Optical wireless communication system, optical wireless communication method, and optical transmitter

Abstract

This optical wireless communication system has a transmission device and a reception device. The transmission device comprises: a communication beam transmission unit that emits, toward the reception device, a communication beam for use in transmitting desired information; a detection beam reception unit for receiving a detection beam which is an object detecting beam emitted from the reception device so as to cover a transmitting path of the communication beam; and a control unit that measures a reception level of the detection beam, and that, upon sensing an attenuation in the reception level, controls the communication beam transmission unit to lower transmission output of the communication beam. The reception device comprises: a communication beam reception unit that receives the communication beam transmitted from the communication beam transmission unit; and a detection beam transmission unit that emits the detection beam toward the transmission device.

Description

[Technical Field]

[0001] The present invention relates to an optical wireless communication system, an optical wireless communication method, and an optical transmitting device. [Background technology]

[0002] Some optical wireless communication systems are susceptible to factors that degrade communication quality, such as atmospheric turbulence and atmospheric particles. One way to achieve longer distances and faster speeds in such optical wireless communication systems is to increase the transmission power of the communication beam. However, high-power laser light can be harmful to the human body when irradiated with it. For this reason, safety standards have been established for the power of laser light.

[0003] To meet the above safety standards, it is conceivable to designate areas where laser light is used as off-limits zones. However, in this case, it is difficult to deploy optical wireless communication systems using high-power laser light in areas where it may be difficult to prohibit people from entering, such as residential areas. Furthermore, even if an area is currently considered to be off-limits to humans, such as between high-rise buildings or in high-altitude areas between the ground and space, it is conceivable that in the future, due to the spread of flying vehicles, for example, such areas may become areas where humans may enter. Therefore, it is difficult to widely deploy optical wireless communication systems using high-power laser light using the method of meeting the above safety standards by establishing off-limits zones.

[0004] In light of this, methods are being considered to prevent laser light from reaching the human body without establishing restricted areas. For example, when a person or object is likely to enter the transmission path of the laser light, methods such as limiting the transmission output of the laser light to a safe level in accordance with the above safety standards, or shutting off the laser light, are conceivable.

[0005] Conventionally, in optical wireless communication between mobile bodies, optical wireless communication systems have been considered that use an object detection device such as a camera, radar, or ultrasonic sensor to detect surrounding people or objects, and share the detection results between the mobile bodies to control the positions of the mobile bodies so that people or objects are not positioned in a transmission path through which a laser beam for communication (hereinafter also referred to as a "communication beam") passes (see, for example, Patent Document 1). In optical wireless communication between mobile bodies, such a method of controlling the mobile bodies can realize safe optical wireless communication in which the communication beam is not irradiated onto a human body.

[0006] On the other hand, when neither the transmitting station nor the receiving station is a mobile object, the above-described control method cannot be used. Therefore, for such a case, an optical wireless communication system has been considered that detects an intruder that has entered the transmission path of the communication beam by observing that the communication beam itself has been blocked (see, for example, Patent Document 2). For such a case, an optical wireless communication system has also been considered that transmits a laser beam for detecting an intruder (hereinafter referred to as a "pilot beam"), which is output within an output range safe for the human body, on a transmission path parallel to the communication beam, and determines that the communication beam has been blocked by observing that the pilot beam has been blocked (see, for example, Patent Document 3).

[0007] To cope with such a situation, an optical wireless communication system has been studied in which a communication beam is surrounded by a pilot beam that is output within an output range that is safe for the human body, and by observing that the pilot beam is blocked, a person or object approaching the communication beam is detected in advance, and the transmission power of the communication beam is reduced or the communication beam is stopped according to the detection result (see, for example, Patent Document 4).With such a configuration, an optical wireless communication system can be realized that can output laser light with a larger transmission power while preventing the communication beam from being irradiated onto a human body by monitoring the presence or absence of a person or object approaching the communication beam. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 6656459 [Patent Document 2] U.S. Patent No. 5,229,593 [Patent Document 3] US Patent Application Publication No. 2004 / 0227057 [Patent Document 4] U.S. Patent No. 6,633,026 [Non-patent literature]

[0009] [Non-Patent Document 1] “Liquid Crystal Polarizing Spiral Plate”, [online], Tokyo Instruments Co., Ltd., [Retrieved March 8, 2022], Internet <URL: https: / / www.tokyoinst.co.jp / products / detail / polarization_elements / AR08 / index.html> Summary of the Invention [Problem to be solved by the invention]

[0010] The optical wireless communication system described in Patent Document 1 requires high-load computational processing, such as image processing and three-dimensional spatial data processing, to detect intrusions into the transmission path of the communication beam. Therefore, unless a high-performance data processing device is used, the computational processing time may be long and the response speed may be slow. This may result in a compromise in safety. Furthermore, the optical wireless communication system described in Patent Document 1 requires cameras and other devices, but because the resolution of cameras is limited, multiple cameras are required to simultaneously monitor the entire transmission path of the communication beam. This increases the number of required device components, which is expected to result in issues such as increased computational load in image processing, larger system size, and increased power consumption.

[0011] Furthermore, in the technology described in Patent Document 2, an intrusion into the transmission path of the communication beam is detected by blocking the communication beam itself, so the high-power communication beam is irradiated onto the human body before the intrusion is detected. Also, in the technology described in Patent Document 3, similar to the technology described in Patent Document 2, there is a possibility that the high-power communication beam may be irradiated onto the human body before the intrusion is detected.

[0012] The technology described in Patent Document 4 detects an intrusion by observing a decrease in reception level due to the obstruction of a pilot beam surrounding a high-power communication beam, thereby enabling safe optical wireless communication without irradiating the communication beam onto a human body. However, because the laser light used for the pilot beam propagates through space while spreading to some extent, if the spatial area where a person or object has entered the transmission path is relatively small compared to the diameter of the wider pilot beam, it may be difficult to detect the decrease in reception level. To address this issue, a conceivable method would be to improve resolution by, for example, dividing the light receiving section of the pilot beam and using multiple photodiodes, thereby increasing the sensitivity for detecting intrusions. However, this would likely result in a problem of increasing the number of components, such as photodiodes.

[0013] The present invention has been made in consideration of the above-described technical background, and aims to provide a technology that can realize optical wireless communication without unintentionally irradiating an object with a high-power communication beam, while suppressing increases in device costs, calculation volume, and power consumption. [Means for solving the problem]

[0014] One aspect of the present invention is an optical wireless communication system having a transmitting device and a receiving device, wherein the transmitting device comprises a communication beam transmitting unit that emits a communication beam used to transmit desired information toward the receiving device, a detection beam receiving unit that receives a detection beam, which is a beam for object detection emitted from the receiving device to cover the transmission path of the communication beam, and a control unit that measures the reception level of the detection beam and, if attenuation of the reception level is detected, controls the communication beam transmitting unit to lower the transmission output of the communication beam, and the receiving device is an optical wireless communication system that comprises a communication beam receiving unit that receives the communication beam transmitted from the communication beam transmitting unit and a detection beam transmitting unit that emits the detection beam to the transmitting device.

[0015] One aspect of the present invention is an optical transmission method by a computer in an optical wireless communication system having a transmitting device and a receiving device, the optical wireless communication method comprising: a detection beam transmitting step in which the receiving device emits a detection beam, which is a beam for object detection, to the transmitting device so as to cover the transmission path of a communication beam used to transmit desired information; a detection beam receiving step in which the transmitting device receives the detection beam transmitted from the receiving device; a control step in which the transmitting device measures the reception level of the detection beam and, if attenuation of the reception level is detected, controls the transmission output of the communication beam to be lower; a communication beam transmitting step in which the transmitting device emits a communication beam toward the receiving device; and a communication beam receiving step in which the receiving device receives the communication beam emitted from the transmitting device.

[0016] One aspect of the present invention is an optical transmitting device comprising: a communication beam transmitting unit that emits a communication beam used to transmit desired information toward a receiving device; a detection beam receiving unit that receives a detection beam, which is a beam for object detection emitted from the receiving device to cover the transmission path of the communication beam; and a control unit that measures the reception level of the detection beam and, if attenuation of the reception level is detected, controls the communication beam transmitting unit to lower the transmission output of the communication beam. [Effects of the Invention]

[0017] The present invention makes it possible to provide a technology that can achieve optical wireless communication without unintentionally irradiating an object with a high-power communication beam, while suppressing increases in device costs, computational complexity, and power consumption. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram showing the overall configuration of an optical wireless communication system 1 according to a first embodiment of the present invention. [Figure 2] 1 is a block diagram showing a functional configuration of an optical wireless communication system 1 according to a first embodiment of the present invention. [Figure 3] 1 is a block diagram showing the configurations of an OAM mode separation circuit 12 and a transmission / reception control device 13 in a first embodiment of the present invention. [Figure 4] 4 is a flowchart showing the operation of the transmitter 10 in the first embodiment of the present invention. [Figure 5] 10 is a diagram showing an example of a cross section of a communication beam CB and a pilot beam PB. FIG. [Figure 6] 1 is a diagram showing an example of a cross section of a communication beam CB and a pilot beam PB composed of beams of multiple OAM modes. [Figure 7] FIG. 10 is a diagram showing an optical configuration of an optical wireless communication system 1a according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an optical wireless communication system, an optical wireless communication method, and an optical transmitter according to embodiments will be described with reference to the drawings.

[0020] First Embodiment An optical wireless communication system 1 according to a first embodiment will be described below. The optical wireless communication system 1 according to the first embodiment is a system that performs communication using laser light, which may be harmful to the human body when irradiated at high power. The optical wireless communication system 1 can realize safe optical wireless communication (where high-power communication beams are not unintentionally irradiated onto objects) by detecting in advance a person or object that is about to enter the transmission path of a communication beam and controlling the transmission power of the communication beam according to the detection result. The optical wireless communication system 1 can detect an intruder by simple information processing based on the observation results of the vicinity of the communication beam. The optical wireless communication system 1 controls the transmission power of the communication beam while constantly monitoring the periphery of the transmission path through which the laser light passes.

[0021] [Overall configuration of optical wireless communication system] The following describes the overall configuration of the optical wireless communication system 1. Fig. 1 is a diagram showing the overall configuration of the optical wireless communication system 1 according to the first embodiment of the present invention. As shown in Fig. 1, the optical wireless communication system 1 includes a transmitter 10 and a receiver 20.

[0022] The optical wireless communication system according to this embodiment performs communication using a communication beam CB and a pilot beam PB. The communication beam CB is a beam for transmitting desired information from the transmitter 10 to the receiver 20. The pilot beam PB is a beam for detecting an intrusion, transmitted from the receiver 20 to the transmitter 10. The pilot beam PB is emitted coaxially with the communication beam CB from the receiver 20 that receives the communication beam CB in a predetermined OAM (Orbital Angular Momentum) mode having orbital angular momentum. The pilot beam PB is emitted so as to cover the transmission path of the communication beam CB, as shown in FIG. 1.

[0023] OAM communication is a technology that enables high-capacity wireless transmission by multiplexing different signals onto electromagnetic waves with different orbital angular momentum. Because electromagnetic waves with different orbital angular momentum are uncorrelated, even if signals are superimposed on each electromagnetic wave and transmitted, the receiving side can distinguish and separate the superimposed signals.

[0024] Furthermore, a classification of the state of an electromagnetic wave with orbital angular momentum is called an OAM mode, and is expressed as "OAM mode + 1" depending on the number of rotations (an integer) of the phase distribution of the electromagnetic wave on a plane perpendicular to the propagation direction. In OAM communication using a single OAM mode, in an ideal space free of obstructions and noise, the signal will not be received in an OAM mode other than the transmission mode. However, if there is a partial obstruction in the transmission path, the wavefront of the electromagnetic wave with orbital angular momentum is disturbed by the obstruction, and electromagnetic waves in an OAM mode other than the transmission mode will be received (occurrence of crosstalk). The optical wireless communication system in this embodiment utilizes this property.

[0025] [Functional configuration of optical wireless communication system] The following describes the functional configuration of the optical wireless communication system 1. Fig. 2 is a block diagram showing the functional configuration of the optical wireless communication system 1 according to the first embodiment of the present invention.

[0026] As shown in FIG. 2, the transmitter 10 includes a communication laser diode (LD) 11, an OAM mode separation circuit 12, a transmission / reception control device 13, and a communication control device 14.

[0027] The communication laser diode 11 emits a communication beam CB (laser light) toward the receiver 20. The OAM mode separation circuit 12 includes a photodiode (not shown) and a spectrometer (not shown). The photodiode receives the pilot beam PB emitted from the receiver 20. The spectrometer separates the received pilot beam for each OAM mode. The photodiode and the spectrometer may be provided separately from the OAM mode separation circuit 12.

[0028] The transmission / reception control device 13 measures the reception level of the pilot beam PB for each OAM mode, and controls the transmission output of the communication beam CB based on the measured reception level. The communication control device 14 controls information communication for transmitting information to the receiver 20.

[0029] As shown in FIG. 2, the receiver 20 includes a communication photodiode (PD) 21, an OAM mode generating circuit 22, and a communication control device .

[0030] The communication photodiode 21 receives the communication beam CB emitted from the transmitter 10. The OAM mode generation circuit 22 is configured to include a laser diode (not shown). The laser diode emits a pilot beam PB toward the transmitter 10. The laser diode may be provided separately from the OAM mode generation circuit 22. The communication control device 23 controls the emission of the pilot beam PB by the OAM mode generation circuit 22 and controls information communication for receiving information transmitted from the transmitter 10.

[0031] The OAM mode generating circuit 22 and the OAM mode separating circuit 12 that transmit and receive the pilot beam PB emitted to cover the communication beam CB can be realized using a spiral phase plate (SPP) described in Non-Patent Document 1, for example.

[0032] [Threshold judgment processing] The following describes an example of the circuit configuration of the OAM mode separation circuit 12 for realizing threshold determination processing by the transmission and reception control device 13 of the transmitter 10. Fig. 3 is a block diagram showing the configurations of the OAM mode separation circuit 12 and the transmission and reception control device 13 in the first embodiment of the present invention.

[0033] 3, the OAM mode separation circuit 12 includes a spectrometer 121, four spiral phase plates (spiral phase plates (SPP) 121-1 to 121-4), five photodiodes (photodiodes (PD) 123-0 to 123-4), an adder circuit (Σ) 124, a divider circuit (÷) 125, and an analog-to-digital converter 126. The transmission / reception control device 13 includes a threshold determination unit 15.

[0034] Pilot beam PB of OAM mode +1 emitted from the laser diode of OAM mode generation circuit 22 of receiver 20 is received by the photodiode of OAM mode separation circuit 12 of transmitter 10. As shown in FIG. 3, pilot beam PB is split by spectrometer 121 into pilot beams PB equal to the number of OAM modes to be measured. The pilot beams PB split by spectrometer 121 are input to photodiodes (PD) 123-0 to 123-4, respectively, via spiral phase plates (SPP) 122-1 to 122-4, and the reception levels are measured for each OAM mode. The reception levels are measured by, for example, transmission / reception control device 13.

[0035] The adder circuit (Σ) 124 adds the outputs from the photodiodes 123-0, 123-2, 123-3, and 123-4. The divider circuit (÷) 125 divides the output from the photodiode 123-1 by the output from the adder circuit 124. The output from the divider circuit 125 is input to the transmission / reception control device 13.

[0036] The threshold determination unit 15 calculates the ratio of the reception level of the transmission mode to the sum of the reception levels of each OAM mode (i.e., OAM mode 0, OAM mode −1, and OAM mode ±2) other than the transmission mode (i.e., OAM mode +1) based on the input from the division circuit 125. The threshold determination unit 15 then determines whether the calculated ratio is equal to or greater than a threshold, and determines the transmission output of the communication beam CB according to the determination result.

[0037] Here, if the calculated ratio value is equal to or greater than the threshold value, the threshold determination unit 15 determines to set the transmission output of the communication beam CB to a normal output level, and if the calculated ratio value is less than the threshold value, determines to set the transmission output of the communication beam CB to a safe output level lower than the normal output level, because it is considered that crosstalk has occurred due to the OAM spiral wavefront being disturbed by the intruder.

[0038] The calculation of the sum of the reception levels of each OAM mode other than the transmission mode and the calculation of the above ratio value may be performed by an analog arithmetic circuit using an operational amplifier or the like, or may be performed by a digital circuit after the reception level for each OAM mode is AD (analog-to-digital) converted.

[0039] The communication laser diode 11 may be controlled entirely based on arithmetic processing using analog quantities without using the analog-to-digital converter (ADC) 126. Specifically, the transmission / reception control device 13 may use the calculated value of the ratio as is in analog quantities, drive the device in accordance with the value in analog quantities, and control the transmission output of the communication beam CB.

[0040] In this case, for example, the transmission / reception control device 13 is configured with a mechanical switch (such as an electromagnetic relay) or an electronic switch (such as a transistor), and controls the on / off switching and output strength of the communication laser diode 11 according to the calculated value of the ratio without AD conversion. In this way, by performing all arithmetic processing based on analog quantity values, it is possible to minimize processing delays and instantly control (reduce or stop transmission) the communication laser diode 11 when an intruder approaches, thereby realizing safer operation of optical wireless communication.

[0041] In accordance with the determination of the transmission output by the threshold determination unit 15, the communication beam CB is emitted into space from the communication laser diode 11 toward the receiver 20. The emitted communication beam CB is then received by the photodiode of the receiver 20.

[0042] [Transmitter operation] An example of the operation of the transmitter 10 will be described below. Fig. 4 is a flowchart showing the operation of the transmitter 10 in the first embodiment of the present invention. The operation of the transmitter 10 shown in the flowchart of Fig. 4 starts when a pilot beam PB is emitted from the receiver 20 toward the transmitter 10.

[0043] Pilot beam PB of OAM mode +1 emitted from the laser diode of OAM mode generation circuit 22 of receiver 20 is received by the photodiode of OAM mode separation circuit 12 of transmitter 10 (step S01). The received pilot beam PB is split into pilot beams PB equal to the number of OAM modes to be measured by spectrometer 121. The pilot beams PB split by spectrometer 121 are input to photodiodes (PD) 123-0 to 123-4, respectively, via spiral phase plates (SPP) 122-1 to 122-4, and the reception level is measured for each OAM mode.

[0044] The adder circuit (Σ) 124 adds the outputs from the photodiodes 123-0, 123-2, 123-3, and 123-4. The divider circuit (÷) 125 divides the output from the photodiode 123-1 by the output from the adder circuit 124. The output from the divider circuit 125 is input to the transmission / reception control device 13.

[0045] Threshold value determination unit 15 of transmission / reception control device 13 calculates the ratio of the reception level of the transmission mode (i.e., OAM mode +1) to the sum of the reception levels of each OAM mode (i.e., OAM mode 0, OAM mode −1, and OAM mode ±2) other than the transmission mode, based on the input from division circuit 125. Then, threshold value determination unit 15 determines whether the calculated ratio is equal to or greater than a threshold value (step S02).

[0046] If the calculated ratio value is greater than or equal to the threshold value (step S02: Yes), the threshold determination unit 15 determines that the transmission output of the communication beam CB should be set to the normal output level, and the communication beam CB at the normal output level is emitted into space from the communication laser diode 11 toward the receiver 20 (step S03).

[0047] On the other hand, if the calculated ratio is less than the threshold value (step S02: No), the threshold determination unit 15 determines to set the transmission output of the communication beam CB to a safe output level lower than the normal output level, and the communication beam CB at the safe output level is emitted into space from the communication laser diode 11 toward the receiver 20 (step S04). This completes the operation of the transmitter 10 shown in the flowchart of FIG.

[0048] As described above, the optical wireless communication system 1 in the first embodiment is a communication system that transmits information from the transmitter 10 to the receiver 20 using a communication beam CB. The receiver 20 transmits a pilot beam PB of a predetermined OAM mode having orbital angular momentum toward the transmitter 10 so as to cover the transmission path of the communication beam CB. When the transmitter 10 detects an OAM mode component (crosstalk) other than the predetermined OAM mode of the pilot beam PB, it controls the transmission output of the communication beam SB to be reduced.

[0049] With this configuration, the optical wireless communication system 1 in the first embodiment can detect intruders with high accuracy without using a large number of photodetector components or laser components, and without involving data processing such as image processing.

[0050] Furthermore, with this configuration, the optical wireless communication system 1 in the first embodiment can detect an intruder that attempts to enter the transmission path of the communication beam CB at a location far from the transmitter 10 or the receiver 20 in advance using the pilot beam PB before it comes into contact with the communication beam CB, and can prevent the high-power communication beam from being irradiated onto the intruder. This allows the optical wireless communication system 1 to operate the laser device safely so as not to cause harm to the human body.

[0051] Furthermore, with this configuration, the optical wireless communication system 1 in the first embodiment uses a beam having orbital angular momentum for the pilot beam PB, and therefore can further improve the detection accuracy of intruders compared to conventional techniques without using a huge number of photodetector components or laser components to increase resolution. Furthermore, the optical wireless communication system 1 can limit the area to be monitored to, for example, a cylindrical area with the transmission path of the communication beam CB as its central axis, and therefore can detect intruders without performing image processing or data processing on images captured by a camera.

[0052] Furthermore, by having such a configuration, the optical wireless communication system 1 in the first embodiment can transmit the communication beam CB using the same wavelength band as the pilot beam PB, because the power of the pilot beam PB is not present near the central axis of the transmission path of the communication beam CB due to the properties of the beam having orbital angular momentum.

[0053] Furthermore, with this configuration, the optical wireless communication system 1 in the first embodiment observes not only the decrease in the reception level of the pilot beam PB but also the reception level for each OAM mode, so that simple attenuation, which causes a uniform decrease in the reception levels of all OAM modes due to, for example, the atmosphere, can be prevented from being mistaken for attenuation due to the intrusion of an intruder. This makes it possible for the optical wireless communication system 1 to prevent an increase in the system downtime rate due to suppression of the transmission output of the communication beam CB, which is not actually required.

[0054] For ease of explanation, in the optical wireless communication system 1 of the first embodiment, one-way information transmission is performed between the opposing transmitter 10 and receiver 20, but the present invention is not limited to this. For example, the optical wireless communication system may be configured such that two opposing wireless devices each include a transmitter and a receiver, enabling two-way communication.

[0055] <Second embodiment> The optical wireless communication system according to the second embodiment will be described below.

[0056] One of the characteristics of electromagnetic waves with orbital angular momentum is that the beam diameter varies depending on the OAM mode. By utilizing this characteristic, it is possible to change the OAM mode of the pilot beam PB according to the size and movement speed of the expected intruder, thereby appropriately changing the diameter of the pilot beam PB. This configuration makes it possible to adaptively change the range to be monitored, thereby controlling the transmission output of the communication beam CB to suit the size and movement speed of the expected intruder.

[0057] Figure 5 is a diagram showing an example of the cross sections of a communication beam CB and a pilot beam PB. As shown in Figure 5, the diameter of the pilot beam PB3 in a higher-order OAM mode (mode +3 in Figure 5) is larger than that of the pilot beam PB1 in a lower-order OAM mode (mode +1 in Figure 5). In this way, the diameter of the pilot beam PB can be changed simply by changing the OAM mode used, making it possible to set an appropriate monitoring range depending on the application.

[0058] Furthermore, in OAM modes of higher orders than ±1, the center of the spatial power distribution is a cavity, and the higher the dimension of the OAM mode, the wider the cavity becomes. By utilizing this property, it is possible to form a pilot beam PB with a cross-sectional shape similar to a multi-ring by simultaneously superimposing and emitting multiple OAM mode beams (Figure 6). This configuration makes it possible to detect the direction of intrusion (direction of movement) of an intruding object.

[0059] Fig. 6 is a diagram showing an example of the cross section of a communication beam CB and a pilot beam PB composed of beams of multiple OAM modes. As shown in Fig. 6, when a pilot beam PB3 of OAM mode +3 and a pilot beam PB1 of OAM mode +1 overlap, the pilot beam PB3 of OAM mode +3 has a larger diameter.

[0060] When an intruder approaches a communication beam CB covered by a pilot beam PB with a cross-sectional shape like this multi-ring (case (1) in Figure 6), the intruder will first be detected by pilot beam PB3 in OAM mode +3, and then by pilot beam PB1 in OAM mode +1. Conversely, when the intruder moves from the vicinity of communication beam CB to outside the monitoring range (case (2) in Figure 6), the attenuation of pilot beam PB1 in OAM mode +1 will first be no longer observed, and then the attenuation of pilot beam PB3 in OAM mode +3 will no longer be observed.

[0061] Thus, the order in which changes in attenuation of the pilot beam PB of multiple OAM modes of different orders are observed varies depending on the direction of movement of the intruder. That is, if the intruder is moving from outside the observation range toward the communication beam CB, attenuation is observed starting with the pilot beam PB of the higher-order OAM mode. Conversely, if the intruder is moving from near the communication beam CB toward outside the observation range, attenuation is gradually lost starting with the pilot beam PB of the lower-order OAM mode.

[0062] With this configuration, the optical wireless communication system in the second embodiment can predict the moving direction of an intruder and the distance from the intruder to the communication beam CB. This makes it possible to, for example, switch the transmission output of the communication beam CB to a lower value earlier when the moving direction of the intruder is toward the communication beam CB, or to return the transmission output of the communication beam CB to its original high output earlier when the moving direction of the intruder is away from the communication beam CB, thereby improving safety and reducing the downtime rate.

[0063] Furthermore, with this configuration, the optical wireless communication system according to the second embodiment can predict the movement speed of an intruder, thereby enabling, for example, the transmission power of the communication beam CB to be switched to a lower level earlier when the movement speed of an intruder approaching the communication beam CB is relatively fast, or the transmission power of the communication beam CB to be switched to a lower level later when the movement speed of an intruder approaching the communication beam CB is relatively slow, thereby improving safety and reducing downtime.

[0064] [Optical configuration] Fig. 7 is a diagram illustrating an optical configuration of an optical wireless communication system 1a according to the second embodiment of the present invention. Fig. 7 illustrates an example of an optical configuration of a transmitter 10 and a receiver 20 for aligning the central axes of pilot beams PB of multiple OAM modes with the central axis of a communication beam CB.

[0065] 7, the transmitter 10 includes a communication laser diode (LD) 11, a transmission / reception control device 13, spiral phase plates (SPP) 122-1, 122-3, and 122-5, photodiodes (PD) 123-1, 123-3, and 123-5, beam splitters 127-1, 127-3, and 127-5, and mirrors 128-1, 128-3, and 128-5. Also, as shown in FIG. 7, the receiver 20 includes a communication photodiode (PD) 21, laser diodes 221-1, 221-2, and 221-3, spiral phase plates (SPP) 222-1, 222-3, and 222-5, mirrors 223-1, 223-3, and 223-5, and beam splitters 224-1, 224-3, and 224-5.

[0066] 7, the receiver 20 includes the same number of laser diodes (laser diodes 221-1, 221-2, 221-3) as the spiral phase plates (spiral phase plates 222-1, 222-3, 222-5), but the present invention is not limited to this configuration. For example, the receiver 20 may include a single laser diode, and the output light from the single laser diode may be branched and incident on each spiral phase plate (e.g., spiral phase plate 222-1, 222-3, 222-5).

[0067] In the above-described embodiment, the case where laser light is used for communication has been described as an example, but the present invention is not limited to this. For example, the laser light control method in the above-described embodiment can also be applied to wireless power transmission, which transmits energy wirelessly using powerful laser light.

[0068] According to the above-described embodiment, the optical wireless communication system includes a transmitting device and a receiving device. For example, the optical wireless communication system is the optical wireless communication system 1 in the embodiment, the transmitting device is the transmitter 10 in the embodiment, and the receiving device is the receiver 20 in the embodiment.

[0069] The above-mentioned transmitting device includes a communication beam transmitting unit, a detection beam receiving unit, and a control unit. For example, the communication beam transmitting unit is a communication laser diode 11 in the embodiment, the detection beam receiving unit is a photodiode included in the OAM mode separation circuit 12 in the embodiment, and the control unit is a transmission / reception control device 13 in the embodiment.

[0070] The communication beam transmitter emits a communication beam used to transmit desired information toward the receiving device. For example, the communication beam is a communication beam CB in the embodiment. The detection beam receiver receives a detection beam, which is a beam for object detection emitted from the receiving device so as to cover the transmission path of the communication beam. For example, the detection beam is a pilot beam PB in the embodiment. The control unit measures the reception level of the detection beam, and when attenuation of the reception level is detected, controls the communication beam transmitter to lower the transmission output of the communication beam.

[0071] The receiving device includes a communication beam receiving unit and a detection beam transmitting unit. For example, the communication beam receiving unit is a communication photodiode 21 in the embodiment, and the detection beam transmitting unit is a laser diode included in the OAM mode generating circuit 22 in the embodiment. The communication beam receiving unit receives the communication beam transmitted from the communication beam transmitting unit. The detection beam transmitting unit emits the detection beam to the transmitting device.

[0072] The detection beam may have orbital angular momentum of a predetermined Orbital Angular Momentum (OAM) mode.

[0073] The control unit may measure the reception levels of a plurality of detection beams in Orbital Angular Momentum modes having different orbital angular momenta, including a detection beam in a predetermined Orbital Angular Momentum mode. For example, the detection beams in Orbital Angular Momentum modes having different orbital angular momenta are pilot beam PB1 and pilot beam PB3 in the embodiment.

[0074] The control unit may control the communication beam transmission unit to lower the transmission output of the communication beam when the ratio of the reception level of the detection beam in the predetermined Orbital Angular Momentum mode to the sum of the reception levels of the detection beams in Orbital Angular Momentum modes other than the predetermined Orbital Angular Momentum mode is less than a predetermined threshold. For example, the sum of the reception levels of the detection beams in Orbital Angular Momentum modes other than the predetermined Orbital Angular Momentum mode is the sum of the reception levels of each OAM mode (i.e., OAM mode 0, OAM mode −1, and OAM mode ±2) other than the transmission mode (i.e., OAM mode +1) in the embodiment, and the reception level of the detection beam in the predetermined Orbital Angular Momentum mode is the reception level of the transmission mode in the embodiment.

[0075] A portion of the configuration of the transmitter 10 and the receiver 20 in the above-described embodiment may be implemented by a computer. In this case, a program for implementing the functions may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" as used herein includes hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system. Furthermore, the term "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within a computer system serving as a server or client. The program may be for implementing a portion of the above-described functions, or may be capable of implementing the above-described functions in combination with a program already stored in the computer system, or may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0076] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Explanation of symbols]

[0077] 1, 1a... Optical wireless communication system, 10... Transmitter, 11... Communication laser diode (LD), 12... OAM mode separation circuit, 13... Transmission / reception control device, 14... Communication control device, 15... Threshold value determination unit, 20... Receiver, 21... Communication photodiode (PD), 22... OAM mode generation circuit, 23... Communication control device, 121... Spectrometer, 122-1 to 122-5... Spiral phase plates (SPP), 123-0 to 123 -5...Photodiode (PD), 124...Adding circuit (Σ), 125...Dividing circuit (÷), 126...Analog-to-digital converter, 127-1 to 127-5...Beam splitters, 128-1 to 128-5...Mirrors, 221-1 to 221-3...Laser diodes, 222-1 to 222-5...Spiral phase plates (SPP), 223-1 to 223-5...Mirrors, 224-1 to 224-5...Beam splitters

Claims

1. An optical wireless communication system having a transmitting device and a receiving device, The transmitting device a communication beam transmitter that emits a communication beam used to transmit desired information toward the receiving device; a detection beam receiving unit that receives a detection beam, which is a beam for detecting an object and in which crosstalk occurs due to the entry of an object, and which is emitted from the receiving device so as to cover the transmission path of the communication beam; a control unit that controls the communication beam transmitting unit to lower the transmission output of the communication beam when the crosstalk is detected in the detection beam; Equipped with The receiving device a communication beam receiving unit that receives the communication beam transmitted from the communication beam transmitting unit; a detection beam transmitter that emits the detection beam to the transmitter; An optical wireless communication system comprising:

2. An optical wireless communication system having a transmitting device and a receiving device, The transmitting device a communication beam transmitter that emits a communication beam used to transmit desired information toward the receiving device; a detection beam receiving unit that receives a detection beam, which is a beam for object detection emitted from the receiving device so as to cover the transmission path of the communication beam; a control unit that measures a reception level of the detection beam, and when attenuation of the reception level is detected, controls the communication beam transmission unit to lower the transmission output of the communication beam; Equipped with The receiving device a communication beam receiving unit that receives the communication beam transmitted from the communication beam transmitting unit; a detection beam transmitter that emits the detection beam to the transmitter; Equipped with The detection beam has an orbital angular momentum of a predetermined orbital angular momentum mode. Optical wireless communication system.

3. The control unit measures the reception levels of the detection beams in a plurality of orbital angular momentum modes having different orbital angular momentums, including the detection beam in the predetermined orbital angular momentum mode.

3. The optical wireless communication system according to claim 2.

4. The control unit controls the communication beam transmission unit to reduce the transmission output of the communication beam when a ratio of a reception level of the detection beam in the predetermined Orbital Angular Momentum mode to a sum of reception levels of the detection beams in Orbital Angular Momentum modes other than the predetermined Orbital Angular Momentum mode is less than a predetermined threshold.

4. The optical wireless communication system according to claim 3.

5. A computer-implemented optical wireless communication method, comprising: a detection beam transmission step in which the computer of the receiving device emits a detection beam, which is a beam for detecting an object that generates crosstalk due to the intrusion of an object, to the transmitting device so as to cover a transmission path of a communication beam used to transmit desired information; a detection beam receiving step in which the computer of the transmitting device receives the detection beam transmitted from the receiving device; a control step of causing the computer of the transmitting device to control the transmission output of the communication beam to be lowered when the crosstalk is detected in the detection beam; a communication beam transmitting step in which the computer of the transmitting device emits the communication beam toward the receiving device; a communication beam receiving step in which the computer of the receiving device receives the communication beam emitted from the transmitting device; An optical wireless communication method comprising:

6. a communication beam transmitter that emits a communication beam used to transmit desired information toward a receiving device; a detection beam receiving unit that receives a detection beam, which is a beam for detecting an object and in which crosstalk occurs due to the entry of an object, and which is emitted from the receiving device so as to cover the transmission path of the communication beam; a control unit that controls the communication beam transmitting unit to lower the transmission output of the communication beam when the crosstalk is detected in the detection beam; An optical transmitting device comprising:

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