JPH0758700A - Optical transmission loss compensation circuit - Google Patents

Abstract

PURPOSE:To take out control information which can be utilized for the compensation of optical transmission loss without transmitting control signals composed of AC signals or influencing the dynamic range of a preamplifier, to prevent constitution from being enlarged, to easily cope with an installation environment or the like and the change and to secure the dynamic range of the preamplifier. CONSTITUTION:On a route for inputting photoelectric conversion signals taken out from one of the terminals of a light receiver 74 to the preamplifier 84, a transmission signal extraction filter 82 and an electric attenuator 83 are interpolated in the order or in an inverse order. The DC components are taken out from the photoelectric conversion signals from the other terminal of the light receiver by a signal detection means 78, attenuator control means 79-81 varies the attenuation amount of the electric attenuator corresponding to the taken-out DC components and the main body of transmission signals limited to a transmission signal band for which an attenuation processing is performed is inputted to the preamplifier 84.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission loss compensating circuit for compensating for transmission loss caused by passing through an optical transmission line (optical fiber) in analog optical communication.

[0002]

2. Description of the Related Art Conventionally, a receiver equipped with an AGC (automatic gain control) circuit has been used to compensate for a transmission loss caused by passing through an optical transmission line (optical fiber) and suppress variations in the transmission line. In many cases, instead of the AGC circuit, or A
In addition to the GC circuit, there is a receiver having an optical transmission loss compensation circuit having another configuration. Hereinafter, three types of such conventional optical transmission loss compensation circuits will be sequentially described.

FIG. 2 shows a first conventional optical transmission loss compensation circuit.

In FIG. 2, a light receiver 2 such as a photodiode is arranged near the output end of an optical fiber 1 as an optical transmission line. One end of this light receiver 2 is
Is connected to a reference potential (for example, ground potential) 4 via a bias circuit 3 for converting the AC current component of the photodetector 2 into an AC voltage, and the other end of the photodetector 2 is referenced by a power source 5. The potential is made higher than the potential 4 by a predetermined voltage. A connection point between the photo detector 2 and the bias circuit 3 is connected to a band pass filter (BPF) 6,
A preamplifier (AMP) is provided at the next stage of the bandpass filter 6.
7 is provided.

Therefore, the analog optical signal transmitted through the optical fiber 1 is photoelectrically converted by the photodetector 2, and the analog electric signal is passed through the band pass filter 6 so that only the signal component is extracted and extracted. The component is amplified by the preamplifier 7 to compensate the optical transmission loss.

FIG. 3 shows a second conventional optical transmission loss compensating circuit.

In FIG. 3, an optical attenuator 12 is provided on the output end side of an optical fiber 11 as an optical transmission line, and a light receiver 13 is provided near the output end of the optical attenuator 12. One end of the photodetector 13 is connected to the reference potential 15 via a bias circuit 14 that applies a DC potential to the photodetector 13 and converts an AC current component of the photodetector 13 into an AC voltage. The end is set to a potential higher than the reference potential 15 by a predetermined voltage by the power supply 16. The connection point between the light receiver 13 and the bias circuit 14 is connected to a preamplifier (AMP) 17.

Therefore, the analog optical signal transmitted through the optical fiber 11 is attenuated by the optical attenuator 12 and then photoelectrically converted by the photodetector 13, and the analog electrical signal is amplified by the preamplifier 17 to be optically transmitted. Compensate for losses.

FIG. 4 shows a third conventional optical transmission loss compensating circuit in the receiver, and also shows the structure of the transmitter side corresponding thereto.

In FIG. 4, two signal sources 21 and 22 are provided.
Is a signal input addition circuit 2 for a first signal (for example, a transmission signal body) and a second signal (for example, a control signal related to the transmission signal body: a lower frequency than the first signal) that are alternating current signals.
Output to 3. The signal input adder circuit 23 includes the first and second
Capacitor 2 that removes unnecessary DC component in the signal
3a and 23b, and these capacitors 23a and 2b
The first and second signals via 3b are added by the wire connection 23c to obtain a final transmission signal (a signal in which the first and second signals are superimposed). A light emitter 26, a matching circuit 27, and a bias circuit 28 are connected in series between the reference potential 24 on the transmission side and the potential reduced by a predetermined voltage from the reference potential 24 by the power supply 25. The connection point of the matching circuit 27 and the bias circuit 28 is connected to the output end of the signal input addition circuit 23, and the light emitting device 26 is caused by the final transmission signal biased while reflection is prevented by impedance matching by the matching circuit 27. Is driven, this light emitter 2
The emitted light from 6 is incident on the optical fiber 29 as a transmission line, one end of which is close to the light emitter 26.

A photodetector 30 is provided near the output end of the optical fiber 29. One end of this light receiver 30 is
It is connected to a reference potential 32 on the receiver side via a bias circuit 31, and the other end of the light receiver 30 is made higher than the reference potential 32 by a predetermined voltage by a power supply 33.
The connection point between the light receiver 30 and the bias circuit 31 is connected to a preamplifier (AMP) 34. This preamplifier 3
The output signal from 4 is divided into two by a divider 35, and first and second band pass filters (BPF) 36 and 37.
Given to. The second band-pass filter 37 takes out the second signal component and supplies it to the controller 38. The controller 38 forms a control signal according to (the dynamic range of) the extracted second signal component, and the electric attenuator 39. Give to. The first bandpass filter 36 has a first
The signal component of is taken out and given to the electric attenuator 39. The electric attenuator 39 attenuates the first signal component extracted according to the control signal from the controller 38.

Therefore, the third optical transmission loss compensation circuit has
An analog optical signal on which the first and second signals are superimposed arrives via the optical fiber 29, the analog optical signal is photoelectrically converted by the photodetector 30, and the analog electric signal is amplified by the preamplifier 34. After being dispensed, the distributor 3
5 and is separated into first and second signal components by the respective bandpass filters 36 and 37, and the controller 38
The electric attenuator 39 attenuates the first signal component according to (the dynamic range of) the second signal component under the control of 1 to compensate the optical transmission loss.

[0013]

However, the above-mentioned first to third conventional optical transmission loss compensating circuits have problems.

Generally, the dynamic range of the preamplifier is required to be equal to or greater than the level variation due to the light emission level, the transmission distance, the number of branches in the transmission path, and the like. Considering the distortion caused by the non-linearity of the light emitter, it is necessary to lower the modulation of the transmission signal.As a result, if the DC bias of the light emitter becomes larger than the transmission signal, the DC bias component , The dynamic range of the preamplifier must be taken. If the dynamic range of the preamplifier is large, the configuration becomes large, and it is difficult to obtain a wide band in which the amplification factor is flat. That is, the dynamic range of the preamplifier has a characteristic that greatly affects the optical transmission loss.

According to the first optical transmission loss compensating circuit, since the DC bias component is removed by the bandpass filter 6 or the like and the preamplifier 7 only amplifies the signal component, its dynamic range can be reduced.

However, since the first optical transmission loss compensating circuit has only a structure for extracting the signal component, the optical fiber 1
Or a signal of a decrease in light input due to an abnormal light source (not shown),
The system control signal cannot be detected. In this respect, the third optical transmission loss compensating circuit is preferable, but the third optical transmission loss compensating circuit also has a problem described later. Further, the first optical transmission loss compensation circuit reduces the dynamic range of the preamplifier 7, but cannot cope with an input that exceeds the dynamic range of the preamplifier 7 in an actually installed environment. . From this point, the second optical transmission loss compensating circuit is preferable, but the second optical transmission loss compensating circuit also has a problem described later.

According to the second optical transmission loss compensating circuit, even when the input signal (the intensity of the input optical signal) exceeds the dynamic range of the preamplifier 17, the maximum input by the optical attenuator 12 can be lowered and dealt with. Preamplifier 17
It prevents the increase of the dynamic range of. That is,
The dynamic range of the preamplifier 17 and A (not shown)
Even if there is a loss variation in the optical transmission line that exceeds the variation compensation function of the GC circuit, it can be absorbed by the optical attenuator 12.

However, in the second optical transmission loss compensating circuit, the optical attenuator 12 must be selected according to the installation location of the receiver, the route of the transmission path, etc. The attenuator 12 must also be changed. Further, considering that the reflection of the optical attenuator 12 affects the quality of the transmission line, the optical attenuator 12 is a wound optical fiber having a length of several Km to several tens of Km (in order to have a predetermined length. When a plurality of optical fibers are connected to each other, it is preferable to apply the fused one. However, such an optical attenuator 12 has a large mounting area and the construction work at the time of laying is complicated.

According to the third optical transmission loss compensating circuit, since the second signal is transmitted and compensated for in addition to the first signal for transmitting the actual information, the optical transmission loss is compensated with high accuracy. be able to.

However, in the third optical transmission loss compensation circuit, in order to secure the dynamic range of the preamplifier 34, the transmission signal (first signal) is taken into consideration in consideration of the presence of the control signal (second signal). Must be reduced or the bias current of the light emitter 26 must be increased, the signal-to-noise ratio deteriorates, and the secondary and third due to the control signal and the transmission signal.
There is a problem that the next distortion occurs and the transmission quality deteriorates. There is also a problem that the hardware of the communication device (especially the transmitter) becomes large.

The first aspect of the present invention has been made in consideration of the problem (referred to as the first problem) in the first conventional optical transmission loss compensating circuit, and transmits a control signal composed of an AC signal. It is an object of the present invention to provide an optical transmission loss compensating circuit capable of taking out control information that can be used for compensation of optical transmission loss without affecting the dynamic range of the preamplifier.

The second aspect of the present invention has been made in consideration of the problem in the second conventional optical transmission loss compensating circuit (referred to as the second problem). It is an object of the present invention to provide an optical transmission loss compensating circuit capable of ensuring the dynamic range of a preamplifier by easily responding to such changes.

The third aspect of the present invention has been made in consideration of the problem (referred to as the third problem) in the third conventional optical transmission loss compensation circuit, and transmits a control signal which is an AC signal. It is an object of the present invention to provide an optical transmission loss compensating circuit that can compensate the optical transmission loss without affecting the dynamic range of the preamplifier.

[0024]

In order to solve the above-mentioned first problem, the present invention according to claim 1 provides a transmission signal extraction filter which extracts only a transmission signal component from a photoelectric conversion signal taken out from one terminal of a photodetector. In the optical transmission loss compensation circuit that extracts and gives to the preamplifier, the signal of a predetermined frequency component is taken out from the photoelectric conversion signal from the other terminal of the photodetector without affecting the photoelectric conversion signal given to the transmission signal extraction filter. It is characterized in that a signal detecting means is provided.

In order to solve the second problem, the second aspect
The present invention, in the optical transmission loss compensation circuit having an attenuator that attenuates the incoming transmission signal by the time the signal is input to the preamplifier, applies an electrical attenuator capable of varying the attenuation amount as an attenuator. It is characterized in that an electrical attenuator is interposed between the optical receiver and the preamplifier.

In order to solve the third problem, the third aspect
The present invention separates the transmission signal body and the control signal from the transmission signal photoelectrically converted by the light receiver, and the separated transmission signal body is electrically set to an attenuation amount according to the separated control signal. In the optical transmission loss compensation circuit that adjusts the level by inputting it to the attenuator, the transmission signal is a DC bias of the transmission signal main body for a predetermined amount, and the transmission signal photoelectrically converted by the photoreceiver is passed through the bandpass filter and low-pass filter. The transmission signal body component and the DC component as a control signal are extracted through a filter, and the attenuation of the electrical attenuator is set according to the extracted DC component, and the extracted transmission signal body component is attenuated and controlled. And

In order to solve all of the above-mentioned first to third problems, the present invention according to claim 4 provides a photoelectric conversion signal taken out from one terminal of a photodetector on a path for inputting to a preamplifier.
The transmission signal extraction filter and the electrical attenuator are intervened in this order or in the reverse order, and the DC component is taken out by the signal detecting means from the photoelectric conversion signal from the other terminal of the photodetector, and is converted into the DC component taken out by the attenuator controlling means. The attenuation amount of the electrical attenuator is changed in response to the transmission signal main body, which is limited to the transmission signal band and is subjected to the attenuation processing, is input to the preamplifier.

[0028]

According to the present invention, the signal detecting means for extracting the signal of the predetermined frequency component from the photoelectric conversion signal from the terminal opposite to the terminal of the optical receiver for extracting the transmission signal to the transmission signal processing system is provided. A signal that can be used for various controls (AGC control and attenuation control) can be obtained without affecting the transmission signal processing system.

According to the present invention of claim 2, as an attenuator for preventing an increase in the dynamic range of the preamplifier, an electrical attenuator is applied unlike the conventional one.
By interposing this attenuator between the photoreceiver and the preamplifier, it is possible to easily cope with the case where the installation location of the receiver or the route of the transmission line is changed, and the presence of the attenuator makes the optical transmission loss compensation circuit. It is designed to be easy to install without increasing the size.

According to the third aspect of the present invention, the transmission signal is DC-biased by a predetermined amount in the transmission signal main body, and the transmission signal photoelectrically converted by the photodetector is transmitted through a bandpass filter and a low-pass filter. By extracting the DC component as the signal body component and the control signal, setting the attenuation amount of the electrical attenuator according to the extracted DC component, and controlling the attenuation of the extracted transmission signal body component, the level of the transmission signal body and The transmission quality of the control signal is not adversely affected by the modulation degree, the transmission quality can be improved, and the transmission side configuration and the internal configuration of the attenuator control means can be simplified.

According to a fourth aspect of the present invention, a transmission signal extraction filter and an electric attenuator are provided in this order or in the reverse order on a path for inputting a photoelectric conversion signal taken out from one terminal of a photodetector to a preamplifier. At the same time, the DC component is extracted from the photoelectric conversion signal from the other terminal of the photodetector by the signal detection means, and the attenuation amount of the electrical attenuator is changed according to the DC component extracted by the attenuator control means, and the transmission signal band The pre-amplifier inputs the transmission signal main body which is limited to and is attenuated.
All of the advantages (effects) of the present invention of 3 to 3 are combined.

[0032]

Embodiment (A) First Embodiment A first embodiment of an optical transmission loss compensating circuit according to the present invention will be described in detail below with reference to FIG.

The optical transmission loss compensation circuit of the first embodiment is
This is configured to solve the problem of the first conventional optical transmission loss compensation circuit (see FIG. 2). Therefore, FIG.
2, the same parts as those in FIG. 2 are designated by the same reference numerals.

The optical transmission loss compensating circuit of the first embodiment is shown in FIG.
As shown in FIG. 1, in addition to the configuration of the first conventional optical transmission loss compensating circuit, the current detector 40, the resistor 41 and the capacitor 4 are provided.
Have two. That is, the high potential side terminal of the power source 5 is not directly connected to one terminal of the light receiver 2, but a series circuit of the current detector 40 and the resistor 41 and the capacitor 42 are connected in parallel between these terminals. . Since the resistor 41 is connected in series to the current detector 40 and the capacitor 42 is connected in parallel to these, a high frequency component flows through the capacitor 42 and a low frequency component flows through the current detector 40. Therefore, the current detector 40 detects the low frequency component of the input signal (analog electric signal) photoelectrically converted by the light receiver 2. As the current detector 40, for example, a current mirror circuit can be applied, and the current projected by the mirror serves as a detection signal (current / voltage conversion may be performed and output).

Also in the optical transmission loss compensating circuit of the first embodiment, since the direct-current bias component is removed by the bandpass filter 6 and the like, and the preamplifier 7 only amplifies the signal component, its dynamic range can be reduced. The effect is obtained.

The optical transmission loss compensating circuit of the first embodiment has the following effects. A signal indicating a decrease in optical input due to an abnormality in the optical fiber 1 or a light emitting device (not shown) facing the optical fiber
The control signal (DC component) of the system can be detected by the current detector 40. Such a detection signal is A
It may be used as one type of control signal of the GC circuit, may be used as a start signal of the abnormality monitoring unit, or may be applied to other purposes.

Since only the signal component is extracted by the bandpass filter 6, it is not possible to provide a detector for low frequency components in the subsequent stage of the bandpass filter 6, and the structure of the first embodiment is the first step. The low frequency component can be detected without affecting the signal component extraction operation.

As a modification of the first embodiment, the photoelectric conversion signal given to the transmission signal processing system and the lead-out terminal in the photodetector of the photoelectric conversion signal given to the detection system of the signal usable for control are reversed, or the control is performed. Examples thereof include a signal that can be used as a voltage signal, a signal in which the high and low potentials applied to the light receiver are reversed, and the like.

(B) Second Embodiment Next, a second embodiment of the optical transmission loss compensation circuit according to the present invention will be described in detail with reference to FIG.

The optical transmission loss compensation circuit of the second embodiment is
It is configured to solve the problem of the second conventional optical transmission loss compensation circuit (see FIG. 3). Therefore, FIG.
3, the same parts as those in FIG. 3 are designated by the same reference numerals.

The optical transmission loss compensating circuit of the second embodiment is shown in FIG.
As shown in FIG. 3, no optical attenuator is provided on the optical fiber 11, and the electrical attenuator 50 is provided in the front stage of the preamplifier 17. This attenuator 50
Is a variable attenuator, for example, which sets a basic attenuation amount according to the length of the optical fiber 11 when the optical transmission loss compensation circuit is installed. Note that the attenuation amount of the attenuator 50 may be controlled according to the detection signal in combination with the first embodiment. For example, if the transmission line loss is less than the maximum, the preamplifier 17
The amount of attenuation is controlled so that the signal input to is the same as when the transmission line loss is maximum.

Also in the optical transmission loss compensating circuit of the second embodiment, the input signal (the intensity of the input optical signal) has a preamplifier 1
Even when the dynamic range of 7 is exceeded, the maximum input by the attenuator 50 can be lowered to cope with it, and the increase of the dynamic range of the preamplifier 17 is prevented.
That is, even if the dynamic range of the preamplifier 17 or the loss variation of the optical transmission line that exceeds the variation compensation function of the AGC circuit (not shown) is absorbed by the attenuator 50. Such an effect is produced by the attenuator 50 being provided in the preceding stage of the preamplifier 17.

Further, according to the optical transmission loss compensating circuit of the second embodiment, since the electric attenuator 50 is applied as the attenuator, not the optical attenuator, the installation location of the receiver, the route of the transmission path, etc. are changed. In this case, the attenuator 50 does not increase the size of the optical transmission loss compensating circuit and the installation work can be simplified.

As a modification of the second embodiment, there may be mentioned one in which the high and low potentials applied to the photodetector 13 are reversed.

(C) Third Embodiment Next, a third embodiment of the optical transmission loss compensating circuit according to the present invention will be described in detail with reference to FIG.

The optical transmission loss compensation circuit of the third embodiment is
The third conventional optical transmission loss compensation circuit (see FIG. 4) is configured to solve the problem. Therefore, FIG.
4, the same parts as those in FIG. 4 are designated by the same reference numerals.

In FIG. 7, in the optical transmission loss compensating circuit of the third embodiment, as the signal source for outputting the transmitted signal, only the signal source 21 for outputting the transmission signal body composed of an AC signal is provided. There is. The signal from the signal source 21 is given to the optical output drive circuit via the signal input circuit formed of the capacitor 23a. The optical output drive circuit includes a light emitter 26, a matching circuit 27, and a bias circuit connected in series between a reference potential 24 on the transmission side and a potential reduced by a predetermined voltage from the reference potential 24 by a power supply 25, as in the conventional case. In the same manner as in the prior art, the DC biased transmission signal is subjected to electro-optical conversion, and the transmission optical signal is incident on the optical fiber 29.

In the optical transmission loss compensation circuit of the third embodiment, the optical signal emitted from the optical fiber 29 is received by the photodetector 30.
Is incident on. One end of the light receiver 30 is connected to the reference potential 32 on the receiver side via the bias circuit 60, and the other end of the light receiver 30 is connected to the reference potential 32 by the power supply 33.
To a potential higher than the predetermined voltage. Light receiver 30
The photoelectric conversion signal, which is photoelectrically converted by the bias circuit 60 and converted into a voltage signal by the bias circuit 60, is amplified by the preamplifier 34 and input to the distributor 35.

One of the halved signals is applied to the band pass filter 36 to extract the signal component related to the signal source 21 and input to the electric attenuator 39 as a controlled signal. The other of the two divided signals is the low pass filter (LP
F) 61 is applied to the power supply 25 on the transmission side and the DC component related to the bias circuit 28 is extracted, and the controller 62
Applies a control signal according to the extracted DC component to the electric attenuator 39, and the electric attenuator 39 attenuates the extracted signal component related to the signal source 21 according to the control signal to compensate for the optical transmission loss. .

For example, the controller 62 is set so that the electric attenuator 39 does not perform the attenuation operation when the line length of the optical fiber 29 is the longest and the transmission loss is the largest. The controller 62 uses this state as a reference, and the DC component (bias) that is the output of the low-pass filter 61.
When N is equal to N times the reference, the electric attenuator 39 controls the electric attenuator 39 so as to execute a damping operation for making the output 1 / N with respect to the input.

Since the optical fiber 29 has a wide band, the transmission signal and the bias in the output optical signal from the light emitter 26 are transmitted at a constant ratio, and therefore the transmission signal can be controlled by the bias (DC component).

As described above, the optical transmission loss compensating circuit of the third embodiment uses the DC bias for the transmission of the transmission signal body as the control signal without transmitting the AC signal as the control signal. It has characteristics.

The optical transmission loss compensating circuit of the third embodiment is similar to the case where the compensating operation is executed by transmitting the control signal in addition to the first signal for transmitting the actual information. The loss can be compensated with high accuracy.

Furthermore, according to the optical transmission loss compensating circuit of the third embodiment, since the control signal is a DC bias, the transmission of the control signal does not adversely affect the level and modulation degree of the transmission signal body, and the transmission quality is improved. It is possible to improve the transmission efficiency and simplify the internal structure of the transmitter and the controller.

(D) Fourth Embodiment Next, a fourth embodiment of the optical transmission loss compensating circuit according to the present invention will be described in detail with reference to the drawings. Here, FIG. 1 is a block diagram showing the configuration of the fourth embodiment, and FIG. 8 is a signal waveform diagram of each part thereof.

The optical transmission loss compensating circuit of the fourth embodiment is
Characteristic configuration (technical idea) of the above-described first to third embodiments
Are combined so that the effects of the first to third embodiments can be directly exerted. Note that FIG. 1 shows a functional block configuration.

In FIG. 1, the transmission signal S1 centered at 0 V shown in FIG. 8A output from the transmission signal input circuit 70 in the transmitter is transmitted by the bias circuit 72 to the transmission signal S1 shown in FIG.
As shown in FIG. 8B, a predetermined direct current component (direct current signal) S2 is applied to a light emitter (for example, a laser diode: accompanied by a matching circuit) 71 which is biased by a current, and is photoelectrically converted by the light emitter 71. The analog optical signal S3 shown in (c) is incident on the optical fiber 73.

The analog optical signal S4 emitted from the optical fiber 73 is, as shown in FIG.
The transmission signal and the direct current signal are uniformly attenuated according to the length of the signal, and this is applied to the photodetector (eg, photodiode) 74 biased by the bias circuit 75 at a constant voltage, and photoelectrically converted. FIG. 8E by the photodetector 74
The photoelectric conversion signal (current signal) S5 shown in (1) is taken out by the first and second signal detection circuits 76 and 77 from both ends of the light receiver 74, respectively.

A low-pass filter (DC signal pass filter) 78 extracts a DC component S6 shown in FIG. 8F from the signal extracted by the first signal detection circuit 76 (current / voltage conversion is also performed). The extracted DC component is given to the comparator 79. This comparator 79
Further, a reference signal (DC signal) is also applied to the reference output circuit 80, and the ratio of the extracted DC component and the reference signal is obtained by the comparator 79, and this ratio signal is supplied to the control circuit 81.
Given to. This ratio signal reflects the state of the transmission path of the optical fiber 73 and the fluctuation of the light emission output of the light emitter 71, and the control circuit 81 forms an attenuation control signal according to the reciprocal of this ratio signal. It is given as a control signal to a variable electric attenuator 83 described later.

The reference signal is, for example, the low-pass filter 7 when the amount of light input to the photodetector 74 is the lowest.
8 is set to the same potential as the output.

The second signal detection circuit 77 causes the light receiver 7
8 is applied to a bandpass filter (transmission signal pass filter) 82, which is equal to the band component of the transmission signal output from the transmission signal input circuit 70 by the bandpass filter 82. A component (transmission signal component: 0V-centered signal) S7 in the photoelectric conversion signal shown in (g) is extracted (current / voltage conversion is also performed). The extracted transmission signal component is given to the variable electric attenuator 83 as a signal to be attenuated, and the electric attenuator 83 executes the attenuation in accordance with the above-mentioned attenuation control signal, and the attenuated signal is attenuated as shown in FIG. The signal S8 shown in FIG. Thus, the attenuated signal is amplified by this preamplifier 84,
The amplified signal S9 shown in FIG. 8 (i) is given to the transmission signal output circuit 85.

The order of the bandpass filter 82 and the variable electric attenuator 83 may be reversed.

As described above, in the optical transmission loss compensating circuit of the fourth embodiment, in addition to the photoelectric conversion signal given to the bandpass filter 82 (6), the DC detection signal that can be used for control from the photodetector 74 (2) is also provided. That you can take out the first
It has the characteristic configurations 76 and 78 (40 to 42) of the embodiment.

The optical transmission loss compensating circuit of the fourth embodiment has an electric attenuator 83 (50) capable of coping with variations in the transmission line while preventing an increase in the dynamic range of the preamplifier 84 (17). It has the features of the second embodiment.

Furthermore, the optical transmission loss compensating circuit of the fourth embodiment is provided with an electric attenuator 83 (39) for suppressing fluctuations in the transmission line and the light emitting device, and a third component for controlling this attenuator by extracting a DC component. It has the characteristics of the embodiment.

Therefore, according to the optical transmission loss compensating circuit of the fourth embodiment, since the preamplifier 84 only needs to amplify the signal component, the dynamic range can be reduced. Further, the control signal (DC component) can be detected without affecting the processing system of the transmission signal. Further, even when the input signal (the intensity of the input optical signal) exceeds the dynamic range of the preamplifier 84, it is possible to reduce the maximum input by the attenuator 83 to cope with it.
An increase in the dynamic range of the preamplifier 84 can be prevented. Since the electric attenuator 83 is applied as the attenuator, it can easily cope with the case where the installation location of the receiver or the route of the transmission line is changed, and the presence of the attenuator 83 enables the optical transmission loss compensation circuit. It can be installed easily without increasing the size. Furthermore, because the compensation operation is performed by transmitting a control signal that is a DC component in addition to the transmission signal, the optical transmission loss can be compensated with high accuracy, and the control signal is a DC bias, so the level of the transmission signal itself It is possible to improve the transmission quality without adversely affecting the modulation degree and the transmission of the control signal and to simplify the configuration on the transmission side.

(E) Fifth Embodiment Next, a fifth embodiment of the optical transmission loss compensating circuit according to the present invention will be described in detail with reference to FIG.

The optical transmission loss compensation circuit of the fifth embodiment is
This is an embodiment in which the fourth embodiment is further embodied.
The principal part structure in a receiver is shown. The detailed description is omitted by leaving it to the description of the fourth embodiment, and here, the correspondence relationship between the fourth embodiment and the fifth embodiment will be described.

In FIGS. 1 and 9, a photodiode 90 is applied as the light receiver 74, and an inductance 91 and a voltage source 92 are applied as the bias circuit 75. The cathode of the photodiode 90 corresponds to the first signal detection circuit 76, and the anode thereof corresponds to the second signal detection circuit 77. A capacitor 93 having one end connected to the anode of the photodiode 90 constitutes a bandpass filter 82, and an electric field in which a source and a drain are connected in series between the other end of the capacitor 93 and the input end of the preamplifier 84. The effect transistor (FET) 94 constitutes the variable electric attenuator 83. The low pass filter 78 is composed of a capacitor 95 and a current mirror circuit 96, and the gate of the field effect transistor 94 is controlled according to the detection signal.

Also in the fifth embodiment, the same effect as that of the fourth embodiment can be obtained.

[0071]

According to the first aspect of the present invention, the photoelectric conversion signal from the photoelectric conversion signal from the terminal opposite to the terminal of the optical receiver for supplying the signal to the transmission signal processing system is supplied to the transmission signal extraction filter. Since the signal detection means for extracting the converted signal without affecting the converted signal is provided, it is possible to compensate for the optical transmission loss without transmitting the control signal composed of the AC signal and without affecting the dynamic range of the preamplifier. You will be able to retrieve the available control information.

According to the second aspect of the present invention, an electric attenuator is applied instead of an optical attenuator.
The dynamic range of the preamplifier can be secured by easily adapting to the installation environment and its changes without increasing the size of the configuration.

According to the third aspect of the present invention, a transmission signal is obtained by subjecting the transmission signal body to a direct current bias by a predetermined amount, and the transmission signal photoelectrically converted by the photodetector is passed through the band pass filter and the low pass filter. The transmission signal body component and the DC component as the control signal are extracted, and the attenuation of the electrical attenuator is set according to the extracted DC component, and the extracted transmission signal body component is controlled for attenuation. The control signal does not adversely affect the modulation degree, the transmission quality can be improved, and the internal structure of the transmitting side and the attenuator control means can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a fourth embodiment.

FIG. 2 is a block diagram showing a first conventional configuration.

FIG. 3 is a block diagram showing a second conventional configuration.

FIG. 4 is a block diagram showing a third conventional configuration.

FIG. 5 is a block diagram showing the configuration of the first embodiment.

FIG. 6 is a block diagram showing a configuration of a second embodiment.

FIG. 7 is a block diagram showing a configuration of a third embodiment.

FIG. 8 is a signal waveform diagram of each part of the fourth embodiment.

FIG. 9 is a block diagram showing the configuration of a fifth embodiment.

[Explanation of reference numerals] 73 ... Optical fiber, 74 ... Photoreceiver, 75 ... Bias circuit, 78 ... Low-pass filter (DC signal extraction filter), 79 ... Comparator, 80 ... Reference output circuit, 81 ... Control circuit, 82 ... band pass filter (transmission signal extraction filter), 83 ... variable electric attenuator, 84 ... preamplifier.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H04B 10/04 10/06 10/02 10/18 (72) Inventor Shun Shiraishi Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (4)

[Claims] 1. An optical transmission loss compensating circuit, in which a transmission signal extraction filter extracts only a transmission signal component from a photoelectric conversion signal taken out from one terminal of a photoreceiver and gives it to a preamplifier, wherein the other terminal of the photoreceiver is provided. An optical transmission loss compensating circuit is provided with signal detection means for extracting a signal of a predetermined frequency component from the photoelectric conversion signal from the device without affecting the photoelectric conversion signal given to the transmission signal extraction filter. 2. An optical transmission loss compensation circuit having an attenuator for attenuating an incoming transmission signal before inputting a signal to a preamplifier, wherein an electric attenuator capable of varying an attenuation amount is applied as the attenuator, An optical transmission loss compensating circuit characterized in that the electrical attenuator is interposed between a light receiver and a preamplifier. 3. A transmission signal main body and a control signal are separated from a transmission signal photoelectrically converted by a light receiver, and the separated transmission signal main body is set to an attenuation amount according to the separated control signal. In the optical transmission loss compensation circuit that adjusts the level by inputting it to the attenuator, the transmission signal is a DC bias of the transmission signal main body for a predetermined amount, and the transmission signal photoelectrically converted by the photoreceiver is converted into a bandpass filter and a low-pass filter. Extracting the transmission signal body component and the DC component as a control signal through a pass filter, setting the attenuation amount of the electrical attenuator according to the extracted DC component, and controlling the extracted transmission signal body component. Optical transmission loss compensation circuit characterized by. 4. A transmission signal extraction filter and an electrical attenuator are inserted in this order or in the reverse order on a path for inputting a photoelectric conversion signal taken out from one terminal of a photodetector to a preamplifier, The DC component of the photoelectric conversion signal from the other terminal of the device is taken out by the signal detecting means, and the attenuation amount of the electric attenuator is varied according to the DC component taken out by the attenuator control means, and the signal is limited to the transmission signal band. Moreover, an optical transmission loss compensating circuit characterized in that the attenuated transmission signal body is input to the preamplifier.