JP7776783B2 - Optical wireless communication system, optical wireless communication method, and optical transmitter - Google Patents

Description

The present invention relates to an optical wireless communication system, an optical wireless communication method, and an optical transmitting device.

Some optical wireless communication systems are susceptible to factors that degrade communication quality, such as atmospheric turbulence and particulate matter in the air. One way to achieve longer distances and faster communication 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.

In order to meet the above safety standards, it is possible to designate areas where laser light is used as off-limits zones. However, in this case, it would be 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, for example, flying vehicles, it could become an area where humans may enter. Therefore, it would be 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.

In light of this, methods are being considered to prevent laser light from being irradiated onto the human body without establishing restricted areas. For example, when a person or object is likely to enter the transmission path through which the laser light passes, one possible method would be to limit the transmission output of the laser light to a safe level in accordance with the safety standards mentioned above, or to shut off the laser light.

Conventionally, in optical wireless communication between mobile units, optical wireless communication systems have been considered that use object detection devices such as cameras, radar, or ultrasonic sensors to detect nearby people or objects, and share the detection results between the mobile units to control the position of the mobile units so that people or objects are not positioned in the transmission path of the communication laser light (hereinafter also referred to as "communication beam") (see, for example, Patent Document 1). In optical wireless communication between mobile units, such a method of controlling the mobile units can achieve safe optical wireless communication that prevents the communication beam from irradiating human bodies.

On the other hand, if neither the transmitting station nor the receiving station is mobile, the above-mentioned control method cannot be used. Therefore, for such cases, optical wireless communication systems are being considered that detect an intruder that has entered the transmission path of a communication beam by observing that the communication beam itself has been blocked (see, for example, Patent Document 2). For such cases, optical wireless communication systems are being considered that transmit an intruder detection laser beam (hereinafter referred to as a "pilot beam") that is output within an output range safe for humans on a transmission path parallel to the communication beam, and determine that the communication beam has been blocked by observing that the pilot beam has been blocked (see, for example, Patent Document 3).

In response to such cases, an optical wireless communication system has been considered in which a communication beam is surrounded by a pilot beam that is output within an output range safe for the human body, and by observing whether 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 depending on the detection results (see, for example, Patent Document 4). With this configuration, an optical wireless communication system can be realized that can output laser light with a higher transmission power while preventing the communication beam from being irradiated onto human bodies by monitoring the presence of people or objects approaching the communication beam.

Patent No. 6656459 U.S. Pat. No. 5,229,593 US Patent Application Publication No. 2004/0227057 U.S. Patent No. 6,633,026

"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>

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 data processing device with high processing performance is used, the time required for computational processing may be long and the response speed may be slow. This could potentially compromise safety. Furthermore, the optical wireless communication system described in Patent Document 1 requires cameras and other devices, but because cameras have finite resolution, 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.

Furthermore, with 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 a high-power communication beam is irradiated onto the human body before the intrusion is detected. Furthermore, with the technology described in Patent Document 3, as with the technology described in Patent Document 2, there is a possibility that a high-power communication beam may be irradiated onto the human body before the intrusion is detected.

The technology described in Patent Document 4 can detect an intrusion by observing a drop in reception level due to the interruption of a pilot beam surrounding a high-power communication beam, thereby enabling safe optical wireless communication without irradiating the communication beam onto human bodies. However, because the laser light used in the pilot beam propagates through space while spreading to a certain 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 a drop in reception level. To address this issue, one possible method is to improve resolution and increase sensitivity for detecting intrusions by, for example, dividing the light-receiving section of the pilot beam into smaller parts and using multiple photodiodes. However, this method is expected to pose the problem of increasing the number of components, such as photodiodes.

The present invention has been made in consideration of the above-mentioned technical background, and aims to provide technology that can achieve optical wireless communication without unintentionally irradiating high-power communication beams onto objects, while suppressing increases in device costs, computational complexity, and power consumption.

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 so as 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.

One aspect of the present invention is a computer-implemented optical transmission method for 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 lowered; 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.

One aspect of the present invention is an optical transmission device comprising: a communication beam transmitter that emits a communication beam used to transmit desired information toward a receiving device; a detection beam receiver 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; 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 transmitter to lower the transmission output of the communication beam.

This invention makes it possible to provide technology that can achieve optical wireless communication without unintentionally irradiating high-power communication beams onto objects, while minimizing increases in device costs, computational complexity, and power consumption.

1 is a diagram illustrating the overall configuration of an optical wireless communication system 1 according to a first embodiment of the present invention. 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. 1 is a block diagram showing the configuration of an OAM mode separation circuit 12 and a transmission/reception control device 13 according to a first embodiment of the present invention. 4 is a flowchart showing the operation of the transmitter 10 according to the first embodiment of the present invention. 1 is a diagram showing an example of a cross section of a communication beam CB and a pilot beam PB. FIG. A figure showing an example of a cross section of a communication beam CB and a pilot beam PB composed of beams of multiple OAM modes. FIG. 10 is a diagram illustrating an optical configuration of an optical wireless communication system 1a according to a second embodiment of the present invention.

The following describes embodiments of an optical wireless communication system, an optical wireless communication method, and an optical transmitting device with reference to the drawings.

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 detects in advance a person or object that is attempting to intrude into the transmission path of the communication beam and controls the transmission power of the communication beam according to the detection results, thereby realizing safe optical wireless communication (preventing unintentional irradiation of an object with a high-power communication beam). The optical wireless communication system 1 can detect an intruder through simple information processing based on observation results in 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.

[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.

The optical wireless communication system of this embodiment communicates 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 intrusions, 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 Figure 1.

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 these superimposed signals.

Furthermore, a classification of the state of electromagnetic waves 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 in a plane perpendicular to the propagation direction. In OAM communication using a single OAM mode, in an ideal space free of obstructions and noise, signals will not be received in OAM modes 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 OAM modes other than the transmission mode are received (occurrence of crosstalk). The optical wireless communication system in this embodiment utilizes this property.

[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.

As shown in Figure 2, the transmitter 10 is composed of a communication laser diode (LD) 11, an OAM mode separation circuit 12, a transmission/reception control device 13, and a communication control device 14.

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. Note that the photodiode and spectrometer may be provided separately from the OAM mode separation circuit 12.

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 the information communication that transmits information to the receiver 20.

As shown in Figure 2, the receiver 20 is composed of a communication photodiode (PD) 21, an OAM mode generating circuit 22, and a communication control device 23.

The communication photodiode 21 receives the communication beam CB emitted from the transmitter 10. The OAM mode generation circuit 22 includes a laser diode (not shown). The laser diode emits a pilot beam PB toward the transmitter 10. Note that 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 communications that receive information transmitted from the transmitter 10.

The OAM mode generation circuit 22 and OAM mode separation circuit 12, which transmit and receive the pilot beam PB emitted to cover the communication beam CB, can be realized, for example, using a spiral phase plate (SPP) as described in non-patent document 1.

[Threshold Determination Processing]
An example of the circuit configuration of the OAM mode separation circuit 12 for realizing threshold determination processing by the transmission/reception control device 13 of the transmitter 10 will be described below. Fig. 3 is a block diagram showing the configuration of the OAM mode separation circuit 12 and the transmission/reception control device 13 in the first embodiment of the present invention.

As shown in FIG. 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 also includes a threshold determination unit 15.

The pilot beam PB of OAM mode +1 emitted from the laser diode of the OAM mode generation circuit 22 of the receiver 20 is received by the photodiode of the OAM mode separation circuit 12 of the transmitter 10. As shown in FIG. 3, the pilot beam PB is split by the spectrometer 121 into pilot beams PB equal to the number of OAM modes being measured. The pilot beams PB split by the 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. The reception level is measured, for example, by the transmission/reception control device 13.

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

Based on the input from the division circuit 125, 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).The threshold determination unit 15 then determines whether the calculated ratio is greater than or equal to a threshold, and determines the transmission output of the communication beam CB depending on the determination result.

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 the normal output level, and if the calculated ratio value is less than the threshold value, it determines to set the transmission output of the communication beam CB to a safe output level lower than the normal output level. This is because it is believed that crosstalk has occurred due to the OAM spiral wavefront being disrupted by the intruder.

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

In addition, the configuration may be such that the communication laser diode 11 is controlled entirely based on calculations 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 an analog quantity, drive according to the analog quantity, and control the transmission output of the communication beam CB.

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 A-D conversion. In this way, by performing all calculations based on analog values, processing delays are minimized and the communication laser diode 11 can be instantly controlled (reduced or stopped) when an intruder approaches, making it possible to achieve safer optical wireless communication operations.

In accordance with the transmission output determined 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.

[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.

The pilot beam PB of OAM mode +1 emitted from the laser diode of the OAM mode generation circuit 22 of the receiver 20 is received by the photodiode of the OAM mode separation circuit 12 of the transmitter 10 (step S01). The received pilot beam PB is split by the spectrometer 121 into pilot beams PB equal to the number of OAM modes being measured. The pilot beams PB split by the 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.

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

Based on the input from the division circuit 125, the threshold determination unit 15 of the transmission/reception control device 13 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).The threshold determination unit 15 then determines whether the calculated ratio is greater than or equal to the threshold (step S02).

If the calculated ratio value is greater than or equal to the threshold value (step S02, Yes), the threshold determination unit 15 decides to set the transmission output of the communication beam CB 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).

On the other hand, if the calculated ratio is less than the threshold value (step S02, No), the threshold determination unit 15 determines that the transmission output of the communication beam CB should be set 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 Figure 4.

As described above, the optical wireless communication system 1 in the first embodiment is a communication system that transmits information from a transmitter 10 to a 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.

By having 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.

Furthermore, by having such a configuration, the optical wireless communication system 1 in the first embodiment can detect an intruder attempting to enter the transmission path of the communication beam CB at a location far from the transmitter 10 or receiver 20 in advance using the pilot beam PB before it comes into contact with the communication beam CB, thereby preventing the high-power communication beam from being irradiated onto the intruder. This allows the optical wireless communication system 1 to operate laser equipment safely so as not to cause harm to the human body.

Furthermore, by having such a configuration, the optical wireless communication system 1 in the first embodiment uses a beam with orbital angular momentum for the pilot beam PB, and therefore, compared to conventional technology, can further improve the detection accuracy of intruders 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 region whose central axis is the transmission path of the communication beam CB, and therefore can detect intruders without requiring work such as image processing of images captured by a camera or data processing.

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.

Furthermore, by having such a configuration, the optical wireless communication system 1 in the first embodiment monitors not only the decrease in the reception level of the pilot beam PB but also the reception level for each OAM mode, thereby preventing simple attenuation, such as that caused by the atmosphere, which causes a uniform decrease in the reception levels of all OAM modes, from being mistaken for attenuation caused by the intrusion of an intruding object. This allows the optical wireless communication system 1 to prevent an increase in the system downtime rate due to the suppression of the transmission output of the communication beam CB, which is not actually necessary.

In the optical wireless communication system 1 in the first embodiment, for simplicity of explanation, one-way information transmission is performed between the opposing transmitter 10 and receiver 20, but this is not limited to this. For example, the optical wireless communication system may be configured such that two opposing radio devices each have a transmitter and a receiver, allowing for two-way communication.

Second Embodiment
The optical wireless communication system according to the second embodiment will be described below.

One of the characteristics of electromagnetic waves with orbital angular momentum is that the beam diameter varies depending on the OAM mode. 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 anticipated 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 anticipated intruder.

Figure 5 shows an example of the cross sections of the communication beam CB and the 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.

Furthermore, in OAM modes of higher orders than OAM mode ±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 characteristic, it is possible to form a pilot beam PB with a cross-sectional shape similar to a multi-ring by simultaneously emitting multiple OAM mode beams in a superimposed manner (Figure 6). This configuration makes it possible to detect the direction of entry (direction of movement) of an intruding object.

Figure 6 shows 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 Figure 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.

When an intruder approaches a communication beam CB covered by a pilot beam PB with such a multi-ring-like cross-sectional shape (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 an 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 cease to be observed, and then the attenuation of pilot beam PB3 in OAM mode +3 will cease to be observed.

As such, the order in which changes in attenuation of pilot beams PB of multiple OAM modes of different orders are observed varies depending on the direction of movement of the intruder. In other words, if the direction of movement of the intruder is from outside the observation range toward the communication beam CB, attenuation is observed starting with pilot beams PB of higher-order OAM modes. Conversely, if the direction of movement of the intruder is from near the communication beam CB toward outside the observation range, attenuation is no longer observed starting with pilot beams PB of lower-order OAM modes.

By having such a configuration, the optical wireless communication system in the second embodiment can predict the movement 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 power of the communication beam CB to a lower level earlier when the movement direction of the intruder is toward the communication beam CB, or to return the transmission power of the communication beam CB to its original high level earlier when the movement direction of the intruder is away from the communication beam CB, thereby increasing safety and reducing downtime.

Furthermore, by having such a configuration, the optical wireless communication system in the second embodiment can predict the movement speed of an intruder. This makes it possible, for example, to switch the transmission power of the communication beam CB to a lower level earlier if the movement speed of an intruder approaching the communication beam CB is relatively fast, or to switch the transmission power of the communication beam CB to a lower level later if the movement speed of an intruder approaching the communication beam CB is relatively slow, thereby increasing safety and reducing downtime.

[Optical configuration]
7 is a diagram showing an optical configuration of an optical wireless communication system 1a according to a second embodiment of the present invention, which shows an example of an optical system configuration including a transmitter 10 and a receiver 20 for aligning the central axes of pilot beams PB and communication beams CB of multiple OAM modes.

As shown in FIG. 7, the transmitter 10 is composed of a communication laser diode (LD) 11, a transmission/reception control device 13, spiral phase plates (SPP) 122-1, 122-3, 122-5, photodiodes (PD) 123-1, 123-3, 123-5, beam splitters 127-1, 127-3, 127-5, and mirrors 128-1, 128-3, 128-5. 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.

In the optical configuration of the optical wireless communication system 1a illustrated in Figure 7, the receiver 20 is equipped with 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 this configuration is not limited to this. For example, the receiver 20 may be equipped with 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 plates 222-1, 222-3, 222-5).

In the above-described embodiment, the use of laser light for communication has been described as an example, but this 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, in which energy is transmitted wirelessly using powerful laser light.

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

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.

The communication beam transmitter emits a communication beam used to transmit desired information toward the receiving device. For example, the communication beam is 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 pilot beam PB in the embodiment. The control unit measures the reception level of the detection beam, and if attenuation of the reception level is detected, controls the communication beam transmitter to lower the transmission output of the communication beam.

The above-mentioned 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 provided in the OAM mode generating circuit 22 in the embodiment. The above-mentioned communication beam receiving unit receives the communication beam transmitted from the communication beam transmitting unit. The above-mentioned detection beam transmitting unit emits the detection beam to the transmitting device.

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

The control unit may also measure the reception levels of multiple detection beams in Orbital Angular Momentum modes with 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 with different orbital angular momenta are pilot beam PB1 and pilot beam PB3 in the embodiment.

The control unit may also 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 specified Orbital Angular Momentum mode to the sum of the reception levels of the detection beams in Orbital Angular Momentum modes other than the specified Orbital Angular Momentum mode is less than a specified threshold. For example, the sum of the reception levels of the detection beams in Orbital Angular Momentum modes other than the specified 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 in the embodiment (i.e., OAM mode +1), and the reception level of the detection beam in the specified Orbital Angular Momentum mode is the reception level of the transmission mode in the embodiment.

Part of the configuration of the transmitter 10 and receiver 20 in the above-described embodiments may be implemented by a computer. In this case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" here includes hardware such as an OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system. Furthermore, "computer-readable recording medium" may also include media that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks such as the Internet or telephone lines, or media that store programs for a fixed period of time, such as volatile memory within the computer system that serves as the server or client. The program may be designed to implement part of the aforementioned functions, or may be capable of implementing the aforementioned 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).

The above describes in detail an embodiment of the present invention with reference to the drawings, but the specific configuration is not limited to this embodiment and also includes designs that do not deviate from the gist of the present invention.

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 determination unit, 20...receiver, 21...communication photodiode (PD), 22...OAM mode generation circuit, 23...communication control device, 121...spectroscope, 122-1 to 122-5...spiral phase plates (SPP), 123-0 to 123 -5...photodiode (PD), 124...addition circuit (Σ), 125...division 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 (6)

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: 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
An optical wireless communication system, wherein the detection beam has an orbital angular momentum of a predetermined orbital angular momentum mode. 3. The optical wireless communication system according to claim 2, wherein the control unit measures the reception levels of the detection beams in a plurality of Orbital Angular Momentum modes having different orbital angular momenta, including the detection beam in the predetermined Orbital Angular Momentum mode. 4. The optical wireless communication system according to claim 3, wherein the control unit controls the communication beam transmitting unit to reduce the transmission output of the communication beam when a ratio of the reception level of the detection beam in the specified Orbital Angular Momentum mode to the sum of the reception levels of the detection beam in Orbital Angular Momentum modes other than the specified Orbital Angular Momentum mode is less than a specified threshold. 1. 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: 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: