Transmitting device

Abstract

A transmission device comprising: a wavelength-tunable laser device configured so as to emit a laser having a frequency corresponding to a desired OAM mode; and a delay line configured so as to delay the laser.

Description

[Technical Field]

[0001] The present invention relates to a technique for spatially multiplexing and transmitting wireless signals using the orbital angular momentum (OAM) of electromagnetic waves. [Background technology]

[0002] In recent years, spatial multiplexing transmission technology for wireless signals using OAM has been studied to improve transmission capacity (for example, Non-Patent Document 1). Electromagnetic waves with OAM have equiphase planes distributed in a spiral pattern along the propagation direction, centered on the propagation axis. Electromagnetic waves with different OAM modes propagating in the same direction have orthogonal spatial phase distributions in the direction of the rotation axis. Therefore, signals can be multiplexed and transmitted by separating the signals of each OAM mode modulated with different signal sequences at the receiving device.

[0003] In a wireless communication system using this OAM multiplexing technology, a uniform circular array antenna (hereinafter referred to as a UCA (Uniform Circular Array)) in which multiple antenna elements are arranged at equal intervals in a circle is used to generate, combine, and transmit multiple OAM modes, thereby achieving spatially multiplexed transmission of different signal sequences (see, for example, Non-Patent Document 2). A Butler circuit (Butler matrix circuit), for example, is used to generate and separate signals for multiple OAM modes.

[0004] Furthermore, technologies for switching OAM modes have been developed. For example, Patent Document 1 discloses a technology for switching between multiple OAM modes using a discrete Fourier transform. Furthermore, Patent Document 2 discloses a technology for switching between OAM modes generated by radiation from a pseudo-traveling wave resonator using a metamaterial structure by changing the applied magnetic field. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2017-515337 [Patent Document 2] Japanese Patent Application Publication No. 2019-153978 [Non-patent literature]

[0006] [Non-Patent Document 1] J.Wang et al., "Terabit free-space data transmission employing orbital angular momentum multiplexing," Nature Photonics, Vol.6, pp.488-496, July 2012. [Non-patent document 2] Y.Yan et al., "High-capacity millimeter-wave communications with orbital angular momentum multiplexing," Nature Commun., vol.5, p.4876, Sep. 2014. Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, a transmitter using a UCA and a Butler circuit enables high-capacity communications, but in the future, there is a need to address issues such as miniaturization and power consumption. However, with conventional wireless transmission technology, it is difficult to realize a variety of OAM modes, such as switching between OAM modes or using fractional OAM mode.

[0008] The disclosed technology aims to realize a variety of OAM modes. [Means for solving the problem]

[0009] The disclosed technology includes a first wavelength tunable laser device configured to generate a laser beam having a wavelength corresponding to a desired OAM mode; an optical modulator configured to modulate a laser generated by the first wavelength tunable laser device; The aforementioned Optical signal modulated by an optical modulatora delay line configured to generate a delay in the second wavelength tunable laser device; and a second wavelength tunable laser device configured to generate a laser having a constant difference frequency with the laser generated by the first wavelength tunable laser device. The delay line caused a delay light a photomixer configured to mix a signal with the laser generated by the second wavelength tunable laser device and output a signal of a constant difference frequency. [Effects of the Invention]

[0010] A variety of OAM modes can be realized. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 10 is a diagram illustrating an example of phase setting of a UCA for generating an OAM mode signal. [Figure 2] 1A and 1B are diagrams illustrating examples of phase distribution and signal intensity distribution of an OAM multiplexed signal. [Figure 3] 1 is a configuration diagram of a communication system according to an embodiment of the present invention; [Figure 4] FIG. 2 is a diagram illustrating an example of a hardware configuration of a transmitting device according to a first embodiment of the present invention. [Figure 5] FIG. 10 is a diagram illustrating specific values ​​of a transmission device according to a first embodiment of the present invention. [Figure 6] FIG. 2 is a diagram illustrating an example of wavelength control performed by a transmitting device according to a first embodiment of the present invention. [Figure 7] FIG. 10 is a diagram illustrating an example of a hardware configuration of a transmitting device according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention (the present embodiment) 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.

[0013] (Previous problems) Conventionally, a wireless communication device that performs wireless transmission using OAM mode with a circular array antenna has been known to use an OAM mode variable array antenna for the purpose of switching between OAM mode modulation and OAM mode. However, when using an OAM mode variable array antenna, it is necessary to control the phase shifter provided in each antenna element. Furthermore, using multiple phase shifters may result in variations in the amount of phase shift variation.

[0014] There is also a method of switching the signal input terminals using a matrix circuit, but it is not possible to change the OAM mode continuously, including the fractional mode.

[0015] (Outline of this embodiment) The transmitter according to this embodiment tunes the optical wavelength while maintaining a constant RF (Radio Frequency) frequency, and includes a delay line in each branch. By changing the optical wavelength according to the OAM mode to be used, the phase shift in the circuit that generates the fixed time delay can be changed.

[0016] (Basic operation example) An example of basic settings and operations related to the UCA used in each device in this embodiment will be described.

[0017] Fig. 1 is a diagram showing an example of phase settings of a UCA for generating an OAM mode signal. The UCA shown in Fig. 1 is a UCA consisting of eight antenna elements.

[0018] In Figure 1, signals for OAM modes 0, 1, 2, 3, ... on the transmitting side are generated by the phase difference of the signals supplied to each antenna element (indicated by ●) of the UCA. That is, signals for OAM mode n are generated by setting the phase of the signal supplied to each antenna element so that the phase rotates n times (n x 360 degrees). For example, when the UCA is configured with m = 8 antenna elements as shown in Figure 1 and a signal for OAM mode n = 2 is generated, a phase difference of 360n / m = 90 degrees counterclockwise is set for each antenna element (0 degrees, 90 degrees, 180 degrees, 270 degrees, 0 degrees, 90 degrees, 180 degrees, 270 degrees) so that the phase rotates twice, as shown in Figure 1 (3).

[0019] Note that a signal with the phase rotation direction reversed to that of an OAM mode n signal is called OAM mode -n. For example, the phase rotation direction of a positive OAM mode signal is counterclockwise, and the phase rotation direction of a negative OAM mode signal is clockwise.

[0020] Spatial multiplexing wireless communication can be performed by generating different signal sequences as signals in different OAM modes and transmitting the generated signals simultaneously. On the transmitting side, signals to be transmitted in each OAM mode can be generated and combined in advance and the combined signal for each OAM mode can be transmitted using a single UCA, or multiple UCAs can be used to transmit signals for each OAM mode using different UCAs for each OAM mode.

[0021] To separate the OAM multiplexed signal on the receiving side, the phase of each antenna element of the UCA on the receiving side can be set to be opposite to the phase of the antenna element on the transmitting side.

[0022] However, if interference occurs between OAM modes due to factors such as misalignment between the transmitting and receiving antennas, it becomes necessary to separate the mixed OAM mode signals through digital signal processing such as channel equalization and successive interference cancellation. Interference between OAM modes means, for example, that a signal transmitted from a transmitting device in OAM mode 1 is output as an OAM mode 2 signal on the receiving side.

[0023] Figure 2 shows examples of the phase distribution and signal intensity distribution of an OAM multiplexed signal. In Figures 2(1) and (2), the arrows represent the phase distribution of OAM mode 1 and OAM mode 2 signals as seen from the transmitter at an end face perpendicular to the propagation direction (orthogonal propagation plane). The arrows start at 0 degrees, and the phase changes linearly until they end at 360 degrees. In other words, an OAM mode n signal propagates with its phase rotating n times (n x 360 degrees) on the orthogonal propagation plane. Note that the arrows for the phase distribution of OAM mode -1 and -2 signals point in opposite directions.

[0024] The signal intensity distribution and the position where the signal intensity is maximized differ for each OAM mode. However, the intensity distribution is the same for the same OAM mode but with a different sign. Specifically, the higher the order of the OAM mode, the farther the position where the signal intensity is maximized is from the propagation axis (Non-Patent Document 2). Here, an OAM mode with a larger value is referred to as a higher-order mode. For example, an OAM mode 3 signal is a higher-order mode than OAM mode 0, OAM mode 1, and OAM mode 2 signals.

[0025] Figure 2(3) shows the position where the signal strength is maximum for each OAM mode as a circle. The higher the OAM mode, the farther the position where the signal strength is maximum is from the central axis. Also, the beam diameter of the OAM mode multiplexed signal expands depending on the propagation distance, and the circle showing the position where the signal strength is maximum for each OAM mode becomes larger.

[0026] The system configuration and operation example of this embodiment will be described in detail below.

[0027] (System configuration of communication system) 3 is a configuration diagram of a communication system according to an embodiment of the present invention. As shown in FIG. 3, the wireless communication system according to this embodiment includes a transmitting device 100 and a receiving device 200.

[0028] The transmitting device 100 and the receiving device 200 each include a UCA. In transmitting and receiving desired data, the transmitting device 100 multiplexes and transmits signals of one or more OAM modes, and the receiving device 200 receives the signal multiplexed with one or more OAM modes transmitted from the transmitting device 100 and separates the signals of each OAM mode.

[0029] The transmitting device 100 and the receiving device 200 are wireless communication devices that perform wireless communication. In this embodiment, it is assumed that the transmitting device 100 is a stationary base station and the receiving device 200 is a mobile terminal. However, this assumption is merely an example. For example, the transmitting device 100 and the receiving device 200 may both be stationary base stations, or the transmitting device 100 and the receiving device 200 may both be mobile terminals. Note that, since multiple wireless communication devices communicate bidirectionally, each wireless communication device may also have the functions of the transmitting device 100 and the receiving device 200, which will be described later.

[0030] Hereinafter, examples 1 and 2 will be described as specific examples of the present embodiment.

[0031] Example 1 In this embodiment, an example of a transmitting device configured with optical circuit components, which includes two wavelength-tunable laser devices and a delay line, modulates laser light f1 with a baseband signal, and inputs a plurality of signals that have been phase-processed by the delay line into a photomixer together with laser light f2 with a constant optical difference frequency.

[0032] (Hardware configuration of the transmitter) The hardware configuration of the transmitting device according to this embodiment will be described.

[0033] 4 is a diagram illustrating an example of a hardware configuration of a transmitting device according to Example 1 of the embodiment of the present invention. The transmitting device 100 includes a first wavelength tunable laser device 110-1, a second wavelength tunable laser device 110-2, an optical modulator 120, one or more delay lines 130, a plurality of photomixers 140, and a plurality of antennas 150.

[0034] The first wavelength tunable laser device 110-1 generates a laser beam having a wavelength corresponding to a desired OAM mode (hereinafter referred to as mode L). The optical modulator 120 modulates the laser beam having an optical frequency f1 generated by the first wavelength tunable laser device 110-1 with a baseband signal. The modulation by the optical modulator 120 may be coherent modulation or intensity-only modulation.

[0035] The delay line 130 generates a fixed time delay in the modulated optical signal. Each of the multiple delay lines 130 may have a length of l, for example, and may be configured to continuously generate a fixed time delay in the modulated optical signal. The delay line 130 may also be a line having optical chromatic dispersion characteristics. In this case, the delay line 130 utilizes chromatic dispersion to generate a time delay in the modulated optical signal that depends on the wavelength of the optical signal. Each of the multiple delay lines 130 may have a length of l, for example, and may be configured to continuously change the time delay in the modulated optical signal that depends on the wavelength of the optical signal. By using such a delay line, it is expected that the variable range of the phase shift of the optical signal when passing through the delay line can be increased by changing the wavelength of the optical signal compared to using a line without chromatic dispersion characteristics.

[0036] The second wavelength tunable laser device 110-2 generates a laser beam with an optical frequency f2. Here, the transmitting device 100 controls the second wavelength tunable laser device 110-2 to set the optical frequency f2 according to Equation 1, thereby keeping the radio frequency (RF) constant.

[0037] f2=f1-RF...(Formula 1)

[0038] The photomixer 140 mixes the optical signal of the optical frequency f2 with the optical signal of the optical frequency f1, and outputs a signal of the difference frequency RF.

[0039] The multiple photomixers 140 and the multiple antennas 150 each comprise a branch with no delay and a branch with a fixed time delay (or a time delay corresponding to the optical wavelength). The multiple antennas 150 may form, for example, a circular array antenna. This allows the transmitting device 100 to assign specific OAM modes to the photomixers 140 and the antennas 150.

[0040] The optical modulator may receive a signal from the opposite side (the dashed arrow in FIG. 4), thereby enabling the transmitting device 100 to generate a signal in a negative OAM mode.

[0041] 5 is a diagram illustrating specific numerical values ​​of a transmitting device according to Example 1 of the embodiment of the present invention. For example, the transmitting device 100 includes five antennas 150. The maximum OAM mode is set to mode 3. That is, the transmitting device 100 can change the OAM mode L from L=1 to L=3. In addition, the maximum wavelength of f1 is set to 1565 nm, and the minimum wavelength of f1 is set to 1560 nm.

[0042] In addition, the value of N (delay line delay amount at maximum wavelength) is set to 188 wavelengths using the calculation method described in the notes section of Figure 5, and the length l of each delay line is set to 294.22 μm using the calculation method described in the notes section of Figure 5.

[0043] 6 is a diagram illustrating an example of wavelength control by a transmitting device according to a first example of an embodiment of the present invention. The value of f1 that realizes the numerical values ​​in FIG. 5 is, for example, the value shown in FIG.

[0044] When transmitting an OAM radio wave in mode L, the transmitting device 100 determines the feeding phase of each antenna #k ​​(k=1, 2, 3, . . . , M) of the plurality of antennas 150 as follows:

[0045]

number

[0046] According to this embodiment, the OAM mode of the output radio wave can be made variable by modulating laser light f1 with a baseband signal, and inputting multiple signals that have been phase-processed by a delay line into a photomixer together with laser light f2 with a constant optical difference frequency.

[0047] Example 2 In this embodiment, an example of a transmitting device configured with optical circuit components, which includes one wavelength-tunable laser device and a delay line, intensity-modulates laser light f1 with an RF signal, and inputs multiple signals that have been phase-processed by the delay line to a photomixer will be described.

[0048] (Hardware configuration of the transmitter) The hardware configuration of the transmitting device according to this embodiment will be described.

[0049] 7 is a diagram illustrating an example of a hardware configuration of a transmitting device according to Example 2 of the embodiment of the present invention. The transmitting device 100 according to this example includes a wavelength tunable laser device 210, an optical modulator 220, one or more delay lines 230, a plurality of photomixers 240, and a plurality of antennas 250.

[0050] The wavelength-tunable laser device 210 generates a laser beam having a wavelength corresponding to a desired OAM mode (hereinafter referred to as mode L). The optical modulator 220 intensity-modulates the laser beam having an optical frequency f1 generated from the wavelength-tunable laser device 210 with an RF signal.

[0051] The delay line 230 is a line having optical chromatic dispersion characteristics. The delay line 230 utilizes chromatic dispersion to generate a time delay for the modulated optical signal that depends on the wavelength of the optical signal. Each of the multiple delay lines 230 may have a length of 1, for example, and may be configured to continuously change the time delay for the modulated optical signal that depends on the wavelength of the optical signal.

[0052] The photomixer 240 outputs an RF signal by optical envelope detection of an optical signal that has been intensity modulated by an RF signal.

[0053] The multiple photomixers 240 and the multiple antennas 250 each form a branch with no delay and a branch with a time delay corresponding to the optical wavelength. The multiple antennas 250 may form, for example, a circular array antenna. This allows the transmitting device 100 to assign specific OAM modes to the photomixers 240 and the antennas 250.

[0054] Transmitting apparatus 100 according to this embodiment can continuously switch the OAM mode of a signal to be transmitted. Also, transmitting apparatus 100 can realize various OAM modes such as integer mode, fractional mode, etc.

[0055] According to the transmitting device 100 according to the present embodiment, it is possible to switch the OAM mode with a simple configuration. For example, multiple SPPs (Serial Port Profiles), phase shift circuits, etc. are not required, and a beam forming circuit, etc. are also not required.

[0056] In each of the above-described embodiments, the optical modulator 120 or the optical modulator 220 may be omitted. For example, a delay line may be used to generate a phase delay in a laser having a wavelength corresponding to a desired OAM mode. This makes it possible to generate OAM waves for use in radar, micromachining, and the like.

[0057] (Summary of the embodiment) This specification describes at least the transmitting devices described in the following sections. (Section 1) a wavelength-tunable laser device configured to generate a laser beam having a wavelength corresponding to a desired OAM mode; a delay line configured to generate a delay in the laser. Transmitting device. (Section 2) an optical modulator configured to modulate an optical signal output from the laser; the delay line is configured to introduce a delay into the modulated optical signal. 2. The transmitting device according to claim 1. (Section 3) The wavelength tunable laser device is a first wavelength tunable laser device, the optical modulator is configured to optically modulate the optical signal with a baseband signal; a second wavelength tunable laser device configured to generate a laser having a constant difference frequency with respect to the laser generated by the first wavelength tunable laser device; and a photomixer configured to mix the delayed signal with the laser generated by the second wavelength tunable laser device to output a signal of a constant difference frequency. 3. The transmitting device according to claim 2. (Section 4) the delay line is configured to generate a fixed time delay; 4. The transmitting device according to claim 3. (Section 5) The delay line is configured to generate a time delay that depends on the wavelength of the optical signal due to optical wavelength dispersion characteristics. 4. The transmitting device according to claim 3. (Section 6) the optical modulator is configured to intensity-modulate the optical signal with an RF signal; the delay line is configured to generate a time delay that depends on the wavelength of the optical signal due to optical wavelength dispersion characteristics; a photomixer configured to output a signal of a constant frequency by envelope detection of light on the delayed signal; 3. The transmitting device according to claim 2.

[0058] Any of the above configurations provides a technology that enables the realization of a variety of OAM modes. According to the second term, the amount of phase rotation in the delay line changes due to optical modulation, thereby changing the generated OAM mode. According to the third term, a desired OAM signal can be generated using two lasers with a constant difference frequency. According to the fourth term, a fixed phase delay can be generated using the delay line. According to the fifth term, a delay with a variable phase shift can be generated by using the optical chromatic dispersion characteristics. According to the sixth term, a mode-variable OAM wave can be generated by using the optical chromatic dispersion characteristics to generate a delay with a variable phase shift for a signal obtained by intensity-modulating an optical signal with an RF signal.

[0059] Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0060] 100 Transmitting device 110-1 First wavelength tunable laser device 110-2 Second wavelength tunable laser device 120 Optical Modulator 130 Delay Line 140 Photomixer 150 antenna 200 receiving device 210 Tunable wavelength laser device 220 Optical Modulator 230 Delay Line 240 Photomixer 250 Antenna

Claims

1. a first wavelength tunable laser device configured to generate a laser having a wavelength corresponding to a desired OAM mode; an optical modulator configured to modulate a laser generated by the first wavelength tunable laser device; a delay line configured to generate a delay in the optical signal modulated by the optical modulator; a second wavelength tunable laser device configured to generate a laser having a constant difference frequency with respect to the laser generated by the first wavelength tunable laser device; a photomixer configured to mix the optical signal delayed by the delay line with the laser generated by the second wavelength tunable laser device and output a signal of a constant difference frequency; A transmitting device comprising:

2. the optical modulator is configured to optically modulate the laser generated by the first wavelength tunable laser device with a baseband signal; The transmitting device according to claim 1 .

3. the delay line is configured to generate a fixed time delay; The transmitting device according to claim 2 .

4. The delay line is configured to generate a time delay that depends on the wavelength of the optical signal due to optical wavelength dispersion characteristics. The transmitting device according to claim 2 .

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