Spatial optical communication system, master unit of spatial optical communication system, and spatial optical communication method

Abstract

The objective is to provide a spatial optical communication system, a master unit for the spatial optical communication system, and a spatial optical communication method that can stabilize communication. [Solution] The spatial optical communication system comprises a light transmitting unit that transmits laser light, a modulation retroreflector unit that receives the laser light transmitted from the light transmitting unit, modulates the laser light according to a sensor signal output by a predetermined sensor, and reflects the modulated laser light back towards the light transmitting unit, and a light transmitting laser light state control unit that controls the state of the laser light transmitted by the light transmitting unit according to the reception state of the modulated laser light.

Description

Technical Field

[0001] The present disclosure relates to a free-space optical communication system, a master device of a free-space optical communication system, and a free-space optical communication method.

Background Art

[0002] Patent Document 1 discloses a configuration example of a free-space optical communication system using a modulation retroreflector. In the free-space optical communication system disclosed in Patent Document 1, a laser beam is transmitted from the information receiving side, the laser beam transmitted using the modulation retroreflector is received on the information transmitting side, the laser beam is modulated based on the information to be transmitted, the modulated laser beam is reflected in the direction of the light source, and the information is transferred by receiving the reflected light at the light source.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a free-space optical communication system as described in Patent Document 1, there is a problem that the intensity of the reflected light changes due to the distance between the laser beam transmitting side and the reflecting side, changes in the state of the space through which the light is transmitted, etc., and in some cases, the communication may become unstable.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a free-space optical communication system, a master device of a free-space optical communication system, and a free-space optical communication method capable of stabilizing communication.

Means for Solving the Problems

[0006] To solve the above problems, the spatial optical communication system according to this disclosure comprises a light transmitting unit that transmits laser light, a modulation retroreflector unit that receives the laser light transmitted from the light transmitting unit, modulates the laser light according to a sensor signal output by a predetermined sensor, and reflects the modulated laser light toward the light transmitting unit, and a light transmitting laser light state control unit that controls the state of the laser light transmitted by the light transmitting unit according to the reception state of the modulated laser light.

[0007] The master unit of the spatial optical communication system according to this disclosure comprises a light transmitting unit that transmits laser light, and a light transmitting laser light state control unit that receives the laser light transmitted from the light transmitting unit, modulates the laser light according to a sensor signal output by a predetermined sensor, and controls the state of the modulated laser light transmitted by the light transmitting unit according to the reception state of the modulated laser light reflected by a modulation retroreflection unit provided on a slave unit which is a mobile body that reflects the modulated laser light toward the light transmitting unit.

[0008] The spatial optical communication method according to this disclosure includes the steps of transmitting laser light, receiving the transmitted laser light, modulating the laser light according to a sensor signal output by a predetermined sensor, and reflecting the modulated laser light toward the light transmitting unit, and controlling the state of the transmitted laser light according to the reception state of the modulated laser light. [Effects of the Invention]

[0009] According to the spatial optical communication system, the master unit of the spatial optical communication system, and the spatial optical communication method of this disclosure, communication can be stabilized. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram showing an example configuration of a spatial optical communication system according to the first embodiment of this disclosure. [Figure 2] This is a schematic diagram illustrating a basic example of operation in a spatial optical communication system according to the first embodiment of this disclosure. [Figure 3] This is a schematic diagram showing an example of the configuration of a slave unit according to the present disclosure. [Figure 4] It is a schematic diagram showing a configuration example of a retroreflective portion according to an embodiment of the present disclosure. [Figure 5] It is a schematic diagram showing another configuration example of a slave unit according to an embodiment of the present disclosure. [Figure 6] It is a schematic diagram showing another configuration example of a retroreflective portion according to an embodiment of the present disclosure. [Figure 7] It is a schematic diagram showing another configuration example of a retroreflective portion according to an embodiment of the present disclosure. [Figure 8] It is a schematic diagram showing yet another configuration example of a slave unit according to an embodiment of the present disclosure. [Figure 9] It is a schematic diagram showing yet another configuration example of a slave unit according to an embodiment of the present disclosure. [Figure 10] It is a block diagram showing a configuration example of a light emitting unit according to the first embodiment of the present disclosure. [Figure 11] It is a block diagram showing a configuration example of a light receiving unit according to the first embodiment of the present disclosure. [Figure 12] It is a waveform diagram showing an example of an output signal of a photoelectric converter according to an embodiment of the present disclosure. [Figure 13] It is a waveform diagram showing another example of an output signal of a photoelectric converter according to an embodiment of the present disclosure. [Figure 14] It is a waveform diagram showing an example of a change in an output signal of a photoelectric converter according to an embodiment of the present disclosure. [Figure 15] It is a flowchart showing an operation example of a light emission state control aperture according to the first embodiment of the present disclosure. [Figure 16] It is a block diagram showing a configuration example of a light receiving unit according to the second embodiment of the present disclosure. [Figure 17] It is a block diagram showing a configuration example of a slave unit according to the third embodiment of the present disclosure. [Figure 18] It is a schematic block diagram showing the configuration of a computer according to at least one embodiment.

Mode for Carrying Out the Invention

[0011] <First Embodiment> (Configuration example of a space optical communication system) Hereinafter, a space optical communication system, a master unit of the space optical communication system, and a space optical communication method according to embodiments of the present disclosure will be described with reference to FIGS. 1 to 15. In each figure of the present application, the same or corresponding components are denoted by the same reference numerals, and the description thereof will be omitted as appropriate. In the present application, space optical communication is communication using light that propagates in free space modulated based on data.

[0012] FIG. 1 is a block diagram showing a configuration example of a space optical communication system according to the first embodiment of the present disclosure. FIG. 2 is a schematic diagram showing a basic operation example in the space optical communication system according to the first embodiment of the present disclosure. The space optical communication system 100 shown in FIG. 1 includes a master unit 1 and a slave unit 2. In the present embodiment, the slave unit 2 is a wireless communication station that transmits data using an optical signal, and the master unit 1 is a wireless communication station that receives the data transmitted by the slave unit. The slave unit 2 and the master unit 1 are mounted, for example, on a moving body in the atmosphere, on the ground or on the water, or fixed or semi-fixed on the ground or on the water. Also, one of the slave unit 2 and the master unit 1 may be moving and the other may be fixed, or both may be fixed or moving. Also, the slave unit 2 and the master unit 1 can be one or more. Also, the slave unit 2 may include movement and fixation, and the slave unit 2 may include movement and fixation. In the present application, sending out light is referred to as light transmission, but light transmission may be read as transmission, irradiation, etc. Also, in the present application, receiving light is referred to as light reception or reception, but light reception and reception can be read interchangeably with each other.

[0013] The master unit 1 comprises a light transmitting unit 11 and a light receiving unit 12. The slave unit 2 comprises a modulated retroreflector unit 21 and a sensor unit 22. The sensor unit 22 is one example of the configuration of the "predetermined sensor" according to this disclosure. As shown in Figure 2, the spatial optical communication system 100 according to the embodiment of this disclosure transmits laser light of a predetermined wavelength (hereinafter also referred to as an optical beam) from the light transmitting unit 11 to the slave unit 2. The optical beam transmitted to the slave unit 2 is not modulated and is an optical signal having a continuously constant light intensity. The modulated retroreflector unit 21 receives the laser light transmitted from the light transmitting unit 11, modulates the received laser light according to the sensor signal output by the sensor unit 22, and reflects the modulated laser light toward the light transmitting unit 11 or the master unit 1. In this embodiment, the modulated retroreflector unit 21 is a configuration in which a retroreflector unit (also called a retroreflector, etc.) and a modulator are combined (or integrally formed). A retroreflective section is a device that reflects incident light in a direction parallel to the incident light and 180° opposite (the direction from which the incident light was emitted).

[0014] In this embodiment, the modulated light reflected by the modulated retroreflection unit 21 is referred to as modulated reflected light or received light as viewed from the master unit 1. The sensor signal is, for example, a 1-bit digital signal sequence (serial digital signal). The modulated reflected light is light reflected in the opposite direction to the incident light beam, and is an optical signal whose light intensity has been modulated by the modulated retroreflection unit 21, for example, based on the sensor signal. In the master unit 1, the received light is received by the light receiving unit 12, and the sensor signal is demodulated from the received light. In the example shown in Figure 2, the sensor unit 22 is configured as a camera that photographs the object to be observed. In this case, the sensor signal is, for example, a signal representing a still image or a moving image. Note that the sensor unit 22 is not limited to a camera, and can be configured to include, for example, sensors that detect physical quantities such as temperature, humidity, pressure, flow rate, light, radio waves, magnetism, etc., or the amount of change therein, or multiple types of sensors.

[0015] Here, with reference to Figures 3 to 9, an example of the configuration of the sub-unit 2 (or modulated retroreflector unit 21) will be described. Figure 3 is a schematic diagram showing an example of the configuration of the sub-unit 2 (shown as sub-unit 2a in Figure 3). The sub-unit 2a shown in Figure 3 comprises a modulated retroreflector unit 21a (a configuration corresponding to the modulated retroreflector unit 21 shown in Figures 1 and 2) and a sensor unit 22. The modulated retroreflector unit 21a comprises a retroreflector unit 211a and a modulator 212a provided in the optical path of the transmitted light and the modulated reflected light. The retroreflector unit 211a can be, for example, a device in which three planar mirror plates 211ap called corner cubes are combined at right angles to each other, as shown in Figure 4. The modulator 212a can be, for example, a device utilizing an MQW (Multiple Quantum Well) structure.

[0016] Figure 5 is a schematic diagram showing another configuration example of the slave unit 2 (shown as slave unit 2b in Figure 5). The slave unit 2b shown in Figure 5 comprises a modulated retroreflector unit 21b (a configuration corresponding to the modulated retroreflector unit 21 shown in Figures 1 and 2) and a sensor unit 22. The modulated retroreflector unit 21b comprises a retroreflector unit 211a shown in Figure 4 and a modulator 212b provided in contact with the planar mirror plate 211ap. The modulator 212b can be, for example, a MEMS (Micro Electro Mechanical Systems) modulator.

[0017] Figures 6 and 7 show examples of retroreflective sections (shown as retroreflective section 211c in Figures 6 and 7) that differ from the retroreflective section 211a shown in Figure 4. The retroreflective section 211c shown in Figures 6 and 7 is a device consisting of a refractive optical element with a reflective surface 211cr at the focal plane of a refractive element called a cat's eye. Figures 6 and 7 show examples with different incident angles of transmitted light.

[0018] Figures 8 and 9 show an example configuration of a slave unit (shown as slave unit 2c in Figure 8 and slave unit 2d in Figure 9) that is different from slave unit 2a shown in Figure 3. Slave unit 2c shown in Figure 8 comprises a modulated retroreflector unit 21c (a configuration corresponding to the modulated retroreflector unit 21 shown in Figures 1 and 2) and a sensor unit 22. The modulated retroreflector unit 21c comprises a retroreflector unit 211c shown in Figures 6 and 7 and a modulator 212c provided in the optical path between the transmitted light and the modulated reflected light. The modulator 212c can be, for example, an AO (Acousto-optics) modulator.

[0019] The sub-unit 2d shown in Figure 9 comprises a modulated retroreflector unit 21d (with a configuration corresponding to the modulated retroreflector unit 21 shown in Figures 1 and 2) and a sensor unit 22. The modulated retroreflector unit 21d comprises a retroreflector unit 211c shown in Figures 6 and 7 (whereas the reflective surface 211cr is separated) and a modulator 212d provided in contact with the reflective surface 211cr. The modulator 212d can be, for example, an EO (Electro-optics) modulator.

[0020] As described above, in this embodiment, the modulated retroreflection unit 21 receives the laser light transmitted from the light transmitting unit 11, modulates the laser light according to the sensor signal output by the sensor unit 22 (a predetermined sensor), and reflects the modulated laser light toward the light transmitting unit 11.

[0021] Next, with reference to Figure 10, an example configuration of the light transmitting unit 11 shown in Figures 1 and 2 will be described. The light transmitting unit 11 shown in Figure 10 comprises a laser light driving circuit 111, a laser light source 112, an optical attenuator 113, an optical amplifier 114, a light transmitting optical system 115, and a distributed control unit 116.

[0022] The laser light driving circuit 111 is a driving circuit for the laser light source 112, and supplies a predetermined driving current to the laser light source 112, and controls the increase or decrease of the driving current based on the light transmission state control signal generated by the light receiving unit 12.

[0023] The laser light source 112 is a CW (Continuous Wave) laser, and the laser light driving circuit 111 uses the supplied driving current as a current source to generate laser light of a predetermined wavelength. When the driving current is increased or decreased, the laser light source 112 increases or decreases the output (energy amount) of the laser light.

[0024] The optical attenuator 113 receives the laser light generated by the laser light source 112, and outputs the input laser light after optically attenuating it according to the light transmission state control signal.

[0025] The optical amplifier 114 receives the laser light output by the optical attenuator 113, amplifies the input laser light according to the light transmission state control signal, and outputs it.

[0026] The light-transmitting optical system 115 includes, for example, multiple lenses whose positions can be adjusted, and by changing the positions of one or more lenses under the control of the dispersion control unit 116, the spatial spread of the light beam transmitted to the slave unit 2 (the divergence angle of the light beam (laser)) is adjusted.

[0027] The distributed control unit 116 controls the light transmission optical system 115 according to the light transmission state control signal.

[0028] The light transmitting unit 11 transmits laser light to the slave unit 2. The light transmitting unit 11 also controls the state of the transmitted laser light based on the light transmitting state control signal. Here, the state of the laser light includes at least one of the degree of the laser light intensity (strength) and the degree of the divergence angle. The light transmitting unit 11 also controls the drive of the laser light source 112 that generates the transmitted laser light, controls the amount of optical attenuation to optically attenuate the transmitted laser light, controls the amount of optical amplification to optically amplify the transmitted laser light, and controls the laser divergence angle of the transmitted laser light based on the light transmitting state control signal. The light transmitting state control signal may include multiple types of control signals corresponding to the types of control, or it may include one or more control signals that are fewer than the number of control types. Of these controls, the control of the amount of optical attenuation by the optical attenuator 113 and the control of the laser divergence angle by the light transmitting optical system 115 can be mechanically controlled using an optical system, for example. Furthermore, the drive control of the laser light source 112 and the control of the amplification amount of the optical amplifier 114 can be electrically controlled without mechanical control. In this case, for example, the changes in the light transmission state control signal can be made different, such as using a slowly changing light transmission state control signal for mechanical control and a faster changing light transmission state control signal for electrical control. Note that some of the controls based on the light transmission state control signal of the laser drive circuit 111, optical attenuator 113, optical amplifier 114, and light transmission optical system 115 may be omitted. Also, the relative positions of the optical attenuator 113 and the optical amplifier 114 may be swapped.

[0029] Next, with reference to Figure 11, an example configuration of the light-receiving unit 12 shown in Figures 1 and 2 will be described. The light-receiving unit 12 shown in Figure 11 comprises a light-receiving optical system 121, a photoelectric converter 122, a demodulator 123, a monitoring device 124, and a light transmission state control circuit 125.

[0030] The light-receiving optical system 121 receives the modulated reflected light emitted by the slave unit 2.

[0031] The photoelectric converter 122 converts the modulated reflected light received by the photoreceiving optical system 121 into an electrical signal and outputs it as the photoelectric converter output signal.

[0032] The demodulator 123 receives the photoelectric converter output signal output by the photoelectric converter 122 and demodulates the sensor signal from the photoelectric converter output signal. The sensor signal is a signal representing sensor information detected by the sensor unit 22 of the slave unit 2. The demodulator 123 also generates and outputs a communication quality signal based on, for example, packet loss when demodulating the sensor signal. The communication quality signal is a signal that represents an indicator of the quality of communication (or the quality of the received signal). The communication quality signal can be a signal with a predetermined value that increases (or decreases) as the packet loss rate decreases, i.e., as the communication quality improves. Alternatively, the demodulator 123 generates and outputs a communication quality signal based on, for example, the signal-noise ratio, which is the ratio of signal to noise when demodulating the sensor signal. In this case, the communication quality signal can be a signal with a predetermined value that increases (or decreases) as the signal-noise ratio increases, i.e., as the communication quality improves. The communication quality signal may be, for example, a single signal based on multiple indicators, or it may be multiple types of signals for each indicator.

[0033] The monitoring device 124 displays information based on the sensor signals output by the demodulator 123 on, for example, the screen of a display unit (not shown) provided by the monitoring device 124.

[0034] The light transmission state control circuit 125 controls the state of the laser light transmitted by the light transmission unit 11 according to the reception state of the modulated laser light at the master unit 1. Here, the reception state of the laser light is represented by one or more elements. The elements representing the reception state of the laser light include, for example, an element representing the intensity of the modulated laser light. In this case, the light transmission state control circuit 125 controls the state of the laser light transmitted by the light transmission unit 11 so that the intensity of the received modulated laser light is within a predetermined range. The elements representing the reception state of the laser light also include, for example, an element corresponding to the quality of communication using the modulated laser light. In this case, the light transmission state control circuit 125 controls the state of the laser light transmitted by the light transmission unit 11 so that the quality of communication is improved. In this embodiment, the elements representing the reception state of the laser light do not necessarily include either an element representing the intensity of the modulated laser light or an element corresponding to the quality of communication using the modulated laser light. Furthermore, the light transmission state control circuit 125 is one example of the configuration of the "light transmission laser light state control unit" according to this disclosure.

[0035] (Example of operation of a spatial optical communication system) Next, an example of the operation of the spatial optical communication system 100 of this embodiment will be described with reference to Figures 12 to 15. First, before describing the operation example, an example of the photoelectric converter output signal when communication is stable (Figure 12) and an example of the photoelectric converter output signal when communication is unstable (Figure 13) will be described with reference to Figures 12 to 14. Figures 12 and 13 show the waveform when the signal-to-noise ratio is relatively good (Figure 12) and when the signal-to-noise ratio is relatively poor (Figure 13), with the horizontal axis being the time axis and the vertical axis being the magnitude of the photoelectric converter output signal. When the amount of modulated reflected light is weak, the photoelectric converter output signal will have a waveform as shown in Figure 13.

[0036] On the other hand, Figure 14 shows examples of the waveforms of the photoelectric converter output signal when the optical modulation scheme is OOK (on-off keying) and NRZ (non-return to zero). Figure 14 shows the waveform W01 of the photoelectric converter output signal when the light intensity of the transmitted laser light is appropriate, the waveform W02 of the photoelectric converter output signal when the light intensity of the transmitted laser light is greater than appropriate (within the usable range), and the waveform W03 of the photoelectric converter output signal when the light intensity of the transmitted laser light is excessive (when the on / off signal cannot be distinguished due to saturation of the photoelectric converter 122). In waveform W01, the on signal and off signal are observed, including their levels. In contrast, in waveform W02, the on signal shows a constant value due to saturation of the photoelectric converter 122. Also, in waveform W03, the off signal also exceeds the saturation level of the photoelectric converter 122.

[0037] As described above, if the intensity of the transmitted light is too low, communication will not be stable, and if it is too high, it will also be unstable. Therefore, in the spatial optical communication system 100, it is necessary to control the state of the laser light transmitted by the light transmitting unit 11 so that the intensity of the light received by the master unit 1 is within a predetermined range.

[0038] Next, an example of the operation of the light transmission state control circuit 125 will be described with reference to Figure 15. The process shown in Figure 15 is repeatedly executed at a predetermined cycle after the light transmission state control circuit 125 is started. In Figure 15, the photoelectric converter output signal is simply referred to as "signal". When the process shown in Figure 15 is started, the light transmission state control circuit 125 determines whether the photoelectric converter output signal is always above the saturation level (for example, for a predetermined time or longer) (step S1). For example, if it is above the saturation level, as shown in waveform W03 in Figure 14 (step S1: YES), the light transmission state control circuit 125 controls the state of the transmitted laser light so that the intensity of the light reaching the modulated retroreflection unit 21 of the slave unit 2 decreases (step S2), and then terminates the process shown in Figure 15. There are no limitations on the method of control in step S2; for example, the control can be such that the light transmission state control signal is changed by proportional-integral operation or the like so that the level of the ON signal approaches a predetermined target value that is less than the saturation level.

[0039] If the photoelectric converter output signal is not always above the saturation level (step S1: NO), the light transmission state control circuit 125 determines whether or not a photoelectric converter output signal above a predetermined value is observed (step S3). In step S3, the light transmission state control circuit 125 determines, for example, whether or not the level of the off signal is above a predetermined value shown in Figure 14. If a photoelectric converter output signal above a predetermined value is not observed (step S3: NO), the light transmission state control circuit 125 controls the state of the transmitted laser light so that the intensity of the light reaching the modulated retroreflection unit 21 of the slave unit 2 increases (step S4), and terminates the process shown in Figure 15. There are no limitations on the method of control in step S4; for example, the light transmission state control signal can be changed by proportional-integral operation or the like so that the level of the off signal approaches a predetermined target value greater than the predetermined value.

[0040] If a photoelectric converter output signal above a predetermined value is observed (Step S3: YES), the light transmission state control circuit 125 determines whether or not an on signal and an off signal can be distinguished (Step S5). If an on signal and an off signal cannot be distinguished (Step S5: NO), the light transmission state control circuit 125 controls the state of the transmitted laser light so that the intensity of the light reaching the modulated retroreflection unit 21 of the slave unit 2 increases (Step S4), and then terminates the process shown in Figure 15.

[0041] If the ON signal and OFF signal can be distinguished (Step S5: YES), the light transmission state control circuit 125 determines whether the ON signal is at a saturation level (Step S6). For example, if the ON signal is at a saturation level, as shown in waveform W02 in Figure 14 (Step S6: YES), the light transmission state control circuit 125 controls the state of the transmitted laser light so that the intensity of the light reaching the modulated retroreflection unit 21 of the slave unit 2 decreases (Step S2), and then terminates the process shown in Figure 15.

[0042] If the ON signal is not at the saturation level (Step S6: NO), the light transmission state control circuit 125 determines whether the communication quality is above a predetermined value (the higher the value representing communication quality, the higher the communication quality) (Step S7). If the communication quality is above the predetermined value (Step S7: YES), the light transmission state control circuit 125 terminates the process shown in Figure 15.

[0043] If the communication quality is not above a predetermined value (step S7: NO), the light transmission state control circuit 125 controls the state of the transmitted laser light according to the communication quality (communication quality signal) (step S8) and terminates the process shown in Figure 15. There are no limitations on the method of control in step S8; for example, the light transmission state control signal can be changed (increased or decreased) by a certain amount, the change in communication quality can be observed, and the light transmission state control signal can be changed (increased or decreased) by a certain amount according to the observation result.

[0044] (Effects / Actions) As described above, in the first embodiment, the spatial optical communication system 100 includes a light transmitting unit 11 that transmits laser light, a modulated retroreflector unit 21 that receives the laser light transmitted from the light transmitting unit 11, modulates the laser light according to a sensor signal output by a sensor unit 22 (a predetermined sensor), and reflects the modulated laser light back towards the light transmitting unit 11, and a light transmitting state control circuit 125 (light transmitting laser light state control unit) that controls the state of the laser light transmitted by the light transmitting unit 11 according to the reception state of the modulated laser light. With this configuration, the reflected light intensity from the modulated retroreflector unit 21 can be easily controlled to a signal level that does not saturate the photoelectric converter 122 and is sufficient for demodulation, thereby stabilizing communication.

[0045] While it is possible to amplify the output signal of the photoelectric converter 122 using automatic gain control (AGC) or the like when the signal is weak, in that case, the signal-to-noise ratio will decrease significantly, especially when the signal is weak. According to this embodiment, the level of the output signal of the photoelectric converter 122 can be increased, so a decrease in the signal-to-noise ratio does not occur.

[0046] Furthermore, in this embodiment, one or more elements representing the reception state include an element representing the intensity of the modulated laser light, and the light transmission state control circuit 125 (light transmission laser light state control unit) controls the state of the laser light transmitted by the light transmission unit 11 so that the light intensity is within a predetermined range. With this configuration, the reflected light intensity from the modulated retroreflection unit 21 can be controlled to a signal level that does not saturate the photoelectric converter 122 and is sufficient for demodulation.

[0047] Furthermore, in this embodiment, one or more elements representing the reception state include elements corresponding to the quality of communication using modulated laser light, and the light transmission state control circuit 125 (light transmission laser light state control unit) controls the state of the laser light transmitted by the light transmission unit 11 so as to improve the quality of communication. With this configuration, the quality of communication (or the quality of the received signal) can be easily improved.

[0048] In this embodiment, the light transmission state control circuit 125 (light transmission laser light state control unit) controls the state of the laser light transmitted by the light transmission unit 11 by controlling at least one of the following: control of the drive of the laser light source that generates the transmitted laser light, control of the amount of optical attenuation that optically attenuates the transmitted laser light, control of the amount of optical amplification that optically amplifies the transmitted laser light, and control of the laser divergence angle of the transmitted laser light.

[0049] Furthermore, in this embodiment, for example, the light transmitting unit 11 and the light transmitting state control circuit 125 (light transmitting laser light state control unit) can be mounted on the master unit 1, and the modulation reflection unit 21 can be mounted on the slave unit 2, which is separate from the master unit 1 and is mobile.

[0050] <Second Embodiment> Referring to Figure 16, a spatial optical communication system, a master unit for the spatial optical communication system, and a spatial optical communication method according to the second embodiment of this disclosure will be described. Figure 16 is a block diagram showing an example configuration of the light receiving unit 12a (a configuration corresponding to the light receiving unit 12 shown in Figure 11) in the second embodiment. The configuration other than the light receiving unit 12a is the same as in the first embodiment.

[0051] The light receiving unit 12a shown in Figure 16 differs from the light receiving unit 12 shown in Figure 11 in that it newly includes a light receiving optical system 121a and a photoelectric converter 122a, and that instead of inputting the photoelectric converter output signal output by the photoelectric converter 122 to the light transmission state control circuit 125, it inputs the photoelectric converter output signal output by the photoelectric converter 122a. In the second embodiment, the photoelectric converter output signal output by the photoelectric converter 122 is used as a signal for communication (demodulation), and the photoelectric converter output signal output by the photoelectric converter 122a is used as a signal for observation (for status observation for controlling the state of transmitted light). In this case, the photoelectric converter 122a may be, for example, a single-element detector or a camera. With this configuration, the signal processing in the light transmission state control circuit 125 and the signal processing for communication can be easily separated.

[0052] The spatial optical communication system 100 of the second embodiment includes a photoelectric converter 122 (communication photoelectric converter) that converts modulated laser light into an electrical signal for demodulation, and a photoelectric converter 122a (observation photoelectric converter) that converts modulated laser light into an electrical signal for observation of the received state. With this configuration, for example, the configuration of the observation photoelectric converter can be made suitable for observation of the received state (for example, a photoelectric converter with a larger dynamic range).

[0053] <Third Embodiment> Referring to Figure 17, a spatial optical communication system, a master unit of the spatial optical communication system, and a spatial optical communication method according to the third embodiment of this disclosure will be described. Figure 17 is a block diagram showing an example configuration of slave unit 2e (a configuration corresponding to slave unit 2 shown in Figure 1) in the third embodiment. The configuration other than slave unit 2e is the same as in the first or second embodiment.

[0054] The slave unit 2e shown in Figure 17 differs from the light receiving unit 12 shown in Figure 1 in that it newly includes a retroreflection unit 23. In the third embodiment, the retroreflection unit 23 receives the laser light transmitted from the light transmitting unit 11 and reflects the received laser light back to the light transmitting unit 11 without modulation. By providing the retroreflection unit 23, the reflected light received by the master unit 1 includes modulated reflected light from the modulated retroreflection unit 21 and unmodulated reflected light from the retroreflection unit 23. With this configuration, since the reflected light includes reflected light in an unmodulated state, signal determination by the light transmission state control circuit 125 can be easily performed.

[0055] (Other embodiments) Although embodiments of this disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and may include design changes and the like that do not depart from the gist of this disclosure.

[0056] <Computer Configuration> Figure 18 is a schematic block diagram showing the configuration of a computer according to at least one embodiment. The computer 90 comprises a processor 91, main memory 92, storage 93, and interface 94. Each part of the master unit 1 and slave unit 2 described above (for example, the light transmission state control circuit 125, demodulator 123, monitoring device 124, laser drive circuit 111, distributed control unit 116, etc.) is implemented in the computer 90. The operation of each of the above-mentioned processing units is stored in the storage 93 in the form of a program. The processor 91 reads the program from the storage 93, loads it into the main memory 92, and executes the above-mentioned processing according to the program. The processor 91 also allocates storage areas in the main memory 92 corresponding to each of the above-mentioned storage units according to the program.

[0057] The program may be for implementing some of the functions that the computer 90 is to perform. For example, the program may perform functions in combination with other programs already stored in storage, or in combination with other programs implemented in other devices. In other embodiments, the computer may include a custom LSI (Large Scale Integrated Circuit) such as a PLD (Programmable Logic Device) in addition to, or instead of, the above configuration. Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), FPGA (Field Programmable Gate Array), etc. In this case, some or all of the functions implemented by the processor may be implemented by the integrated circuit.

[0058] Examples of storage 93 include HDDs (Hard Disk Drives), SSDs (Solid State Drives), magnetic disks, magneto-optical disks, CD-ROMs (Compact Disc Read Only Memory), DVD-ROMs (Digital Versatile Disc Read Only Memory), and semiconductor memory. Storage 93 may be an internal medium directly connected to the bus of the computer 90, or an external medium connected to the computer 90 via an interface 94 or a communication line. Furthermore, if this program is distributed to the computer 90 via a communication line, the computer 90 that receives the program may expand it into main memory 92 and execute the above processing. In at least one embodiment, storage 93 is a tangible storage medium that is not temporary.

[0059] <Note> The spatial optical communication system 100, master unit 1, and spatial optical communication method described in each embodiment can be understood, for example, as follows.

[0060] (1) The spatial optical communication system 100 according to the first embodiment includes a light transmitting unit that transmits laser light, a modulation retroreflector unit that receives the laser light transmitted from the light transmitting unit, modulates the laser light according to a sensor signal output by a predetermined sensor, and reflects the modulated laser light toward the light transmitting unit, and a light transmitting laser light state control unit that controls the state of the laser light transmitted by the light transmitting unit according to the reception state of the modulated laser light. According to this embodiment and each of the following embodiments, communication can be stabilized.

[0061] (2) The spatial optical communication system 100 according to the second embodiment is the spatial optical communication system 100 of (1), wherein one or more elements representing the reception state include an element representing the intensity of the modulated laser light, and the light transmitting laser light state control unit controls the state of the laser light transmitted by the light transmitting unit so that the intensity of the light is within a predetermined range.

[0062] (3) The spatial optical communication system 100 according to the third embodiment is the spatial optical communication system 100 of (1) or (2), wherein one or more elements representing the reception state include elements corresponding to the quality of communication by the modulated laser light, and the light transmitting laser light state control unit controls the state of the laser light transmitted by the light transmitting unit so as to improve the quality of the communication.

[0063] (4) The spatial optical communication system 100 according to the fourth embodiment is the spatial optical communication system 100 according to (1) to (3), wherein the light-transmitting laser light state control unit controls the state of the laser light transmitted by the light-transmitting unit by controlling at least one of the following: controlling the drive of the laser light source that generates the laser light to be transmitted; controlling the amount of optical attenuation that optically attenuates the laser light to be transmitted; controlling the amount of optical amplification that optically amplifies the laser light to be transmitted; and controlling the laser divergence angle of the laser light to be transmitted.

[0064] (5) The spatial optical communication system 100 according to the fifth embodiment is the spatial optical communication system 100 of (1) to (4), wherein the light transmitting unit and the light transmitting laser light state control unit are mounted on a master unit, and the modulation reflection unit is mounted on a slave unit which is separate from the master unit and is mobile.

[0065] (6) The spatial optical communication system 100 according to the sixth embodiment is the spatial optical communication system 100 according to (1) to (5), wherein the slave unit further comprises a retroreflector that receives laser light transmitted from the light transmitting unit and reflects the laser light toward the light transmitting unit.

[0066] (7) The spatial optical communication system 100 according to the seventh embodiment is the spatial optical communication system 100 according to (1) to (6), comprising: a communication photoelectric converter that converts the modulated laser light into an electrical signal for demodulation; and an observation photoelectric converter that converts the modulated laser light into an electrical signal for observing the reception state.

[0067] (8) The master unit 1 of the spatial optical communication system 100 according to the eighth embodiment is the master unit 1 of the spatial optical communication system 100 according to (1) to (7), comprising: a light transmitting unit that transmits laser light; and a light transmitting laser light state control unit that receives the laser light transmitted from the light transmitting unit, modulates the laser light according to a sensor signal output by a predetermined sensor, and controls the state of the modulated laser light transmitted by the light transmitting unit according to the reception state of the modulated laser light reflected by a modulation retroreflection unit provided on a slave unit which is a mobile body that reflects the modulated laser light toward the light transmitting unit.

[0068] (9) A spatial optical communication method according to the ninth aspect is a communication method in the spatial optical communication system 100 of (1) to (7), comprising the steps of transmitting laser light, receiving the transmitted laser light, modulating the laser light in accordance with a sensor signal output by a predetermined sensor, reflecting the modulated laser light toward the light transmitting unit, and controlling the state of the transmitted laser light in accordance with the reception state of the modulated laser light. [Explanation of Symbols]

[0069] 100...Spatial optical communication system 1…Main unit 2… Cordless handset 11…Light transmitting unit 12...Light receiving section 21... Modulated retroreflector section 22...Resensing unit 23… Retroreflective part 122, 122a... Photoelectric converters 125...Light transmission state control circuit

Claims

1. A light-transmitting unit that transmits laser light, A modulated retroreflector unit receives the laser light transmitted from the light transmitting unit, modulates the laser light according to a sensor signal output by a predetermined sensor, and reflects the modulated laser light toward the light transmitting unit. A laser light transmission state control unit controls the state of the laser light transmitted by the light transmission unit according to the reception state of the modulated laser light. A spatial optical communication system equipped with [the following features].

2. One or more elements representing the reception state include an element representing the intensity of the modulated laser light, The light-transmitting laser light state control unit controls the state of the laser light transmitted by the light-transmitting unit so that the intensity of the light is within a predetermined range. The spatial optical communication system according to claim 1.

3. One or more elements representing the reception state include elements corresponding to the quality of communication by the modulated laser light, The light-transmitting laser light state control unit controls the state of the laser light transmitted by the light-transmitting unit in order to improve the quality of the communication. The spatial optical communication system according to claim 2.

4. The light transmission laser light state control unit is: Control of the drive of the laser light source that generates the laser light to be transmitted, Control of the amount of optical attenuation that optically attenuates the transmitted laser light, Control of the amount of optical amplification for optically amplifying the laser light transmitted, and The state of the laser beam transmitted by the light transmitting unit is controlled by controlling at least one of the laser beam divergence angles of the transmitted laser beam. The spatial optical communication system according to claim 3.

5. The light transmission unit and the light transmission laser light state control unit are mounted on the master unit. The aforementioned modulation retroreflection unit is mounted on a slave unit, which is separate from the master unit and is a mobile unit. The spatial optical communication system according to claim 4.

6. The aforementioned sub-unit receives the laser light transmitted from the light transmitting unit and has a retroreflector that reflects the laser light back toward the light transmitting unit, The spatial optical communication system according to claim 5, further comprising:

7. A communication photoelectric converter that converts the modulated laser light into an electrical signal for demodulation, An observation photoelectric converter that converts the modulated laser light into an electrical signal for observing the received state, The spatial optical communication system according to claim 6, comprising:

8. A light-transmitting unit that transmits laser light, A laser light state control unit is provided in a mobile slave unit that receives laser light transmitted from the light transmitting unit, modulates the laser light according to a sensor signal output by a predetermined sensor, and reflects the modulated laser light back towards the light transmitting unit. The control unit controls the state of the laser light transmitted by the light transmitting unit according to the reception state of the modulated laser light reflected by the modulated laser light. A master unit for a spatial optical communication system equipped with the following features.

9. The light transmitting unit transmits laser light, The steps include receiving the transmitted laser light, modulating the laser light according to a sensor signal output by a predetermined sensor, and reflecting the modulated laser light toward the light transmitting unit, A step of controlling the state of the transmitted laser light according to the reception state of the modulated laser light. A spatial optical communication method including

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