JPH03100483A - Light beam scanning device - Google Patents

Abstract

PURPOSE:To accomplish capture and tracking between satellites in optical communication by extracting only received light beam by means of a beam splitter and controlling a deflector. CONSTITUTION:A point ahead deflector 1 inputs transmitted beacon light polarized in a Y-axis direction in accordance with a command signal for making the beam turn to a movement predicted position and deflects it in terms of a Y-axis. The light is rotated by 90 deg. by a lambda/2 wavelength plate, deflected in terms of an X-axis to be two-dimensionally deflected and allowed to scan. Then, it is made to pass the beam splitter 2 and guided to a capture and tracking deflector 3. The deflector 3 outputs Y-axis polarized light, which is converted to counterclockwise circularly polarized light by a lambda/4 wavelength plate 4, beam-expanded 6 and transmitted to a target satellite through a pointing mirror 5. The received beacon light is set clockwise circularly polarized light, converted to X-axis polarized light orthogonally crossed with the transmitted beam by the lambda/4 wavelength plate 4, converted to the Y-axis polarized light by the deflector 3 and reflected by the beam splitter 2 to be guided to a photodetector 7. By controlling the deflector 3 according to the deviation of relative angle detected by a detector 7, the target satellite and the direction of the line of sight of an operator are made coincident.

Description

[Detailed Description of the Invention] [Summary] Regarding an optical beam scanning device applied to acquisition and tracking technology between space optical communication satellites, the present invention relates to an optical beam scanning device that can perform acquisition and tracking by optical communication without relying on mechanical methods. With the aim of realizing a beam scanning device, we use electrical/optical acquisition/tracking and point-ahead deflectors to control the deflectors based on the received optical beam to separate the transmitted and received optical beams. In addition to capturing and tracking, the deflection axes of both deflectors are orthogonal to each other with a beam splitter in between, and only the received light beam is extracted by the beam splitter.

[Industrial application field]

The present invention relates to a light beam scanning device, and more particularly to a light beam scanning device applied to acquisition and tracking technology between space optical communication satellites.

Large-capacity optical communication between satellites or in deep space is expected to be realized around the 21st century, but the pointing and tracking technology in this case can be compared to a telescope. This technology captures the signal light emitted by the target satellite, which is the other party of optical communication, within its field of view and keeps it centered in its field of view, and is one of the essential technologies for forming optical lines in space. .

[Conventional technology and issues]

As a milestone for the realization of space optical communications, as shown in Fig.
), the orbital velocities VG and VL of GEO and LEO with respect to the earth are given by the following approximate expressions.

ve=F77go1go1 Liuko: GEO ■L-f ding7go711τgo: LEO However, the gravitational constant u = 398,603 kl"/s - Earth's radius r-6,3781ai.

Based on the above formula, the values regarding the orbits of GEO and LEO are approximately as shown in the following table.

table Also, the relative angular velocity ω of LEO as seen from GEO.

If both satellites are in the same orbital plane, then CO3ω7Δ
T! (r+hc)-(r+ht)CO5(ωL-ωc)Δt
÷ [((r+he)"+(r+ht)'2(r+h
G) (r+h t)CO5(a+ L-ωG)ht
) ] I/! is given by Note that the maximum angular velocity is Max (ω, ) = 0.012 (deg/s).

ht = 1,000k]I becomes.

Here, the round trip time of light between GEO and LEO is approximately 0.25
seconds, GEO receives LEO's beacon light and
By the time the GEO beacon light, which is controlled by determining the direction of O and directing the light beam in that direction, reaches LEO, LEO will have moved a maximum of 21 am even if there is no processing delay.

On the other hand, the diffraction angle θ4 of the beacon light is given by θd −2,44Xλ/D (λ is the wavelength used and D is the antenna diameter), so λ−0.8μs, D=30
Even if the beacon light is narrowed down to the diffraction limit of θ−6.
5, crrad, and the light beam with a diameter of 30c + m is 40
．． If you move OOOkm away, it will expand to 260+w.

In this case, if a 100s+H semiconductor laser is used, the received power will be 0.1 even if the propagation loss in the middle is zero.
decreases to 3 μ−.

Therefore, widening the beam width to facilitate acquisition and tracking has a limit in terms of received power, but the control range of the optical beam can absorb random errors such as thermal distortion of the antenna pool and attitude fluctuation. Therefore, it must be widened to about 0.6 degrees.

Space optical communication is still in the research stage at this stage, but methods that control light beams by mechanical scanning have been proposed as this type of acquisition and tracking technology. Because of the slow speed, high-speed capture and tracking is not possible.■
The scanning movable part cannot withstand long-term use in the space environment.
■It is naturally expected that there will be problems such as interference with the attitude control of the satellite body due to the scanning reaction force, and even adverse effects on the control of the light beam.

Therefore, an object of the present invention is to realize a light beam scanning device that can capture and track by optical communication without relying on a mechanical method.

[Means to solve the problem]

In order to achieve the above object, in the optical beam scanning device according to the present invention, as shown in principle in FIG. A point ahead deflector 1 is arranged in series on the optical path and receives a command signal for directing the beam to a predicted moving position.
, a beam splitter 2 that transmits the transmitted beacon light outputted from the point-ahead deflector 1 as it is, and an electrical/optical device arranged symmetrically with the point-ahead deflector 1 with respect to the beam splitter 2. an acquisition/tracking deflector 3 consisting of a deflector and a λ/2 wavelength plate, which deflects the transmitted beacon light transmitted through the beam splitter 2 in mutually orthogonal directions;
λ/ which converts the transmitted beacon light output from the
4 wavelength plate 4 and the λ/4. While transmitting the output light of the wavelength plate 4, the receiving beacon light having a circularly polarized light set in advance in a rotation direction opposite to the circularly polarized light of the output light of the λ/4 wavelength Fi4 is reflected to the λ/4 wavelength plate 4. A pointing mirror 5 to send, a beam expander 6 provided between the pointing mirror 5 and the λ/4 wavelength plate 4, and a beam splitter 2 that detects the reflected light and deflects it for capturing and tracking. The beam splitter 2 reflects only the received beacon light output from the capture/tracking deflector 3.

[For production]

In Figure 1, the coordinates of the optical system are set such that the X-axis is perpendicular to the plane of the paper and the Y-axis is within the plane of the paper. The point ahead deflector 1 and the acquisition/tracking deflector 3 are an X deflector and a λ
The basic components are a /2 wavelength plate and an X deflector.
As shown in Figure 2, the X deflector deflects the incident light beam of Y-axis linearly polarized light by θ in the Y-axis direction, and the polarization direction of the linearly polarized light output from this X deflector is set to a λ/2 wavelength plate. By 9
How many times is it rotated by 0 degrees so that it becomes the same deflection axis as the X deflector?
The beam is deflected by θ8 using an X deflector.

The beam splitter 2 is selected to reflect only the Y-axis polarized light and transmit the X-axis polarized light, thereby separating transmitted and received light.

In addition, the beam expander 6 is used to convert the beam diameter of transmitted and received light, and consists of two parabolic mirrors with different focal lengths facing each other, and the beam diameter expansion/reduction ratio is the same. It is determined by the ratio of the focal lengths of As mentioned above, since the spread angle of the beam is proportional to the antenna diameter, in order to obtain sharp directivity, the beams are arranged in a direction in which the transmitted beam diameter is expanded.

The pointing mirror 5 covers large offsets that cannot be tracked by the deflector 1.3.
Only this part needs to be scanned mechanically.

First, it is assumed that the transmitted beacon light is linearly polarized in the Y-axis direction through a light source, a collimator lens, and a polarizer (not shown).

This transmitted beacon light is input to the point ahead deflector 1, first deflected in the Y axis by the X deflector in response to a command signal to direct the beam to the predicted movement position, and then rotated by 90 degrees by the λ/2 wavelength plate. The beam is then subjected to an X-axis deflection by an X deflector, and is deflected and scanned two-dimensionally.

Passing through the beam splitter 2 and capturing/tracking deflector 3
The transmitted beacon light guided to the X deflector of
Since the eigenaxis of the deflector coincides with the eigenaxis of the beam, it is deflected in the X-axis direction, and by passing through the λ/2 wavelength plate, the polarization direction of the beam coincides with the eigenaxis of the X-deflector, so the beam is It will also be deflected in the Y-axis direction.

Therefore, since the output beam from the acquisition/tracking deflector 3 is Y-axis polarized light, the wavelength plate is set so that the relative angle θ with the fast axis of the λ/4 wavelength plate 4 is 45 degrees. In this case, the output beam is converted into left-handed circularly polarized light, as is known in the art.

Then, the output light from the λ/4 wavelength plate 4 is expanded by a beam expander 6, and the beacon light is sent out in an arbitrary direction toward the target satellite via the pointing mirror 5.

On the other hand, the received beacon light is set to be right-handed circularly polarized light, which is opposite to that of the transmitted beacon light. This can be done by predetermining between the two satellites so that the polarization directions of the linearly polarized beacon lights incident on the point-ahead deflector 1 are orthogonal. This can be easily achieved by manipulating the child.

Therefore, the received beacon light is converted into X-axis polarized light orthogonal to the transmitted beacon light by the λ/4 wavelength plate 4, and the eigenaxis of the Y-axis deflector of the acquisition/tracking deflector 3 forms 90 degrees. Therefore, the received beacon light passes through without being deflected,
After being converted into Y-axis polarized light by the λ/2 wavelength plate, it enters the X-axis deflector, but it is not deflected here as it is perpendicular to the eigenaxis.

The beam splitter 2 that reflects only this Y-axis polarized light separates only the received beacon light and guides it to the photodetector 7.

In order to completely change the line-of-sight direction between the target satellite and itself, the transmitting optical system of the target satellite calculates the relative angular deviation between the beacon light of the target satellite detected by its own photodetector 6 and the line-of-sight of its own receiving optical system. It is regarded as a deviation in the line of sight direction of the system, and the own beacon light is deflected by that amount by controlling the capture/tracking deflector 3 and transmitted to the target satellite, thereby correcting the line of sight of the target satellite.

That is, when considering optical beam control in two-way optical communication, the light detection signal of each satellite is received by the beacon light of one satellite. For this reason, the capture/tracking deflector 3 acts only on its own beacon light and does not act on the received beacon light. The deflector arrangement is reversed,
The transmitted beacon light is transmitted by deflector 1 for Bonito Ahead.
Since it rotates by 0 degrees and becomes X-polarized light, beam splitter 2
Since the light passes through the light and is not guided to the photodetector 7, isolation between transmission and reception is increased.

In this way, it is possible to perform light beam scanning with fewer mechanically movable parts and with increased isolation of light transmission and reception.

〔Example〕

FIG. 3 shows an embodiment of the deflector control system of the optical scanning beam device according to the present invention, in which the point-ahead deflector 1 shown in FIG.
It is controlled by the amplifier 12 and the deflection sensor 13 of the deflector 1. Note that this command value must be used to direct the beam to the predicted position ahead in the direction of movement in order to compensate for the propagation delay of light due to the distance between the satellites and direct the light beam to the target satellite with the desired accuracy. , which indicates a predicted angle commensurate with the predicted position ahead of the movement, and is given from the ground or by onboard instructions from the satellite.

The photodetector 7 shown in FIG. 1 also has a line-of-sight angle θ7. ? It is composed of a CCD sensor 71, a four-quadrant sensor 72, and a mode selector 73, which receive the line of sight angle θ, .
is being sent to.

The switch position of the mode selection switch 20 is initially in the initial acquisition position shown in the figure, which is the mode for capturing the target satellite for the first time within a narrow field of view at the initial stage of optical line formation in space. The limiter 2 calculates the deviation between the command value derived from the three-dimensional coordinate axis information that predicted the line of sight of the partner satellite from the board and the feedback signal received from the pointing mirror 5 via the encoder 21.
2, the signal is applied to the acquisition/tracking deflector 3 by a VCO 14 and an amplifier 15.

Incidentally, the output of the deflector 3 detected by a sensor 16 and given a constant gain 17 is added to the output of the limiter 22. Furthermore, since the command value is large in this loop, only the pointing mirror operates mainly. This pointing mirror 5 is used when the LEO is a polar orbit satellite because it requires scanning of ±180 degrees and cannot be replaced with an electric/optical deflector that cannot take a large deflection angle. In addition, deflectors, such as acousto-optic devices, are currently capable of deflection of 2 degrees or more, and the access time to a predetermined deflection angle is about 10 μs, which is sufficient for high-speed beam scanning of about 0.6 degrees. can.

Claims (1)

[Claims] Two electrical/optical deflectors whose deflection axes are orthogonal to each other are
A point-ahead deflector (1) that is arranged in series on an optical path with a two-wavelength plate in between and receives a command signal for directing a beam to a predicted moving position;
a beam splitter (2) that transmits the transmitted beacon light output from 1) as it is; and an electric/optical deflector arranged symmetrically with the point-ahead deflector (1) with respect to the beam splitter (2). and a λ/2 wavelength plate, and the beam splitter (
an acquisition/tracking deflector (3) that deflects the transmitted beacon light transmitted through the acquisition/tracking deflector (3) in mutually orthogonal directions; and a capture/tracking deflector (3) that converts the transmitted beacon light output from the acquisition/tracking deflector (3) into circularly polarized light. λ/4 wavelength plate (4) and the λ/4 wavelength plate (4);
It transmits the output light of the 4-wavelength plate (4), and also reflects the received beacon light, which is circularly polarized light set in advance in the direction of rotation opposite to the circularly polarized light of the output light of the λ/4-wavelength plate (4). a pointing mirror (5) feeding the /4 wavelength plate (4); and the pointing mirror (5) and the λ/4 wavelength plate (4).
a beam expander (6) provided between the beam expander (6) and a photodetector (7) that detects the reflected light of the beam splitter (2) and controls the capture/tracking deflector (3); Equipped with
An optical beam scanning device characterized in that the beam splitter (2) reflects only the received beacon light output from the acquisition/tracking deflector (3).