JP7123340B2 - Spatial optical communication device and spatial optical communication method - Google Patents

Description

The present invention relates to a spatial optical communication apparatus and a spatial optical communication method for performing optical communication with a spacecraft such as an artificial satellite orbiting in outer space, for example.

2. Description of the Related Art In recent years, research has been progressing on optical satellite communication with a ground station on the earth using a spacecraft such as an artificial satellite orbiting the earth in outer space. This optical satellite communication is capable of large-capacity data transmission, can be realized with a lightweight and compact system configuration, and has advantages such as less interference compared to radio waves. is attracting attention as

Space-to-ground optical space transmission is performed in a cloud-free space (under the earth's atmosphere) so that the transmission section is not blocked by clouds. On the other hand, the downlink transmitted from the spacecraft to the ground station is affected by atmospheric turbulence, reducing the power that can be received on the receiving side, degrading communication quality, and in the worst case, bursting information loss. sometimes Therefore, some kind of compensation technique is required that can suppress the influence of the atmosphere.

Conventionally, in order to compensate for atmospheric effects, a mechanism is adopted in which the optical energy collected by the telescope of the ground station that receives the downlink is compensated by a post-compensation system. It loses a lot of light energy. For this reason, the ground station continuously illuminates the uplink to the spacecraft or for a short period of time, and guides the downlink in the direction of the ground station like a beacon that informs the spacecraft of the direction of the ground station. However, the uplink is similarly affected by the atmosphere and often does not reach the sensor field of view of the optical communication device of the spacecraft, so simple uplink irradiation is less effective.

In order to solve such a problem, for example, in Patent Document 1, there is proposed a path propagation method in which received light waves emitted from an artificial satellite are condensed and a transmission light wave emitted toward the artificial satellite propagates through a space including a propagation path. Light is collected by a telescope, and based on the received light wave and the wavefront distortion of the light propagated along the path, the angle of the propagation path of the transmitted light wave that takes into account atmospheric fluctuations and fading is calculated and transmitted at that angle. A spatial optical communication system is disclosed for controlling a deformable mirror of a telescope so that light waves reach a satellite.

JP 2018-121281 A

When the uplink is emitted from the ground, the propagation direction of the transmission laser is influenced by the space from the ground to outer space, especially the atmospheric effect (continuous refractive index change accompanying continuous atmospheric concentration change from the ground to outer space). and light scattering by fine particles in the atmosphere such as aerosols), the beam propagates while bending in the atmosphere (beam wandering phenomenon). For this reason, even if the telescope tracks the spacecraft according to the forecast value, the uplink does not reach the spacecraft ahead. It becomes impossible to grasp whether it is emitted. In addition, since atmospheric influences change randomly temporally and spatially from moment to moment, the adaptability to changes in atmospheric conditions is insufficient.

In view of the circumstances as described above, it is an object of the present invention to provide a free-space optical communication apparatus and a free-space optical communication method capable of maintaining good communication with a spacecraft while adapting to atmospheric influences.

A free-space optical communication device according to one aspect of the present invention includes a transmitter, a receiver, a first detector, and a controller.
The transmitter transmits the first laser beam toward the spacecraft.
The receiving section receives a second laser beam transmitted from the spacecraft.
A said 1st detection part detects the light reception intensity|strength of a said 2nd laser beam.
The control section generates a control signal for controlling the divergence angle and power of the first laser light based on the output of the first detection section.

The free-space optical communication device is configured to correct the emission condition of the first laser beam so that the received light intensity of the second laser beam becomes a target value. As a result, it is possible to optimize the emission conditions of the first laser light by following the atmospheric conditions that change from moment to moment, and to ensure stable communication quality without being influenced by the atmosphere.

The control unit may be configured to generate a control signal for expanding the divergence angle of the first laser light and increasing the power when the received light intensity of the second laser light is less than a predetermined range.

Further, the control unit may be configured to generate a control signal for narrowing the divergence angle of the first laser light and reducing the power when the received light intensity of the second laser light exceeds the predetermined range. good.

The free-space optical communication device may further include a second detector.
A said 2nd detection part has a light-receiving surface which receives a said 2nd laser beam, and detects the fluctuation|fluctuation of the atmosphere on the propagation path|route of a said 2nd laser beam. The control section generates a control signal for controlling the divergence angle and power of the first laser light based on the outputs of the first detection section and the second detection section.

The second detector may be attached to the receiver.

The free-space optical communication device may further include a third detector that detects a propagation direction of the first laser beam. The control section may generate a control signal for correcting the emission direction of the first laser beam transmitted from the transmission section based on the output of the third detection section.

The third detection unit may include a camera that is arranged in the transmission unit and captures the scattered light of the first laser light due to the atmosphere.
The camera acquires a projected image of the scattered light onto a first plane and a projected image of the scattered light onto a second plane that intersects the first plane at a predetermined angle. may be configured.

The receiver may be a telescope that collects the second laser beam.

A spatial optical communication method according to one aspect of the present invention includes:
transmitting the first laser beam toward the spacecraft,
receiving a second laser beam transmitted from the spacecraft;
The divergence angle and power of the first laser beam are controlled based on the received light intensity of the second laser beam.

According to the present invention, a free-space optical communication device can maintain good communication with a spacecraft while adapting to atmospheric influences.

1 is a schematic configuration diagram showing a free-space optical communication system including a free-space optical communication device according to an embodiment of the present invention; FIG. It is a schematic diagram showing a configuration example of a transmission unit in the free-space optical communication device. FIG. 4 is a schematic diagram for explaining the influence of atmospheric fluctuations on a downlink (second laser beam) transmitted from a spacecraft to a free-space optical communication device; FIG. 4 is a schematic perspective view showing one configuration example of a seeing monitor as a first detection unit; FIG. 4 is a schematic diagram showing a formed image of the second laser beam on the light receiving surface of the seeing monitor. It is a schematic diagram which shows one structural example of the light reception intensity monitor as a 2nd detection part. FIG. 4 is a schematic diagram for explaining a beam wandering phenomenon of an uplink (first laser beam) transmitted toward a spacecraft; FIG. 10 is a diagram showing a configuration example of a beam monitor as a third detection unit; FIG. 4 is an explanatory diagram of the configuration of the beam monitor; It is a figure explaining the effect|action of the said beam monitor. It is a figure which shows the other structural example of the said beam monitor. 3 is a functional block diagram showing the configuration of a control unit in the above spatial optical communication device; FIG. 4 is a sequence diagram showing the operation of each part of the spatial optical communication device in time series; FIG. It is a flow chart which shows an example of a processing procedure performed in the above-mentioned control part. It is a flow chart which shows an example of a processing procedure performed in the above-mentioned control part. 15 is a flow chart showing a modification of FIG. 14;

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a spatial optical communication system 100 according to one embodiment of the present invention. The free-space optical communication system 100 includes a free-space optical communication device G and a spacecraft S, and performs optical communication (satellite communication) between the free-space optical communication device G and the spacecraft S.

A spacecraft S typically means a structure having a communication function capable of moving in outer space, such as an artificial satellite or a space station. Artificial satellites include geostationary orbit (GEO: Geostationary Earth Orbit), as well as low earth orbit (LEO: Low Earth Orbit) and medium orbit (MEO: Medium Earth Orbit) regardless of the rotation period of the earth. Furthermore, it includes artificial satellites that fly in deep space and the like. That is, the altitude of the spacecraft S from the ground surface is not particularly limited. Artificial satellites are typically meteorological satellites, communication satellites, etc., but may be launched for any purpose.

[Space optical communication device]
The free-space optical communication device G is configured as a ground station that performs optical space transmission with the spacecraft S. The free-space optical communication device G includes a telescope 10 for receiving optical signals (downlink) transmitted from the spacecraft S, or for transmitting/receiving optical signals to/from the spacecraft S. In this embodiment, the telescope 10 is mainly configured as a receiver that receives the downlink (second laser beam L2) transmitted from the spacecraft S.

The second laser beam L2 may be a continuous laser beam or a pulse laser beam. The second laser light L2 is typically infrared light and has a wavelength of, for example, 1550 nm or 1064 nm.

A telescope 10 is installed on a base 11 installed on the ground. The base 11 has an adjustment mechanism 11a that adjusts the attitude of the telescope 10, and the telescope 10 is supported by the base 11 so that the spacecraft S can be tracked. The base 11 controls the azimuth and/or elevation of the optical axis of the telescope 10 so as to track the spacecraft S according to the forecast values. The forecast value is the spatial coordinates of the spacecraft S calculated from the orbit of the spacecraft S, and the first laser beam L1 or the second laser beam L2 of the space transmission path from the installation location of the base 11 to the spacecraft S. It may be one that considers the refractive index at the wavelength of .

The diameter of the telescope 10 is not particularly limited, and is, for example, 30 cm to 10 m. The number of apertures of the telescope 10 is not limited to one, and may be plural. The telescope 10 has a signal processing unit (not shown) that converts the condensed second laser beam L2 into an electrical signal and performs predetermined signal processing such as analysis of received information.

Note that the free-space optical communication device G is not limited to being configured as a ground station, and may be mounted on a moving object such as a vehicle, ship, or aircraft. Further, the free-space optical communication device G may be connected to a communication body such as a gateway, a ground communication network installed on the ground, a vehicle, a ship, an aircraft, or the like. In this case, the gateway, ground communication network, communication body, etc. transmit and receive optical signals to and from the spacecraft S via the free-space optical communication device G. FIG.

The free-space optical communication device G includes a transmitter 20, a seeing monitor 31 as a second detector, a received light intensity monitor 32 as a first detector, a beam monitor 33 as a third detector, and a controller 40. Prepare.
The transmitter 20 emits a first laser beam L1 to be transmitted toward the spacecraft S. Based on the second laser beam L2 transmitted from the spacecraft S, the seeing monitor 31 detects the state of the atmosphere (or beam position information reflecting the state of the atmosphere) on the propagation path of the second laser beam L2. . The received light intensity monitor 32 detects the received light intensity of the second laser beam L2. The beam monitor 33 detects the emission direction of the first laser beam L1 (in this embodiment, the beam emission angle (azimuth, elevation angle) affected by beam wander is detected by scattering the first laser beam L1). monitor the light L1s). The control unit 40 controls the azimuth and elevation angle of the optical axis of the telescope 10 so that the spacecraft S can be tracked according to the forecast values. The controller 40 controls the transmitter 20 based on the outputs of the seeing monitor 31 , the received light intensity monitor 32 and the beam monitor 33 .
The free-space optical communication device G further includes an observer 34 that observes the sky above the emission direction of the first laser beam L1.

The optical space transmission between the spacecraft S and the spatial optical communication device G is performed in a cloud-free space (under the earth's atmosphere). is affected by atmospheric turbulence, the power that can be received by the receiving side decreases, and the communication quality deteriorates. For this reason, the ground station G irradiates the uplink toward the spacecraft S continuously or for a short period of time to inform the spacecraft S of the direction of the ground station G and guide the downlink in the direction of the ground station. .
However, the uplink is similarly affected by the atmosphere and often does not reach the spacecraft S, and simple uplink irradiation is less effective.
Therefore, the free-space optical communication device G of this embodiment uses the optical characteristics of the downlink (the second laser beam L2) detected by the seeing monitor 31 or the like to determine the uplink (the first laser beam L2) emitted toward the spacecraft S. It is arranged to control the divergence angle and power of the laser light L1). The details will be described below.

(Transmitter)
The transmitter 20 has a laser light source that generates the first uplink laser light L1. The first laser beam L1 mainly functions as guiding light for emitting the downlink of the spacecraft S toward the free-space optical communication device G. As shown in FIG. The first laser beam L1 may be a continuous laser beam or a pulse laser beam. The first laser light L1 is typically infrared light and has a wavelength of, for example, 1550 nm or 1064 nm. The spread angle and power of the first laser beam L1 are not particularly limited, either.

The transmission unit 20 is attached to the outer peripheral portion of the telescope 10 so as to be integrated with the telescope 10 and relatively movable with respect to the base 11 . The emission optical axis of the first laser beam L1 in the transmitter 20 is set parallel to the optical axis of the telescope 10 . In this embodiment, multiple laser emitting units are provided, and each laser emitting unit is configured to emit the first laser beam L1 toward the spacecraft S. As shown in FIG. Of course, the number of laser emitting units is not limited to plural, and may be single. Moreover, the transmitter 20 is not limited to being attached to the outer periphery of the telescope 10 , and may be arranged inside the telescope 10 .

FIG. 2 is a schematic diagram showing a configuration example of the transmission section 20. As shown in FIG. The transmitter 20 has a casing 21 and a plurality of (two in this example) laser emitting units 22 . The laser emission unit 22 is arranged inside the casing 21 and has a laser light source 221, a lens unit 222, an emission mirror 223, a shutter 224, and the like.

A casing 21 is fixed to the outer periphery of the telescope 10 . The light emitting surface of the casing 21 is provided with a window portion 21W (see FIG. 1) through which the first laser beam L1 emitted from each laser emitting unit 22 is transmitted. The laser light source 221 is a laser diode that emits the first laser light L1, and the lens unit 222 includes a plurality of lenses that can arbitrarily adjust the divergence angle of the light emitted from the laser light source 221 . A lens unit typically called a beam expander can be used for the lens unit 222 . Emission mirror 223 includes a plurality of mirror elements that guide the light emitted from lens unit 222 to window 21W. The plurality of mirrors typically include a plurality of variable mirrors that can individually adjust the emission angle of the first laser light L1 from the window 21W in two axial directions that are orthogonal to each other with respect to the optical axis. The shutter 224 is arranged at an arbitrary position on the laser light emission path, and is configured to be able to block the light emitted from the laser light source 221 .

The transmitter 20 further includes a drive circuit 23 that supplies power to each laser light source 221 and an amplifier 24 that adjusts the current value supplied to each laser light source 221 . The laser emission unit 22, the drive circuit 23, and the amplifier 24 are configured to be individually controlled based on commands from the controller 40, which will be described later.

(seeing monitor)
The seeing monitor 31 detects the state of the atmosphere on the propagation path of the second laser beam L2 transmitted from the spacecraft S toward the free-space optical communication device G. As shown in FIG. In this embodiment, a DIMM (Differential Image Motion Monitor) is employed as the seeing monitor 31 in order to detect the beam position of the second laser beam L2 reflecting the state of the atmosphere as position information.

Here, the state of the atmosphere typically means the fluctuation (seeing) of the atmosphere. Atmospheric turbulence varies depending on weather conditions, air pollution, surrounding terrain, time, season, and so on. Spatial optical transmission between the spacecraft S and the free-space optical communication device G is strongly affected by the ground atmosphere (for example, continuous refractive index change). The spread angle, transmission intensity, and transmission direction are set in advance so that the link (first laser beam L1) reaches the spacecraft S.
However, since the pattern of atmospheric fluctuations changes from moment to moment, if the uplink transmission conditions are fixed, the uplink (first laser beam L1) acquisition by the spacecraft S becomes insufficient due to changes in atmospheric conditions. , the detection accuracy of the direction of arrival of the uplink is lowered, and the received light intensity of the downlink (the second laser beam L2) is lowered in the free-space optical communication device G, thereby degrading the communication quality.
Therefore, in this embodiment, the atmospheric condition is detected by the seeing monitor 31, and based on the detection signal, the spread angle and transmission intensity of the first uplink laser beam L1 are corrected in real time. An optimum communication environment with the free-space optical communication device G is maintained.

FIG. 3 is a schematic diagram for explaining the influence of atmospheric fluctuations on the downlink (second laser beam L2) transmitted from the spacecraft S to the free-space optical communication device G. As shown in FIG. As shown in FIG. 3, the wavefront L2w of the second laser beam L2 transmitted from the spacecraft S is flat in outer space, but is distorted in the atmosphere. The degree of this distortion varies depending on atmospheric conditions, and increases as the intensity of atmospheric fluctuation increases, resulting in a shift of the focal position. In this way, by detecting the shift amount of the focal position of the second laser beam L2 in the seeing monitor 31, it is possible to detect the intensity of atmospheric fluctuations in the propagation path of the second laser beam L2.

FIG. 4 is a schematic perspective view showing a configuration example of the seeing monitor 31. As shown in FIG. The seeing monitor 31 has, for example, a reflecting telescope structure with a diameter of 10 cm or less. The seeing monitor 31 includes a cylindrical portion 311 fixed to the outer periphery of the telescope 10 , two prisms (or wedges) 312 spaced apart from each other at the tip of the cylindrical portion 311 , and the cylindrical portion through the prisms 312 . It has a first mirror 313 and a second mirror 314 that reflect the second laser beam L2 that has traveled to 311, and an infrared camera 315 that has a light receiving surface 315a that receives the reflected light from the second mirror 314. FIG.

FIG. 5 is a schematic diagram showing a formed image of the second laser beam L2 on the light receiving surface 315a. In the drawing, the X-axis and Y-axis indicate the horizontal and vertical axes of the light receiving surface 315 a , respectively, and the Z-axis corresponds to the optical axis (center of axis) of the seeing monitor 31 . In the figure, P0 indicates the focal position (hereinafter also referred to as reference point) of each laser beam transmitted through the two prisms 312 at the reference value (initial value at the start of light reception). The seeing monitor 31 detects the amount of shift (X/Y) in the X-axis and Y-axis directions from the reference point P0 of the two imaging points P of the laser light on the light receiving surface 315a. Specifically, the seeing [arcsec] is calculated by a known method from the incident angle obtained from the focal length of the optical system that constitutes the seeing monitor 31 and the amount of shift in the X-axis and Y-axis directions from the reference point P0. calculate.

A detection signal from the seeing monitor 31 is output to the calculator 50 (see FIG. 1). The calculator 50 calculates a Fried parameter r0 [mm] relating to atmospheric fluctuations from the amount of shift of the two imaging points P detected by the infrared camera 315 from the reference point P0. The freed parameter r0 is an index for quantitatively evaluating seeing, and is calculated by a predetermined arithmetic expression and output to the control section 40. FIG. Note that the arithmetic unit 50 may be configured as part of the seeing monitor 31 or may be configured as part of the control unit 40 . Also, the processing of calculating the seeing and freed parameters may be performed by the control unit 40 .

In calculating the freed parameter r0 , a correction coefficient corresponding to the aperture of the seeing monitor 31 may be multiplied. A DIMM generally has a diameter of 25 cm or more, and it is known that a diameter smaller than that size results in a large measurement error. However, in order to simultaneously measure the downlink light during satellite tracking and control the uplink, it is necessary to make the DIMM small enough to be mounted on the telescope aperture (0.3m to 10m) assumed for space communications. need to be transformed.

Therefore, in the present embodiment, for a DIMM with a diameter of 10 cm or less applied to the seeing monitor 31, a correction coefficient is calculated in advance based on a statistical analysis in comparison with a reference telescope with a diameter of about 25 cm, and the correction coefficient is applied to the viewing monitor 31. The freed parameter r0 is calculated from the value obtained by multiplying the output. This makes it possible to suppress adverse effects caused by DIMM measurement errors due to miniaturization, and to measure atmospheric conditions with high accuracy.

(Received light intensity monitor)
The received light intensity monitor 32 detects the received light intensity of the second laser beam L2 transmitted from the spacecraft S toward the free-space optical communication device G. FIG. In this embodiment, the received light intensity monitor 32 is arranged adjacent to the seeing monitor 31 on the outer periphery of the telescope 10, but the mounting position is not limited to this. The received light intensity monitor 32 is composed of a photoelectric conversion element capable of detecting the received light intensity of the second laser beam L2 per unit area.

FIG. 6 is a schematic diagram showing a configuration example of the received light intensity monitor 32. As shown in FIG. The received light intensity monitor 32 has a condensing lens 322 in the cylindrical portion 321 and a light receiving sensor 323 that receives the second laser beam L2 condensed by the condensing lens 322 . The light receiving sensor 323 is a photoelectric conversion element that outputs a current value corresponding to the intensity of the second laser beam L2, and its output (Rx [dBm]) is supplied to the control unit 40 .

(beam monitor)
The beam monitor 33 detects beam meandering caused by beam wandering of the first laser beam L1. The uplink (first laser beam L1) emitted from the transmission unit 20 is also affected by fluctuations in the atmosphere above, the refractive index that changes stepwise with altitude, and the like, and the intensity is attenuated or the propagation direction is meandering. do. This phenomenon is called beam wandering, and its state is schematically shown in FIG.

If the meandering of the first laser beam L1 for uplink due to beam wandering is larger than a predetermined value, the first laser beam L1 is less likely to reach the spacecraft S. Therefore, for the spacecraft S, the first laser beam The detection accuracy of L1 is lowered. As a result, since the accuracy of the emission direction of the second laser beam L2 for downlink is lowered, the received light intensity of the second laser beam L2 in the free-space optical communication device G is also lowered. Therefore, in this embodiment, the beam monitor 33 observes the beam meandering affected by the beam wandering of the first laser beam L1 for uplink, and the emission direction of the first laser beam L1 is determined according to the result of the observation value. is configured to control

Specifically, the beam emission direction (azimuth, elevation angle) is calculated from the observed value, and the difference value from the predicted value (azimuth, elevation angle) regarding the spatial position of the spacecraft S is calculated. The control unit 40 generates a control signal for correcting the emission direction of the first laser beam L1 so as to cancel the difference value.

8 and 9 are principle diagrams showing one configuration example of the beam monitor 33. FIG. The beam monitor 33 is configured to be able to photograph the scattered light L1s of the first laser light L1 emitted from the transmission unit 20 to the sky due to particles in the air or the like. The beam monitor 33 has a housing 331 , and a first mirror 332 , a second mirror 333 , a third mirror 334 , a beam splitter 335 , a camera 336 and an image processing section 337 arranged inside the housing 331 .

The first mirror 332 and the second mirror 333 reflect the atmospheric scattered light L1s (L1sx, L1sy) of the first laser light L1 emitted from the transmitter 20 . Scattered light L1sx reflected by the first mirror 332 enters the camera 336 via the beam splitter 335 . On the other hand, the scattered light L1sy reflected by the second mirror 333 enters the camera 336 via the third mirror 334 and beam splitter 335 . At this time, the beam splitter 335, the first mirror 332, and the second mirror 333 are arranged so that the two reflected lights incident on the beam splitter 335 form a predetermined angle. 8 and 9, the beam splitter 335, the first mirror 332, and the second mirror 333 are arranged so that the two reflected lights incident on the beam splitter 335 are orthogonal to each other. Also, as will be described later, an image 336 v captured by the camera 336 is output to the image processing section 337 .

In FIG. 9, the Z-axis indicates the emission center of the first laser beam L1 in the transmitter 20, and the X-axis and Y-axis directions indicate two axial directions orthogonal to the Z-axis. The first mirror 332 reflects the scattered light L1sx of the first laser beam L1 seen from the X plane (first plane) parallel to the XZ plane, and the second mirror 333 intersects the X plane at a predetermined angle ( Scattered light L1sy of the first laser light L1 viewed from the Y plane (second plane) parallel to the XY plane, which is perpendicular to the XY plane in this embodiment, is reflected. The camera 336 is an infrared camera, and includes a projected image of the scattered light L1sx of the first laser beam L1 traveling while refracting or diverging in the X plane onto the X plane, and a scattered light L1sx traveling while refracting or diverging in the Y plane. A projected image of the scattered light L1sy of the first laser light L1 onto the Y plane is obtained at the same time.

FIG. 10 is a diagram showing an image 336v of the scattered lights L1sx and L1sy acquired by the camera 336. As shown in FIG. Camera 336 is an infrared camera. In the figure, the angle between the +X direction and the -X direction corresponds to the scattering angle of the scattered light L1x, and the angle between the +Y direction and the -Y direction corresponds to the scattering angle of the scattered light L1y. The image processing unit 337 analyzes the images of the scattered lights L1x and L1y to analyze the shape of the emitted beam affected by the beam wandering of the first laser light L1, and outputs the result to the control unit 40. Typically, the controller 40 superimposes the images of the scattered light L1sx and the scattered light L1sy to determine the propagation direction of the first laser light L1. Note that the calculation of the propagation direction is not limited to being performed by the control unit 40 and may be performed by the image processing unit 337 .

Note that the beam monitor 33 is not limited to the example configured with one camera 336, and may be configured with two cameras. A configuration example thereof is schematically shown in FIG. In FIG. 11, the scattered lights L1sx and L1sy reflected by the first mirror 332 and the second mirror 333 enter the first camera 336a and the second camera 336b via the beam splitter 338, respectively. In this case, the image processing unit 337 determines the propagation direction of the emitted beam affected by the beam wandering of the first laser light L1 from the images of the scattered lights L1sx and L1sy acquired by the first camera 336a and the second camera 336b. measure.

(Observer)
The observation device 34 (see FIG. 1) is composed of a thermal infrared camera, a visible light camera, or the like capable of observing clouds C in the sky and flying objects F such as aircraft. The observer 34 is attached integrally with the transmitter 20 and outputs its output image to the controller 40 . The control unit 40 monitors the output from the observation device 34, and when confirming the presence of a cloud C or a flying object F in the direction in which the first laser beam L1 is emitted, drives the shutter 224 to release the first laser beam L1. Stop the emission. Note that the viewing angle of the observer 34 is wider than the viewing angle of the beam monitor 33, so that clouds C and flying objects F approaching the irradiation area of the first laser beam L1 can be detected in advance.

(control part)
FIG. 12 is a functional block diagram showing the configuration of the control section 40. As shown in FIG.

The control unit 40 controls the operation of each unit of the free-space optical communication device G in an integrated manner. The control unit 40 is typically configured by a computer having a CPU (Central Processing Unit) and memory. The control unit 40 includes an acquisition unit 41 that acquires each output of the seeing monitor 31 (or the computing unit 50), the received light intensity monitor 32, the beam monitor 33, and the observation device 34, and the output of each monitor acquired by the acquisition unit 41. Based on this, a determination unit 42 for determining whether or not the beam divergence angle (beam width) and power of the first laser light L1 are corrected, and a control signal for controlling the transmission unit 20 based on the output of the determination unit 42 is generated. It has a signal generator 43 .

[Operation of Spatial Optical Communication Device]
The details of the configuration of the controller 40 will be described below together with the operation of the free-space optical communication device G. FIG. FIG. 13 is a sequence diagram showing the operation of each part of the free-space optical communication device G in time series, and FIGS.

As shown in FIG. 1, the free-space optical communication device G transmits the first laser beam L1 for uplink from the transmission unit 20 to the spacecraft S, and the spacecraft S receives the arrival direction of the first laser beam L1. to transmit the second laser beam L2 for downlink. The telescope 10 converges the second laser beam L2 and performs predetermined signal processing.

The control unit 40 controls the transmission unit 20 that emits the first laser beam L1 by executing first to third loop processes described later based on the received light intensity Rx of the second laser beam L2.

(First loop processing)
The control unit 40 obtains or calculates the atmospheric fluctuation (seeing) and Freed parameter r0 based on the outputs of the seeing monitor 31 and the calculator 50 (steps 101 and 102). Further, the control unit 40 acquires or calculates the received light intensity Rx of the second laser beam L2 based on the output of the received light intensity monitor 32 (step 103).

Subsequently, the control unit 40 determines whether or not the received light intensity Rx of the second laser beam L2 has reached a predetermined intensity range (step 104). The predetermined intensity range typically refers to the intensity range of the second laser light L2 necessary for appropriately performing signal processing of the received signal by the telescope 10, even if it is an arbitrary point (target value). Although it is good, in order to improve the stability of control, in this example, it is set within a predetermined range centered on the target value.

When the received light intensity Rx of the second laser beam L2 is within the predetermined intensity range, it can be considered that there is no fluctuation in atmospheric fluctuations. Therefore, in this case, the control unit 40 maintains the current emission conditions (beam divergence angle, transmission power (Tx)) of the first laser beam L1 (steps 105 and 106), and performs the processes of steps 101 to 106 described above. (hereinafter also referred to as first loop processing) is repeated.

In the above-described example, the first loop processing is executed with only the received light intensity Rx of the second laser beam L2 as the monitoring object. The first loop process may be executed with both w and the received light intensity Rx of the second laser beam L2 as monitoring targets (the same applies to the second loop process described later). In this case, for example, a process 102a for calculating the beam wander w of the second laser light L2 is added between steps 102 and 103 (see FIG. 16). The beam wander w of the second laser beam L2 can be calculated based on the Freed parameter obtained in step 102, the laser wavelength and beam diameter of the second laser beam L2, the propagation distance, and the like.

(Second loop processing)
One of the reasons why the received light intensity of the second laser beam L2 does not fall within the predetermined intensity range is that atmospheric fluctuations change over time. One reason is that the incoming direction of the captured first laser beam L1 cannot be accurately detected. Therefore, in the second loop process, the divergence angle and transmission angle of the first laser beam L1 emitted from the transmitter 20 are adjusted so that the spacecraft S can accurately detect the arrival direction of the first laser beam L1. Power Tx is corrected.

When the controller 40 determines that the received light intensity of the second laser beam L2 is not within the predetermined intensity range, it executes a second loop process (steps 108 to 112). In this embodiment, when the second loop process is repeated N times in succession exceeding a predetermined value, the third loop process shown in FIG. 15 is executed (step 107).

The controller 40 determines whether or not the received light intensity of the second laser beam L2 is less than a predetermined intensity range (step 108). Then, if the determination result in step 108 is "Yes", the control unit 40 increases the beam divergence angle of the first laser light L1 by n (n is a positive number greater than 1) times the current value, and increases the transmission power (Tx). generates a control signal for increasing the current value by ⁿ² times, and outputs this to the transmission unit 20 (steps 109 and 110).

As a result, the beam width of the first laser beam L1 is widened, so that the light amount of the first laser beam L1 reaching the spacecraft S can be increased. As a result, the direction of arrival of the first laser beam L1 captured by the spacecraft S can be detected with high accuracy. Accuracy is improved, and the received light intensity Rx can be increased. In addition, since the transmission power Tx is also increased in accordance with the expansion of the beam divergence angle, the decrease in light energy per unit area due to the expansion of the beam divergence angle can be suppressed.

The divergence angle of the first laser beam L1 can be changed to any size by adjusting the distance between each lens in the lens unit 222 of the transmitter 20, and the transmission power Tx can be adjusted by adjusting the amplifier 24 of the transmitter 20. can be resized to any size.

The value of n may be a fixed value, or a variable value predetermined corresponding to the amount of shift from the predetermined range of the received light intensity Rx (or beam wander w) of the second laser beam L2. The value of n may be the same value as the beam divergence angle and transmission power control amount, or may be different values. Also, the value of n may be dynamically changed based on a predetermined table or algorithm based on the information on atmospheric fluctuations obtained in step 101, the Freed parameter obtained in step 102, and the like.

The value of n is not particularly limited, and is typically a numerical value of 1.5 or more and 10 or less, preferably 2 or more and 5 or less. Although it depends on the state of the atmosphere, if the value of n is less than 1.5, the effect of the spacecraft S capturing the first laser beam L1 may not be sufficient. Also, if the value of n exceeds 10, the transmission power of the first laser beam L1 becomes excessive, and there is a possibility that efficient operation of power in the free-space optical communication device G will be hindered.

If the determination result in step 108 is "No", the controller 40 reduces the beam divergence angle of the first laser beam L1 by n times (n is a positive number greater than 1) from the current value, and increases the transmission power (Tx). is ⁿ² times smaller than the current value, and this is output to the transmitter 20 (steps 112, 113). As a result, the beam width of the first laser beam L1 is narrowed and the transmission power is also reduced, so that excessive output of the first laser beam L1 can be suppressed.

After executing the above-described second loop process, the control unit 40 executes the first loop process again. The control unit 40 repeatedly executes the second loop processing until the received light intensity Rx (or the received light intensity Rx and the beam wander w (FIG. 16)) of the second laser beam L2 falls within a predetermined range.

As described above, by correcting the emission condition of the first uplink laser beam L1 in real time according to the atmospheric conditions that change from moment to moment, the second laser beam L2 transmitted from the spacecraft S can be stabilized. Reception can be maintained. Therefore, according to this embodiment, it is possible to realize highly adaptable free-space optical communication that can follow atmospheric conditions that change from moment to moment.

On the other hand, even if the above-described second loop control is executed multiple times, the received light intensity Rx of the second laser beam L2 may not fall within the predetermined intensity range. Therefore, in the present embodiment, if the received light intensity Rx does not fall within the predetermined range even after the second loop process is executed N times in succession ("Yes" in step 108), the control unit 40 executes the third loop process. configured to run The value of N can be set arbitrarily, and is set to a natural number of 3 or more, for example.

(Third loop processing)
Even if the above-described second loop processing is executed, the received light intensity Rx of the second laser beam L2 does not fall within the predetermined range. For example, the point (spacecraft S) is not properly reached. Therefore, in the third loop process, the emission direction of the first laser beam L1 from the transmitter 20 is corrected so that the first laser beam L1 appropriately reaches the target point.

In the third loop process, as shown in FIG. 15, the control unit 40 acquires imaging data of scattered lights L1sx and L1sy of the first laser light L1 in the atmosphere from the beam monitor 33 (step 201). The control unit 40 determines the beam position (emission direction from the transmission unit 20) of the scattered light L1s of the first laser light L1 in the X plane and the Y plane (see FIG. 9) from the image captured by the camera 336 of the beam monitor 33. ) is detected (steps 202 and 203). In the example shown in FIG. 9, the beam position in the X plane is obtained from the image of the scattered light L1sx directly incident on the camera 336, and the beam position in the Y plane is obtained from the third mirror 334 located on the X axis. from the image of the scattered light L1sy incident on the camera 336 via .

The controller 40 calculates and determines the two-dimensional coordinates of the first scattered laser beam L1s given from the beam positions on the X plane and the Y plane (steps 204 and 205, FIG. 10). This makes it possible to grasp the propagation direction of the first laser beam L1 in each of the X plane and the Y plane, and by superimposing these, it is possible to estimate at which point in the sky the first laser beam L1 is located. .

The controller 40 determines whether or not the first laser beam L1 is traveling toward the target point from the beam positions on the X plane and the Y plane (step 206). If the determination result here is "No", when the control unit 40 determines that the beam position has shifted in a predetermined direction from the initial set value in at least one of the X plane and the Y plane, The output mirror 223 of the transmitter 20 is adjusted in the direction of eliminating the shift amount (steps 207, 208, 209). As a result, the arrival accuracy of the first laser beam L1 to the spacecraft S is improved, and as a result, the received light intensity Rx of the second laser beam L2 transmitted from the spacecraft S can be improved.

If it is determined that the first laser beam L1 is traveling toward the target point from the beam positions in the X plane and the Y plane ("Yes" in step 206), another factor is the decrease in the received light intensity Rx. Therefore, the control unit 40 ends the process while maintaining the current set value for the emission direction of the first laser beam L1 (step 210).

As described above, the free-space optical communication device G according to the present embodiment is configured so that the received light intensity Rx of the downlink (second laser beam L2) from the spacecraft S becomes the target value. Automatically corrects the extraction conditions. As a result, it is possible to optimize the uplink by following the atmospheric conditions that change from moment to moment, thereby ensuring stable communication quality without being influenced by the atmosphere.

Further, according to this embodiment, since the seeing monitor 31 and the received light intensity monitor 32 are integrally attached to the telescope 10 that tracks the spacecraft S, the reliability of the uplink optimization control based on the downlink described above can be improved. can be enhanced.

Although the embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to the above-described embodiments and can be modified in various ways.

For example, in the above embodiments, optical communication with a spacecraft has been described as an example, but the present invention is not limited to this. For example, a system that uses a laser to measure the distance between a spacecraft and a ground station with the earth's atmosphere in between (optical satellite ranging, active debris observation), The present invention can also be applied to a system for transmitting energy by means of light (optical energy transmission). Further, although the laser used in the free-space optical communication device has been described as a typical example of an infrared laser, the laser is not limited to this, and visible light may be used.

In the above embodiment, the seeing monitor 31 as the first detector and the received light intensity monitor 32 as the second detector are integrally attached to the outer periphery of the telescope 10. However, these It is also possible to place the detector inside the telescope. Also, the received light intensity monitor as the second detection unit may be composed of a light receiving sensor for the downlink laser light condensed by the telescope.

Furthermore, in the above embodiment, the divergence angle and emission intensity of the first laser beam L1 are determined based on the state of the atmosphere (output of the seeing monitor 31) and the received light intensity of the second laser beam L2 (output of the received light intensity monitor 32). Although configured to control, it is not limited to this. For example, the above conditions for the first laser beam L1 may be controlled based only on the received light intensity of the second laser beam L2.
Similarly, the beam monitor 33 shown in FIGS. 8 to 11 is used to detect the emission direction (beam position) of the first laser beam L1, but the detection is not limited to this, and the emission direction of the first laser beam L1 can be detected. Other configurations of beam monitors may be employed.

DESCRIPTION OF SYMBOLS 10... Telescope 20... Transmission part 31... Seeing monitor (2nd detection part)
32... Received light intensity monitor (first detector)
33... Beam monitor (third detector)
34... Observation device 40... Control unit G... Spatial optical communication device L1... First laser beam (uplink)
L2: second laser light (downlink)
S…Spacecraft

Claims (6)

a transmitter that transmits the first laser beam toward the spacecraft;
a receiver that receives a second laser beam transmitted from the spacecraft;
a first detection unit that detects the received light intensity of the second laser light;
a second detection unit having a light receiving surface for receiving the second laser beam and detecting atmospheric fluctuations on the propagation path of the second laser beam;
a third detection unit that detects the emission direction of the first laser light;
a control unit that generates a control signal for controlling the first laser light based on the outputs of the first detection unit , the second detection unit, and the third detection unit ;
The control unit
performing a first process of generating a control signal for increasing the divergence angle of the first laser beam and increasing the power thereof when the received light intensity of the second laser beam is less than a predetermined range;
executing a second process of generating a control signal for narrowing the divergence angle of the first laser beam and reducing the power when the received light intensity of the second laser beam exceeds the predetermined range;
When the received light intensity of the second laser light does not fall within the predetermined range even after repeating the first process or the second process a predetermined number of times, beam meandering due to beam wandering of the first laser light is detected. to generate a control signal for correcting the emission direction.
Spatial optical communication device. The free-space optical communication device according to claim 1 ,
The free-space optical communication device, wherein the second detector is attached to the receiver. The free-space optical communication device according to claim 1 or 2 ,
The free-space optical communication device, wherein the third detection unit includes a camera that is arranged in the transmission unit and captures the scattered light of the first laser light due to the atmosphere. The free-space optical communication device according to claim 3 ,
The camera acquires a projected image of the scattered light onto a first plane and a projected image of the scattered light onto a second plane that intersects the first plane at a predetermined angle. Spatial light Communication device. The free-space optical communication device according to any one of claims 1 to 4 ,
The free-space optical communication device, wherein the receiving unit is a telescope that collects the second laser light. transmitting the first laser beam toward the spacecraft by the transmission unit ;
receiving a second laser beam transmitted from the spacecraft by a receiving unit ;
Detecting the received light intensity of the second laser light by the first detection unit,
detecting atmospheric fluctuations on the propagation path of the second laser light by a second detection unit;
detecting the emission direction of the first laser light by a third detection unit;
performing a first process of generating a control signal for increasing the divergence angle of the first laser beam and increasing the power thereof when the received light intensity of the second laser beam is less than a predetermined range;
executing a second process of generating a control signal for narrowing the divergence angle of the first laser beam and reducing the power when the received light intensity of the second laser beam exceeds the predetermined range;
When the received light intensity of the second laser light does not fall within the predetermined range even after repeating the first process or the second process a predetermined number of times, beam meandering due to beam wandering of the first laser light is detected. to generate a control signal for correcting the emission direction.
Spatial optical communication method.

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