screen
The computer processor includes instructions to add a secondary obscuration element, such as from a telescope secondary mirror and mount, to the simulated phase screen.
The independent claim covers a computer-controlled optical testbed system employing a liquid crystal spatial light modulator to simulate atmospheric turbulence with selectable simulation methods including Karhunen-Loeve, Zernike, and Frozen Seeing techniques, incorporating user-adjustable parameters like the Fried parameter and secondary obscurations, and optionally including a Fourier filter to extend phase modulation range.
Stated Advantages
Enables realistic and dynamic simulation of atmospheric turbulence with higher fidelity and lower cost compared to etched glass or rotating physical phase screens.
Allows selection among multiple mathematical models of turbulence (Karhunen-Loeve, Zernike, and Frozen Seeing) for versatile testing scenarios.
Generates temporally smooth turbulence simulations through spline-interpolated noise factors, enhancing accuracy over discontinuous phase screen transitions.
Facilitates rapid modification of simulation parameters such as aperture size, turbulence strength (Fried parameter), and inclusion of secondary obscurations, improving adaptability for various optical systems.
Supports evaluation and calibration of adaptive optics systems and optical components under controlled, repeatable atmospheric conditions in laboratory environments.
Documented Applications
Testing and calibration of adaptive optics systems for telescopes, free space laser communication systems, and high energy laser applications.
Simulating atmospheric turbulence effects in laboratory optical testbeds to evaluate the performance of optical components and systems subjected to environmental aberrations.
Generating arbitrary wavefront aberrations required for optical system testing beyond atmospheric seeing conditions.
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