Underwater communication system and underwater communication method

Abstract

To provide an underwater communication system and an underwater communication method that can communicate a large volume of data over a longer distance.SOLUTION: An underwater communication system 1 includes a transmitting device and a receiving device. The transmitting device includes: a laser light source 101; a collimator lens 104 for collimating laser light; an optical deflector 106 for deflecting the collimated laser light B10; an acoustic communication unit; and a control unit 11 for controlling the optical deflector 106 based on control information received via the acoustic communication unit. The receiving device includes: an optical deflector 201 for changing a receiving direction of the laser light; a branching element 202 for branching an optical path of the laser light; an optical detector 204 for receiving laser light B11 that is one that has branched; an image sensor 205 that receives laser light B12 that is the other that has branched; an acoustic communication unit; and a control unit 21 that causes the acoustic communication unit to transmit control information controlling a transmission direction of the laser light B10 based on an output signal of the image sensor 205.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an underwater communication system and an underwater communication method for performing communication underwater. [Background technology]

[0002] Conventionally, underwater communication systems that communicate underwater have been used in marine systems and the like. For example, communication is performed between underwater devices such as underwater unmanned vehicles, underwater drones, and submersibles, and offshore devices such as offshore ships and offshore bases. In this case, data can be transmitted and received by acoustic communication using sound waves. However, in communication using sound waves, the carrier frequency is low (for example, 10 kHz or less), making it difficult to transmit and receive large amounts of data such as video data.

[0003] Therefore, in underwater communication systems, a communication method using laser light for transmitting and receiving large volumes of data is being considered.

[0004] For example, in this type of communication method, the transmitting device has a variable transmission direction of laser light, and the receiving device has a variable reception direction of laser light. The transmitting device irradiates laser light over a wide angle range toward the receiving device. The receiving device detects the direction with the best reception sensitivity for the received laser light, and sets the reception direction to that direction. Furthermore, the receiving device transmits transmission direction control data according to the reception state to the transmitting device. The transmitting device controls the transmission direction of the laser light based on the transmission direction control data. This type of underwater communication system is described in Patent Document 1 listed below. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-055408 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the above configuration, the laser light is emitted over a wide angle range, so the light density of the laser light decreases according to the transmission distance. Therefore, as the transmission distance increases, the intensity of the light received by the receiving device decreases, and the received signal becomes more susceptible to noise. Therefore, in the above configuration, it is difficult to extend the communication distance of the underwater communication system.

[0007] In view of the above problems, an object of the present invention is to provide an underwater communication system and an underwater communication method capable of communicating large volumes of data over longer distances. [Means for solving the problem]

[0008] A first aspect of the present invention relates to an underwater communication system. The underwater communication system according to this aspect includes a transmitting device, a receiving device, a position and orientation detection unit for detecting positions and orientations of the transmitting device and the receiving device; The transmitting device comprises a laser light source that emits laser light, a collimator lens that collimates the laser light, a first optical deflector that deflects the collimated laser light, a first communication unit that communicates with the receiving device, and a first control unit that controls the first optical deflector based on control information received via the first communication unit. The receiving device comprises a second optical deflector that changes the receiving direction of the laser light, a branching element that branches the optical path of the laser light that has passed through the second optical deflector, a photodetector that receives one of the branched laser lights, an image sensor that receives the other of the branched laser lights, a second communication unit that communicates with the transmitting device, and a first control unit that controls the first optical deflector based on an output signal of the image sensor. For receiving the laser light and a second control unit that causes the second communication unit to transmit the control information for controlling the transmission direction of the laser light. The first control unit sets the transmission direction of the laser light to a direction toward the receiving device based on the positions and attitudes of the transmitting device and the receiving device detected by the position and attitude detection unit, and performs control of the first optical deflector based on the control information.

[0009] According to the underwater communication system of this embodiment, since laser light is used for transmitting and receiving data, a large amount of data can be transmitted from the transmitting device to the receiving device. In addition, since the laser light used for communication is collimated, even if the distance from the transmitting device to the receiving device is long, the density of the laser light is unlikely to decrease. Therefore, the distance over which communication can be performed between the transmitting device and the receiving device can be expanded. In addition, since the image sensor is used to monitor the receiving state of the laser light in the receiving device, when the laser light is collimated as described above, the receiving state of the laser light in the receiving device can be precisely monitored with high resolution. Therefore, from the output signal from the image sensor, control information for controlling the transmission direction of the laser light toward the receiving device can be smoothly and accurately generated, and the transmission direction of the laser light can be appropriately controlled by this control information. Therefore, according to the underwater communication system of this embodiment, a large amount of data can be transmitted and received over a longer distance.

[0010] In the underwater communication system according to this aspect, the first control unit controls the first optical deflector to deflect the laser light. , centered on the set direction The second control unit may be configured to scan a predetermined range, and the second control unit may transmit the control information regarding the scan position at which the image sensor received the laser light to the transmitting device via the second communication unit, and the first control unit may be configured to control the first optical deflector to set the transmission direction of the laser light to a direction based on the control information received via the first communication unit.

[0011] According to this configuration, by scanning the collimated laser light, the transmission direction in which the laser light can be received by the receiving device can be detected, and therefore the transmission direction of the laser light can be smoothly set before transmitting a large amount of data.

[0012] In this case, the control information regarding the scanning position may be information that specifies the timing at which the image sensor receives the laser light.

[0013] According to this configuration, by adjusting the time axis between the transmitting device and the receiving device in advance, the transmitting device can identify, based on the control information, which scanning position is a position at which the receiving device can receive the laser light. Therefore, the transmitting device can set the transmission direction of the laser light by a simple process.

[0014] In the underwater communication system of the present aspect, the second control unit may be configured to transmit the control information for correcting the misalignment between the center of the second optical deflector and the center of the laser light to the transmitting device via the second communication unit based on the output signal of the image sensor, and the first control unit may be configured to control the first optical deflector based on the control information received via the first communication unit to correct the transmission direction of the laser light in a direction that eliminates the misalignment.

[0015] According to this configuration, the transmission direction of the laser light transmitted from the transmitting device can be corrected so that the center of the second optical deflector and the center of the laser light approach each other. This allows a larger amount of laser light to be captured by the second optical deflector and guided to the photodetector. This allows data to be transmitted and received more accurately using the laser light.

[0016] In this case, the second control unit may be configured to extract the maximum light receiving position and the light receiving center position within the laser light receiving range of the image sensor based on the output signal of the image sensor, and to generate the control information for correcting the deviation based on the difference between the maximum light receiving position and the light receiving center position.

[0017] According to this configuration, it is possible to smoothly generate control information for correcting the deviation between the center of the second optical deflector and the center of the laser light, based on the output signal of the image sensor.

[0018] In the underwater communication system according to this aspect, the first communication unit and the second communication unit may be configured to communicate by acoustic signals.

[0019] According to this configuration, the control information can be smoothly and reliably provided from the receiving device to the transmitting device, and therefore the transmission direction of the laser light can be controlled quickly and appropriately.

[0020] In the underwater communication system according to this aspect, the wavelength of the laser light emitted from the laser light source can be set to be within the range of 400 nm or more and 550 nm or less.

[0021] Light in this wavelength band is not easily absorbed or scattered by water, so by setting the wavelength of the laser light as described above, it is possible to more effectively increase the communication distance between a transmitting device and a receiving device using the laser light.

[0022] In the underwater communication system according to this aspect, the first optical deflector and the second optical deflector may each be a reflective optical deflector having a mirror.

[0023] This makes it possible to change the transmission and reception direction of the laser light over a wide angle with simple control.

[0024] A second aspect of the present invention relates to an underwater communication method using laser light, comprising: setting a transmission direction of a laser beam transmitted from the transmitting device to a direction toward the receiving device based on positions and attitudes of the transmitting device and the receiving device; The collimated laser light transmitted from the transmitter , the above-mentioned setting direction Centered on A predetermined range is scanned, and control information regarding the scan position at which the laser light is received is transmitted from the receiving device to the transmitting device, and the direction of the laser light transmitted from the transmitting device is set to a direction based on the control information.

[0025] According to the underwater communication method of this aspect, the transmission direction in which the laser light can be received by the receiving device can be detected by scanning the collimated laser light, and therefore the transmission direction of the laser light can be smoothly set before transmitting a large amount of data.

[0026] A third aspect of the present invention relates to an underwater communication method using laser light, comprising: In the receiving device, the center position of the laser light is calculated based on the intensity distribution of the laser light receiving range in the image sensor, and control information for correcting the deviation between the center of the laser light and the center of an optical deflector that guides the laser light to the image sensor is generated based on the calculated center position and transmitted to the transmitting device, and in the transmitting device, the direction of the laser light is corrected in a direction that eliminates the deviation based on the received control information.

[0027] According to the underwater communication method of this aspect, the transmission direction of the laser light transmitted from the transmitting device can be corrected so that the center of the optical deflector and the center of the laser light approach each other. This allows a larger amount of laser light to be captured by the optical deflector and guided to the photodetector. This allows data to be transmitted and received more accurately using the laser light. Effect of the Invention

[0028] As described above, according to the present invention, it is possible to provide an underwater communication system and an underwater communication method capable of communicating large amounts of data over longer distances.

[0029] The effects and significance of the present invention will become clearer from the following description of the embodiment. However, the embodiment described below is merely an example of how the present invention can be put into practice, and the present invention is not limited to the embodiment described below. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a diagram showing a usage pattern of an underwater communication system according to an embodiment. [Diagram 2] FIG. 2 is a block diagram showing a configuration of an underwater communication system according to an embodiment. [Diagram 3] FIG. 3 is a diagram showing the configurations of an optical transmitting unit and an optical receiving unit according to the embodiment. [Figure 4] FIG. 4 is a flowchart showing control during transmission and reception of video data according to the embodiment. [Diagram 5] 5(a) and 5(b) are flowcharts showing control performed by a control unit of a transmitting device and a control unit of a receiving device in a first search control according to the embodiment. [Figure 6] FIG. 6 is a diagram illustrating a light receiving state of an image sensor when a laser is incident on a light receiving surface of the image sensor by a scanning operation according to an embodiment. [Figure 7] Fig. 7(a) is a time chart showing a change in the rotation angle of a laser beam during a scanning operation in a transmitting device according to an embodiment. Fig. 7(b) is a time chart showing a state in which a laser beam is received by an image sensor during a scanning operation in a receiving device according to an embodiment. [Figure 8] 8(a) and 8(b) are flowcharts showing control performed by a control unit of a transmitting device and a control unit of a receiving device in a second search control according to the embodiment. [Figure 9] FIG. 9 is a diagram showing a method of generating control information in the second search control according to the embodiment. [Figure 10] FIG. 10 is a diagram showing communication servo control in a control unit of a receiving device according to an embodiment. [Figure 11] FIG. 11 is a diagram showing a schematic light receiving state of an image sensor when a laser is incident on a light receiving surface of the image sensor by a scanning operation, according to a modified example. [Figure 12] FIG. 12 is a diagram showing a method of generating control information in the second search control according to another modification. [Figure 13] Fig. 13(a) is a graph showing a simulation result of the distribution of the light receiving intensity of each pixel when the center position of the laser light is out of the light receiving range of the image sensor according to another modification. Fig. 13(b) is a graph showing a simulation result when logarithm is applied to the calculation formula of the intensity distribution of Fig. 13(a) according to another modification. Fig. 13(c) is a graph showing a simulation result when the calculation formula of Fig. 13(b) is partially differentiated with respect to x according to another modification. Fig. 13(d) is a graph showing a simulation result when the calculation formula of Fig. 13(b) is partially differentiated with respect to y according to another modification. [Figure 14]Fig. 14(a) is a graph showing a simulation result of the distribution of the light receiving intensity of each pixel when the center position of the laser light coincides with the center position of the light receiving range of the image sensor, according to another modification. Fig. 14(b) is a graph showing a simulation result when logarithm is applied to the calculation formula of the intensity distribution of Fig. 14(a), according to another modification. Fig. 14(c) is a graph showing a simulation result when the calculation formula of Fig. 14(b) is partially differentiated with respect to x, according to another modification. Fig. 14(d) is a graph showing a simulation result when the calculation formula of Fig. 14(b) is partially differentiated with respect to y, according to another modification. [Figure 15] Fig. 15(a) is a graph showing an approximation line obtained by the least squares method from the data group of Fig. 14(c) according to another modified example. Fig. 15(b) is a graph showing an approximation line obtained by the least squares method from the data group of Fig. 14(d) according to another modified example. [Figure 16] Fig. 16(a) is a graph showing an approximation line obtained by the least squares method from the data group of Fig. 13(c) according to another modified example. Fig. 16(b) is a graph showing an approximation line obtained by the least squares method from the data group of Fig. 13(d) according to another modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0032] FIG. 1 is a diagram showing a usage pattern of the underwater communication system 1. As shown in FIG.

[0033] As shown in Fig. 1, in this usage form, communication takes place between a surface device 2 floating on the water surface S1 and an underwater device 3 that detects underwater conditions. The underwater device 3 is a device capable of moving underwater under its own power, such as an underwater drone. The underwater device 3 captures images of the water or the bottom of the water through a window 3a and transmits the image data to the surface device 2 as appropriate. The surface device 2 transmits the received image data to an information collection device on land via wireless communication as appropriate.

[0034] The underwater device 3 includes a transmission device 10 for transmitting data using laser light. The water surface device 2 includes a reception device 20 for receiving the laser light transmitted from the underwater device 3. The underwater communication system 1 is constituted by the transmission device 10 and the reception device 20.

[0035] The transmission direction of the transmission device 10 and the reception direction of the reception device 20 can be changed in the circumferential direction within a predetermined angular range. The transmission device 10 controls the transmission direction of the laser light in the direction of the reception device 20. Also, the reception device 20 controls the reception direction of the laser light in the direction of the transmission device 10.

[0036] The transmission device 10 disposed in the underwater device 3 does not necessarily have to be one. For example, as shown by the dashed line in FIG. 1, the transmission device 10 may be further disposed on both side surfaces of the underwater device 3. In this case, the underwater device 3 may transmit video data using the transmission device 10 whose transmission direction is easily directed toward the water surface device 2. Similarly, a plurality of reception devices may be arranged on the water surface device 2 on the reception side in different directions from each other.

[0037] FIG. 2 is a block diagram showing the configuration of the underwater communication system 1. In FIG. 2, the dashed arrows other than B10 and S10 indicate the flow of signals in the control system, and the solid arrows indicate the flow of signals in the data system.

[0038] The underwater communication system 1 includes a transmission device 10 and a reception device 20.

[0039] The transmission device 10 includes a control unit 11, a storage unit 12, an optical transmission unit 13, a transmission signal generation unit 14, an imaging unit 15, a position and orientation detection unit 16, an acoustic communication unit 17, and a signal processing unit 18.

[0040] The control unit 11 includes an arithmetic processing circuit such as a CPU (Central Processing Unit) and controls each unit according to a program stored in the storage unit 12. The control unit 11 may include an FPGA (Field-Programmable Gate Array). The storage unit 12 includes a storage medium such as a ROM (Read Only Memory) or a RAM (Random Access Memory) and stores the program executed by the control unit 11. The storage unit 12 is also used as a work area in the control of the control unit 11. Furthermore, the storage unit 12 stores video data input from the imaging unit 15 under the control of the control unit 11 at any time.

[0041] The optical transmitting unit 13 transmits the laser light B10 in response to control from the control unit 11. The optical transmitting unit 13 modulates the laser light B10 in response to a transmission signal generated by a transmission signal generating unit 14. For example, the optical transmitting unit 13 modulates the laser light B10 by pulse modulation (e.g., PWM: Pulse Width Modulation). In addition, the optical transmitting unit 13 changes the transmission direction of the laser light B10 in response to control from the control unit 11.

[0042] The transmission signal generating unit 14 generates a transmission signal in response to control from the control unit 11. Specifically, the transmission signal generating unit 14 reads video data from the storage unit 12 and generates a transmission signal. The transmission signal generating unit 14 stores the video data in a data packet of a predetermined format, and further converts the data packet into a pulse signal to generate a transmission signal.

[0043] The imaging unit 15 includes a camera and captures images of underwater or the water bottom through the window 3a in Fig. 1. The imaging unit 15 outputs the image data obtained by imaging to the storage unit 12 as needed, and causes the storage unit 12 to store the image data.

[0044] The position and orientation detection unit 16 detects the position and orientation of the underwater device 3 shown in Fig. 1. The position and orientation detection unit 16 includes a GPS (Global Positioning System) and an acceleration sensor. The position and orientation detection unit 16 calculates the current position and orientation of the underwater device 3 at any time by integrating the direction and distance detected by the acceleration sensor with the position detected by the GPS when the underwater device 3 enters the water, and outputs information about the calculated position and orientation to the control unit 11 at any time. The position and orientation detection unit 16 also outputs information about the current position and orientation to the signal processing unit 18 in response to control from the control unit 11. The position and orientation detection unit 16 may be disposed inside the underwater device 3 other than the transmitting device 10.

[0045] The acoustic communication unit 17 performs communication using an acoustic signal S10 under the control of the control unit 11. The acoustic communication unit 17 includes a plurality of ultrasonic transducers, and drives these ultrasonic transducers to transmit ultrasonic waves (acoustic signals S10) into water. The acoustic communication unit 17 modulates the transmitted ultrasonic waves in response to a transmission signal input from the signal processing unit 18. The acoustic communication unit 17 also receives ultrasonic waves (acoustic signals S10) transmitted from the receiving device 20 with the ultrasonic transducers to generate a reception signal, and outputs the generated reception signal to the signal processing unit 18.

[0046] The signal processing unit 18 processes signals for the acoustic communication unit 17 under the control of the control unit 11. The signal processing unit 18 converts information based on the detection result input from the position and orientation detection unit 16 into a signal corresponding to acoustic communication, and outputs the signal to the acoustic communication unit 17. The signal processing unit 18 also performs processes such as amplification, noise removal, and decoding on the received signal input from the acoustic communication unit 17, and outputs the signal to the control unit 11.

[0047] The receiving device 20 includes a control unit 21, a storage unit 22, an optical receiving unit 23, a signal processing unit 24, a wireless communication unit 25, a position and orientation detection unit 26, an acoustic communication unit 27, and a signal processing unit .

[0048] The control unit 21 includes a calculation circuit such as a CPU, and controls each unit according to a program stored in the storage unit 12. The control unit 11 may include an FPGA. The storage unit 22 includes a storage medium such as a ROM or a RAM, and stores a program executed by the control unit 21. The storage unit 22 is also used as a work area in the control of the control unit 21. The storage unit 22 stores video data input from the signal processing unit 24 under the control of the control unit 21 as needed.

[0049] The optical receiving unit 23 receives the laser light B10 in response to control from the control unit 21. The optical receiving unit 23 receives the laser light B10 modulated by the optical transmitting unit 13 in response to video data, and outputs a detection signal in response to the received light intensity of the laser light B10 to the signal processing unit 24. In addition, the optical receiving unit 23 changes the receiving direction of the laser light B10 in response to control from the control unit 21.

[0050] Under the control of the control unit 21, the signal processing unit 24 performs processes such as amplification, noise removal, and decoding on the detection signal input from the optical receiving unit 23 to demodulate the video data, and outputs the demodulated video data to the storage unit 22. The storage unit 22 stores the input video data.

[0051] The wireless communication unit 25 performs wireless communication with the information collection device on land in response to control from the control unit 21. The wireless communication unit 25 reads the video data stored in the storage unit 22, generates transmission data, and transmits the generated transmission data to the information collection device on land by wireless communication.

[0052] The position and attitude detection unit 26 is equipped with a GPS and an acceleration sensor, and detects the position and attitude of the surface unit 2 shown in Fig. 1. The position and attitude detection unit 26 outputs information relating to the current position and attitude to the signal processing unit 28 in response to control from the control unit 21. The position and attitude detection unit 26 may be disposed inside the surface unit 2 other than the receiving device 20.

[0053] The acoustic communication unit 27 communicates using the acoustic signal S10 under the control from the control unit 21. The acoustic communication unit 27 includes a plurality of ultrasonic transducers, drives these ultrasonic transducers, and transmits ultrasonic waves (acoustic signal S10) into the water. The acoustic communication unit 27 modulates the ultrasonic waves to be transmitted according to the transmission signal input from the signal processing unit 28. Further, the acoustic communication unit 27 receives the ultrasonic waves (acoustic signal S10) transmitted from the transmission device 10 with the ultrasonic transducers to generate a reception signal, and outputs the generated reception signal to the signal processing unit 28.

[0054] The signal processing unit 28 processes signals for the acoustic communication unit 27 under the control from the control unit 21. The signal processing unit 28 converts the information based on the detection result input from the position and attitude detection unit 26 into a signal corresponding to the acoustic communication, and outputs it to the acoustic communication unit 27. Further, the signal processing unit 28 performs processes such as amplification, noise removal, and decoding on the reception signal input from the acoustic communication unit 27, and outputs it to the control unit 21.

[0055] FIG. 3 is a diagram showing the configurations of the optical transmission unit 13 and the optical reception unit 23.

[0056] The optical transmission unit 13 includes, as the configuration of the optical system, a laser light source 101, a condenser lens 102, an optical fiber 103, a collimator lens 104, a mirror 105, and an optical deflector 106. Further, the optical transmission unit 13 includes, as the configuration of the circuit system, a light source drive circuit 111 and a mirror drive circuit 112.

[0057] The laser light source 101 emits laser light of a predetermined wavelength. The emission wavelength of the laser light source 101 is included in the range of, for example, 400 nm or more and 550 nm or less. The laser light source 101 is, for example, an end-face emitting type laser diode. The laser light source 101 may be other types of laser light sources. Also, the number of arrangements of the laser light source 101 does not necessarily have to be one, and the laser light emitted from a plurality of laser light sources 101 may be incident on a plurality of bundled optical fibers.

[0058] The condenser lens 102 condenses the laser light emitted from the laser light source 101 onto an entrance port of the optical fiber 103. The optical fiber 103 propagates the incident laser light and emits it from an exit port.

[0059] The collimator lens 104 collimates the laser light emitted from the optical fiber 103. The laser light does not necessarily have to be converted into a completely parallel light by the collimator lens 104, and may be slightly diverged or slightly converged from the parallel light. The mirror 105 reflects the laser light collimated by the collimator lens 104 and bends the optical path of the laser light.

[0060] The optical deflector 106 deflects the laser light B10 reflected by the mirror 105. The optical deflector 106 includes a mirror 106a, and changes the transmission direction of the laser light B10 two-dimensionally by rotating the mirror 106a about two axes perpendicular to each other. The optical deflector 106 is formed of, for example, a MEMS (Micro Electro Mechanical Systems) mirror. In the configuration of FIG. 3, the optical system is laid out so that the incident angle of the laser light to the mirror 106a is 45° when the mirror 106a is in a neutral position.

[0061] The light source driving circuit 111 drives the laser light source 101 in response to a transmission signal (pulse signal) input from the transmission signal generating unit 14. As a result, a laser light B10 modulated by video data is transmitted. Furthermore, the light source driving circuit 111 drives the laser light source 101 with a constant output under the control of the control unit 11 in a communication search control described later. As a result, a laser light B10 with a constant output is transmitted.

[0062] The mirror driving circuit 112 drives the optical deflector 106 in response to control from the control unit 11. This changes the transmission direction of the laser light B10.

[0063] The optical receiving unit 23 includes, as its optical system configuration, an optical deflector 201, a branching element 202, a condenser lens 203, a photodetector 204, and an image sensor 205. The optical receiving unit 23 also includes, as its circuit system configuration, a detection signal processing circuit 211, a pixel signal processing circuit 212, and a mirror driving circuit 213.

[0064] The optical deflector 201 changes the receiving direction of the laser beam B10. The optical deflector 201 includes a mirror 201a, and rotates the mirror 201a about two axes perpendicular to each other to two-dimensionally change the receiving direction of the laser beam B10. The optical deflector 201 is formed of, for example, a MEMS mirror. In the configuration of FIG. 3, the optical system is laid out such that, when the mirror 201a is in a neutral position, the optical axis of the focusing lens 203 coincides with the center of the mirror 201a and is at an angle of 45° with respect to the normal to the mirror 201a.

[0065] The branching element 202 reflects a part of the laser beam B10 reflected by the mirror 201a and transmits the rest. The branching element 202 has a reflective film with a reflectance set to about 10%, for example. In this case, of the laser beam B10 passing through the optical deflector 201, about 90% is transmitted through the branching element 202 to become laser beam B11, and about 10% is reflected by the branching element 202 to become laser beam B12.

[0066] Other optical elements such as a diffraction grating may be used as the branching element 202. When the branching element 202 is a diffraction grating, for example, a blazed diffraction grating may be used in which the diffraction efficiency of the zeroth order light is about 90% and the diffraction efficiency of the first order diffracted light is about 10% for the wavelength of the laser light B10.

[0067] The focusing lens 203 focuses the laser beam B11 transmitted through the branching element 202 onto the light receiving area of ​​the photodetector 204. As described above, the optical axis of the focusing lens 203 is disposed so as to coincide with the center of the mirror 201a and to be at an angle of 45° with respect to the normal to the mirror 201a when the mirror 201a is in the neutral position. Therefore, in FIG. 3, when the laser beam B10 is reflected directly upward by the mirror 201a, the laser beam B11 is properly focused onto the light receiving area of ​​the photodetector 204.

[0068] The photodetector 204 outputs a detection signal in response to the laser light B11 focused by the focusing lens 203 being incident on the light receiving region. The photodetector 204 is, for example, an avalanche photodiode (APD). This allows the photodetector 204 to detect the weak laser light B11. The photodetector 204 may be a normal photodiode that does not use the avalanche multiplication phenomenon.

[0069] The image sensor 205 is an imaging element in which pixels are arranged in a matrix. The image sensor 205 is, for example, a CCD (charge-coupled device) or a CMOS image sensor. The image sensor 205 is arranged so that, when the laser light B10 is reflected directly upward by the mirror 201a, the central axis of the laser light B12 coincides with the center of the light receiving surface of the image sensor 205 and is perpendicular to the light receiving surface. A large number of pixels are arranged vertically and horizontally on the light receiving surface of the image sensor 205. The image sensor 205 may be any type as long as each pixel can detect the wavelength of the laser light B12.

[0070] The detection signal processing circuit 211 shapes the detection signal output from the photodetector 204 into a pulse waveform and outputs it to the signal processing unit 24. The pixel signal processing circuit 212 controls the driving of the image sensor 205, and performs processing such as noise removal on the pixel signals from each pixel of the image sensor 205, and outputs the processed pixel signals to the signal processing unit 24.

[0071] The mirror driving circuit 213 drives the optical deflector 201 in response to control from the control unit 21. This changes the receiving direction of the laser light B10.

[0072] Next, control regarding transmission and reception of video data will be described.

[0073] FIG. 4 is a flowchart showing control during transmission and reception of video data.

[0074] When transmitting and receiving video data, first, a communication search control is performed to form a communication path of laser light B10 between the transmitting device 10 and the receiving device 20 (S11). In the communication search control, the control unit 11 of the transmitting device 10 and the control unit 21 of the receiving device 20 cooperate with each other to perform a first search control and a second search control. The first search control and the second search control will be described later with reference to Figs. 5(a) to 9.

[0075] When a communication path is formed by the communication search control, next, a communication servo control is performed to maintain the communication path (S12). The communication servo control is mainly performed by the control unit 21 of the receiving device 20. The communication servo control will be described later with reference to FIG.

[0076] In this way, video data is transmitted while the communication path of the laser light is maintained (S14). That is, laser light B10 modulated by the video data is transmitted from the transmitting device 10 to the receiving device 20. If the communication servo is lost during the transmission of the video data and the communication path cannot be maintained (S13: NO), a communication search is performed again (S11). As a result, the communication path of the laser light is formed and maintained again (S11, S12, S13: YES), and the remaining video data is transmitted (S14). In this way, when the transmission of the currently transmitted video data is completed (S15: YES), the transmission and reception control of the video data is terminated.

[0077] 5(a) and 5(b) are flowcharts showing the control performed by the control unit 11 of the transmitting device 10 and the control unit 21 of the receiving device 20 in the first search control, respectively.

[0078] The control unit 11 of the transmitting device 10 transmits a search request to the receiving device 20 via the acoustic communication unit 17 (S101). At this time, the control unit 11 transmits information related to the current position and orientation detected by the position and orientation detection unit 16, together with the search request. Furthermore, in response to the transmission of the search request, the control unit 11 resets its own time axis to zero and starts timing.

[0079] When the control unit 21 of the receiving device 20 receives a search request via the acoustic communication unit 27 (S201: YES), it transmits information about the current position and orientation detected by the position and orientation detection unit 26 to the transmitting device 10 via the acoustic communication unit 27 (S202). At this time, the control unit 21 resets its own time axis to zero and starts clocking at the same time as receiving the search request. This causes the time axis of the transmitting device 10 and the time axis of the receiving device 20 to be aligned.

[0080] Furthermore, the control unit 21 sets the receiving direction to a direction toward the transmitting device 10 based on the received information on the position and attitude and the information on the current position and attitude detected by the position and attitude detection unit 26 (S203). Specifically, the control unit 21 controls the optical deflector 201 to tilt the mirror 201a so that the receiving direction of the laser beam B10 faces the transmitting device 10. Then, the control unit 21 executes a laser beam receiving process (scanning beam receiving process) (S204).

[0081] When the control unit 11 of the transmitting device 10 receives the information on the position and attitude transmitted from the receiving device 20 in step S202 (S102: YES), it sets the transmission direction to the direction toward the receiving device 20 based on the received information on the position and attitude and the information on the current position and attitude detected by the position and attitude detection unit 16 (S103). Specifically, the control unit 11 controls the optical deflector 106 to tilt the mirror 106a so that the transmission direction of the laser light B10 is toward the receiving device 20.

[0082] Then, the control unit 11 controls the laser light source 101 and the optical deflector 106 so that the laser light B10 scans within a predetermined angle range with the set transmission direction as the center (S104). At this time, the control unit 11 drives the laser light source 101 at a constant output. This causes the laser light B10 with the constant output to scan along a predetermined scanning trajectory. The scanning is repeated a predetermined number of times (for example, three times) along the same scanning trajectory. In this embodiment, the scanning operation is performed so that the laser light B10 rotates along a circular trajectory centered on the transmission direction set in step S103.

[0083] In this scan, when laser light B10 is incident on mirror 201a of receiving device 20, laser light B12 is incident on the light receiving surface of image sensor 205. In this case, a pixel signal according to the received light intensity is output from the corresponding pixel of image sensor 205. On the other hand, in this scan, if laser light B10 is not incident on mirror 201a of receiving device 20, laser light B12 is not incident on the light receiving surface of image sensor 205. In this case, no pixel signal due to reception of laser light is output from any pixel of image sensor 205.

[0084] The control unit 21 of the receiving device 20 sets a monitoring period including a period during which the laser light B10 is scanned a predetermined number of times on the common time axis aligned with the transmitting device 10 as described above, and executes the process of step S204 during this monitoring period. Then, when this monitoring period ends, the control unit 21 transmits a search result indicating whether or not the image sensor 205 received the laser light B12 during the monitoring period to the transmitting device 10 via the acoustic communication unit 27 (S205). If the image sensor 205 receives the laser light B12, time information indicating the timing of reception is further included in the search result. The time information is defined by the elapsed time on the common time axis.

[0085] FIG. 6 is a diagram showing a schematic light receiving state of the image sensor 205 when the laser light B12 is incident on the light receiving surface 205a of the image sensor 205 by the scanning operation.

[0086] As described above, in this embodiment, the scanning operation is performed such that the laser light B10 rotates along a circular trajectory. Therefore, the laser light B12 branched by the branching element 202 also moves along the circular scanning trajectory L12. For convenience, in FIG. 6, the scanning trajectory L12 and the laser light B12 are shown by dashed lines even during a period in which the laser light is not incident on the mirror 201a of the optical deflector 201.

[0087] Fig. 7(a) is a time chart showing a change in the rotation angle of the laser beam B10 during a scanning operation in the transmitting device 10. Fig. 7(b) is a time chart showing a state in which the laser beam B12 is received by the image sensor 205 during a scanning operation in the receiving device 20. The vertical axis of Fig. 7(b) is an integrated value obtained by integrating the signal values ​​of all pixels of the image sensor 205.

[0088] As shown in Fig. 7(a), the control unit 11 of the transmitting device 10 controls the optical deflector 106 so that the laser light B10 rotates once in one scanning period T1. As described above, one rotation of the scan is repeated a predetermined number of times (for example, three times). When the laser light B10 is incident on the optical deflector 201 (mirror 201a) of the receiving device 20 at a predetermined scanning position during one rotation of the laser light B10, the signal value (integrated value of all pixels) of the image sensor 205 rises in a pulse shape as shown in Fig. 7(b).

[0089] The control unit 11 of the receiving device 20 compares the signal value (integrated value of all pixels) of the image sensor 205 with a predetermined threshold value Sth, and determines that the optical deflector 201 has received the laser beam B10 when the signal value is equal to or greater than the threshold value Sth. Then, the control unit 11 obtains the time of the midpoint of the period during which the signal value is equal to or greater than the threshold value Sth as time information indicating the timing at which the optical deflector 201 received the laser beam B10. In the example of FIG. 7(b), during the first and second scanning periods T1, the laser beam B10 is received by the optical deflector 201, and time information of times t1 and t2 is obtained.

[0090] 5(a) and 5(b), in step S205, the control unit 21 of the receiving device 20 transmits the search result to the transmitting device 1 by acoustic communication. As described above, the search result includes information indicating whether the image sensor 205 has received the laser beam B12, and if the image sensor 205 has received the laser beam B12, further includes time information indicating the timing of reception.

[0091] After transmitting the search result in this way, the control unit 21 judges whether or not the image sensor 205 has received the laser light B12 in the current scanning operation (S206). If the image sensor 205 has received the laser light B12 (S206: YES), the first search control ends. On the other hand, if the image sensor 205 has not received the laser light B12 (S206: NO), the control unit 21 returns the process to step S204.

[0092] When the control unit 11 of the transmission device 10 receives the search result transmitted in step S205 by acoustic communication (S105), it refers to the search result and determines whether the image sensor 205 has received the laser beam B12 (S106). Then, when the image sensor 205 has received the laser beam B12 (S106: YES), the control unit 11 ends the first search control. When the image sensor 205 has not received the laser beam B12 (S106: NO), the control unit 11 returns the process to step S103.

[0093] When the process is returned to step S103, the control unit 11 re - sets the transmission direction of the laser beam B10. Here, the control unit 11 sets a new transmission direction in a direction shifted by a predetermined angle from the transmission direction set in step S103 last time by a predetermined direction. Then, the control unit 11 scans the laser beam B10 a predetermined number of times again around the newly set transmission direction (S104).

[0094] Also, when the control unit 21 of the reception device 20 returns the process to step S204, it sets a monitoring period again on the same time axis as the transmission device 10 and executes a light reception process using the image sensor 205. The monitoring period is set to a period including the execution period of the predetermined number of scan operations performed in step S104 again. When the monitoring period ends, the control unit 21 generates a search result for the monitoring period and transmits it to the transmission device 10 by acoustic communication (S205). The transmitted search result is received by the control unit 11 of the transmission device 10 in step S105.

[0095] In this way, the control unit 11 of the transmission device 10 and the control unit 21 of the reception device 20 repeatedly execute the processes of steps S103 - S106 and steps S204 - S206 while correcting the scan direction of the laser beam B10 until the image sensor 205 receives the laser beam B12. Then, when the determinations in steps S106 and S206 become YES, the control unit 11 and the control unit 21 each end the first search control and shift to the second search control.

[0096] 5(a) and (b), if the determination in steps S106 and S206 is NO, the transmission direction is corrected and the scanning operation is performed again, but the scanning trajectory of the scan may be corrected without correcting the transmission direction. For example, when performing the scanning operation again, the control unit 11 may change the diameter of the scanning trajectory centered on the transmission direction. Also, if the determination in steps S106 and S206 is NO, the control units 11 and 21 may return the process to steps S101 and S201, respectively, and redo the first search control.

[0097] 8(a) and 8(b) are flowcharts showing the control performed by the control unit 11 of the transmitting device 10 and the control unit 21 of the receiving device 20 in the second search control, respectively.

[0098] The control unit 11 of the transmitting device 10 sets the transmission direction of the laser light B10 based on the search result received in step S105 of Fig. 5(a) (S111). Specifically, the control unit 11 sets the transmission direction of the laser light B10 based on the time information included in the search result.

[0099] 7(a) and (b), the search result includes times t1 and t2. In this example, even in the third and subsequent scan periods T1, there may be a period during which the signal value of the image sensor 205 (the integrated value of the signal values ​​of all pixels) rises. Therefore, even in the third and subsequent scan periods T1, a time indicating the light reception timing may be similarly acquired, and the acquired time may be further included in the search result.

[0100] The control unit 11 of the transmitting device 10 acquires the rotation angle of the laser light B10 corresponding to the time included in the search result. In the example of Figs. 7(a) and (b), the rotation angle θ1 corresponding to the time t1 is acquired, and the rotation angle θ2 corresponding to the time t2 is acquired. Similarly, for the remaining scanning period T1, the rotation angles corresponding to the time included in the search result are acquired. The control unit 11 sets the transmission direction corresponding to the rotation angle obtained by averaging the acquired rotation angles as the transmission direction in step S111 of Fig. 8(a). At this time, the control unit 11 may exclude rotation angles that deviate significantly from other rotation angles from the targets of averaging.

[0101] Here, the rotation angle of the laser light B10 is acquired as the scanning position of the laser light B10 corresponding to each time, but other parameter values ​​such as the rotation position or amount of rotation of the mirror 106a in the optical deflector 106 may be acquired as the scanning position of the laser light B10 corresponding to each time.

[0102] 8(a) and (b), the control unit 11 controls the laser light source 101 and the optical deflector 106 to irradiate a constant output laser light B10 in the transmission direction set in step S111 (S112). Since this transmission direction is the transmission direction in which the laser light B10 was received by the receiving device 20 in the above-mentioned first search process, the laser light B10 irradiated this time is usually also received by the receiving device 20. Thereafter, the control unit 11 waits for control information to be transmitted from the receiving device 20 (S113).

[0103] In the second search control, the control unit 21 of the receiving device 20 executes a process of receiving the laser light B12 with the image sensor 205 (S211). Then, the control unit 21 generates control information for correcting a deviation between the center of the optical deflector 201 (mirror 201a) and the center of the laser light B10 based on the output signal of the image sensor 205 (S212), and transmits the generated control information to the transmitting device 10 via the acoustic communication unit 27 (S213). As a result, the control unit 21 ends the second search control and proceeds to the subsequent communication servo control (step S12 in FIG. 4).

[0104] FIG. 9 is a diagram illustrating a method of generating control information in the second search control.

[0105] In the example of FIG. 9, the laser light B12 branched by the branching element 202 is incident on the vicinity of a corner of the light receiving surface 205a of the image sensor 205. The control unit 21 specifies a light receiving range of the laser light B12 on the light receiving surface 205a of the image sensor 205 based on a pixel signal output from each pixel 205b of the image sensor 205. For example, the control unit 21 specifies a range of a pixel group whose pixel signal is equal to or greater than a predetermined threshold as the light receiving range. In the example of FIG. 9, the range of the hatched pixel group 205b is specified as the light receiving range. The control unit 21 extracts the position of the pixel 205b that has the highest signal value (maximum light receiving position P1) among the pixels 205b included in the specified light receiving range, and further extracts a center position of the signal value in the light receiving range (light receiving center position P2) from the signal value of each pixel 205b.

[0106] Usually, the intensity of the laser light B12 is highest near the center and gradually decreases with distance from the center. In the example of FIG. 9, the center of the laser light B12 is included in the light receiving surface 205a, so the signal value of the pixel 205b near the center of the laser light B12 is highest. Therefore, in the example of FIG. 9, the position of the pixel 205b near the center of the laser light B12 becomes the maximum light receiving position P1. Also, in the example of FIG. 9, the light receiving range is greatly expanded from the center of the laser light B12 in the lower left direction in FIG. 9. Therefore, the light receiving center position P2 is shifted in the lower left direction from the maximum light receiving position P1.

[0107] In this way, the shift direction of the maximum light receiving position P1 relative to the light receiving center position P2 is roughly aligned with the shift direction of the center of the laser light B12 relative to the center of the light receiving surface 205a. Also, a certain relationship (rule) can be defined between the shift amount between the light receiving center position P2 and the maximum light receiving position P1, the light receiving range (position and area), and the shift amount of the center of the laser light B12 relative to the center of the light receiving surface 205a. Therefore, by identifying the maximum light receiving position P1, the light receiving center position P2, and the light receiving range, the shift direction and shift amount of the center of the laser light B12 relative to the center of the light receiving surface 205a can be estimated.

[0108] On the other hand, the direction and amount of deviation of the center of the laser beam B12 from the center of the light receiving surface 205a correspond to the direction and amount of deviation of the center of the laser beam B10 from the center of the optical deflector 201 (mirror 201a). Therefore, the direction and amount of deviation of the center of the laser beam B10 from the center of the optical deflector 201 (mirror 201a) can be estimated from the direction and amount of deviation of the maximum light receiving position P1 from the light receiving center position P2 and the light receiving range.

[0109] After extracting the maximum light receiving position P1 and the light receiving center position P2, the control unit 21 calculates the horizontal and vertical differences Δd1 and Δd2 between the maximum light receiving position P1 and the light receiving center position P2 (the shift direction and shift amount of the maximum light receiving position P1 from the light receiving center position P2). Then, based on the calculated differences Δd1 and Δd2 and the position and number of pixels (area) of the light receiving range, the control unit 21 calculates the shift direction and shift amount of the center of the laser light B10 from the center of the optical deflector 201 (mirror 201a), and calculates the correction direction and correction amount of the transmission direction of the laser light B10 required to eliminate the shift direction and shift amount. The control unit 21 acquires the correction direction and correction amount calculated in this way as control information in step S212 of FIG. 8(b).

[0110] Returning to Fig. 8(a) and (b), when the control unit 11 of the transmitting device 10 receives the control information via the acoustic communication unit 17 (S113: YES), it corrects the transmission direction of the laser light B10 based on the control information (S114). That is, the control unit 11 controls the optical deflector 106 to correct the transmission direction of the laser light B10 in a direction that eliminates the deviation of the center of the laser light B10 from the center of the optical deflector 201 (mirror 201a). As a result, the center of the laser light B10 and the center of the optical deflector 201 (mirror 201a) approach each other, and at the same time, the center of the laser light B12 and the center of the light receiving surface 205a of the image sensor 205 approach each other. Thereafter, the control unit 11 ends the second search control and proceeds to the subsequent communication servo control (step S12 in Fig. 4).

[0111] FIG. 10 is a diagram showing communication servo control in the control unit 21 of the receiving device 20. As shown in FIG.

[0112] In the communication servo control, the control unit 21 extracts the maximum light receiving position P1 in the light receiving range, and calculates the differences Δd3 and Δd4 between the maximum light receiving position P1 and the central pixel position P0 of the light receiving surface 205a. Then, the control unit 21 controls the optical deflector 201 so as to eliminate the differences Δd3 and Δd4. This allows the focusing position of the laser light B10 by the focusing lens 203 to be properly positioned in the light receiving region of the photodetector 204. The control unit 21 repeatedly executes the above control as needed.

[0113] In the communication servo control, when the rotation angle of the mirror 201a in the optical deflector 201 reaches near the upper limit of the rotational range, the control unit 21 transmits control information to the transmitting device 10 via the acoustic communication unit 27 to correct the transmission direction of the laser light B10 in a direction in which the mirror 201a approaches the neutral position. In response to this, the control unit 11 of the transmitting device 10 controls the position of the underwater device 3 and the optical deflector 106 to correct the transmission direction of the laser light B10. As a result, the mirror 201a of the optical deflector 201 of the receiving device 20 returns to near the neutral position by the communication servo control. In this way, the communication servo control is smoothly continued.

[0114] <Effects of the embodiment> According to the above embodiment, the following effects can be achieved.

[0115] Since the laser light B10 is used to transmit the video data, a large amount of data can be transmitted from the transmitting device 10 to the receiving device 20. Furthermore, since the laser light B10 used for communication is collimated, the density of the laser light B10 is unlikely to decrease even if the distance from the transmitting device 10 to the receiving device 20 is long. Therefore, the distance over which communication is possible between the transmitting device 10 and the receiving device 20 can be extended. Furthermore, since the image sensor 205 having a wide light receiving area (light receiving surface 205a) is used to monitor the light receiving state of the laser light B10 in the receiving device 20, when the laser light B10 is collimated as described above, the light receiving state of the laser light in the receiving device 20 can be precisely monitored with high resolution. Therefore, from the output signal from the image sensor 205, control information for controlling the transmission direction of the laser light B10 to the direction toward the receiving device 20 can be smoothly and accurately generated, and the transmission direction of the laser light B10 can be appropriately controlled by this control information. Therefore, according to the underwater communication system 1 according to this embodiment, a large amount of video data can be transmitted and received over a longer distance.

[0116] As shown in Fig. 5(a) and (b), the control unit 11 (first control unit) of the transmitting device 10 controls the optical deflector 106 (first optical deflector) to scan the laser light B10 in a predetermined range (S104), the control unit 21 (second control unit) of the receiving device 20 transmits a search result (control information) regarding the scan position where the image sensor 205 received the laser light B12 to the transmitting device 10 via the acoustic communication unit 27 (second communication unit) (S205), and the control unit 11 (first control unit) controls the optical deflector 106 (first optical deflector) to set the transmission direction of the laser light B10 to a direction based on the search result (control information) received via the acoustic communication unit 17 (first communication unit) (step S111 in Fig. 8(a)). According to this control (first search control), the receiving device 20 can detect a transmission direction in which the laser light can be received by scanning the collimated laser light B10. Therefore, the transmission direction of the laser light B10 can be smoothly set before transmitting a large amount of video data.

[0117] As shown in Fig. 7(b), the search result (control information) regarding the scan position at which the image sensor 205 received the laser light B12 includes time information specifying the timing at which the image sensor 205 received the laser light B12. According to this configuration, by adjusting the time axis between the transmitting device 10 and the receiving device 20 in advance, the transmitting device 10 can specify which scan position is a position at which the receiving device 20 can receive the laser light B10 based on the time information included in the search result. Therefore, the transmitting device 10 can set the transmission direction of the laser light B10 by simple processing.

[0118] 8(a) and 8(b), the control unit 21 (second control unit) of the receiving device 20 transmits control information for correcting the deviation between the center of the optical deflector 201 (second optical deflector) and the center of the laser light B10 to the transmitting device 10 via the acoustic communication unit 27 (second communication unit) based on the output signal of the image sensor 205 (S213), and the control unit 11 (first control unit) of the transmitting device 10 controls the optical deflector 106 (first optical deflector) based on the control information received via the acoustic communication unit 17 (first communication unit) to correct the transmission direction of the laser light B10 in a direction that eliminates the deviation (S114). According to this control, the transmission direction of the laser light B10 transmitted from the transmitting device 10 can be corrected so that the center of the optical deflector 201 (second optical deflector) and the center of the laser light B10 approach each other. This allows a larger amount of laser light B10 to be captured by the optical deflector 201 (second optical deflector) and guided to the photodetector 204. This makes it possible to transmit and receive video data using the laser light B10 with higher accuracy.

[0119] 9, in the second search control, the control unit 21 (second control unit) of the receiving device 20 extracts the maximum light receiving position P1 and the light receiving center position P2 in the light receiving range of the laser light B12 in the image sensor 205 based on the output signal of the image sensor 205, and generates control information for correcting the above-mentioned deviation based on the differences Δd1, Δd2 between the maximum light receiving position P1 and the light receiving center position P2. According to this configuration, as described above, it is possible to smoothly generate control information for correcting the deviation between the center of the optical deflector 201 (second optical deflector) and the center of the laser light B10 based on the output signal of the image sensor 205.

[0120] As shown in FIG. 2, acoustic communication units 17, 27 use acoustic signals to transmit and receive information (search results, control information, etc.) in the first search control and second search control. With this configuration, wide-angle transmission and reception is possible, so that the search results and control information can be smoothly and reliably provided from the receiving device 20 to the transmitting device 10. Therefore, the transmission direction of the laser light B10 can be controlled quickly and appropriately. Note that the search results and control information have small data volumes. As described above, it is preferable that the wavelength of the laser light emitted from the laser light source 101 is set to be within the range of 400 nm to 550 nm. Since light in this wavelength band is not easily absorbed or scattered by water, by setting the wavelength of the laser light B10 in this manner, the communication distance between the transmitting device 10 and the receiving device 20 using the laser light B10 can be more effectively increased.

[0121] 3, the optical deflector 106 (first optical deflector) of the transmitting device 10 and the optical deflector 201 (second optical deflector) of the receiving device 20 are reflection-type optical deflectors having mirrors 106a and 201a, respectively. This allows the transmitting and receiving direction of the laser light B10 to be changed over a wide angle by simple control.

[0122] <Example of change> In the above embodiment, the scanning trajectory of the laser light B10 in the first search control is circular, but the scanning trajectory is not limited to this. For example, the scanning trajectory may be rectangular, or a scanning trajectory that meanders within a predetermined range may be used. When a scanning trajectory that meanders within a predetermined range is used, the scanning trajectory L12 of the laser light B12 in the image sensor 205 becomes, for example, as shown in FIG. 11. In this case, the laser light B12 can be received by the image sensor 205 at a predetermined scanning position.

[0123] In the above embodiment, in the second search control, the deviation between the center of the optical deflector 201 and the center of the laser beam B10 is detected by the method shown in Fig. 9, but the method of detecting this deviation is not limited to this, and other methods may be used. For example, the deviation between the center of the optical deflector 201 and the center of the laser beam B10 may be detected based on the deviation (deviation direction, deviation amount) between the light receiving center position P2 or the maximum light receiving position P1 and the central pixel position P0 of the light receiving surface 205a. Alternatively, the central position of the laser beam B12 may be obtained based on the intensity distribution of the light receiving range of the laser beam B12 in the image sensor 205.

[0124] FIG. 12 is a diagram for explaining a method for determining the center position of the laser beam B12 based on the intensity distribution in the light receiving range of the image sensor 205 for the laser beam B12.

[0125] Here, an x-axis and a y-axis are set on the image sensor 205. The zero coordinate positions of the x-axis and y-axis are set to the center of the image sensor 205. The x-axis direction is the horizontal direction of the light receiving surface 102a, and the y-axis direction is the vertical direction of the light receiving surface 102a. The light receiving range of the image sensor 205 is a range of ±d in the x-axis direction and a range of ±d in the y-axis direction. Here, the light receiving surface 205a is set to a range in the positive direction. The number of pixels in the vertical and horizontal directions is the same.

[0126] In the example of FIG. 12, the center position (x0, y0) of the laser beam B12 is off the light receiving surface 205a. Each pixel 205b is hatched to indicate the intensity of the received light. For example, 1 / e 2 The beam range of the laser beam B12 is indicated by a dashed circle. An output according to the received light intensity is also generated in the pixel 205b, which is covered by the range of the base of the intensity distribution of the laser beam B12. The received light intensity of each pixel 205b decreases in a normal distribution shape as it moves away from the center position (x0, y0) of the laser beam B12.

[0127] Here, the received light intensity of the laser light B12 at each position on the xy coordinate plane can be expressed by the following equation.

[0128]

number

[0129] In the above formula (1), I 0 is the intensity (peak intensity) of the center position of the laser beam B12, and ω x and ω y are the beam diameters of the laser beam B12 in the x-axis direction and the y-axis direction, respectively. As described above, the beam diameter is, for example, 1 / e 2 is specified for a beam range of

[0130] Taking the natural logarithm of both sides of the above equation (1) gives the following equation:

[0131]

number

[0132] Furthermore, by partially differentiating the above equation (2) with respect to x and y, the following equation is obtained.

[0133]

number

[0134] From the data groups calculated by the above formulas (3) and (4), approximate straight lines are calculated by the least squares method or the like, and the approximate straight lines obtained are z x =0 plane and z y The intercept positions in the x-axis and y-axis directions, which are tangent to the plane at x=0, can be obtained as the coordinates of the center position of the laser light B12.

[0135] 13(a) to 13(d) are simulation results showing an example of a data group calculated by the above formulas (1) to (4). In this example, the center position (x0, y0) of the laser light B12 is set to (15.0 mm, 15.0 mm). Also, the parameter value d that defines the light receiving range of the image sensor 205 is set to 5 mm.

[0136] FIG. 13(a) shows a data group of the intensity distribution of the above formula (1), and FIG. 13(b) shows a data group of the above formula (2). FIG. 13(c) shows a data group of the above formula (3), and FIG. 13(d) shows a data group of the above formula (4). In this example, since the center of the laser light B12 is far from the center of the light receiving range of the image sensor 205, the light receiving range includes a range where the light receiving intensity is significantly low (a position where the x position and the y position are close to -5 mm). This range is easily affected by noise. For this reason, the simulation results of FIG. 13(c) and FIG. 13(d) include noise components in the range where the light receiving intensity is low.

[0137] 14(a) to 14(d) are simulation results showing another example of a data group calculated by the above formulas (1) to (4). In this example, the center position (x0, y0) of the laser light B12 is set to (0 mm, 0 mm). Also, the parameter value d that defines the light receiving range of the image sensor 205 is set to 5 mm, similarly to Figs. 13(a) to 13(d).

[0138] FIG. 14(a) shows a data group of the intensity distribution of the above formula (1), and FIG. 14(b) shows a data group of the above formula (2). FIG. 14(c) shows a data group of the above formula (3), and FIG. 14(d) shows a data group of the above formula (4). In this example, since the center of the laser light B12 coincides with the center of the light receiving range of the image sensor 205, the light receiving range does not include a range where the light receiving intensity is significantly low. Therefore, in the simulation results of FIG. 14(c) and FIG. 14(d), noise components are suppressed in the range where the light receiving intensity is low.

[0139] Figures 15(a) and 15(b) are graphs showing the results of approximation of a straight line by the least squares method for the data groups in Figures 14(c) and (d), respectively. In Figures 15(a) and 15(b), the circles represent the data groups, and the thick lines represent the approximation lines. Here, the approximation line is calculated from all the data groups in Figures 14(c) and (d).

[0140] In this example, the position (intercept) in the x-axis direction of the approximated straight line tangent to the plane of Zx=0 is -0.075 mm, and the position (intercept) in the y-axis direction of the approximated straight line tangent to the plane of Zy=0 is -0.077 mm. Therefore, in this example, the center position (x0, y0) of the laser beam B12 is calculated to be (-0.075 mm, 0.077 mm). This calculation result precisely matches the original center position (0 mm, 0 mm) of the laser beam B12 set for this example.

[0141] Figures 16(a) and 16(b) are graphs showing the results of calculating an approximation line by the least squares method for the data groups in Figures 13(c) and (d), respectively. In Figures 16(a) and 16(b), the circles represent the data groups, and the thick lines represent the approximation lines. Here, the approximation line is calculated from all the data groups in Figures 13(c) and (d).

[0142] In this example, the position (intercept) in the x-axis direction of the approximation line tangent to the plane of Zx=0 is 14.3 mm, and the position (intercept) in the y-axis direction of the approximation line tangent to the plane of Zy=0 is 13.9 mm. Therefore, in this example, the center position (x0, y0) of the laser beam B12 is calculated to be (14.3 mm, 13.9 mm). This calculation result precisely matches the original center position (15.0 mm, 15.0 mm) of the laser beam B12 set for this example.

[0143] In the above simulation, the beam diameter ω x , ω y are parameters in the calculation formulas (3) and (4) above. Even if these values ​​change, the variation in the data values ​​and the slope of the approximation line in the above formulas (3) and (4) change, but the x and y positions of the intercept where the approximation line touches the plane at z = 0 do not change much. Therefore, the calculation of the data group using the above formulas (3) and (4) is performed with the beam diameter ω x , ω y This can be done by setting a predetermined fixed value.

[0144] In the above simulation, the approximate straight line was obtained from all the data groups in Figures 13(c) and (d), but for example, in Figures 13(c) and 13(d), the range for calculating the approximate straight line may be limited to the data group in the y-axis range where the influence of noise is small (for example, the y-axis value range of 0 to 5 mm). This allows the calculation result of the center position of the laser beam B12 to be closer to the original center position with higher accuracy.

[0145] As described above, this calculation method can accurately calculate the center position of the laser beam B12. Therefore, by using this calculation method in the second search control, the accuracy of the control information for correcting the deviation between the center of the optical deflector 201 and the center of the laser beam B10 can be improved, and a smooth transition to the subsequent communication servo control can be achieved.

[0146] However, this calculation method imposes a higher data processing load than the method shown in Fig. 9. Therefore, when the second search control is to be performed quickly with a lower processing load, it is preferable to use the method shown in Fig. 9.

[0147] In the above embodiment, the time information is transmitted from the receiving device 20 to the transmitting device 10 as the control information in the first search control, but the control information regarding the scan position at which the receiving device 20 receives the laser light B10 may be other information. For example, a signal of a peculiar pulse train or a signal of a peculiar modulation form may be transmitted from the receiving device 20 to the transmitting device 10 as the control information at the timing at which the receiving device 20 receives the laser light B10. In this case, the control unit 11 of the transmitting device 10 may set the direction corresponding to the scan position at the timing at which these signals are received as the transmission direction in the second search control, or may set the direction corresponding to the scan position at the timing preceding the timing at which these signals are received by the transmission and reception time lag as the transmission direction in the second search control.

[0148] Furthermore, in the above embodiment, the first search control and the second search control are performed as the communication search control, but only one of the first search control and the second search control may be performed.

[0149] For example, when the first search control identifies the scan position where the receiving device 20 receives the laser light B10, the laser light B10 is transmitted with the direction corresponding to the scan position as the transmission direction, and then servo control is performed to draw the center of the laser light B12 into the center of the image sensor 205.

[0150] Alternatively, the laser light B10 may be transmitted without scanning in a transmission direction set based on the positions and attitudes of the transmitting device 10 and the receiving device 20, and when the transmitted laser light B10 is received by the receiving device 20, a second search control may be executed, and then a transition may be made to servo control.

[0151] In the above embodiment, the transmission and reception of information in the first search control and the second search control are performed by acoustic signals. However, the transmission and reception of such information may be performed using other carrier waves such as ultra-long wave electromagnetic waves with a frequency of about 30 to 300 Hz.

[0152] In the above embodiment, the data transmitted using the laser light B10 is video data. However, the data to be transmitted is not limited to this, and other types of large-capacity data may be transmitted using the laser light B10.

[0153] In the above embodiment, the position and orientation of the transmission device 10 (underwater device 3) are detected by the position and orientation detection unit 16 in FIG. 2. However, when the surface device 2 is equipped with a sonar, the position of the transmission device 10 (underwater device 3) may be detected by the sonar. In this case, in step 202 of FIG. 5, the receiving device 20 further transmits information indicating the detected position to the transmission device 10, and the transmission device 10 may specify its own position based on the received information.

[0154] In addition, the configuration of the optical systems of the optical transmission unit 13 and the optical reception unit 23 is not limited to the configuration in FIG. 3 and can be changed as appropriate. For example, in the configuration of FIG. 3, the laser light emitted from the laser light source 101 is guided to the collimator lens 104 via the optical fiber 103. However, a configuration in which the laser light emitted from the laser light source 101 directly enters the collimator lens 104 may also be used. Also, in the configuration of FIG. 3, the optical path of the laser light collimated by the collimator lens 104 is bent by the mirror 105. However, a configuration in which the laser light collimated by the collimator lens 104 directly enters the mirror 106a of the optical deflector 106 may also be used.

[0155] In the configuration of FIG. 3, an optical deflector 106 in which the mirror 106a can be rotated about two axes is used. However, a configuration in which two optical deflectors in which the mirror can be rotated about one axis are used to two-dimensionally drive the laser light B10 may also be used. In this case, the two optical deflectors are arranged opposite to each other such that their respective rotation axes are perpendicular to each other. The optical deflector 201 on the receiving device 20 side can also be replaced with a similar configuration.

[0156] In addition, the optical deflectors 106 and 201 do not necessarily have to be reflective optical deflectors using mirrors, and may be configured to move or rotate a lens, for example. The laser light source 101 is also not limited to a laser diode, and may be another type of laser light source such as a gas laser.

[0157] Furthermore, the image sensor 205 is not limited to a CCD or CMOS image sensor, and may be an image sensor having a configuration in which a plurality of photodetectors or optical sensors are arranged in a matrix. In this case, in order to perform the second search control with high accuracy, it is preferable to increase the number of photodetectors or optical sensors arranged and increase the resolution of light detection.

[0158] In addition, the embodiments of the present invention can be modified in various ways as appropriate within the scope of the claims. [Explanation of symbols]

[0159] 1 Underwater communication system 10 Transmitting device 11 Control section (first control section) 17 Acoustic Communication Unit (First Communication Unit) 20 Receiving device 21 Control section (second control section) 27 Acoustic Communication Unit (Second Communication Unit) 101 Laser light source 104 Collimator Lens 106 Optical deflector (first optical deflector) 201 Optical deflector (second optical deflector) 202 Branching element 204 Photodetector 205 Image Sensor

Claims

1. A transmitting device, a receiving device, and a position and orientation detection unit that detects positions and orientations of the transmitting device and the receiving device, The transmitting device A laser light source that emits laser light; a collimator lens for collimating the laser light; a first optical deflector that deflects the collimated laser light; A first communication unit that communicates with the receiving device; a first control unit that controls the first optical deflector based on control information received via the first communication unit, The receiving device includes: a second optical deflector that changes a receiving direction of the laser light; a branching element that branches an optical path of the laser light that has passed through the second optical deflector; a photodetector that receives one of the split laser beams; an image sensor that receives the other branched laser light; A second communication unit that communicates with the transmitting device; a second control unit that causes the second communication unit to transmit the control information for controlling a transmission direction of the laser light for receiving the laser light based on an output signal of the image sensor; the first control unit sets a transmission direction of the laser light to a direction toward the receiving device based on the positions and orientations of the transmitting device and the receiving device detected by the position and orientation detection unit, and executes control of the first optical deflector based on the control information.

1. An underwater communication system comprising:

2. 2. The underwater communication system according to claim 1, the first control unit controls the first optical deflector to cause the laser light to scan a predetermined range centered on the set direction; The second control unit transmits the control information regarding a scan position at which the image sensor receives the laser light to the transmission device via the second communication unit, the first control unit controls the first optical deflector to set a transmission direction of the laser light to a direction based on the control information received via the first communication unit; 1. An underwater communication system comprising:

3. 3. The underwater communication system according to claim 2, The control information regarding the scanning position is information for identifying a timing at which the image sensor receives the laser light.

1. An underwater communication system comprising:

4. 4. The underwater communication system according to claim 1, the second control unit transmits the control information for correcting a misalignment between a center of the second optical deflector and a center of the laser light to the transmitting device via the second communication unit based on an output signal of the image sensor; the first control unit controls the first optical deflector based on the control information received via the first communication unit to correct the transmission direction of the laser light in a direction that eliminates the deviation.

1. An underwater communication system comprising:

5. 5. The underwater communication system according to claim 4, The second control unit is extracting a maximum light receiving position and a light receiving center position in a light receiving range of the laser light in the image sensor based on an output signal of the image sensor; generating the control information for correcting the deviation based on a difference between the maximum light receiving position and the light receiving center position; 1. An underwater communication system comprising:

6. 5. The underwater communication system according to claim 4, The second control unit is calculating a center position of the laser light based on an intensity distribution of the laser light in a light receiving area of ​​the image sensor; generating the control information for correcting the deviation based on the calculated center position; 1. An underwater communication system comprising:

7. 7. The underwater communication system according to claim 1, the first communication unit and the second communication unit communicate with each other by acoustic signals; 1. An underwater communication system comprising:

8. 8. The underwater communication system according to claim 1, The wavelength of the laser light emitted from the laser light source is in the range of 400 nm to 550 nm.

1. An underwater communication system comprising:

9. 9. The underwater communication system according to claim 1, the first optical deflector and the second optical deflector are each a reflective optical deflector having a mirror; 1. An underwater communication system comprising:

10. In the underwater communication system according to any one of claims 1 to 8, The transmitting device is disposed in one of two devices performing underwater communication; the receiving device is disposed in the other of the two devices; One of the two devices is a device capable of propelling itself through water.

1. An underwater communication system comprising:

11. An underwater communication method using laser light, comprising: setting a transmission direction of a laser beam transmitted from the transmitting device to a direction toward the receiving device based on positions and attitudes of the transmitting device and the receiving device; Scanning the collimated laser light transmitted from the transmitting device within a predetermined range centered on the set direction; transmitting control information relating to a scanning position at which the laser light is received from the receiving device to the transmitting device; setting a direction of the laser light transmitted from the transmitting device to a direction based on the control information; 2. An underwater communication method comprising:

12. An underwater communication method using laser light, comprising: In the receiving device, Calculating a center position of the laser light based on an intensity distribution of the laser light in a receiving range of the image sensor; generating control information for correcting a deviation between a center of an optical deflector that guides the laser light to an image sensor and a center of the laser light based on the calculated center position, and transmitting the control information to a transmitting device; and correcting the direction of the laser light in a direction that eliminates the deviation based on the received control information in the transmitting device.

2. An underwater communication method comprising:

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