Underwater optical wireless communication device and underwater optical wireless communication system

Abstract

To provide an underwater optical wireless communication device and an underwater optical wireless communication system that suppress decrease in communication accuracy due to green light noise caused by green light other than second light, which is green light received from a communication partner.SOLUTION: A first communication device 1 is an underwater optical wireless communication device that performs optical wireless communication underwater, and includes: a first light emitting unit 10 that emits first light 30 having a first wavelength included in a blue wavelength band as a center wavelength; a first light receiving unit 11 that receives second light 31 having a second wavelength included in a green wavelength band as a center wavelength: and a noise suppression unit (green light noise removal unit 12a and green light noise generation suppression unit 12b) that suppresses noise caused by green light generated due to the first light 30.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an underwater optical wireless communication device and an underwater optical wireless communication system, and particularly to an underwater optical wireless communication device and an underwater optical wireless communication system that perform bidirectional optical wireless communication underwater.

Background Art

[0002] Conventionally, an underwater optical wireless communication device that performs bidirectional optical wireless communication underwater has been known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses an underwater optical communication system including a first optical wireless communication device and a second optical wireless communication device. The first optical wireless communication device disclosed in Patent Document 1 is configured to irradiate blue signal light and receive green signal light. Further, the second optical wireless communication device disclosed in Patent Document 1 is configured to irradiate green signal light and receive blue signal light. That is, the underwater optical communication system disclosed in the patent document is configured to perform bidirectional optical wireless communication using signal lights of different colors in the first optical wireless communication device and the second optical wireless communication device. The first optical wireless communication device disclosed in Patent Document 1 is configured to emit blue light and receive green light. Further, the second optical wireless communication device disclosed in Patent Document 1 is configured to emit green light and receive blue light.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In this case, when performing bidirectional wireless communication underwater using blue and green light, the green light received by the first optical wireless communication device (first optical wireless communication device) may be interfered with by green light other than the green light (second light) emitted by the second optical wireless communication device (second optical wireless communication device). In this case, the inventors of the present invention have diligently investigated and found that the emission of blue light (first light) from the first optical wireless communication device causes the generation of green light other than the second light, and that this has such an impact that it reduces the accuracy of communication as noise. This noise caused by green light is called green light noise.

[0006] This invention was made to solve the above-mentioned problems, and one of its objectives is to provide an underwater optical wireless communication device and underwater optical wireless communication system that can suppress the loss of communication accuracy due to green light noise caused by green light other than the second light, which is the green light received from the communication partner. [Means for solving the problem]

[0007] To achieve the above objective, the underwater optical wireless communication device in the first aspect of this invention is an underwater optical wireless communication device that performs optical wireless communication underwater, comprising: a light-emitting unit that emits first light with a first wavelength centered on a first wavelength included in the blue wavelength band; a light-receiving unit that receives second light with a second wavelength centered on a second wavelength included in the green wavelength band; and a noise suppression unit that suppresses noise caused by green light generated by the first light.

[0008] Furthermore, in order to achieve the above objective, the underwater optical wireless communication system in the second aspect of this invention is an underwater optical wireless communication system that performs optical wireless communication underwater, comprising: a first underwater optical wireless communication device that emits first light with a first wavelength centered on a first wavelength included in the blue wavelength band and receives second light with a second wavelength centered on a second wavelength included in the green wavelength band; and a second underwater optical wireless communication device that emits second light and receives first light, wherein the first underwater optical wireless communication device comprises a light-emitting unit that emits first light, a light-receiving unit that receives second light, and a noise suppression unit that suppresses noise caused by green light generated due to the first light. [Effects of the Invention]

[0009] In the underwater optical wireless communication device according to the first aspect of the present invention, as described above, a noise suppression unit is provided to suppress noise caused by green light generated by the first light. As a result, the noise suppression unit suppresses noise caused by green light generated by the first light, thereby preventing a decrease in the signal-to-noise ratio (SNR) of the second light due to green light noise. Consequently, a decrease in communication accuracy due to green light noise caused by green light other than the second light, which is the green light received from the communication partner, can be prevented.

[0010] Furthermore, in the underwater optical wireless communication system according to the second aspect of the present invention, as described above, the first optical wireless communication device is equipped with a noise suppression unit that suppresses noise caused by green light generated by the first light. This makes it possible to provide an underwater optical wireless communication system that, similar to the underwater optical wireless communication system according to the first aspect, can suppress the deterioration of communication accuracy caused by green light noise other than the second light, which is the green light received from the communication partner. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing an outline of an underwater optical wireless communication device and underwater optical wireless communication system according to one embodiment. [Figure 2]This is a block diagram showing the schematic of the first optical wireless communication device. [Figure 3] This is a block diagram showing the general layout of the second optical wireless communication device. [Figure 4] This is a schematic diagram illustrating the wavelength range of light transmitted by an absorbing green transmission filter. [Figure 5] This is a schematic diagram illustrating the wavelength range of light transmitted by a reflective blue transmission filter. [Figure 6] These are schematic diagrams (A) to (D) illustrating the green noise light that may be incident on the first light-receiving unit and the causes of the generation of green noise light. [Figure 7] This block diagram illustrates the configuration of a green light noise signal rejection circuit that acquires the delay time and compensation signal until the green light noise signal is acquired. [Figure 8] This is a block diagram illustrating the configuration of a green light noise signal removal circuit that removes green light noise signals. [Figure 9] This is a schematic diagram illustrating the delay time between the output of the drive signal and the input of the green light noise signal. [Figure 10] This is a schematic diagram illustrating the received signal with green light noise, the compensated signal, and the received signal with the green light noise removed. [Figure 11] This is a schematic diagram illustrating the configuration in which a green noise removal filter removes second green noise. [Figure 12] This is a schematic diagram illustrating a configuration in which the second optical path forming member suppresses the generation of the third green noise light. [Figure 13] This is a schematic diagram illustrating a configuration in which a reflective green transmission filter suppresses the generation of a fourth green noise light. [Figure 14] This is a schematic diagram illustrating the wavelength range of light transmitted by a reflective green transmission filter. [Figure 15] These are schematic diagrams (A) and (B) illustrating the structure of the reflective green light transmission filter holder. [Figure 16]This is a flowchart for explaining the calibration process by the green light noise signal removal circuit. [Figure 17] This is a flowchart for explaining the process of removing the green light noise signal by the green light noise signal removal circuit.

Embodiments for Carrying out the Invention

[0012] Hereinafter, embodiments of the present invention will be described based on the drawings.

[0013] Referring to FIGS. 1 and 2, the configuration of the first communication device 1 and the underwater optical wireless communication system 100 according to an embodiment will be described. Note that the first communication device 1 is an example of the "underwater optical wireless communication device" and the "first underwater optical wireless communication device" in the claims.

[0014] As shown in FIG. 1, the underwater optical wireless communication system 100 is an underwater optical wireless communication system that performs optical wireless communication underwater. The underwater optical wireless communication system 100 includes a first communication device 1 and a second communication device 2. Each of the first communication device 1 and the second communication device 2 is an optical wireless communication that performs optical wireless communication underwater. The first communication device 1 and the second communication device 2 are configured to be capable of simultaneous two-way optical communication. In other words, the first communication device 1 and the second communication device 2 are configured to be capable of full-duplex communication using light (communication light) underwater. Note that the signal light is light for transmitting information by changing the intensity of the light source at a predetermined timing. Also, the second communication device 2 is an example of the "second underwater optical wireless communication device" in the claims.

[0015] The first communication device 1 is disposed underwater. Specifically, the first communication device 1 is provided on a moving body 80 that moves underwater. The moving body 80 includes, for example, an AUV (Autonomous Underwater Vehicle).

[0016] The second communication device 2 is located underwater. Specifically, the second communication device 2 is mounted on a fixed body 81 that is fixed underwater. The fixed body 81 is fixed underwater by being installed on the seabed 90 via a holding member 82.

[0017] (First Optical Wireless Communication Device) Next, the configuration of the first communication device 1 will be described with reference to Figure 2.

[0018] As shown in Figure 2, the first communication device 1 includes a transmitting unit (first light-emitting unit 10), a receiving unit (first light-receiving unit 11), a noise suppression unit, a first control unit 13, a first storage unit 14, an absorbing green light transmission filter 15, a first window 16, a second window 17, and a first storage unit 18. The first light-emitting unit 10 and the first light-receiving unit 11 are examples of the "light-emitting unit" and "light-receiving unit" as defined in the claims, respectively.

[0019] The first communication device 1 is configured to transmit an optical signal (information) to a communication partner (second communication device 2 (see Figure 3)) by emitting signal light (first light 30) from a transmitting unit (first light-emitting unit 10) through a first light-transmitting unit 18f and a first window 16. The first communication device 1 is also configured to receive an optical signal (information) from the second communication device 2 by receiving signal light (second light 31) from the second communication device 2 via a second window 17 and a second light-transmitting unit 122a using a receiving unit (first light-receiving unit 11). The first control unit 13 converts the data to be transmitted to the second communication device 2 into an electrical signal and controls the emission of the first light 30 from the first light-emitting unit 10. The first control unit 13 also converts the received signal 33 (see Figure 8) of the first light-receiving unit 11 into data by controlling the operation of the first light-receiving unit 11.

[0020] The first light-emitting unit 10 is configured to emit first light 30 with a first wavelength 40 (see Figure 5) as its center wavelength, which is included in the blue wavelength band. The first wavelength 40 is, for example, included in the wavelength band from 440 nm to 455 nm. In this embodiment, the first wavelength 40 is, for example, 448 nm. The first light 30 is light with the first wavelength 40 as its center wavelength, and does not include red, etc., but includes blue and green in its wavelength band. The first light-emitting unit 10 includes a first laser light source 10a that generates the first light 30. The first laser light source 10a is, for example, a semiconductor laser light source.

[0021] The first light-receiving unit 11 is configured to receive second light 31 with a central wavelength of second wavelength 41 (see Figure 4) which is included in the green wavelength band. Specifically, the first light-receiving unit 11 is configured to receive second light 31 emitted from the second light-emitting unit 20 (see Figure 3), which will be described later. The first light-receiving unit 11 includes, for example, a photomultiplier tube.

[0022] The noise suppression unit is configured to suppress noise caused by green light generated by the first light 30. Specifically, the noise suppression unit includes at least one of a green light noise removal unit 12a that removes green light noise, which is noise caused by green light generated by the first light 30, and a green light noise generation suppression unit 12b that suppresses the generation of green light noise. In this embodiment, the noise suppression unit includes both the green light noise removal unit 12a and the green light noise generation suppression unit 12b.

[0023] The green light noise includes at least one of the following: green noise light 50a (see Figure 6(A)), which is green light generated by the first light 30, and green light noise signal 50b (see Figure 7), which is obtained by converting the green noise light 50a into an electrical signal by the first light receiving unit 11. In this embodiment, the green light noise includes both green noise light 50a and green light noise signal 50b. Details of the green noise light 50a will be described later.

[0024] The green light noise reduction unit 12a includes at least one of a green light noise signal reduction circuit 120 and a green noise light reduction filter 121. In this embodiment, the green light noise reduction unit 12a includes both the green light noise signal reduction circuit 120 and the green noise light reduction filter 121.

[0025] The green light noise signal removal circuit 120 is a circuit that electrically removes the green light noise signal 50b (see Figure 7). Details of the configuration in which the green light noise signal removal circuit 120 removes the green light noise signal 50b will be described later. In this specification, electrically removing means removing the signal to the extent that it does not become noise. In other words, electrically removing does not mean completely (100%) removing the signal.

[0026] The green noise removal filter 121 optically removes green noise light 50a (see Figure 6). Details of the green noise removal filter 121 will be described later.

[0027] The green light noise generation suppression unit 12b includes at least one of the third green light noise generation suppression unit (second optical path forming member 122) and the fourth green light noise generation suppression member (reflective green transmission filter 123). In this embodiment, the green light noise generation suppression unit 12b includes both the third green light noise generation suppression unit (second optical path forming member 122) and the fourth green light noise generation suppression member (reflective green transmission filter 123). Details of the third green light noise generation suppression unit (second optical path forming member 122) and the fourth green light noise generation suppression member (reflective green transmission filter 123) will be described later.

[0028] The first control unit 13 is a computer, processor, or circuit composed of a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory), etc. The first control unit 13 functions as a control unit that controls each part of the first communication device 1 by executing a predetermined control program stored in the first storage unit 14. The first control unit 13 as hardware also includes a first signal processing unit 13a as a software (program) functional block. The first control unit 13 functions as the first signal processing unit 13a by executing a program stored in the first storage unit 14.

[0029] The first signal processing unit 13a is configured to convert the second light 31, which is irradiated from the second communication device 2 (see Figure 1) and received by the first light receiving unit 11, into data.

[0030] The first storage unit 14 is configured to store various programs executed by the first control unit 13. The first storage unit 14 is also configured to store a delay time 35 (see Figure 7), which will be described later. The first storage unit 14 is, for example, a non-volatile storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0031] The absorbing green light transmission filter 15 is configured to selectively transmit light that includes light in the wavelength band of the second light 31 but does not include light in a predetermined wavelength band of the first light 30. Furthermore, the absorbing green light transmission filter 15 is positioned before the first light receiving unit 11. Specifically, the absorbing green light transmission filter 15 is positioned between the first light receiving unit 11 and the reflective green light transmission filter 123. Details of the wavelength band transmitted by the absorbing green light transmission filter 15 will be described later.

[0032] The first communication device 1 is configured to emit first light 30 through a first window 16. The first communication device 1 is also configured to receive second light 31 through a second window 17. The first window 16 and the second window 17 are formed from, for example, a glass plate or an acrylic plate.

[0033] The first housing section 18 includes a first optical path forming member 18a, a first peripheral wall section 18b, a first opening 18c blocked by a first window 16, and a second opening 18d blocked by a second window 17. The first peripheral wall section 18b, the first window 16 blocking the first opening 18c, and the second window 17 blocking the second opening 18d constitute a closed first internal space 18e that is sealed in a watertight state.

[0034] As shown in Figure 2, the first light-emitting unit 10 and the green noise light removal filter 121 are held within the first housing unit 18 by the first optical path forming member 18a.

[0035] The first optical path forming member 18a holds the first light-emitting unit 10 and forms the first optical path, which is the optical path of the first light 30. In this embodiment, the first optical path forming member 18a is configured to hold the green noise light removal filter 121 together with the first light-emitting unit 10. The first optical path forming member 18a has a cylindrical shape. Furthermore, the first optical path forming member 18a is made of a metallic material. The metallic material is, for example, aluminum. That is, the first optical path forming member 18a does not transmit light.

[0036] Furthermore, a first light-transmitting portion 18f is provided on the surface of the first optical path forming member 18a facing the first window 16. The first light-transmitting portion 18f is formed of, for example, a glass plate or an acrylic material. Therefore, the first light 30 emitted from the first light-emitting portion 10 is irradiated to the outside of the first communication device 1 through the first light-transmitting portion 18f and the first window 16.

[0037] As shown in Figure 2, the green noise removal filter 121 is positioned after the first light-emitting unit 10 in the first optical path forming member 18a. Specifically, the green noise removal filter 121 is positioned between the first light-emitting unit 10 and the first window 16.

[0038] Furthermore, as shown in Figure 2, the first light-receiving unit 11, the absorbing green transmission filter 15, and the reflective green transmission filter 123 are held within the first housing unit 18 by the second optical path forming member 122. The second optical path forming member 122 holds the first light-receiving unit 11 and also forms the second optical path, which is the optical path of the second light 31. In this embodiment, the second optical path forming member 122 holds the absorbing green transmission filter 15 and the reflective green transmission filter 123 together with the first light-receiving unit 11. The second optical path forming member 122 has a cylindrical shape.

[0039] Furthermore, a second light-transmitting portion 122a is provided on the surface of the second optical path forming member 122 that faces the second window 17. The second light-transmitting portion 122a is formed of, for example, a glass plate or an acrylic material. Therefore, the second light 31 that enters the first communication device 1 through the second window 17 enters the first light-receiving portion 11 through the second light-transmitting portion 122a.

[0040] As shown in Figure 2, the absorbing green light transmission filter 15 is positioned in front of the first light receiving unit 11 in the second optical path forming member 122. Specifically, the absorbing green light transmission filter 15 is positioned between the first light receiving unit 11 and the reflective green light transmission filter 123. The fourth green light noise generation suppression member (reflective green light transmission filter 123) is also positioned in front of the absorbing green light transmission filter 15 in the second optical path forming member 122. Specifically, the reflective green light transmission filter 123 is positioned between the absorbing green light transmission filter 15 and the second window 17.

[0041] (Second optical wireless communication device) Next, the configuration of the second communication device 2 will be described with reference to Figure 3.

[0042] As shown in Figure 3, the second communication device 2 includes a second light-emitting unit 20, a second light-receiving unit 21, a second control unit 22, a second storage unit 23, a third optical path forming member 24, a reflective blue light transmission filter 25, a fourth optical path forming member 26, a third window 27, a fourth window 28, and a second housing unit 29.

[0043] The second communication device 2 is configured to transmit an optical signal (information) to the communication partner (first communication device 1 (see Figure 2)) by emitting signal light (second light 31) from the transmitting unit (second light-emitting unit 20) through the third light-transmitting unit 24a and the third window 27. The second communication device 2 also receives the signal light (first light 30) from the first communication device 1 through the fourth window 28 and the fourth light-transmitting unit 26a via the receiving unit (second light-receiving unit 21) and receives the optical signal (information). The second control unit 22 converts the data to be transmitted to the first communication device 1 into an electrical signal and controls the emission of the second light 31 from the second light-emitting unit 20. The second control unit 22 also converts the received signal of the second light-receiving unit 21 into data by controlling the operation of the second light-receiving unit 21.

[0044] The second light-emitting unit 20 is configured to emit light using the second light 31 as signal light. The second light 31 is light with a second wavelength 41 (see Figure 4), which is in the green wavelength band. The second wavelength 41 is, for example, included in the wavelength band from 518 nm to 532 nm. In this embodiment, the second wavelength 41 is, for example, 525 nm. The second light 31 is light with the second wavelength 41 as its center wavelength, and does not include red or other colors, but includes green in its wavelength band. The second light-emitting unit 20 includes a second laser light source 20a that generates the second light 31. The second laser light source 20a is, for example, a semiconductor laser light source.

[0045] The second light-receiving unit 21 is configured to receive the first light 30 emitted from the first light-emitting unit 10 (see Figure 2). The second light-receiving unit 21 includes, for example, a photomultiplier tube.

[0046] The second control unit 22 is a computer, processor, or circuit (including a CPU, ROM, and RAM). The second control unit 22 functions as a control unit that controls each part of the second communication device 2 by executing a predetermined control program stored in the second storage unit 23. The second control unit 22 as hardware also includes a second signal processing unit 22a as a software (program) functional block. The second control unit 22 functions as the second signal processing unit 22a by executing a program stored in the second storage unit 23.

[0047] The second signal processing unit 22a is configured to convert the first light 30, which is irradiated from the first communication device 1 (see Figure 2) and received by the second light receiving unit 21, into data.

[0048] The second storage unit 23 is configured to store various programs executed by the second control unit 22. The second storage unit 23 is, for example, a non-volatile storage device such as an HDD or an SSD.

[0049] The third optical path forming member 24 is configured to hold the second light receiving unit 21 and the reflective blue light transmission filter 25 within the second housing unit 29. The third optical path forming member 24 has a cylindrical shape. Furthermore, the third optical path forming member 24 is made of a metallic material. The metallic material is, for example, aluminum. Therefore, the third optical path forming member 24 is configured not to transmit light.

[0050] The reflective blue light transmission filter 25 is configured to selectively transmit the first light 30 from the light incident on the second light receiving unit 21. Furthermore, as shown in Figure 3, the reflective blue light transmission filter 25 is located in front of the second light receiving unit 21. Specifically, the reflective blue light transmission filter 25 is positioned between the second light receiving unit 21 and the third window 27. The detailed configuration of the reflective blue light transmission filter 25 will be described later.

[0051] The fourth optical path forming member 26 is configured to hold the second light-emitting unit 20 within the second housing unit 29. The fourth optical path forming member 26 has a cylindrical shape. Furthermore, the fourth optical path forming member 26 is made of a metallic material. Therefore, the fourth optical path forming member 26 is configured not to transmit light.

[0052] The second communication device 2 is configured to receive the first light 30 through the third window 27. It is also configured to emit the second light 31 through the fourth window 28. The third window 27 and the fourth window 28 are formed from, for example, a glass plate or an acrylic plate.

[0053] Furthermore, a third light-transmitting portion 24a is provided on the surface of the third optical path forming member 24 that faces the third window 27. The third light-transmitting portion 24a is formed of, for example, a glass plate or an acrylic material. Therefore, the first light 30 that enters the second communication device 2 through the third window 27 enters the second light-receiving unit 21 through the third light-transmitting portion 24a.

[0054] Furthermore, a fourth light-transmitting portion 26a is provided on the surface of the fourth optical path forming member 26 that faces the fourth window 28. The fourth light-transmitting portion 26a is formed of, for example, a glass plate or an acrylic material. Therefore, the second light 31 emitted from the second light-emitting portion 20 is irradiated to the outside of the second communication device 2 through the fourth light-transmitting portion 26a and the fourth window 28.

[0055] The second storage section 29 has a second peripheral wall 29a, a third opening 29b blocked by a third window 27, and a fourth opening 29c blocked by a fourth window 28. The second peripheral wall 29a, the third window 27 blocking the third opening 29b, and the fourth window 28 blocking the fourth opening 29c constitute a closed second internal space 29d that is sealed in a watertight state.

[0056] In this embodiment, the underwater optical wireless communication system 100 (see Figure 1) is configured such that the first communication device 1 (see Figure 2) emits a first light 30, which the second communication device 2 receives, thereby enabling communication between the first communication device 1 and the second communication device 2, and the second communication device 2 emits a second light 31, which the first communication device 1 receives, thereby enabling communication between the second communication device 2 and the first communication device 1.

[0057] In this embodiment, the mobile body 80 (see Figure 1) moves through the sea to perform inspections of structures laid on the seabed 90, for example. The second communication device 2 is configured to transmit the inspection results acquired by a detection unit (not shown) provided on the mobile body 80 to the first communication device 1 via a second optical signal 31. The first communication device 1 is also configured to receive the inspection results transmitted from the second communication device 2 and to transmit the received inspection results to a communication device located on land or on a mother ship. When communication is to be performed between the first communication device 1 and the second communication device 2, the mobile body 80 is moved to a communication area and communication is performed.

[0058] Furthermore, the first light 30 and the second light 31 are lights of different colors. Therefore, the first communication device 1 and the second communication device 2 are configured to enable bidirectional communication through multiplex optical communication by simultaneously emitting the first light 30 and the second light 31.

[0059] (Absorbing green transmission filter and reflective blue transmission filter) Next, with reference to Figures 4 and 5, the absorbing green transmission filter 15 (see Figure 2) and the reflective blue transmission filter 25 (see Figure 3) will be described.

[0060] Figure 4 is a graph 60 showing the predetermined wavelength band transmitted by the absorbing green transmission filter 15 (see Figure 2). In graph 60, the vertical axis represents transmittance and the horizontal axis represents wavelength.

[0061] The transmittance change curve 60a shown in Figure 4 is a curve representing the relationship between the wavelength of light and transmittance in the absorbing green transmission filter 15 (see Figure 2). As shown in the transmittance change curve 60a, in this embodiment, the absorbing green transmission filter 15 is configured to absorb light with wavelengths shorter than the second wavelength 41. In other words, the absorbing green transmission filter 15 is a so-called absorbing long-pass filter that selectively transmits light that includes light in the wavelength band of the second light 31 (see Figure 2) but does not include light in the predetermined wavelength band of the first light 30 (see Figure 2). An absorbing long-pass filter is a filter that absorbs light outside the predetermined wavelength range and converts it into heat.

[0062] The absorption-type green transmission filter 15 (see Figure 2) has a first transmission band 200 with a second wavelength 41 as its center wavelength, and a first lower stop zone 201 that is shorter in wavelength than the first transmission band 200. In this embodiment, since the second light 31 is green light, the first transmission band 200 is set within a range that allows transmission of the green wavelength band. Also, the second light 31 emitted from the second light-emitting unit 20 will have some wavelength deviation due to manufacturing tolerances. Therefore, the lower limit of the first transmission band 200 is set to be a predetermined wavelength shorter than 500 nm.

[0063] Since the first communication device 1 (see Figure 2) has an absorbing green light transmission filter 15, it can selectively transmit the second light 31 (see Figure 2) that enters through the second window 17 (see Figure 2) and allow it to enter the first light receiving unit 11 (see Figure 2).

[0064] Figure 5 is a graph 61 showing the wavelength range transmitted by the reflective blue transmission filter 25 (see Figure 3). In graph 61, the vertical axis represents transmittance and the horizontal axis represents wavelength.

[0065] The transmittance change curve 61a shown in Figure 5 is a curve representing the relationship between the wavelength of light and transmittance in the reflective blue transmission filter 25 (see Figure 3). As shown in the transmittance change curve 61a, in this embodiment, the reflective blue transmission filter 25 is configured to selectively transmit light in a predetermined wavelength band that includes the first wavelength 40 but does not include the second wavelength 41. The reflective blue transmission filter 25 is a so-called reflective bandpass filter that selectively transmits light in a wavelength band including the first wavelength 40 by reflecting light of wavelengths other than the wavelength band including the first wavelength 40. A reflective bandpass filter is a filter that selectively transmits light of wavelengths in a predetermined wavelength band by reflecting light of wavelengths in wavelength bands other than the predetermined wavelength band and transmitting light of wavelengths in the predetermined wavelength band without reflection.

[0066] The reflective blue light transmission filter 25 (see Figure 3) has a second transmission band 202 with a first wavelength 40 as its center wavelength, a second lower stop zone 203 that is shorter in wavelength than the second transmission band 202, and a second upper stop zone 204 that is longer in wavelength than the second transmission band 202. In this embodiment, since the first light 30 is blue light, the second transmission band 202 is configured to transmit blue wavelengths. Also, the first light 30 emitted from the first light-emitting unit 10 (see Figure 2) will have some wavelength deviation due to manufacturing tolerances. For this reason, the lower limit of the second transmission band 202 is set to a wavelength that is a predetermined wavelength shorter than 440 nm. The upper limit of the second transmission band 202 is set to a wavelength that is a predetermined wavelength longer than 450 nm.

[0067] Since the second communication device 2 (see Figure 3) has a reflective blue light transmission filter 25 (see Figure 3), it can selectively transmit the first light 30 (see Figure 3) that enters through the third window 27 (see Figure 3) and direct it into the second light receiving unit 21 (see Figure 3).

[0068] (Green noise light) As a result of diligent research by the inventors of the present invention, it was found that the green light received by the first communication device 1 (see Figure 2) includes green light other than the second light 31 (see Figure 3), which is the green light emitted by the second communication device 2 (see Figure 3), (green noise light 50a).

[0069] Specifically, as shown in Figures 6(A) to 6(D), the inventors of the present invention have found that green noise light 50a is included as green light other than the second light 31 (see Figure 3). Green noise light 50a includes, for example, the first green noise light 51a to the fourth green noise light 51d.

[0070] As shown in Figure 6(A), the first green noise light 51a is green Raman scattered light produced when the first light 30 (see Figure 2) undergoes Raman scattering in water. When blue light, such as the first light 30, is shone into water, Raman scattering generates green light (first green noise light 51a) with a wavelength shift to the longer wavelength side. When the first green noise light 51a is generated, it passes through the absorption-type green transmission filter 15 (see Figure 2). Therefore, the signal-to-noise ratio of the second light 31 (see Figure 2) decreases due to the first green noise light 51a.

[0071] As shown in Figure 6(B), the light emitted from the first light-emitting unit 10 includes blue light, the first light 30, and green light. That is, the second green noise light 51b is green light emitted from the first light-emitting unit 10 together with the first light 30 (see Figure 2). After the second green noise light 51b is emitted from the first light-emitting unit 10 (see Figure 2) together with the first light 30, it may be reflected or scattered within the first communication device 1 (see Figure 2) or in water, and then incident on the first light-receiving unit 11 (see Figure 2). In this case, the signal-to-noise ratio of the second light 31 (see Figure 2) decreases due to the second green noise light 51b.

[0072] As shown in Figure 6(C), when the optical path forming member and the like are formed from a resin member 3, when the resin member 3 is irradiated with the first light 30, which is blue light, green fluorescence is generated. That is, the third green noise light 51c is the green fluorescence emitted from the resin member 3 when the first light 30 (see Figure 2) is irradiated onto the resin member 3. When the third green noise light 51c is incident on the first light receiving unit 11 (see Figure 2), the signal-to-noise ratio of the second light 31 (see Figure 2) decreases due to the third green noise light 51c.

[0073] As shown in Figure 6(D), when the first light 30, which is blue light, is irradiated onto the absorbing green transmission filter 15, green fluorescence is generated. That is, the fourth green noise light 51d is the green fluorescence emitted from the absorbing green transmission filter 15 when the first light 30 is irradiated onto the absorbing green transmission filter 15. A first light receiving unit 11 (see Figure 2) is provided downstream of the absorbing green transmission filter 15. Therefore, the fourth green noise light 51d generated when the first light 30 is irradiated onto the absorbing green transmission filter 15 is incident on the first light receiving unit 11. When the fourth green noise light 51d is incident on the first light receiving unit 11, the signal-to-noise ratio of the second light 31 is reduced by the fourth green noise light 51d.

[0074] Therefore, in this embodiment, the green light noise signal removal circuit 120 (see Figure 2), the green noise light removal filter 121 (see Figure 2), the second optical path forming member 122 (see Figure 2), and the reflective green transmission filter 123 (see Figure 2) suppress the decrease in communication accuracy of the second light 31 caused by the first green noise light 51a to the fourth green noise light 51d.

[0075] (Removal of green light noise signal caused by the first green noise light) Referring to Figures 7 to 10, the configuration of the green light noise signal removal circuit 120 (see Figure 7) that removes the green light noise signal 50b caused by the first green noise light 51a (see Figure 7) will be explained.

[0076] The first green noise light 51a (see Figure 7) is green light generated by Raman scattering in water from the first light 30 (see Figure 2) emitted by the first light-emitting unit 10 (see Figure 2). The green light noise signal removal circuit 120 can obtain the timing at which the first green noise light 51a is generated from the first control unit 13 (see Figure 2) because it can obtain the timing at which the first green noise light 51a is generated.

[0077] Therefore, in this embodiment, as shown in Figures 7 and 8, the green light noise signal removal circuit 120 is configured to remove the green light noise signal 50b based on the first green noise light 51a (see Figure 7) included in the light received signal 33 (see Figure 10) at the first light receiving unit 11 (see Figure 2), based on the drive signal 32 when the first light emitting unit 10 (see Figure 2) emits the first light 30 (see Figure 2).

[0078] The process by which the green light noise signal removal circuit 120 removes the green light noise signal 50b includes the process of the green light noise signal removal circuit 120 acquiring the delay time 35 and waveform information 36 of the green light noise signal during calibration, and the process of generating a compensation signal 34 based on the delay time 35 and waveform information 36 of the green light noise signal when the first light 30 (see Figure 2) is emitted while the second light 31 is being received, and removing the green light noise signal 50b using the generated compensation signal 34.

[0079] (Acquisition of compensation signal and delay time) First, referring to Figure 7, the configuration in which the green light noise signal removal circuit 120 acquires the delay time 35 and the waveform information 36 of the green light noise signal will be described. The green light noise signal removal circuit 120 acquires a compensation signal 34 during calibration when the first light receiving unit 11 is not receiving the second light 31 (see Figure 2). The compensation signal 34 is the electrical signal of the light received by the first light receiving unit 11 when the first light emitting unit 10 (see Figure 2) emits the first light 30 (see Figure 2). In addition, during calibration, the green light noise signal removal circuit 120 acquires the delay time 35 from when the first light 30 is emitted until the first green noise light 51a is detected.

[0080] As shown in Figure 7, the green light noise signal removal circuit 120 includes an AD conversion unit 120a, a delay time acquisition unit 120b, and a green light noise information acquisition unit 120c.

[0081] The AD conversion unit 120a is configured to convert the analog signal of the first green noise light 51a received by the first light receiving unit 11 into a digital signal, which is a green light noise signal 50b. The AD conversion unit 120a includes, for example, an AD conversion circuit. The AD conversion unit 120a outputs the converted green light noise signal 50b to the delay time acquisition unit 120b. The AD conversion unit 120a also outputs the converted green light noise signal 50b to the green light noise information acquisition unit 120c.

[0082] The delay time acquisition unit 120b and the green light noise information acquisition unit 120c are functional blocks that function when the green light noise signal removal circuit 120 executes a program stored in the first storage unit 14.

[0083] The delay time acquisition unit 120b is configured to acquire a delay time 35 based on the drive signal 32 and the green light noise signal 50b. Specifically, the delay time acquisition unit 120b acquires the drive signal 32 from the first control unit 13 to drive the first light-emitting unit 10 (see Figure 2). The delay time acquisition unit 120b also acquires the green light noise signal 50b from the AD conversion unit 120a. The delay time acquisition unit 120b acquires the difference between the rise time t1 of the drive signal 32 (see Figure 10) and the rise time t2 of the green light noise signal 50b (see Figure 10) as the delay time 35. The delay time acquisition unit 120b then outputs the acquired delay time 35 to the first storage unit 14.

[0084] Furthermore, the green light noise information acquisition unit 120c acquires waveform information 36 of the green light noise signal 50b acquired from the AD conversion unit 120a. The waveform information 36 of the green light noise signal includes, for example, information such as the waveform and amplitude of the green light noise signal 50b. The green light noise information acquisition unit 120c outputs the acquired waveform information 36 of the green light noise signal to the first storage unit 14.

[0085] The first storage unit 14 stores the delay time 35 input from the delay time acquisition unit 120b. The first storage unit 14 also stores the waveform information 36 of the green light noise signal input from the green light noise information acquisition unit 120c.

[0086] In this embodiment, the first communication device 1 (see Figure 1) is installed on a mobile body 80 (see Figure 1) that moves underwater, and is capable of moving underwater. Therefore, the amplitude and other properties of the compensation signal 34 may change depending on the environment surrounding the mobile body 80. For this reason, in this embodiment, the green light noise signal removal circuit 120 is configured to generate (update) the compensation signal 34 at preset time intervals.

[0087] (Removal of green light noise signal) Next, referring to Figure 8, we will describe the configuration in which the green light noise signal removal circuit 120 removes the green light noise signal 50b (see Figure 7).

[0088] In this embodiment, the green light noise signal removal circuit 120 acquires the time required from the output of the drive signal 32 until the input of the compensation signal 34. The green light noise signal removal circuit 120 is configured to remove the green light noise signal 50b using a compensation signal 34 that has been delayed by the time required until the input of the compensation signal 34. The time required until the input of the compensation signal 34 is the delay time 35 acquired during calibration and stored in the first storage unit 14.

[0089] Specifically, as shown in Figure 8, the green light noise signal removal circuit 120 further comprises a compensation signal generation unit 120d, a DA conversion unit 120e, and a first green light noise removal unit 120f. The compensation signal generation unit 120d is a functional block that operates when the green light noise signal removal circuit 120 executes a program stored in the first storage unit 14. The DA conversion unit 120e is configured to convert a compensation signal 34, which is a digital signal, into a compensation waveform 34a, which is an analog signal. The DA conversion unit 120e includes, for example, a DA conversion circuit. The first green light noise removal unit 120f includes, for example, a differential amplifier.

[0090] When the first control unit 13 outputs a drive signal 32, the drive signal 32 is input to the first light-emitting unit 10 (see Figure 2) and the compensation signal generation unit 120d. When the drive signal 32 is input, the compensation signal generation unit 120d obtains a delay time 35 and waveform information 36 of the green light noise signal from the first storage unit 14. Then, the compensation signal generation unit 120d generates a compensation signal 34 based on the waveform information 36 of the green light noise signal. Furthermore, after the drive signal 32 is input, the compensation signal generation unit 120d delays the compensation signal 34 by the delay time 35 and outputs it to the DA conversion unit 120e. Note that the compensation signal generation unit 120d generates and outputs the compensation signal 34 only when the drive signal 32 is ON. Also, the compensation signal generation unit 120d does not generate or output the compensation signal 34 when the drive signal 32 is OFF.

[0091] The DA conversion unit 120e converts the compensation signal 34, which is a digital signal input from the compensation signal generation unit 120d, into an analog compensation waveform 34a. The DA conversion unit 120e then outputs the converted compensation waveform 34a to the first green noise light removal unit 120f.

[0092] The first green noise removal unit 120f receives a received signal 33a from the first light receiving unit 11. The received signal 33a is the electrical signal of the second light 31, which includes the first green noise light 51a (see Figure 7). The first green noise removal unit 120f also receives a compensated waveform 34a from the DA conversion unit 120e. The first green noise removal unit 120f obtains the second light 31 by removing the first green noise light 51a from the received signal 33a. Specifically, the first green noise removal unit 120f obtains the received signal 33, which is the electrical signal of the second light 31 from which the first green noise light 51a has been removed, by subtracting the compensated waveform 34a from the received signal 33a. The first green noise removal unit 120f outputs the obtained received signal 33 to the first signal processing unit 13a.

[0093] Figure 9 is a graph 62 showing the waveforms of the drive signal 32 and the green light noise signal 50b. The horizontal axis of graph 62 is time.

[0094] As shown in Graph 62, there is a difference between the rise time t1 of the drive signal 32 and the rise time t2 of the green light noise signal 50b. The difference between time t1 and time t2 is the difference in time required from when the drive signal 32 rises, when the first light 30 (see Figure 2) emitted from the first light-emitting unit 10 (see Figure 2) undergoes Raman scattering to become the first green noise light 51a (see Figure 6(A)), when it is received by the first light-receiving unit 11 (see Figure 2), until it is converted into an electrical signal. Since the first green noise light 51a is generated instantaneously after the first light 30 is emitted, the difference between time t1 and time t2 is mainly the time required for the first green noise light 51a to be converted into an electrical signal. Furthermore, the difference between time t1 and time t2 is the delay time 35 (see Figure 7), as described above.

[0095] Furthermore, as shown in Graph 62, there is a difference between the time t3 when the drive signal 32 falls and the time t4 when the green light noise signal 50b falls. This difference is also at the same time interval as the delay time 35. Therefore, as shown in Graph 62, when the first communication device 1 (see Figure 2) communicates using the first light 30, the green light noise signal 50b rises after the delay time 35 has elapsed following the rise of the drive signal 32, and the green light noise signal 50b falls after the delay time 35 has elapsed following the fall of the drive signal 32, and this process repeats.

[0096] Figure 10(A) is graph 63 showing the received signal 33a of the second light 31a (see Figure 8) which includes the first green noise light 51a (see Figure 7). Figure 10(B) is graph 64 showing the compensation signal 34. Figure 10(C) is graph 65 showing the received signal 33 of the second light 31 (see Figure 8) after the first green noise light 51a has been removed. In graphs 63 to 65, the vertical axis represents signal intensity, and the horizontal axis represents time.

[0097] As shown in Graph 63, the received signal 33a of the second light 31a (see Figure 8), which includes the first green noise light 51a (see Figure 7), contains the signal component 31b of the second light 31 (see Figure 8) and the green light noise signal 50b. For simplicity, in Graph 63, the signal component 31b of the second light 31 and the green light noise signal 50b are given different hatching colors.

[0098] By subtracting the compensation signal 34 shown in Graph 64 from the received signal 33a shown in Graph 63, we can obtain the received signal 33 from which the green light noise signal 50b has been removed, as shown in Graph 65.

[0099] (Removal of the second green noise light) Next, referring to Figure 11, we will describe the configuration in which the green noise removal filter 121 removes the second green noise light 51b.

[0100] The green noise light removal filter 121 has optical properties similar to the reflective blue transmission filter 25 (see Figure 3), and is configured to selectively transmit blue wavelength light while not transmitting green wavelength light. In other words, the green noise light removal filter 121 is configured to selectively transmit the first light 30 while not transmitting the second green noise light 51b. Therefore, as shown in Figure 11, of the first light 30 emitted from the first light-emitting unit 10 and the second green noise light 51b, which is green light contained in the first light 30, only the first light 30 is irradiated to the outside of the first communication device 1 (see Figure 2) through the first window 16 (see Figure 2).

[0101] (Suppression of the generation of the third green noise light) Next, referring to Figure 12, a configuration in which the third green light noise generation suppression unit (second optical path forming member 122) suppresses the generation of the third green noise light 51c will be described. The third green light noise generation suppression unit (second optical path forming member 122) is configured to suppress the generation of the third green noise light 51c caused by the first light 30 irradiated onto the second optical path forming member 122. Specifically, the second optical path forming member 122 is made of a metallic material. The metallic material is, for example, aluminum. Therefore, the second optical path forming member 122 does not transmit light.

[0102] Here, metallic materials such as aluminum do not easily produce green fluorescence even when irradiated with blue light. Therefore, as shown in Figure 12, even when the first light 30, which is blue light, is irradiated onto the second optical path forming member 122, which is made of a metallic material such as aluminum, the generation of the third green noise light 51c, which is green fluorescence, is suppressed. In Figure 12, the suppression of the generation of the third green noise light 51c is represented by showing the third green noise light 51c as a dashed line.

[0103] (Suppression of the generation of the fourth green noise light) Next, with reference to Figures 13 and 14, a configuration for suppressing the generation of the fourth green noise light 51d (see Figure 6(D)) will be described. The fourth green noise generation suppression member is configured to suppress the generation of the fourth green noise light 51d. The fourth green noise generation suppression member is a reflective green transmission filter 123 that suppresses the generation of the fourth green noise light 51d.

[0104] As shown in Figure 13, by providing a reflective green light transmission filter 123 in front of the absorbing green light transmission filter 15, even when the first light 30 and the second light 31 are incident toward the absorbing green light transmission filter 15 through the second window 17 (see Figure 2) and the second light-transmitting section 122a (see Figure 2), the first light 30 is removed by the reflective green light transmission filter 123. Therefore, it is possible to suppress the irradiation of the absorbing green light transmission filter 15 with the first light 30. Consequently, it is possible to suppress the generation of the fourth green noise light 51d (see Figure 6) from the absorbing green light transmission filter 15 due to irradiation of the absorbing green light transmission filter 15 with the first light 30. Note that Figure 13 shows an example of a configuration in which one reflective green light transmission filter 123 is provided in front of the absorbing green light transmission filter 15.

[0105] Figure 14 is a graph 66 showing the predetermined wavelength band transmitted by the reflective green transmission filter 123 (see Figure 13). In graph 66, the vertical axis represents transmittance and the horizontal axis represents wavelength.

[0106] The transmittance change curve 66a shown in Figure 14 is a curve representing the relationship between the wavelength of light and transmittance in the reflective green transmission filter 123. As shown in the transmittance change curve 66a, in this embodiment, the fourth green light noise generation suppression member (reflective green transmission filter 123 (see Figure 13)) is configured to suppress the generation of fourth green noise light 51d (see Figure 6) caused by the first light 30 (see Figure 2) irradiated onto the absorptive green transmission filter 15 (see Figure 2). Specifically, the reflective green transmission filter 123 selectively transmits light in a predetermined wavelength band that does not include the wavelength band of the first light 30 by reflecting light in the wavelength band of the first light 30. The reflective green transmission filter 123 is a so-called reflective bandpass filter that selectively transmits light in a wavelength band including the second wavelength 41 by reflecting light of wavelengths other than the wavelength band including the second wavelength 41. Therefore, the first light 30, which is light in a wavelength band including the first wavelength 40, is reflected by the reflective green transmission filter 123.

[0107] The reflective green transmission filter 123 has a third transmission band 205 with a second wavelength 41 as its center wavelength, a third lower stop zone 206 that is shorter in wavelength than the third transmission band 205, and a third upper stop zone 207 that is longer in wavelength than the third transmission band 205. In this embodiment, since the second light 31 is blue light, the third transmission band 205 is configured to allow transmission of the green wavelength band. Also, the second light 31 (see Figure 13) emitted from the second light-emitting unit 20 (see Figure 3) will have some wavelength deviation due to manufacturing tolerances. Therefore, the lower limit of the third transmission band 205 is set to a wavelength that is a predetermined wavelength shorter than 518 nm. The upper limit of the third transmission band 205 is set to a wavelength that is a predetermined wavelength longer than 532 nm.

[0108] (Reflective green light transmission filter holding member) As shown in Figure 15(A), in this embodiment, the first communication device 1 includes a pair of reflective green transmission filter holding members 124 that hold the reflective green transmission filter 123 by sandwiching it. The pair of reflective green transmission filter holding members 124 includes one holding member 124a and the other holding member 124b. The pair of reflective green transmission filter holding members 124 also have a U-shape. Specifically, the one holding member 124a has a protrusion 125a that projects toward the other holding member 124b. Therefore, the one holding member 124a has a U-shape when viewed from the side surface 123b direction of the reflective green transmission filter 123. Note that the examples shown in Figures 15(A) and 15(B) are diagrams assuming that the first light 30 (see Figure 2) is irradiated from the direction of the other holding member 124b.

[0109] Furthermore, the other side retaining member 124b has a protruding portion 125b that projects toward the one side retaining member 124a. Therefore, the other side retaining member 124b has a U-shape when viewed from the side surface 123b direction of the reflective green transmission filter 123.

[0110] The pair of reflective green-transmitting filter holding members 124 are configured to form an overlapping region 70 when viewed from the side surface 123a (see Figure 15(A)) of the reflective green-transmitting filter 123. Specifically, as shown in Figure 15(B), when the reflective green-transmitting filter 123 is held by the pair of reflective green-transmitting filter holding members 124, the reflective green-transmitting filter 123 is sandwiched between the one holding member 124a and the other holding member 124b, and the two holding members 124a and the other holding member 124b are fixed in place. At this time, the protrusions 125a of the one holding member 124a and the protrusions 125b of the other holding member 124b overlap each other when viewed from the side surface 123a of the reflective green-transmitting filter 123, forming a region 70.

[0111] Region 70 is a region that is not irradiated by the first light 30 (see Figure 2) by the one-sided retaining member 124a and the other-sided retaining member 124b. Therefore, for example, even when the one-sided retaining member 124a and the other-sided retaining member 124b are fixed by applying adhesive 126 to region 70, the irradiation of the adhesive 126 with the first light 30 can be suppressed. As a result, the generation of green fluorescence caused by irradiation of the adhesive 126 with the first light 30 can be suppressed. Furthermore, when viewed from the side surface 123a (see Figure 15(A)) of the reflective green transmission filter 123, regions 70 overlap each other. Therefore, even if the first light 30 is scattered multiple times within the reflective green transmission filter retaining member 124, the first light 30 only reaches the inner surface of the protrusion 125a. Thus, in this embodiment, the reflective green transmission filter retaining member 124 can suppress the irradiation of the adhesive 126 with the first light 30.

[0112] (Calibration process) Next, referring to Figure 16, we will explain the process by which the green light noise signal removal circuit 120 (see Figure 7) acquires the delay time 35 (see Figure 7).

[0113] In step 101, the first control unit 13 (see Figure 7) outputs a drive signal 32 (see Figure 7) to the first light-emitting unit 10 (see Figure 2), thereby emitting the first light 30 (see Figure 2).

[0114] In step 102, the delay time acquisition unit 120b (see Figure 7) acquires the drive signal 32 from the first control unit 13. The drive signal 32 is output to the delay time acquisition unit 120b when it is output from the first control unit 13 to the first light-emitting unit 10. Therefore, the delay time acquisition unit 120b can acquire the timing when the first light 30 is emitted from the first light-emitting unit 10.

[0115] In step 103, the delay time acquisition unit 120b acquires the green light noise signal 50b.

[0116] In step 104, the delay time acquisition unit 120b acquires the delay time 35 (see Figure 7). Specifically, the delay time acquisition unit 120b acquires the delay time 35 based on the drive signal 32 acquired in step 102 and the green light noise signal 50b acquired in step 103.

[0117] In step 105, the first storage unit 14 stores the delay time 35.

[0118] In step 106, the green light noise information acquisition unit 120c (see Figure 7) acquires waveform information 36 of the green light noise signal.

[0119] In step 107, the first storage unit 14 stores the waveform information 36 of the green light noise signal. After that, the process ends.

[0120] Note that the processes in steps 102-104 and the processes in steps 106 and 107 may be performed in either order. Also, the processes in steps 102-104 and the processes in steps 106 and 107 may be executed in parallel.

[0121] (Green light noise signal removal processing) Next, referring to Figure 17, the process by which the green light noise signal removal circuit 120 (see Figure 8) removes the green light noise signal 50b (see Figure 8) will be explained. Note that the process shown in Figure 17 is started when the compensation signal generation unit 120d (see Figure 8) acquires the drive signal 32 (see Figure 8) from the first control unit 13 (see Figure 8).

[0122] In step 110, the compensation signal generation unit 120d determines whether or not the drive signal 32 (see Figure 8) has been output. If the drive signal 32 has been output, the process proceeds to step 111. If the drive signal 32 has not been output, the process ends.

[0123] In step 111, the compensation signal generation unit 120d acquires the delay time 35 (see Figure 8) and the waveform information 36 (see Figure 8) of the green light noise signal from the first storage unit 14 (see Figure 8).

[0124] In step 112, the compensation signal generation unit 120d generates a compensation signal 34 (see Figure 8).

[0125] In step 113, the compensation signal generation unit 120d acquires the drive signal 32 and then outputs the compensation signal 34 with a delay of 35.

[0126] In step 114, the first green noise removal unit 120f (see Figure 8) obtains the received signal 33 (see Figure 8) of the second light 31 (see Figure 3) by subtracting a compensation signal 34 from the received signal 33a (see Figure 8) of the second light 31 (see Figure 3) which includes the first green noise light 51a (see Figure 7). That is, the first green noise removal unit 120f removes the green light noise signal 50b (see Figure 7) from the second light 31a which includes the first green noise light 51a.

[0127] In step 115, the compensation signal generation unit 120d determines whether the drive signal 32 has been stopped. If the drive signal 32 has not been stopped, the process proceeds to step 114. If the drive signal 32 has been stopped, the process proceeds to step 116.

[0128] In step 116, the compensation signal generation unit 120d stops the output of the compensation signal 34. Note that if the output of the drive signal 32 stops, the emission of the first light 30 (see Figure 2) stops. However, even if the emission of the first light 30 stops, the first green noise light 51a received by the first light receiving unit 11 (see Figure 2) is converted into a green light noise signal 50b. Therefore, even if the output of the drive signal 32 stops, the green light noise signal 50b is acquired after a delay of 35 minutes. Accordingly, the green light noise signal removal circuit 120 continues the process of removing the green light noise signal 50b for a delay of 35 minutes even after the output of the drive signal 32 stops. After that, the process ends.

[0129] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0130] In this embodiment, as described above, the underwater optical wireless communication device (first communication device 1) is an underwater optical wireless communication device that performs optical wireless communication underwater, and comprises a first light-emitting unit 10 that emits first light 30 with a first wavelength 40 centered on a wavelength included in the blue wavelength band, a first light-receiving unit 11 that receives second light 31 with a second wavelength 41 centered on a wavelength included in the green wavelength band, and a noise suppression unit that suppresses noise caused by green light generated due to the first light 30.

[0131] As a result, the noise suppression unit suppresses noise caused by green light originating from the first light 30, thereby preventing a decrease in the signal-to-noise ratio of the second light 31. Consequently, it is possible to prevent a decrease in communication accuracy due to green light noise caused by green light other than the second light 31, which is the green light received from the communication partner (second communication device 2).

[0132] Furthermore, in this embodiment, as described above, the underwater optical wireless communication system 100 is an underwater optical wireless communication system that performs optical wireless communication underwater, and comprises a first underwater optical wireless communication device (first communication device 1) that emits a first light 30 with a first wavelength 40 centered on a first wavelength band included in the blue wavelength band and receives a second light 31 with a second wavelength 41 centered on a second wavelength band included in the green wavelength band, and a second underwater optical wireless communication device (second communication device 2) that emits the second light 31 and receives the first light 30, and the first underwater optical wireless communication device (first communication device 1) comprises a first light-emitting unit 10 that emits the first light 30, a first light-receiving unit 11 that receives the second light 31, and a noise suppression unit that suppresses noise caused by green light generated due to the first light 30.

[0133] This makes it possible to provide an underwater optical wireless communication system 100 that, like the underwater optical wireless communication device (first communication device 1), can suppress the reduction in communication accuracy caused by green light noise other than the second light 31, which is the green light received from the communication partner (second communication device 2).

[0134] Furthermore, in the above embodiment, the following additional effects can be obtained by configuring it as follows.

[0135] In other words, in this embodiment, as described above, the noise suppression unit includes at least one of a green light noise removal unit 12a that removes green light noise, which is noise caused by green light generated due to the first light 30, and a green light noise generation suppression unit 12b that suppresses the generation of green light noise. As a result, for example, if the noise suppression unit includes the green light noise removal unit 12a, even if green light noise is generated due to the light received by the first light receiving unit 11, the green light noise removal unit 12a removes the green light noise, thus suppressing a decrease in the communication accuracy of the second light 31 due to green light noise. Also, for example, if the noise suppression unit includes the green light noise generation suppression unit 12b, the generation of green light noise is suppressed by the green light noise generation suppression unit 12b, thus reducing the amount of green light noise. As a result, it is possible to suppress an increase in the ratio of green light noise to the second light 31.

[0136] Furthermore, in this embodiment, as described above, the green light noise includes at least one of the green noise light 50a, which is green light generated by the first light 30, and the green light noise signal 50b, which is the green noise light 50a converted into an electrical signal by the first light receiving unit 11. The green light noise removal unit 12a includes at least one of the green light noise signal removal circuit 120, which electrically removes the green light noise signal 50b, and the green noise light removal filter 121, which optically removes the green noise light 50a. As a result, for example, if the green light noise includes the green light noise signal 50b, and the green light noise removal unit 12a includes the green light noise signal removal circuit 120, the green light noise signal 50b will be removed by the green light noise signal removal circuit 120 even if the light received by the first light receiving unit 11 includes the green noise light 50a. Therefore, it is possible to suppress a decrease in the communication accuracy of the second light 31 due to the green light noise signal 50b. Furthermore, for example, if the green light noise includes green noise light 50a and the green light noise removal unit 12a includes a green noise light removal filter 121, it is possible to suppress the incidence of green noise light 50a on the first light receiving unit 11. As a result, it is possible to reduce the amount of green light noise caused by green noise light 50a, thereby suppressing an increase in the ratio of green light noise to the second light 31.

[0137] Furthermore, in this embodiment, as described above, the green noise light 50a is at least one of the first green noise light 51a, which is green Raman scattered light generated when the first light 30 undergoes Raman scattering in water, and the second green noise light 51b, which is green light contained in the first light 30. This makes it possible to provide an underwater optical wireless communication device (first communication device 1) that can suppress a decrease in the communication accuracy of the second light 31 caused by at least one of the first green noise light 51a and the second green noise light 51b, which are the cause of green light noise.

[0138] Furthermore, in this embodiment, as described above, the green light noise signal removal circuit 120 is configured to remove the green light noise signal 50b based on the first green noise light 51a included in the received signal 33 at the first light receiving unit 11, based on the drive signal 32 when the first light emitting unit 10 emits the first light 30. As a result, even if the received signal 33 contains the green light noise signal 50b, the green light noise signal 50b is removed by the green light noise signal removal circuit 120. Therefore, even if the first green noise light 51a is incident on the first light receiving unit 11, it is possible to suppress a decrease in the communication accuracy of the second light 31 due to the green light noise signal 50b based on the first green noise light 51a.

[0139] Furthermore, in this embodiment, as described above, the green light noise signal removal circuit 120 acquires, during calibration when the first light receiving unit 11 is not receiving the second light 31, the compensation signal 34 which is the electrical signal of the light received by the first light receiving unit 11 when the first light emitting unit 10 emits the first light 30, and the time required from when the drive signal 32 is output until the compensation signal 34 is input (delay time 35). The circuit is configured to remove the green light noise signal 50b using the compensation signal 34 delayed by the time required until the compensation signal 34 is input. As a result, when the first communication device 1 communicates with the second communication device 2, the green light noise signal 50b can be easily removed using the compensation signal 34 acquired during calibration and the delay time 35.

[0140] Furthermore, in this embodiment, as described above, the first optical path forming member 18a is provided to hold the first light-emitting unit 10 and to form the first optical path which is the optical path of the first light 30. The green noise light removal filter 121 is positioned after the first light-emitting unit 10 in the first optical path forming member 18a and is configured to selectively transmit the first light 30 without transmitting the second green noise light 51b. This makes it possible to suppress the irradiation of the second green noise light 51b from the first optical path forming member 18a. Therefore, it is possible to suppress the reflection (or scattering) of the second green noise light 51b in water or within the first communication device 1 and irradiation of the second light-receiving unit 21. As a result, it is possible to reduce the amount of green light noise caused by the second green noise light 51b, and thus it is possible to suppress an increase in the ratio of green light to the second light 31.

[0141] Furthermore, in this embodiment, as described above, the device further includes an absorbing green transmission filter 15 positioned in front of the first light receiving unit 11, which selectively transmits light that includes light in the wavelength band of the second light 31 and does not include light in a predetermined wavelength band of the first light 30 by absorbing light in the wavelength band of the first light 30, and a second optical path forming member 122 that holds the first light receiving unit 11 and forms a second optical path which is the optical path of the second light 31, wherein the green noise light 50a is at least one of a third green noise light 51c, which is green fluorescence emitted from the resin member 3 when the first light 30 is irradiated onto the resin member 3, and a fourth green noise light 51d, which is green fluorescence emitted from the absorbing green transmission filter 15 when the first light 30 is irradiated onto the absorbing green transmission filter 15. This makes it possible to provide an underwater optical wireless communication device (first communication device 1) that can suppress an increase in the ratio of green light noise to the second light 31 caused by at least one of the third green noise light 51c and the fourth green noise light 51d, which are the causes of green light noise.

[0142] Furthermore, in this embodiment, as described above, the green light noise generation suppression unit 12b includes a third green light noise generation suppression unit that suppresses the generation of third green noise light 51c caused by the first light 30 irradiated onto the second light path forming member 122. Here, if the second light path forming member 122 is formed of a resin member 3 or otherwise does not include the third green light noise generation suppression unit, it emits third green noise light 51c, which is green fluorescence, when irradiated with the first light 30. As a result, the third green noise light 51c emitted from the resin material becomes noise to the first light receiving unit 11, and the ratio of green light noise to the second light 31 increases. Therefore, as described above, by including the third green noise light suppression unit in the second light path forming member 122, it is possible to suppress the generation of third green noise light 51c from the second light path forming member 122 even when the first light 30 is irradiated onto the second light path forming member 122. As a result, it becomes possible to suppress the generation of the third green noise light 51c, which is noise, from the second optical path forming member 122, and thus suppress the increase in green light noise for the second light 31.

[0143] Furthermore, in this embodiment, as described above, the third green light noise generation suppression unit is a second optical path forming member 122 made of a metal material. Here, metal materials do not easily generate green fluorescence even when irradiated with the first light 30, which is blue light. Therefore, as described above, by forming the second optical path forming member 122 of a metal material, it is possible to easily suppress the generation of fluorescence from the second optical path forming member 122 even when the first light 30 is irradiated onto the second optical path forming member 122.

[0144] Furthermore, in this embodiment, as described above, the green light noise generation suppression unit 12b includes a fourth green light noise generation suppression member that suppresses the generation of fourth green noise light 51d caused by the first light 30 irradiated onto the absorption-type green transmission filter 15. As a result, the generation of fourth green noise light 51d from the absorption-type green transmission filter 15 is suppressed by the fourth green noise light generation suppression member, and thus it is possible to suppress the increase in the ratio of green light noise to the second light 31 due to the fourth green noise light 51d.

[0145] Furthermore, in this embodiment, as described above, the absorbing green transmission filter 15 is positioned in front of the first light receiving unit 11 in the second optical path forming member 122 and is configured to absorb light with a wavelength shorter than the second wavelength 41. The fourth green light noise generation suppression member is positioned in front of the absorbing green transmission filter 15 in the second optical path forming member 122 and is a reflective green transmission filter 123 that selectively transmits light in a predetermined wavelength band that does not include the wavelength band of the first light 30 by reflecting light in the wavelength band of the first light 30. As a result, since the reflective green transmission filter 123 is positioned in front of the absorbing green transmission filter 15, it is possible to suppress the irradiation of the absorbing green transmission filter 15 with light in the wavelength band of the first light 30. As a result, it is possible to easily suppress the generation of the fourth green noise light 51d from the absorbing green transmission filter 15.

[0146] Furthermore, in this embodiment, as described above, a pair of reflective green-transmitting filter holding members 124 are provided, which have a U-shape and hold the reflective green-transmitting filter 123 by sandwiching it. The pair of reflective green-transmitting filter holding members 124 are configured to form overlapping regions 70 when viewed from the side surface 123a direction of the reflective green-transmitting filter 123. As a result, when the pair of reflective green-transmitting filter holding members 124 hold the reflective green-transmitting filter 123, even if the pair of reflective green-transmitting filter holding members 124 are fixed by an adhesive 126 applied to the region 70, it is possible to prevent the adhesive 126 from being irradiated with the first light 30. As a result, it is possible to prevent the generation of green fluorescence caused by the adhesive 126 that fixes the pair of reflective green-transmitting filter holding members 124.

[0147] [Differentiation] It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and further includes all modifications (exceptions) within the meaning and scope equivalent to the claims.

[0148] For example, the above embodiment shows an example of a noise suppression unit configuration that includes both a green light noise removal unit 12a and a green light noise generation suppression unit 12b, but the present invention is not limited thereto. For example, the noise suppression unit may include either the green light noise removal unit 12a or the green light noise generation suppression unit 12b. However, in the case where the noise suppression unit includes only one of the green light noise removal unit 12a or the green light noise generation suppression unit 12b, the communication accuracy of the second optical fiber 31 will be reduced due to green light noise compared to the case where the noise suppression unit includes both the green light noise removal unit 12a and the green light noise generation suppression unit 12b. Therefore, it is preferable that the noise suppression unit includes both the green light noise removal unit 12a and the green light noise generation suppression unit 12b.

[0149] Furthermore, in the above embodiment, an example was shown in which the green light noise includes both green noise light 50a and green light noise signal 50b, and the green light noise removal unit 12a includes both a green light noise signal removal circuit 120 and a green noise light removal filter 121. However, the present invention is not limited to this. The green light noise removal unit 12a does not have to include both the green light noise signal removal circuit 120 and the green noise light removal filter 121. If the green light noise is only green noise light 50a, the green light noise removal unit 12a only needs to include the green noise light removal filter 121. Also, if the green light noise includes the green light noise signal 50b, the green light noise removal unit 12a only needs to include the green light noise signal removal circuit 120.

[0150] Furthermore, although the above embodiment shows an example in which the green noise light 50a includes both the first green noise light 51a and the second green noise light 51b, the present invention is not limited thereto. The green noise light 50a may include only the first green noise light 51a. Alternatively, the green noise light 50a may include only the second green noise light 51b. If the green noise light 50a includes only the first green noise light 51a, the green noise removal unit 12a may include a green noise signal removal circuit 120. If the green noise light 50a includes only the second green noise light 51b, the green noise removal unit 12a may include a green noise light removal filter 121.

[0151] Furthermore, although the above embodiment shows an example in which the green light noise signal removal circuit 120 removes the green light noise signal 50b from the received light signal 33 based on the drive signal 32, the present invention is not limited thereto. The green light noise signal removal circuit 120 may be configured in any way as long as it is possible to remove the green light noise signal 50b from the received light signal 33.

[0152] Furthermore, in the above embodiment, an example was shown in which the green noise light 50a includes both the third green noise light 51c and the fourth green noise light 51d, and the green light noise generation suppression unit 12b includes both a second optical path forming member 122 made of a metal material and a reflective green transmission filter 123. However, the present invention is not limited thereto. For example, if only the third green noise light 51c is generated as the green noise light 50a, the green light noise generation suppression unit 12b only needs to include the second optical path forming member 122 made of a metal material. Also, if only the fourth green noise light 51d is generated as the green noise light 50a, the green light noise generation suppression unit 12b may include only the reflective green transmission filter 123. However, if the second optical path forming member 122 is made of a resin material, the third green noise light 51c will be generated when blue light such as the first light 30 is irradiated onto it. Furthermore, when an absorbing green light transmission filter 15 is placed before the first light receiving unit 11, a fourth green noise light 51d is generated when blue light such as the first light 30 is irradiated onto the absorbing green light transmission filter 15. Therefore, it is preferable that the green light noise generation suppression unit 12b includes both a second optical path forming member 122 made of a metallic material and a reflective green light transmission filter 123.

[0153] Furthermore, although the above embodiment shows an example in which the first optical path forming member 18a and the second optical path forming member 122 are formed from aluminum as the metallic material, the present invention is not limited thereto. For example, the first optical path forming member 18a and the second optical path forming member 122 may be made from a metallic material other than aluminum. However, from the viewpoint of weight, processability, etc., it is preferable that the first optical path forming member 18a and the second optical path forming member 122 are made from aluminum.

[0154] Furthermore, although the above embodiment shows an example in which one reflective green transmission filter 123 is provided before the absorbing green transmission filter 15, the present invention is not limited thereto. For example, multiple reflective green transmission filters 123 may be provided before the absorbing green transmission filter 15. For example, two reflective green transmission filters 123 may be provided as multiple reflective green transmission filters 123.

[0155] Furthermore, although the above embodiment shows an example in which the reflective green transmission filter holding member 124 is a pair of holding members having a U-shape, the present invention is not limited thereto. The shape of the reflective green transmission filter holding member 124 is not limited as long as it is possible to suppress the generation of green fluorescence caused by the first light 30 when fixing the reflective green transmission filter 123.

[0156] Furthermore, the optical characteristics such as wavelength band and transmittance of the first light-emitting unit 10, second light-emitting unit 20, absorption-type green transmission filter 15, reflection-type blue transmission filter 25, green noise light removal filter 121, and reflection-type green transmission filter 123 described in the above embodiment are merely examples and are not limited to the optical characteristics described above.

[0157] Furthermore, although the above embodiment shows an example in which the second communication device 2 is provided on the fixed body 81, the present invention is not limited thereto. For example, the second communication device 2 may be provided on a mobile body different from the mobile body 80 on which the first communication device 1 is provided.

[0158] [Pattern] Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0159] (Item 1) An underwater optical wireless communication device that performs optical wireless communication underwater, A light-emitting unit that emits a first light with a first wavelength centered on a wavelength included in the blue wavelength band, A light-receiving unit that receives a second light with a central wavelength of the second wavelength included in the green wavelength band, An underwater optical wireless communication device comprising: a noise suppression unit that suppresses noise caused by green light generated by the first light;

[0160] (Item 2) The underwater optical wireless communication device according to item 1, wherein the noise suppression unit includes at least one of a green light noise removal unit that removes green light noise, which is noise caused by green light generated by the first light, and a green light noise generation suppression unit that suppresses the generation of the green light noise.

[0161] (Item 3) The green light noise includes at least one of the following: green noise light, which is green light generated by the first light, and a green light noise signal obtained by converting the green noise light into an electrical signal by the light receiving unit. The underwater optical wireless communication device according to item 2, wherein the green light noise removal unit includes at least one of a green light noise signal removal circuit for electrically removing the green light noise signal and a green noise light removal filter for optically removing the green noise light.

[0162] (Item 4) The underwater optical wireless communication device according to item 3, wherein the green noise light is at least one of a first green noise light, which is green Raman scattered light produced when the first light is Raman scattered in water, and a second green noise light, which is green light contained in the first light.

[0163] (Item 5) The underwater optical wireless communication device according to item 4, wherein the green light noise signal removal circuit is configured to remove the green light noise signal based on the first green noise light included in the light-receiving signal in the light-receiving unit, based on the drive signal when the light-emitting unit emits the first light.

[0164] (Item 6) The underwater optical wireless communication device according to item 5, wherein the green light noise signal removal circuit is configured to remove the green light noise signal by delaying the compensation signal by the compensation signal, when the light receiving unit is not receiving the second light during calibration, when the light emitting unit emits the first light, and the time required from the time the drive signal is output until the compensation signal is input, and during calibration when the light receiving unit is not receiving the second light.

[0165] (Item 7) The system further includes a first optical path forming member that holds the light-emitting portion and forms a first optical path which is the optical path of the first light, The underwater optical wireless communication device according to any one of items 4 to 6, wherein the green noise light removal filter is arranged in the first optical path forming member after the light-emitting portion and is configured to selectively transmit the first light without transmitting the second green noise light.

[0166] (Item 8) An absorption-type green transmission filter is positioned in front of the light-receiving unit and selectively transmits light that includes light in the wavelength band of the second light and does not include light in a predetermined wavelength band of the first light by absorbing light in the wavelength band of the first light, The system further comprises a second optical path forming member that holds the light receiving portion and forms a second optical path which is the optical path of the second light, The underwater optical wireless communication device according to any one of items 3 to 7, wherein the green noise light is at least one of a third green noise light, which is green fluorescence emitted from the resin member when the first light is irradiated onto the resin member, and a fourth green noise light, which is green fluorescence emitted from the absorbing green transmission filter when the first light is irradiated onto the absorbing green transmission filter.

[0167] (Item 9) The underwater optical wireless communication device according to item 8, wherein the green light noise generation suppression unit includes a third green light noise generation suppression unit that suppresses the generation of the third green noise light caused by the first light irradiated onto the second optical path forming member.

[0168] (Item 10) The underwater optical wireless communication device according to item 9, wherein the third green light noise generation suppression unit is the second optical path forming member formed of a metallic material.

[0169] (Item 11) The underwater optical wireless communication device according to any one of items 8 to 10, wherein the green light noise generation suppression unit includes a fourth green light noise generation suppression member that suppresses the generation of the fourth green noise light caused by the first light irradiated onto the absorbing green transmission filter.

[0170] (Item 12) The aforementioned absorbing green transmission filter is positioned in front of the light receiving section in the second optical path forming member and is configured to absorb light with a wavelength shorter than the second wavelength. The underwater optical wireless communication device according to item 11, wherein the fourth green light noise generation suppression member is a reflective green light transmission filter that is placed in the second optical path forming member before the absorbing green light transmission filter and selectively transmits light in a predetermined wavelength band that does not include the wavelength band of the first light by reflecting light in the wavelength band of the first light.

[0171] (Item 13) The system further comprises a pair of reflective green transmission filter holding members having a U-shape and holding the reflective green transmission filter by sandwiching it, The underwater optical wireless communication device according to item 12, wherein the pair of reflective green-transmitting filter holding members are configured to form overlapping regions when viewed from the side of the reflective green-transmitting filter.

[0172] (Item 14) An underwater optical wireless communication system that performs optical wireless communication underwater, A first communication device that emits first light with a first wavelength centered on a wavelength included in the blue wavelength band, and receives second light with a second wavelength centered on a wavelength included in the green wavelength band, The system comprises a second underwater optical wireless communication device that emits the second light and receives the first light, The aforementioned first underwater optical wireless communication device is, The light-emitting part that emits the first light, A light-receiving unit that receives the second light, An underwater optical wireless communication system comprising: a noise suppression unit that suppresses noise caused by green light generated by the first light; [Explanation of symbols]

[0173] 1. First communication device (underwater optical wireless communication device, first underwater optical wireless communication device) 2. Second communication device (second underwater optical wireless communication device) 10. First light-emitting section (light-emitting section) 11 1st light receiving section (light receiving section) 12a Green light noise reduction section 12b Green light noise generation suppression unit 15 Absorption-type green transmission filter 30 1st light 31 Second light 32 Drive signal 33 Received light signal 34 Compensation signal 35 Delay time 40 1st wavelength 41 Second wavelength 50a Green Noise Light 50b Green light noise signal 51a First green noise light 51b Second Green Noise Light 51c Third Green Noise Light 51d Fourth green noise light 70 regions (regions that overlap each other) 80 Mobile Units 100 Underwater Optical Wireless Communication Systems 120 Green light noise signal removal circuit 121 Green Noise Removal Filter 122 Second optical path forming member (third green light noise generation suppression unit) 123 Reflective green light transmission filter (4th green light noise generation suppression member) 123 Side view (side view of the reflective green transmission filter) 124 Reflective green transmission filter holding member

Claims

1. An underwater optical wireless communication device that performs optical wireless communication underwater, A light-emitting unit that emits a first light with a first wavelength centered on a wavelength included in the blue wavelength band, A light-receiving unit that receives a second light with a second wavelength centered on the second wavelength included in the green wavelength band, An underwater optical wireless communication device comprising: a noise suppression unit that suppresses noise caused by green light generated by the first light;

2. The underwater optical wireless communication device according to claim 1, wherein the noise suppression unit includes at least one of a green light noise removal unit that removes green light noise, which is noise caused by green light generated by the first light, and a green light noise generation suppression unit that suppresses the generation of the green light noise.

3. The green light noise includes at least one of the following: green noise light, which is green light generated by the first light, and a green light noise signal obtained by converting the green noise light into an electrical signal by the light receiving unit. The underwater optical wireless communication device according to claim 2, wherein the green light noise removal unit includes at least one of a green light noise signal removal circuit for electrically removing the green light noise signal and a green noise light removal filter for optically removing the green noise light.

4. The underwater optical wireless communication device according to claim 3, wherein the green noise light is at least one of a first green noise light which is green Raman scattered light produced when the first light is Raman scattered in water, and a second green noise light which is green light emitted together with the first light.

5. The underwater optical wireless communication device according to claim 4, wherein the green light noise signal removal circuit is configured to remove the green light noise signal based on the first green noise light included in the light-receiving signal in the light-receiving unit, based on the drive signal when the light-emitting unit emits the first light.

6. The underwater optical wireless communication device according to claim 5, wherein the green light noise signal removal circuit is configured to remove the green light noise signal by delaying the compensation signal by the compensation signal, when the light receiving unit is not receiving the second light during calibration, when the light emitting unit emits the first light, and the time required from the time the drive signal is output until the compensation signal is input, and during calibration when the light receiving unit is not receiving the second light.

7. The system further includes a first optical path forming member that holds the light-emitting portion and forms a first optical path which is the optical path of the first light, The underwater optical wireless communication device according to any one of claims 4 to 6, wherein the green noise light removal filter is arranged in the first optical path forming member after the light-emitting portion and is configured to selectively transmit the first light without transmitting the second green noise light.

8. An absorption-type green transmission filter is positioned in front of the light-receiving unit and selectively transmits light that includes light in the wavelength band of the second light and does not include light in a predetermined wavelength band of the first light by absorbing light in the wavelength band of the first light, The system further comprises a second optical path forming member that holds the light receiving unit and forms a second optical path which is the optical path of the second light, The underwater optical wireless communication device according to any one of claims 3 to 6, wherein the green noise light is at least one of a third green noise light which is green fluorescence emitted from the resin member when the first light is irradiated onto the resin member, and a fourth green noise light which is green fluorescence emitted from the absorbing green transmission filter when the first light is irradiated onto the absorbing green transmission filter.

9. The underwater optical wireless communication device according to claim 8, wherein the green light noise generation suppression unit includes a third green light noise generation suppression unit that suppresses the generation of the third green noise light caused by the first light irradiated onto the second optical path forming member.

10. The underwater optical wireless communication device according to claim 9, wherein the third green light noise generation suppression unit is the second optical path forming member formed of a metallic material.

11. The underwater optical wireless communication device according to claim 9, wherein the green light noise generation suppression unit includes a fourth green light noise generation suppression member that suppresses the generation of the fourth green noise light caused by the first light irradiated onto the absorbing green transmission filter.

12. The aforementioned absorbing green light transmission filter is positioned in front of the light receiving section in the second optical path forming member and is configured to absorb light with a wavelength shorter than the second wavelength. The underwater optical wireless communication device according to claim 11, wherein the fourth green light noise generation suppression member is a reflective green light transmission filter that is arranged in the second optical path forming member before the absorbing green light transmission filter and selectively transmits light in a predetermined wavelength band that does not include the wavelength band of the first light by reflecting light in the wavelength band of the first light.

13. The device further comprises a pair of reflective green-transmitting filter holding members, each having a U-shape and holding the reflective green-transmitting filter by sandwiching it between them. The underwater optical wireless communication device according to claim 12, wherein the pair of reflective green-transmitting filter holding members are configured to form overlapping regions when viewed from the side of the reflective green-transmitting filter.

14. An underwater optical wireless communication system that performs optical wireless communication underwater, A first underwater optical wireless communication device that emits first light with a first wavelength centered on a wavelength included in the blue wavelength band and receives second light with a second wavelength centered on a wavelength included in the green wavelength band, The system comprises a second underwater optical wireless communication device that emits the second light and receives the first light, The first underwater optical wireless communication device is The light-emitting part that emits the first light, A light-receiving unit that receives the second light, An underwater optical wireless communication system comprising: a noise suppression unit that suppresses noise caused by green light generated by the first light;

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