Patent Description:
The following description sets forth the inventor's knowledge of the related art and problems therein and should not be construed as an admission of knowledge in the prior art.

Conventionally, an underwater optical wireless communication device is known. Such a device is disclosed in, for example, <CIT>.

The above-described <CIT> discloses an underwater optical wireless communication device equipped with a first underwater communication device and a second underwater optical wireless communication device. The first underwater communication device is equipped with an irradiation unit that irradiates visible light, a light receiver that receives visible light, and a controller that controls the irradiation unit and the light receiver. The second underwater communication device is equipped with an irradiation unit that irradiates visible light, a light receiver that receives visible light, and a controller that controls the irradiation unit and the light receiver. The first underwater communication device is configured to communicate with the second underwater communication device by receiving visible light emitted from the second light receiving device.

Here, although not disclosed in the above-described <CIT>, depending on the position (depth) where the first underwater communication device (underwater optical wireless communication device) is placed, ambient light other than communication light may be incident to the underwater optical wireless communication device, together with visible light (communication light). In other words, in the light receiver (first light receiver) of an underwater optical wireless communication device, both communication light and ambient light may be received in the case where the depth at which the underwater optical wireless communication device is located is shallow.

Moreover prior art document <CIT> discloses an underwater optical wireless system comprising several photo-detectors with different photo-sensitivity wherein, with a switch, the receiver selects the photo-detectors which can pass a wavelength range that is different from the ambient light to effectively filter out ambient light and controls the gain of the amplifier depending on the switch position.

In this case, there is an inconvenience that the ambient light received together with the communication light interferes with communication by the communication light. Therefore, there is a need for an underwater optical wireless communication device that can suppress the interference of communication light by ambient light even when ambient light is received together with communication light.

The present invention has been made to solve the above problems. One object of the present invention is to provide an underwater optical wireless communication device capable of suppressing interference of communication by communication light due to ambient light, even when ambient light is received together with communication light.

In order to attain the above-described objects, an underwater optical wireless communication device includes:.

In the underwater optical wireless communication device according to one aspect of the present invention, it is equipped with a controller that performs control to adjust the gain of the first light receiver based on the intensity of the communication light received by the first light receiver and the intensity of the ambient light received by the second light receiver, as described above.

With this, the gain of the first light receiver is adjusted based on the intensity of the communication light received by the first light receiver and the intensity of the ambient light received by the second light receiver, so that the amplitude of the communication light can be increased when the ambient light is strong. Therefore, it becomes possible to increase the ratio of the amplitude of the communication light to the noise due to ambient light included in the communication light, thereby improving the S/N ratio of the communication light. As a result, even in the case where ambient light is received together with the communication light, it is possible to suppress the communication by the communication light <NUM> from being interfered with by the ambient light.

The above and/or other aspects, features and/or advantages of various embodiments will be further appreciated in view of the following description in conjunction with the accompanying figures. Various embodiments can include and/or exclude different aspects, features and/or advantages where applicable. In addition, various embodiments can combine one or more aspect or feature of other embodiments where applicable. The descriptions of aspects, features and/or advantages of particular embodiments should not be construed as limiting other embodiments or the claims.

The preferred embodiments of the present disclosure are shown by way of example, and not limitation, in the accompanying figures.

In the following paragraphs, some preferred embodiments of the present disclosure will be described by way of example and not limitation. It should be understood based on this disclosure that various other modifications can be made by those in the art based on these illustrated embodiments.

Hereinafter, some embodiments in which the present invention is embodied will be described based on the attached drawings.

Referring to <FIG> and <FIG>, the configuration of an underwater optical wireless communication system <NUM> equipped with a first underwater optical wireless communication device <NUM> and a second underwater optical wireless communication device <NUM> according to one embodiment will be described.

As shown in <FIG>, the underwater optical wireless communication system <NUM> is equipped with a first underwater optical wireless communication device <NUM> and a second underwater optical wireless communication device <NUM>. The first underwater optical wireless communication device <NUM> and the second underwater optical wireless communication device <NUM> are configured to perform bidirectional optical communication simultaneously. The underwater optical wireless communication system <NUM> is used for inspecting underwater structures, such as offshore wind generators and fish preserves.

The first underwater optical wireless communication device <NUM> is located underwater. Specifically, the first underwater optical wireless communication device <NUM> is installed on an underwater moving body <NUM>. The moving body <NUM> includes, for example, an AUV (Autonomous Underwater Vehicle). Further, the moving body <NUM> is equipped with a propulsion mechanism 80a. Further, the moving body <NUM> is configured to emit illumination light 91b.

The propulsion mechanism 80a is configured to provide propulsion to the moving body <NUM> under the control of the controller <NUM> (see <FIG>). The propulsion mechanism 80a includes, for example, a propeller (not illustrated) and a drive source (not illustrated) that drives the propeller. The propulsion mechanism 80a may be a so-called screw configuration, which obtains propulsion by stirring water by rotating a propeller, or a so-called water jet propulsion mechanism, which obtains propulsion by jetting a high-pressure stream of water backward.

The second underwater optical wireless communication device <NUM> is located underwater. Specifically, the second underwater optical wireless communication device <NUM> is installed on a fixed body <NUM> fixed underwater. The fixed body <NUM> is fixed underwater by being installed on the seabed <NUM> via a holding member 81a.

Note that, as shown in <FIG>, the first underwater optical wireless communication device <NUM> and the second underwater optical wireless communication device <NUM> communicate using communication light <NUM> in an environment where ambient light <NUM> is incident. Ambient light <NUM> includes, for example, sunlight 91a emitted from the sun <NUM> and illumination light 91b emitted from the moving body <NUM>. In other words, the first underwater optical wireless communication device <NUM> and the second underwater optical wireless communication device <NUM> perform wireless communication using the communication light <NUM> at a relatively shallow depth.

As shown in <FIG>, the first underwater optical wireless communication device <NUM> is equipped with a light emitter <NUM>, a first light receiver <NUM>, a second light receiver <NUM>, and a controller <NUM>. Further, in this embodiment, the first underwater optical wireless communication device <NUM> is equipped with a storage unit <NUM>. Further, the first underwater optical wireless communication device <NUM> is equipped with a gain adjustment unit <NUM> and a signal acquisition unit <NUM>.

The light emitter <NUM> is configured to emit the communication light <NUM> (see <FIG>) as optical signal light. The communication light <NUM> is light with a center wavelength band of blue or violet. The blue wavelength band is a wavelength band in the range of <NUM> to <NUM>. Further, the purple wavelength band is a wavelength band in the range of <NUM> to <NUM>. The light emitter <NUM> includes a semiconductor laser light source or an LED (Light Emitting Diode). Note that the signal light is the light used to transmit information by changing the intensity of the light source at a predetermined time.

The first light receiver <NUM> is configured to receive the communication light <NUM> emitted from another wireless communication device (the second underwater optical wireless communication device <NUM> (see <FIG>)). In this embodiment, the first light receiver <NUM> includes a photomultiplier tube. Further, in this embodiment, the first light receiver <NUM> includes a plurality of light receiving elements <NUM>. That is, each of the plurality of light receiving elements <NUM> is a photomultiplier tube. Note that the first light receiver <NUM> is equipped with a filter (not illustrated) for removing light in wavelength bands other than the communication light <NUM>. Therefore, the first light receiver <NUM> receives light in a wavelength band equal to the wavelength band of the communication light <NUM>.

Note that the ambient light <NUM> includes light of various wavelength bands. Therefore, a part of the ambient light <NUM> passes through the filter to remove light in wavelength bands other than the communication light <NUM>, and is received by the first light receiver <NUM> together with the communication light <NUM>.

The second light receiver <NUM> is configured to receive ambient light <NUM>, which is light other than the communication light <NUM>. In this embodiment, the second light receiver <NUM> includes a photodiode capable of receiving light with a higher intensity than that of the photomultiplier tube.

Note that the second light receiver <NUM> is equipped with a filter (not illustrated) for removing light in wavelength bands other than the communication light <NUM>. Therefore, the second light receiver <NUM> receives ambient light <NUM> other than the communication light <NUM>.

The controller <NUM> is configured to perform control of the various parts of the first underwater optical wireless communication device <NUM> and control of the movement of the moving body <NUM> (see <FIG>). Further, the controller <NUM> is configured to control the adjustment of the gain of the first light receiver <NUM>. The controller <NUM> is a computer configured to include a processor, such as a CPU (Central Processing Unit) and circuitry, a ROM (Read Only Memory), and a RAM (Random Access Memory). Further, the controller <NUM> includes a first gain calculation unit 14a and a second gain calculation unit 14b as functional blocks. The controller <NUM> functions as a controller that controls each part of the first underwater optical wireless communication device <NUM> and the moving body <NUM> by having the CPU execute predetermined control programs. The details of the configuration in which the controller <NUM> adjusts the gain of the first light receiver <NUM> will be described below.

The first gain calculation unit 14a and the second gain calculation unit 14b are configured as functional blocks in software, which are realized by the controller <NUM> executing various programs stored in the storage unit <NUM>. The first gain calculation unit 14a and the second gain calculation unit 14b may be configured by separate hardware with a dedicated processor (processing circuit). The details of the functions of the first gain calculation unit 14a and the details of the functions of the second gain calculation unit 14b will be described below.

The storage unit <NUM> stores various programs to be executed by the controller <NUM>. Further, the storage unit <NUM> is configured to store the target value correlation information <NUM>. The storage unit <NUM> includes a non-volatile storage device, such as an HDD (Hard Disk Drive) and an SSD (Solid State Drive).

The target value correlation information <NUM> is information indicating the correlation between the target value <NUM> of the current value <NUM> (see <FIG>), which is based on the intensity of the communication light <NUM>, received by the first light receiver <NUM> and the intensity <NUM> of the ambient light <NUM>. In this embodiment, the storage unit <NUM> is configured to store the target value correlation information <NUM> in the form of a data table. Note that the format for storing the target value correlation information <NUM> is not restricted as long as it is information that indicates the correlation between the target value <NUM> of the current value <NUM>, which is based on the intensity of the communication light <NUM>, and the intensity <NUM> of the ambient light <NUM>. Further, the target value correlation information <NUM> is acquired experimentally in advance and stored in the storage unit <NUM>.

The gain adjustment unit <NUM> is configured to adjust the gain of the first light receiver <NUM> under the control of the controller <NUM>. The details of the configuration of the gain adjustment unit <NUM> and the details of the configuration in which the gain adjustment unit <NUM> adjusts the gain of the first light receiver <NUM> will be described below.

The signal acquisition unit <NUM> is configured to acquire a signal based on the communication light <NUM> received by the first light receiver <NUM> under the control of the controller <NUM>. The details of the configuration of the signal acquisition unit <NUM> and the details of the configuration in which the signal acquisition unit <NUM> acquires the signal will be described below.

Further, in this embodiment, the first underwater optical wireless communication device <NUM> is equipped with a housing 1a. The housing 1a houses the light emitter <NUM>, the first light receiver <NUM>, the second light receiver <NUM>, the controller <NUM>, the storage unit <NUM>, the gain adjustment unit <NUM>, and the signal acquisition unit <NUM>. The first light receiver <NUM> and the second light receiver <NUM> are each provided at a position in the housing 1a where the incident direction of the ambient light <NUM> is equal. Further, each of the plurality of light receiving elements <NUM> is installed in the housing 1a so that the incident angle of the incident light becomes approximately equal.

Further, in this embodiment, the first underwater optical wireless communication device <NUM> is equipped with a window (not illustrated) that transmits the communication light <NUM> emitted from the light emitter <NUM>, a window (not illustrated) that transmits the light irradiated onto the first light receiver <NUM>, and a window (not illustrated) that transmits the light irradiated onto the second light receiver <NUM>. Each window is formed, for example, of an acrylic or glass plate.

As shown in <FIG>, the second underwater optical wireless communication device <NUM> is equipped with a light emitter <NUM>, a first light receiver <NUM>, a second light receiver <NUM>, a controller <NUM>, a storage unit <NUM>, a gain adjustment unit <NUM>, and a signal acquisition unit <NUM>. The second underwater optical wireless communication device <NUM> has the same configuration as the first underwater optical wireless communication device <NUM> (see <FIG>), except that it is installed in a fixed body <NUM> (see <FIG>).

That is, the light emitter <NUM>, the first light receiver <NUM>, the second light receiver <NUM>, the controller <NUM>, the storage unit <NUM>, the gain adjustment unit <NUM>, and the signal acquisition unit <NUM> are respectively the same configuration as the light emitter <NUM> (see <FIG>), the first light receiver <NUM> (see <FIG>), the second light receiver <NUM> (see <FIG>), the controller <NUM> (see <FIG>), the storage unit <NUM> (see <FIG>), the gain adjustment unit <NUM> (see <FIG>), and the signal acquisition unit <NUM> (see <FIG>). The first light receiver <NUM> is composed of a plurality of light receiving elements <NUM>. The configuration of the light receiving element <NUM> is similar to that of the light receiving element <NUM>. Further, the controller <NUM> includes a first gain calculation unit 24a and a second gain calculation unit 24b as functional blocks. Further, the storage unit <NUM> is configured to store the target value correlation information <NUM>.

Next, referring to <FIG>, the configuration in which the first underwater optical wireless communication device <NUM> (see <FIG>) acquires the signal of the communication light <NUM> (see <FIG>) will be described. The first underwater optical wireless communication device <NUM> acquires the signal of the communication light <NUM> by the gain adjustment unit <NUM> and the signal acquisition unit <NUM> under the control of the controller <NUM> (see <FIG>).

As shown in <FIG>, the gain adjustment unit <NUM> includes an AD conversion unit 16a, a current-to-voltage conversion unit 16b, an AD conversion unit 16c, and a DA conversion unit 16d. The AD conversion unit 16a is configured to acquire a current value <NUM> amplified by the gain based on the intensity of the communication light <NUM> received by the first light receiver <NUM>. The AD conversion unit 16a and the AD conversion unit 16c include, for example, an AD conversion unit that converts an analog current value to a digital current value. Further, the current-to-voltage conversion unit 16b includes, for example, a current-to-voltage conversion unit. The DA conversion unit 16d includes a DA conversion unit that converts a digital voltage value to an analog voltage value.

Note that the AD conversion unit 16a is an example of the "current value acquisition unit" as recited in claims. Since the first light receiver <NUM> includes a plurality of light receiving elements <NUM>, the AD conversion unit 16a and the DA conversion unit 16d include the number of channels corresponding to the number of light receiving elements <NUM>. In this embodiment, since the first light receiver <NUM> includes four light receiving elements <NUM>, each of the AD conversion unit 16a and the DA conversion unit 16d includes four channels.

Further, as shown in <FIG>, the signal acquisition unit <NUM> includes a current-to-voltage conversion unit 17a, a DC component removal unit 17b, a voltage adding unit 17c, a voltage gain adjustment unit 17d, an AD conversion unit 17e, a DA conversion unit 17f, a DC component removal unit <NUM>, and a limit amplifier <NUM>. The current-to-voltage conversion unit 17a includes, for example, a current-to-voltage conversion unit. Further, the DC component removal unit 17b and the DC component removal unit <NUM> each include a capacitor. The voltage adding unit 17c includes a voltage adding circuit. Further, the voltage gain adjustment unit 17d includes a gain adjustment circuit. Further, the AD conversion unit 17e includes an AD conversion unit that converts an analog voltage value to a digital voltage value. The DA conversion unit 17f includes a DA conversion unit that converts a digital voltage value to an analog voltage value.

The signal acquisition unit <NUM> converts the current signal of the current received and output by the first light receiver <NUM> into a voltage signal to acquire the signal of the communication light <NUM>. Further, the gain adjustment unit <NUM> processes the current output from the first light receiver <NUM> as a signal of the communication light <NUM> and adjusts the gain of the first light receiver <NUM>.

As shown in <FIG>, each of the plurality of light receiving elements <NUM> outputs a current of a current value <NUM> corresponding to the intensity of the received communication light <NUM>. The current output from each of the plurality of light receiving elements <NUM> is input to the AD conversion unit 16a and the current-to-voltage conversion unit 17a.

In this embodiment, the current-to-voltage conversion unit 17a includes a plurality of current-to-voltage conversion units corresponding to the number of the plurality of light receiving elements <NUM>. Further, the DC component removal unit 17b includes a plurality of DC component removal units corresponding to the number of the plurality of light receiving elements <NUM>.

The current-to-voltage conversion unit 17a changes the current output from each of the plurality of light receiving elements <NUM> into a voltage. From each of the voltage signals converted by the current-to-voltage conversion unit 17a, its DC component is removed by the corresponding DC component removal unit 17b. The light received by the first light receiver <NUM> includes communication light <NUM> and ambient light <NUM>. Since the ambient light <NUM> is composed of a DC component, the voltage signal of the communication light <NUM> can be acquired by removing the DC component with the DC component removal unit 17b. Thereafter, the voltage signals of the communication light <NUM> will be added by the voltage adding unit 17c. The voltage signal of the communication light <NUM> after being added by the voltage adding unit 17c is input to the limit amplifier <NUM> after the DC component is removed by the DC component removing unit <NUM>. The voltage signal of the communication light <NUM> input to the limit amplifier <NUM> is converted to a predetermined amplitude and output to the controller <NUM>. In this way, the signal of the communication light <NUM> is acquired.

Note that in this embodiment, the second gain calculation unit 14b is configured to control the voltage gain adjustment unit 17d to adjust the amplification ratio of the voltage signal of the communication light <NUM> that is input to the limit amplifier <NUM>. Specifically, the second gain calculation unit 14b acquires the total value <NUM> of the voltages, which is converted to a digital value in the AD conversion unit 17e, output from the voltage gain adjustment unit 17d.

The second gain calculation unit 14b applies a control voltage to the voltage gain adjustment unit 17d so that the total value <NUM> of the voltages falls within the input allowable voltage range of the limit amplifier <NUM>. Specifically, the second gain calculation unit 14b applies the analog second gain control voltage <NUM>, which is digital-to-analog converted by the DA conversion unit 17f, to the voltage gain adjustment unit 17d. The voltage gain adjustment unit 17d adjusts the gain of the output voltage based on the applied second gain control voltage <NUM>. In other words, the second gain calculation unit 14b controls the voltage gain adjustment unit 17d by means of feedback control such as a PID (Proportional Integral Differential) control.

Here, the intensity of the sunlight 91a (<FIG>) emitted from the sun <NUM> (<FIG>) and the intensity of the illumination light 91b (<FIG>) emitted from the moving body <NUM> (<FIG>) are greater than the intensity of the communication light <NUM>. Therefore, when the ambient light <NUM>, such as the sunlight 91a and the illumination light 91b, is received together with the communication light <NUM>, the ratio of the intensity of the communication light <NUM> among the intensities of the light received by the first light receiver <NUM> becomes small. Consequently, when the ambient light <NUM> is received together with the communication light <NUM>, the wireless communication using the communication light <NUM> is interfered with.

Therefore, in this embodiment, even in the case where the ambient light <NUM> is received together with the communication light <NUM>, the controller <NUM> (see <FIG>) is configured to control so that wireless communication using the communication light <NUM> can be performed between the first underwater optical wireless communication device <NUM> and the second underwater optical wireless communication device <NUM>. Note that the controller <NUM> (see <FIG>) also performs control when the ambient light <NUM> is received together with the communication light <NUM>, using the same configuration as the controller <NUM>. Therefore, the control in the case where the ambient light <NUM> is received together with the communication light <NUM> will be described with reference to the controller <NUM>.

In this embodiment, the controller <NUM> (first gain calculation unit 14a) is configured to perform control to adjust the gain of the first light receiver <NUM> based on the intensity of the communication light <NUM> received by the first light receiver <NUM> and the intensity <NUM> (see <FIG>) of the ambient light <NUM> received by the second light receiver <NUM>. Specifically, in this embodiment, the first gain calculation unit 14a is configured to perform control to adjust the gain of the first light receiver <NUM> based on the intensity <NUM> of the ambient light <NUM> received by the second light receiver <NUM> such that the current value <NUM>, which is based on the intensity of the communication light <NUM>, acquired by the AD conversion unit 16a approaches the preset target value <NUM> (see <FIG>).

As shown in <FIG>, the controller <NUM> is configured to adjust the gain of the first light receiver <NUM> by controlling the gain adjustment unit <NUM>. Note that in the example shown in <FIG>, the first light receiver <NUM> (see <FIG>) includes four light receiving elements <NUM> as a plurality of light receiving elements <NUM>. The AD conversion unit 16a converts the current value <NUM> of the current output from each of the plurality of light receiving elements <NUM> from an analog value to a digital value. The AD conversion unit 16a then outputs the current value <NUM>, which is converted to a digital value, to the first gain calculation unit 14a.

Further, the first gain calculation unit 14a acquires the intensity <NUM> of the ambient light <NUM>. Specifically, the first gain calculation unit 14a acquires the ambient light voltage value <NUM> converted by the current-to-voltage conversion unit 16b. Note that the first gain calculation unit 14a acquires the ambient light voltage value <NUM> that has been converted from a digital value to an analog value by the AD conversion unit 16c.

The first gain calculation unit 14a acquires the first gain control voltage <NUM> to be applied to each of the plurality of light receiving elements <NUM> based on the current value <NUM>, the ambient light voltage value <NUM>, and the target value correlation information <NUM> (see <FIG>) stored in the storage unit <NUM> (see <FIG>). The first gain calculation unit 14a applies the acquired first gain control voltage <NUM> to each of the plurality of light receiving elements <NUM>. In other words, in this embodiment, the first gain calculation unit 14a is configured to perform control to adjust the target value <NUM> based on the intensity <NUM> of the ambient light <NUM> received by the second light receiver <NUM> and the target value correlation information <NUM>.

Note that in this embodiment, the first gain calculation unit 14a is configured to perform gain control to adjust the gain of the first light receiver <NUM> by adjusting the first gain control voltage <NUM> applied to the first light receiver <NUM> so that the current value <NUM> based on the intensity of the communication light <NUM> received by the light receiver <NUM> approaches the set target value <NUM>. In other words, the first gain calculation unit 14a is configured to adjust the gain of the first light receiver <NUM> by performing a feedback control such as a PID control, which is based on the current value <NUM>, based on the intensity of the communication light <NUM>, the target value <NUM>, and the intensity <NUM> of the ambient light <NUM>.

Further, in this embodiment, the first gain calculation unit 14a is configured to perform control to independently adjust the gain of each of the plurality of light receiving elements <NUM> based on the current value <NUM>, which is based on the intensity of the communication light <NUM>, received by each of the plurality of light receiving elements <NUM>, the target value <NUM>, and the intensity <NUM> of the ambient light <NUM>. Note that in the case where the intensity <NUM> of the ambient light <NUM> is high, the first gain calculation unit 14a is configured to perform control to increase the target value <NUM>, and in the case where the intensity <NUM> of the ambient light <NUM> is low, the controller is configured to perform control to decrease the target value <NUM>.

As described above, the controller <NUM> is configured to perform control to acquire the total value <NUM> of the voltages output from the plurality of light receiving elements <NUM> after the gain adjustment and converted by the plurality of current-to-voltage conversion units 17a as the signal of the communication light <NUM>. Therefore, even in cases where the ambient light <NUM> is received together with the communication light <NUM>, it is possible to perform communication using the signal based on the communication light <NUM> by adjusting the gain of the first light receiver <NUM> (each of the plurality of light receiving elements <NUM>) in accordance with the intensity <NUM> of the ambient light <NUM>.

The graph <NUM> shown in <FIG> is a graph showing the current signal <NUM> of the current output from the first light receiver <NUM> (see <FIG>) before performing the gain adjustment. In the graph <NUM>, the vertical axis represents the current value, and the horizontal axis represents the time.

The signal based on the communication light <NUM> (see <FIG>) transmits information by turning the communication light <NUM> on and off. For this reason, as shown in the graph <NUM>, the current signal <NUM> based on the current output from the first light receiver <NUM> before the gain adjustment is a so-called pulse signal with a peak portion 41a and a valley portion 41b. Note that in the case of communication using light, the communication by the communication light <NUM> is carried out at a communication speed of several tens of Mbps. Therefore, the intensity of the average value 41c of the current signal <NUM> is treated as the intensity of the current signal <NUM>. Note that in this embodiment, the first gain calculation unit 14a (see <FIG>) is configured to perform control to adjust the gain of the first light receiver <NUM> so that the average value 41c of the current signal <NUM> approaches a set target value <NUM> (see <FIG>).

When the ambient light <NUM> (see <FIG>) is received together with the communication light <NUM>, the current signal <NUM> is offset by the current value <NUM> corresponding to the intensity <NUM> of the ambient light <NUM> (see <FIG>), as shown in the graph <NUM>. Therefore, in the case where the gain of the first light receiver <NUM> is adjusted without considering the intensity <NUM> of the ambient light <NUM>, the current signal <NUM> based on the current output from the first light receiver <NUM> after the gain adjustment may exceed the rated current 38a.

Therefore, in this embodiment, in the case where the intensity <NUM> of the ambient light <NUM> is high, and the first gain calculation unit 14a performs control to increase the target value <NUM>, it is configured to perform the control of the target value <NUM> so that the current value <NUM> output from the first light receiver <NUM> becomes less than or equal to the rated current 38a of the first light receiver <NUM>.

The graph <NUM> shown in <FIG> shows the current signal <NUM> of the current output from the first light receiver <NUM> (see <FIG>) after the gain adjustment. In the graph <NUM>, the vertical axis represents the current value, and the horizontal axis represents the time. Like the current signal <NUM> (see <FIG>), the current signal <NUM> is also a pulse signal with a peak portion 43a and a valley portion 43b. Note that the graph <NUM> shown in <FIG> is a graph of the current signal <NUM> in the case where the gain of the first light receiver <NUM> is increased.

As shown in the graph <NUM>, the gain of the first light receiver <NUM> has been adjusted, and therefore the average value 43c of the current signal <NUM> becomes larger than the average value 41c of the current signal <NUM> (see <FIG>). Further, the gain of the first light receiver <NUM> is adjusted, and therefore, the amount of light received by the first light receiver <NUM> increases. Therefore, the current value 37a corresponding to the intensity <NUM> of the ambient light <NUM> also becomes larger than the current value <NUM> corresponding to the intensity <NUM> of the ambient light <NUM> before the gain of the first light receiver <NUM> is adjusted.

In this embodiment, the first gain calculation unit 14a (see <FIG>) adjusts the gain of the first light receiver <NUM> so as not to exceed the rated current 38a, based on the target value correlation information <NUM> (see <FIG>). As a result, the amplitude <NUM> of the current signal <NUM> of the current output from the first light receiver <NUM> becomes larger than the amplitude <NUM> (see <FIG>) of the current signal <NUM> (see <FIG>) of the current output from the first light receiver <NUM> before the gain adjustment. In this case, the current value due to the noise components contained in the communication light <NUM> also increases. However, it is possible to improve the ratio of the amplitude <NUM> of the current signal <NUM> to the noise component than the ratio of the amplitude <NUM> of the current signal <NUM> to the noise component. In other words, by adjusting the gain of the first light receiver <NUM>, the S/N ratio of the signal component of the communication light <NUM> received by the first light receiver <NUM> can be enhanced. Note that the amplitude <NUM> of the current signal <NUM> is the difference between the peak portion 43a and the valley portion 43b of the current signal <NUM>.

Here, in the case of installing the first light receiver <NUM> in the first underwater optical wireless communication device <NUM>, the light receiving area of the first light receiver <NUM> is limited by the space and other factors. Therefore, in the configuration in which the first light receiver <NUM> includes a plurality of light receiving elements <NUM>, the case in which the light receiving area of the plurality of light receiving elements <NUM> is reduced will be described. For example, in the case where the first light receiver <NUM> is composed of four light receiving elements <NUM>, the light receiving area of each of the light receiving elements <NUM> is reduced to one-fourth of that of the case in which the first light receiver <NUM> is composed of one light receiving element <NUM>. Since the intensity of the light received by the light receiving element <NUM> is proportional to the light receiving area of the light receiving element <NUM>, when the light receiving area of the light receiving element <NUM> is reduced, the intensity of the light received at the light receiving element <NUM> is also reduced.

In this case, as shown in the graph <NUM> in <FIG>, the amplitude <NUM> of the current signal <NUM> of the current output from the light receiving element <NUM> (see <FIG>) with a reduced light receiving area becomes smaller than the amplitude of the signal when the area of the light receiving element <NUM> is not reduced. For example, if the light receiving area of light receiving element <NUM> is reduced to <NUM>/<NUM>, the amplitude <NUM> of the current signal <NUM> becomes <NUM>/<NUM> of the amplitude of the signal when the area of the light receiving element <NUM> is not reduced. In this case, the difference 38b between the average value 45c of the current signal <NUM> and the value of the rated current 38a becomes larger, which increases the adjustment range when adjusting the gain of the first light receiver <NUM>. Note that in the graph <NUM>, the vertical axis represents the current value, and the horizontal axis represents the time. Further, the current signal <NUM> is a so-called pulse signal with a peak portion 45a and a valley portion 45b.

The graph <NUM> shown in <FIG> shows the current signal <NUM> of the current output from the light receiving element <NUM> (see <FIG>) after the light receiving area of the light receiving element <NUM> (see <FIG>) is set to <NUM>/<NUM>, and the gain of the light receiving element <NUM> is adjusted. In the graph <NUM>, the vertical axis represents the current value, and the horizontal axis represents the time. Further, the current signal <NUM> is a so-called pulse signal with a peak portion 47a and a valley portion 47b.

Since the gain of the light receiving element <NUM> has been adjusted, the average value 47c of the current signal <NUM> is greater than the average value 45c of the current signal <NUM> before the adjustment of the gain of the light receiving element <NUM>. Further, the amplitude <NUM>, which is the magnitude of the difference between the peak portion 47a and the valley portion 47b of the current signal <NUM>, is also larger than the amplitude <NUM> (see <FIG>), which is the magnitude of the difference between the peak portion 45a (see <FIG>) and the valley portion 45b (see <FIG>) of the current signal <NUM> (see <FIG>) before the adjustment of the gain of the light receiving element <NUM>.

Further, in this embodiment, the signal acquisition unit <NUM> (see <FIG>) acquires the total value <NUM> (see <FIG>) of the voltages, which are based on the current value <NUM> (see <FIG>) output from each of the plurality of light receiving elements <NUM> (see <FIG>), as the voltage of the signal including the communication light <NUM> (see <FIG>). The graph <NUM> shown in <FIG> shows the voltage signal <NUM> output from one light receiving element <NUM> and converted by the current-to-voltage conversion unit 17a (see <FIG>). In the graph <NUM>, the vertical axis represents the voltage value, and the horizontal axis represents the time. Further, the voltage signal <NUM> is a so-called pulse signal with a peak portion 51a and a valley portion 51b.

As shown in the graph <NUM>, the voltage signal <NUM> based on the light received by the first light receiver <NUM> is offset by the amount of the voltage value <NUM>, which corresponds to the intensity <NUM> of the ambient light <NUM>. Since the voltage signal <NUM> is offset by the amount of the voltage value <NUM> corresponding to the intensity <NUM> of the ambient light <NUM>, it may exceed the rated voltage 37c in the case where the gain adjustment of the first light receiver <NUM> is made without considering the voltage value <NUM> corresponding to the intensity <NUM> of the ambient light <NUM>. In the case where the total value <NUM> of the voltages based on the current output from the first light receiver <NUM> exceeds the rated voltage 37c, the voltage signal based on the communication light <NUM> will be saturated, and the communication based on the communication light <NUM> will not become available.

Therefore, in this embodiment, the controller <NUM> (see <FIG>) controls the signal acquisition unit <NUM> (see <FIG>) to remove the voltage value <NUM> based on the ambient light <NUM> by the DC component removal unit 17b. With this, the voltage signal <NUM> shown in <FIG>, which is shown in the graph <NUM>, can be obtained. In the graph <NUM>, the vertical axis represents the voltage value, and the horizontal axis represents the time. Further, the voltage signal <NUM> is a so-called pulse signal with a peak portion 53a and a valley portion <NUM><NUM> b. Since the voltage signal <NUM> shown in the graph <NUM> is the signal obtained by removing the voltage value <NUM> corresponding to the intensity <NUM> of the ambient light <NUM> from the voltage signal <NUM> (see <FIG>) shown in the graph <NUM> (see <FIG>), the amplitude <NUM> of the voltage signal <NUM> has the same amplitude as the amplitude <NUM> (see <FIG>) of the voltage signal <NUM>.

In this embodiment, the first light receiver <NUM> (see <FIG>) is composed of a plurality of light receiving elements <NUM> (see <FIG>), and the signal acquisition unit <NUM> acquires the signals of the communication light <NUM> based on the current output from each of the plurality of light receiving elements <NUM>. Specifically, the signal acquisition unit <NUM> converts the current output from each of the plurality of light receiving elements <NUM> into a voltage by the plurality of current-to-voltage conversion units 17a. Then, after removing the voltage value <NUM> corresponding to the intensity <NUM> of the ambient light <NUM> from each voltage corresponding to the current output from the plurality of light receiving elements <NUM> by the DC component removal unit 17b, they are added by the voltage adding unit 17c. Note that, in this embodiment, the controller <NUM> adjusts the gain of the first light receiver <NUM> so that the voltage value (total value <NUM> of the voltages (see <FIG>)) after the addition does not exceed the rated voltage 37c.

The graph <NUM> shown in <FIG> shows the voltage signal <NUM> resulting from adding the plurality of voltages corresponding to the current values <NUM> (see <FIG>) output from the plurality of light receiving elements <NUM> (see <FIG>). In other words, the voltage signal <NUM> represents the total value <NUM> of the voltages. In the graph <NUM>, the vertical axis represents the voltage value, and the horizontal axis represents the time. Further, the voltage signal <NUM> is a so-called pulse signal with a peak portion 55a and a valley portion <NUM><NUM> b. As shown in the graph <NUM>, the amplitude <NUM> of the voltage signal <NUM>, resulting from adding up the plurality of voltages, is larger than the amplitude <NUM> of the voltage signal <NUM> (see <FIG>) before adding up the voltages. In this embodiment, as it includes four light-receiving elements <NUM>, the amplitude <NUM> of the voltage signal <NUM> is four times larger than the amplitude <NUM> of the voltage signal <NUM>.

Next, referring to <FIG>, the configuration in which the controller <NUM> (see <FIG>) acquires the signal of the communication light <NUM> (see <FIG>) will be described. Note that the processing shown in <FIG> is continuously performed at predetermined intervals during which the first underwater optical wireless communication device <NUM> (see <FIG>) communicates by receiving the communication light <NUM> from the second underwater optical wireless communication device <NUM> (see <FIG>), and concludes upon termination of the communication.

In Step <NUM>, the controller <NUM> determines whether the communication via the communication light <NUM> can be performed. Specifically, the controller <NUM> determines whether the communication via the communication light <NUM> can be performed, based on whether the intensity of the communication light <NUM> is greater than a predetermined intensity. If the communication via the communication light <NUM> can be performed, the processing proceeds to Step <NUM>. If the communication via the communication light <NUM> is not possible, the processing proceeds to Step <NUM>.

In Step <NUM>, the controller <NUM> converts the current output from the first light receiver <NUM> (see <FIG>) into a voltage by the current-to-voltage conversion unit 17a (see <FIG>). In this embodiment, the controller <NUM> converts the current output from each of the plurality of light receiving elements <NUM> (see <FIG>) into a voltage by the plurality of current-to-voltage conversion units 17a.

In Step <NUM>, the controller <NUM> controls the signal acquisition unit <NUM> (see <FIG>) to acquire the total value <NUM> of the voltages converted in Step <NUM> as the voltage value of the signal of the communication light <NUM>. Thereafter, the processing is terminated.

If the processing advances from Step <NUM> to Step <NUM>, in Step <NUM>, the controller <NUM> (first gain calculation unit 14a (see <FIG>)) adjusts the gain of the first light receiver <NUM> by controlling the gain adjustment unit <NUM> (see <FIG>). The details of the processing in which the first gain calculation unit 14a adjusts the gain of the first light receiver <NUM> will be described below.

In Step <NUM>, the controller <NUM> converts the current output from the first light receiver <NUM> after the gain adjustment to a voltage by the current-to-voltage conversion unit 17a. In this embodiment, the controller <NUM> converts the current output from each of the plurality of light receiving elements <NUM> after the gain adjustment into a voltage by the plurality of current-to-voltage conversion units 17a. Thereafter, the processing proceeds to Step <NUM>.

Note that the processing proceeds from Step <NUM> to Step <NUM>, in Step <NUM>, the controller <NUM> acquires the total value <NUM> of the voltages, which is converted in Step <NUM>, as the voltage value of the signal of the communication light <NUM> by controlling the signal acquisition unit <NUM>.

Next, referring to <FIG>, the processing in which the first gain calculation unit 14a (see <FIG>) adjusts the gains of the plurality of light receiving elements <NUM> (see <FIG>) will be described.

In Step 104a, the first gain calculation unit 14a acquires the current value <NUM> (see <FIG>) amplified by the gains of the plurality of light receiving elements <NUM>. In this embodiment, the first gain calculation unit 14a acquires the current value <NUM>, which is amplified by the gains of the plurality of light receiving elements <NUM> and is converted from an analog value to a digital value by the AD conversion unit 16a (see <FIG>), from each of the plurality of light receiving elements <NUM>.

In Step 104b, the first gain calculation unit 14a acquires the intensity <NUM> (see <FIG>) of the ambient light <NUM> (see <FIG>). In this embodiment, the first gain calculation unit 14a converts the analog value of the voltage, which is output from the second light receiver <NUM> (see <FIG>) and converted from a current to a voltage by the current-to-voltage conversion unit 16b (see <FIG>), into a digital value by the AD conversion unit 16c, to acquire the intensity <NUM> of the ambient light <NUM>.

In Step 104c, the first gain calculation unit 14a acquires the target value <NUM> (see <FIG>). Specifically, the first gain calculation unit 14a acquires the target value <NUM> that has already been set. Note that if the target value <NUM> is not set, the first gain calculation unit 14a will set a predetermined value as the target value <NUM>.

In Step 104d, the first gain calculation unit 14a determines whether the intensity <NUM> of the ambient light <NUM> is high. Specifically, the first gain calculation unit 14a compares the target value <NUM> acquired in Step 104c with the current value <NUM> acquired in Step 104a. If the value of the current value <NUM> is smaller than the target value <NUM>, the first gain calculation unit 14a concludes that the intensity <NUM> of the ambient light <NUM> is high. Further, if the current value <NUM> is greater than the target value <NUM>, the first gain calculation unit 14a concludes that the intensity <NUM> of the ambient light <NUM> is low. If the intensity of the ambient light <NUM> is high, the processing proceeds to Step 104e. If the intensity <NUM> of the ambient light <NUM> is low, the processing proceeds to Step 104f.

In Step 104e, the first gain calculation unit 14a increases the target value <NUM>. Specifically, the first gain calculation unit 14a acquires the target value <NUM> based on the value of the current value <NUM> acquired in Step 104a, the intensity <NUM> of the ambient light <NUM> acquired in Step 104b, and the target value correlation information <NUM> (see <FIG>) stored in the storage unit <NUM> (see <FIG>).

Note that if the intensity <NUM> of the ambient light <NUM> is high, by acquiring the target value <NUM> based on the target value correlation information <NUM>, the target value <NUM> that can be communicated by the communication light <NUM> is acquired. In other words, through the processing of Step 104e, the target value <NUM> can be increased. Thereafter, the processing proceeds to Step <NUM>.

Further, if the processing proceeds from Step 104d to Step 104f, the first gain calculation unit 14a reduces the target value <NUM>. Specifically, the first gain calculation unit 14a acquires the target value <NUM> based on the value of the current value <NUM> acquired in Step 104a, the intensity <NUM> of the ambient light <NUM> acquired in Step 104b, and the target value correlation information <NUM> stored in the storage unit <NUM>.

Note that by acquiring the target value <NUM> based on the target value correlation information <NUM> when the intensity <NUM> of the ambient light <NUM> is low, as a result, it is possible to reduce the target value <NUM> below the target value <NUM> acquired in Step 104c. Thereafter, the processing proceeds to Step <NUM>.

In Step <NUM>, the first gain calculation unit 14a applies the first gain control voltage <NUM> (see <FIG>) to each of the plurality of light receiving elements <NUM> based on the target value <NUM> acquired (changed) in Step 104e or Step 104f. In this embodiment, the first gain calculation unit 14a adjusts the gain individually for each of the plurality of light receiving elements <NUM> by applying an individually set first gain control voltage <NUM> to each of the plurality of light receiving elements <NUM>. Thereafter, the processing proceeds to Step <NUM>.

Note that the processing of Step 104a or the processing of Step 104b may be performed first. Further, in this embodiment, the processing of Steps 104d to <NUM> is carried out individually for each of the plurality of light receiving elements <NUM>.

Further, the second underwater optical wireless communication device <NUM> (see <FIG>) may also receive ambient light <NUM> (see <FIG>) together with the communication light <NUM> (see <FIG>) when receiving the communication light <NUM> (see <FIG>) emitted by the underwater optical wireless communication device <NUM> (see <FIG>). Therefore, the controller <NUM> (see <FIG>) of the second underwater optical wireless communication device <NUM> is also configured to adjust the gain of the first light receiver <NUM> (see <FIG>) in the same way as the controller <NUM> (see <FIG>) of the first underwater optical wireless communication device <NUM>. With this, bidirectional communication using the communication light <NUM> can be performed in both the first underwater optical wireless communication device <NUM> and the second underwater optical wireless communication device <NUM>.

In this embodiment, the following effects can be obtained.

In this embodiment, as described above, the first underwater optical wireless communication device <NUM> is provided with a first light receiver <NUM> that receives communication light <NUM> emitted from another optical wireless communication device (second underwater optical wireless communication device <NUM>), a second light receiver <NUM> that receives ambient light <NUM>, which is light other than the communication light <NUM>, and a controller <NUM> that performs control to adjust the gain of the first light receiver <NUM> based on the intensity of the communication light <NUM> received by the first light receiver <NUM> and the intensity <NUM> of the ambient light <NUM> received by the second light receiver <NUM>.

With this, the gain of the first light receiver <NUM> is adjusted based on the intensity of the communication light <NUM> received by the first light receiver <NUM> and the intensity <NUM> of the ambient light <NUM> received by the second light receiver <NUM>, so that the amplitude of the communication light <NUM> can be increased when the ambient light <NUM> is strong. Therefore, it becomes possible to increase the ratio of the amplitude of the communication light <NUM> relative to the noise caused by the ambient light <NUM> contained in the communication light <NUM>, thereby improving the S/N ratio of the communication light <NUM>. As a result, even in the case where the ambient light <NUM> is received together with the communication light <NUM>, it is possible to suppress the communication by the communication light <NUM> from being interfered with by the ambient light <NUM>.

Further, in the above-described embodiment, the following further effects can be obtained by configuring as follows.

In other words, in this embodiment, as described above, it is further provided with an AD conversion unit 16a (current value acquisition unit) that acquires a current value <NUM> amplified by the gain based on the intensity of the communication light <NUM> received by the first light receiver <NUM>, and the controller <NUM> is configured to perform control to adjust the gain of the first light receiver <NUM> so that the current value <NUM> based on the intensity of the communication light <NUM> acquired by the AD conversion unit 16a approaches the preset target value <NUM>, based on the intensity <NUM> of the ambient light <NUM> received by the second light receiver <NUM>. With this, the gain of the first light receiver <NUM> is adjusted to approach the preset target value <NUM> based on the intensity <NUM> of the ambient light <NUM>, and therefore, the gain of the first light receiver <NUM> can be adjusted without having to calculate the target value <NUM>. As a result, the processing burden of the controller <NUM> (first gain calculation unit 14a) when adjusting the gain of the first light receiver <NUM> can be reduced.

Further, in this embodiment, as described above, the controller <NUM> is configured to adjust the first gain control voltage <NUM> (gain control voltage) applied to the first light receiver <NUM> so that the current value <NUM>, which is based on the intensity of the communication light <NUM> received by the first light receiver <NUM>, approaches the set target value <NUM>, thereby controlling the adjustment of the gain of the first light receiver <NUM>. With this, by adjusting the gain of the first light receiver <NUM> with the first gain control voltage <NUM>, it becomes possible to easily bring the current value <NUM>, which is based on the intensity of the communication light <NUM> received by the first light receiver <NUM>, closer to the set target value <NUM>. As a result, the gain of the first light receiver <NUM> can be easily adjusted.

Further, in this embodiment, as described above, the controller <NUM> is configured to perform control to increase the target value <NUM> when the intensity <NUM> of the ambient light <NUM> is high, and to decrease the target value <NUM> when the intensity <NUM> of the ambient light <NUM> is low. Here, when the intensity of the ambient light <NUM> is high, the intensity of the communication light <NUM> becomes relatively small among the intensity of the light received by the first light receiver <NUM>. In other words, when the intensity <NUM> of the ambient light <NUM> is high, communication by the communication light <NUM> becomes difficult. On the other hand, when the intensity <NUM> of the ambient light <NUM> is low, the intensity <NUM> of the communication light <NUM> becomes relatively higher among the intensity of the light received by the first light receiver <NUM>.

In other words, if the target value <NUM> is set without considering the intensity of the ambient light <NUM>, there may be cases where the gain of the first light receiver <NUM> is increased excessively. Therefore, by configuring as described above, it is possible to set the target value <NUM> such that the increase rate of the current value <NUM> by the gain of the first light receiver <NUM> is set to an appropriate value in accordance with the intensity <NUM> of the ambient light <NUM>. As a result, even when the intensity <NUM> of the ambient light <NUM> changes, it is possible to easily perform the gain adjustment of the first light receiver <NUM> so that the increase rate of the current value <NUM> due to the gain of the first light receiver <NUM> becomes the appropriate increase rate.

Further, in this embodiment, as described above, the controller <NUM> is configured to perform control to set the target value <NUM> so that the current value <NUM> output from the first light receiver <NUM> becomes less than or equal to the rated current 38a of the first light receiver <NUM>, when the intensity <NUM> of the ambient light <NUM> is high, and the control to increase the target value <NUM> is performed.

With this, it becomes possible to prevent the current value <NUM> output from the first light receiver <NUM> from exceeding the rated current 38a when increasing the gain of the first light receiver <NUM>. As a result, it is possible to prevent saturation of the current value output from the first light receiver <NUM> caused by excessively increasing its gain, thus preventing the communication by the communication light <NUM> from being interfered with due to the saturation of the current value output from the first light receiver <NUM>.

Further, in this embodiment, as described above, the first light receiver <NUM> includes a plurality of light receiving elements <NUM>, and the controller <NUM> is configured to perform control to independently adjust the gain of each of the plurality of light receiving elements <NUM> based on the current value <NUM>, which is derived from the intensity of the communication light <NUM> received by each of the plurality of light receiving elements <NUM>, the target value <NUM>, and the intensity <NUM> of the ambient light <NUM>.

Here, for example, when the number of the light receiving elements <NUM> is increased while reducing the light receiving area of the light receiving element <NUM>, the intensity of the light received by each of the light receiving elements <NUM> can be lowered. Further, since the value of the rated current 38a of the light receiving element <NUM> does not change, it is possible to increase the difference between the current value <NUM> based on the intensity of the light received at each of the plurality of light receiving elements <NUM> and the rated current 38a. As a result, it is possible to widen the adjustment range when adjusting the gain of the light receiving element <NUM>. In this case, by arranging each of the plurality of light receiving elements <NUM> in different directions relative to each other, it is possible to receive the communication light <NUM> from a plurality of directions.

In this case, since the gain of each of the plurality of light receiving elements <NUM> is adjusted independently, it is possible to appropriately adjust the gain of the corresponding light receiving element <NUM> individually, even when the light received by the light receiving element <NUM>, corresponding to the direction of incident communication light <NUM>, includes both the communication light <NUM> and ambient light <NUM>. As a result, even when communicating with the communication light <NUM> received from a plurality of directions, it is possible to minimize interference in communication caused by the ambient light <NUM>.

Further, in this embodiment, as described above, it further includes a plurality of current-to-voltage conversion units 17a that converts the current output from the plurality of light receiving elements <NUM> into voltage. The controller <NUM> is configured to control the acquisition of the total value <NUM> of the voltages, which are output from the plurality of light receiving elements <NUM> after the gain has been adjusted and are converted by the plurality of current-to-voltage conversion units 17a, as the signal of communication light <NUM>.

With this, for example, even if the amplitude of the signal based on the voltage converted from the current output from one light receiving element <NUM> is small, the amplitude of the signal based on the total value <NUM> of the voltage can be increased because the voltages converted from the currents output from the plurality of light receiving elements <NUM> are summed. Thus, even if it is difficult to increase the amplitude of the signal based on the voltage acquired after adjusting the gain of each light receiving element <NUM>, the amplitude of the signal derived from the communication light <NUM> can be increased by a signal based on the total value <NUM> of the voltages acquired by summing a plurality of voltages. As a result, since it becomes possible to increase the amplitude of the signal based on communication light <NUM>, the strength of communication via the communication light <NUM> can be enhanced.

In addition, in this embodiment, as described above, the storage unit <NUM> is further provided that stores target value correlation information <NUM>, which shows the correlation between the target value <NUM> for the current value <NUM>, derived from the intensity of communication light <NUM> received by the first light receiver <NUM>, and the intensity <NUM> of ambient light <NUM>. The controller <NUM> is configured to control the adjustment of the target value <NUM> based on the intensity <NUM> of ambient light <NUM> received by the second light receiver <NUM> and the target value correlation information <NUM>.

With this configuration, it is possible to easily acquire the target value <NUM> for adjusting the gain of the first light receiver <NUM> to the appropriate gain according to the intensity <NUM> of the ambient light <NUM> by using the target value correlation information <NUM> along with the intensity <NUM> of the ambient light <NUM>. As a result, the gain of the first light receiver <NUM> can be easily adjusted to the appropriate gain according to the intensity <NUM> of the ambient light <NUM>.

Further, in this embodiment, as described above, the housing 1a for housing the first light receiver <NUM>, the second light receiver <NUM>, and the controller <NUM> is further provided, and each of the first light receiver <NUM> and the second light receiver <NUM> is located within the housing 1a at positions where the incident direction of the ambient light <NUM> is the same.

With this, it is possible to suppress the difference between the intensity <NUM> of the ambient light <NUM> received by the first light receiver <NUM> and the intensity <NUM> of the ambient light <NUM> received by the second light receiver <NUM> from becoming larger. As a result, it is possible to suppress the reduction of the accuracy of adjusting the gain of the first light receiver <NUM> based on the intensity <NUM> of the ambient light <NUM>.

Further, in this embodiment, as described above, the first light receiver <NUM> includes a photomultiplier tube, and the second light receiver <NUM> includes a photodiode capable of receiving light of higher intensity than that of the photomultiplier tube.

Here, a photodiode has a larger upper limit of the amount of light it can receive compared with a photomultiplier tube. Further, in water, the ambient light <NUM> is generally more intense than the communication light <NUM>. Therefore, as described above, by configuring the second light receiver <NUM> that includes a photodiode, which has a higher upper limit of light reception than a photomultiplier tube, to receive the ambient light <NUM> that is more intense than communication light <NUM>, it is possible to increase the upper limit of the intensity <NUM> of the ambient light <NUM> that can be received by the second light receiver <NUM>, compared with the configuration that includes a photomultiplier tube. As a result, even in an environment where the intensity <NUM> of the ambient light <NUM> is higher, and the communication by the communication light <NUM> is more difficult to perform, it is possible to adjust the gain of the first light receiver <NUM> with high accuracy according to the intensity <NUM> of the ambient light <NUM>. Therefore, even in an environment where the influence of the ambient light <NUM> is stronger, it is possible to provide the first underwater optical wireless communication device <NUM> (underwater optical wireless communication device) that enables communication by the communication light <NUM>.

Note that the embodiments disclosed here should be considered illustrative and not restrictive in all respects. It should be noted that the scope of the invention is indicated by claims and is intended to include all modifications (modified examples) within the meaning and scope of the claims.

For example, in the above-described embodiment, a configuration example is shown in which the controller <NUM> (first gain calculation unit 14a) adjusts the gain of the first light receiver <NUM> so that the current value <NUM> output from the first light receiver <NUM> approaches the target value <NUM>, but the present invention is not limited thereto. For example, the controller <NUM> may be configured to directly change the gain of the first light receiver <NUM>.

Further, in the above-described embodiment, a configuration example is shown in which the first gain calculation unit 14a adjusts the gain of the first light receiver <NUM> based on the current value <NUM> output from the first light receiver <NUM>, but the present invention is not limited thereto. For example, the first gain calculation unit 14a may be configured to adjust the gain of the first light receiver <NUM> based on the voltage value converted by the current-to-voltage conversion unit 17a from the current output from the first light receiver <NUM>. In this case, the target value correlation information can be information that indicates the correlation between the target value of the voltage value output from the first light receiver <NUM> and the light intensity <NUM> of the ambient light <NUM>.

Further, in the embodiment described above, a configuration example is shown in which each of the plurality of light receiving elements <NUM> has one-fourth of the light receiving area as compared with the case in which the first light receiver <NUM> includes one light receiving element <NUM>, but the present invention is not limited thereto. For example, each of the plurality of light receiving elements <NUM> could be configured to have the same light-receiving area as when the first light receiver <NUM> includes a single light receiving element <NUM>, with the entire light-receiving section having a total light-receiving area that is four times larger.

In this configuration, as compared with the configuration in which the light-receiving area of each light-receiving element <NUM> is reduced to one-fourth, the difference between the average value of the current signal and the value of the rated current 38a is reduced, leading to a narrower adjustment range for the gain of the first light receiver <NUM>. However, unlike the case where the first light receiver <NUM> is composed of one light receiving element <NUM>, the signals of the communication light <NUM> received by each light receiving element <NUM> can be added together, this allows for an increase in the amplitude of the signal (voltage signal) acquired by the signal acquisition unit <NUM>.

Further, in the above-described embodiment, a configuration example is shown in which the first light receiver <NUM> is composed of four light-receiving elements <NUM>, but the present invention is not limited thereto. The number of the light receiving elements <NUM> included by the first light receiver <NUM> may be other than four. For example, the first light receiver <NUM> may be configured to include one light receiving element <NUM>. Further, the first light receiver <NUM> may be composed of a plurality of light receiving elements <NUM>, which may be less than four, or more than four.

Further, in the above-described embodiment, a configuration example is shown in which each of the plurality of light receiving elements <NUM> is arranged in an equal orientation with respect to each other is shown, but the present invention is not limited thereto. For example, each of the plurality of light receiving elements <NUM> may be configured to be oriented differently from one another. By configuring as described above, it is possible to perform communication by the communication light <NUM> incident from a plurality of directions by each of the plurality of light receiving elements <NUM>.

Further, in the above-described embodiment, a configuration example is shown in which the first underwater optical wireless communication device <NUM> is provided with one first light receiving light receiver <NUM>, but the present invention is not limited thereto. For example, the first underwater optical wireless communication device <NUM> may be provided with a plurality of first light receivers <NUM>. In this case, by arranging the plurality of first light receivers <NUM> in different directions, the communication light <NUM> incident from a plurality of directions can be used for the communication light <NUM>.

Further, in the above-described embodiment, a configuration example is shown in which the second light receiver <NUM> is provided with a photodiode, but the present invention is not limited thereto. The second light receiver <NUM> may include any light receiving element as long as the second light receiver <NUM> is capable of receiving light of higher intensity than the first light receiver <NUM>.

Further, in the above-described embodiment, a configuration example is shown in which the first underwater optical wireless communication device <NUM> is installed in an AUV, which is a moving body <NUM>. For example, the first underwater optical wireless communication device <NUM> may be installed on a manned submarine (HOV: Human Occupied Vehicle). Further, the first underwater optical wireless communication device <NUM> may be installed in a remotely operated vehicle (ROV) that is controlled by a person via a cable.

Claim 1:
An underwater optical wireless communication device (<NUM>) comprising:
a first light receiver (<NUM>) configured to receive communication light (<NUM>) emitted from another wireless communication device (<NUM>);
a second light receiver (<NUM>) configured to receive ambient light (<NUM>), which is light other than the communication light (<NUM>); and characterized in that the underwater optical wireless communication device comprises:
a controller (<NUM>) configured to perform control to adjust a gain of the first light receiver (<NUM>), based on intensity of the communication light (<NUM>) received by the first light receiver (<NUM>) and intensity of the ambient light (<NUM>) received by the second light receiver (<NUM>).