JPH0983436A - Optical space communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic tracking device minimizing vibration of itself and an angular error of an optical beam caused by observed noise. SOLUTION: An optical beam angular error caused by vibration included in an output signal of an angular error detection means 46 is mostly low frequency components of several tens of Hz or below and the angular error caused by observed noise has almost uniform frequency component from a low frequency to several hundreds Hz. An observed noise amount measurement circuit 52 eliminates the components of several tens Hz or below by using a high pass filter from an output signal of the angular error detection means, squares and averages it by using a low pass filter with a proper time constant so as to estimate the observed noise amount in real time. A system control circuit 53 estimates the optical beam angle fluctuation caused by the vibration of the equipment based on the difference from the observed noise amount estimated to be square of the output signal of the angular error detection means and an optimum transfer function of a controller 51 minimizing the angular error between the transmission optical beam and the reception optical beam is decided in real time based on the estimated value and the estimate value of observed noise amount and automatic adjustment is made to the value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical space communication device for propagating a light beam into the atmosphere and performing communication over a long distance.

[0002]

2. Description of the Related Art Generally, an optical communication system using a light beam is capable of high-speed and large-capacity communication, and in particular, optical space communication using a transmission path as a free space is more portable than wired communication such as optical fiber. It is rich and easy to set up communication channels. In order to be easy to use and to improve reliability, it is possible to easily adjust the direction during installation, and an automatic tracking mechanism that can correct the angle so that the light beam does not come off from the other device during communication. Is effective.

FIG. 3 is a block diagram of a conventional optical space communication device having an automatic tracking mechanism. When the devices are installed facing each other, the direction of the other device is manually adjusted by looking into the collimation scope 1. To do. When the automatic tracking start switch 2 is pressed, an electric signal is input from the input terminal 3, becomes an optical signal at the light emitting element 5 via the amplifier 4, and is reflected by the movable mirror 8 via the focus variable collimating lens 6 and the polarization beam splitter 7. , Is transmitted as a transmission light beam from the lenses 9 and 10.

The collimating lens 6 is an actuator 11
The system control circuit 12 drives the actuator 11 based on the communication distance information from the distance setter 13 to the partner device, whereby the transmission light beam has a predetermined spread angle. The collimator lens 6 moves in the optical axis direction so that the focus is adjusted.

The received light beam from the other device is the lens 1
The present signal, which is incident on 0, is reflected by the polarization beam splitter 7 through the lens 9 and the movable mirror 8, and is reflected by the partial reflection mirror 14, is received by the light receiving element 16 through the lens 15, and is transmitted through the amplifier 17. The electric signal is output from the output terminal 18.

On the other hand, a part of the reception beam transmitted through the partial reflection mirror 14 passes through the lens 19 and is divided into four light receiving elements 2.
Focus on 0. The angle formed by the optical axes of the transmission light beam and the reception light beam, that is, the automatic tracking error angle is calculated from the reception light spot position obtained by comparing the respective outputs of the four-division light receiving element 20, and the angle error signal is It is sent to the controller 21. The controller 21 sends a command value to the movable mirror control circuit 22 so that the angle error becomes zero. The movable mirror control circuit 22 drives the actuator 23,
The angle of the movable mirror 8 is adjusted. The angle of the movable mirror 8 is detected by a sensor 24 provided in the vicinity thereof and fed back to the movable mirror control circuit 22, and the movable mirror control circuit 22 controls the movable mirror 8 to an angle corresponding to a command value from the controller 21. can do.

When there is a spot at the center of the four-division light receiving element 20, the angle of the optical axis of the transmitted light and the angle of the optical axis of the received light coincide with each other, that is, the direction of the transmitted light beam of the other device. The position of the light emitting element 5 is adjusted so as to match the direction. Here, when the device tilts and the angle of the optical axis of the received light changes and the spot position on the four-division light receiving element 20 deviates from the center, the movable mirror 8 immediately moves to return the spot position to the center. The angle of the optical axis is corrected. By such an automatic tracking operation, the transmission light beam direction is always kept in the direction of the partner device, and bidirectional communication can be performed.

FIG. 4 shows a simplified feedback loop diagram of this automatic tracking control system. Here, X is the fluctuation of the light beam angle due to the vibration of the device, Y is the angular error between the transmission light beam and the reception light beam, N is the observation noise caused by scintillation, G is the transfer function of the controlled object, and K is the transfer of the controller 21. It is a function, and there is a relation of Y = {1 / (1 + GK)} · X + {GK / (1 + GK)} · N.

[0009]

The purpose of automatic tracking is to appropriately set the suitability of the controller 21 and adjust the angle of the movable mirror 8 as described above, so that the angular error between the transmitted light beam and the received light beam can be reduced. It is to cancel, that is, to make the above-mentioned angle error Y as small as possible. First, in order to reduce the first term {1 / (1 + GK)} · X that depends on the angular fluctuation X, the transfer function K may be increased as long as the automatic tracking control system is stable. However, if so, {GK / (1 + GK)} · N of the second term becomes large, and the influence of the observation noise N is large. On the contrary, if the transfer function K is reduced in order to reduce the second term that depends on the observation noise N, then the first term becomes larger and it becomes difficult to follow the angle change due to the vibration of the device. Therefore, at a certain time, the optimum transfer function K that minimizes the angular error Y is obtained.
Exists.

However, in the above-mentioned conventional example, the light beam angle variation X due to the vibration of the device which changes gradually with time
The problem arises that the characteristics of the controller cannot always be optimized by adapting to the amount of observation noise N.

That is, the amounts of the angle fluctuation X and the observation noise N gradually change depending on the vibration condition of the place where the device is installed, wind and rain, and other weather conditions. The characteristics of the controller that minimizes the angular error of the beam will also change in accordance with the amount of angular fluctuation X and observation noise N. However, in the conventional example, the angle variation X,
Since there is no means for separating the angle fluctuation X and the observation noise N from the output signal of the angle error detecting means that is measured by adding the observation noise N and measuring the quantities thereof, the characteristics of the controller can be measured at a constant time. There is a drawback in that it is not possible to realize automatic tracking that appropriately changes the angle and minimizes the angular error between the transmitted light beam and the received light beam.

The object of the present invention is to solve the above-mentioned problems,
By optimally changing the controller characteristics in real time by adapting to changes in the amount of angular fluctuation X and observation noise N, the transmitted light beam and the received light beam can be changed even when the installation location of the device or weather conditions change. It is an object of the present invention to provide an optical space communication device having an automatic tracking function that minimizes the angle error of.

[0013]

In order to achieve the above-mentioned object, the invention according to the present application is an optical space communication device for propagating a light beam in free space for communication, and an optical beam for adjusting the beam angle of transmitted light. From angle adjusting means, angle error detecting means for detecting an angle error between the transmitted light beam and the received light beam, and a controller for processing a signal from the angle error detecting means and outputting a command signal to the light beam angle adjusting means. An automatic tracking function consisting of, an observation noise amount measuring means for estimating an observation noise amount based on a signal from the angle error detecting means, and an optimal observation noise amount and an optimum signal based on the signal from the angle error detecting means. And a control means for calculating the characteristics of the controller and adjusting the controller characteristics to the optimum value in real time.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 shows the configuration of this embodiment. The output of a transmission signal input terminal 30 is connected to a light emitting element 32 such as a semiconductor laser via an amplifier 31, and a transmission light beam spreads in front of the light emitting element 32. The collimator lens 33 whose focus is variable in order to change the tilt angle, the polarization beam splitter 34 which transmits the light having the plane of polarization parallel to the paper surface and reflects the light having the plane of polarization perpendicular to the paper surface, the intensity of the received light in the radiation direction Movable mirrors 35 that can be freely moved in all directions for adjustment are sequentially arranged, and lenses 36 and 37 for transmitting and receiving a light beam are arranged in the reflection direction of the movable mirror 35.

The collimator lens 33 is driven by a collimator lens driving actuator 38, the movable mirror 35 is driven by a movable mirror driving actuator 39, and a movable mirror angle sensor 40 is provided near the movable mirror 35. It is provided. The output of the movable mirror angle sensor 40 is connected to a movable mirror control circuit 41, and the movable mirror 35, the driving actuator 38, the movable mirror angle sensor 40, and the movable mirror control circuit 41 constitute a light beam angle adjusting means 42. ing.

In the reflection direction of the polarization beam splitter 34, a partial reflection mirror 43, a lens 44, and a four-division light-receiving element 45 composed of four-division photodiodes are sequentially arranged. The angle error detecting means 46 is configured. A lens 47 and a light receiving element 48 including an avalanche photodiode and a PIN photodiode are arranged in the reflection direction of the partial reflection mirror 43. The output of the light receiving element 48 is connected to the reception signal output terminal 50 via the amplifier 49.

The output of the four-division light receiving element 45 is connected to the controller 51, the observed noise amount estimation circuit 52 and the system control circuit 53. The output of the controller 51 is connected to the movable mirror control circuit 41, and the output of the observation noise amount estimation circuit 52 is connected to the system control circuit 53. Furthermore, the outputs of the distance setter 54 and the automatic tracking start switch 55 for setting the communication distance information with the partner device are connected to the system control circuit 53, and the output of the system control circuit 53 is the collimator lens driving actuator 3.
8 and the controller 51.

Further, the apparatus is provided with a collimating scope 56 having an optical axis parallel to the optical axis of the transmitted / received light, so that the direction can be adjusted by observing the partner's apparatus with the collimating scope 56. Has become.

First, in the first adjustment performed when the device is installed, the movable mirror 35 is fixed at the initial position near the center, and the automatic tracking operation is possible while observing the other device with the collimating scope 56. The direction is manually adjusted up to and then the automatic tracking start switch 55 is pressed to input the automatic tracking operation.

A transmission signal is input from the transmission signal input terminal 30, and the light emitting element 32 is driven through the amplifier 31 to generate an intensity-modulated optical signal. Since this optical signal is polarized in the horizontal direction on the paper surface, it passes through the polarization beam splitter 34, is reflected by the movable mirror 35, and is reflected by the lenses 36, 37.
As a result, it becomes a transmission light beam and is projected toward the partner device.

On the other hand, the received light beam sent from the other device enters the lens 37, passes through the lens 36 and is reflected by the movable mirror 35, and this light is polarized in the direction perpendicular to the plane of the drawing. The light is reflected by the bonding surface of the beam splitter 34, proceeds to the partial reflection mirror 43, and most of the light is reflected by the partial reflection mirror 43 and received by the light receiving element 48 via the lens 47. This light is converted into an electric signal in the light receiving element 45, reaches a predetermined level in the amplifier 49, and is output as the main signal from the reception signal output terminal 50.

Further, a part of the light transmitted through the partial reflection mirror 43 passes through the lens 44 of the angle error detecting means 46 and is
The angle formed by the received light with respect to the optical axis of the device is known from the position of the received light spot which is focused on the divided light receiving element 45 and is obtained by comparing the respective outputs of the four-divided light receiving element 45. The light intensity can be known, the angle error between the transmission light beam and the reception light beam is calculated, and the angle error signal is sent to the controller 51.

The controller 51 sends a command value to the movable mirror control circuit 41 of the light beam angle adjusting means 42 so that the angle error becomes zero. The movable mirror control circuit 41 drives the driving actuator 39 to adjust the angle of the movable mirror 35, and performs an automatic tracking operation for correcting the angular error between the transmitted light beam and the received light beam. The angle of the movable mirror 35 is detected by a movable mirror angle sensor 40 provided in the vicinity thereof and is fed back to a movable mirror control circuit 41, and the movable mirror control circuit 41 is movable to an angle corresponding to a command value from a controller 51. The mirror 35 can be controlled.

In the present embodiment, the following operation is performed in order to further optimize the characteristics of the controller 51 in real time. First, as shown in FIG. 2, the light beam angle error A due to the vibration of the device included in the output signal of the angle error detecting means 46.
Is dominated by low frequency components of several tens of Hz or less, and the angular error B due to the observation noise N is several hundreds of Hz from low frequencies.
It has almost uniform frequency components. Therefore, in the observation noise amount measuring circuit 52, the angle error detecting means 46
If a high-pass filter removes components of several tens of Hz or less from the output signal of, then squares it, and averages it with a low-pass filter with an appropriate time constant, it is estimated that the observed noise amount is estimated in real time. It can be changed.

Next, in the system control circuit 53, the difference between the square of the output signal of the angle error detecting means 46 and the observation noise amount estimated as described above is obtained, and the light beam angle fluctuation due to the vibration of the apparatus is obtained. The controller 51 that minimizes the angular error between the transmission light beam and the reception light beam based on this estimation value and the above-described estimation value of the observed noise amount.
The optimum transfer function K of is determined in real time, and the transfer function of the controller 51 is automatically adjusted to that value.

Specifically, in order to reduce the calculation time, the angular fluctuation X of the light beam due to the vibration of the device and the observation noise N are classified into several types within the respective expected ranges, and the combination is obtained. The optimum transfer function K of the controller 51 is calculated and stored in advance for all the possible cases. Then, the system control circuit 53 performs an operation of selecting the transfer function K of the controller 51 to be used based on the input estimated amount and appropriately switching the characteristics of the controller 51.

As an example, at a certain time, the vibration of the installation location of the device is small, but the scintillation becomes severe and the angular error between the transmitted light beam and the received light beam caused by the observation noise N causes the transmitted light beam caused by the vibration of the device. And if it becomes larger than the angular error of the received light beam,
The transfer function K of the controller is switched to a small characteristic,
By narrowing the control bandwidth, automatic tracking is performed so that the influence of the observation noise N is reduced.

As described above, in the present embodiment, the angle error between the transmission light beam and the reception light beam can be minimized by switching the controller to an appropriate characteristic.

[0029]

As described above, the optical space communication device according to the present invention adapts the controller characteristics in real time by adapting to the fluctuation of the light beam angle and the amount of observed noise due to the vibration of the device which changes gradually with time. By changing it, automatic tracking works and stable bidirectional optical communication can be realized so that the angular error between the transmitted light beam and the received light beam is always minimized even if the vibration of the installation location of the device or the weather conditions change.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is an explanatory diagram of the incident beam angle fluctuation due to the vibration of the apparatus and the frequency component of the observation noise included in the output signal of the angle error detecting means.

FIG. 3 is a configuration diagram of a conventional example.

FIG. 4 is a feedback loop diagram of an automatic tracking control system.

[Explanation of symbols]

 32 light emitting element 33 collimating lens 34 polarizing beam splitter 35 movable mirror 40 movable mirror angle sensor 41 movable mirror control circuit 42 light beam angle adjusting means 45 four-division light receiving element 46 angle error detecting means 48 light receiving element 51 controller 52 observation noise amount measuring circuit 53 System control circuit

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04Q 9/00 311

Claims (1)

[Claims] 1. An optical space communication device for propagating a light beam in free space for communication, and a light beam angle adjusting means for adjusting a beam angle of transmitted light, and detecting an angular error between the transmitted light beam and the received light beam. Based on the signal from the angle error detecting means, and an automatic tracking function consisting of an angle error detecting means and a controller for processing a signal from the angle error detecting means and outputting a command signal to the light beam angle adjusting means. An observation noise amount measuring means for estimating the observation noise amount, an optimum controller characteristic is calculated based on the estimated observation noise amount and a signal from the angle error detecting means, and the controller characteristic is set to the optimum value in real time. An optical space communication device, comprising: an adjusting control unit.