JP3368103B2 - Bidirectional optical space transmission equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has an angle correction function,
The present invention relates to a bidirectional optical space transmission device that performs bidirectional information transmission by an optical signal.

[0002]

2. Description of the Related Art Conventionally, in a two-way optical space transmission device for transmitting information to a remote place by an optical signal, a reception transmitted from a partner device by an external action such as wind and rain or solar radiation or an artificial action. The optical axis of the light and the optical axis of the light receiving unit of the device itself are deviated from each other, and in the worst case, the problem of disconnection of communication is likely to occur. Therefore, the optical axes of the transmitted light and the received light are matched in advance in the own device, and the deviation angle between the optical axis of the light receiving part of the own device and the optical axis of the received light transmitted from the partner device is measured during operation. The means for avoiding the deviation of the optical axis by constantly detecting and correcting is adopted.

FIG. 8 is a block diagram of a conventional bidirectional optical space transmission apparatus in which a transmission signal is an electro-optical conversion element 2 of a light transmitting section 1.
Is converted into an optical signal by the beam splitter 3, the optical axis angle adjusting drive mechanism 4, and the light is projected from the lens 5 toward the partner device. On the other hand, the received light transmitted from the partner device is taken into the device through the lens 5, guided through the optical axis angle adjustment drive mechanism unit 4 and the beam splitter 3 to the light receiving unit 6, and is received by the half mirror 7. It is divided into a main signal light receiving element 8 and an optical axis angle error detection system 9.

FIG. 9 is a block diagram of the optical axis angle error detection system 9. A part of the received light is received by the photoelectric conversion elements 10a to 10d which are divided into four elements of the angle error detection system 9, respectively. The current-voltage converters 11a to 11d such as resistors form voltage signals. Then, by performing addition and subtraction of these signals, an angular deviation between the optical axis of the received light and the optical axis of the light receiving unit 6 is detected, and the optical axis angle adjustment control unit 12 determines the optical deviation based on this angle error information. The shaft angle adjustment drive mechanism unit 4 is driven to correct the angle deviation.

By performing the above-mentioned operations in the respective devices facing each other, the optical axes of the light transmitting section 1 and the light receiving section 6 in the apparatus are adjusted in advance so that they coincide with each other. The transmitted light can be projected on the same optical axis as the received light transmitted from the device, and stable bidirectional optical space transmission can always be performed.

[0006]

However, in the above-mentioned conventional example, when the intensity of the optical signal is attenuated on the transmission line by an external or artificial action, the so-called S / N ratio of the signal ratio between the received light and the noise is called. The ratio deteriorates and the optical axis angle error information detected based on these signals is significantly impaired,
There arises a problem that it becomes impossible to accurately correct the angle between the transmitted light and the received light. In addition, when the optical signal is partially blocked or the optical axis is displaced and it is not possible to receive at the correct position, the imbalance occurs in the reception voltage due to the dark current generated in the conversion element and the noise level variation in the additional circuit. However, there is a problem that the angle is corrected in the wrong direction.

The object of the present invention is to solve the above problems,
It is an object of the present invention to provide a bidirectional optical space transmission device capable of performing accurate optical axis angle correction without causing any practical problems.

[0008]

A bidirectional optical space transmission apparatus according to the present invention for achieving the above object is a counterpart apparatus which is placed opposite to each other with a predetermined distance and which performs bidirectional information transmission by an optical signal. Corresponding to the signal light intensity of the plurality of optical-electrical conversion elements, the light-transmitting section that emits the transmission light, the light-receiving section that includes a plurality of optical-electrical conversion elements that receive the signal light from the other party device. Voltage generating means for generating a plurality of voltage signals,
Based on the output of the deviation detecting means for detecting the deviation of the optical axis of the received light from the optical axis of the received light based on the plurality of voltage signals obtained from the voltage generating means, and the output of the deviation detecting means. An angle correction mechanism that performs an angle correction so that the optical axis of the transmitted light coincides with the optical axis of the received light, and a voltage that limits each voltage signal from the voltage generation means so as not to be below a predetermined lower limit value. And a limiting means.

[0009]

The bidirectional optical space transmission device having the above-mentioned configuration is
The angle of the transmitted light is corrected in advance so that the optical axes of the light-transmitting unit and the light-receiving unit are aligned, and the optical signal from the other party's device is received by the divided optical-electrical conversion element, and these plural The voltage generating means generates voltage signals corresponding to the respective light intensities based on the signals, and limits the voltage signals by the voltage limiting means so as to prevent the voltage signals from falling below a predetermined lower limit value and converts them into angle deviation signals.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on the embodiments shown in FIGS. FIG. 1 shows a configuration diagram of the present embodiment in which a lower limit limiter circuit is provided in an optical axis angle error detection system of a bidirectional optical space transmission device of a conventional example, and other configurations are similar to those of FIGS. 8 and 9 of the conventional example. Has been done. In the optical axis angle error detection system 20, the outputs of the four opto-electric conversion elements 21a to 21d, which generate a current corresponding to the intensity of the light received from the other device, are current-voltage conversion elements each including a resistor or the like. Bowl 22
a to 22d, and further a comparator as shown in FIG.
Lower limit limiter circuits 23a to 23 including rectifiers and resistors
It is connected to d.

As shown in FIG. 3, a photoelectric conversion element 21a.
Between 21d to 21d, a gap t is provided to separate the elements 21a to 21d from each other. The outputs of the lower limit limiter circuits 23a and 23b are calculated by the arithmetic circuit 24a.
The outputs of the lower limit limiter circuits 23b and 23c are connected to the arithmetic circuit 24b, the outputs of the lower limit limiter circuits 23c and 23d are connected to the arithmetic circuit 24c, and the outputs of the lower limit limiter circuits 23a and 23d are connected to the arithmetic circuit 24d.
The outputs of a and 24c are supplied to the arithmetic circuit 24e and the arithmetic circuit 24b.
The outputs of 24d and 24d are connected to the arithmetic circuit 24f, and the error voltages Vx and Vy indicating the deviation angles in the X and Y directions, respectively.
Is to occur.

As in the conventional example of FIG. 8, the transmission signal is transmitted from the electro-optical conversion element 2 of the light transmitting section 1 to the beam splitter 3,
The light is emitted from the lens 5 through the optical axis angle adjustment drive mechanism section 4. On the other hand, the received light enters the lens 5, passes through the optical axis angle adjusting drive mechanism section 4, the beam splitter 3, and the half mirror 7 and is received by the main signal light receiving element 8 and becomes a reception signal.

A part of the received light reflected by the half mirror 7 is 4 in the angle error detection system 20 as shown in FIG.
The light-to-electricity conversion elements 21a to 21d are incident as circular spots having a radius r and converted into current signals. These current signals are converted into voltage signals Va to Vd by the current-voltage converters 22a to 22d, respectively. Here, assuming that the gap t between the photoelectric conversion elements 21a to 21d is 0 and the loss of the received light at the gap t is ignored, the voltage signal is
Va to Vd and the received light intensities at the respective elements 21a to 21d are shown in FIG.
There is a proportional relationship as shown in.

The voltage signals Va to Vd are input to the lower limit limiter circuits 23 to 23d, respectively, and compared with a predetermined lower limit voltage value Vo which is preset through a comparator as shown in FIG.
The voltage signals Va ′ to Vd ′ are automatically adjusted so as not to be lower than the lower limit voltage value Vo. These voltage signals Va '~ Vd'
Is calculated by the arithmetic circuits 24a to 24f, and the error voltage Vx in the X and Y directions between the optical axis of the received light and the optical axis of the light receiving portion,
It is converted to Vy and becomes an angle deviation signal.

As shown in FIG. 8 of the conventional example, the optical axis angle drive control section 12 drives the optical axis angle adjustment drive mechanism section 4 on the basis of this angle deviation signal to control so as to correct the angular deviation. I do. As shown in FIG. 5, the amount of movement of the received light spot S, which represents the amount of optical axis angle error between the received light and the light receiving section when the gap t is 0, is proportional to the error voltage in the X and Y directions. is there. However, since the actual gap t is not 0, when a certain numerical value is taken into consideration for the gap t, a slight deviation from the straight line occurs as shown by the dotted line in FIG.

Now, if the received light spot S is at the center position on the opto-electric conversion elements 21a to 21d and its intensity distribution is uniform, the voltage signals from the elements 21a to 21d are all the same and the error voltage is It becomes 0. Here, since the light intensity on the transmission path is attenuated, each of the elements 21a to 21d is
If the intensity of the received light received at
Of the received light spot S is shifted in the X direction by the position Δx shown by the dotted line in FIG. 3, the error voltage is 0. May be. Therefore, the received light spot S fluctuates in a range centered on a circle having a radius of Δx indicated by diagonal lines.

For simplifying the explanation, consider the two-divided opto-electric conversion elements 21a and 21b as shown in FIG. 6. The received light attenuated in the transmission path is at the spot S, and the elements 21a and 21b are located. The received light intensity is converted into voltage signals VA and VB by the current-voltage converters 22a and 22b, respectively. These voltage signals VA and VB are shown in Fig. 7 (a),
As shown in (b), a sinusoidal noise voltage with amplitudes Va and Vb is superimposed.

Now, since the received light spot S is located at the center of the opto-electric conversion elements 21a and 21b, VA = VB, and at some point the converter 22a side is point A in FIG. If the 22b side is at the position of point B in FIG. 7 (b), the error voltage at this time is (VA + Va) − (VB−Vb) = Va + Vb, and the received light spot S is shifted to the position indicated by the dotted line in FIG. Then, it becomes necessary to perform angle correction. Therefore, by repeating such an operation at each time point, the received light spot S fluctuates in a range centered on a circle having a radius of Δx indicated by the diagonal line in FIG.

Here, the lower limit limiter voltage is previously set to VA (= V
If it is set to B), VB = 0 on the conversion unit 22b side at the position of point B ′ in FIG. 7B, and the error voltage becomes Va. Therefore, even if the intensity of the received light received by each of the elements 21a and 21b is reduced and the S / N ratio of the voltage signal is reduced and the influence of the noise voltage becomes relatively large, the lower limit limiter voltage is provided. The range where the received light spot S fluctuates can be narrowed.

Further, when the attenuation of the received light intensity on the transmission line is very large and the sensitivities of the opto-electric conversion elements 21a to 21d are lost, or when the optical signal is partially blocked, all the elements 21a to 21d. When the light cannot be received at 21d, each current-voltage converter 2 is caused by the dark current generated in each element 21a to 21d or the noise level variation in the additional circuit.
The noise voltage output from 2a to 22d may vary, and the movable mirror for adjusting the optical axis angle may stick to one direction in both the X axis and the Y axis. Even if the optical signal is restored in this state, the received light spot S is out of the field of view of the optical-electrical conversion elements 21a to 21d, and the normal communication state cannot be restored. However, such a problem also sets the lower limiter voltage. It can be solved by keeping it.

The voltage signals from the current-voltage converters 22a-22d corresponding to the opto-electric conversion elements 21a-21d are converted from analog to digital, and the respective lower limit limiter circuits 23-23d are controlled by software. It is also possible to do so.

[0022]

As described above, the bidirectional optical space transmission apparatus according to the present invention includes a plurality of optical fibers for detecting an angle error.
By providing voltage limiting means so that the output level from the current-voltage converter corresponding to each electric conversion element does not fall below a predetermined lower limit value, the light intensity is attenuated on the transmission line and output by the optical-electric conversion element. Even when the S / N ratio of the generated voltage signal is deteriorated, the fluctuation range of the received light spot caused by the influence of the noise voltage can be narrowed, so that the angle of the transmitted light can be corrected without any practical problems. , Even when the optical signal is blocked on the transmission line and the optical-electrical conversion element does not receive the optical signal at all, the movable mirror for adjusting the optical axis angle is stuck in a certain direction and communication becomes impossible. Can be prevented.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical axis angle error detection unit of the present embodiment.

FIG. 2 is a configuration diagram of a lower limit limiter circuit.

FIG. 3 is an explanatory diagram of a photoelectric conversion element.

FIG. 4 is a graph of received light intensity and voltage signal.

FIG. 5 is a graph showing the amount of movement of the received light spot and the error voltage.

FIG. 6 is a connection circuit diagram of a photoelectric conversion element divided into two parts.

FIG. 7 is an explanatory diagram of S / N ratio deterioration of a voltage signal.

FIG. 8 is a block diagram of a conventional bidirectional optical space transmission apparatus.

FIG. 9 is a configuration diagram of an optical axis angle error detection unit.

[Explanation of symbols]

20 Optical axis angle error detection system 21a-21d photoelectric conversion element 22a-22d current-voltage converter 23a-23d lower limit limiter circuit 24a to 24d arithmetic circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04B 10/00-10/28

Claims (4)

(57) [Claims] 1. An optical signal which is arranged to face each other at a predetermined distance.
Emits transmission light to the other device that performs bidirectional information transmission
A light transmitting unit, a light receiving unit including a plurality of photoelectric conversion elements for receiving signal light from the other device, and a plurality of voltage signals corresponding to signal light intensities of the plurality of photoelectric conversion elements. a voltage generating means for generating a, obtained from the voltage generating unit
The optical axis of the received light is detected based on the multiple voltage signals
A deviation detecting means for detecting a deviation of the transmitted light from the optical axis,
The optical axis of the transmitted light is moved forward based on the output of the deviation detecting means.
Angle to perform angle correction to match the optical axis of the received light
A bidirectional optical space transmission device comprising: a correction mechanism; and a voltage limiting unit that limits each voltage signal from the voltage generating unit so as not to become a predetermined lower limit value or less . 2. The bidirectional optical space transmission device according to claim 1, wherein the lower limit values of the plurality of voltage signals are all the same. 3. The bidirectional optical space transmission device according to claim 1, wherein the voltage limiting means is an electric circuit that limits an input voltage to a preset value and outputs the limited voltage. 4. The bidirectional optical space transmission device according to claim 1, wherein the voltage limiting means is controlled by software after analog-digital conversion.