JP2021027437A - Spatial optical communication device and spatial optical communication method - Google Patents

Abstract

To provide a spatial optical communication device and a spatial optical communication method that can maintain good communication with a spacecraft while adapting to atmospheric effects.SOLUTION: A spatial optical communication device according to one embodiment of the present invention includes a transmission unit, a reception unit, a first detection unit, and a control unit. The transmission unit transmits a first laser beam to a spacecraft. The reception unit receives a second laser beam transmitted from the spacecraft. The first detection unit detects the received intensity of the second laser beam. The control unit generates a control signal that controls the spread angle and power of the first laser beam based on an output of the first detection unit.SELECTED DRAWING: Figure 1

Description

The present invention relates to a space optical communication device and a space optical communication method that perform optical communication with a spacecraft such as an artificial satellite that orbits outer space.

In recent years, research has been conducted on optical satellite communication with ground stations on the earth using spacecraft such as artificial satellites that orbit 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 than radio waves, so it will be a technology that will be responsible for future space communication. It is attracting attention as.

Space-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 the atmospheric disturbance, the power that can be received on the receiving side decreases, the communication quality deteriorates, and in the worst case, information is lost in a burst. May be called. Therefore, some kind of compensation technology capable of suppressing the influence of the atmosphere is required.

Conventionally, in order to compensate for atmospheric effects, a mechanism has been adopted in which the light energy collected by the telescope of the ground station that receives the downlink is compensated by the subsequent compensation system, but due to the atmospheric effects in the space before the telescope is incident. It has lost a considerable amount of light energy. For this reason, the ground station side continuously or briefly irradiates the spacecraft with the uplink, and guides the downlink toward the ground station like a lighthouse that informs the spacecraft of the direction of the ground station. However, the uplink is also affected by the atmosphere and often does not reach the sensor field of view of the optical communication device of the spacecraft, and the effect is small with simple uplink irradiation.

In order to solve such a problem, for example, Patent Document 1 describes path propagation in a space including a propagation path of a transmitted light wave emitted toward an artificial satellite while condensing the received light wave emitted from the artificial satellite. Light is focused by a telescope, and the angle of the propagation path of the transmitted light wave, which takes into account the effects of atmospheric fluctuations and fading, is calculated based on the wave surface distortion of the collected received light wave and path propagating light, and transmitted at that angle. A spatial optical communication device that controls a variable mirror of a telescope so that a light wave reaches an artificial satellite is disclosed.

Japanese Unexamined Patent Publication No. 2018-12281

When the uplink is emitted from the ground, the propagation direction of the transmitting laser is the influence of space from the ground to outer space, especially the atmospheric influence (continuous change in refractive index due to continuous change in atmospheric concentration from the ground to outer space). In addition, it propagates while bending in the atmosphere due to light scattering by fine particles in the atmosphere such as aerosols (Beam Wandering phenomenon). Therefore, even if the telescope tracks the spacecraft according to the forecast value, the uplink does not reach the spacecraft beyond it well, and as a result, the ground station moves the uplink from any position below the spacecraft. It becomes impossible to grasp whether it is emitted. In addition, the influence of the atmosphere changes randomly from moment to moment in time and space, so the adaptability to changes in atmospheric conditions is insufficient.

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

The spatial optical communication device according to one embodiment of the present invention includes a transmission unit, a reception unit, a first detection unit, and a control unit.
The transmitter transmits the first laser beam to the spacecraft.
The receiving unit receives the second laser beam transmitted from the spacecraft.
The first detection unit detects the light receiving intensity of the second laser beam.
The control unit generates a control signal for controlling the spread angle and power of the first laser beam based on the output of the first detection unit.

The spatial optical communication device is configured to correct the emission condition of the first laser beam so that the light receiving intensity of the second laser beam becomes a target value. As a result, the emission conditions of the first laser beam can be optimized by following the ever-changing atmospheric conditions, and stable communication quality can be ensured regardless of the influence of the atmosphere.

When the light receiving intensity of the second laser beam is less than a predetermined range, the control unit may be configured to generate a control signal that increases the spread angle of the first laser beam and increases the power.

Further, the control unit may be configured to generate a control signal that narrows the spread angle of the first laser beam and reduces the power when the light receiving intensity of the second laser beam exceeds the predetermined range. Good.

The spatial optical communication device may further include a second detection unit.
The second detection unit has a light receiving surface that receives the second laser beam, and detects fluctuations in the atmosphere on the propagation path of the second laser beam. The control unit generates a control signal for controlling the spread angle and power of the first laser beam based on the outputs of the first detection unit and the second detection unit.

The second detection unit may be attached to the reception unit.

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

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

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

The spatial optical communication method according to one embodiment of the present invention is
Send the first laser beam to the spacecraft,
Upon receiving the second laser beam transmitted from the spacecraft,
The spread angle and power of the first laser beam are controlled based on the light receiving intensity of the second laser beam.

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

It is a schematic block diagram which shows the space optical communication system which includes the space optical communication apparatus which concerns on one Embodiment of this invention. It is the schematic which shows one configuration example of the transmission part in the said space optical communication apparatus. It is a schematic diagram explaining the influence of the fluctuation of the atmosphere of the downlink (second laser beam) transmitted from the spacecraft to the space optical communication device. It is a schematic perspective view which shows one configuration example of the seeing monitor as a 1st detection part. It is a schematic diagram which shows the image formation image of the 2nd laser light on the light receiving surface of the seeing monitor. It is a schematic diagram which shows one structural example of the light receiving intensity monitor as a 2nd detection part. It is a schematic diagram explaining the beam wandering phenomenon of the uplink (first laser beam) transmitted to a spacecraft. It is a figure which shows one configuration example of the beam monitor as a 3rd detection part. It is explanatory drawing of the structure of the said beam monitor. It is a figure explaining the operation of the said beam monitor. It is a figure which shows the other configuration example of the said beam monitor. It is a functional block diagram which shows the structure of the control part in the said space optical communication apparatus. It is a sequence diagram which shows the operation of each part of the space optical communication apparatus in time series. It is a flowchart which shows an example of the processing procedure executed in the said control part. It is a flowchart which shows an example of the processing procedure executed in the said control part. It is a flowchart which shows the modification of FIG.

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 an embodiment of the present invention. The space optical communication system 100 includes a space optical communication device G and a spacecraft S, and performs optical communication (satellite communication) between the space optical communication device G and the spacecraft S.

The 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 satellites that orbit in geostationary earth orbit (GEO), low earth orbit (LEO) and medium earth orbit (MEO), regardless of the rotation period of the earth. Furthermore, it includes artificial satellites that fly in deep space. That is, the altitude of the spacecraft S from the ground surface is not particularly limited. The artificial satellite is typically a meteorological satellite, a communication satellite, or the like, but may be launched for any purpose.

[Spatial optical communication device]
The space optical communication device G is configured as a ground station that performs optical space transmission with the spacecraft S. The space optical communication device G includes a telescope 10 for receiving an optical signal (downlink) transmitted from the spacecraft S or transmitting and receiving an optical signal to and from the spacecraft S. In the present embodiment, the telescope 10 is mainly configured as a receiving unit that receives the downlink (second laser beam L2) transmitted from the spacecraft S.

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

The telescope 10 is installed on a base 11 installed on the ground. The base 11 has an adjustment mechanism 11a for adjusting the attitude of the telescope 10, and the telescope 10 is supported by the base 11 so as to be able to track the spacecraft S. The base 11 controls the orientation and / or elevation angle of the optical axis of the telescope 10 so as to track the spacecraft S according to the forecast value. The predicted value is the space coordinate of the spacecraft S calculated from the orbit of the spacecraft S, and is 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. The refractive index at the wavelength of is taken into consideration.

The aperture of the telescope 10 is not particularly limited, and is, for example, 30 cm to 10 m. The aperture of the telescope 10 is not limited to a single number, and may be a plurality of openings. The telescope 10 has a signal processing unit (not shown) that converts the focused second laser beam L2 into an electric signal and performs predetermined signal processing such as analysis of received information.

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

The spatial optical communication device G includes a transmission unit 20, a seeing monitor 31 as a second detection unit, a light receiving intensity monitor 32 as a first detection unit, a beam monitor 33 as a third detection unit, and a control unit 40. To be equipped.
The transmission unit 20 emits the first laser beam L1 transmitted toward the spacecraft S. The seeing monitor 31 detects the atmospheric state (or beam position information reflecting the atmospheric condition) on the propagation path of the second laser beam L2 based on the second laser beam L2 transmitted from the spacecraft S. .. The light receiving intensity monitor 32 detects the light receiving intensity of the second laser beam L2. The beam monitor 33 detects the emission direction of the first laser beam L1 (in the present embodiment, the beam monitor 33 scatters the first laser beam L1 in order to detect the beam emission angle (direction, elevation angle) affected by the beam wonder. Monitor the light L1s). The control unit 40 controls the direction and elevation angle of the optical axis of the telescope 10 so that the spacecraft S can be tracked according to the forecast value. The control unit 40 controls the transmission unit 20 based on the outputs of the seeing monitor 31, the light receiving intensity monitor 32, and the beam monitor 33.
The space optical communication device G further includes an observer 34 for observing the sky above the emission direction of the first laser beam L1.

Optical space transmission between spacecraft S and space optical communication device G is performed in a space where clouds do not exist (under the earth's atmosphere), but the downlink transmitted from spacecraft S to space optical communication device G. However, due to the influence of atmospheric disturbance, the power that can be received on the receiving side may decrease and the communication quality may deteriorate. Therefore, the ground station G side continuously or briefly irradiates the uplink toward the spacecraft S to notify the spacecraft S of the direction of the ground station G and guide the downlink toward the ground station. ..
However, the uplink is also affected by the atmosphere in many cases and does not reach the spacecraft S, and the effect of simple uplink irradiation is small.
Therefore, the spatial optical communication device G of the present embodiment is an uplink (first) emitted toward the spacecraft S based on the optical characteristics of the downlink (second laser beam L2) detected by the seeing monitor 31 or the like. It is configured to control the spread angle and power of the laser beam L1). The details will be described below.

(Transmitter)
The transmission unit 20 has a laser light source that generates a first laser beam L1 for uplink. The first laser beam L1 mainly functions as guided light for emitting the downlink of the spacecraft S toward the space optical communication device G. The first laser beam L1 may be a continuous laser or a pulse laser. The first laser beam L1 is typically infrared light, the wavelength of which is, for example, 1550 nm or 1064 nm. The spread angle and power of the first laser beam L1 are not particularly limited, and for example, the spread angle is 50 μrad to 1 mrad and the power is 1 W to several tens of kW (for example, 50 kW).

The transmission unit 20 is attached to the outer peripheral portion of the telescope 10 so that it can move relative to the base 11 integrally with the telescope 10. The optical axis of the first laser beam L1 in the transmission unit 20 is installed parallel to the optical axis of the telescope 10. In the present embodiment, there are multiple laser emitting units, and each laser emitting unit is configured to emit the first laser beam L1 toward the spacecraft S. Of course, the number of laser emitting units is not limited to a plurality, and may be a single number. Further, the transmission unit 20 is not limited to the example of being attached to the outer peripheral portion of the telescope 10, and may be arranged inside the telescope 10.

FIG. 2 is a schematic view showing a configuration example of the transmission unit 20. The transmission unit 20 has a casing 21 and a plurality of (two in this example) laser emission 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, respectively.

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

The transmission unit 20 further includes a drive circuit 23 that supplies electric 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 can be individually controlled based on a command from the control unit 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 to the space optical communication device G. In the present embodiment, a DIMM (Differential Image Motion Monitor) is adopted as the seeing monitor 31 in order to detect the beam position of the second laser beam L2 reflecting the atmospheric condition as position information.

Here, the state of the atmosphere typically means the fluctuation of the atmosphere (seeing). Atmospheric fluctuations fluctuate depending on weather conditions, air pollution, surrounding terrain, time, seasons, etc. Spatial light transmission between the spacecraft S and the space optical communication device G is strongly affected by the atmosphere on the ground (for example, continuous change in refractive index). Therefore, based on this influence on the atmosphere, the light is increased as guided light. The spread angle, transmission intensity, and transmission direction of the link (first laser beam L1) are set in advance so as to reach 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) cannot be sufficiently captured by the spacecraft S due to changes in the atmospheric conditions. In addition to lowering the detection accuracy in the arrival direction of the uplink, the light receiving intensity of the downlink (second laser beam L2) in the spatial optical communication device G is lowered, and the communication quality is deteriorated.
Therefore, in the present embodiment, the atmospheric state is detected by the seeing monitor 31, and the spread angle and the transmission intensity of the first laser beam L1 for uplink are corrected in real time based on the detection signal to obtain the spacecraft S. Maintain the optimum communication environment with the spatial optical communication device G.

FIG. 3 is a schematic diagram illustrating the influence of atmospheric fluctuations of the downlink (second laser beam L2) transmitted from the spacecraft S to the space optical communication device G. As shown in FIG. 3, the wave surface L2w of the second laser beam L2 transmitted from the spacecraft S is a flat surface in outer space, whereas it is a distorted surface in the atmosphere. The degree of this distortion changes depending on the atmospheric condition, and as the intensity of atmospheric fluctuation increases, the focal position shifts. In this way, by detecting the shift amount of the focal position of the second laser beam L2 on 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. The seeing monitor 31 has, for example, a reflecting telescope structure having a diameter of 10 cm or less. The seeing monitor 31 has a tubular portion 311 fixed to the outer peripheral portion of the telescope 10, two prisms (or wedges) 312 arranged apart from each other at the tip of the tubular portion 311 and a tubular portion via the prism 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 having a light receiving surface 315a that receives the reflected light of the second mirror 314.

FIG. 5 is a schematic view showing an image of the second laser beam L2 on the light receiving surface 315a. In the figure, the X-axis and the Y-axis indicate the horizontal axis and the vertical axis of the light receiving surface 315a, respectively, and the Z-axis corresponds to the optical axis (axis center) of the seeing monitor 31. In the figure, P0 indicates the focal position (hereinafter, also referred to as a 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 shift amount (X / Y) in the X-axis and Y-axis directions from the reference point P0 of the two imaging points P of the laser beam on the light receiving surface 315a. Specifically, seeing [arcsec] is performed by a known method from the incident angle obtained from the focal length of the optical system constituting the seeing monitor 31 and the shift amount in the X-axis and Y-axis directions from the reference point P0. calculate.

The detection signal of the seeing monitor 31 is output to the arithmetic unit 50 (see FIG. 1). The arithmetic unit 50 calculates the Fried parameter Ro [mm] related to the fluctuation of the atmosphere from the shift amount of the two imaging points P detected by the infrared camera 315 from the reference point P0. The freed parameter Ro is an index for quantitatively evaluating seeing, is calculated by a predetermined arithmetic expression, and is output to the control unit 40. The arithmetic unit 50 may be configured as a part of the seeing monitor 31 or as a part of the control unit 40. Further, the seeing and freed parameter calculation processing may be executed by the control unit 40.

When calculating the freed parameter Ro, a correction coefficient corresponding to the diameter of the seeing monitor 31 may be multiplied. It is known that DIMMs generally have a diameter of 25 cm or more, and a measurement error becomes large when the diameter is smaller than that size. However, in order to measure the downlink light at the same time and control the upling during satellite tracking, the DIMM is small enough to be mounted on the telescope diameter (about 0.3m to 10m) assumed in space communication. Need to be converted.

Therefore, in the present embodiment, with respect to the DIMM having a diameter of 10 cm or less applied to the seeing monitor 31, a correction coefficient based on statistical analysis compared with a reference telescope having a diameter of about 25 cm is calculated in advance, and the correction coefficient is calculated by the seeing monitor 31. The freed parameter R0 is calculated from the value obtained by multiplying the output. This makes it possible to suppress the harmful effects of DIMM measurement errors due to miniaturization and measure the atmospheric condition with high accuracy.

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

FIG. 6 is a schematic view showing a configuration example of the light receiving intensity monitor 32. The light receiving intensity monitor 32 has a condenser lens 322 and a light receiving sensor 323 that receives the second laser beam L2 focused by the condenser lens 322 in the tubular portion 321. 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 the output (Rx [dBm]) is supplied to the control unit 40.

(Beam monitor)
The beam monitor 33 detects the beam meandering associated with the 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, refractive index that gradually changes depending on altitude, and the like, and the intensity is attenuated or the propagation direction is meandering. To do. This phenomenon is called beam wandering, and the state is schematically shown in FIG.

When the beam meandering caused by the beam wandering of the first laser beam L1 for uplink is larger than a predetermined value, it becomes difficult for the first laser beam L1 to reach the spacecraft S. Therefore, for the spacecraft S, the first laser beam The detection accuracy of L1 is lowered. As a result, the accuracy of the emission direction of the second laser beam L2 for downlink is lowered, so that the light receiving intensity of the second laser beam L2 in the space optical communication device G is also lowered. Therefore, in the present 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 observed value. Is configured to control.

Specifically, the beam emission direction (direction, elevation angle) is calculated from the observed value, and the difference value from the forecast value (direction, 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 a configuration example of the beam monitor 33. The beam monitor 33 is configured to be capable of photographing scattered light L1s by atmospheric particles or the like of the first laser light L1 emitted from the transmission unit 20 in the sky. The beam monitor 33 includes a housing 331, a first mirror 332, a second mirror 333, a third mirror 334, a beam splitter 335, a camera 336, and an image processing unit 337 arranged inside the housing 331, respectively.

The first mirror 332 and the second mirror 333 reflect the scattered light L1s (L1sx, L1sy) of the first laser light L1 emitted from the transmission unit 20 due to the atmosphere. The scattered light L1sx reflected by the first mirror 332 is incident on 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 the 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. In FIGS. 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. Further, as will be described later, the captured image 336v of the camera 336 is output to the image processing unit 337.

In FIG. 9, the Z-axis indicates the emission center of the first laser beam L1 in the transmission unit 20, and the X-axis and Y-axis directions indicate biaxial 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 ( In this embodiment, the scattered light L1sy of the first laser beam L1 viewed from the Y plane (second plane) parallel to the XY plane, which is orthogonal to the XY plane, is reflected. The camera 336 is an infrared camera, and travels while refracting or diverging in the X-plane with a projected image of scattered light L1sx on the X-plane of the first laser beam L1 traveling while refracting or diverging in the Y-plane. The projected image of the scattered light L1sy on the Y plane of the first laser light L1 is acquired at the same time.

FIG. 10 is a diagram showing an image 336v of scattered light L1sx and L1sy acquired by the camera 336. The camera 336 is an infrared camera. In the figure, the angle formed by the + X direction and the −X direction corresponds to the scattering angle of the scattered light L1x, and the angle formed by the + Y direction and the −Y direction corresponds to the scattering angle of the scattered light L1y. The image processing unit 337 analyzes the image of the scattered light L1x and L1y to analyze the shape of the emitted beam affected by the beam wandering of the first laser light L1 and outputs it to the control unit 40. Typically, the control unit 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. The calculation of the propagation direction is not limited to the case where it is executed by the control unit 40, and may be executed by the image processing unit 337.

The beam monitor 33 is not limited to the example of being composed of one camera 336, and may be composed of two cameras. An example of the configuration is schematically shown in FIG. In FIG. 11, the scattered light L1sx and L1sy reflected by the first mirror 332 and the second mirror 333 are incident on 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 beam L1 from the images of the scattered light L1sx and L1sy acquired by the first camera 336a and the second camera 336b. measure.

(Observer)
The observer 34 (see FIG. 1) is composed of a thermal infrared camera or a visible light camera capable of observing clouds C in the sky and flying objects F such as aircraft. The observer 34 is integrally attached to the transmitter 20, and the output image thereof is output to the control unit 40. The control unit 40 monitors the output from the observer 34, and when it confirms the existence of the cloud C or the flying object F in the emission direction of the first laser beam L1, drives the shutter 224 to drive the first laser beam L1. Stop the emission. The viewing angle of the observer 34 is wider than the viewing angle of the beam monitor 33, so that the cloud C and the flying object F approaching the irradiation region of the first laser beam L1 can be detected in advance.

(Control unit)
FIG. 12 is a functional block diagram showing the configuration of the control unit 40.

The control unit 40 comprehensively controls the operation of each unit of the spatial optical communication device G. The control unit 40 is typically composed of a computer having a CPU (Central Processing Unit) and a memory. The control unit 40 uses the seeing monitor 31 (or the arithmetic unit 50), the light receiving intensity monitor 32, the beam monitor 33, and the acquisition unit 41 to acquire the outputs of the observation aircraft 34, and the output of each monitor acquired by the acquisition unit 41. Based on this, a determination unit 42 for determining the beam spread angle (beam width) of the first laser beam L1 and the presence / absence of power correction, etc., and a control signal for controlling the transmission unit 20 based on the output of the determination unit 42 are generated. It has a signal generation unit 43.

[Operation of spatial optical communication device]
Hereinafter, the details of the configuration of the control unit 40 will be described together with the operation of the spatial optical communication device G. FIG. 13 is a sequence diagram showing the operation of each part of the space optical communication device G in time series, and FIGS. 14 and 15 are flowcharts showing an example of a processing procedure executed by the control unit 40.

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

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

(First loop processing)
The control unit 40 acquires or calculates atmospheric fluctuations (seeing) and freed parameter Ro based on the outputs of the seeing monitor 31 and the arithmetic unit 50 (steps 101 and 102). Further, the control unit 40 acquires or calculates the light receiving intensity Rx of the second laser beam L2 based on the output of the light receiving intensity monitor 32 (step 103).

Subsequently, the control unit 40 determines whether or not the light receiving 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 beam L2 required for proper signal processing of the received signal by the telescope 10, even if it is an arbitrary point (target value). It is good, but in this example, it is set in a predetermined range centered on the target value in order to improve the stability of control.

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

In the above example, the first loop process is executed with only the light receiving intensity Rx of the second laser beam L2 as the monitoring target, but the present invention is not limited to this, and as shown in FIG. 16, the beam wonder of the second laser beam L2 The first loop process may be executed with both w and the light receiving 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 wonder w of the second laser beam L2 is added between the step 102 and the step 103 (see FIG. 16). The beam wonder w of the second laser beam L2 can be calculated based on the freed parameter acquired in step 102, the laser wavelength and beam diameter of the second laser beam L2, the propagation distance, and the like.

(Second loop processing)
As a factor that the light receiving intensity of the second laser beam L2 does not fall within the predetermined intensity range, the atmospheric fluctuation fluctuates with time, which attenuates the intensity of the first laser beam L1 reaching the spacecraft S, and the spacecraft S. It is possible to accurately detect the arrival direction of the captured first laser beam L1. Therefore, in the second loop processing, the spread angle and the transmission of the first laser beam L1 emitted from the transmission unit 20 so that the spacecraft S can accurately detect the arrival direction of the first laser beam L1. The power Tx is corrected.

When the control unit 40 determines that the light receiving intensity of the second laser beam L2 is not within the predetermined intensity range, the control unit 40 executes the second loop process (steps 108 to 112). In the present embodiment, when the second loop processing exceeds a predetermined value and is continuously repeated N times, the third loop processing shown in FIG. 15 is executed (step 107).

The control unit 40 determines whether or not the light receiving intensity of the second laser beam L2 is less than a predetermined intensity range (step 108). When the determination result in step 108 is "Yes", the control unit 40 increases the beam spreading angle of the first laser beam L1 by n (n is a positive number larger than 1) times the current value, and transmits power (Tx). There generates a control signal for ^{n 2} times greater than the current value, and outputs this to the transmission unit 20 (step 109, 110).

As a result, the beam width of the first laser beam L1 is widened, so that the amount of light 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 accurately detected, so that the direction of the second laser beam L2 transmitted from the spacecraft S toward the space optical communication device G The accuracy is improved, and the light receiving intensity Rx can be increased. Further, since the transmission power Tx is increased at the same time as the beam expansion angle is expanded, the decrease in light energy per unit area due to the beam expansion angle is suppressed.

The spread angle of the first laser beam L1 can be changed to an arbitrary size by adjusting the distance between each lens in the lens unit 222 of the transmission unit 20, and the transmission power Tx adjusts the amplifier 24 of the transmission unit 20. You can change it to any size with.

The value of n may be a fixed value, or may be a variable value predetermined according to the amount of shift of the light receiving intensity Rx (or beam wonder w) of the second laser beam L2 from a predetermined range. The value of n may be the same value as the control amount of the beam spreading angle and the transmission power, or may be different values. Further, the value of n may be dynamically changed based on a predetermined table or algorithm from the information on the fluctuation of the atmosphere acquired in step 101, the freed parameter acquired in step 102, and the like.

The value of n is not particularly limited, and is typically a value of 1.5 or more and 10 or less, preferably 2 or more and 5 or less. Although it depends on the atmospheric condition, when 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. Further, when the value of n exceeds 10, the transmission power of the first laser beam L1 becomes excessive, which may hinder the efficient operation of the electric power in the space optical communication device G.

When the determination result in step 108 is "No", the control unit 40 reduces the beam spread angle of the first laser beam L1 by n (n is a positive number larger than 1) times the current value, and transmits power (Tx). There generates a control signal for ^{n 2} times smaller current value, and outputs this to the transmission unit 20 (step 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 the excessive output of the first laser beam L1 can be suppressed.

The control unit 40 executes the first loop process again after executing the second loop process described above. The control unit 40 repeatedly executes the second loop process until the light receiving intensity Rx (or the light receiving intensity Rx and the beam wonder w (FIG. 16)) of the second laser beam L2 fall within a predetermined range.

As described above, by correcting the emission conditions of the first laser beam L1 for uplink in real time according to the ever-changing atmospheric conditions, the second laser beam L2 transmitted from the spacecraft S is stabilized. Reception can be maintained. Therefore, according to the present embodiment, it is possible to realize highly adaptable spatial optical communication capable of following the ever-changing atmospheric state.

On the other hand, even if the above-mentioned second loop control is executed a plurality of times, the light receiving intensity Rx of the second laser beam L2 may not be within the predetermined intensity range. Therefore, in the present embodiment, when the light receiving intensity Rx does not fall within the predetermined range even after the second loop processing is continuously executed N times (“Yes” in step 108), the control unit 40 performs the third loop processing. Is configured to run. The value of N can be arbitrarily set, and is set to, for example, a natural number of 3 or more.

(Third loop processing)
As a factor that the light receiving intensity Rx of the second laser beam L2 does not fall within the predetermined range even if the above-mentioned second loop processing is executed, the first laser beam L1 emitted from the transmission unit 20 is targeted due to the atmospheric condition or its fluctuation. It can be mentioned that the point (spacecraft S) has not been properly reached. Therefore, in the third loop process, the emission direction of the first laser beam L1 from the transmission unit 20 is modified 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 the imaging data of the scattered lights L1sx and L1sy of the first laser beam L1 in the atmosphere from the beam monitor 33 (step 201). The control unit 40 uses the image captured by the camera 336 of the beam monitor 33 to determine the beam position of the scattered light L1s of the first laser light L1 on the X-plane and the Y-plane (see FIG. 9) (emission direction from the transmission unit 20. ) Is detected (steps 202, 203). In the example shown in FIG. 9, the beam position on the X plane is obtained from the image of the scattered light L1sx directly incident on the camera 336, and the beam position on the Y plane is the third mirror 334 installed on the X axis. It is obtained from the image of the scattered light L1sy incident on the camera 336 via the camera.

The control unit 40 calculates and determines the two-dimensional coordinates of the first laser light scattered light L1s given from the beam positions of the X-plane and the Y-plane, respectively (steps 204 and 205, FIG. 10). As a result, the propagation direction of the first laser beam L1 on each of the X-plane and the Y-plane can be grasped, and by superimposing these, it is possible to estimate at which point in the sky the first laser beam L1 is located. ..

The control unit 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). When the determination result here is "No", when the control unit 40 determines that the beam position is shifted in a predetermined direction from the initially set value on at least one of the X-plane and the Y-plane, The emission mirror 223 of the transmission unit 20 is adjusted in the direction of eliminating the shift amount (steps 207, 208, 209). As a result, the accuracy of reaching the spacecraft S of the first laser beam L1 is improved, and as a result, the light receiving intensity Rx of the second laser beam L2 transmitted from the spacecraft S can be improved.

When it is determined from the beam positions on the X-plane and the Y-plane that the first laser beam L1 is traveling toward the target point (“Yes” in step 206), the decrease in the light receiving intensity Rx is another factor. Since it is determined to be based on the above, the control unit 40 ends the process while maintaining the emission direction of the first laser beam L1 at the current set value (step 210).

As described above, the space optical communication device G of the present embodiment has an uplink (first laser beam L1) so that the light receiving intensity Rx of the downlink (second laser beam L2) from the spacecraft S becomes a target value. The emission conditions are automatically corrected. As a result, the uplink can be optimized by following the ever-changing atmospheric conditions, and as a result, stable communication quality can be ensured regardless of atmospheric influences.

Further, according to the present embodiment, since the seeing monitor 31 and the light receiving 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, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made.

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 measures the distance between a spacecraft and a ground station with a laser across the earth's atmosphere (optical satellite distance measurement, active debris observation), and a laser between the spacecraft and power receiving equipment with the earth's atmosphere sandwiched between a transmission line. The present invention can also be applied to a system (optical energy transmission) or the like that transmits energy by means of. Further, the laser used in the space optical communication device has been described as an infrared laser which is a typical example, but the present invention is not limited to this, and visible light may be used.

Further, in the above embodiments, examples in which the seeing monitor 31 as the first detection unit, the light receiving intensity monitor 32 as the second detection unit, and the like are integrally attached to the outer peripheral portion of the telescope 10 have been described. It is also possible to install the detector inside the telescope. Further, the light receiving intensity monitor as the second detection unit may be composed of a light receiving sensor of the downlink laser light focused by the telescope.

Further, in the above embodiment, the spreading angle and the emission intensity of the first laser beam L1 are determined based on the atmospheric condition (output of the seeing monitor 31) and the light receiving intensity of the second laser beam L2 (output of the light receiving intensity monitor 32). It was configured to control, but is not limited to this. For example, the above conditions of the first laser beam L1 may be controlled based only on the light receiving intensity of the second laser beam L2.
Similarly, the beam monitors 33 shown in FIGS. 8 to 11 were used to detect the emission direction (beam position) of the first laser beam L1, but the present invention is not limited to this, and the emission direction of the first laser beam L1 can be detected. A beam monitor having other configurations may be adopted.

10 ... Telescope 20 ... Transmitter 31 ... Seeing monitor (second detector)
32 ... Light receiving intensity monitor (first detector)
33 ... Beam monitor (3rd detector)
34 ... Observer 40 ... Control unit G ... Spatial optical communication device L1 ... First laser beam (uplink)
L2 ... 2nd laser beam (downlink)
S ... Spacecraft

Claims (10)

A transmitter that transmits the first laser beam to the spacecraft,
A receiver that receives the second laser beam transmitted from the spacecraft, and
The first detection unit that detects the light receiving intensity of the second laser beam, and
A spatial optical communication device including a control unit that generates a control signal for controlling the spread angle and power of the first laser beam based on the output of the first detection unit. The air-optical communication device according to claim 1.
The control unit is a spatial optical communication device that generates a control signal that expands the spread angle of the first laser beam and increases the power when the light receiving intensity of the second laser beam is less than a predetermined range. The spatial optical communication device according to claim 1.
The control unit is a spatial optical communication device that generates a control signal that narrows the spread angle of the first laser beam and reduces the power when the light receiving intensity of the second laser beam exceeds the predetermined range. The spatial optical communication device according to any one of claims 1 to 3.
It has a light receiving surface that receives the second laser beam, and further includes a second detection unit that detects atmospheric fluctuations on the propagation path of the second laser beam.
The control unit is a spatial optical communication device that generates a control signal for controlling the spread angle and power of the first laser beam based on the outputs of the first detection unit and the second detection unit. The spatial optical communication device according to claim 4.
The second detection unit is a spatial optical communication device attached to the reception unit. The spatial optical communication device according to any one of claims 1 to 5.
A third detection unit for detecting the emission direction of the first laser beam is further provided.
The control unit is a spatial optical communication device that generates a control signal for correcting the emission direction of the first laser beam transmitted from the transmission unit based on the output of the third detection unit. The spatial optical communication device according to claim 6.
The third detection unit is a spatial optical communication device including a camera arranged in the transmission unit and photographing scattered light of the first laser light by the atmosphere. The spatial optical communication device according to claim 7.
The camera acquires a projected image of the scattered light on a first plane and a projected image of the scattered light on a second plane that intersects the first plane at a predetermined angle. Communication device. The spatial optical communication device according to any one of claims 1 to 8.
The receiving unit is a spatial optical communication device that is a telescope that collects the second laser beam. Send the first laser beam to the spacecraft,
Upon receiving the second laser beam transmitted from the spacecraft,
A spatial optical communication method for controlling the spread angle and power of the first laser beam based on the light receiving intensity of the second laser beam.

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