US-12619093-B2 - Method and apparatus for compensating for atmospheric distortion

US12619093B2US 12619093 B2US12619093 B2US 12619093B2US-12619093-B2

Abstract

An atmospheric distortion compensator for a free space optical beam comprising: a disc that is rotationally balanced about a center point and that comprises a phase-modifying structure; an optical beam source configured to generate a free space optical beam that propagates through the disc and then through turbulence in open air to a point in space where reducing scintillation is desired, wherein the point in space is separated from the disc only by the open air; and a rotator mechanically coupled to the disc's center point and configured to spin the disc about an axis parallel to the free space optical beam, wherein the disc, when spinning, is configured to control a property of the free space optical beam thereby reducing scintillation effects as experienced at the point in space, which effects are caused by propagation of the free space optical beam through the open air.

Inventors

Kyle Robert Drexler

Assignees

THE UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF THE NAVY

Dates

Publication Date: 20260505
Application Date: 20240617

Claims (19)

1 . An atmospheric distortion compensator for compensating for atmospheric distortion of a free space optical beam comprising: a disc that is rotationally balanced about a center point and that comprises a phase-modifying structure; an optical beam source configured to generate a free space optical beam that propagates through the disc and then through open air to a point in space where reducing scintillation caused by atmospheric turbulence is desired, wherein the point in space is separated from the disc only by the open air; and a rotator mechanically coupled to the disc's center point and configured to spin the disc about an axis parallel to the free space optical beam, wherein the disc, when spinning, is configured to control a property of the free space optical beam thereby reducing scintillation effects as experienced at the point in space, which effects are caused by propagation of the free space optical beam through the open air.
2 . The atmospheric distortion compensator of claim 1 , wherein the free space optical beam is a fully coherent, narrow-band LASER, and wherein the LASER has an at-disc spatial intensity distribution that differs from an at-range spatial intensity distribution at the point in space.
3 . The atmospheric distortion compensator of claim 2 , wherein the disc is a diffractive optical element.
4 . The atmospheric distortion compensator of claim 3 , wherein the phase-modifying structure comprises a pattern controlled by a Gaussian-Schell model of partial coherence to control the free space optical beam's spatial coherence property.
5 . The atmospheric distortion compensator of claim 3 , wherein the phase-modifying structure is designed to control the free space optical beam's optical orbital angular momentum.
6 . The atmospheric distortion compensator of claim 4 , wherein the disc further comprises a plurality of N tracks, wherein each track is configured to apply a different degree of partial coherence to the free space optical beam, and wherein the tracks are disposed on the disc such that the free space optical beam may be brought into contact with different tracks by moving the disc in a direction that is orthogonal to the free space optical beam.
7 . The atmospheric distortion compensator of claim 6 , wherein one of the tracks is a reference track, which is configured with a uniform phase profile that does not distort the free space optical beam.
8 . The atmospheric distortion compensator of claim 7 , further comprising a camera configured to capture an image of an object illuminated at range (that is, disposed at the point in space) by the free space optical beam, wherein the disc is spun at a rate that is at least 30 times greater than an integration time of the camera.
9 . The atmospheric distortion compensator of claim 7 , further comprising: a processor operatively coupled to the rotator and configured to adjust a rotational speed of the disc; a linear actuator communicatively coupled to the processor, wherein the rotator is mounted to the linear actuator, and wherein the linear actuator is configured to move the rotator such that the disc moves in a direction that is orthogonal to the axis, wherein the processor is configured to adjust a linear motion of the disc such that the LASER interacts with a desired track.
10 . The atmospheric distortion compensator of claim 9 , wherein the processor is configured to encode information on the LASER as part of a free space optical communication link.
11 . The atmospheric distortion compensator of claim 1 , wherein the disc further comprises at least two tracks that each comprise phase-modifying structures that differ from each other, and wherein the tracks are disposed on the disc such that the beam may be brought into contact with different tracks by moving the disc in a direction that is orthogonal to the free space optical beam.
12 . A method for compensating for atmospheric distortion of a free space optical beam comprising: generating the free space optical beam; propagating the free space optical beam through a disc that is rotationally-balanced and that comprises a phase-modifying structure; propagating the free space optical beam through open air so as to impinge on a point in space where reducing scintillation is desired after the free space optical beam has passed through the disc; and spinning the disc about an axis that is parallel to the free space optical beam so as to reduce, at the point in space, scintillation effects caused by propagation of the free space optical beam through atmospheric turbulence in the open air.
13 . The method of claim 12 , further comprising: illuminating an object located at the point in space with the free space optical beam.
14 . The method of claim 13 , further comprising: using a camera to capture an image of the object, wherein the disc, which is positioned between the camera and the object, is spun at a rate that is at least 30 times greater than an integration time of the camera.
15 . The method of claim 12 , further comprising applying the free space optical beam, after it has propagated through the disc and the open air, to controlling a targeting beacon disposed at the point in space.
16 . The method of claim 12 , further comprising controlling a targeting beacon disposed at the point in space with the free space optical beam after the free space optical beam has propagated through the disc and through atmospheric turbulence in the open air.
17 . The method of claim 12 , further comprising illuminating an object at range, wherein the object is disposed at the point in space, with the free space optical beam after the free space optical beam has propagated through the disc and through atmospheric turbulence in the open air.
18 . A method for compensating for atmospheric distortion of a free space optical beam comprising: generating the free space optical beam, wherein the free space optical beam is a free space optical communication signal, and wherein the free space optical beam is a pulsed LASER having a pulse repetition rate, and further comprising spinning the disc at a rate based on the LASER pulse repetition rate so as to impart independent phase realizations on the LASER so the spinning disc does not to get stuck in frequency nodes between the disc spin rate and the LASER pulse repetition rate; propagating the free space optical beam through a disc that is rotationally-balanced and that comprises a phase-modifying structure and a plurality of N tracks, each track configured to apply a different degree of partial coherence to the free space optical beam; propagating the free space optical beam through open air so as to impinge on a point in space where reducing scintillation is desired after the free space optical beam has passed through the disc; spinning the disc about an axis that is parallel to the free space optical beam so as to reduce, at the point in space, scintillation effects caused by propagation of the free space optical beam through the open air; adjusting a rotational speed of the disc with a processor operatively coupled to the rotator; and using a processor to instruct a linear actuator to move the disc in a direction that is orthogonal to the free space optical beam so as to bring the free space optical beam into contact with different tracks until a desired track is identified that increases a signal-to-noise ratio (SNR) of the free space optical communication signal as compared to a reference track that has a uniform phase profile.
19 . The method of claim 18 , further comprising using the processor to change, on the fly, the track that is in contact with the free space optical beam.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a divisional of prior U.S. Application No. 17/583,421, filed 25 Jan. 2022, titled “Atmospheric Compensation Disc” FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT The United States Government has ownership rights in this invention. Licensing and technical inquiries may be directed to the Office of Research and Technical Applications, Naval Information Warfare Center Pacific, Code 72120, San Diego, CA, 92152; voice (619) 553-5118; ssc_pac_t2@navy.mil. BACKGROUND OF THE INVENTION Adaptive optics systems that employ LASERs to create artificial guide stars are currently used to actively compensate for atmospheric turbulence. These adaptive optics systems contain imaging systems to measure these guide stars and then use deformable mirrors or spatial light modulators to apply a compensating spatial phase to the propagating light field to correct the atmospheric distortion. Traditional adaptive optics systems, while precise, are inherently expensive, large, complicated, and difficult to implement. There is a need for an improved atmospheric distortion compensator. BRIEF DESCRIPTION OF THE DRAWINGS Throughout the several views, like elements are referenced using like references. The elements in the figures are not drawn to scale and some dimensions are exaggerated for clarity. FIG. 1 is a perspective view of an embodiment of an atmospheric distortion compensator. FIG. 2 is a front view illustration of an embodiment of a diffractive optical element disc. FIG. 3 is a perspective view of an embodiment of an atmospheric distortion compensator. DETAILED DESCRIPTION OF EMBODIMENTS The disclosed apparatus below may be described generally, as well as in terms of specific examples and/or specific embodiments. For instances where references are made to detailed examples and/or embodiments, it should be appreciated that any of the underlying principles described are not to be limited to a single embodiment, but may be expanded for use with any of the other apparatus described herein as will be understood by one of ordinary skill in the art unless otherwise stated specifically. References in the present disclosure to “one embodiment,” “an embodiment,” or any variation thereof, means that a particular element, feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment. The appearances of the phrases “in one embodiment,” “in some embodiments,” and “in other embodiments” in various places in the present disclosure are not necessarily all referring to the same embodiment or the same set of embodiments. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. Additionally, use of words such as “the,” “a,” or “an” are employed to describe elements and components of the embodiments herein; this is done merely for grammatical reasons and to conform to idiomatic English. This detailed description should be read to include one or at least one, and the singular also includes the plural unless it is clearly indicated otherwise. FIG. 1 is a perspective view illustration of an example embodiment of an atmospheric distortion compensator 10 (hereinafter referred to as compensator 10) that comprises, consists of, or consists essentially of a disc 12 and a rotator 14. The disc 12 is rotationally balanced about a center point 16 and comprises a phase-modifying structure on a surface 18. The rotator 14 is mechanically coupled to the disc's center point 16 and configured to spin the disc 12 about an axis A. The compensator 10 may be used to reduce scintillation effects within an electro-optical field of a heterogeneous medium 22, such as air, which effects are caused by a beam 20 as it propagates through the heterogeneous medium 22. The compensator 10 is configured such that the beam 20, while propagating parallel to the axis A, impinges on the disc 12 while the disc 12 is spinning, thereby allowing the compensator 10 to control a property of a beam 20 in an effort to reduce scintillation effects. The beam 20 may be any free space optical beam. Suitable examples of the beam 20 include, but are not limited to, LASERs and Gaussian beams. In one example embodiment, the beam 20 is a fully coherent, monochromatic or narrow-band LASER. The compensator 10 can be applied to any application where reducing the scintillation at a point in space through turbulence is desired. Common examples would be illuminating an object at range, controlling a targeting beacon, or increasing th