Transmission directivity control device

Abstract

A transmission directivity control device according to the present invention comprises a splitter that splits an optical signal into a first optical signal and a second optical signal, a first selector switch that outputs the first optical signal from an output terminal that has been determined by the wavelength of the first optical signal, a second selector switch that outputs the second optical signal from an output terminal that has been determined by the wavelength of the second optical signal, a first weighting unit that phases the first optical signal along a first axis that is an axis in space, the phase depending on the terminal of the first selector switch from which the first optical signal was outputted, a second weighting unit that phases the first optical signal along a second axis that is orthogonal to the first axis, the phase depending on the terminal of the first selector switch from which the first optical signal was outputted, and a photomixing unit that photomixes the phased first optical signal and the phased second optical signal.

Description

Transmission directivity control device

[0001] The present invention relates to a transmission directivity control device.

[0002] When wavelength multiplexing is performed within an optical circuit, the number of wavelengths multiplexed is determined by the band and the frequency interval of the wavelength multiplexing. For example, when a device is compatible with the C-band and the band is 4.4 THz, if wavelengths are multiplexed at 100 GHz intervals, the upper limit of the number of wavelengths multiplexed is 44.

[0003] JP 2004-023400 A JP 2007-165956 A International Publication No. 2023 / 242930

[0004] H. Watanabe, S. Uga, H. Nakamizo, T. Tsutsumi, S. Shinjo, and Y. Kuriyama, “Millimeter-Wave Antenna and RF Front-End Technology for 5th Generation Mobile Communication Base Stations,” IEICE Communications Society Magazine, 2020, Vol. 14, No. 3, pp. 222-231. Dong-Hun KIM, Jiro HIROKAWA, and Makoto ANDO, “One-Body 2-D Beam-Switching Butler Matrix with Waveguide Short-Slot 2-Plane Couplers,” IEICE TRANSACTIONS on Electronics, Vol. E100-C, No. 10, pp. 884-892, 2017. C. Tsokos et al., “Analysis of a Multibeam Optical Beamforming Network Based on Blass Matrix Architecture,” in Journal of Lightwave Technology, vol. 36, no. 16, pp. 3354-3372, 15 Aug.15, 2018.Y. Liu and J. Klamkin, "Scalable Integrated Photonics Beamforming Circuits," 2020 Asia Communications and Photonics Conference (ACP) and International Conference on Information Photonics and Optical Communications (IPOC), 2020, pp. 1-3.B. Ortega, J. Mora and R. Chulia, "Optical Beamformer for 2-D Phased Array Antenna With Subarray Partitioning Capability," in IEEE Photonics Journal, vol. 8, no. 3, pp. 1-9, June 2016.

[0005] In order to increase the capacity of wireless communication, it is necessary to increase the number of multiplexed signals.

[0006] In view of the above circumstances, an object of the present invention is to provide a technique that can increase the number of multiplexed beams.

[0007] One aspect of the present invention is a transmission directivity control device comprising: a demultiplexer that demultiplexes an optical signal into a first optical signal and a second optical signal; a first changeover switch that outputs the first optical signal from an output terminal determined by the wavelength of the first optical signal; a second changeover switch that outputs the second optical signal from an output terminal determined by the wavelength of the second optical signal; a first weighting unit that imparts a phase on a first axis, which is an axis in space, to the first optical signal, which varies depending on the terminal of the first changeover switch to which the signal is output; a second weighting unit that imparts a phase on a second axis, which is orthogonal to the first axis, to the first optical signal, which varies depending on the terminal of the first changeover switch to which the signal is output; and a photomixing unit that photomixes the first optical signal to which a phase has been imparted and the second optical signal to which a phase has been imparted.

[0008] According to the present invention, the number of beams to be multiplexed can be increased.

[0009] Fig. 1 is a diagram showing an example of the configuration of a transmission directivity control device 1 according to a first embodiment. Fig. 2 is a diagram showing an example of the configuration of an antenna element 171. Fig. 3 is a diagram showing an example of the configuration of an antenna element 171. Fig. 4 is a flowchart showing the operation of the transmission directivity control device 1 according to the first embodiment. Fig. 5 is a diagram showing an example of the configuration of a transmission directivity control device 1 according to a second embodiment.

[0010] (First embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment.

[0011] FIG. 1 is a diagram showing an example of the configuration of a transmission directivity control device 1 according to the first embodiment.

[0012] The transmission directivity control device 1 includes a light source 11, an optical modulator 12, a splitter 13, a first changeover switch 14, a second changeover switch 15, a first weighting unit 16-1, a second weighting unit 16-2, a photomixing unit 17, and a control unit 18.

[0013] The light source 11 outputs light to the optical modulator 12. The light source 11 can change the wavelength of the light it outputs.

[0014] The optical modulator 12 generates an optical signal by modulating the input light. The demultiplexer 13 demultiplexes the optical signal input from the optical modulator 12. The demultiplexer 13 demultiplexes the optical signal into a carrier wave and a sideband wave. The demultiplexer 13 may demultiplex the optical signal into a carrier wave and an upper sideband wave, or into a carrier wave and a lower sideband wave. In the following description, the carrier wave L Ｈ is expressed as Equation (1), and the sideband wave L Ｓ is expressed by equation (2) which shows the upper sideband.

[0015]

[0016] The demultiplexer 13 branches the carrier wave and the sideband wave, and outputs them to the first changeover switch 14 and the second changeover switch 15. The demultiplexer 13 is, for example, an AWG (Arrayed Waveguide Grating).

[0017] The demultiplexer 13 includes a distributor 131 and an SSB (single side-band) modulator 132, and Ｈ and sideband wave L Ｓ The splitter 131 splits an input optical signal into two optical signals. The SSB modulator 132 suppresses the carrier component of one of the two optical signals and converts it into a sideband. This allows the splitter 131 and the SSB modulator 132 to generate a carrier and a sideband.

[0018] The demultiplexer 13 includes a distributor 131 and two optical comb filters 133 having periodic pass characteristics, and transmits the carrier L Ｈ and sideband wave L ＳThe splitter 131 splits an input optical signal into two optical signals. One optical comb filter 133 passes only light of multiple wavelengths with different carrier waves from one optical signal, and the other optical comb filter 133 passes only light of multiple wavelengths with different sideband waves from the other optical signal. When the splitter 13 includes the splitter 131 and the SSB modulator 132, or when the splitter 131 and the optical comb filter 133 are included, an optical signal with two or more different wavelengths can be split into a carrier wave and sideband waves.

[0019] The first changeover switch 14 has one input terminal and three output terminals, and outputs a carrier wave from any one of the output terminals to the first weighting unit 16-1.

[0020] The second changeover switch 15 has one input terminal and three output terminals, and outputs the carrier wave from any one of the output terminals to the second weighting unit 16-2.

[0021] The first weighting unit 16-1 has three input terminals and three output terminals. The output terminals of the first changeover switch 14 correspond one-to-one to the input terminals of the first weighting unit 16-1. The three output terminals of the first changeover switch 14 are the first output terminal, the second output terminal, and the third output terminal. When the three input terminals of the first weighting unit 16-1 are the first input terminal, the second input terminal, and the third input terminal, for example, the first output terminal corresponds to the first input terminal, the second output terminal corresponds to the second input terminal, and the third output terminal corresponds to the third input terminal. In this case, a carrier wave is input from the first output terminal of the first changeover switch 14 to the first input terminal of the first weighting unit 16-1, a carrier wave is input from the second output terminal of the first changeover switch 14 to the second input terminal of the first weighting unit 16-1, and a carrier wave is input from the third output terminal of the first changeover switch 14 to the third input terminal of the first weighting unit 16-1.

[0022] The first weighting unit 16-1 assigns a phase on a first axis, which is a certain axis in space, to the carrier wave input from the first changeover switch 14, and outputs the result from all of the multiple output terminals to the photomixing unit 17. The first weighting unit 16-1 changes the phase to be assigned depending on the input terminal to which the carrier wave is input. The first weighting unit 16-1 is, for example, a delay line, a high-dispersion line, a resonant ring, or a matrix circuit. The matrix circuit is, for example, a Butler matrix or a Blass matrix.

[0023] For example, the first weighting unit 16-1 outputs carrier waves to which different phases are imparted depending on the input terminal to which the carrier wave is input from the first output terminal, the second output terminal, and the third output terminal. For example, the first weighting unit 16-1 imparts a phase slope φ to the carrier wave input to the first input terminal. first,1 and outputs an optical signal with no phase added from the first output terminal, and a phase φ first,1 and outputs the optical signal having the phase 2φ from the second output terminal. first,1 For example, the first weighting unit 16-1 applies a phase slope φ to the carrier wave input to the second input terminal and outputs the optical signal to which the phase slope φ is applied from the third output terminal. first,2 and outputs an optical signal with no phase added from the first output terminal, and a phase φ first,2 and outputs the optical signal having the phase 2φ from the second output terminal. first,2 For example, the first weighting unit 16-1 applies a phase slope φ to the carrier wave input to the third input terminal. first,3 and outputs an optical signal with no phase added from the first output terminal, and a phase φ first,3 and outputs the optical signal having the phase 2φ from the second output terminal. first,3 In the first weighting unit 16-1, when a carrier wave is input to the p-th input terminal, the phase φ is assigned to the carrier wave output from the i-th output terminal. Hip is expressed by equation (3).

[0024] In equation (3), φ first,p is the phase tilt on the first axis that is applied when a carrier wave is input to the p-th input terminal of the first weighting unit 16-1.first,p is, for example, 45 degrees or 90 degrees.

[0025] The second weighting unit 16-2 has three input terminals and three output terminals. The output terminals of the second changeover switch 15 correspond one-to-one to the input terminals of the second weighting unit 16-2. The three output terminals of the second changeover switch 15 are the first output terminal, the second output terminal, and the third output terminal. When the three input terminals of the second weighting unit 16-2 are the first input terminal, the second input terminal, and the third input terminal, for example, the first output terminal corresponds to the first input terminal, the second output terminal corresponds to the second input terminal, and the third output terminal corresponds to the third input terminal. In this case, a sideband wave is input from the first output terminal of the second changeover switch 15 to the first input terminal of the second weighting unit 16-2, a sideband wave is input from the second output terminal of the second changeover switch 15 to the second input terminal of the second weighting unit 16-2, and a sideband wave is input from the third output terminal of the second changeover switch 15 to the third input terminal of the second weighting unit 16-2.

[0026] The second weighting unit 16-2 assigns a phase on a second axis orthogonal to the first axis to the sideband waves input from the second changeover switch 15, and outputs the sideband waves from all of the multiple output terminals to the photomixing unit 17. The second weighting unit 16-2 changes the phase to be assigned depending on the input terminal to which the sideband waves are input. The second weighting unit 16-2 is, for example, a delay line, a high-dispersion line, a resonant ring, or a matrix circuit. The matrix circuit is, for example, a Butler matrix or a Blass matrix.

[0027] For example, the second weighting unit 16-2 outputs carrier waves to which different phase gradients are applied depending on the input terminal to which the sideband waves are input from the first output terminal, the second output terminal, and the third output terminal. For example, the second weighting unit 16-2 applies a phase gradient φ second,1 and outputs an optical signal with no phase added from the first output terminal, and a phase φ second,1 and outputs the optical signal having the phase 2φ from the second output terminal. second,1 For example, the second weighting unit 16-2 applies a phase slope φ to the carrier wave input to the second input terminal and outputs the optical signal to which the phase slope φ is applied from the third output terminal. second,2and outputs an optical signal with no phase added from the first output terminal, and a phase φ second,2 and outputs the optical signal having the phase 2φ from the second output terminal. second,2 For example, the second weighting unit 16-2 applies a phase slope φ to the carrier wave input to the third input terminal. second,3 and outputs an optical signal with no phase added from the first output terminal, and a phase φ second,3 and outputs the optical signal having the phase 2φ from the second output terminal. second,3 In the second weighting unit 16-2, when a carrier wave is input to the q-th input terminal, a phase φ is assigned to the sideband wave output from the j-th output terminal. Vjq is expressed by equation (4).

[0028] In equation (3), φ second,q is the phase tilt on the second axis that is applied when a carrier wave is input to the q-th input terminal of the second weighting unit 16-2. second,q is, for example, 45 degrees or 90 degrees.

[0029] The photomixing unit 17 includes a plurality of antenna elements 171. The plurality of antenna elements form a two-dimensional array antenna with three rows and three columns. The antenna element 171 located in the ith row and jth column receives the optical signal L from the ith output terminal of the first weighting unit 16-1. H,i is input, and the optical signal L is output from the j-th output terminal of the second weighting unit 16-2. S,j is input. H,i is the phase φ of equation (3) Hi is defined by equation (5) using

[0030] Optical signal L S,j is the phase φ of equation (4) Vjq is defined by equation (6) using

[0031] In equation (6), s(t) is a radio signal transmitted by the transmission directivity control device 1. The antenna element 171 generates an electromagnetic wave based on the two input optical signals. The frequency of the generated electromagnetic wave is the difference between the frequencies of the two input optical signals. FIG. 2 is a diagram showing an example of the configuration of the antenna element 171. The antenna element 171 includes a multiplexer 1711, a square-law detector 1712, and an antenna 1713. The multiplexer 1711 multiplexes the carrier wave and sideband waves input from the weighting unit 16. The multiplexed optical signal is L Ｈ +L Ｓ The square-law detector 1712 converts the combined optical signal into an RF signal. The square-law detector 1712 is, for example, a photodiode. The antenna 1713 outputs only components of a predetermined RF frequency band that depends on the output frequency characteristics of the square-law detector 1712. In other words, the output v from the antenna 1713 of the antenna element 171 installed in the i-th row and j-th column is ＲＦｉｊ (L Ｈ +L Ｓ ) ２ is extracted from the RF band and is proportional to equation (7).

[0032] From the above, the phase given to the output of the antenna element 171 in the i-th row and j-th column is φ Vjq -φ Hip is.

[0033] 3 is a diagram showing an example of the configuration of the antenna element 171. In the antenna element 171, a mirror 1714 may be used instead of the multiplexer 1711 to multiplex an optical signal to which a phase has been assigned by the weighting unit 16 and an optical signal to which a phase has been assigned by the weighting unit 16.

[0034] The wavelength of the light output from the light source 11 corresponds to the direction of the beam output from the photomixing unit 17. The control unit 18 changes the wavelength of the light output from the light source 11 to control the direction of the beam output from the photomixing unit 17. More specifically, the control unit 18 controls the first changeover switch 14 to control which output terminal the first changeover switch 14 will use to output the carrier wave. The control unit 18 controls the second changeover switch 15 to control which output terminal the second changeover switch 15 will use to output the sideband wave. This controls the phase imparted to the output from the antenna element 171 of the photomixing unit 17, thereby controlling the beam direction.

[0035] Assume that two optical signals are output from the light source 11. At this time, the two carrier waves are output from the same output terminal of the first changeover switch 14, and the two sideband waves are output from different output terminals of the second changeover switch 15. For example, if the two carrier waves are output from the first output terminal of the first changeover switch 14, and the two sideband waves are output from the first output terminal and the second output terminal of the second changeover switch 15, the four optical signals L input to the antenna element 171 installed in the i-th row and j-th column will be H1,i , L H2,i , L S1,j , L S2,j are expressed by equations (8) to (11).

[0036] In this case, the RF signal output from the antenna element 171 placed in the i-th row and j-th column is proportional to equation (12).

[0037] As a result, two beams are generated in the same plane.

[0038] In the description so far, the first weighting unit 16-1 and the second weighting unit 16-2 have three input terminals and three output terminals, and the array antenna included in the photomixing unit 17 has antenna elements 171 arranged in three rows and three columns, but this is not limited to this. For example, the array antenna may have two rows, four or more rows, or two or four or more columns. Furthermore, the array antenna does not have to be configured with square antenna elements 171, such as three rows and three columns or four rows and four columns. The input terminals and output terminals of the first weighting unit 16-1 and the second weighting unit 16-2 may vary depending on the number of rows and columns of the antenna elements 171 included in the array antenna. By outputting N (N is an integer greater than or equal to 2) optical signals from the light source 11, outputting N carrier waves from the same output terminal of the first selector switch 14, and outputting N sideband waves from different output terminals of the second selector switch 15, N beams can be generated within the same plane, similar to the case of generating two beams within the same plane.

[0039] As described above, in the first embodiment, the transmission directivity control device 1 can generate multiple beams in the same plane from a single optical signal output from the light source 11. This allows for an increase in the number of multiplexed beams. For example, when wavelength multiplexing is performed at 100 GHz intervals in the C-band, which has a bandwidth of 4.4 THz, 44 wavelengths is the limit, and when signal processing is performed using one wavelength per beam, 44 beams can be multiplexed at most. However, since the first embodiment can generate multiple beams of the same wavelength in the same plane, when wavelength multiplexing is performed at 100 GHz intervals in the C-band, the number of beams can be increased beyond 44.

[0040] 4 is a flowchart showing the operation of the transmission directivity control device 1 according to the first embodiment. The control unit 18 controls the first changeover switch 14 and the second changeover switch 15 to control the output terminals from which the input carrier wave and sideband waves are output (step S1). Here, the control unit 18 may control the first changeover switch 14 and the second changeover switch 15 in accordance with the wavelength of the light output from the light source 11 to control the direction of the beam output from the photomixing unit 17, or may change the wavelength of the light output from the light source 11 in accordance with the direction of the beam output from the photomixing unit 17.

[0041] The optical modulator 12 modulates the light output from the light source 11 to generate an optical signal (step S10). Then, the demultiplexer 13 demultiplexes the optical signal input from the optical modulator 12 into a carrier wave and sideband waves (step S11). The first selector switch 14 outputs the carrier wave from one of its multiple output terminals to the first weighting unit 16-1 (step S12-1). The second selector switch 15 outputs the sideband waves from one of its multiple output terminals to the second weighting unit 16-2 (step S12-2). The first weighting unit 16-1 assigns a phase on the first axis to the carrier wave (step S13-1). The second weighting unit 16-2 assigns a phase on the second axis to the sideband waves (step S13-2). The photomixing unit 17 photomixes the carrier wave and sideband waves in each antenna element 171 (step S14). The photomixed optical signal is output as an RF signal from an antenna 1713 .

[0042] Second Embodiment Fig. 5 is a diagram showing an example of the configuration of a transmission directivity control device 1 according to a second embodiment. The transmission directivity control device 1 according to the second embodiment is a device in which the first changeover switch 14 of the transmission directivity control device 1 according to the first embodiment is replaced with a demultiplexer 24. The demultiplexer 24 has one input terminal and multiple output terminals. The demultiplexer 24 outputs a carrier wave to a first weighting unit 16-1 from an output terminal corresponding to the wavelength of the carrier wave input to the input terminal.

[0043] As described above, in the transmission directivity control device 1 according to the second embodiment, carrier waves are input to different input terminals of the first weighting unit 16-1 according to their wavelengths, and phases are assigned to them. As a result, in the second embodiment as well, a phase can be assigned according to the wavelength of the light output from the light source 11, and a beam can be output from the photomixing unit 17 in a desired direction. Furthermore, the size of a typical changeover switch is larger than that of a branching filter having the same number of input terminals and output terminals. In the second embodiment, by replacing the changeover switch with a branching filter, a transmission directivity control device can be realized on a smaller scale.

[0044] In the above description, the first changeover switch 14 is replaced with the branching filter 24, but the second changeover switch 15 may be replaced with a branching filter to provide different phases depending on the wavelength of the sideband waves.

[0045] One embodiment of the present invention has been described in detail above with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes and the like can be made within the scope that does not deviate from the gist of the present invention.

[0046] In the above-described embodiment, the demultiplexer 13 first demultiplexes the optical signal into a carrier wave and sideband waves, but this is not limited thereto and the demultiplexer 13 may demultiplex the optical signal into a first optical signal and a second optical signal. For example, the demultiplexer 13 may demultiplex the optical signal into an upper sideband wave and a lower sideband wave and output the signals to the first changeover switch 14 and the second changeover switch 15, respectively. For example, the demultiplexer 13 may include a distributor that divides the optical signal into two optical signals, an SSB converter that converts one optical signal into the upper sideband wave, and an SSB converter that converts the other optical signal into the lower sideband wave, and output the upper sideband wave and the lower sideband wave to the first changeover switch 14 and the second changeover switch 15, respectively.

[0047] The processing of the control unit 18 in the above-described embodiment may be implemented by a computer using software. In this case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" as used herein includes hardware such as an OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system. Furthermore, "computer-readable recording medium" may also include media that dynamically store programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or telephone lines, or media that store programs for a fixed period of time, such as volatile memory within a computer system that serves as a server or client. The program may be a program that implements only a portion of the above-described functions, or may be a program that can implement the above-described functions in combination with a program already stored in the computer system, or may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0048] REFERENCE SIGNS LIST 1 transmission directivity control device, 11 light source, 12 optical modulator, 13 demultiplexer, 14 first changeover switch, 15 second changeover switch, 16-1 first weighting unit, 16-2 second weighting unit, 17 photomixing unit, 171 antenna element, 1711 multiplexer, 1712 square-law detection unit, 1713 antenna, 1714 mirror

Claims

1. A transmission directivity control device comprising: a demultiplexer that demultiplexes an optical signal into a first optical signal and a second optical signal; a first changeover switch that outputs the first optical signal from an output terminal determined by the wavelength of the first optical signal; a second changeover switch that outputs the second optical signal from an output terminal determined by the wavelength of the second optical signal; a first weighting unit that imparts a phase on a first axis, which is a certain axis in space, to the first optical signal, which varies depending on the terminal of the first changeover switch to which the first optical signal is output; a second weighting unit that imparts a phase on a second axis, which is orthogonal to the first axis, to the first optical signal, which varies depending on the terminal of the first changeover switch to which the first optical signal is output; and a photomixing unit that photomixes the first optical signal to which a phase has been imparted and the second optical signal to which a phase has been imparted.

2. The transmission directivity control device according to claim 1, wherein the first changeover switch or the second changeover switch is a branching filter.

3. A transmission directivity control device according to claim 1 or 2, wherein the first optical signal is a carrier wave of the optical signal, and the second optical signal is a sideband wave of the optical signal.

4. A transmission directivity control device according to claim 1 or 2, further comprising a control unit that controls the output terminal of the first changeover switch from which the first optical signal is output in accordance with the wavelength of the first optical signal, and that controls the output terminal of the second changeover switch from which the second optical signal is output in accordance with the wavelength of the second optical signal.

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