JP2017123500A - Optical space communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical space communication device that can miniaturize the dimension of an optical antenna.SOLUTION: An optical space communication device includes: a primary mirror having a through-hole at the central portion thereof; a secondary mirror which has a through-hole at the center portion thereof, into which light reflected from the primary mirror is incident, and from which the light is reflected as a first beam to the through-hole of the primary mirror; a transmission lens which is disposed at the opening portion of the secondary mirror to be coaxial with the secondary mirror, and refracts incident light and passes the incident light as a second beam through the through-hole of the secondary mirror; a reflecting mirror having a through-hole for reflecting the first beam and passing the second beam therethrough; receiving means for receiving the first beam reflected by the reflecting mirror; and angle deviation detecting means for receiving the second beam passing through the through-hole of the reflecting mirror and detecting an angular deviation of the second beam.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical space communication device for performing space communication with a device at a distant place using light.

  For example, a laser beam that has been signal-modulated in one device is emitted into space, and the other device installed at a distance from the device receives the laser beam and performs signal demodulation to perform communication. Optical space communication systems are known. (For example, Patent Document 1)

  In such an optical space communication system in which a laser beam is transmitted from a transmitter to space and a laser beam after long-distance spatial propagation is received by a receiver, the beam diameter of the transmitted laser beam is expanded to a predetermined size. An optical antenna is provided that collects a laser beam that is emitted into the space and transmitted from the partner station and propagated through the space for a long distance to expand the beam diameter and is introduced into the receiver. Since the beam diameter increases as the communication distance becomes longer, the conventional optical antenna for long distance communication requires a large aperture. The optical antenna described in Patent Document 1 is configured using a Cassegrain type reflective telescope. On the other hand, the angle range of the laser beam that can be received by the receiver of the conventional optical space communication system is limited to a narrow range. This is because the angle deviation of the laser beam with respect to the optical antenna is enlarged when the light is collected by the optical antenna, so that it is easy to deviate from the angular range in which the receiver can receive light. Therefore, even if the optical antenna receives the laser beam, the probability of reaching the receiving device is extremely low.

  In order to solve this problem, in a conventional optical space communication system, a laser beam is collected by an optical antenna, and a part of the laser beam is branched by a beam splitter while being introduced into a receiving device. It is configured to detect with an optical sensor using an image sensor such as a coupled device. This optical sensor transmits a signal related to the light receiving position on the sensor surface to the optical antenna control unit. Based on this signal, the optical antenna control unit calculates the angular deviation of the laser beam and adjusts the direction or angle of the entire optical antenna or its internal optical elements to adjust the laser beam within the receivable angle range of the receiver. The angle deviation is corrected. Furthermore, in the conventional optical space communication system, the detection resolution and the detection speed are insufficient with one optical sensor. Therefore, in addition to the first optical sensor with a wide detection angle range, the detection resolution is not limited to a narrow detection angle range. The second optical sensor, which is excellent in detection speed, is used in a complementary manner. A quadrant photo detector (QD) is typically used as the second optical sensor.

JP 2007-150455 A

Since the conventional optical space communication system is configured as described above, even if the angular deviation of the transmitted beam from the partner station that was first received by the optical antenna is large, the angular deviation is detected and optically adjusted by the optical sensor. It is possible to receive the laser beam by the receiving device by the correction control by. However, the conventional optical space communication system has the following problems.
A part of the laser beam received by the optical antenna needs to be branched to the first optical sensor and the second optical sensor by a beam splitter. For this reason, since the energy of the laser beam received by the optical antenna decreases when reaching each optical sensor, it is necessary to set the aperture of the optical antenna large in consideration of this energy decrease. This leads to an increase in the size and size of the apparatus. In particular, there is a great problem when the apparatus is mounted on a mobile body having a limited mounting dimension such as a satellite.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an optical space communication device capable of reducing the size of an optical antenna.

An optical space communication apparatus according to the present invention is
A primary mirror having a through hole in the center;
A sub-mirror having a through-hole at the center, the light reflected by the primary mirror being incident, and reflecting the light toward the through-hole of the primary mirror as a first beam;
A transmission lens that is installed coaxially with the secondary mirror at the opening of the secondary mirror, refracts incident light, and passes through the through-hole of the secondary mirror as a second beam;
A reflector having a through-hole at the center for reflecting the first beam and allowing the second beam to pass;
Receiving means for receiving the first beam reflected by the reflecting mirror;
An angular deviation detecting means for receiving the second beam that has passed through the through-hole of the reflecting mirror and detecting an angular deviation of the second beam;
It is characterized by comprising.

  According to the present invention, there is an effect that an optical space communication device capable of reducing the size of the optical antenna can be realized.

The block diagram which shows the optical space communication apparatus by Embodiment 1 of this invention Configuration diagram showing a space optical communication apparatus according to Embodiment 2 of the present invention

  Hereinafter, in order to describe the present invention in more detail, the best mode for carrying out the present invention will be described with reference to the accompanying drawings.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram showing a configuration of an optical space communication apparatus according to Embodiment 1 of the present invention. In FIG. 1, 1 is an optical antenna, 2 is a primary mirror constituting the optical antenna, 3 is a secondary mirror constituting the optical antenna, 4 is a transmission lens, 5 is a collimator lens, and 6 is a polarization beam splitter which is a beam splitter. , 7 is a beam splitter that is a reflection mirror, 8 is a relay lens that is a relay optical system, 10 is a transmission device, 11 is a reception device that is reception means, 12 is a coarse capture sensor that is angle deviation detection means, and 13 is a focus. is there.

  The transmission apparatus 10 generates a signal-modulated laser beam (transmission laser beam, transmission light). The transmission laser beam is incident on the polarization beam splitter 6. The polarization beam splitter 6 is a component that transmits light of P-polarized light component and reflects light of S-polarized light component, and is typically composed of a cubic glass component. Since the laser beam emitted from the transmitter 10 is polarized in a substantially straight line in which the P-polarized component is dominant, almost all energy is transmitted through the polarization beam splitter 6.

  The transmitted laser beam that has passed through the polarizing beam splitter 6 is focused on the focal point 13 by the collimating lens 5 that is a refractive lens having positive power. The primary mirror 2 and the secondary mirror 3 constitute a Cassegrain type reflective telescope. The focal point of the Cassegrain type telescope coincides with the focal point 13. Therefore, the transmission laser beam that has passed through the focal point 13 is reflected in the order of the secondary mirror and the primary mirror, so that the beam diameter is enlarged, converted into parallel light, and emitted to the space (right side in FIG. 1). .

  When the optical space communication device is used only for reception, a configuration in which the transmission device 10 and the polarization beam splitter 6 are not provided is also possible.

  Next, reception will be described. The received laser beam arriving from the other station is incident on a main mirror 2 having a through-hole at the center (from the right side in FIG. 1) due to diffraction spread due to propagation over a long distance, and spreading into a large aperture (from the right side in FIG. 1). To do. At this time, the received laser beam is first shielded by the secondary mirror 3, and then only the portion cut out by the effective reflection range of the primary mirror 2 is reflected, and then reflected by the secondary mirror 3 to be the first beam. The light is condensed at the focal point 13.

  Typically, since the primary mirror 2 and the secondary mirror 3 are circular, the reception laser beam is a donut-shaped circular beam with the center removed. Here, the secondary mirror 3 is also provided with a through-hole which is a through-hole in the central portion. The through hole is manufactured so that the through hole and the inner diameter of the donut beam substantially coincide with each other when the donut-shaped received laser beam reaches the secondary mirror 3. That is, the ratio of the width of the through hole of the secondary mirror 3 to the width of the secondary mirror 3 is substantially equal to the ratio of the width of the through hole of the primary mirror 2 to the width of the primary mirror 2. Accordingly, since the receiving laser beam does not originally have a portion corresponding to the through hole, there is no loss of light intensity due to the through hole.

  The received laser beam is converted into substantially parallel light by the collimator lens 5 and enters the polarization beam splitter 6. The reception laser beam incident on the polarization beam splitter 6 is set so that the S-polarized component is almost the same. Alternatively, adjustment is made by using a wave plate (not shown) or the like so that the incident received laser beam becomes almost an S-polarized component. For this reason, the received laser beam is reflected by the polarization beam splitter 6 and bent downward on the paper surface.

  Although FIG. 1 shows a configuration in which the transmission laser beam is caused to travel straight by the polarization beam splitter 6 and the reception laser beam is bent, the present invention is not limited to this, and a configuration in which the transmission laser beam is bent and the reception laser beam is caused to travel straight. It can also be.

  The received laser beam passes through a relay lens 8 that is an equal-magnification telescope composed of two convex lenses and reaches a beam splitter 7. The relay lens 8 is disposed so that the beam splitter 7 and the aperture of the optical antenna 1 (a plane connecting A-A ′ in FIG. 1) have a conjugate relationship by using an imaging function of the lens. That is, due to this conjugate relationship, the beam incident on the center of the opening of the optical antenna 1 reaches the center of the beam splitter 7 even if it has an inclination with respect to the optical axis. The beam splitter 7 is a plane mirror disposed to be inclined with respect to the incident received laser beam, and reflects and bends the received laser beam and introduces it into the receiving device 11.

  The receiving device 11 includes a photodetector that photoelectrically converts the received laser beam and a signal demodulation circuit. Further, a through hole which is a through hole is provided near the center of the beam splitter 7. The inner diameter of the through-hole is substantially the same as the inner diameter of the receiving laser beam whose center portion is cut out in a donut shape, and the center of the through-hole and the inner diameter of the receiving laser beam are substantially the same. ing. Accordingly, since the portion corresponding to the through hole of the received laser beam is originally missing, the received laser beam is bent to the receiving device 11 without causing a loss due to the through hole.

  Next, rough capture will be described. As described above, the angle range of the received laser beam that can be received by the receiver 11 is extremely narrow (typically about several tens of μrad), and some angle correction control is essential for the received laser beam. In order to perform this angle correction control, means for measuring the deviation of the received laser beam from the predetermined target angle range at that time is necessary.

  The correction of the angle deviation is performed by first detecting the angle in real time, and detecting the angle range of a fine capture sensor (corresponding to the QD of the conventional example, which is built in the receiver 11 in FIG. 1) for performing feedback control. It starts with the control of introducing the receiving laser beam into the inside. This initial angle control is referred to herein as coarse capture. In order to perform coarse capture, it is necessary to make the received laser beam incident on a coarse capture sensor 12 (corresponding to a conventional CCD) that detects an angular deviation of the received laser beam. For this reason, it is necessary to branch a part of the received laser beam and supply it to the coarse capture sensor 12.

  Hereinafter, a method of introducing a reception laser beam (hereinafter referred to as a coarse capture laser beam) for the coarse capture sensor 12 will be described. As the coarse capture laser beam, a reception laser beam incident on the transmission lens 4 is used. The transmission lens 4 is installed coaxially with the secondary mirror 3 and is composed of a convex lens and a concave lens that have substantially the same aperture diameter as the secondary mirror 3. The coarsely captured laser beam incident on the transmission lens 4 propagates as a second beam in the portion indicated by the oblique lines in FIG. That is, the light passes through a through hole provided in the secondary mirror 3 and propagates without being reflected by the primary mirror 2 and the secondary mirror 3. The transmission lens 4 is also configured so that its focal length is substantially equal to the focal length of the reflective telescope composed of the primary mirror 2 and the secondary mirror 3. Further, the focal point of the transmission lens 4 is arranged so as to substantially coincide with the focal point 13.

  Accordingly, the coarsely captured laser beam is condensed toward the focal point 13, then propagates along the same optical path as the received laser beam reflected by the primary mirror 2 and the secondary mirror 3, and reaches the beam splitter 7. Here, the beam diameter of the coarse capture laser beam is configured to substantially match the inner diameter of the donut-shaped reception laser beam. Therefore, since the diameter of the through hole, which is a through hole provided in the beam splitter 7, is almost equal to the diameter, it passes through the through hole of the beam splitter 7 with almost no loss.

  At this time, since the aperture of the transmission lens 4 is substantially at the same position as the aperture of the optical antenna 1, the aperture of the transmission lens 4 and the arrangement of the beam splitter 7 are still in a conjugate relationship. That is, due to this conjugate relationship, the beam incident on the center of the aperture of the transmission lens 4 still reaches the center of the beam splitter 7 even if it has an inclination with respect to the optical axis. Therefore, the coarsely captured laser beam incident on the aperture of the transmission lens 4 passes through the through hole provided in the beam splitter 7 with almost no loss even if it is tilted from the optical axis. The coarse capture sensor 12 receives the coarse capture laser beam that has passed through the through hole provided in the beam splitter 7 and detects the angular deviation of the received laser beam.

  Although not shown in FIG. 1, the optical antenna 1 composed of the primary mirror 2 and the secondary mirror 3 is arranged according to the angular deviation of the second beam detected by the coarse capture sensor 12 which is an angular deviation detection means. Direction control means for controlling the direction can also be provided.

The space optical communication apparatus according to Embodiment 1 of the present invention is configured as described above, and therefore has the following effects.
The coarse capture laser beam received by the transmission lens 4 provided in the vicinity of the secondary mirror 3 is measured by the coarse capture sensor 12. Accordingly, in the conventional example, the received laser beam reflected by the primary mirror 2 and the secondary mirror 3 is partially branched and introduced into the coarse capture sensor 12, thereby reducing the intensity of the received laser beam received by the receiving device 11. Although this occurred, this strength reduction can be eliminated. Therefore, the aperture diameter of the optical antenna 1 can be reduced as compared with the conventional case, and the apparatus can be downsized.

Embodiment 2. FIG.
FIG. 2 is a block diagram showing the configuration of the optical space communication apparatus according to Embodiment 2 of the present invention. 2, the same symbols and numerals as those in FIG. 1 indicate the same function and operation, and the description thereof is omitted. In FIG. 2, 20 is a convex lens (large), and 21 is a convex lens (small). The convex lens (large) 20 and the convex lens (small) 21 constitute the transmission lens 4.

  The convex lens (large) 20 and the convex lens (small) 21 have functions equivalent to those of the transmission lens 4 in the first embodiment of the present invention. The difference is that the convex lens (small) 21 is placed on the opposite side of the convex lens (large) 20 with the secondary mirror 3 in between.

The space optical communication apparatus according to the second embodiment of the present invention is configured as described above, and thus has the following effects.
Normally, when the transmissive lens 4 is configured by combining the convex lens (large) 20 and the convex lens (small) 21, the entire length becomes long because the focal point is focused once in the middle. However, even if the overall length becomes long, the convex lens (large) 20 and the convex lens (small) 21 are arranged with the secondary mirror 3 in between, so that the length protrudes outward from the secondary mirror 3 (right side in FIG. 2). Can be shortened. Therefore, even if the convex lens (large) 20 and the convex lens (small) 21 are used, the total length of the apparatus is not increased, so that the degree of design freedom of the configuration of the transmission lens 4 can be ensured.

1 optical antenna, 2 primary mirror, 3 secondary mirror, 4 transmission lens, 5 collimator lens, 6 polarization beam splitter, 7 beam splitter, 8 relay lens, 10 transmission device, 11 reception device, 12 coarse acquisition sensor, 13 focus, 20 Convex lens (large), 21 Convex lens (small)

Claims (7)

A primary mirror having a through hole in the center;
A sub-mirror having a through-hole at the center, the light reflected by the primary mirror being incident, and reflecting the light toward the through-hole of the primary mirror as a first beam;
A transmission lens that is installed coaxially with the secondary mirror at the opening of the secondary mirror, refracts incident light, and passes through the through-hole of the secondary mirror as a second beam;
A reflection mirror having a through hole at the center for reflecting the first beam and allowing the second beam to pass;
Receiving means for receiving the first beam reflected by the reflecting mirror;
An angular deviation detecting means for receiving the second beam that has passed through the through hole of the reflecting mirror and detecting an angular deviation of the second beam;
An optical space communication device comprising: A transmission device that generates transmission light transmitted from the primary mirror;
A beam splitter that separates the transmission light from the first beam and the second beam;
The optical space communication apparatus according to claim 1, further comprising: A relay optical system having a plurality of lenses and having a conjugate relationship between the position of the reflection mirror and the aperture of the transmission lens in the second beam;
The optical space communication apparatus according to claim 1 or 2, further comprising: The ratio of the width of the through hole of the secondary mirror to the width of the secondary mirror is substantially equal to the ratio of the width of the through hole of the primary mirror to the width of the primary mirror. 4. The optical space communication apparatus according to any one of 3 above. The optical space communication device according to any one of claims 1 to 4, wherein the transmission lens includes a convex lens and a concave lens. The optical space communication device according to any one of claims 1 to 4, wherein the transmissive lens has two convex lenses. Direction control means for controlling the direction of the optical antenna composed of the primary mirror and the secondary mirror according to the angular deviation of the second beam detected by the angular deviation detection means;
The optical space communication device according to any one of claims 1 to 6, further comprising:

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