Optical signal output device and transmission directivity control device

Abstract

An optical signal output device outputs a first optical signal and a second optical signal and, on the basis of beam direction information, switches the second optical signal between a high-frequency second optical signal that has a higher frequency than the first optical signal and a low-frequency second optical signal that has a lower frequency than the first optical signal.

Description

Optical signal output device and transmission directivity control device

[0001] The present invention relates to an optical signal output device and a transmission directivity control device.

[0002] The use of millimeter-wave and higher frequency bands is advancing as a means to achieve faster and larger capacity wireless communications. Because the spatial propagation loss of radio waves increases with frequency (e.g., free-space propagation loss increases in proportion to the square of frequency), high-gain antennas are often used in these high-frequency bands. High-gain antennas are necessarily highly directional, so their beam direction must be aligned with the wireless communication partner. When the direction of the wireless communication partner is dynamic, a means for dynamically controlling the beam direction, i.e., beam steering, is essential. Furthermore, beam steering in antennas is required not only for wireless communications but also for other applications, such as radar, imaging, and wireless power transmission.

[0003] As a means of beam steering, methods have been devised and used, such as mechanically controlling the direction of the antenna, and controlling the radio waves emitted from the antenna by refracting or reflecting them with movable lenses or reflectors. However, phased array antennas are widely used because they do not use mechanical moving parts, are highly durable, have good tracking ability, and are suitable for making antennas smaller and lighter.

[0004] A phased array antenna performs electronic beam steering by controlling (called weighting) the phase and amplitude of the RF (Radio Frequency) signal supplied to each antenna element using means such as variable delay circuits, variable attenuator circuits, and digital signal processing connected to multiple antenna elements arranged on a line or surface.

[0005] 2. Description of the Related Art Phased array antennas that perform weighting using analog circuits are widely used in fifth generation mobile communication systems and millimeter wave band wireless LAN (Local Area Network) systems that use millimeter wave bands.

[0006] As the use of high-frequency bands advances, higher antenna gains are required, and phased array antennas that weight a larger number of antenna elements are expected to be necessary. For example, Non-Patent Document 1 discloses a configuration method for a 256-element phased array antenna used in fifth-generation mobile communication base stations in the 28 GHz band. For sixth-generation mobile communications, which aim to provide even faster transmission rates, the use of frequency bands above 100 GHz, the so-called terahertz band (e.g., the 300 GHz band), is being considered. Considering that if the radio frequency becomes about 10 times higher than the 28 GHz band, the free-space propagation loss will increase by 100 times (free-space propagation loss increases by 20 dB), it is expected that more than 10,000 antenna elements will be required to compensate for this with the antenna gain of the base station, for example.

[0007] To minimize power loss to antenna elements, the RF transmission line feeding power from the phase shifter circuit to the antenna element must be as short as possible. Therefore, in high-frequency phased array antennas, particularly those in the millimeter-wave band, the phase shifter circuit is configured to be located near each antenna element. However, as the radio frequency increases, the antenna element spacing narrows, making it difficult to arrange multiple phase shifter circuits at the same spacing as the antenna element spacing. For example, for a radio frequency of 300 GHz, the free-space wavelength is 1 mm, so the antenna element spacing is typically half the wavelength, or 0.5 mm. Furthermore, to configure a circuit that forms multiple beams (a multi-beam forming circuit), the same number of phase shifters as the number of beams must be arranged in parallel, further increasing the difficulty.

[0008] Therefore, by applying optical circuit manufacturing technology that can implement low-loss waveguides in a small size, a method has been proposed in which signals are converted into light and then weighted using an optical circuit, as in Non-Patent Document 2. This is thought to increase the possibility of constructing a multi-element, two-dimensional weighting circuit, but since the number of components in the weighting circuit increases in accordance with the number of antenna elements, a method is needed that can accommodate an increase in the number of antenna elements while minimizing the increase in the number of components as much as possible.

[0009] The following means have been disclosed as existing techniques for performing weighting using optical circuits.

[0010] Patent Document 1 discloses an "optically controlled array antenna device" that controls two-dimensional multi-beams by utilizing a wavelength dispersion line.

[0011] Patent Document 1: JP 2004-023400 A, US Patent Document 6,337,660, International Publication No. 2023 / 242930

[0012] 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. 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. 2018.

[0013] The device disclosed in Patent Document 1 provides a phase tilt in both the horizontal and vertical planes, but there is a problem in that a large number of one-dimensional phase shift circuits are required depending on the number of antenna elements in the vertical direction and the number of antenna elements in the horizontal direction.

[0014] In view of the above circumstances, an object of the present invention is to provide a technique that can reduce the scale of a circuit that performs weighting.

[0015] One aspect of the present invention is an optical signal output device that outputs a first optical signal and a second optical signal, and that switches the second optical signal between a high-frequency second optical signal, which is an optical signal having a frequency higher than the frequency of the first optical signal, and a low-frequency second optical signal, which is an optical signal having a frequency lower than the frequency of the first optical signal, based on beam direction information.

[0016] According to the present invention, the scale of the circuit that performs weighting can be reduced.

[0017] 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 a transmission directivity control device 1 according to a second embodiment. FIG. 4 is a diagram showing an example of the configuration of a transmission directivity control device 1 according to a third embodiment. FIG. 5 is a flowchart showing the operation of the transmission directivity control device 1 according to the present embodiment. FIG. 6 is a flowchart showing the operation of an optical signal output device 2 according to the first embodiment. FIG. 7 is a diagram showing a first example of the configuration of an optical signal output device 2. FIG. 8 is a diagram showing an example of the configuration of a control unit 25. FIG. 9 is a diagram showing a second example of the configuration of an optical signal output device 2. FIG.

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are merely examples, and the embodiments to which the present invention is applied are not limited to the following embodiments.

[0019] 1 is a diagram showing an example of the configuration of a transmission directivity control device 1 according to a first embodiment. The transmission directivity control device 1 according to the first embodiment includes an optical signal output device 2, a weighting unit 16, and a photomixing unit 17.

[0020] The optical signal output device 2 outputs the first optical signal to the photomixing unit 17. The optical signal output device 2 outputs the second optical signal to the weighting unit 16. Based on information on the direction of the beam finally output from the photomixing unit 17 (hereinafter referred to as "beam direction information"), the optical signal output device 2 switches the second optical signal between a high-frequency second optical signal, which is an optical signal with a frequency higher than the frequency of the first optical signal, and a low-frequency second optical signal, which is an optical signal with a frequency lower than the frequency of the first optical signal.

[0021] In the following description, the first optical signal L Ｈ is expressed by equation (1). Ｓ＋ is expressed by equation (2). Ｓ－ is expressed by equation (3). Ｓ＋ and a low frequency second optical signal L Ｓ－ When describing these signals without distinction, the second optical signal L Ｓ The second optical signal L Ｓcan be expressed by equation (4).

[0022] The weighting unit 16 imparts a phase tilt on a second axis, which is a certain axis in space, to the second optical signal input from the optical signal output device 2, and outputs the signal to the photomixing unit 17. The weighting unit 16 replicates the input second optical signal to generate N second optical signals. Hereinafter, the N second optical signals will be referred to as L Ｓｉ (i=1, 2, . . . , N). Ｓｉ The phase gradient φ applied to Ｓｉ (i=1, 2, . . . , N) is expressed by equation (5).

[0023] In equation (5), φ Ｓ０ is a constant. The N second optical signals to which a phase tilt is applied, output from the weighting unit 16, are expressed as L Ｓｉ is expressed by equation (6).

[0024] The photomixing unit 17 photomixes the first optical signal and the second optical signal. The photomixing unit 17 includes a plurality of antenna elements 171. The plurality of antenna elements 171 form a one-dimensional array antenna with one row and N columns. The antenna element 171 installed in the i-th column receives the first optical signal L. Ｈ is input, and the second optical signal L Ｓｉ is entered.

[0025] The antenna element 171 generates an electromagnetic wave with a frequency that is the difference between 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 multiplexer 1711 is, for example, an AWG.

[0026] 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 ＲＦ＿ｉ (L Ｈ +L Ｓｉ ) ２ The RF band is extracted from the

[0027] Second optical signal L Ｓ is the high frequency second optical signal L Ｓ＋ If v ＲＦ＿ｉ is proportional to equation (7). On the other hand, the second optical signal L Ｓ is the low frequency second optical signal L Ｓ－ If v ＲＦ＿ｉ is proportional to equation (8).

[0028] From the above, the second optical signal L outputted by the optical signal output device 2 Ｓ The high frequency second optical signal L Ｓ＋ and a low frequency second optical signal L Ｓ－ By switching between these, the output v from the antenna element 171 ＲＦ＿ｉ Therefore, the direction of the beam output from the photomixing unit 17 can be switched.

[0029] Assume that the antenna elements 171-1 to 171-N are arranged in order from top to bottom. In this case, the optical signal output device 2 outputs the second optical signal L Ｓ as a high frequency second optical signal L Ｓ＋ Therefore, when each antenna element 171 outputs radio waves in the same direction, the direction of the synthesized beam is downward from the output direction of the radio waves.

[0030] On the other hand, the optical signal output device 2 outputs the second optical signal L Ｓ as a low frequency second optical signal L Ｓ－Therefore, when each antenna element 171 outputs radio waves in the same direction, the direction of the synthesized beam is upward from the output direction of the radio waves.

[0031] Therefore, when the beam direction information indicates a downward direction, the optical signal output device 2 outputs the second optical signal L Ｓ as a high frequency second optical signal L Ｓ＋ If the beam direction information indicates an upward direction, the second optical signal L Ｓ as a low frequency second optical signal L Ｓ－ By outputting the signal, the direction of the beam output from the photomixing unit 17 can be controlled.

[0032] (Second Embodiment) Fig. 3 is a diagram showing an example of the configuration of a transmission directivity control device 1 according to a second embodiment. In the second embodiment, the weighting unit 16 imparts a phase tilt on a first axis, which is a certain axis in space, to the first optical signal input from the optical signal output device 2, and outputs the signal to the photomixing unit 17. In the second embodiment, the second optical signal is output to the photomixing unit 17 without being imparted with a phase tilt. In the photomixing unit 17 according to the second embodiment, a one-dimensional array antenna with M rows and 1 column is formed. The operation of the optical signal output device 2 is the same in the first and second embodiments.

[0033] In the second embodiment, the weighting unit 16 replicates the input first optical signal to generate M first optical signals. Hereinafter, the M first optical signals will be referred to as L Ｈｊ (j=1, 2, ..., M). Ｈｊ The phase gradient φ applied to Ｈｊ (j=1, 2, . . . , M) is expressed by equation (9).

[0034] In equation (9), φ Ｈ０ is a constant. The M first optical signals to which the phase tilt is applied and output from the weighting unit 16 are expressed as L Ｈｊ is expressed by equation (10).

[0035] In the second embodiment, the plurality of antenna elements 171 provided in the photomixing unit 17 form a one-dimensional array antenna with M rows and one column. The antenna element 171 installed in the j-th row transmits the first optical signal L Ｈｊ is input, and the second optical signal L Ｓ is entered.

[0036] In the second embodiment, the output v from the antenna 1713 ＲＦ＿ｊ (L Ｈｊ +L Ｓ ) ２ The RF band is extracted from the

[0037] Second optical signal L Ｓ is the high frequency second optical signal L Ｓ＋ If v ＲＦ＿ｊ is proportional to equation (11). On the other hand, the second optical signal L Ｓ is the low frequency second optical signal L Ｓ－ If v ＲＦ＿ｉ is proportional to equation (8).

[0038] In the second embodiment, as in the first embodiment, the second optical signal L outputted from the optical signal output device 2 Ｓ The high frequency second optical signal L Ｓ＋ and a low frequency second optical signal L Ｓ－ By switching between these, the output v from the antenna element 171 ＲＦ＿ｊ Therefore, the direction of the beam output from the photomixing unit 17 can be switched.

[0039] Assume that the antenna elements 171-1 to 171-M are arranged in order from left to right. In this case, the optical signal output device 2 outputs the second optical signal L Ｓ as a high frequency second optical signal L Ｓ＋ Therefore, if each antenna element 171 outputs radio waves in the same direction, the direction of the combined beam will be to the left of the output direction of the radio waves.

[0040] On the other hand, the optical signal output device 2 outputs the second optical signal L Ｓas a low frequency second optical signal L Ｓ－ Therefore, when each antenna element 171 outputs radio waves in the same direction, the direction of the combined beam is to the right of the output direction of the radio waves.

[0041] Therefore, when the beam direction information indicates the left direction, the optical signal output device 2 outputs the second optical signal L Ｓ as a high frequency second optical signal L Ｓ＋ If the beam direction information indicates the right direction, the second optical signal L Ｓ as a low frequency second optical signal L Ｓ－ By outputting the signal, the direction of the beam output from the photomixing unit 17 can be controlled.

[0042] Third Embodiment FIG. 4 is a diagram showing an example of the configuration of a transmission directivity control device 1 according to a third embodiment. The transmission directivity control device 1 according to the third embodiment includes an optical signal output device 2, weighting units 16-1 and 16-2, and a photomixing unit 17. In the photomixing unit 17 according to the third embodiment, a two-dimensional array antenna is formed. The weighting unit 16-1 according to the third embodiment operates in the same manner as the weighting unit 16 according to the second embodiment. The weighting unit 16-2 according to the third embodiment operates in the same manner as the weighting unit 16 according to the first embodiment. The weighting unit 16-1 imparts a phase tilt on a first axis to the first optical signal, and the weighting unit 16-2 imparts a phase tilt on a second axis to the second optical signal, but the first axis and the second axis are orthogonal to each other. The operation of the optical signal output device 2 according to the third embodiment is the same as that of the optical signal output device 2 according to the first and second embodiments.

[0043] In the third embodiment, the plurality of antenna elements 171 provided in the photomixing unit 17 form a one-dimensional array antenna with M rows and N columns. The antenna element 171 installed in the j-th row and the i-th column transmits the first optical signal L Ｈｊ is input, and the second optical signal L Ｓｉ is entered.

[0044] In the third embodiment, the output v from the antenna 1713 of the antenna element 171 installed in the jth row and the ith column ＲＦ＿ｊｉ (L Ｈｊ +L Ｓｉ ) ２ The RF band is extracted from the

[0045] Second optical signal L Ｓ is the high frequency second optical signal L Ｓ＋ If v ＲＦ＿ｊｉ is proportional to equation (13). On the other hand, the second optical signal L Ｓ is the low frequency second optical signal L Ｓ－ If v ＲＦ＿ｊｉ is proportional to equation (14).

[0046] In the third embodiment, similarly to the first and second embodiments, the second optical signal L outputted from the optical signal output device 2 Ｓ The high frequency second optical signal L Ｓ＋ and a low frequency second optical signal L Ｓ－ By switching between these, the output v from the antenna element 171 ＲＦ＿ｊｉ Therefore, the direction of the beam output from the photomixing unit 17 can be switched.

[0047] Assume that the antenna elements 171 are arranged in order from the first column to the Nth column from top to bottom, and in order from the first row to the Mth row from left to right. Ｓ as a high frequency second optical signal L Ｓ＋ Therefore, when the antenna elements 171 output radio waves in the same direction, the direction of the synthesized beam is in the lower left direction from the output direction of the radio waves.

[0048] On the other hand, the optical signal output device 2 outputs the second optical signal L Ｓ as a low frequency second optical signal L Ｓ－Therefore, when the antenna elements 171 output radio waves in the same direction, the direction of the synthesized beam becomes upper right and to the right of the output direction of the radio waves.

[0049] Therefore, when the beam direction information indicates the lower left direction, the optical signal output device 2 outputs the second optical signal L Ｓ as a high frequency second optical signal L Ｓ＋ When the beam direction information indicates the upper right direction, the second optical signal L Ｓ as a low frequency second optical signal L Ｓ－ By outputting the signal, the direction of the beam output from the photomixing unit 17 can be controlled.

[0050] In the first to third embodiments, the weighting unit 16 weights the first optical signal L Ｈ and the second optical signal L Ｓ A phase tilt is applied to at least one of the optical signals.

[0051] 5 is a flowchart showing the operation of the transmission directivity control device 1 according to this embodiment. Ｈ and the second optical signal L Ｓ (Step S11). After that, the weighting unit 16 outputs the first optical signal L Ｈ and the second optical signal L Ｓ In the first embodiment, a phase tilt is applied to at least one of the second optical signal L Ｓ In the second embodiment, a phase gradient is applied to the first optical signal L Ｈ In the third embodiment, a phase gradient is applied to the first optical signal L Ｈ and the second optical signal L Ｓ A phase ramp is applied to

[0052] The photomixing unit 17 outputs the first optical signal L Ｈ and the second optical signal L Ｓ The photomixing unit 17 then photomixes the two signals (step S13), and outputs an RF signal.

[0053] 6 is a flowchart showing the operation of the optical signal output device 2 according to the first embodiment. The optical signal output device 2 acquires beam direction information (step S21). If the beam direction information indicates a downward direction (step S22: YES), the optical signal output device 2 outputs the second optical signal L Ｓ as a high frequency second optical signal L Ｓ＋ (Step S23). If the beam direction information does not indicate a downward direction (Step S22: NO), the optical signal output device 2 outputs the second optical signal L Ｓ as a low frequency second optical signal L Ｓ－ is output (step S24).

[0054] In the second embodiment, when the beam direction information indicates the left direction, the optical signal output device 2 outputs the second optical signal L Ｓ as a high frequency second optical signal L Ｓ＋ If the beam direction information does not indicate the left direction, the optical signal output device 2 outputs the second optical signal L Ｓ as a low frequency second optical signal L Ｓ－ In the third embodiment, when the beam direction information indicates the lower left direction, the optical signal output device 2 outputs the second optical signal L Ｓ as a high frequency second optical signal L Ｓ＋ If the beam direction information does not indicate the lower left direction, the optical signal output device 2 outputs the second optical signal L Ｓ as a low frequency second optical signal L Ｓ－ Output.

[0055] In this embodiment, when the weighting unit 16 uses a matrix circuit (for example, a Butler matrix circuit or a Blass matrix circuit), the number of directions in which a beam can be transmitted can be doubled compared to the conventional case in which one second optical signal is input to the weighting unit 16 and the photomixing unit 17. Therefore, a smaller-scale weighting unit 16 and photomixing unit 17 allows the photomixing unit 17 to output beams in the same number of transmission directions as conventional cases. Furthermore, in this embodiment, by using a weighting unit 16 and photomixing unit 17 of the same scale as conventional cases, the photomixing unit 17 can output beams over a wider range or with higher resolution.

[0056] Furthermore, in this embodiment, when the weighting unit 16 uses an array of variable phase shifters, the photomixing unit 17 can output beams in the same number of transmission directions as in the conventional case even if the required phase shift range of the variable phase shifters is halved compared to the conventional case. Since the time required to change the beam direction can be shortened by that amount when the required phase shift range is reduced, in this embodiment, the time required to change the beam direction can be shortened while maintaining the number of directions in which the beam can be transmitted.

[0057] Furthermore, in this embodiment, when the weighting unit 16 uses an array of variable phase shifters, the time required to change the beam direction can be reduced compared to the conventional method, thereby improving the accuracy of phase setting and improving the accuracy of the beam.

[0058] Furthermore, in this embodiment, part of the beam direction switching process can be performed by the optical signal output device 2. Therefore, the processing load on the weighting unit 16 can be reduced.

[0059] (Configuration Example of Optical Signal Output Device) Hereinafter, a specific configuration example of the optical signal output device 2 will be described. Fig. 7 is a diagram showing a first configuration example of the optical signal output device 2. The optical signal output device 2 includes a light source 21, an optical modulator 22, a demultiplexer 23, a sideband switching unit 24, and a control unit 25.

[0060] The light source 21 outputs a first optical signal to the optical modulator 22. The optical modulator 22 intensity-modulates the input first optical signal. The intensity modulation generates an upper sideband and a lower sideband. In a first configuration example of the optical signal output device 2, the high-frequency second optical signal is the upper sideband, and the low-frequency second optical signal is the lower sideband.

[0061] The demultiplexer 23 demultiplexes the first optical signal, upper sideband wave, and lower sideband wave generated by the intensity modulation by the optical modulator 22 into the first optical signal, upper sideband wave, and lower sideband wave. The demultiplexer 23 outputs the first optical signal to the outside. In the first embodiment, the demultiplexer 23 outputs the first optical signal to the photomixing unit 17, in the second embodiment, the demultiplexer 23 outputs the first optical signal to the weighting unit 16, and in the third embodiment, the demultiplexer 23 outputs the first optical signal to the weighting unit 16-1. The demultiplexer 23 outputs the upper sideband wave and the lower sideband wave to the sideband wave switching unit 24.

[0062] The sideband wave switching unit 24 outputs one of the input upper and lower sideband waves to the outside. In the first embodiment, the sideband wave switching unit 24 outputs one of the upper and lower sideband waves to the weighting unit 16, in the second embodiment, it outputs one of the upper and lower sideband waves to the photomixing unit 17, and in the third embodiment, it outputs one of the upper and lower sideband waves to the weighting unit 16-2. The sideband wave switching unit 24 is, for example, an optical switch.

[0063] 8 is a diagram showing an example configuration of the control unit 25. The control unit 25 includes a processor 91, such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an NPU (Neural Network Processing Unit), and a memory 92, which are connected by a bus. The control unit 25 executes, for example, a beam direction information acquisition process and a sideband wave switching unit control process. The beam direction information acquisition process is a process of acquiring beam direction information from an external device. For example, the control unit 25 is provided with an interface for inputting beam direction information, and the beam direction information is acquired by inputting it via the interface.

[0064] The sideband wave switching unit control process is a process of controlling the sideband wave switching unit 24 based on beam direction information, and switching the sideband wave output from the sideband wave switching unit 24 between an upper sideband wave and a lower sideband wave.

[0065] As described above, the optical signal output device 2 shown in the first configuration example can switch between and output the second optical signal as an upper sideband wave and a lower sideband wave, thereby switching between and outputting a high-frequency second optical signal, which is an optical signal with a frequency higher than the frequency of the first optical signal, and a low-frequency second optical signal, which is an optical signal with a frequency lower than the frequency of the first optical signal.

[0066] 9 is a diagram showing a second configuration example of the optical signal output device 2. In the second configuration example, the optical signal output device 2 includes a first optical signal source 31, a second optical signal source 32, and a control unit 33.

[0067] The first optical signal source 31 outputs a first optical signal, and the second optical signal source 32 outputs a second optical signal.

[0068] The control unit 33, like the control unit 25, has a processor and memory, and executes a beam direction information acquisition process and a first optical signal wavelength change process. The beam direction information acquisition process is similar to the beam direction information acquisition process in the first configuration example, and is a process of acquiring beam direction information from outside. The first optical signal frequency change process is a process of changing the frequency of the first optical signal output from the first optical signal source 31 based on the beam direction information. By the first optical signal frequency change process, the frequency of the first optical signal output from the first optical signal source 31 is changed to a frequency higher or lower than the frequency of the second optical signal.

[0069] The first optical signal source 31 is, for example, a wavelength-tunable laser, and changes the frequency of the output first optical signal to a frequency higher or lower than the frequency of the second optical signal. The first optical signal source 31 may generate an optical signal having a frequency higher than the frequency of the second optical signal and an optical signal having a frequency lower than the frequency of the second optical signal, for example, by optical modulation, and switch the frequency of the output first optical signal between a frequency higher than the frequency of the second optical signal and a frequency lower than the frequency of the second optical signal by passing the optical signal through a filter with a variable pass band.

[0070] When an optical signal having a higher frequency than the frequency of the second optical signal is output as the first optical signal, the second optical signal is a low-frequency second optical signal. When an optical signal having a lower frequency than the frequency of the second optical signal is output as the first optical signal, the second optical signal is a high-frequency second optical signal. As described above, the optical signal output device 2 shown in the second configuration example can switch between a high-frequency second optical signal and a low-frequency second optical signal and output the second optical signal.

[0071] Each element of the transmission directivity control device 1 may be realized by a separate device. Also, each element of the optical signal output device 2 may be realized by a separate device. For example, the light source 21 and the optical modulator 22 may be provided in the central station, and the demultiplexer 23, the sideband switching unit 24, the control unit 25, the weighting unit 16, and the photomixing unit 17 may be provided in the base station. Also, for example, the optical signal output device 2 may be provided in the central station, and the weighting unit 16 and the photomixing unit 17 may be provided in the base station.

[0072] The transmission directivity control device 1 may be compatible with multiple beams. That is, a plurality of first optical signals and a plurality of second optical signals may be input to the weighting unit 16, and the optical signal to be output to the photomixing unit 17 may be switched according to the desired beam direction. In this case, an optical signal output device 2 may be provided for each beam generated by the photomixing unit 17. Note that the plurality of first optical signals and the plurality of second optical signals may be multiplexed, and in this case, the optical signal output device 2 is provided with a demultiplexer that demultiplexes the multiplexed plurality of first optical signals and the plurality of second optical signals for each combination of the first optical signals and the second optical signals that generate a beam.

[0073] 10 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.

[0074] Other Embodiments 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.

[0075] REFERENCE SIGNS LIST 1 transmission directivity control device, 2 optical signal output device, 16 weighting unit, 17 photomixing unit, 171 antenna element, 1711 multiplexer, 1712 square-law detection unit, 1713 antenna, 1714 mirror

Claims

1. An optical signal output device that outputs a first optical signal and a second optical signal, and switches the second optical signal between a high-frequency second optical signal, which is an optical signal having a frequency higher than the frequency of the first optical signal, and a low-frequency second optical signal, which is an optical signal having a frequency lower than the frequency of the first optical signal, based on beam direction information.

2. A transmission directivity control device comprising: an optical signal output device according to claim 1; a weighting unit that imparts a phase tilt to at least one of the first optical signal and the second optical signal; and a photomixing unit that photomixes the first optical signal and the second optical signal.

3. An optical signal output device according to claim 1, wherein the high-frequency second optical signal is an upper sideband generated when the first optical signal is intensity-modulated, and the low-frequency second optical signal is a lower sideband generated when the first optical signal is intensity-modulated.

4. The optical signal output device according to claim 1, wherein the second optical signal is switched between the high-frequency second optical signal and the low-frequency second optical signal by switching the frequency of the first optical signal.

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