Patent Application
20180241497
This application claims priorities to Korean Patent Applications No. 2017-0023517 filed on Feb. 22, 2017 and No. 2017-0067658 filed on May 31, 2017 in the Korean Intellectual Property Office (KIPO), the entire contents of which are hereby incorporated by reference.
Example embodiments of the present invention relate in general to a technique for providing focused Bessel beams having orbital angular momentum (OAM) to a plane in an existing technical field in which light waves and electromagnetic waves are generated and used, and more specifically to an electromagnetic wave generation apparatus and method for implementing the technique.
Most frequency bands that are currently used in wireless communication are densely divided and used without an idle band. Due to the expanding trend of multimedia data service, it is necessary to improve the efficiency of an existing frequency band. To this end, it is possible to use electromagnetic wave polarization or multi-antenna characteristics. Since there is a limitation in improving transmission efficiency even when several multiplexing techniques are used, a new communication method in which an OAM mode is used is being researched in the optical communication field and the like. In particular, according to OAM mode multiplexing, even when frequency, polarization, and multi-antenna arrangement characteristics and the like are the same, it is possible to distinguish a communication signal carried by each mode using mathematical orthogonality between OAM modes. Also, as known as Emmy Noether's theorem, OAM (L) is conserved in a system that is symmetrical with respect to an axis of rotation. Due to the characteristic of conservation, OAM may be used to improve efficiency of radio wave spectrum that may be transmitted in free-space optical communication (FSO) and microwave communication.
According to related art, an OAM mode is a Laguerre-Gaussian (LG) mode that is a solution of the paraxial Helmholtz equation, and has a main beam in a donut shape around a propagation axis of electromagnetic waves when the electromagnetic waves are transmitted. Therefore, the LG mode has problems in that a beam size increases along with a propagation distance and it is difficult to increase a transmission distance. In addition, there is a limitation in that a receiving antenna is required to be large and complicated.
Accordingly, example embodiments of the present invention are provided to substantially obviate one or more problems due to limitations and disadvantages of the related art.
Example embodiments of the present invention reduce the size of beams having orbital angular momentum (OAM), and detailed means for the purpose are as follows.
The present invention has two elements.
First, a phased-array structure that generates an equiphase surface in a conical shape inclined toward an axis generates Bessel beams.
Second, a helical phased-array structure having a phase difference of 2πL (L=−1, . . . −1, 0, 1, . . . , and +1) in the direction of an azimuth Φ with respect to an axis has OAM.
Consequently, example embodiments of the present invention combine the two elements so that the two elements are simultaneously satisfied, and provide an electromagnetic wave generation apparatus for generating focused Bessel beams having OAM by adjusting an equiphase surface in which the two elements are combined by a circular-array antenna on one plane, and a method of generating focused Bessel beams having OAM.
Example embodiments of the present invention will become more apparent by describing in detail example embodiments of the present invention with reference to the accompanying drawings, in which:
Example embodiments of the present invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention, and example embodiments of the present invention may be embodied in many alternate forms and should not be construed as limited to example embodiments of the present invention set forth herein.
Accordingly, while the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like numbers refer to like elements throughout the description of the figures.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (i.e., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.).
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
It should also be noted that in some alternative implementations, the functions/acts noted in the blocks may occur out of the order noted in the flowcharts. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
Hereinafter, an apparatus and method for generating an electromagnetic wave according to exemplary embodiments of the present invention will be described with reference to drawings.
A representative drawing of the present invention is
According to an exemplary embodiment of the present invention, the distribution of complex-number amplitudes of a Laguerre-Gaussian (LG) mode having OAM is represented by Equation 1 below.
Here, Lpl denotes a Laguerre polynomial, ρ3=x2+y2, ξ(z) denotes a Gouy phase, R(z) denotes a beam curvature, and w(z) denotes a beam radius, which is represented by Equation 2 below.
With regard to this, helical beams of an LG mode being generated by the SPP according to an exemplary embodiment of the present invention are shown.
According to an exemplary embodiment of the present invention, the distribution of complex-number amplitudes of a higher-order Bessel mode having OAM is represented by Equation 3 below.
Referring to
In the present invention, a planar circular array instead of two voluminous lens systems is used to generate helicoidal and conical electromagnetic waves such that focused electromagnetic waves having OAM may be generated.
Each symbol shown in
According to an exemplary embodiment of the present invention, the electromagnetic wave generation apparatus may concentrate electromagnetic wave energy by generating electromagnetic waves having a helicoidal and conical equiphase surface.
According to an exemplary embodiment of the present invention, the electromagnetic wave generation apparatus may generate an electromagnetic wave in a higher-order pseudo-Bessel pattern having OAM.
According to an exemplary embodiment of the present invention, it is possible to generate Bessel beams using a phased-array structure whose equiphase surface has a conical shape inclined toward an axis.
According to an exemplary embodiment of the present invention, it is possible to shift a phase by 2πL (L=−1, . . . , −1, 0, 1, . . . , and +1) in the direction of an azimuth Φ with respect to an axis so as to generate a helicoidal wavefront in which the phase of light has the term “exp(±ilϕ)” in the azimuthal direction.
According to an exemplary embodiment of the present invention, a kth unit structure from a center may be phase-shifted by k·d sin θ so that a radial equiphase surface has a conical shape.
According to an exemplary embodiment of the present invention, it is possible to generate focused electromagnetic waves having OAM using a planar array.
According to an exemplary embodiment of the present invention, an electromagnetic wave generation apparatus for can generate focused electromagnetic waves having OAM using a planar circular array whose central portion is empty or which has an irregular arrangement in radial directions.
In consideration of the above description, a method of improving a distance over which a beam is transmitted by an OAM mode is proposed according to an example embodiment of the present invention. In particular, when an antenna apparatus is configured on the basis of an LG mode included in the OAM mode, a maximum distance Zmax may be limited. A method of improving a distance by overcoming limitations of the maximum distance Zmax is proposed according to an example embodiment of the present invention.
In consideration of a structure of the antenna structure 15, the signal controller 11 may control a signal so that a signal output through the antenna structure 15 forms a tractroid-helicoidal phase surface.
In an example embodiment of the present invention, a tractroid-helicoidal shape 20 may be formed by combining a helicoidal wavefront having a helicoidal phase surface and a tractroid-parabolic shape 30 having a phase surface forming a diverging Bessel mode, which is formed on the basis of a tractroid surface 31 and a parabolic surface 32 for correcting an error caused by using a single source.
Here, the tractroid-helicoidal shape 20 may be formed on the basis of OAM, and an OAM-based helical mode may be set in various ways. As an example, the OAM-based helical mode may be set to −m, . . . , −2, −1, 0, +1, +2, . . . , and +m (m is an integer).
As described above, a signal of the tractroid-helicoidal shape 20 output by an OAM-mode antenna apparatus according to an example embodiment of the present invention may ensure concentration of OAM mode beams and a transmission distance of the beams.
Referring to
The 2×2 feeder 42 and the auxiliary reflecting plate 43 may be arranged at opposite positions, and the auxiliary reflecting plate 43 may be provided at a position opposite to the reflecting plate 41. Due to this structure, a signal output from the 2×2 feeder 42 is reflected by the auxiliary reflecting plate 43 first and provided to the reflecting plate 41. The signal which is reflected by the auxiliary reflecting plate 43 first and incident on the reflecting plate 41, is reflected by the reflecting plate 41 second and output.
The signal output from the 2×2 feeder 42 may be controlled by the above-described signal controller 11. In consideration of the configuration of the antenna structure 41, 42, and 43 according to the first example embodiment, the signal controller 11 may control the signal so that a signal output by the antenna structure 41, 42, and 43 forms a tractroid-helicoidal phase surface. For example, the signal controller 11 may control a phase of the signal output from the 2×2 feeder 42 on the basis of OAM modulation. Here, the signal controller 11 may control a phase of the output signal by setting an OAM-based helical mode variously (−m, . . . , −2, −1, 0, +1, +2, . . . , and +m).
Referring to
The reflecting plate 51 may be formed in a tractroid-parabolic shape, and a reflecting surface thereof may have a helicoidal shape having a certain step 55. Here, the step 55 of the reflecting surface formed in the reflecting plate 51 may be set in consideration of a mode of a signal reflected by the reflecting plate 51, for example, an OAM-based helical mode (−m, . . . , −2, −1, 0, +1, +2, . . . , and +m).
The feeder horn 53 may be provided at a position opposite to the reflecting plate 51. Due to this structure, a signal output from the feeder horn 53 is provided to the reflecting plate 51, and the signal incident on the reflecting plate 51 is reflected by the reflecting plate 51 and output.
Since the reflecting plate 51 is formed in a tractroid-helicoidal shape, the signal output from the feeder horn 53 may naturally form a tractroid-helicoidal shape. Accordingly, the signal controller 11 may output the signal output from the feeder horn 53 without phase control in consideration of the configuration of the antenna structure 50 according to the second example embodiment.
Referring to
The plurality of radiating elements 61 may be arranged on the antenna plate 63 in a circular shape, a rectangular shape, or various predetermined shapes. Further, the plurality of radiating elements 61 may have a metamaterial or an artificial electromagnetic structure.
Also, the plurality of radiating elements 61 may be connected to the signal controller 11, and the signal controller 11 may control a phase of a signal output from each of the plurality of radiating elements 61 according to the arrangement of the plurality of radiating elements 61 in consideration of the configuration of the antenna structure 60 according to the third example embodiment. Here, the signal controller 11 may variously set an OAM-based helical mode (−m, . . . , −2, −1, 0, +1, +2, . . . , and +m) to control phases of output signals.
The signal controller 11 may control the signals output from the plurality of radiating elements 61 on the basis of OAM modulation so that the output signals of the plurality of radiating elements 61 may form a tractroid-helicoidal phase surface.
Referring to
The feeder horn 75 may be fixed at a position opposite to the auxiliary reflecting plate 77, and the auxiliary reflecting plate 77 may be fixed at a position opposite to the antenna plate 73. Accordingly, a signal output from the feeder horn 75 is reflected by the auxiliary reflecting plate 77 first and provided to the antenna plate 73. Then, the signal which is reflected first by the auxiliary reflecting plate 77 and incident on the antenna plate 73, is reflected second by the plurality of reflecting arrangement elements 71 provided in the antenna plate 73 and output.
Here, since the auxiliary reflecting plate 77 is formed in a tractroid shape and a reflecting surface thereof has a helicoidal shape having a certain step, the signal reflected by the auxiliary reflecting plate 77 first may form a tractroid-helicoidal phase surface.
Accordingly, signals which are finally output from the plurality of reflecting arrangement elements 71 provided in the antenna plate 73, may also form a tractroid-helicoidal phase surface.
Further, the step of the reflecting surface formed in the auxiliary reflecting plate 77 may be set in consideration of a mode of the signal reflected by the auxiliary reflecting plate 77, for example, an OAM-based helical mode (−m, . . . , −2, −1, 0, +1, +2, . . . , and +m).
Meanwhile, the signal controller 11 may be connected to the feeder horn 75, and may output the signal output through the feeder horn 75 without phase control in consideration of the configuration of the antenna structure 70 according to the fourth example embodiment.
As another example, the auxiliary reflecting plate 77 may be formed in a tractroid shape. Also, the feeder horn 75 may have a feeder which outputs signals of different phases. For example, the feeder may be a 2×2 feeder. In this structure, a signal output from the 2×2 feeder may be controlled by the above-described signal controller 11. As an example, in consideration of the configuration of the auxiliary reflecting plate 77 in a tractroid shape, the signal may be controlled so that a signal provided to the antenna plate 73 through the auxiliary reflecting plate 77 forms a tractroid-helicoidal phase surface, like in the first example embodiment. For example, the signal controller 11 may control a phase of the signal output from the 2×2 feeder on the basis of OAM modulation.
Meanwhile, an antenna structure provided in an OAM-mode antenna apparatus according to an example embodiment of the present invention may include a circular leaky-wave antenna. In this case, the signal controller 11 may be connected to the leaky-wave antenna, and may control a signal output from the leaky-wave antenna. In other words, the signal controller 11 may control the signal output from the leaky-wave antenna on the basis of OAM modulation so that the output signal may form a tractroid-helicoidal phase surface. Here, the signal controller 11 may control a phase of the output signal by setting an OAM-based helical mode variously (−m, . . . , −2, −1, 0, +1, +2, . . . , and +m).
An antenna shown in
Using an apparatus of the present invention, it is possible to generate a higher-order Bessel beam pattern having OAM concentrated close to a propagation axis and, and it is possible to provide an electromagnetic wave generation apparatus that is relatively miniaturized by making an existing voluminous system into a plane and combining two functions of a OAM mode and a collimated mode.
While the example embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2017-0023517 | Feb 2017 | KR | national |
| 10-2017-0067658 | May 2017 | KR | national |
