JP2000068934A - Optical communication device mounted on satellite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain optical communication whose communication performance is enhanced by using an optical signal whose received intensity is maximized at all times independently of fluctuation in air and whose wave front has no fluctuation. SOLUTION: A CCD sensor 9 detects part of an optical signal (a) that is caught by an optical antenna 1 and whose wave front has fluctuation, the signal is fed back to a compensation circuit 15 to control a focus adjustment device 2. Thus, a focus (b) of the optical signal (a) is controlled to maximize the received intensity on the CCD sensor 9. An optical mirror drive circuit 5 modifies a compensation optical mirror 4 to correct a wave front curvature attended with the movement of the focus (b) based on a cross reference table according to a relative equation between the maximum light receiving intensity and the wave front curvature. A precision capture tracing sensor 12 detects fluctuation in a very weak reception optical axis due to the effect of air and the compensation optical mirror drive circuit 5 corrects it by deforming the compensation optical mirror 4. Thus, an optical receiver 14 receives an optical signal with the maximum intensity and whose wave front is flat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication device mounted on a satellite for performing optical communication between an artificial satellite and a ground station, and particularly to an optical communication device capable of performing highly accurate communication even with a weak optical signal. About.

[0002]

2. Description of the Related Art Satellite-mounted optical communication equipment to which the technology of a satellite-mounted optical system is applied is widely used. The technology of this optical system device is disclosed in, for example, Japanese Patent Application Laid-Open No. 3-248118. The focus adjustment can be performed. That is, the temperature change of the atmosphere is detected by a temperature detecting element such as a bimetal, and the shift amount of one of the opposed wedge glasses is adjusted by the temperature detecting element, thereby correcting the focal length shift and aberration caused by the temperature fluctuation. Things. As a result, it is possible to control so that the light is always focused on the light receiving sensor unit. If such a technique is used for an optical communication device, highly accurate optical communication can be performed by compensating for temperature fluctuations.

[0003]

However, when optical communication is performed between a satellite and a ground station, the optical communication is not performed due to the unevenness of the air density, which is a medium for space propagation, in addition to the above-mentioned factors of temperature fluctuation. Failure occurs. That is, the refractive index of light changes depending on the density of the atmospheric density, and as a result, the wavefront of light appears as fluctuation. As a result, the optical wavefront is distorted, and the error in capturing and tracking the light increases. As a result, a communication error is caused, and high-precision optical communication cannot be performed. Further, even if an adaptive optics mirror that changes the shape of the reflecting surface in accordance with the fluctuation of the light wavefront is added to correct the distortion of the light wavefront, only a large fluctuation of the light wavefront can be corrected. That is, in the case of a weak optical signal having a sensitivity equal to or lower than the detection sensitivity of the photodetector, the fluctuation of the wavefront cannot be detected, and thus the distortion of the light wavefront cannot be completely corrected. For this reason, there is a problem that high-precision optical communication cannot be performed for a weak optical signal.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to increase the light receiving intensity of an optical signal and to correct the influence of atmospheric fluctuation even if the optical signal is weak. To be able to perform capture and tracking,
An object of the present invention is to provide a satellite-mounted optical communication device capable of performing highly accurate optical communication.

[0005]

According to a first aspect of the present invention, there is provided an optical communication device for mounting on a satellite for receiving an optical signal captured by an optical antenna by an optical system device and performing predetermined optical communication. First detecting means for detecting the intensity of the signal, and focus adjusting means for receiving the output of the first detecting means and controlling the focal length of the optical signal so that the peak received light intensity of the optical signal has a maximum value. And an optical wavefront curvature correction unit that corrects the wavefront curvature of the optical signal that changes based on the movement of the focal length controlled by the focus adjustment unit.

According to a second aspect of the present invention, in the optical communication device mounted on a satellite according to the first aspect, the focus adjusting means controls the focal length of the optical signal based on the output of the first detecting means. And a focus adjusting mechanism for controlling the focal length of the optical signal by the drive signal generated by the compensation circuit.

According to a third aspect of the present invention, in the optical communication device mounted on a satellite according to the first or second aspect, the light wavefront curvature correcting means is set in advance in response to an output of the first detecting means. Generating means for generating a drive signal based on the correspondence between the peak received light intensity of the optical signal and the wavefront curvature, and a compensating optical mirror for displacing the mirror surface for each minute section according to the output of the generating means. And According to a fourth aspect of the present invention, in the optical communication device mounted on a satellite according to any one of the first to third aspects, a second detecting means for detecting a deviation of a reception optical axis of a received signal, And a correction means for receiving the output of the second detection means and correcting the deviation of the receiving optical axis.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a satellite-mounted optical communication device according to an embodiment of the present invention. This figure also shows the flow of the optical signal. In the figure, an optical antenna 1 is an antenna that receives an optical signal from a ground station (not shown). The optical antenna 1 uses a Cassegrain optical system configured to obtain a long focal length with a short lens barrel by turning light incident on the main reflecting mirror 1-1 by the sub-reflecting mirror 1-2. I have. By using such a Cassegrain optical system antenna, loss of an optical signal can be reduced. The focus adjusting mechanism 2 has a structure in which two inclined wedge-shaped glass pieces are slidably contacted with each other, and at least one of the wedge-shaped glass pieces slides through the wedge-shaped glass piece. The focal length of the light to be emitted can be varied. The lens 3 and the lens 18 are collimating lenses for forming a parallel beam from light diverging from a focal point or a light source.

The adaptive optical mirror 4 is a shape variable mirror capable of changing the shape of the reflection surface to an arbitrary shape for each minute area. That is, according to the fluctuation of the wavefront of the incident light, the shape of the reflection surface of the adaptive optical mirror 4 is deformed, and the wavefront whose fluctuation is reflected is reflected by the reflection surface so that the wavefront can be made flat. Has become. On the back surface of the compensating optical mirror 4, a large number of actuators each composed of a piezo piezoelectric element displaced in proportion to an applied voltage are arranged for each minute section. The adaptive optics mirror driving circuit 5 is a control circuit that varies the amount of deformation of the adaptive optics mirror 4 by an applied voltage generated by feeding back a signal proportional to the fluctuation of the wavefront. The beam splitter 6, the beam splitter 7, and the beam splitter 10
This is a device that divides one light beam into two light beams at an arbitrary ratio. The lens 8, the lens 11, and the lens 13
Beam splitter 7 and beam splitter 1 respectively
It is a condenser lens for condensing the light beam divided by zero.

The coarse capturing and tracking sensor 9 is a CCD (Charge C).
Oupled Device (charge coupled device) is a sensor that receives a part of the optical signal incident on the optical antenna 1 and detects the peak value of the received light intensity projected on the CCD sensor 9. In addition, the fine capture tracking sensor 12
It is constituted by a four-quadrant sensor (QD) or the like, and detects a deviation of an optical axis of an optical signal incident on the optical antenna 1 with high accuracy and determines a feedback amount for correcting and deforming the adaptive optical mirror 4. It is a sensor. The fine capture and tracking sensor 12 is a light receiving sensor composed of four detection elements arranged at 90-degree intervals around one point. From the output of each detection element, the spot position of light applied to the sensor is determined. It has a function to detect. The optical receiver 14 is a receiver that can receive the optical signal of the ground station received by the optical antenna 1 with low noise and high gain. The optical receiver 14 is constituted by an avalanche photodiode (APD) or the like in order to increase the response to light.

The compensation circuit 15 is a control circuit for varying the focal length by sliding the wedge-shaped glass of the focus adjustment mechanism 2 based on a feedback signal from the coarse capturing and tracking sensor (CCD) 9. The precise capture and tracking processing unit 16 includes the fine capture and tracking sensor 12 and the compensation circuit 1.
The adaptive optics mirror driving circuit 5 determines a voltage to be applied to the adaptive optics mirror 4 based on the control signal from the control optical mirror 5. The optical transmitter 17 includes a laser diode (LD) that emits an optical signal. The optical path difference correction mechanism (PAM) 19 is a mechanism for correcting an optical path difference with a communication partner. This mechanism 19 is provided for the following purpose. That is, when communication is performed between devices having relatively different speeds, the relative positional relationship changes while light propagates. Therefore, it is necessary to previously shift the pointing angle of the communication beam from the direction of the target at the start of transmission.
The deviation angle is the optical path difference, and the mechanism for correcting this is the optical path difference correction mechanism 19. In this embodiment, a piezoelectric actuator is used to change the direction of the communication beam.

Next, the operation of the satellite-mounted optical communication device shown in FIG. 1 will be described in accordance with the flow of optical signals. In the optical antenna 1,
An optical signal a whose wavefront fluctuates due to the influence of the atmosphere is incident, and this optical signal a is transmitted to a Cassegrain optical system (main reflecting mirror 1-1).
A focal point b is formed by the sub-reflecting mirror 1-2) near the focus adjusting mechanism (wedge-shaped glass) 2. And
The optical signal diverging from the focal point b is converted into a parallel beam optical signal c by the lens 3 and is incident on the compensation optical mirror (shape variable mirror) 4. Further, the optical signal d reflected by the compensating optical mirror 4 passes through the beam splitter 6, is split by the beam splitter 7, and a part of the signal becomes a coarse / light detection signal i, which is condensed by the lens 8 and coarsely captured and tracked. Sensor (CC
D) Projected on 9.

The CCD 9 constitutes a feedback system by the compensating circuit 15 and the focus adjusting mechanism 2 so that the peak received light intensity of the light signal (that is, the coarse / light detection signal i) projected on the CCD 9 becomes the maximum value. . That is,
Since the peak light receiving intensity on the CCD 9 changes with time due to the fluctuation of the atmosphere, the CCD 9 feeds back a signal x proportional to the received coarse / light detection signal i to the compensation circuit 15, and controls the focus adjustment mechanism 2 by the compensation circuit 15. I do. Thereby, the focus adjusting mechanism 2 slides the wedge-shaped glass, automatically adjusts the focus b of the received optical signal a, and increases the peak received light intensity of the received light signal (that is, the coarse / light detection signal i) projected on the CCD 9. Control is performed so as to be the maximum.

At this time, since the wavefront curvature of the optical signal c incident on the compensating optical mirror 4 changes with the movement of the focal point b, the compensating circuit 15 estimates the wavefront curvature with respect to the position of the focal point b, and The drive circuit 5 performs control to correct the wavefront curvature by deforming the mirror surface of the adaptive optical mirror 4. That is, when the focal point b is adjusted so that the peak received light intensity i of the CCD 9 becomes maximum, the peak received light intensity i at that time and the wavefront curvature ρ of the optical signal a incident on the optical antenna 1 are obtained.
Is expressed by the following equation (Equation 1).

[0015]

(Equation 1)

Therefore, the relationship between the wavefront curvature ρ and the peak received light intensity i is calculated in advance by using the above (Equation 1), and is provided in the compensation circuit 15 as a reference table. Then, the compensating circuit 15 reads out the wavefront curvature ρ for each peak received light intensity i, and sends a control signal corresponding to the wavefront curvature ρ to the adaptive optics mirror driving circuit 5 via the fine acquisition tracking processing unit 16. Then, in accordance with the control signal, the adaptive optics mirror driving circuit 5 generates a predetermined applied voltage, and displaces the piezoelectric element actuator of the adaptive optics mirror 4 for each minute section. As a result, the mirror surface of the adaptive optical mirror 4 is displaced, so that a reflected light distribution with high flatness can be created. That is, the compensation optical mirror 4 corrects the fluctuation of the wavefront curvature of the incident optical signal c and reflects the optical signal d having a flat wavefront. Thus, the optical signal d becomes an optical signal having a flat wavefront. This optical signal is split again by the beam splitter 7, and a part of the signal is the coarse / light detection signal i described above, and the other is transmitted as an optical signal j.

The optical signal j is further divided by a beam splitter 19, and a part of the optical signal j is condensed by a lens 11 as a fine / light detection signal k and projected as a detection signal on a fine capture and tracking sensor (four-quadrant sensor) 12. Is done. The fine capturing and tracking sensor 12 detects a deviation of the light receiving spot caused by the wavefront accuracy, and outputs a detection result to the fine capturing and tracking processing unit 16. The fine capture and tracking processing unit 16 receives the output of the fine capture and tracking sensor 12, drives the compensating optical mirror 4 via the adaptive optical mirror driving circuit 5, and corrects the above-described deviation (that is, the deviation of the receiving optical axis). . On the other hand, the optical signal that has passed through the beam splitter 10 is condensed by a lens 13 and is incident on an optical receiver (avalanche photodiode) 14, where predetermined reception processing is performed. The optical receiver 14 using an avalanche photodiode can receive an optical signal having a high received light intensity and a flat wavefront with low noise and high gain in an extremely fast response.

Thus, in the above embodiment,
Adjustment is performed by the feedback loop of the coarse capture tracking sensor 9, the compensation circuit 15, and the focus adjustment mechanism 2 so that the peak intensity of the optical signal is maximized. The coarse capture tracking sensor 9, the compensation circuit 15, and the compensating optical mirror driving circuit 5 The distortion of the wavefront curvature is corrected by the feedback loop of the compensating optical mirror 4, and the precise capturing and tracking sensor 12, the fine capturing and tracking processing unit 16, the adaptive optical mirror driving circuit 5, and the adaptive optical mirror 4
The correction of the receiving optical axis is performed by the feedback loop described above. As a result, in optical communications between satellites and ground stations,
An optical signal which is always at the maximum light receiving intensity and is not affected by the atmosphere can be received, and an optical communication device mounted on a satellite with high communication accuracy can be realized.

The embodiment described above is an example for describing the present invention, and the present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the invention. is there. For example, an optical element other than the wedge-shaped glass can be used as the focus adjustment mechanism. Note that a function of compensating for the effects of atmospheric turbulence can be realized using a microlens array, but in this case, a sensor for wavefront monitoring is required in addition to the coarse capture tracking sensor and the fine capture tracking sensor. On the other hand, in the above-described embodiment, the coarse capturing and tracking sensor can also be used, and the configuration can be simplified.

[0020]

As described above, according to the optical communication device mounted on a satellite according to the present invention, it is possible to suppress the influence of the fluctuation of the atmosphere in the communication between the satellite and the ground station. Can be further improved. In particular, even a weak optical signal can be efficiently amplified and detected, and even a small fluctuation of the wavefront can be corrected, so that a satellite-mounted optical communication device with high communication efficiency can be provided. Also, since communication is possible even with a weak optical signal, the output power of the transmitting device can be reduced, and an economic effect can be expected.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a satellite-mounted optical communication device according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical antenna (Cassegrain type), 2 ... Focus adjustment mechanism (wedge-shaped glass), 3, 18 ... Lens (for collimation), 4 ... Compensating optical mirror (shape variable mirror), 5 ... Compensating optical mirror driving circuit, 6 , 7, 10 ... Beam splitter (BS), 8, 11, 13 ... Lens (for focusing), 9 ... Coarse capture tracking sensor (CCD), 12 ... Fine capture tracking sensor (four quadrant sensor), 14 ... Optical reception (Avalanche photodiode), 15: compensating circuit, 16: precise acquisition and tracking processing unit, 17: optical transmitter (laser diode), 19: optical line difference correction mechanism

Claims (4)

[Claims] 1. An optical communication device mounted on a satellite for receiving an optical signal captured by an optical antenna by an optical system device and performing predetermined optical communication, wherein: a first detecting means for detecting the intensity of the optical signal; A focus adjustment unit that receives an output of the first detection unit and controls a focal length of the optical signal so that a peak received light intensity of the optical signal becomes a maximum value; a focal length controlled by the focus adjustment unit And an optical wavefront curvature correction means for correcting the wavefront curvature of the optical signal that changes based on the movement of the optical signal. 2. A compensation circuit for producing a drive signal for controlling a focal length of the optical signal based on an output of the first detection means, wherein the focus adjustment means comprises: The optical communication device for mounting on a satellite according to claim 1, further comprising a focus adjustment mechanism that controls a focal length of the optical signal by a signal. 3. The light wavefront curvature correction means receives the output of the first detection means and generates a drive signal based on a predetermined relationship between the peak light receiving intensity of the optical signal and the wavefront curvature. The satellite-mounted optical communication device according to claim 1, further comprising: a generation unit; and an adaptive optical mirror that displaces a mirror surface for each minute section according to an output of the generation unit. 4. A second detecting means for detecting a deviation of a receiving optical axis of the optical signal, and a correcting means for receiving an output of the second detecting means and correcting the deviation of the receiving optical axis. The satellite-mounted optical communication device according to any one of claims 1 to 3, wherein: