JP2004015134A - Optical space communication unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical space communication unit, having a function performing automatic tracking by correcting the shift of optical axis and conducting communication with another optical space communication unit, disposed facing at a remote position using a light beam, in which the possibility of resetting the counterpart unit by supplementing the light is significantly increased, even if the angle of the unit is varied during stoppage of tracking. <P>SOLUTION: Positional information is stored at all times during automatic tracking operation, and if the light is not detected even after waiting a specified time, when automatic tracking operation is stopped due to attenuation of light, positions stored in the past positional information are searched sequentially, retroactively in time. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical space communication device which is installed opposite to two distant points and transmits an optical signal by a light beam propagating in free space and performs communication, and in particular, an optical axis correction function of a light beam due to an angle shift of the device. It is related to a device having.
[0002]
[Prior art]
In general, an optical space communication device that communicates by propagating a light beam in free space needs to transmit the light beam with a narrow light beam with a minimum divergence angle in order to transmit the light power efficiently. is there. However, if the light beam is narrowed, the light beam is likely to be detached from the partner device due to fluctuations due to wind pressure and vibration of the building or the installation stand, distortion due to temperature fluctuations, and angle fluctuations due to changes in diameter, and stable communication is difficult. For this purpose, as shown in FIG. 5, a device having an optical axis deviation correction function has been devised in which the change in angle is corrected even when the angle of the device changes, so that the light beam always faces the partner device.
[0003]
FIG. 5 shows one side of a pair of opposed devices. In FIG. 5, reference numeral 10 denotes an optical system for transmitting / receiving a light beam. An optical signal transmitted to the other device is emitted from a light emitting element 21 such as a semiconductor laser. The light of the semiconductor laser is polarized, and the polarization direction is set so as to be horizontal to the paper surface. The polarized light in this direction is reflected by the polarization beam splitter 22 in the direction of the light transmitting and receiving lens 23, and is transmitted by the light transmitting and receiving lens 23 as a substantially parallel light beam 24 having a slight divergence toward the partner device.
[0004]
On the other hand, the light transmitted from the partner device follows the reverse path on the same optical axis as the transmission optical signal from the own device, enters the polarization beam splitter 22 from the transmission / reception lens 23, and receives the light from the partner device. Since the polarization direction of the light is set to be orthogonal to the transmission light (the polarization direction is perpendicular to the plane of the paper), the light passes through the polarization beam splitter 22 as it is and enters the beam splitter 25. Most of the received light is reflected by the beam splitter 25 and enters the light receiving element 26 for detecting an optical signal, and a signal for communication is detected. However, a part of the light is transmitted through the beam splitter 25 and The light enters the position detection element 27.
[0005]
The light position detecting element 27 is, for example, a photodiode divided into four as shown in FIG. FIG. 6 shows a state in which the light spot 42 hits the four divided photodiodes 27a to 27d. By comparing the outputs of the four photodiodes 27a to 27d, the position of the light spot 42 can be known. The signal from the optical position detection element 27 is subjected to arithmetic processing by the control circuit 28 as angle correction information, and a drive signal is output to the drive circuit 29 of the optical system 10. Then, the driving circuit 29 moves the vertical driving mechanism 30 and the horizontal driving mechanism 31 so that the position of the light spot 42 comes to the center of the light position detecting element 27, and the outputs of the four photodiodes 27a to 27d are output. It is driven and controlled in such a direction that they are all equal.
[0006]
The position of the light position detecting element 27, the light emitting element 21, and the light receiving element 26 for light signal detection are all adjusted so that the optical axes coincide with each other, and when the light spot 32 hits the center of the light position detecting element 27, Light is also incident on the center of the light receiving element 26 for detecting an optical signal, and the center of the light from the light emitting element 21 is emitted in the direction of the other device.
In this manner, the optical axis deviation correction is performed so that the transmission light always becomes the direction of the reception light, that is, the direction of the partner device.
[0007]
However, due to the nature of wireless communication, there may be a state in which an optical signal propagating due to weather conditions such as rain, fog, and snow is attenuated and communication cannot be performed. In such a case, the optical axis deviation correction performed by detecting the light of the partner device cannot be performed, so that the automatic tracking operation is also stopped. In this case, when the level of the detected optical signal falls below a certain value (threshold value), the tracking operation is stopped at that time, and the light level is maintained while the position of the angle driving mechanism at that time is maintained. Is recovered and the tracking operation can be performed again.
[0008]
[Problems to be solved by the invention]
In the above conventional example, even if the angle of the device changes, by performing the optical axis shift correction, stable communication can be performed even when the divergence angle of the light beam is reduced, but the weather condition such as rain, fog, snow, etc. When the optical signal propagating is attenuated and communication becomes impossible, the tracking operation is stopped as described above, and while the position of the angle drive mechanism is held at that time, the light level is recovered. It will wait until the tracking operation becomes possible again.
[0009]
However, if the tracking stop state becomes longer, if the direction of the device changes from before the stop because the building or gantry is distorted due to environmental changes such as temperature change during the stop period, even if it recovers due to the weather, Since the light beam is deviated, the automatic tracking operation cannot be started, and the communication cannot be restored.
[0010]
Further, when the level of the optical signal falls below the threshold value and the tracking operation is stopped at that time, the output of the optical position detecting element 27 is noisy and the position accuracy is poor because the level of the optical signal is low. Therefore, there is a possibility that the position itself at which the tracking operation is stopped is slightly out of the original position. Therefore, if the angle overlaps with the angle shift during the stop period, the restoration of communication becomes more uncertain.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the first invention according to the present application is:
An optical space communication device which is installed oppositely between distant points and communicates with a light beam,
An optical system for transmitting the light beam to the other device and receiving the light beam from the other device;
Light position detection means for detecting the arrival direction of the light beam from the other device,
Control means for controlling the direction angle of a light beam to be transmitted to a partner apparatus from a signal from the light position detection means,
A means for driving a direction angle of a light beam to be transmitted to a partner apparatus by a command from the control means, performing an automatic tracking, having an optical axis deviation correction function,
A drive position detecting means for detecting in which direction the means for driving the direction angle of the light beam is directed, and a memory for storing a plurality of pieces of position information from the drive position detecting means,
The following operation is performed.
[0012]
{Circle around (1)} When the signal from the light position detecting means falls below a predetermined level, the tracking operation is stopped.
[0013]
{Circle around (2)} When the stop time exceeds a predetermined value t1, at a predetermined time interval t2, in order from the newest to the oldest stored time, at the positions indicated by the plurality of drive position information stored in the memory. Driving direction sequentially.
[0014]
{Circle around (3)} After driving the direction to the position indicated by the predetermined number of pieces of position information, return to the initial direction and stop.
[0015]
(4) Repeat the above (2) and (3).
[0016]
(5) If the signal from the light position detecting means exceeds a predetermined level during the operations (2) and (3), the automatic tracking is resumed at that point.
[0017]
Further, the second invention and the third invention according to the present application are the optical space communication device according to the first invention according to the present application, wherein the waiting time t1 or the time interval t2 is not a fixed value, It is a variable value whose value changes randomly around a predetermined value.
[0018]
The fourth invention and the fifth invention according to the present application are the optical space communication apparatus according to the first invention according to the present application, wherein the waiting time t1 or the time interval t2 is different between two opposing devices. The value is a fixed value.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
(First embodiment)
FIG. 1 shows an optical space transmission apparatus having an optical axis shift correction function by automatic tracking according to the present invention.
[0020]
In FIG. 1, light from a light emitting element 21 is reflected by a polarizing beam splitter 22 in the direction of a light transmitting / receiving lens 23 in the same manner as in the conventional embodiment in FIG. The beam 24 is transmitted in the direction of the other device.
[0021]
On the other hand, the light sent from the partner device also passes through the polarization beam splitter 22 as it is, similarly to the conventional embodiment of FIG. 5, and enters the beam splitter 25. Most of the received light is reflected by the beam splitter 25 and enters the light receiving element 26 for detecting an optical signal, and a signal for communication is detected. However, a part of the light is transmitted through the beam splitter 25 and The light enters the position detection element 27. The signal from the light position detecting element 27 is subjected to arithmetic processing by the control circuit 28 as angle correction information, and a drive signal is output to the drive circuit 29 of the optical system 10. Then, the drive circuit 29 moves the vertical drive mechanism 30 and the horizontal drive mechanism 31 so that the transmission light beam is directed toward the partner device detected by the optical position detection element 27.
[0022]
Further, it has angle sensors 33 and 34 for detecting the positions of the drive mechanisms 30 and 31 (in this case, the drive angles), and the angle information from the angle sensors 33 and 34 is sent to the control circuit 28 and appropriate numerical data Is stored in the memory 32 in the control circuit 28. As the angle sensors 33 and 34, a rotary encoder, a potentiometer, a Hall element, an optical position detecting element, or the like can be used.
[0023]
Next, the automatic tracking operation of the optical free space communication apparatus according to the present embodiment will be described.
[0024]
FIG. 2 is a flowchart of a basic operation in a normal state. At first, a manual coarse adjustment operation is performed until the automatic tracking is performed. When the operation is completed, the normal automatic tracking operation is started after the initialization process (1). First, in (2), it is determined whether or not an optical signal is detected. If an optical signal is detected, an automatic tracking routine is started. The term "optical signal detection" used here means that the level of an optical signal is equal to or higher than a normally detectable level.
[0025]
FIG. 3 shows an automatic tracking routine. First, position information is read from the optical position detecting element 27 in (5), arithmetic processing for correcting optical axis deviation is performed by the control circuit 28 in (6), and driving is performed in (7). The driving mechanisms 30 and 31 are moved from the circuit 29 to drive the direction of the optical system 10. Thereafter, in (8), it is checked whether or not the current time is the designated timing for writing the angle information from the angle sensors 33 and 34 into the memory 32. In most cases, it is not the timing, so the routine exits as it is, returns to (2), and repeats similarly.
[0026]
If it is the write timing, in step (9), the data already in the memory is sequentially moved to a new memory location and updated, and then the current angle information is written to the memory location for writing the latest free data. . As a result, the contents of the memory are arranged as follows: "current angle information, angle information A1 hours ago, angle information A2 hours ago ... angle information An time ago".
[0027]
The write timing may be set appropriately according to the installation environment. However, considering that the angle change of the apparatus due to temperature change is a one-day cycle, at least the position information at least 24 hours before the present time is stored in the memory. It is desirable to keep it.
[0028]
If the optical signal propagating due to weather conditions such as rain, fog, and snow is attenuated and the optical signal is no longer detected in (2), the angle information at that point is written to the memory, and then automatic in (4). The tracking operation is stopped, and the process enters a return waiting routine shown in FIG.
[0029]
In the return wait routine, the process first enters an input wait state, and waits until an optical signal is detected in (10). In most cases, if you wait as it is, you will be able to detect light when the weather recovers and the light is no longer attenuated. If an optical signal is detected, the routine immediately exits the return waiting routine and can proceed to the normal automatic tracking routine. However, as described in "Problems to be Solved by the Invention", if the direction of the device changes due to distortion of the building or gantry due to environmental changes such as temperature changes during the period of suspension, the light Cannot be detected. Then, when the predetermined waiting time t1 has elapsed in (12), the routine proceeds to the routine of the search operation.
[0030]
In the search operation routine, first, in (13), the angle is driven from the current angular position immediately before the automatic tracking stop to the position indicated by the closest position information stored in the memory. If an optical signal is detected at (14) at the new position, the routine immediately exits the return waiting routine and proceeds to the normal automatic tracking routine. However, if the optical signal is not detected even after the lapse of the predetermined time t2 in (15), the position information at the next and earlier time point is read, and the angle is driven to that position. Search backwards until the search is completed. Then, in step (16), if no optical signal is detected even when all the memory locations have been moved, it is determined that there is a high possibility that the light attenuation is still large, and immediately before the first automatic tracking stop is stopped. It returns to the angle position and enters the input waiting state again. Then, after the elapse of the waiting time t1, the processing shifts to the search operation routine again and is repeated.
[0031]
Although the initial waiting time t1 depends on the requirements of the system, it is appropriate to be several tens minutes to several hours. The interval t2 before moving to the next position is sufficient if an optical signal is detected during that time, and a short time of about several seconds or less is sufficient.
[0032]
Environmental changes such as temperature changes are mainly in the diurnal cycle, as described above. Therefore, if several pieces of past position information for one day or more are stored, the device can be automatically stopped during automatic tracking stop. Even if the angle changes, there is a very high possibility that the stored position can be restored by successively searching. In addition, most of the stored position information is data when the normal reception condition is good, and since the data is accurate with little noise, the possibility of return is further increased (however, depending on weather conditions, one day may be required). In such a case, the automatic tracking may be stopped many times, and in such a case, the position information at the time of the automatic tracking and the position information immediately before the stop of the automatic tracking are mixed. It is effective to store the position information immediately after the is returned.)
[0033]
(Second embodiment)
In the second embodiment, the waiting time t1 in the input waiting state and the time interval t2 before moving to the next position in the search operation in the first embodiment are not fixed values but fixed values. It is an irregular variable value whose length changes randomly around the given time value.
[0034]
When the optical signal is not detected in the own device, it is considered that the optical signal is not detected in the other device as well, and the other device performs the same operation as that of the own device in FIG. In this case, if the two devices have the same operation cycle, the devices may run away from each other in some cases, and it may be impossible to supplement the light of the other device. Therefore, if the waiting time t1 in the input waiting state is not set to a fixed value, and the length is set to a variable value that changes irregularly around a standard value in accordance with a pseudo random numerical sequence, the operations of each other are performed. Without a match, most of the time, when one side is moving, one side is stopped, and the supplement is more reliable. Further, if the time interval t2 before moving to the next position in the search operation is also a variable value that randomly changes around the standard value, two units are set even if the start of the search operation coincides with two devices. The probability of the time when both are moving is reduced, making supplementation easier.
[0035]
Note that the waiting time t1 in the input waiting state and the time interval t2 before moving to the next position in the search operation are fixed values, but if the values are changed between two opposing devices, they are randomly set. Although an effect similar to that of changing is obtained, the specifications of the two opposing devices are different, which makes the management of time setting at the time of installation or replacement troublesome.
[0036]
【The invention's effect】
As described above, according to the present invention, in an optical space communication device that has a function of performing automatic tracking by correcting optical axis deviation, and that is installed facing each other between distant points and communicates with a light beam,
When a plurality of pieces of past position information are stored, and when the light is attenuated and the automatic tracking operation is stopped, if no light is detected even after waiting for a predetermined time, the stored position is searched backward and sequentially searched. Accordingly, even if the angle of the apparatus changes during the automatic tracking stop, the possibility of recovering by supplementing the light of the partner apparatus becomes extremely high, and a highly reliable optical space communication apparatus can be realized.
[Brief description of the drawings]
FIG. 1 shows an embodiment of the present invention. FIG. 2 shows a basic operation flow in an embodiment of the present invention. FIG. 3 shows a flow of automatic tracking in an embodiment of the present invention. FIG. 5: Conventional embodiment [FIG. 6] Example of spot position detecting element [Description of symbols]
21 light emitting element 22 polarizing beam splitter 26 light receiving element 27 light spot position detecting element 28 control circuit 29 driving circuits 30, 31 driving the optical system Mechanism 32: Memory

Claims (5)

An optical space communication device which is installed oppositely between distant points and communicates with a light beam,
An optical system for transmitting the light beam to the other device and receiving the light beam from the other device;
Light position detection means for detecting the arrival direction of the light beam from the other device,
Control means for controlling the direction angle of a light beam to be transmitted to a partner apparatus from a signal from the light position detection means,
A means for driving a direction angle of a light beam to be transmitted to a partner apparatus by a command from the control means, performing automatic tracking, having an optical axis deviation correction function,
A drive position detecting means for detecting in which direction the means for driving the direction angle of the light beam is directed, and a memory for storing a plurality of pieces of position information from the drive position detecting means,
An optical free-space communication device, which performs the following operation.
{Circle around (1)} When the signal from the light position detecting means falls below a predetermined level, the tracking operation is stopped.
{Circle around (2)} When the stop time exceeds a predetermined value t1, at a predetermined time interval t2, in order from the newest to the oldest stored time, at the positions indicated by the plurality of drive position information stored in the memory. Driving direction sequentially.
{Circle around (3)} After driving the direction to the position indicated by the predetermined number of pieces of position information, return to the initial direction and stop.
(4) Repeat the above (2) and (3).
(5) If the signal from the light position detecting means exceeds a predetermined level during the operations (2) and (3), the automatic tracking is resumed at that point. 2. The optical space communication apparatus according to claim 1, wherein the waiting time t1 is not a fixed value but a variable value that randomly changes around a predetermined value at each operation cycle. 2. The optical space communication apparatus according to claim 1, wherein the time interval t2 is not a fixed value but a variable value that randomly changes around a predetermined value every time the memory is moved to the next memory location. 2. The optical space communication apparatus according to claim 1, wherein the waiting time t1 is a different fixed value for each of two opposing devices. 2. The optical space communication apparatus according to claim 1, wherein the time interval t2 is a different fixed value for each of two opposing devices.

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