JP2002335218A - Laser directing method for spatial optical communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the establishment of a laser link or stability in the maintenance of laser link by correcting a fluctuation in the directed direction of laser caused by atmospheric oscillation in spatial laser communication between the ground and an artificial satellite. SOLUTION: A laser for artificial star generation for generating an artificial star and a laser for communication are emitted in the same propagating direction, the artificial star is generated by generating a light emission by a resonance disturbance in an Na layer around the height of about 100 km, the light of this artificial star is observed by a ground optical station and a fluctuation in the position of the observed image of the artificial star is measured. Thus, the transmitting direction of the laser for communication is controlled to correct the direction fluctuation caused by the atmospheric oscillation and the laser for communication is directed to an artificial satellite S.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention carries out spatial optical communication between a communication partner station, such as an artificial satellite, which has an optical communication function and is higher than the atmospheric layer and a ground station having an optical communication function. A laser pointing method for spatial optical communication that corrects the fluctuation of the pointing direction of the laser emitted from the ground station to the communication partner station due to the fluctuation of the atmosphere, especially to correct the fluctuation of the pointing direction of the laser due to the fluctuation of the atmosphere The present invention relates to a technology that can improve the pointing accuracy of a laser and facilitate maintenance of a laser communication line.

[0002]

2. Description of the Related Art In laser communication in space, the spread angle of a laser is reduced depending on the intensity of a laser used, a transmission distance to a communication partner station, a desired communication speed, and signal detection performance on a receiving side. Laser transmission may be required. When such spatial optical communication is applied to the communication between the communication partner station, which is higher than the atmospheric layer such as a satellite, and the ground, the effects of laser beam direction fluctuations due to atmospheric fluctuations can be avoided. Absent. In other words, the phase of the laser wavefront is disturbed by the fluctuation of the atmosphere on the transmission line of the laser up to an altitude of about 10 km, so that the direction of the laser fluctuates slightly and the shape of the laser beam is deformed with propagation. Therefore, it is necessary to correct the directivity direction.

For a downlink laser transmitted from an artificial satellite to the ground, fluctuations in the received light intensity due to variations in the intensity distribution at the telescope aperture caused by atmospheric turbulence are suppressed by increasing the aperture of the telescope on the ground. can do. In addition, the distance from the point where the laser was affected by atmospheric turbulence to the receiving point on the ground (about 10 km)
, It is unlikely that the downlink laser line would be cut off due to atmospheric turbulence.

On the other hand, in the case of an uplink laser transmitted from the ground to an artificial satellite, the distance from a point subject to atmospheric turbulence to the satellite (at an altitude of about 300 km or more) is long, so that the directional fluctuation angle due to the fluctuation varies with the laser itself. If it is large compared to the divergence angle, the laser cannot reach the satellite. In other words, in the case of an uplink laser from the ground to an artificial satellite, the distance from the influence of atmospheric turbulence to the arrival of the artificial satellite is long, so even a small change in direction leads to interruption of the uplink laser line. Such a situation is a concern. Therefore, in order to irradiate the satellite with the uplink laser, it is very important to correct the direction of the laser in the optical communication device on the ground.

As a method of correcting the pointing direction of the uplink laser from the ground to the artificial satellite, a downlink laser is received by a light receiving telescope on the ground, and the incident direction of the downlink laser to the light receiving telescope is detected by using a camera device. ,
A method is known in which an optical path difference angle is added to the incident direction, and the emitted laser is directed to a satellite.

[0006] The optical path difference angle means that the distance between communication points such as laser communication between the ground and a satellite is long, and
This is a factor to consider when moving with each other. This angle adjusts the direction of the laser to be emitted in anticipation of the distance the opponent moves before the laser reaches the opponent. Of the moving speed vector of the other party when looking at the other party from the laser transmitting side, it can be obtained from the component perpendicular to the line of sight, and in optical communication between the ground and artificial satellites, It can be calculated based on the planned trajectory data.

[0007]

However, in the above-described method of pointing an uplink laser for correcting a direction change due to atmospheric turbulence in optical communication between terrestrial satellites as described above, a case where a downlink laser does not arrive is described. Cannot measure the direction change with the light receiving telescope on the ground, and cannot correct the direction change. In other words, this correction method aims at maintaining the laser link after the laser link between the ground and the satellite is established, and cannot be applied in the process of establishing the laser link.

Further, in optical communication between terrestrial satellites, the optical path difference angle is about several tens μrad at the maximum, and the propagation path of the uplink laser and the downlink laser is slightly different depending on the optical path difference angle. The difference between the propagation paths based on the optical path difference angle is equivalent to several tens of cm at an altitude of 10 km. Due to such a shift in the path between the downlink laser and the uplink laser, the direction fluctuation due to atmospheric fluctuation measured using the downlink laser does not always match the direction fluctuation due to atmospheric fluctuation in the propagation path of the uplink laser. Without this, there is a problem that the direction fluctuation of the uplink laser is not accurately corrected.

[0009]

According to a first aspect of the present invention, there is provided a communication partner station having an optical communication function and having a higher communication layer than an atmospheric layer and a ground station having an optical communication function. When performing spatial optical communication with a station, a laser pointing method for spatial optical communication that corrects the fluctuation due to atmospheric fluctuations in the pointing direction of the laser emitted from the ground station to the communication partner station, wherein the ground station Is to provide an artificial star generation laser light source for generating artificial stars between the atmosphere layer and the communication partner station, so that the propagation direction of the artificial star generation laser and the communication laser is the same, By emitting the star-generating laser in the direction of the communication partner station, observing the generated artificial star at the ground station, and considering the observed light receiving position of the artificial star as the emission direction of the communication laser, the communication laser Due to atmospheric turbulence Characterized in that so as to correct the direction change.

Therefore, in the laser pointing method for space optical communication according to the first aspect, an artificial star is generated between the atmosphere layer and the communication partner station by using an artificial star generating laser for generating an artificial star. By observing the generated artificial star, it is possible to know the beam direction fluctuation due to the fluctuation of the atmosphere in the propagation path from the ground station to the artificial star, and to set the communication laser in the same propagation direction as the artificial star generating laser. By setting it to emit, the light receiving position of the artificial star is regarded as the emission direction of the communication laser because the fluctuation due to atmospheric fluctuation acts almost equally on the artificial star generation laser and the communication laser. Accordingly, it is possible to correct the direction fluctuation due to the atmospheric fluctuation of the communication laser.

According to a second aspect of the present invention, in the first aspect, the communication partner station is an artificial satellite orbiting a known orbit, and the ground station is a communication laser based on an observed artificial star image. The communication laser is emitted so that the emission direction matches the target position of the artificial satellite in view of the optical path difference angle.

Therefore, in the laser pointing method for spatial optical communication according to the second aspect of the present invention, even when the communication laser is emitted to a target position in which an optical path difference angle of an artificial satellite as a communication partner station is projected, the communication laser is emitted. Can be known based on the observation image of the artificial star generated by the artificial star generating laser beam propagating along the same path.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, a laser pointing method for spatial optical communication according to the present invention will be described with reference to a terrestrial optical station E as a ground station and an artificial satellite S equipped with an optical communication device as a communication partner station. An embodiment applied to communication with the server will be described.

FIG. 1 is a principle explanatory diagram for explaining a basic principle of a laser pointing method for optical communication between terrestrial satellites using artificial stars. In FIG. 1, a terrestrial optical station E
Has an optical communication device and forms a laser link with an artificial satellite S equipped with an optical communication device. A downlink laser is emitted from an artificial satellite S traveling in a satellite orbit, and a communication laser and an artificial star generating laser are emitted from the optical communication device of the ground optical station E in anticipation of the optical path difference angle. .

The artificial star generating laser is tuned to the Na-D line wavelength of 589 nm and has an altitude of about 100 km.
When an artificial star-generating laser is incident on a nearby Na layer, resonance scattering occurs and light is emitted, so that it can be observed from the ground like a star. In addition, artificial star (artifis)
The method of generating the ial star is not limited to the method using the resonance scattering, but may be any method that can generate a light emitting point that can be observed on the ground in a higher layer than an atmospheric layer having an atmospheric fluctuation that affects a communication laser. For example, as another artificial star generation method, there is a method using Rayleigh scattering. This method uses scattering by atmospheric molecules, emits a laser with a short pulse, scatters it in the sky, and observes it with the camera shutter slightly delayed so that the scattered light reaches the ground. It is. However, since an artificial star due to Rayleigh scattering can be generated only at a height of about 20 km at most, a higher altitude is desirable for tracking the artificial satellite S. Therefore, in this embodiment, the resonance scattering of the Na layer is used. Was applied.

On the other hand, the communication laser uses a laser having a different wavelength from that of the artificial star generating laser. Note that the difference in wavelength between the laser for artificial star generation and the laser for communication does not cause a noticeable difference in the influence of atmospheric turbulence, and the difference in directional fluctuation due to the difference in wavelength between the two lasers can be ignored.

Since the light emission due to the resonance scattering occurs at a sufficiently high speed as compared with the fluctuation speed of the atmospheric fluctuation, the fluctuation of the direction of the communication laser due to the fluctuation of the air can be observed as the fluctuation of the position of the artificial star.

Accordingly, the ground station E is provided with an optical communication device for emitting an artificial star generating laser so that the propagation direction of the artificial star generating laser and the communication laser is the same. Laser for star generation is used for artificial satellite S
In the direction of, observe the generated artificial star at the ground station,
By regarding the observed light receiving position of the artificial star as the emission direction of the communication laser, it is possible to correct the direction change due to the atmospheric fluctuation of the communication laser.

That is, if the light from the artificial star generated between the atmospheric layer and the artificial satellite S is observed using the artificial star generating laser, the atmospheric air in the propagation path from the ground optical station E to the artificial star is observed. The direction fluctuation due to fluctuation can be known, and by setting the communication laser to be emitted in the same propagation direction as the artificial star generation laser, the fluctuation due to the atmospheric fluctuation communicates with the artificial star generation laser. Since it acts almost equally to the communication laser, the light receiving position of the artificial star is regarded as the emission direction of the communication laser, so that it is possible to correct the direction fluctuation due to the atmospheric fluctuation of the communication laser.

Further, when the communication partner station is the artificial satellite S orbiting in a known orbit as in this embodiment, the terrestrial optical station E emits the communication laser based on the observed artificial star image. However, by emitting the communication laser so as to match the target (S ′) of the artificial satellite that allows for the optical path difference angle, the fluctuation due to atmospheric fluctuation in the propagation path of the communication laser propagates along the same path. It can be known based on the observation image of the artificial star generated by the artificial star generating laser.

Next, the schematic configuration of the optical communication device installed in the terrestrial optical station E is as shown in FIG. 2, and includes a telescope 1 for laser transmission, a laser directing device 2, a telescope 3 for light reception,
The camera device 4 includes a gimbal mechanism 5.
A laser 6 for communication and a laser 7 for artificial star generation are emitted from the telescope 1 for laser transmission, and the transmission directions of both are set so as to be substantially the same.

In this optical communication device, the camera device 4 is driven by driving the gimbal mechanism 5 in the direction of the target (S ') calculated from the planned flight trajectory of the artificial satellite S.
If the direction of the field of view is adjusted to the direction of the artificial satellite, tracking of the artificial satellite is completed. That is, the gimbal mechanism 5
With the operation of (1), the transmitting direction of the laser transmitting telescope 1 (the irradiation direction of the communication laser 6 and the artificial star generating laser 7) and the receiving direction of the light receiving telescope 3 (the downlink laser 6 'from the artificial satellite S). The light receiving direction) also changes, and the laser link with the artificial satellite S is maintained well.

Here, a specific operation flow of the laser pointing method by the above-described optical communication device will be described with reference to FIG. The laser pointing device 2 includes a pointing direction adjusting mechanism 8, a laser light source 9 for communication, a laser light source 10 for artificial star generation,
And a beam splitter 11 having transmission / reflection characteristics depending on the wavelength of the laser.
The transmission direction of the communication laser and the artificial star generation laser is matched by 1, and the emission direction from the laser transmission telescope 1 is finely adjusted by the directivity adjustment mechanism 8. In addition, mirrors 8a and 8b which can be rotated at a minute angle with high precision are arranged in the directivity adjusting mechanism 8, and the mirrors 8a and 8b
A and 8b receive a drive signal from the camera device 4 and operate to finely adjust the emission direction.

FIG. 4 shows an example of an output screen of the camera device 4 which processes a light-receiving image of the light-receiving telescope 3 and performs fine adjustment control of the emission direction of the communication laser and the artificial star generating laser. The artificial star has a high light emission altitude of about 100 km, and is observed as a substantially point-like image. The point image changes its position due to a change in the pointing direction of the artificial star generating laser due to fluctuations in the atmosphere. In addition, the influence of the fluctuation of the atmosphere during the incidence from the light emission of the artificial star to the light-receiving telescope 3 can be reduced by increasing the aperture of the light-receiving telescope 3 as in the case of receiving the star.

When the output image of the camera device as shown in FIG. 4 is obtained, the tracking of the artificial satellite S is completed by driving the gimbal mechanism 5, and the center of the output screen is the downlink laser. Satellite S based on reception
The received image of the artificial star, which can be regarded as the emission direction of the communication laser 6, is slightly shifted, so that the image of the artificial star overlaps the direction (center position) of the artificial satellite.
If the emission direction of the communication laser 6 is adjusted by the pointing direction adjusting mechanism 8, the fluctuation due to the fluctuation of the atmosphere can be corrected with high precision, and the pointing from the ground optical station E to the artificial satellite S can be performed well. . In addition, laser 7 for artificial star generation
(7 ') from the artificial star generated by the above-mentioned method is subjected to a direction change due to the fluctuation of the atmosphere on the path reaching the ground optical station E. Therefore, strictly speaking, the observation image of the artificial star is used for communication. Although it deviates from the emission direction of the laser 6, even if it undergoes a direction change in the low altitude (about 10 km altitude) atmospheric layer, the deviation in the propagation direction from when it reaches the ground optical station is extremely small. Therefore, it is sufficient to correct the emission direction of the communication laser 6 in the process of establishing the laser link and maintaining the laser link after the establishment.

When the communication partner station is an artificial satellite which cannot be stopped at a fixed position such as an orbiting satellite, the light receiving telescope 3 is used.
The point at which the satellite S is predicted to move according to the time that elapses from the time when the satellite S emits the downlink laser received by the satellite S to the time when the communication laser 6 emitted from the terrestrial optical station E reaches the satellite S. A communication laser must be sent to the computer. The target (S ') of the artificial satellite in which the optical path difference is included can be calculated from the planned flight trajectory of the artificial satellite, and the position of the target changes every moment as the optical path difference changes. The target S ′ on the output screen, which includes the optical line difference angle, is added in the process of processing the output screen in the camera device 4.

As described above, the drive signal is continuously output to the pointing direction adjusting mechanism 8 so that the target (S ') of the artificial satellite in which the optical path difference angle is included and the image of the artificial star overlap. In the transmission of the communication laser to the artificial satellite S,
In addition to following the change in the optical path difference angle, it is possible to correct a change in the directivity of the communication laser due to the fluctuation of the atmosphere. Also, since the altitude of an artificial star generated using resonance scattering in the Na layer is as high as about 100 km, even if there is a difference between the direction of the artificial star viewed from the ground and the actual direction of the artificial satellite S, the The difference can be kept small compared to the spread angle of the communication laser. Therefore, by finely adjusting the emission direction by driving the above-described pointing direction adjusting mechanism 8, it becomes possible to satisfactorily direct the communication laser toward the artificial satellite.

[0028]

As described above, according to the laser pointing method for spatial optical communication according to the first aspect of the present invention, the atmosphere layer and the communication partner station are communicated with each other by using the artificial star generating laser for generating the artificial star. If an artificial star is generated during the observation and the light from the generated artificial star is observed, the fluctuation due to the fluctuation of the atmosphere in the propagation path from the ground station to the artificial star can be known.
By setting to emit the communication laser in the same propagation direction as the artificial star generation laser, the direction fluctuation due to atmospheric fluctuation acts almost equally on the artificial star generation laser and the communication laser, By regarding the light receiving position of the artificial star as the emission direction of the communication laser, it becomes possible to correct the direction fluctuation due to the atmospheric fluctuation of the communication laser. As a result, even when the laser link with the communication partner station is not established, it is possible to correct the direction fluctuation due to atmospheric turbulence, and to apply to the process of generating the laser link between the communication partner station and the ground station. Can be done.

In addition, unlike the conventional case where all the light incident on the aperture of the light receiving telescope is measured when measuring the fluctuation of the atmosphere using the downlink laser, the communication from the ground to the communication partner station is performed. The effect of atmospheric fluctuations in the direction of propagation of the communication laser (directional fluctuation) can be measured directly, so that the fluctuation of the directivity can be measured with high accuracy, and the It is possible to improve the pointing accuracy of the communication laser.

According to the laser pointing method for spatial optical communication according to the second aspect of the present invention, even when the communication laser is emitted to a target position in which an optical path difference angle of an artificial satellite as a communication partner station is projected, the communication laser is emitted. Fluctuations due to atmospheric turbulence in the propagation path of the laser can be known based on the observation image of the artificial star generated by the artificial star generating laser propagating along the same path. As a result, highly accurate correction of direction fluctuation due to atmospheric fluctuations of the communication laser can be realized.

[Brief description of the drawings]

FIG. 1 is a principle explanatory diagram for explaining a basic principle of a laser pointing method for spatial optical communication according to the present invention.

FIG. 2 is a schematic perspective view illustrating a main configuration of an optical communication device installed in a terrestrial optical station.

FIG. 3 is a configuration diagram showing an outline of optical transmission and reception together with an internal configuration of a laser directing device.

FIG. 4 is an image diagram of an output screen of a camera device when an artificial star is observed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Telescope for laser transmission 2 Laser pointing device 3 Telescope for light reception 4 Camera device 5 Gimbal mechanism 6 Laser for communication 6 'Downlink leather 7 Laser for artificial star generation 7' Light from artificial star 8 Direction adjustment mechanism 8a Mirror 8b Mirror 9 Laser light source for communication 10 Laser light source for artificial star generation 11 Beam splitter

Claims (2)

[Claims] 1. An optical communication function is carried out from a ground station to a communication partner station when optical communication is performed between a communication partner station having an optical communication function and located above the atmospheric layer and a ground station having an optical communication function. A laser pointing method for spatial optical communication that corrects the fluctuation of the pointing direction of the laser due to atmospheric fluctuations, wherein the ground station includes an artificial star for generating an artificial star between the atmospheric layer and a communication partner station. A laser light source for generation is provided so that the propagation direction of the artificial star generation laser and the communication laser is the same, and the artificial star generation laser is emitted in the direction of the communication partner station, and the generated artificial star is grounded. Observed by a station, and the observed position of the artificial star is regarded as the emission direction of the communication laser, so that the direction fluctuation due to atmospheric fluctuations of the communication laser is corrected. Laser finger Method. 2. The communication partner station is an artificial satellite orbiting in a known orbit, and the ground station is configured such that an emission direction of a communication laser based on an image of an observed artificial star is determined by an artificial satellite in which an optical path difference angle is anticipated. 2. The laser pointing method for space optical communication according to claim 1, wherein the communication laser is emitted so as to coincide with the target position.