WO2023281733A1

WO2023281733A1 - Underwater optical communication system

Info

Publication number: WO2023281733A1
Application number: PCT/JP2021/025964
Authority: WO
Inventors: 和真大脇
Original assignee: 株式会社島津製作所
Priority date: 2021-07-09
Filing date: 2021-07-09
Publication date: 2023-01-12
Also published as: TW202306338A

Abstract

Provided is an underwater optical communication system 50 in which communications are conducted between a first optical communication device 1 placed on a fixed structure 51 that is fixed under water WA and a second optical communication device 2 placed on a movable body 52 that moves under water WA, each of the first optical communication device 1 and the second optical communication device 2 comprising: a laser light source 3 or 4 for emitting communication lights TL that are laser lights; and a light receiving unit 5 or 6 for receiving the communication lights TL. The underwater optical communication system 50 further comprises a reflection member 11 that reflects at least part of the communication lights TL emitted from the laser light source 3 or 4 comprised by one of the first optical communication device 1 and the second optical communication device 2 and that causes the light receiving unit 5 or 6 comprised by the other of the first optical communication device 1 and the second optical communication device 2 to receive the reflected communication lights TL.

Description

underwater optical communication system

The present invention relates to an underwater optical communication system that performs optical communication underwater.

Conventionally, communication using sound waves with low attenuation underwater was used as an underwater wireless communication means for transmitting data from underwater vehicles that conduct underwater exploration. Such wireless communication using sound waves has a problem that only a low communication speed of about several tens of kbps can be realized due to the low propagation speed of sound waves in water and the low frequency of sound waves.

Therefore, in recent years, as an underwater wireless communication means, an optical wireless communication system using an underwater optical communication device that uses visible light as communication light has been proposed. An underwater optical communication device includes a laser light source that emits visible laser light and a light receiving section that receives the laser light emitted from the laser light source. As an example of an optical wireless communication system, a first underwater optical communication device provided in a moving body that navigates underwater and a second underwater optical communication device provided in a base station fixedly installed underwater. There is a configuration in which wireless communication is performed by mutually transmitting communication light between them (for example, Patent Documents 1 and 2).

Compared to sound waves, visible light has a relatively small attenuation in water. Since visible light has a higher propagation speed and frequency than sound waves, optical wireless communication using visible light can achieve a high communication speed of several tens of Mbps. Therefore, visible light wireless communication enables high-speed communication of large amounts of information such as moving images.

JP 2018-007069 A JP 2019-114939 A

However, the conventional example having such a configuration has the following problems.

Since communication light has higher directivity than general electromagnetic waves such as sound waves, there are restrictions on the directions in which a single optical wireless communication device can transmit communication light. Therefore, as shown in FIG. 12, when the underwater optical communication device 102 is installed so as to transmit the communication light TL toward the front (to the left in the drawing) of the moving body 101 navigating the underwater WA, the moving body The underwater optical communication device 102 mounted on the mobile body 101 cannot transmit the communication light TL to the side or rear of the moving body 101. FIG.

Therefore, as shown in FIG. 12, when the moving body 101 is sailing underwater so as to turn its back to the base station 103 in which the underwater optical communication device 104 is arranged, the moving body 101 will move to the underwater optical communication device 102. can not be used to perform optical communication with the underwater optical communication device 104 of the base station 103 . In order to enable optical communication with the underwater optical communication device 104, it is necessary to change the direction of the moving body 101 underwater so that the moving body 101 and the base station 103 face each other. Since it takes time to change direction underwater, underwater optical communication may be interrupted for a certain period of time.

As a method of relaxing such restrictions on communication directions and enabling continuous communication, as shown in FIG. A configuration in which TL can be transmitted is conceivable. However, there is a concern that increasing the number of underwater optical communication devices 102 mounted on the moving body 101 will inevitably increase the size and weight of the moving body 101 . Further, for example, when observing a narrow space, it is necessary to limit the size of the moving object 101 to a certain size or less depending on the observation target and the observation environment. In this case, it is difficult to add the underwater optical communication device 102 to the moving object 101 .

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an underwater optical communication system capable of communicating over a wider range while avoiding the addition of underwater optical communication devices.

In order to achieve these objects, the present invention has the following configuration.
That is, one aspect of the present invention is a first optical communication device installed on a fixed structure that is fixed underwater, and a second optical communication device installed on a moving object that moves underwater. wherein each of the first optical communication device and the second optical communication device includes an optical transmitter that transmits laser light and a light transmitter that receives the laser light and an optical receiver, wherein the underwater optical communication system receives at least part of the laser light emitted from the optical transmitter included in one of the first optical communication device and the second optical communication device. The optical communication device further includes an optical reflection unit that reflects and causes the optical reception unit provided in the other of the first optical communication device and the second optical communication device to receive the reflected laser light.

In an underwater optical communication system according to the present invention, a first optical communication device arranged on a fixed structure fixed underwater, and a second optical communication device arranged on a moving body moving underwater. An underwater optical communication system for communicating with a device, comprising a light reflector. The light reflecting section reflects at least part of the laser light transmitted from the light transmitting section provided in one of the first optical communication device and the second optical communication device, and transmits the reflected laser light to the first optical communication device. An optical receiving unit provided in the other of the optical communication device and the second optical communication device is caused to receive the signal.

In the underwater optical communication system according to this embodiment, by using the light reflector, not only direct underwater optical communication in which the laser light transmitted from the light transmitter is directly received by the light receiver, but also It also enables indirect underwater optical communication in which a laser beam transmitted and reflected by a light reflecting portion is received by a light receiving portion. In indirect underwater optical communication, by reflecting the laser beam emitted from the light transmitting part into the water with the light reflecting part, the traveling direction of the laser beam is changed to a direction different from the direction in which the laser beam was originally emitted. can. As an example, by reflecting the laser light emitted forward of the moving body by the light reflecting portion, the reflected laser light can be transmitted to the side or rear of the moving body.

For this reason, indirect underwater optical communication can be used even in a range where direct underwater optical communication is impossible for a moving object that is limited in the number and size of the second optical communication device that can be mounted. If so, communication becomes possible. Therefore, by enabling indirect communication in which the light reflected by the light reflecting portion is received, the communicable range of the mobile body can be dramatically expanded without adding a second optical communication device to the mobile body.

1 is a front view illustrating a schematic configuration of an underwater optical communication system according to a first embodiment; FIG. 1 is a functional block diagram illustrating the configuration of an underwater optical communication system according to a first embodiment; FIG. FIG. 4 is a front view for explaining a state in which underwater optical communication is performed by direct communication in the first embodiment; FIG. 4 is a front view for explaining a state in which underwater optical communication is performed by indirect communication in the first embodiment; FIG. 4 is a plan view for explaining a state in which underwater optical communication is performed by indirect communication in the first embodiment; FIG. 10 is a vertical cross-sectional view illustrating a schematic configuration of an underwater optical communication system according to a second embodiment; FIG. 11 is a cross-sectional view for explaining a state in which underwater optical communication is performed by direct communication in the second embodiment; FIG. 11 is a cross-sectional view for explaining a state in which underwater optical communication by direct communication is blocked by a shield in the second embodiment; FIG. 11 is a cross-sectional view for explaining a state in which underwater optical communication is performed by indirect communication in the second embodiment; FIG. 10 is a plan view showing a state in which underwater optical communication is performed by indirect communication in a modified example; FIG. 11 is a front view showing a state in which underwater optical communication is performed by indirect communication in a modified example; FIG. 10 is a diagram showing a state in which underwater optical communication is performed and its problems in a conventional configuration; It is a figure which shows the problem in a conventional form.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1st embodiment

<Explanation of overall configuration>
A schematic configuration of an underwater optical communication system 50 according to the first embodiment will be described with reference to FIG. 1 and the like. In the first embodiment, a communication system that performs underwater optical communication in the deep sea or the bottom of a lake will be described as an example. Note that, as shown in FIG. 1 and the like, two horizontal directions orthogonal to each other are defined as the x direction and the y direction, respectively. The x-direction corresponds to the left-right horizontal direction in the drawing. Also, let the vertical direction be the z-direction.

As shown in FIG. 1, an underwater optical communication system 50 includes a first optical communication device 1, a second optical communication device 2, and a reflector 11 in an underwater WA, for example, underwater.

The first optical communication device 1 is arranged on a fixed structure 51 installed on the bottom of the water WB. An example of the fixed structure 51 is an observation base station. The fixed structure 51 is connected to an external station (not shown) via a cable. Examples of external stations include ships located on water or ground bases located on the ground.

The second optical communication device 2 is installed on a moving body 52 that moves in the underwater WA. The moving body 52 moves through the underwater WA to inspect an underwater structure such as a pipeline. Examples of the moving body 52 include an ROV (Remotely Operated Vehicle) or an AUV (Autonomous Underwater Vehicle).

As shown in FIG. 2, the first optical communication device 1 includes a laser light source 3, an optical receiver 5, and a controller 7. The second optical communication device 2 includes a laser light source 4 , an optical receiver 6 , a controller 8 and an observation device 9 .

The laser light source 3 and the laser light source 4 each have a semiconductor laser and a collimator lens, and the laser light generated by the semiconductor laser is adjusted by the collimator lens and emitted to the underwater WA as communication light TL containing communication information. As shown in FIG. 1, the communication light TL passes through the windows WD provided in each of the first optical communication device 1 and the second optical communication device 2 and is emitted to the underwater WA. The laser light source 3 and the laser light source 4 correspond to the light transmitting section in the present invention.

The optical receiver 5 receives laser light emitted from the laser light source 4 provided in the second optical communication device 2 . The control unit 7 includes a central processing unit (CPU: Central Processing Unit) and the like, and performs various processes on information contained in the laser light received by the optical receiving unit 5, and also controls the operation of the first optical communication device. 1, and controls the components provided in 1. That is, the control unit 7 generates communication information such as image information or moving image information by performing various types of information processing on the signal of the communication light TL that has undergone photoelectric conversion and amplification processing.

The optical receiver 6 receives laser light emitted from the laser light source 3 provided in the first optical communication device 1 . The control unit 8 performs various processes on the information contained in the laser beam received by the optical receiving unit 6 to generate communication information, and also performs overall control of each component provided in the second optical communication device 2 . . The observation device 9 is, for example, an underwater camera, observes an observation target in the underwater WA, and acquires information such as images or moving images.

The optical receiver 5 and the optical receiver 6 each have a light receiving element. Each of the light-receiving elements is configured to receive light, for example, communication light TL, and perform photoelectric conversion. Examples of light receiving elements include photomultiplier tubes and avalanche photodiodes. The light-receiving element is arranged inside a protective container, which is a sealed water-pressure-resistant container, and is isolated from the external environment such as an underwater WA.

In this embodiment, the moving body 52 is a relatively small structure, and is equipped with one second optical communication device 2 as shown in FIG. The second optical communication device 2 is provided with a window portion WD and the like so that the communication light TL can be emitted toward the traveling direction FW of the moving object 52 . On the other hand, the fixed structure 51 is a relatively large structure, and is capable of mounting a plurality of first optical communication devices 1 thereon.

The plurality of first optical communication devices 1 mounted on the fixed structure 51 are arranged so that their windows WD face different directions. Since the respective windows WD face different directions, light incident on the fixed structure 51 from various directions is received by any one of the first optical communication devices 1 . Further, by using any one of the first optical communication devices 1, the communication light TL can be emitted from the fixed structure 51 in various directions. The spread angle θ of the communication light TL emitted from the first optical communication device 1 or the second optical communication device 2 is, for example, approximately 40°.

As an example, the reflector 11 is installed on the bottom of the water WB and reflects the communication light TL. Examples of the material forming the reflector 11 include a reflecting mirror or a prism. When the reflector 11 is a reflecting mirror, examples of the configuration include a specular reflecting mirror whose reflecting surface is a mirror surface, or a frosted glass-like scattering reflecting mirror whose reflecting surface is subjected to scattering treatment. More preferably, the reflector 11 is a scattering reflection mirror in that the reflected communication light TL is radially reflected at a wider spread angle.

In the reflector 11, the shape of the reflective surface that reflects light may be planar or may have a curved surface. In this embodiment, it is assumed that the reflector 11 is a plate-shaped member installed on the bottom of the water WB. In the first embodiment, the reflector 11 corresponds to the light reflector in the invention.

The reflector 11 is fixedly arranged around the fixed structure 51 . Specifically, a predetermined number of reflectors 11 are arranged inside a circular area centered on the fixed structure 51 and having a radius equal to the reachable distance F of the communication light TL. The position and orientation at which the reflector 11 is arranged reflect the communication light TL emitted from one of the first optical communication device 1 and the second optical communication device 2, It is predetermined to be incident on the other of the second optical communication devices 2 .

That is, the optical receiver 5 provided in the first optical communication device 1 not only directly receives the communication light TL emitted from the laser light source 4, but also receives the communication light TL after it is emitted from the laser light source 4 and reflected by the reflector 11. It is configured to be able to receive the communication light TL (reflected communication light TLR). Similarly, the optical receiver 6 provided in the second optical communication device 2 not only directly receives the communication light TL emitted from the laser light source 3, but also receives the communication light TL after it is emitted from the laser light source 3 with a reflector 11. It is configured to receive reflected communication light TL (reflected communication light TLR).

Thus, the first optical communication device 1 and the second optical communication device 2 not only directly transmit and receive the communication light TL to each other, but also indirectly transmit and receive the communication light TL via the reflector 11. It is configured to perform underwater optical wireless communication. By previously adjusting the direction in which the light reflecting surface of the reflector 11 faces, the direction in which the reflected communication light TLR travels can be arbitrarily determined.

<Usage example of the first embodiment>
Here, a usage example of the underwater optical communication system 50 according to the first embodiment will be described. In the first embodiment, a case where the second optical communication device 2 transmits laser light to the first optical communication device 1 will be described as an example. That is, the moving object 52 navigates in the underwater WA along the traveling direction FW, performs inspection by the observation device 9, and acquires inspection information such as moving images. The second optical communication device 2 converts the obtained inspection information into communication light TL, and communicates the communication light TL to the first optical communication device 1 provided on the fixed structure 51 .

FIG. 3 is a diagram showing a state in which the underwater optical communication system 50 performs underwater optical wireless communication by direct communication. When the fixed structure 51 is in the traveling direction FW of the moving body 52, the window WD of the first optical communication device 1 and the window WD of the second optical communication device 2 are opposed to each other. In this case, the communication light TL emitted from the laser light source 4 provided in the second optical communication device 2 travels straight toward the first optical communication device 1 and enters the first optical communication device 1 directly. can be done. That is, the communication light TL emitted from the laser light source 4 is directly received by the light receiving element of the light receiving section 5 and converted into communication information by information processing such as photoelectric conversion. Thus, when the first optical communication device 1 exists within the range of the communication light TL emitted by the second optical communication device 2, underwater optical wireless communication can be performed by direct communication.

On the other hand, depending on the traveling direction FW of the moving body 52, underwater optical wireless communication cannot be performed by direct communication. That is, when the fixed structure 51 exists behind the moving body 52 (in the direction opposite to the traveling direction FW), the second optical communication device 2 cannot emit the communication light TL behind the moving body 52 . Therefore, the communication light TL emitted from the second optical communication device 2 cannot be directly received by the first optical communication device 1 .

When direct communication is not possible, the underwater optical communication system 50 according to this embodiment uses the reflector 11 to indirectly perform underwater optical wireless communication. FIG. 4 is a diagram showing a state in which the underwater optical communication system 50 performs underwater optical wireless communication by indirect communication.

In FIG. 4, the traveling direction FW of the moving body 52 is the left direction, and the fixed structure 51 is positioned behind the moving body 52 . On the other hand, the reflector 11 is present in the traveling direction FW of the moving body 52 . Therefore, the moving body 52 emits the communication light TL from the laser light source 4 of the second optical communication device 2 toward the reflector 11 . The communication light TL emitted from the window WD of the second optical communication device 2 to the underwater WA is reflected by the reflecting surface of the reflector 11 .

The orientation of the reflecting surface of the reflector 11 is set in advance so that at least part of the communication light TL reflected by the reflector 11 (reflected communication light TLR) is received by the first optical communication device 1 . . Therefore, at least part of the reflected communication light TLR enters the window of the first optical communication device 1, is received by the light receiving element of the light receiving section 5, and is converted into communication information by information processing such as photoelectric conversion.

Note that the spread angle θa of the reflected communication light TLR is, for example, about 120°. By making the divergence angle θa of the reflected communication light TLR wider than the divergence angle θ of the communication light TL, compared with the direct communication in which the communication light TL is directly received by the first optical communication device 1, the reflecting material 11 is used to reflect the communication light TL. In indirect communication in which the first optical communication device 1 receives the communication light TLR, the first optical communication device 1 can more reliably receive light.

As shown in FIG. 5, a plurality of reflectors 11 are arranged so as to surround fixed structure 51 . As an example, when the moving body 52 is traveling in the traveling direction FW1 at the position indicated by the solid line in FIG. Therefore, the communication light TL emitted from the moving body 52 is reflected by the reflector 11a, and the reflected communication light TL can be transmitted to the fixed structure 51 existing behind the moving body 52. FIG. Further, when the moving object is navigating the position indicated by the dotted line in FIG. , the reflected communication light TLR can be transmitted to the fixed structure 51 existing on the side of the moving body 52 .

By arranging the reflecting material 11 that reflects the communication light TL in this way, even in a configuration in which the communication light TL is emitted only in front of the moving body 52, communication targets existing on the side or behind the moving body 52 can be detected. Underwater optical communication becomes possible with respect to the object (fixed structure 51 in this case). That is, even if the first optical communication device 1 does not exist within the reachable range of the communication light TL of the second optical communication device 2, If the reflector 11 exists, underwater optical communication is possible between the first optical communication device 1 and the second optical communication device 2 . Therefore, while reducing the number of the second optical communication devices 2 mounted on the moving body 52, it is possible to dramatically expand the range in which the moving body 52 can perform underwater optical communication around the moving body 52. .

Also, the reflector 11 can always reflect the communication light TL if it is made of a material that reflects light. That is, there is no need to supply power to the reflector 11 when the underwater optical communication system 50 performs indirect underwater optical communication using the reflected communication light TLR. Moreover, it is not necessary to connect a wired communication device such as a communication cable to the reflector 11 . Therefore, the communicable range of the moving body 52 can be expanded while simplifying the underwater optical communication system 50 . Furthermore, since it is possible to avoid a situation in which indirect underwater optical communication is interrupted due to troubles in the power supply or wired communication equipment, it is possible to carry out continuous underwater optical communication more reliably.

The number of reflectors 11 arranged in the underwater optical communication system 50 and the positions at which the reflectors 11 are arranged may be appropriately set according to the spread angle θ of the communication light TL. By arranging a plurality of reflectors 11 according to the spread angle θ, the communication light TL emitted from the moving body 52 is determined regardless of the position and traveling direction FW of the moving body 52 in the underwater WA. At least one reflector 11 can be more reliably present within the reachable range of .

In particular, by arranging (360/θ) pieces of reflectors 11 around the fixed structure 51, the communicable range of the mobile body 52 can be expanded. As an example, when the spread angle θ is 40°, by arranging the nine reflectors 11 around the fixed structure 51, the movable body 52 can be fixed regardless of the traveling direction FW of the movable body 52. Underwater optical wireless communication can be performed with the structure 51 . In other words, regardless of the traveling direction FW of the moving body 52 with its back to the fixed structure 51, at least one reflector 11 is surely within the reach of the communication light TL emitted from the moving body 52. exists in Therefore, the communication light TL emitted from the second optical communication device 2 is reflected by the reflector 11 , and the reflected communication light TLR can be reliably transmitted to the fixed structure 51 .

<Effects of Configuration of First Embodiment>
In the underwater optical communication system 50 according to the present embodiment, the distance between the first optical communication device 1 arranged on the fixed structure 51 and the second optical communication device 2 arranged on the moving body 52 is can perform indirect underwater optical wireless communication. That is, the communication light TL emitted from one of the first optical communication device 1 and the second optical communication device 2 is reflected by the reflector 11 . The other of the first optical communication device 1 and the second optical communication device 2 receives the communication light TL reflected by the reflector 11 to obtain communication information related to the communication light TL.

In conventional underwater optical communication systems, only direct underwater optical communication is performed. That is, the communication light emitted from one optical communication device travels straight toward the other optical communication device, and the other optical communication device directly receives the communication light that has traveled straight, thereby performing underwater optical wireless communication. However, since communication light has high directivity, the range in which information can be transmitted by underwater optical wireless communication is limited to a very narrow range in a conventional system that only performs direct communication.

In the underwater optical communication system 50 according to this embodiment, by using the reflector 11, not only direct underwater optical communication that directly receives light but also indirect underwater optical communication that receives reflected light is possible. do. In other words, the first optical communication device 1 and the second optical communication device 2 not only receive the communication light TL directly emitted toward themselves, but also receive the communication light TL reflected by the reflector 11, i.e., reflected communication. configured to receive an optical TLR;

If the size of the mobile body 52 is restricted to a certain size or less due to the inspection environment or the like, the number and size of the second optical communication devices 2 that can be mounted on the mobile body 52 are limited. Furthermore, since the communication light TL has high directivity and a narrow spread angle, the range in which the communication light TL can be emitted from the moving object 52 is limited to a narrow range. As an example, the possible emission range of the communication light TL is limited to the front of the moving body 52 .

However, by reflecting the communication light TL emitted from the second optical communication device 2 to the underwater WA by the reflecting material 11, the traveling direction of the communication light TL is changed to a direction different from the direction in which the communication light TL was originally emitted. can be changed. That is, by reflecting the communication light TL emitted forward of the moving object 52 by the reflector 11, the reflected communication light TLR, which is the reflected communication light TL, can be transmitted to the side or rear of the moving object 52. can.

The direction in which the communication light TL travels through reflection can be arbitrarily changed according to the shape or orientation of the reflecting surface of the reflector 11 . Therefore, by enabling indirect communication by receiving the light reflected by the reflector 11, the communicable range of the mobile body 52 can be dramatically expanded without adding the second optical communication device 2 to the mobile body 52. can.

Second embodiment

Next, a second embodiment of the present invention will be described. In the first embodiment, the configuration for performing underwater optical wireless communication in an open space, such as underwater, is shown, but in the second embodiment, the configuration for performing underwater optical wireless communication inside a water storage tank 21, that is, in a closed space is taken as an example. explain. In addition, the same code|symbol is attached|subjected and illustrated about the structure which is common in 1st Embodiment, and the description is abbreviate|omitted.

FIG. 6 shows a vertical sectional view and FIG. 7 shows a horizontal sectional view of the water storage tank 21 in which the underwater optical communication system 50A according to the second embodiment is used. The water storage tank 21 has a cylindrical outer wall 23 and a column 25 . That is, the inside of the water storage tank 21 is a closed space surrounded by the outer wall 23 . The inner surface of the outer wall 23 forming the closed space is configured to reflect the communication light TL emitted from the laser light source 3 or the laser light source 4 . Examples of the configuration of the inner surface of the outer wall 23 include a specular reflection mirror whose reflection surface is a mirror surface, or a frosted glass-like scattering reflection mirror whose reflection surface is subjected to scattering treatment. In the second embodiment, the outer wall 23 corresponds to the light reflector in the invention.

The strut 25 is erected on the bottom KB of the water storage tank 21 and is made of a material that blocks the communication light TL. In the second embodiment, the strut 25 is shown as an example of a structure that blocks the communication light TL. The first optical communication device 1 is arranged on a fixed structure 51 installed at the bottom KB of the water storage tank 21 . The second optical communication device 2 is installed in a moving body 52, and the moving body 52 performs various inspections on the inside of the water storage tank 21 while navigating the underwater WA.

<Usage example of the second embodiment>
Here, a usage example of the underwater optical communication system 50A according to the second embodiment will be described. In the second embodiment, as in the first embodiment, the second optical communication device 2 transmits communication light TL and the first optical communication device 1 receives the communication light TL.

As shown in FIG. 7, when the fixed structure 51 exists in the traveling direction FW of the moving body 52 and there is no shielding object such as the support pillar 25 in the traveling direction FW, underwater optical communication by direct communication is possible. be. In this case, the communication light TL emitted from the laser light source 4 provided in the second optical communication device 2 can enter the first optical communication device 1 directly. That is, the communication light TL emitted from the laser light source 4 is directly received by the light receiving element of the light receiving section 5 and converted into communication information by information processing such as photoelectric conversion.

On the other hand, when the fixed structure 51 does not exist in the traveling direction FW of the moving object 52 and when the support 25 exists between the moving object 52 and the fixed structure 51, underwater optical communication by direct communication is performed. can't do That is, when the fixed structure 51, the moving body 52, and the pillar 25 are in the positional relationship shown in FIG. However, since the support 25 that shields the light exists between the fixed structure 51 and the moving body 52, the transmission light TL emitted toward the traveling direction FW of the moving body 52 is blocked by the support 25. . Therefore, even if the fixed structure 51 exists in the traveling direction FW of the moving body 52, the communication light TL emitted from the second optical communication device 2 can be directly transmitted to the first optical communication device 1. Can not.

In order to perform direct underwater optical communication between the first optical communication device 1 and the second optical communication device 2 in the state shown in FIG. It is necessary to move to a position where it is not shielded by the struts 25 . As an example, the vehicle 52 needs to make a detour from the position shown in FIG. 8 to the position shown in FIG. It takes a very long time to perform such roundabout movement. Direct underwater optical communication is interrupted during the roundabout movement.

Therefore, when direct underwater optical communication is difficult, in the underwater optical communication system 50A according to the second embodiment, indirect underwater optical communication is performed using the outer wall 23 configured to reflect light. That is, the moving direction FW of the moving body 52 is changed from the direction shown in FIG. 8 to the direction shown in FIG. In other words, the traveling direction FW of the moving body 52 is changed so that the moving body 52 faces the outer wall 23 from the state where the moving body 52 faces the column 25 .

After changing the traveling direction FW of the moving object 52 , the moving object 52 emits the communication light TL from the second optical communication device 2 toward the outer wall 23 . The emitted communication light TL strikes the outer wall 23 and is reflected. The communication light TL reflected by the outer wall 23 , that is, the reflected communication light TLR travels toward the fixed structure 51 without being blocked by the post 25 and is received by the first optical communication device 1 . In this way, even if the moving body 52 is not moved, by reflecting the communication light TL along a trajectory that bypasses the support column 25, the underwater light transmission between the first optical communication device 1 and the second optical communication device 2 can be achieved. Wireless communication is possible.

In this case, the moving direction FW of the moving body 52 is slightly changed to enable indirect underwater optical wireless communication, so the moving body 52 itself does not need to move around the support 25 . The time required to change the traveling direction FW of the moving body 52 is much shorter than the time required to move the moving body 52 itself around. Therefore, the continuity of underwater optical wireless communication can be greatly improved by reflecting the communication light TL along a trajectory that bypasses the strut 25, which is a light shield.

<Effects of Second Embodiment>
In the underwater optical communication system 50A according to the present embodiment, indirect underwater optical wireless communication is performed by reflecting light using the outer wall 23 forming the closed space inside the water storage tank 21, which is the closed space. That is, the communication light TL emitted from the second optical communication device 2 arranged on the moving body 52 is reflected by the light reflecting surface formed on the inner surface of the outer wall 23 and arranged on the fixed structure 51 . The communication light TL is transmitted by causing the first optical communication device 1 to receive the light.

As in the first embodiment, when indirect underwater optical wireless communication using reflected communication light TLR is performed in an open space, a structure that reflects light, such as the reflector 11, is placed around the fixed structure 51. must be placed. On the other hand, when indirect underwater optical wireless communication is performed in a closed space such as a water storage tank 21 as in the second embodiment, the inner surface of the outer wall 23 forming the closed space is configured to reflect light. As a result, the outer wall 23 itself can be used as a light reflector. By using the outer wall 23 as a light reflector, there is no need to arrange a new structure such as the reflector 11 inside the water storage tank 21 . Therefore, the cost of the underwater optical communication system 50A can be reduced.

In addition, since the number and size of the reflectors 11 used in the first embodiment are limited, the size of the reflecting surface that reflects light is limited. On the other hand, in the second embodiment, the outer wall 23 forming the closed space is arranged in advance so as to surround the fixed structure 51 and the moving body 52 without gaps. Therefore, by using the inner surface of the outer wall 23 as a light reflector, the size of the light reflecting surface can be increased. As a result, even when light with high directivity is used as communication information, it is possible to greatly improve the frequency with which the light reflecting surface exists within the transmission range of the communication light TL emitted from the second optical communication device 2. . Therefore, the range that the reflected communication light TLR reflected by the outer wall 23 reaches can be widened, so that the effective range of indirect underwater optical wireless communication can be further widened.

<Aspect>
It will be appreciated by those skilled in the art that the exemplary embodiments described above are specific examples of the following aspects.

(Section 1)
An underwater optical communication system 50 according to one aspect includes a first optical communication device 1 arranged on a fixed structure 51 fixed to an underwater WA, and a moving body 52 arranged on a moving body 52 moving in the underwater WA. an underwater optical communication system that communicates with a second optical communication device 2, wherein each of the first optical communication device 1 and the second optical communication device 2 has a communication light TL which is laser light. and optical receivers (5, 6) for receiving communication light TL. At least part of the communication light TL emitted from the laser light sources (3, 4) provided in one of the communication devices 2 is reflected, and the reflected communication light TL is sent to the first optical communication device 1 and the second light. It further includes a reflector 11 that causes the optical receivers (5, 6) of the other communication device 2 to receive the signal.

According to the underwater optical communication system described in item 1, by using the reflecting material 11 that reflects the communication light TL, the communication light TL emitted from the laser light source is directly received by the optical receiving unit. Not only communication but also indirect underwater optical communication is possible in which the optical receiver receives the communication light TL that is emitted from the laser light source and then reflected by the reflector 11 . In indirect underwater optical communication, the communication light TL emitted underwater from the laser light source is reflected by the reflecting material 11, so that the traveling direction of the communication light TL is changed in a direction different from the direction in which the communication light TL was originally emitted. can be changed. As an example, by reflecting the communication light TL emitted in front of the moving body 52 by the light reflecting portion, the reflected communication light TL can be transmitted to the side or rear of the moving body 52 .

Therefore, even in a range where communication is impossible by direct underwater optical communication, indirect underwater In the case of optical communication, communication is possible within the range. Therefore, by enabling indirect communication by receiving the light reflected by the reflector 11, the communicable range of the mobile body 52 can be dramatically expanded without adding the second optical communication device 2 to the mobile body 52. can.

(Section 2)
In the underwater optical communication system according to item 1, the reflector 11 is a scattering reflection mirror whose reflecting surface that reflects the communication light TL is subjected to scattering treatment, and the reflector 11 is subjected to the scattering treatment. The communication light TL may be radially reflected by the reflecting surface.

According to the underwater optical communication system described in the second item, the reflector 11 is a scattering reflection mirror whose reflection surface that reflects the communication light TL is subjected to scattering treatment. Therefore, the spread angle of the communication light TL scattered and reflected by the reflector 11 is increased. Therefore, the communication light TL reflected by the reflector 11 can reach a wider range, so that the communicable range of the mobile body 52 can be further expanded without adding the second optical communication device 2 to the mobile body 52 .

(Section 3)
In the underwater optical communication system described in item 1, the reflecting surface of the reflecting material 11 that reflects the communication light TL is a convex spherical surface, and the reflecting surface of the reflecting material 11 that is a convex spherical surface reflects the communication light TL. may be reflected radially.

According to the underwater optical communication system described in item 3, since the reflection surface of the reflector 11 that reflects the communication light TL is a convex spherical surface, the spread angle of the communication light TL reflected by the reflector 11 is can be bigger. Therefore, since the range that the reflected communication light TL reaches can be widened, the communicable range of the mobile body 52 can be further expanded without adding the second optical communication device 2 to the mobile body 52 .

(Section 4)
In the underwater optical communication system according to any one of items 1 to 3, the moving body 52 and the fixed structure 51 are arranged inside the water storage tank 21 partitioned by the outer wall 23, and transmit the communication light TL. The outer wall 23 may be the light reflecting portion that reflects the light.

According to the underwater optical communication system described in item 4, the pre-formed outer wall 23 which is an essential component of the water storage tank 21 can be used as a light reflector. Therefore, since it is not necessary to install a new structure for reflecting light, an increase in cost of the underwater optical communication system can be suppressed. In addition, since the outer wall 23 is arranged without gaps around the moving body 52 and the fixed structure 51, the light reflecting surface capable of reflecting the communication light TL is wide. Therefore, it is possible to more reliably avoid the situation where the communication light TL emitted from the laser light source into the water does not reach the light reflecting surface.

(Section 5)
In the underwater optical communication system according to any one of items 1 to 5, the plurality of reflectors 11 are arranged inside a circle centered on the fixed structure 51 and having a radius equal to the range of the communication light TL. The positions where the reflectors 11 are arranged are determined so that at least one of the plurality of reflectors 11 receives the communication light TL emitted from the first optical communication device 1 or the second optical communication device 2. It's okay.

According to the underwater optical communication system described in item 5, at least one of the reflectors 11 receives the communication light TL emitted from the first optical communication device 1 or the second optical communication device 2. A position where the reflector 11 is arranged is determined. Therefore, it is possible to more reliably avoid a situation in which the communication light TL emitted from the laser light source into the water cannot be reflected because the reflecting material 11 is not present within the reach of the communication light TL.

<Other embodiments>
Note that the embodiments disclosed this time are illustrative in all respects and are not restrictive. The scope of the present invention includes the claims and all changes within the meaning and range of equivalents to the claims. As an example, the present invention can be modified and implemented as follows.

(1) In each of the above-described embodiments, the configuration in which the second optical communication device 2 arranged on the moving body 52 is the transmitting side of the communication light TL was explained as an example. The first optical communication device 1 provided may be the transmission side of the communication light TL. That is, as an example, the first optical communication device 1 emits, as a communication light TL, the information instructing the operation of the moving body 52 to the underwater WA, and the second optical communication device 2 directly or indirectly transmits the communication light. Receive TL. Thus, the first optical communication device 1 and the second optical communication device 2 may be configured to perform two-way underwater optical wireless communication.

(2) In each of the above-described embodiments, the reflecting material 11 or the outer wall 23 reflects the communication light TL once to perform indirect underwater optical wireless communication. By doing so, the communication light TL may be transmitted toward the communication target. FIG. 10 shows a configuration in which the communication light TL is transmitted from the second optical communication device 2 to the first optical communication device 1 by reflecting the communication light TL twice with the reflector 11 .

In this way, by reflecting the communication light TL multiple times, the trajectory of the communication light TL can be diversified, so that the reachable range of the communication light TL becomes wider. Therefore, even if the number of second optical communication devices 2 mounted on the mobile object 52 is small, the communicable range of the mobile object 52 can be further expanded. Further, even if there is a light shielding object with a complicated shape such as a rocky place P, wiring, or a pipeline, the light shielding object is avoided by reflecting the communication light TL multiple times. It becomes easy to transmit the reflected communication light TLR.

(3) In the above-described second embodiment, the underwater optical communication system 50A is used inside a closed space, but the closed space is limited to a space sealed by walls such as the outer wall 23. However, it is sufficient if the space is separated from the outside by a wall. As an example, the water storage tank 21 may not have the outer wall 23 formed on the top. Also, although the water storage tank 21 is illustrated as an example of a closed space in which the underwater optical communication system 50A performs underwater optical wireless communication, that is, a space separated from the outside, the present invention is not limited to this. Other examples in which the underwater optical communication system 50A is used include water pipes, drain pipes, water purification tanks, and the like. By making the inner surface of the wall that separates the closed space from the outside a light reflecting surface, the wall can be used to reflect the communication light TL to enable indirect underwater optical wireless communication.

(4) In each of the above-described embodiments, the underwater optical communication system 50 is configured to perform optical wireless communication between two optical communication devices. may be performed.

(5) In each of the above-described embodiments, the light reflecting surface of the reflector 11 or the outer wall 23 is not limited to being planar, and may be convex or concave. FIG. 11 shows a state in which indirect underwater optical wireless communication is performed using a reflector 11 having a convex spherical surface. In particular, when the light reflecting surface is a convex spherical surface, the expansion ratio of the spread angle θa of the reflected communication light TLR with respect to the spread angle θ of the communication light TL before reflection is increased compared to when the light reflecting surface is planar. can improve. Therefore, it is possible to further widen the communicable range of underwater optical wireless communication using laser light.

(6) In each of the above-described embodiments, the number of first optical communication devices 1 and second optical communication devices 2 can be changed as appropriate. As an example, the number of second optical communication devices 2 installed in the moving body 52 is not limited to one, and a plurality of second optical communication devices 2 may be installed according to the size of the moving body 52. . By enabling indirect communication in which the reflected communication optical TLR is transmitted to the communication target, the number of second optical communication devices 2 can be maintained while maintaining the number of second optical communication devices 2 compared to the conventional underwater optical communication system which enables only direct communication. The communicable range of the mobile body 52 can be expanded.

REFERENCE SIGNS LIST 1 first optical communication device 2 second optical communication device 3 laser light source 4 laser light source 5 optical receiver 6 optical receiver 7 controller 8 controller 9 observation device 11 reflector 21... Water storage tank 23... Outer wall 25... Post 51... Fixed structure 52... Moving object WD... Window part TL... Communication light TLR... Reflected communication light

Claims

Underwater light for communicating between a first optical communication device installed on a fixed structure fixed in water and a second optical communication device installed on a moving body that moves underwater A communication system,
each of the first optical communication device and the second optical communication device,
an optical transmitter that transmits laser light;
an optical receiver that receives the laser light;
with
The underwater optical communication system comprises:
at least a part of the laser light transmitted from the light transmission unit provided in one of the first optical communication device and the second optical communication device is reflected, and the reflected laser light is transmitted to the first optical communication device; An underwater optical communication system further comprising a light reflecting section that causes the optical receiving section provided in the other of the optical communication device and the second optical communication device to receive the light.
In the underwater optical communication system according to claim 1,
the light reflecting portion is a scattering reflection mirror having a reflecting surface that reflects the laser beam and having undergone a scattering treatment;
In the underwater optical communication system, the light reflecting section radially reflects the laser light by the reflecting surface subjected to the scattering treatment.
In the underwater optical communication system according to claim 1,
the light reflecting portion has a convex spherical reflecting surface for reflecting the laser light,
In the underwater optical communication system, the light reflecting section radially reflects the laser light by the reflecting surface which is the convex spherical surface.
In the underwater optical communication system according to any one of claims 1 to 3,
The moving body and the fixed structure are arranged inside a water storage tank partitioned by a wall,
The underwater optical communication system, wherein the light reflector is the wall.
In the underwater optical communication system according to any one of claims 1 to 4,
a plurality of the light reflecting portions are arranged inside a circle centered on the fixed structure and having a radius corresponding to the range of the laser light;
The underwater optical communication system, wherein at least one of the plurality of light reflectors is positioned so as to receive the laser beam emitted from the first optical communication device.