The present disclosure pertains generally to correction of distortion in an optical signal. More particularly, the present disclosure pertains to correction of distortion in an optical signal caused by atmospheric turbulence.
The performance of an electro-optical detector is limited by the conditions of the atmosphere it must operate in. When an optical signal travels through an atmosphere, atmospheric turbulence induces distortion in the optical signal. Such distortion can cause a loss of intensity at the detector, due to beam wander and defocusing.
Typically, such distortions are accounted for by increasing detector size, widening the field of view, or adding a fast-steering mirror. However, these solutions may increase the total cost and footprint of the electro-optical detector, degrade the detector's bandwidth, and reduce the signal to noise ratio.
In view of the above, it would be desirable to have a compact electro-optical detector that is capable of efficiently and accurately correcting for distortion in an optical signal caused by atmospheric turbulence.
According to an illustrative embodiment, an optical signal passing through an atmosphere is received by a liquid lens. Distortion of the received optical signal caused by turbulence in the atmosphere is measured. An adjustment of at least one of a focal length and a focal position of the liquid lens to correct for the distortion is determined. At least one of the focal length and the focal position of the liquid lens is adjusted to correct for the distortion.
These, as well as other objects, features and benefits will now become clear from a review of the following detailed description, the illustrative embodiments, and the accompanying drawings.
The novel features of the present disclosure will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similarly-referenced characters refer to similarly-referenced parts, and in which:
According to illustrative embodiments, distortion in an optical signal caused by atmospheric turbulence is efficiently corrected for using a liquid lens with an adjustable focal length and focal position. In particular, a liquid lens may be used to correct blur and tilt in an optical signal caused by atmospheric turbulence. This may be achieved by adjusting the focal length (i.e., the meniscus height) and the focal position (i.e., meniscus location on the liquid lens plane) of the liquid lens in response to feedback.
The modified optical signal 132 exiting from the liquid lens 130 is split by a beam splitter 140 into two paths A and B. That is, the beam splitter 140 feeds the modified optical signal 132 through path A to a detector 150 that is configured to detect the modified optical signal 132. The beam splitter 140 also feeds the modified optical signal 132 via path B to a feedback device 160. The feedback device 160 is configured to measure distortion present in the received optical signal 110 caused by turbulence in the atmosphere 120 and to adjust at least one of a focal length and a focal position of the liquid lens 130 to correct for the distortion. The modified optical signal 132 may be continuously fed from the beam splitter 140 to the feedback device 160, and the focal length and/or the focal position of the liquid lens 130 may be continually adjusted by the feedback device 160 to correct for the blur and tilt of the received optical signal 110 as detected in the modified optical signal 132 that is fed to the detector 150.
According to the illustrative embodiment of the distortion correction system 100 shown in
The distortion sensor 170 may be implemented with any suitable sensor or combination of sensors for detecting blur and tilt in the modified optical signal 132. The lens adjuster 180 may be implemented with any suitable component, such as a microprocessor for determining adjustments needed to correct for blur and tilt and outputting a signal to the liquid lens 130 as appropriate. In one embodiment, the lens adjuster 180 includes a signal processor that performs calculations based on the measured blur and tilt and provides voltage signals to the liquid lens 130 to adjust the focal length and focal position of the liquid lens 130 to correct for blur and tilt, respectively.
In one embodiment of the feedback device 160, the distortion sensor 170 includes a camera, such as a charge coupled device (CCD) camera, for measuring blur and tilt of the received optical signal. The camera measures blur of the received optical signal 110 by detecting a beam size of the modified optical signal 132. Blur is measured as deviation of the detected beam size of the modified optical signal 132 from an optimal beam size stored in a memory 190, such as a computer database. The camera measures tilt of the received optical signal 110 by detecting a beam position of the modified optical signal 132. Tilt is measured as a deviation of the detected beam position of the modified optical signal 132 from an optimal beam position or an expected beam position (e.g., a center position).
According to the embodiment of the feedback sensor described immediately above, the lens adjuster 180, which is also included in the camera, determines adjustment of the focal length of the liquid lens 130 needed to correct for the blur by comparing the detected beam size of the modified optical signal 132 received by the camera with an optimal beam or expected size stored in the memory 190. Similarly, the lens adjuster 180 determines adjustment of the focal position of the liquid lens 130 needed to correct for the tilt by comparing the detected beam position of the modified optical signal 132 with an optimal or expected beam position stored in memory 190. In one example embodiment, the lens adjuster 180 may include a microprocessor configured to perform such comparisons and to communicate with the memory 190, which is configured to store optimal or expected beam sizes and positions. The lens adjuster 180 and memory 190 may be included within the camera as an auto-focus component.
According to another embodiment of the distortion correction system 100, the distortion sensor 170 may be configured to detect a number of high frequency components within the modified optical signal 132 as a measure of blur. A sharper good quality optical signal has a higher number of high frequency components compared to a blurred optical signal. According to this embodiment, an optimal threshold number of high frequency components may be stored in memory 190, and the lens adjuster 180 may determine and perform adjustment of the focal length of the liquid lens 130 needed to correct for the blur by comparing the detected number of high frequency components within the received optical signal with the threshold optimal number of high frequency components. For this purpose, the lens adjuster 180 may include a microprocessor configured to perform such a comparison and to communicate with the memory 190, which is configured to store an optimal threshold number of high frequency components.
According to another embodiment of the distortion correction system 100, the distortion sensor 170 may include a simple image quality metric sensor that is configured to measure an image quality metric of the modified optical signal 132, such as sharpness. According to this embodiment, a reference or expected image quality level, such as a reference or expected sharpness level, is stored in memory 190. The lens adjuster 180 may determine adjustment of the focal length of the liquid lens 130 needed to correct for blur by comparing the measured sharpness of the modified optical signal 132 with the reference or expected sharpness level.
It should be appreciated that the distortion sensors described above are provided as examples. There may be other suitable distortion sensors that may be used to measure blur and tilt. For example, the distortion sensor 170 may include a wavefront sensor, such as a Shack-Hartmann wavefront sensor that includes a series of lenses that measure tilt of the modified optical signal 132 over a given plane. Another example of the distortion sensor 170 capable of measuring tilt is a quadrant cell detector.
Other suitable distortion sensors capable of measuring blur and/or tilt may be used, in conjunction with a suitable lens adjuster, to provide correction for blur and tilt by causing adjustment of the focal length and focal position of the liquid lens, respectively.
Although one liquid lens 130 is depicted in
Further, although one beam splitter 140 and one feedback device 160 are shown in
As noted above, the signal from the lens adjuster 180 that causes adjustment of the focal length and/or the focal position of the liquid lens 130 may include one or more voltages that are applied to electrodes of the liquid lens 130. This may be understood with reference to
As depicted in
For example, referring to
Referring to
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By varying the voltages applied to the top electrodes 260A and 270A and/or the bottom electrodes 260B and 270B, the focal length of the lens formed by the interface between the liquids 210 and 220 can be adjusted, e.g., the lens may be made concave or convex, to correct for blur. Tilt may be simultaneously corrected for by varying the voltages applied to the top electrodes 260A and 270A and/or the bottom electrodes 260B and 270B to adjust the focal position of the lens formed by the interface 250 between the liquids 210 and 220, i.e., causing the lens to tilt clockwise or counterclockwise. The focal length and/or focal position of the liquid lens 200 may be adjusted in a repeatable manner at a high repetition rate. The voltages needed to cause desired corrections for different measured levels of blur and tilt may be determined in advance and stored in memory 190 which may be included in or accessed by the lens adjuster 180.
Referring to
The embodiments described herein leverage the high speed adaptiveness of a liquid lens to correct for distortion in an optical signal caused by atmospheric turbulence in near real-time. A liquid lens is smaller, weighs less, uses less power, has a faster response time, and is less costly than a traditional mirror-based distortion correction system. Additionally, using a liquid lens for distortion correction provides for reduced vibration sensitivity with a minimal field of view.
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.
The United States Government has ownership rights in this invention. Licensing inquiries may be directed to Office of Research and Technical Applications, Space and Naval Warfare Systems Center, Pacific, Code 72120, San Diego, Calif., 92152; telephone (619) 553-5118; email: ssc_pac_t2@navy.mil, referencing Navy Case 103746.