Optical space communication device and optical space communication method

Abstract

An optical spatial communication device according to an embodiment of the present invention comprises: an optical antenna that receives a laser beam emitted as a result of multiplexing a main signal to be used in communication and a control signal to be used in maintaining or controlling the communication; an optical branching element that splits the laser beam received by the optical antenna into a plurality of laser beams; a first optical fiber through which one of the laser beams split by the optical branching element is transmitted to a photodetector; a second optical fiber through which the other of the laser beams split by the optical branching element is transmitted, in a core diameter larger than that of the first optical fiber, to the photodetector; and an extraction unit that extracts a control signal from the other laser beam transmitted through the second optical fiber.

Description

[Technical field]

[0001] The present invention relates to an optical space communications device and an optical space communications method. [Background technology]

[0002] For the fifth-generation mobile communication system (5G) and the like, in addition to wireless communication using radio waves and wired communication using optical fiber, optical wireless communication technology that transmits signals using spatial light is being considered.

[0003] For example, in spatial communication, a transmitting device modulates and multiplexes control signals related to maintaining communication, such as commands and device information notifications, and a signal that is the main purpose of communication (main signal) using different modulation methods (see, for example, Non-Patent Document 1). Also, in optical spatial communication using light, a transmitting device drives a laser light source (LD: laser diode) and emits a signal obtained by modulating and multiplexing the main signal and control signal from an optical antenna as a laser beam (laser light).

[0004] A receiving device for optical space communications receives the laser light by an optical antenna, and makes the laser light incident on a photodetector (PD: photodiode) via optical elements such as a reflector, a focusing lens, and a single-mode optical fiber arranged downstream of the optical antenna (see, for example, Non-Patent Document 2).The receiving device separates and extracts the main signal and the control signal from the output of the PD, and demodulates each of them. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Kazuki Takeda et al., "NR Physical Layer Specifications for 5G," NTT DOCOMO Technical Journal, Vol. 26, No. 3, Nov. 2018, pp. 47-58 [Non-Patent Document 2] Yoshinori Arimoto, "Design and Performance Evaluation of Free-Space Optical Communication Device Using Single-Mode Fiber Coupling," IEICE Transactions on Electronics, Information and Communication Engineers, Vol. J91-C No. 1, Jan. 2008, pp. 38-49 Summary of the Invention [Problem to be solved by the invention]

[0006] For example, in optical space communications using laser light, a receiving device is positioned directly opposite the optical axis of the laser light transmitted by a transmitting device, and the laser light is received by introducing it into the core portion of a single-mode optical fiber.

[0007] However, the positional relationship between the optical axis and the receiver may change from moment to moment due to external disturbances such as vibrations of the device and atmospheric turbulence, and in this case, there is a problem that even a slight deviation in the optical axis may cause the introduction of the laser light into the single-mode optical fiber to fail, resulting in the loss of both the main signal and the control signal.

[0008] If the main signal is lost, it can be compensated for by retransmitting it. On the other hand, if the control signal is lost, there is a risk that it will be impossible to maintain communication. Therefore, it is more important to prevent the loss of the control signal than the main signal.

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an optical space communications device and an optical space communications method that can reduce loss of control signals even when the main signal is lost due to misalignment of the optical axis. [Means for solving the problem]

[0010] An optical space communications device according to one embodiment of the present invention includes an optical antenna that receives laser light emitted by multiplexing a main signal to be communicated and a control signal used to maintain or control the communications, an optical branching element that branches the laser light received by the optical antenna into a plurality of laser lights, and a first optical fiber that transmits one of the laser lights branched by the optical branching element to a light receiving element; a first demodulation unit that demodulates the main signal based on the laser light transmitted through the first optical fiber;a second optical fiber having a core diameter larger than that of the first optical fiber and configured to transmit the other laser light branched by the optical branching element to a light receiving element; and an extracting unit configured to extract the control signal from the other laser light transmitted by the second optical fiber. a second demodulation unit that demodulates the control signal extracted by the extraction unit; and The present invention is characterized by having the following.

[0011] Moreover, an optical space communication method according to one embodiment of the present invention includes a receiving step of receiving a laser beam emitted by multiplexing a main signal to be communicated and a control signal used to maintain or control the communication, an optical branching step of branching the received laser beam into a plurality of laser beams, and a first transmission step of transmitting one of the branched laser beams to a light receiving element via a first optical fiber. a first demodulation step of demodulating the main signal based on the laser light transmitted through the first optical fiber; a second transmitting step of transmitting the other branched laser light to a light receiving element through a second optical fiber having a core diameter larger than that of the first optical fiber; and an extracting step of extracting the control signal from the other laser light transmitted through the second optical fiber. a second demodulation step of demodulating the extracted control signal; The present invention is characterized by comprising: Effect of the Invention

[0012] According to the present invention, even when the main signal is lost due to misalignment of the optical axis, the loss of the control signal can be reduced. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating a first configuration example of an optical space communications device according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a second configuration example of an optical space communications device according to an embodiment. [Diagram 3] FIG. 11 is a diagram illustrating a third configuration example of an optical space communications device according to an embodiment. [Figure 4] FIG. 11 is a diagram illustrating a fourth configuration example of an optical space communications device according to an embodiment. [Diagram 5] FIG. 1 is a diagram illustrating an example of an outline of an optical space communication system that performs optical space communication using laser light. [Figure 6] FIG. 1 is a diagram showing a configuration of an optical space communications device of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Before describing an optical space communications device according to an embodiment, the background to the invention will be specifically described.

[0015] 5 is a diagram illustrating an example of an outline of an optical space communication system 1 that performs optical space communication using laser light. As shown in FIG. 5, in the optical space communication system 1, for example, two optical space communication devices 2 perform bidirectional space communication using space light such as laser light.

[0016] Each of the optical space communications devices 2 includes a transmitting optical antenna 21 and a receiving optical antenna 22, and has a function as an optical space transmitting device and a function as an optical space receiving device. Note that the optical space communications device 2 may be configured to have only the function as an optical space transmitting device or the function as an optical space receiving device.

[0017] Fig. 6 is a diagram showing the configuration of an optical space communications device 2 of the comparative example. As shown in Fig. 6, the optical space communications device 2 of the comparative example includes a control unit 200, a signal processing unit 202, a signal multiplexing modulation unit 204, a laser light source (LD: laser diode) 206, an optical antenna 21, an optical antenna 22, a reflecting mirror 210, a reflecting mirror 211, a focusing lens 221, a single mode optical fiber (first optical fiber) 231, a light receiving element (PD: photodiode) 241, an extraction unit 250, a first demodulation unit 260, and a second demodulation unit 270.

[0018] The control unit 200 controls each unit constituting the optical space communications device 2. For example, the control unit 200 generates a control signal including a command or device information notification used for maintaining or controlling communication when the optical space communications device 2 performs optical space communications using laser light with another optical space communications device 2, and outputs the control signal to the signal multiplexing modulation unit 204.

[0019] The signal processing unit 202 performs predetermined signal processing under the control of the control unit 200. For example, the signal processing unit 202 generates a main signal that is the target (main purpose) of optical space communication using laser light, and outputs it to the signal multiplexing modulation unit 204.

[0020] The signal multiplexing modulation unit 204 modulates and multiplexes the control signal output by the control unit 200 and the main signal output by the signal processing unit 202 using different modulation methods, and outputs the multiplexed signal to the laser light source 206.

[0021] The laser light source 206 is driven by the signal output from the signal multiplexing modulation unit 204 to generate modulated laser light and output it to the optical antenna 21 .

[0022] The optical antenna 21 forms an image of the laser light output by the laser light source 206 with, for example, diffraction-limited accuracy, shapes the laser light so that it is suitable for optical space communications, and emits the laser light into space toward an optical antenna 22 equipped in another optical space communications device 2.

[0023] The optical antenna 22 receives the laser light emitted by the optical antenna 21 included in the other optical space communications device 2 , and outputs it toward the reflecting mirror 210 .

[0024] The reflecting mirror 210 reflects the laser light outputted by the optical antenna 22 towards the reflecting mirror 211. The reflecting mirror 211 reflects the laser light reflected by the reflecting mirror 210 towards the focusing lens 221.

[0025] The condenser lens 221 condenses the laser light reflected by the reflecting mirror 211 and forms an image toward the core of the single mode optical fiber 231 .

[0026] The single mode optical fiber 231 is an optical fiber having an effective aperture diameter (mode field diameter) of, for example, about 10 μm. The single mode optical fiber 231 transmits the laser light focused by the focusing lens 221 to the light receiving element 241.

[0027] The light receiving element 241 is an optical signal receiving element that receives the laser light transmitted by the single mode optical fiber 231 , performs photoelectric conversion, and outputs the signal to the extraction section 250 .

[0028] The extraction unit 250 separates and extracts the modulated control signal and the main signal from the signal that has been photoelectrically converted by the photodetector 241, outputs the modulated main signal to the first demodulation unit 260, and outputs the modulated control signal to the second demodulation unit 270.

[0029] The first demodulation unit 260 is a main signal demodulation unit that demodulates the main signal extracted by the extraction unit 250 and outputs the demodulated signal to the signal processing unit 202. The second demodulation unit 270 is a control signal demodulation unit that demodulates the control signal extracted by the extraction unit 250 and outputs the control signal to the signal processing unit 202.

[0030] The optical space communications device 2 may be configured such that the signal multiplexing modulation unit 204 further performs error correction coding, and the first demodulation unit 260 and the second demodulation unit 270 perform decoding, respectively. The optical space communications device 2 is configured such that one light receiving element 241 is connected to one single mode optical fiber 231, but may be configured such that a hybrid light receiving element is provided in which a plurality of light receiving elements 241 are connected to one single mode optical fiber 231.

[0031] In the optical space communications device 2, the main signal requires faster and larger capacity communication than the control signal. For example, the main signal needs to be transmitted with an increased modulation level or an increased bit rate. Therefore, the required receiving optical power tends to increase in order to receive the main signal. On the other hand, low-speed and small-capacity communication is sufficient for the control signal, and it is possible to keep the required receiving optical power low.

[0032] Furthermore, in the optical space communications device 2, the positional relationship between the optical axis of the received laser light and the aperture of the single mode optical fiber 231 may change due to disturbances such as vibrations of the device and atmospheric turbulence.

[0033] Therefore, the optical space communications device according to the embodiment is configured to be able to reduce the loss of the control signal even when the main signal is lost due to misalignment of the optical axis.

[0034] Next, several configuration examples of the optical space communications device according to the embodiment will be described with reference to Fig. 1 to Fig. 4. In the optical space communications devices 2a, 2b, 2c, and 2d according to the embodiment shown in Fig. 1 to Fig. 4, the configurations substantially the same as those of the optical space communications device 2 shown in Fig. 6 are denoted by the same reference numerals.

[0035] Fig. 1 is a diagram showing an example of the configuration of an optical space communications device 2a according to an embodiment. As shown in Fig. 1, the optical space communications device 2a includes a control unit 200, a signal processing unit 202, a signal multiplexing modulation unit 204, a laser light source 206, an optical antenna 21, an optical antenna 22, a reflecting mirror 210, a reflecting mirror 211, a beam splitter 212, a focusing lens 221, a focusing lens 222, a single mode optical fiber 231, a large core diameter optical fiber 232, a light receiving element 241, a light receiving element 242, a first extraction unit 251, a second extraction unit 252, a first demodulation unit 260, and a second demodulation unit 270.

[0036] The beam splitter 212 is an optical branching element that branches the laser light received by the optical antenna 22 into a plurality of laser lights. Specifically, the beam splitter 212 reflects a part of the laser light received by the optical antenna 22 toward the focusing lens 222 and transmits the remaining laser light toward the reflecting mirror 211.

[0037] The condenser lens 221 condenses the laser light that has been transmitted by the beam splitter 212 and reflected by the reflecting mirror 211 , and forms an image toward the core of the single mode optical fiber 231 .

[0038] Here, the single mode optical fiber 231 is a first optical fiber that transmits one of the laser beams split by the beam splitter 212 to the light receiving element 241.

[0039] The light receiving element 241 receives the laser light transmitted by the single mode optical fiber 231 , performs photoelectric conversion, and outputs a signal to the first extraction section 251 .

[0040] The first extraction unit 251 extracts the modulated main signal from the signal that has been photoelectrically converted by the light receiving element 241 , and outputs the main signal to the first demodulation unit 260 .

[0041] The focusing lens 222 focuses the laser light reflected by the beam splitter 212 and forms an image toward the core of the large-core optical fiber 232 .

[0042] The large-core optical fiber 232 transmits the laser light split by reflection by the beam splitter 212 to the light receiving element 242 with a core diameter larger than that of the single-mode optical fiber 231. Here, the large-core optical fiber 232 is a second optical fiber that transmits the laser light focused by the focusing lens 222 to the light receiving element 242. The large-core optical fiber 232 may be a multimode optical fiber or the like.

[0043] The light receiving element 242 is an optical signal receiving element that receives the laser light transmitted by the large-core diameter optical fiber 232 , performs photoelectric conversion, and outputs a signal to the second extraction section 252 .

[0044] The second extraction section 252 extracts the control signal modulated from the laser light transmitted by the large-core diameter optical fiber 232 , and outputs it to the second demodulation section 270 .

[0045] That is, the optical space communications device 2a uses a beam splitter 212 that performs optical branching to input a part of the laser light in which the control signal and the main signal are multiplexed into a large-core optical fiber 232 having a larger core diameter than the single-mode optical fiber 231. Then, the optical space communications device 2a extracts the control signal from the signal that has passed through the large-core optical fiber 232.

[0046] Furthermore, the optical space communications device 2 a inputs the laser light transmitted by the beam splitter 212 into a single mode optical fiber 231 , and extracts a main signal from the signal that has passed through the single mode optical fiber 231 .

[0047] Optical fibers with large core diameters are generally not suitable for high-speed signal transmission, but control signals are low-speed and can be transmitted through optical fibers with large core diameters.

[0048] In addition, since the large-core optical fiber 232 has a larger core diameter than the single-mode optical fiber 231, it is easier to introduce the laser light than the single-mode optical fiber 231 even if the optical axis of the laser light is misaligned.

[0049] Furthermore, even if the optical axis misalignment causes a malfunction in the introduction of laser light into the large-core diameter optical fiber 232, resulting in optical loss, the optical space communications device 2a is likely to be able to receive the control signal because the required receiving optical power of the control signal is smaller than the required receiving optical power of the main signal.

[0050] Since the required received optical power of the control signal is smaller than the required received optical power of the main signal, the branching ratio of the light by the beam splitter 212 may be set to be small for the light receiving element 242 and large for the light receiving element 241.

[0051] The optical space communications device 2a may be configured to split a part of the laser light by a second beam splitter (not shown) and input the split part to an optical element for measuring the optical axis position of the laser light. In this case, the second beam splitter may be disposed immediately before the focusing lens 222 or immediately before the focusing lens 221.

[0052] In this way, the optical space communications device 2a can reduce the possibility of losing a control signal even if the laser light fails to be introduced into the single-mode optical fiber 231 due to a misalignment of the optical axis, and the main signal cannot be received.

[0053] The main signal and the control signal may be time-multiplexed so as to be transmitted alternately at a predetermined time interval, or the control signal may be intensity-modulated with respect to the main signal. When the main signal and the control signal are time-multiplexed, the first extraction unit 251 and the second extraction unit 252 extract the main signal or the control signal in accordance with a predetermined time interval. When the main signal and the control signal are intensity-modulated, the first extraction unit 251 and the second extraction unit 252 each extract the main signal or the control signal using a predetermined frequency filter.

[0054] Fig. 2 is a diagram showing an example of the configuration of an optical space communications device 2b according to an embodiment. As shown in Fig. 2, the optical space communications device 2b includes a control unit 200, a signal processing unit 202, a signal multiplexing modulation unit 204, a laser light source 206, an optical antenna 21, an optical antenna 22, a reflecting mirror 210, a reflecting mirror 211, a beam splitter 212, a focusing lens 221, a focusing lens 222, a single mode optical fiber 231, a large core diameter optical fiber 232, a light receiving element 241, a light receiving element 242, a switch 281, an extracting unit 282, a timing extracting unit 283, a first demodulating unit 260, and a second demodulating unit 270.

[0055] Switch 281 is a 2-to-1 changeover switch that switches the signal path to select either the signal output by light receiving element 241 or the signal output by light receiving element 242 based on information indicating the timing extracted by timing extraction unit 283, and output the selected signal to extraction unit 282.

[0056] For example, when the optical antenna 22 receives laser light in which a main signal and a control signal are time-multiplexed, the switch 281 switches to input to the extraction unit 282 either a signal output by a photodetector 241 that receives one laser light transmitted by a single-mode optical fiber 231, or a signal output by a photodetector 242 that receives another laser light transmitted by a large-core diameter optical fiber 232, based on the timing extracted by the timing extraction unit 283.

[0057] The extraction unit 282 separates and extracts the control signal and the main signal from the signal input via the switch 281, and outputs the modulated main signal to the first demodulation unit 260 and outputs the modulated control signal to the second demodulation unit 270. The extraction unit 282 also outputs the signal input via the switch 281 to the timing extraction unit 283.

[0058] Based on the signal input from the extraction unit 282, the timing extraction unit 283 extracts the timing at which at least one of the main signal and the control signal is transmitted to either the photodetector 241 or the photodetector 242, and outputs information indicating the extracted timing to the switch 281.

[0059] That is, the timing extraction unit 283 extracts timing based on at least one of the multiple laser beams split by the beam splitter 212. For example, the timing extraction unit 283 may extract the timing at which a main signal is transmitted to the light receiving element 241, or may extract the timing at which a control signal is transmitted to the light receiving element 242.

[0060] As a result, the extraction unit 282 may extract a main signal from the laser light transmitted by the single mode optical fiber 231, or may extract a control signal from the laser light transmitted by the large core diameter optical fiber 232, based on the timing extracted by the timing extraction unit 283.

[0061] The optical space communications device 2b is configured such that the switch 281 outputs the output from either the light receiving element 241 or the light receiving element 242 to the extraction unit 282, for example, at the start of operation.

[0062] Thereafter, in the optical space communications device 2b, when a signal is input to the extractor 282 from, for example, the light receiving element 241 or the light receiving element 242, the timing extractor 283 measures the input timing of each of the control signal and the main signal that are alternately sent at a predetermined time period. Then, the timing extractor 283 drives the switch 281 to switch in synchronization with the measured input timing of each of the control signal and the main signal.

[0063] For example, switch 281 outputs the signal output from light receiving element 242 to extraction unit 282 when a control signal is received, and outputs the signal output from light receiving element 241 to extraction unit 282 when a main signal is received.

[0064] In this way, the optical space communications device 2b can reduce the possibility of losing the control signal even if the laser beam fails to be introduced into the single mode optical fiber 231 due to misalignment of the optical axis, and the main signal cannot be received. Also, the optical space communications device 2b can be configured with fewer electronic circuits than the optical space communications device 2 and the optical space communications device 2a described above.

[0065] 3 is a diagram showing a configuration example of an optical space communications device 2c according to an embodiment. As shown in FIG. 3, the optical space communications device 2c includes a control unit 200, a signal processing unit 202, a signal multiplexing modulation unit 204, a laser light source 206, an optical antenna 21, an optical antenna 22, a reflecting mirror 210, a reflecting mirror 211, a beam splitter 212, a switching unit 213, a focusing lens 221, a focusing lens 222, a single mode optical fiber 231, a large core diameter optical fiber 232, a light receiving element 241, a light receiving element 242, a timing extraction unit 283, a synthesis unit 284, an extraction unit 285, a first demodulation unit 260, and a second demodulation unit 270.

[0066] The switching unit 213 has optical shutters A and B, and when the optical antenna 22 receives laser light in which a main signal and a control signal are time-multiplexed, for example, it allows the laser light to pass through one of the optical shutters A and B and blocks the laser light through the other one.

[0067] For example, based on the timing extracted by the timing extraction unit 283, the switching unit 213 switches between having the light receiving element 241 receive one of the laser beams branched by the beam splitter 212 and having the light receiving element 242 receive the other laser beam branched by the beam splitter 212.

[0068] The optical shutters A and B are not limited to the above-mentioned arrangement, and may be arranged, for example, midway between the single mode optical fiber 231 and the large core diameter optical fiber 232, or may be arranged downstream of the single mode optical fiber 231 and the large core diameter optical fiber 232, respectively.

[0069] The synthesis unit 284 synthesizes a signal output from the photodetector 241 that receives one of the laser beams branched by the beam splitter 212 and a signal output from the photodetector 242 that receives the other laser beam branched by the beam splitter 212, and outputs the result to the extraction unit 285.

[0070] The extraction unit 285 separates and extracts the control signal and the main signal from the signal input via the synthesis unit 284, and outputs the modulated main signal to the first demodulation unit 260 and outputs the modulated control signal to the second demodulation unit 270. The extraction unit 285 also outputs the signal input via the synthesis unit 284 to the timing extraction unit 283.

[0071] The optical space communications device 2c is configured such that the switching unit 213 inputs the output from either the light receiving element 241 or the light receiving element 242 to the extraction unit 285, for example, at the start of operation.

[0072] Thereafter, in the optical space communications device 2c, when a signal is input to the extractor 285 from, for example, either the light receiving element 241 or the light receiving element 242, the timing extractor 283 measures the input timing of each of the control signal and main signal sent alternately at a predetermined time period. Then, the timing extractor 283 drives the optical shutters A and B of the switching unit 213 to switch between transmitting and blocking the laser light in synchronization with the input timing of the measured control signal and main signal.

[0073] For example, the switching unit 213 switches so that when a control signal is received, the synthesis unit 284 outputs the signal output by the photodetector 242 to the extraction unit 285, and when a main signal is received, the synthesis unit 284 outputs the signal output by the photodetector 241 to the extraction unit 285.

[0074] In this way, the optical space communications device 2c can reduce the possibility of losing the control signal even if the laser beam fails to be introduced into the single mode optical fiber 231 due to misalignment of the optical axis, and the main signal cannot be received. Moreover, the optical space communications device 2c can be configured with fewer electronic circuits than the optical space communications device 2 and the optical space communications device 2a described above.

[0075] Fig. 4 is a diagram showing a configuration example of an optical space communications device 2d according to an embodiment. As shown in Fig. 4, the optical space communications device 2d includes a control unit 200, a signal processing unit 202, a signal multiplexing modulation unit 204, a laser light source 206, an optical antenna 21, an optical antenna 22, a reflecting mirror 210, a reflecting mirror 211, a beam splitter 212, a focusing lens 221, a focusing lens 222, a single mode optical fiber 231, a large core diameter optical fiber 232, a timing extraction unit 283, an optical switch 290, a light receiving element 291, an extraction unit 292, a first demodulation unit 260, and a second demodulation unit 270.

[0076] When the optical antenna 22 receives laser light in which the main signal and control signal are time-multiplexed, the optical switch 290 switches so that one laser light transmitted by the single mode optical fiber 231 and another laser light transmitted by the large core diameter optical fiber 232 are alternately input to the photodetector 291 based on the timing extracted by the timing extraction unit 283.

[0077] For example, the optical switch 290 switches so that when a control signal is received, the signal output from the photodetector 242 is output to the photodetector 291, and when a main signal is received, the signal output from the photodetector 241 is output to the photodetector 291.

[0078] The light receiving element 291 is an optical signal receiving element that receives the laser light output by the optical switch 290 , performs photoelectric conversion, and outputs a signal to the extraction section 292 .

[0079] The extractor 292 alternately extracts a control signal and a main signal from a signal output by a light receiving element 291 which alternately receives one laser light transmitted by the single mode optical fiber 231 and the other laser light transmitted by the large core diameter optical fiber 232. Then, the extractor 292 outputs the modulated main signal to the first demodulator 260 and outputs the modulated control signal to the second demodulator 270. The extractor 292 also outputs the signal input from the light receiving element 291 to the timing extractor 283.

[0080] The optical space communications device 2d is configured such that the optical switch 290 inputs the output from either the light receiving element 241 or the light receiving element 242 to the light receiving element 291, for example, at the start of operation.

[0081] Thereafter, in the optical space communications device 2d, when a signal is input from the light receiving element 291 to the extraction unit 292, the timing extraction unit 283 measures the input timing of each of the control signal and main signal that are alternately sent at a predetermined time period. Then, the timing extraction unit 283 drives the optical switch 290 to switch the output of the laser light in synchronization with the measured input timing of each of the control signal and main signal.

[0082] For example, the optical switch 290 switches so that when a control signal is received, the signal output from the photodetector 242 is output to the photodetector 291, and when a main signal is received, the signal output from the photodetector 241 is output to the photodetector 291.

[0083] In this way, the optical space communications device 2d can reduce the possibility of losing the control signal even if the laser beam fails to be introduced into the single mode optical fiber 231 due to misalignment of the optical axis, and the main signal cannot be received. Moreover, the optical space communications device 2d can be configured with fewer electronic circuits than the optical space communications device 2 and the optical space communications device 2a described above. [Explanation of symbols]

[0084] 1...optical free space communication system, 2, 2a, 2b, 2c, 2d...optical free space communication device, 21...optical antenna, 22...optical antenna, 200...control unit, 202...signal processing unit, 204...signal multiplexing modulation unit, 206...laser light source, 210...reflector, 211...reflector, 212...beam splitter, 213...switching unit, 221...condensing lens, 222...condensing lens, 231... Single mode optical fiber, 232...large core diameter optical fiber, 241, 242, 291...light receiving element, 250...extraction unit, 251...first extraction unit, 252...second extraction unit, 260...first demodulation unit, 270...second demodulation unit, 281...switch, 282...extraction unit, 283...timing extraction unit, 284...combination unit, 285...extraction unit, 290...optical switch, 292...extraction unit

Claims

1. an optical antenna for receiving a laser beam that is emitted by multiplexing a main signal to be communicated and a control signal used to maintain or control the communication; an optical branching element that branches the laser light received by the optical antenna into a plurality of laser lights; a first optical fiber that transmits one of the laser beams branched by the optical branching element to a light receiving element; a first demodulation unit that demodulates the main signal based on the laser light transmitted through the first optical fiber; a second optical fiber having a core diameter larger than that of the first optical fiber and configured to transmit the other laser light branched by the optical branching element to a light receiving element; an extractor for extracting the control signal from another laser light transmitted through the second optical fiber; a second demodulation unit that demodulates the control signal extracted by the extraction unit; An optical space communications device comprising:

2. a timing extraction unit that extracts a timing at which at least one of the main signal and the control signal is transmitted to the light receiving element based on at least one of the plurality of laser beams branched by the light branching element; and The extraction unit is Further extracting the main signal from the single laser light transmitted through the first optical fiber based on the timing extracted by the timing extraction unit.

2. The optical space communications device according to claim 1,

3. a switch for switching so that, when the optical antenna receives laser light in which the main signal and the control signal are time-multiplexed, either a signal output from a light receiving element that receives one laser light transmitted through the first optical fiber or a signal output from a light receiving element that receives another laser light transmitted through the second optical fiber is input to the extraction unit based on the timing extracted by the timing extraction unit. Further possessing 3. The optical space communications device according to claim 2,

4. a switching unit that switches, when the optical antenna receives the laser light in which the main signal and the control signal are time-multiplexed, between receiving by the light receiving element one of the laser lights branched by the optical branching element and receiving by the light receiving element another laser light branched by the optical branching element, based on the timing extracted by the timing extraction unit; a synthesis unit that synthesizes a signal output from a light receiving element that receives one of the laser beams branched by the optical branching element and a signal output from a light receiving element that receives the other laser beam branched by the optical branching element, and outputs the synthesized signal to the extraction unit; Further possessing 3. The optical space communications device according to claim 2,

5. an optical switch that switches so that one laser light transmitted through the first optical fiber and another laser light transmitted through the second optical fiber are alternately input to a light receiving element based on the timing extracted by the timing extraction unit when the optical antenna receives laser light in which the main signal and the control signal are time-multiplexed. and The extraction unit is Alternately extracting the control signal and the main signal from a signal output by a light receiving element that alternately receives one laser light transmitted through the first optical fiber and another laser light transmitted through the second optical fiber.

3. The optical space communications device according to claim 2,

6. a receiving step of receiving a laser beam emitted by multiplexing a main signal to be communicated and a control signal used to maintain or control the communication; a light branching step of branching the received laser light into a plurality of laser lights; a first transmitting step of transmitting one of the branched laser beams to a light receiving element through a first optical fiber; a first demodulation step of demodulating the main signal based on the laser light transmitted through the first optical fiber; a second transmitting step of transmitting the other branched laser light to a light receiving element through a second optical fiber having a core diameter larger than that of the first optical fiber; an extraction step of extracting the control signal from another laser light transmitted by the second optical fiber; a second demodulation step of demodulating the extracted control signal; A method for free space optical communication comprising:

7. A timing extraction step of extracting a timing at which at least one of the main signal and the control signal is transmitted to a light receiving element based on at least one of the plurality of branched laser beams. Further comprising: In the extraction step, Further extracting the main signal from the single laser light transmitted through the first optical fiber based on the timing extracted in the timing extraction step.

7. The optical space communication method according to claim 6,

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