TW202306338A - Underwater optical communication system - Google Patents

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 invention relates to an underwater optical communication system for optical communication in water.

Conventionally, as an underwater wireless communication means for transmitting data from an underwater vehicle or the like for underwater exploration, there has been a communication using "sound waves with small attenuation in water". Such wireless communication using sound waves has the problem of "only a low communication speed of tens of kbps can be realized because the propagation speed of sound waves in water is low and the frequency of sound waves is low."

Therefore, in recent years, as an underwater wireless communication means, an optical wireless communication system using an underwater optical communication device using visible light as communication light has been proposed. The underwater optical communication device includes: a laser light source that emits laser light composed of visible light; and a light receiving unit that receives the laser light emitted from the laser light source. As an example of an optical wireless communication system, we can cite the difference between "the first underwater optical communication device installed on a mobile body navigating in water" and "the second underwater optical communication device installed at a base station fixedly installed in water". A configuration in which wireless communication is performed by transmitting communication light between them (for example, Patent Documents 1 and 2).

Visible light is less attenuated in water than sound waves. In addition, since visible light has a higher propagation speed and frequency than sound waves, optical wireless communication using visible light can achieve high communication speeds on the order of tens of Mbps. Therefore, large-capacity information such as animation can be communicated at high speed by visible light wireless communication. [Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2018-007069 [Patent Document 2] Japanese Patent Laid-Open No. 2019-114939

﹝The problem the invention intends to solve﹞

However, in the case of the conventional example with such a structure, the following problems arise.

Since communication light is more directional than general electromagnetic waves such as sound waves, a single optical wireless communication device is limited in the direction in which communication light can be transmitted. Therefore, as shown in FIG. 12 , when the underwater optical communication device 102 is installed so as to transmit the communication light TL forward (to the left in the figure) of the mobile body 101 navigating in the water WA, the underwater optical communication device 102 mounted on the mobile body 101 The underwater optical communication device 102 cannot transmit the communication light TL to the side or rear of the mobile body 101 .

Therefore, as shown in FIG. 12 , when the mobile body 101 navigates underwater with its back facing the base station 103 on which the underwater optical communication device 104 is disposed, the mobile body 101 cannot use the underwater optical communication device 102 and the base station 103. The communication device 104 performs optical communication. In order to enable optical communication with the underwater optical communication device 104 , it is necessary to change the direction of the mobile body 101 underwater so that the mobile body 101 faces the base station 103 . Since it takes time to perform such direction switching in water, optical communication in water may be interrupted for a certain period of time.

As a method of alleviating such communication direction restriction and realizing continuous communication, as shown in FIG. It is what we want. However, if the number of underwater optical communication devices 102 mounted on the mobile body 101 is increased, problems such as an increase in the size and weight of the mobile body 101 may not be avoided. In addition, as an example, in the case of observing a narrow space, etc., it may be necessary to limit the size of the moving object 101 to a certain value or less depending on the object of observation and the observation environment. In this case, it is difficult to add the underwater optical communication device 102 to the mobile body 101 .

The present invention is made in view of such circumstances, and its purpose is to provide an underwater optical communication system that can avoid the addition of underwater optical communication devices and can communicate over a wider area. [Technical means to solve the problem]

In order to achieve such an object, the present invention employs the following constitutions. That is, according to one aspect of the present invention, between "the first optical communication device disposed on a fixed structure fixed in water" and "the second optical communication device disposed on a mobile body moving in water", An underwater optical communication system for communication; the first optical communication device and the second optical communication device each include: an optical sending unit for sending laser light, and a light receiving unit for receiving the laser light; the underwater optical communication system further includes: a light reflection unit that reflects at least a part of the laser light transmitted from the optical transmission unit included in one of the first optical communication device and the second optical communication device, and makes the reflected laser light be captured by the first light The light receiving unit included in the other of the communication device and the second optical communication device receives the light. [Invention effect]

According to the underwater optical communication system of the present invention, communication is performed between "the first optical communication device arranged on a fixed structure fixed in water" and "the second optical communication device arranged on a mobile body moving in water". The underwater optical communication system includes a light reflection part. The light reflection unit reflects at least a part of the laser light transmitted from the "optical transmission unit included in one of the first optical communication device and the second optical communication device", and makes the reflected laser light reflected by the first optical communication device and the second optical communication device. The light receiving unit included in the other of the second optical communication devices receives the light.

In the underwater optical communication system according to this embodiment, by using the light reflecting part, not only the direct underwater optical communication in which the laser light transmitted from the light transmitting part is directly received by the light receiving part, but also the optical receiving part can be performed. The indirect underwater optical communication in which the part receives the laser light transmitted from the light transmitting part and reflected by the light reflecting part. In the indirect underwater optical communication, the traveling direction of the laser light can be changed to a direction different from the direction in which the laser light was originally emitted by reflecting the laser light emitted from the light transmitting part into the water by the light reflecting part. For example, by reflecting the laser light emitted to the front of the moving body by the light reflecting part, the reflected laser light can be transmitted to the side or rear of the moving body.

Therefore, for a mobile body whose mountable second optical communication devices are limited in number and size, even in a range where direct underwater optical communication cannot communicate, only indirect underwater optical communication can communicate. Therefore, through the indirect communication that can receive the light reflected by the light reflection part, the communication range of the mobile body can be greatly expanded without adding a second optical communication device to the mobile body.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. [First Embodiment]

＜Description of overall structure＞ Referring to Fig. 1 etc., the schematic configuration of the underwater optical communication system 50 according to the first embodiment will be described. The first embodiment is described by taking a communication system for underwater optical communication in deep sea or lake bottom as an example. Moreover, as shown in FIG. 1 etc., let two horizontal directions orthogonal to each other be an x direction and a y direction, respectively. The x-direction is equivalent to the left-right horizontal direction in the drawings. Also, let the vertical direction be the z direction.

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

The 1st optical communication apparatus 1 is arrange|positioned at the fixed structure 51 installed in the water bottom WB. As an example of the fixed structure 51, a base station for observation, etc. are mentioned. The fixed structure 51 is connected to an unillustrated external station via a cable. As an example, an external station may be a ship on water or a base on the ground.

The second optical communication device 2 is disposed on a mobile body 52 that moves underwater WA. The mobile body 52 performs inspection of underwater structures such as pipelines by moving in the water WA. As an example of the mobile body 52 , an ROV (Remotely Operated Vehicle) or an AUV (Autonomous Underwater Vehicle) may be mentioned.

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

The laser light source 3 and the laser light source 4 respectively include a semiconductor laser and a collimator lens, and the laser light generated by the semiconductor laser is adjusted by the collimator lens to be emitted toward the water WA as communication light TL including communication information. As shown in FIG. 1 , the communication light TL passes through the window portions WD respectively provided in the first optical communication device 1 and the second optical communication device 2 , and is emitted toward the water WA. The laser light source 3 and the laser light source 4 correspond to the light transmitting unit in the present invention.

The light receiving unit 5 receives laser light transmitted 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, central processing unit), etc., performs various processing on the information contained in the laser light received by the light receiving unit 5, and at the same time coordinates and controls the first optical communication device Each composition of 1. That is, the control unit 7 generates communication information such as video information or video information by performing various information processing on the signal of the communication light TL subjected to photoelectric conversion and amplification processing.

The light receiving unit 6 receives laser light transmitted from the laser light source 3 provided in the first optical communication device 1 . The control unit 8 performs various processes on the information included in the laser light received by the light receiving unit 6 to generate communication information, and at the same time controls each component provided in the second optical communication device 2 as a whole. The observation device 9 is, for example, an underwater camera, which observes the observation object in the water WA, and obtains information such as a photo or a video.

The light receiving unit 5 and the light receiving unit 6 each include a light receiving element. Each of the light receiving elements can receive light such as communication light TL and perform photoelectric conversion. As an example of a light receiving element, a photomultiplier tube, an avalanche photodiode, etc. are mentioned. The light-receiving element is arranged inside a sealed water pressure-resistant container, that is, a protective container, and is isolated from the external environment such as water WA.

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

The plurality of first optical communication devices 1 mounted on the fixed structure 51 are arranged so that the windows WD face in different directions. By orienting the windows WD in different directions, any one of the first optical communication devices 1 can receive light incident on the fixed structure 51 from various directions. Moreover, by using any one of the first optical communication devices 1 , the communication light TL can be emitted in various directions from the fixed structure 51 . The diffusion 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, about 40°.

The reflection material 11 is provided in the water bottom WB, for example, and reflects the communication light TL. As a material which comprises the reflective material 11, a reflective mirror or a enamel can be mentioned, for example. When the reflective material 11 is a reflector, a specular reflector whose reflective surface is a mirror surface, or a ground glass-like diffuse reflector in which a diffuse treatment is performed on the reflective surface can be cited as configuration examples. In terms of radially reflecting the reflected communication light TL at a wider spread angle, the reflection material 11 is preferably a diffuse mirror.

In the reflection material 11, the shape of the reflection surface that reflects light may be flat or may have a curved surface. In this embodiment, as the reflector 11, a plate-shaped member provided on the water bottom WB is used. In the first embodiment, the reflection material 11 corresponds to the light reflector in the present invention.

The reflective material 11 is fixedly disposed around the fixed structure 51 . Specifically, a predetermined number of reflectors 11 are arranged inside a circular region centered on the fixed structure 51 and whose radius is the reachable distance F of the communication light TL. The position and direction of disposing the reflecting material 11 are set in advance so that the communication light TL emitted from one of the first optical communication device 1 and the second optical communication device 2 can be reflected and incident on the first optical communication device 1 and the second optical communication device 2. The other of the second optical communication device 2 .

That is, the optical receiver 5 disposed in the first optical communication device 1 can not only directly receive the communication light TL emitted from the laser light source 4, but also receive the communication light emitted from the laser light source 4 and reflected by the reflective material 11. TL (reflected communication light TLR). Similarly, the optical receiver 6 disposed in the second optical communication device 2 can not only directly receive the communication light TL emitted from the laser light source 3, but also receive the communication light emitted from the laser light source 3 and reflected by the reflective material 11. TL (reflected communication light TLR).

In this way, the first optical communication device 1 and the second optical communication device 2 can not only directly transmit and receive the communication light TL to each other, but also indirectly transmit and receive the communication light TL through the reflector 11, thereby performing underwater optical wireless communication. Also, by adjusting in advance the direction in which the light reflecting surface of the reflecting material 11 faces, the traveling direction of the reflected communication light TLR can be arbitrarily determined.

<Use example of the first embodiment> Here, an example of use of the underwater optical communication system 50 according to the first embodiment will be described. In the first embodiment, the case where the second optical communication device 2 transmits laser light to the first optical communication device 1 is taken as an example for description. That is, the mobile body 52 sails in the water WA along the traveling direction FW, and is inspected by the observation device 9 to obtain inspection information such as animation. The second optical communication device 2 converts the acquired inspection information into communication light TL, and communicates the communication light TL with the first optical communication device 1 installed 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 through direct communication. When there is the fixed structure 51 in the traveling direction FW of the moving body 52 , the window WD included in the first optical communication device 1 and the window WD included in the second optical communication device 2 face each other. In this case, the communication light TL emitted from the laser light source 4 included in the second optical communication device 2 travels straight to the first optical communication device 1 and can directly enter the first optical communication device 1 . 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 unit 5, and converted into communication information by information processing such as photoelectric conversion. In this way, 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 by direct communication can be performed.

On the other hand, depending on the traveling direction FW of the mobile body 52, underwater optical wireless communication by direct communication may not be possible. That is, when there is the fixed structure 51 behind the moving body 52 (opposite to the traveling direction FW), the second optical communication device 2 cannot emit the communication light TL toward the rear of the moving body 52 . Therefore, the first optical communication device 1 cannot directly receive the communication light TL emitted from the second optical communication device 2 .

In the case where 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 through indirect communication.

In FIG. 4 , the traveling direction FW of the mobile body 52 is the left direction, and the fixed structure 51 is in a state located behind the mobile body 52 . On the other hand, the reflector 11 exists in the traveling direction FW of the moving body 52 . Therefore, the mobile body 52 emits the communication light TL from the laser light source 4 of the second optical communication device 2 to the reflector 11 . The communication light TL emitted from the window portion WD of the second optical communication device 2 toward the water WA is reflected by the reflection surface of the reflection material 11 .

The direction of the reflection surface of the reflection material 11 is set in advance so that at least part of the communication light TL (reflected communication light TLR) reflected by the reflection material 11 is received by the first optical communication device 1 . Therefore, at least part of the reflected communication light TLR is incident on the window of the first optical communication device 1, received by the light receiving element of the light receiving unit 5, and converted into communication information by information processing such as photoelectric conversion.

In addition, 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 larger than the divergence angle θa of the communication light TL, the reflected communication light TLR can be made larger than the direct communication in which the communication light TL is directly received by the first optical communication device 1 by using the reflective material 11 . The indirect communication received by the first optical communication device 1 enables the light to be received by the first optical communication device 1 more reliably.

As shown in FIG. 5 , a plurality of reflectors 11 are arranged so as to surround a fixed structure 51 . For example, when the mobile body 52 travels in the traveling direction FW1 at the position indicated by the solid line in FIG. 5 , among the plurality of reflectors 11 , the reflector 11 a exists within the range of the communication light TL. Therefore, the communication light TL emitted from the moving body 52 is reflected by the reflective material 11 a, so that the reflected communication light TL can be transmitted to the fixed structure 51 existing behind the moving body 52 . Moreover, when the mobile body sails toward the traveling direction FW2 at the position shown by the dotted line in FIG. The optical TLR can be transmitted to the fixed structure 51 existing on the side of the moving body 52 .

In this way, by arranging the reflector 11 that reflects the communication light TL, even if the communication light TL is emitted only to the front of the mobile body 52, it is possible to reflect on the communication object existing on the side or rear of the mobile body 52 (here, The place is a fixed structure 51) for underwater optical communication. That is, even if there is no first optical communication device 1 within the reach of the communication light TL of the second optical communication device 2, as long as there is reflection within the reach of the communication light TL of the second optical communication device 2 With the material 11, underwater optical communication can be performed between the first optical communication device 1 and the second optical communication device 2. Therefore, the number of second optical communication devices 2 mounted on the mobile body 52 can be reduced, and the range around the mobile body 52 in which the mobile body 52 can perform underwater optical communication can be dramatically expanded.

In addition, as long as the reflector 11 is made of a material capable of reflecting light, it can always reflect the communication light TL. That is, the underwater optical communication system 50 does not need to supply power to the reflector 11 when performing indirect underwater optical communication by reflecting the communication light TLR. Also, it is not necessary to connect a wired communication device such as a communication cable to the reflector 11 . Therefore, the underwater optical communication system 50 can be simplified, and the communication range of the mobile body 52 can be expanded. Furthermore, since it is possible to avoid situations such as "interruption of indirect underwater optical communication due to problems with power supply or wired communication equipment", continuous underwater optical communication can be performed more reliably.

The number of reflectors 11 arranged in the underwater optical communication system 50 and the positions where the reflectors 11 are arranged should be appropriately set according to the diffusion angle θ of the communication light TL and the like. By arranging a plurality of reflectors 11 according to the diffusion angle θ, regardless of the position and traveling direction FW of the moving body 52 in the water WA, within the reach range of the communication light TL emitted from the moving body 52, at least A reflective material 11.

In particular, by arranging (360/θ) reflectors 11 around the fixed structure 51 , it is possible to expand the communication range of the mobile body 52 . As an example, when the diffusion angle θ is 40°, by arranging the nine reflectors 11 around the fixed structure 51, no matter which direction the moving direction FW of the moving body 52 is, it is possible to move the moving body 52. 52 and the fixed structure 51 for underwater optical wireless communication. That is, no matter which traveling direction FW the mobile body 52 facing away from the fixed structure 51 moves, at least one reflective material 11 will surely exist within the reach range of the communication light TL emitted from the mobile body 52 . Therefore, the communication light TL emitted from the second optical communication device 2 is reflected by the reflector 11 , so that the reflected communication light TLR can be reliably transmitted to the fixed structure 51 .

<Effects achieved by the configuration of the first embodiment> According to the underwater optical communication system 50 of this embodiment, indirect underwater optical wireless communication can be performed between the first optical communication device 1 disposed on the fixed structure 51 and the second optical communication device 2 disposed on the mobile body 52 . 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 reflective material 11 . Also, the other of the first optical communication device 1 and the second optical communication device 2 can obtain communication information related to the communication light TL by receiving the communication light TL reflected by the reflector 11 .

In conventional underwater optical communication systems, only direct underwater optical communication is performed. That is, the communication light emitted from one of the optical communication devices travels straight to the other optical communication device, and the other optical communication device directly receives the straight communication light to perform underwater optical wireless communication. However, due to the high directivity of communication light, in conventional systems that only perform direct communication, the range in which information can be transmitted by underwater optical wireless communication is limited to a very narrow range.

In the underwater optical communication system 50 according to this embodiment, by using the reflector 11, not only the direct underwater optical communication that directly receives light but also the indirect underwater optical communication that receives reflected light can be performed. That is, the first optical communication device 1 and the second optical communication device 2 can receive not only the communication light TL emitted directly toward them, but also the communication light TL reflected by the reflector 11 , that is, the reflected communication light TLR.

When the size of the mobile body 52 is limited to a certain value or less due to the inspection environment, etc., 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 small diffusion angle, the range in which the communication light TL can be emitted from the moving body 52 is limited to a narrow range. In one example, the range in which the communication light TL can be emitted 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 in the water WA by the reflector 11 , the traveling direction of the communication light TL can be changed to a direction different from the direction in which the communication light TL was originally emitted. That is, by reflecting the communication light TL emitted to the front of the moving body 52 by the reflector 11 , the reflected communication light TL, that is, the reflected communication light TLR can be transmitted to the side or rear of the moving body 52 .

According to the shape or direction of the reflection surface of the reflection material 11, the traveling direction of the communication light TL can be arbitrarily changed by reflection. Therefore, through the indirect communication capable of receiving the light reflected by the reflector 11 , the communication range of the mobile body 52 can be greatly expanded without adding the second optical communication device 2 to the mobile body 52 . [Second Embodiment]

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

Regarding the water storage tank 21 using the underwater optical communication system 50A according to the second embodiment, FIG. 6 shows its longitudinal section, and FIG. 7 shows its cross section. The water storage tank 21 includes a cylindrical outer wall 23 and a pillar 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 can 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 reflector whose reflective surface is a mirror surface, or a ground glass-like diffuse reflector in which a diffuse treatment is performed on the reflective surface. In the second embodiment, the outer wall 23 is equivalent to the light reflector in the present invention.

The pillar 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 pillar 25 is used as an example of a structure that blocks the communication light TL. The first optical communication device 1 is disposed on "the fixed structure 51 provided at the bottom KB of the water storage tank 21". The second optical communication device 2 is installed on the mobile body 52 , and the mobile body 52 navigates in the water WA and performs various inspections of the inside of the water storage tank 21 .

<Example of use of the second embodiment> Here, an example of use of the underwater optical communication system 50A according to the second embodiment will be described. In the second embodiment, the same as the first embodiment, the case where the communication light TL is transmitted by the second optical communication device 2 and the communication light TL is received by the first optical communication device 1 will be described as an example.

As shown in FIG. 7 , when there is a fixed structure 51 in the traveling direction FW of the moving body 52 and there is no shelter such as the pillar 25 in the traveling direction FW, underwater optical communication can be performed by direct communication. In this case, the communication light TL emitted from the laser light source 4 included in the second optical communication device 2 can directly enter the first optical communication device 1 . 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 unit 5, and converted into communication information by information processing such as photoelectric conversion.

On the other hand, in addition to the fact that there is no fixed structure 51 in the traveling direction FW of the mobile body 52, when there is a support 25 between the mobile body 52 and the fixed structure 51, it is also impossible to conduct underwater optical communication through direct communication. communication. That is, when the fixed structure 51 , the mobile body 52 , and the pillar 25 are in the positional relationship as shown in FIG. 8 , the fixed structure 51 exists in the traveling direction FW of the mobile body 52 . However, since the light-shielding pillar 25 exists between the fixed structure 51 and the moving body 52 , the communication light TL emitted in the traveling direction FW of the moving body 52 is blocked by the pillar 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 cannot be directly transmitted to the first optical communication device 1 .

In the state shown in FIG. 8, in order to perform direct underwater optical communication between the first optical communication device 1 and the second optical communication device 2, it is necessary to make the mobile body 52 largely bypass the support 25 and move to the point where The position shaded by the pillar 25. As an example, the moving body 52 must move in a detour from the position shown in FIG. 8 to the position shown in FIG. 7 . It takes a very long time to perform such a roundabout movement. During the detour, direct underwater optical communication is interrupted.

Therefore, when it is difficult to perform direct underwater optical communication, the underwater optical communication system 50A according to the second embodiment uses the outer wall 23 configured to reflect light to perform indirect underwater optical communication. That is, the traveling direction FW of the moving body 52 is changed from the direction shown in FIG. 8 to the direction shown in FIG. 9 . In other words, the traveling direction FW of the mobile body 52 is changed from a state in which the mobile body 52 faces the pillar 25 to a state in which the mobile body 52 faces the outer wall 23 .

After the traveling direction FW of the moving body 52 is changed, the moving body 52 emits the communication light TL from the second optical communication device 2 toward the outer wall 23 . The emitted communication light TL hits 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 pillar 25 , and is received by the first optical communication device 1 . In this way, underwater optical wireless communication between the first optical communication device 1 and the second optical communication device 2 can be performed by reflecting the communication light TL in a trajectory that bypasses the support 25 without moving the moving body 52 .

In this case, since the indirect underwater optical wireless communication can be performed by slightly changing the traveling direction FW of the mobile body 52 , it is not necessary to move the mobile body 52 itself so as to bypass the pillar 25 . The time required to change the traveling direction FW of the mobile body 52 is very short compared to the time required to detour the mobile body 52 itself. Therefore, by reflecting the communication light TL in such a trajectory as to bypass the support 25 which is the light shield, the continuity of underwater optical wireless communication can be greatly improved.

<Effect according to the second embodiment> The underwater optical communication system 50A according to the present embodiment performs indirect underwater optical wireless communication by using reflected light from the outer wall 23 forming the enclosed space inside the closed space, that is, the water storage tank 21 . That is, by reflecting the communication light TL emitted from the second optical communication device 2 arranged on the moving body 52 with the light reflection surface formed on the inner surface of the outer wall 23 , and communicating with the first light arranged on the fixed structure 51 The device 1 receives and transmits the communication light TL.

As described in the first embodiment, when the indirect underwater optical wireless communication using the reflected communication light TLR is performed in an open space, light-reflecting structures such as the reflective material 11 must be arranged around the fixed structure 51 . On the other hand, as described in the second embodiment, when performing indirect underwater optical wireless communication in a closed space such as the water storage tank 21, the inner surface of the outer wall 23 forming the closed space can reflect light Structured in such a way that the outer wall 23 itself can be used as a light reflector. By using the outer wall 23 as a light reflector, it is not necessary 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 reflective material 11 used in the first embodiment are limited, the breadth of the reflective 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 without gaps so as to surround the fixed structure 51 and the movable body 52 . Therefore, the size of the light reflection surface can be enlarged by using the inner surface of the outer wall 23 as a light reflector. As a result, even when light with high directivity is used as communication information, the frequency at which the light reflecting surface exists within the transmission range of the communication light TL emitted from the second optical communication device 2 can be significantly increased. Therefore, since the reflected communication light TLR reflected by the outer wall 23 can reach a wider range, the effective range of the indirect underwater optical wireless communication can be wider.

＜Specification＞ Those with ordinary knowledge in the technical field to which this case belongs should be able to understand that the above illustrative implementation aspects are specific examples of the following aspects.

(item 1) According to one aspect of the underwater optical communication system 50, the "first optical communication device 1 arranged on a fixed structure 51 fixed in water WA" and "the second optical communication device 1 arranged in a mobile body 52 moving in water WA" In an underwater optical communication system for communicating between devices 2", the first optical communication device 1 and the second optical communication device 2 each include: a laser light source (3, 4), which sends laser light, that is, communication light TL; and light receiving The part (5, 6) receives the communication light TL; the underwater optical communication system 50 further includes a reflector 11, so that the laser light source (3, 4) At least part of the transmitted communication light TL is reflected, and the reflected communication light TL is received by the light receiving unit ( 5 , 6 ) included in the other of the first optical communication device 1 and the second optical communication device 2 .

According to the underwater optical communication system described in item 1, by using the reflector 11 that reflects the communication light TL, not only direct underwater optical communication in which the communication light TL transmitted from the laser light source is directly received by the light receiving part can be performed, It is also possible to perform indirect underwater optical communication in which the light receiving unit receives the communication light TL transmitted from the laser light source and reflected by the reflector 11 . In indirect underwater optical communication, by reflecting the communication light TL emitted from the laser light source into the water by the reflector 11, the traveling direction of the communication light TL can be changed to a direction different from the direction in which the communication light TL was originally emitted. For example, by reflecting the communication light TL emitted toward the front of the moving body 52 by the light reflection part, the reflected communication light TL can be transmitted to the side or rear of the moving body 52 .

Therefore, for the mobile body 52 where the number and size of the second optical communication devices 2 that can be mounted are limited, even if it is a range where direct underwater optical communication cannot communicate, as long as the indirect underwater optical communication can communicate This range is used for communication. Therefore, by performing indirect communication for receiving light reflected by the reflector 11 , the communication range of the mobile body 52 can be greatly expanded without adding the second optical communication device 2 to the mobile body 52 .

(item 2) In the underwater optical communication system described in Item 1, the reflection material 11 is a diffusion mirror that has been subjected to a diffusion treatment on the reflection surface that reflects the communication light TL. The communication light TL is radially reflected by the reflective surface.

According to the underwater optical communication system described in item 2, the reflector 11 is a diffuse reflector that has undergone a diffusion process on the reflective surface that reflects the communication light TL. Therefore, the diffusion angle of the communication light TL diffusely reflected by the reflection material 11 can be made larger. Therefore, since the communication light TL reflected by the reflector 11 can reach a wider range, the communication range of the mobile body 52 can be further expanded without adding the second optical communication device 2 to the mobile body 52. .

(item 3) In the underwater optical communication system described in item 1, the reflective surface of the reflective material 11 that reflects the communication light TL is a convex spherical surface, and the reflective material 11 preferably radiates the communication light TL through the reflective surface that becomes a convex spherical surface. reflectively.

According to the underwater optical communication system described in item 3, since the reflection surface of the reflection material 11 that reflects the communication light TL is a convex spherical surface, the diffusion angle of the communication light TL reflected by the reflection material 11 can be made larger. Therefore, since the reflected communication light TL can reach a wider range, the communication range of the mobile body 52 can be further expanded without adding the second optical communication device 2 to the mobile body 52 .

(item 4) In the underwater optical communication system described in any one of items 1 to 3, the mobile body 52 and the fixed structure 51 are arranged inside the water storage tank 21 partitioned by the outer wall 23, so that the communication light TL The reflective light reflector may be the outer wall 23 .

According to the underwater optical communication system described in item 4, the preformed outer wall 23 which is an essential component of the water storage tank 21 can be used as the light reflection part. Therefore, since there is no need to newly install a light-reflecting structure, an increase in the cost of the underwater optical communication system can be suppressed. In addition, since the outer wall 23 is disposed around the movable body 52 and the fixed structure 51 without gaps, the light reflection surface capable of reflecting the communication light TL is wide. Therefore, it is possible to more reliably avoid the situation that the light reflecting surface does not exist within the reach range of the communication light TL emitted from the laser light source into the water.

(item 5) In the underwater optical communication system described in any one of items 1 to 4, a plurality of reflectors 11 are arranged inside a circle centered on the fixed structure 51 and whose radius is the range distance of the communication light TL. The position where the reflection material 11 is arranged is preferably set so that at least one of the plurality of reflection materials 11 can receive the communication light TL transmitted from the first optical communication device 1 or the second optical communication device 2 .

According to the underwater optical communication system described in Item 5, the position where the reflecting material 11 is arranged is set so that at least one of the reflecting materials 11 can receive the communication sent from the first optical communication device 1 or the second optical communication device 2 Light TL. Therefore, the situation that the communication light TL cannot be reflected due to the absence of the reflector 11 within the reach range of the communication light TL emitted from the laser light source into the water can be more reliably avoided.

＜Other forms of implementation＞ In addition, all the content of the embodiment disclosed this time is an illustration and a limitation. The scope of the present invention includes the scope of the patent application and all changes within the meaning and range equivalent to the scope of the patent application. As an example, the present invention can be modified and implemented as follows.

(1) In each of the above-mentioned embodiments, the second optical communication device 2 arranged on the mobile body 52 is used as an example and described as the transmission side of the communication light TL, but it may also be arranged on the fixed structure 51 The first optical communication device 1 is the transmission side of the communication light TL. That is, as an example, the first optical communication device 1 emits the content information instructing the operation of the mobile body 52 as communication light TL to the water WA, and directly or indirectly makes the second optical communication device 2 This communication light TL is received. In this way, the first optical communication device 1 and the second optical communication device 2 may be configured to perform bidirectional underwater optical wireless communication.

(2) In each of the above-mentioned embodiments, the indirect underwater optical wireless communication is performed by reflecting the communication light TL once by the reflector 11 or the outer wall 23 as an example. The TL is reflected a plurality of times, and the communication light TL is transmitted toward the communication partner. FIG. 10 shows a configuration in which the communication light TL is reflected twice by the reflector 11 to transmit the communication light TL from the second optical communication device 2 to the first optical communication device 1 .

In this way, since the trajectory of the communication light TL can be diversified by reflecting the communication light TL multiple times, the reachable range of the communication light TL becomes wider. Therefore, even when the number of second optical communication devices 2 mounted on the mobile body 52 is small, the communicable range of the mobile body 52 can be further significantly expanded. Also, even in the case where there is a light shield of complex shape such as rocks P, wiring, or pipelines, it is easier to dodge the light shield by reflecting the communication light TL multiple times, Transmit reflected communication light TLR.

(3) In the above-mentioned second embodiment, the underwater optical communication system 50A is used as an example for the inside of the closed space, but the closed space is not limited to the space sealed by the wall part of the outer wall 23 as an example. , as long as it is a space separated from the outside by the wall. As an example, the water storage tank 21 may not have the outer wall 23 formed on the top. In addition, 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, it is not limited thereto. As another example of using the underwater optical communication system 50A, water pipes, drain pipes, clean water tanks, etc. may be mentioned. Furthermore, by using the inner surface of the wall portion that partitions the closed space from the outside as a light reflection surface, the communication light TL can be reflected using the wall portion to perform indirect underwater optical wireless communication.

(4) In the above embodiments, the underwater optical communication system 50 is configured to perform optical wireless communication between two optical communication devices, but it may also be configured to perform underwater optical wireless communication between more than three optical communication devices. communication.

(5) In the above-mentioned embodiments, the light reflecting surface of the reflective material 11 or the outer wall 23 is not limited to a flat shape, and may also be convex or concave. FIG. 11 shows the state of indirect underwater optical wireless communication using a convex spherical reflector 11 . In particular, when the light reflection surface is a convex spherical surface, the amplification of the diffusion angle θa of the reflected communication light TLR relative to the diffusion angle θ of the communication light TL before reflection can be greatly improved compared to the case where the light reflection surface is flat. Rate. Therefore, the communicable range of underwater optical wireless communication using laser light can be further expanded.

(6) In the above embodiments, the numbers of the first optical communication devices 1 and the second optical communication devices 2 can be appropriately changed. As an example, the number of second optical communication devices 2 disposed on the mobile body 52 is not limited to one, and a plurality of second optical communication devices 2 may be provided according to the size of the mobile body 52 . Compared with the conventional underwater optical communication system that can only perform direct communication, by indirect communication that can transmit the reflected communication light TLR to the communication partner, it is possible to expand the mobile body 52 while maintaining the number of second optical communication devices 2 communication range.

1: The first optical communication device 2: The second optical communication device 3,4: Laser light source 5,6: Light receiving part 7,8: Control Department 9: Observation device 11, 11a, 11b: reflector 21: Water storage tank 23: outer wall 25: Pillar 50,50A: underwater optical communication system 51: fixed structure 52: Moving body F: reachable distance FW, FW1, FW2: direction of travel KB: bottom P: Rock TL: communication light TLR: reflective communication light WA: in water WB: underwater WD: window department θa: Diffusion angle

Fig. 1 is a front view illustrating a schematic configuration of an underwater optical communication system according to a first embodiment. Fig. 2 is a functional block diagram illustrating the constitution of the underwater optical communication system according to the first embodiment. Fig. 3 is a front view illustrating a state of underwater optical communication by direct communication in the first embodiment. Fig. 4 is a front view illustrating a state of underwater optical communication by indirect communication in the first embodiment. Fig. 5 is a plan view illustrating a state of underwater optical communication by indirect communication in the first embodiment. Fig. 6 is a longitudinal sectional view illustrating a schematic configuration of an underwater optical communication system according to a second embodiment. Fig. 7 is a cross-sectional view illustrating a state of underwater optical communication by direct communication in the second embodiment. Fig. 8 is a cross-sectional view illustrating a state in which underwater optical communication by direct communication is blocked by a shelter in the second embodiment. Fig. 9 is a cross-sectional view illustrating a state of underwater optical communication by indirect communication in the second embodiment. Fig. 10 is a plan view illustrating a state in which underwater optical communication is performed by indirect communication in a modified example. Fig. 11 is a front view illustrating a state in which underwater optical communication is performed by indirect communication in a modified example. FIG. 12 is a diagram illustrating the state of performing underwater optical communication and its problems in the conventional mode. Fig. 13 is a diagram showing problematic points in the conventional aspect.

1: The first optical communication device

2: The second optical communication device

11: reflective material

51: fixed structure

52: Moving body

FW: direction of travel

TL: communication light

TLR: reflective communication light

WA: in water

WB: underwater

θa: Diffusion angle

Claims (5)

An underwater optical communication system that communicates between a first optical communication device disposed on a fixed structure fixed in water and a second optical communication device disposed on a mobile body moving in water; The first optical communication device and the second optical communication device each include: a light transmitting unit for transmitting laser light; and a light receiving unit for receiving the laser light; The underwater optical communication system further includes: The light reflection unit reflects at least a part of the laser light transmitted from the optical transmission unit included in one of the first optical communication device and the second optical communication device, and makes the reflected laser light be captured by the first light The light receiving unit included in the other of the communication device and the second optical communication device receives the light. The underwater optical communication system as claimed in claim 1, wherein, The light reflector is a diffuse reflector that has undergone diffuse treatment on the reflective surface that reflects the laser light; The light reflection part reflects the laser light radially through the reflection surface subjected to the diffusion treatment. The underwater optical communication system as claimed in claim 1, wherein, The reflection surface of the light reflection part reflecting the laser light is a convex spherical surface; The light reflection part reflects the laser light radially through the reflection surface which becomes the convex spherical surface. The underwater optical communication system according to any one of claims 1 to 3, wherein, The mobile body and the fixed structure are arranged inside the water storage tank partitioned by the wall; The light reflection part is the wall part. In the underwater optical communication system according to any one of claims 1 to 3, wherein, A plurality of the light reflecting parts are arranged inside a circle centered on the fixed structure and having the range distance of the laser light as the radius; The position of disposing the light reflection part is set so that at least one of the plurality of light reflection parts can receive the laser light transmitted from the first optical communication device or the second optical communication device.

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