JPH0832520A - Two-way optical space transmitter - Google Patents

Abstract

PURPOSE:To detect accurately an angular deviation in the two-way optical space transmitter. CONSTITUTION:A photoelectric conversion section 11 comprised of four elements 11a-11d is provided on an optical path. Outputs of the elements 11a-11d are connected to current/voltage conversion sections 12-15 converting a current signal into a voltage signal and outputs of the current/voltage conversion sections 12-15 are connected respectively to logarithmic amplifiers 16-19. The light detected by the elements 11a-11d is amplified by the logarithmic amplifiers 16-19 to make the relation between the received luminous quantity of the elements 11a-11d and the output of the logarithmic amplifiers 16-19 linear thereby making an error voltage with respect to an angular deviation constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional optical space transmission device for transmitting / receiving information to / from a remote place by using a light beam with a common optical axis of transmitted / received light.

[0002]

2. Description of the Related Art Generally, in the case of transmitting information to a remote place by a light flux, the optical axis of the received light transmitted from the partner device and the own device are affected by the action of wind, solar radiation or the like or the artificial action. The optical axis of the light receiving portion may be displaced, the S / N ratio of the signal may deteriorate, and in the worst case, communication may be impossible. For this reason, in the conventional two-way optical space transmission device, the optical axis of the transmitted light transmitted from the device itself and the optical axis of the light receiving part are made to coincide with each other in the device in advance, and they are always transmitted from the partner device during operation. The optical axis deviation is prevented by detecting and correcting the angular deviation between the optical axis of the received light and the optical axis of the light receiving portion of the device, that is, the optical axis of the transmitted light.

FIG. 7 is a block circuit diagram of the inside of the apparatus, in which the transmitted light from the electro-optical converting section 1 is transmitted through the beam splitter 2.
Then, the light passes through the optical axis angle adjusting drive mechanism section 3 and is sent out through the lens 4. On the other hand, the received light transmitted from the partner device is taken into the device via the lens 4, guided to the light receiving part 5 through the optical axis angle adjusting drive mechanism part 3 and the beam splitter 2, and further by the half mirror 6. Main signal receiver 7
And the angle error detection unit 8 is divided. The angle error detection unit 8 detects an angle deviation between the optical axis of the received light and the optical axis of the light receiving unit, and the optical axis angle adjustment drive control unit 9 detects the optical axis angle adjustment drive mechanism unit 3 based on this angle deviation information. It is configured to control and correct the angular deviation.

Since the optical axis of the light-transmitting section and the optical axis of the light-receiving section in the device coincide with each other in advance, the received light transmitted from the other device will be sent on the same optical axis, and both of the opposing devices will be sent. By performing such an operation also in the device, it is possible to always perform stable bidirectional optical space transmission.

FIG. 8 is a front view of a conventional photodetector in the angle error detection section 8, and a photoelectric conversion section composed of four divided elements 8a to 8d is arranged on the optical path. These elements 8a to 8d respectively generate electric signals corresponding to the amount of received light, and add / subtract these signals to generate angle deviation information between the optical axis of the received light and the optical axis of the light receiving unit. .

[0006]

However, in the above-mentioned conventional example, when the amount of light on the transmission line is attenuated by rain or fog and the total amount of light received by the elements 8a to 8d in FIG. Even if the amount of angular deviation between the optical axis of the light and the optical axis of the light receiving section is the same, the angular deviation information detected by the angular error detecting section 8 changes, so that the elements 8a to It is necessary to perform processing such as normalization on all signals received at 8d.

An object of the present invention is to solve the above problems and to provide a bidirectional optical space transmission device capable of accurately detecting the amount of angular deviation even when the total amount of light of the photoelectric conversion unit is reduced. is there.

[0008]

A bidirectional optical space transmission apparatus according to the present invention for achieving the above object performs bidirectional information transmission by a light beam with a common optical axis of transmission / reception light to a remote place, In a bidirectional optical space transmission device having an angle correction function for correcting the angular deviation of the transmitted / received light, a photoelectric conversion element divided into a plurality of pieces for receiving the received light transmitted from the partner device, and an input from the photoelectric conversion element A current / voltage conversion unit for converting the current signal into a voltage signal, a logarithmic amplifier for amplifying the voltage signal input from the current / voltage conversion unit by a logarithmic function, and the sum and difference of the outputs of the logarithmic amplifier It is characterized in that it is provided with a detection means for detecting the amount of angular deviation between the optical axis of the partner device and the optical axis of the own device.

[0009]

The bidirectional optical space transmission device having the above-mentioned configuration is
The received light transmitted from the other device is received by the photoelectric conversion element, the signal is converted into a voltage signal by the current / voltage conversion unit, this voltage signal is amplified by a logarithmic amplifier, and the sum and difference of the amplified signals are calculated. The amount of angular deviation between the optical axis of the partner device and the optical axis of the own device is detected.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a configuration diagram of an angle error detection unit according to the embodiment, in which four elements 11a to 1 are provided on the optical path of the light receiving unit.
A photoelectric conversion unit 11 composed of 1d is provided. The outputs of these elements 11a to 11d are connected to current / voltage converters 12 to 15 that convert current signals into voltage signals, and the outputs of the current / voltage converters 12 to 15 are logarithmic amplifiers 16 to 19.
Respectively connected to.

The outputs of the logarithmic amplifiers 16 and 17 are the adder 20.
And the outputs of the logarithmic amplifiers 18 and 19 are connected to the adder 21.
Further, the outputs of the adders 20 and 21 are connected to the subtractor 22 so that the subtractor 22 outputs the X-direction error voltage. The outputs of the logarithmic amplifiers 16 and 19 are connected to the adder 23, the outputs of the logarithmic amplifiers 17 and 18 are connected to the adder 24, and the outputs of the adders 23 and 24 are connected to the subtractor 25. ,
The subtractor 25 outputs the Y-direction error voltage.

The elements 11a to 11d of the photoelectric converter 11 generate currents proportional to the amount of received light, and these current signals are converted into voltage signals by the current / voltage converters 12 to 15, respectively. Next, these voltage signals are amplified by logarithmic amplifiers 16 to 19 and then added by an adder 20,
Addition and subtraction are performed by 21, 23, 24 and subtractors 22, 25, and angle deviation signals in the X and Y directions between the optical axis of the received light and the optical axis of the receiving unit are obtained.

FIG. 2 is a graph showing the relationship between the amount of received light of the elements 11a to 11d and the outputs of the logarithmic amplifiers 16 to 19, and the amount of received light of the elements 11a to 11d is from -80 dBm to-.
Even if it is increased to 70 dBm, it is -30 dBm to -20 dBm
It also shows that the voltage difference becomes 0.5 V even when the voltage increases to 0, that is, the proportional relationship is 0.05 V / dB.
Further, FIG. 3 is a graph showing a similar relationship when the logarithmic amplifiers 16 to 19 are not inserted, and in this case, the proportional relationship as shown in FIG. 2 cannot be obtained.

FIG. 4 is an explanatory view when the position of the received light spot S is changed. The diameter of the received light spot S is 2r, the total amount of light is P dBm, and the intensity distribution of the received light spot S is uniform. . Although the elements 11a to 11d are actually separated from each other by the gap width t, the gap width t = 0 for the sake of explanation. In this way, the received light spot S
Is shifted in the X direction by Δx (<r), the photoelectric conversion unit 11
If the total amount of light is P, the outputs of the elements 11a and 11b are P-6-q1, and the outputs of the elements 11c and 11d are P-6.
It becomes −q2.

At this time, if the diameter 2r of the received light spot S is constant, the values q1 and q2 corresponding to the deviation amount Δx are the total light amount P.
It becomes constant regardless of. That is, the total amount of light P can be obtained by providing the characteristic that the relationship between the received light amount of the elements 11a to 11d and the output of the logarithmic amplifiers 16 to 19 is proportional.
The error voltage with respect to the amount of deviation Δx of the received light spot S, that is, the amount of angular deviation between the optical axis of the received light and the optical axis of the light receiving section can be made constant as shown in FIG. In addition, in FIG. 5, the dotted line shows the case where the gap width t is finite.

Further, in the optical space transmission device, when detecting an angular deviation of a main signal to be transmitted, in order to eliminate the influence of background light, a signal having a narrower occupied band than that of the main signal is superimposed and transmitted. There is. In this case, the same effect as that of the embodiment can be obtained by inserting the detection circuits 31 to 34 in the subsequent stages of the logarithmic amplifiers 16 to 19 as shown in FIG. It should be noted that the detection circuits 31 to 34 may be provided before the logarithmic amplifiers 16 to 19 without any problem.

[0017]

As described above, in the two-way optical space transmission apparatus according to the present invention, the total amount of light received by the photoelectric conversion element is changed by providing the photoelectric conversion element in the optical space transmission apparatus with the logarithmic amplifier. However, it is possible to accurately detect the amount of angular deviation between the optical axis of the received light and the optical axis of the light receiving unit, that is, the optical axis of the transmitted light transmitted from the device. In addition, the process of normalizing the received light amount of each photoelectric conversion element with the total amount of light becomes unnecessary, and the device can be simplified.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is a graph showing the relationship between the amount of received light and the output of a logarithmic amplifier.

FIG. 3 is a graph diagram when a logarithmic amplifier is not used.

FIG. 4 is an explanatory diagram when the position of a received light spot S changes.

FIG. 5 is a graph showing a relationship between an angular deviation amount and an error voltage.

FIG. 6 is a configuration diagram of another embodiment.

FIG. 7 is a configuration diagram of a conventional example.

FIG. 8 is a front view of an angle error detection unit.

[Explanation of symbols]

 11 Photoelectric conversion part 12-15 Current / voltage conversion part 16-19 Logarithmic amplifier 20, 21, 23, 24 Adder 22, 25 Subtractor 31-34 Detection circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H04B 10/02 10/18 10/28 10/26 10/14 10/04 10/06 H04B 9 / 00 Y

Claims (2)

[Claims] 1. A bidirectional optical space transmission device having an angle correction function for performing bidirectional information transmission by a light beam with a common optical axis of transmitted / received light to a remote place and correcting an angular deviation of the transmitted / received light, A photoelectric conversion element divided into a plurality of parts for receiving the received light transmitted from the partner device, and a current / current for converting a current signal input from the photoelectric conversion element into a voltage signal.
A voltage converter, a logarithmic amplifier that amplifies the voltage signal input from the current / voltage converter by a logarithmic function, and an optical axis of the partner device and an optical axis of the own device based on the sum and difference of outputs of the logarithmic amplifier. And a detecting means for detecting the amount of angular deviation of the bidirectional optical space transmission device. 2. The bidirectional optical space transmission device according to claim 1, wherein a detector is provided in a stage before or after the logarithmic amplifier.