JPH0837499A - Optical signal receiver - Google Patents

Abstract

PURPOSE:To prevent excess optical intensity from being made incident an a main light receiving device even when an optical signal having an excess luminous intensity is received. CONSTITUTION:The receiver is provided with an optical branching device 25 branching an optical signal a received externally into two directions, a monitor light receiving device 26 receiving the one optical signal b branched by the branching device and converting it into a luminous intensity signal d, a variable optical attenuator 28 attenuating the other optical signal c branched by the optical branching device 25, and a main light receiving device 29 receiving the optical signal e attenuated by the variable optical attenuator 28 and converting the signal into an electric signal f. A control section 27 varies an attenuation A of the variable optical attenuator 28 based on the luminous intensity signal d outputted from the monitor light receiving device 26 to control the luminous intensity of the optical signal e received by the main light receiving device 29 optimizingly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal receiving apparatus for receiving an optical signal input from the outside via an optical fiber or the like and converting it into an electric signal.

[0002]

2. Description of the Related Art In an optical communication system, communication bases are connected to each other by an optical cable and optical signals are transmitted and received through an optical fiber. In this case, before actually operating the optical communication system, it is necessary to test that a correct optical signal is input to each optical communication device arranged in each communication base.

An optical signal analyzer for performing such a test is constructed as shown in FIG. 8, for example. An optical signal input into the optical signal analyzing device 2 via the optical fiber 1 is first converted into an electrical signal by a PIN-PD (pin photodiode) 4 in the optical signal receiving section 3 and then predetermined by the equalizing amplifier 5. It is amplified to the signal level of.

The amplified electric signal output from the optical signal receiving section 3 is input to the decoding circuit 6 and the clock recovery circuit 7. The clock recovery circuit 7 receives the clock signal CL from the received signal.
K is reproduced and sent to the decoding circuit 6 and the signal analysis unit 8. The decoding circuit 6 demodulates the inputted electric signal into the digital data D by using the clock signal CLK, and the signal analysis unit 8
Send to. The signal analyzer 8 analyzes the corresponding digital data D to determine whether the received optical signal is normal.

FIG. 9 is also a block diagram showing a schematic configuration of an optical signal analyzing apparatus 2a used for the same purpose. In this optical signal analyzing apparatus 2a, P is provided in the optical signal receiving section 3a.
An APD (avalanche photodiode) 9 is incorporated in place of the IN-PD 4. And this APD
The bias of 9 is set by the APD bias circuit 10.
The APD 9 is a highly sensitive light receiving element having a light detection function and an output electric signal amplification function.

As shown in FIGS. 8 and 9, a PIN-PD is used as a light receiving element for an optical signal in the optical signal receiving sections 3 and 3a.
4 or APD9 is used. And, in general, PIN
-The PD 4 is used for receiving an optical signal in short-distance transmission in which the attenuation of the optical signal is relatively small. On the other hand, APD9
As described above, since it has high sensitivity, it is generally used for receiving an optical signal in long-distance transmission in which attenuation of the optical signal is relatively large.

In the above-mentioned photodetectors such as PIN-PD4 and APD9, in order to accurately convert the input optical signal into an electric signal, an optimum range exists in the light intensity range of each optical signal incident on each photodetector. To do. When the light intensity of the incident optical signal is excessively low, the S / N ratio of the output electric signal decreases, and when the optical intensity of the incident optical signal is high, the output electric signal is saturated and excessively high. May damage the light receiver itself.

Therefore, the standard of the incident light intensity is set for each light receiver. For example, the upper limit light intensity of PIN-PD is about +3 dBm, and the upper limit light intensity of APD is -5.
It is about dBm. Then, when an optical signal is incident on the optical signal receiving device, it is necessary to take care so that an optical signal having an optical intensity higher than the upper limit optical intensity is not incident.

The light intensity of the optical signal transmitted through the optical fiber of the conventional optical communication system usually does not exceed the above-mentioned respective upper limit light intensities.

On the other hand, in recent years, an erbium (Er) -doped optical amplifier having a simple structure, capable of easily obtaining a high amplification factor in a wide wavelength band and having low noise characteristics has been put into practical use.

More specifically, this erbium (E
The r) -doped optical amplifier uses an Er-doped optical fiber doped with erbium (Er), which is a rare earth element,
It has a function of directly amplifying an optical signal inputted from the outside in the Er-doped optical fiber.

In an optical amplifier using such an Er-doped optical fiber, high output and amplification characteristics in a wide wavelength range are easily realized in the 1.55 μm band which is a low loss wavelength of a general optical fiber. Since this erbium (Er) -doped optical amplifier operates with high efficiency for power amplification, the saturation output can be increased by increasing the pumping input. With the current technology, it has become possible to easily output an optical signal having a light intensity of +20 dBm or more.

By inserting the optical amplifier having such excellent characteristics into a general optical fiber, it becomes possible to transmit an optical signal at a stretch to a distant place using an optical cable.

FIGS. 10A and 10B are schematic diagrams showing an optical communication system in which the above-mentioned optical amplifier is incorporated. The distance between the transmission / reception base stations 11a and 11b is set long, for example, to exceed 50 km. Then, the optical fibers 12a and 12 for connecting the transmitting / receiving bases 11a and 11b to each other.
Erbium (Er) -doped optical amplifier 1 described in b.
3a and 13b are inserted.

In FIG. 10A, each transmitting / receiving base 1
Optical amplifiers 13a and 13b are inserted in the optical fibers 12a and 12b near the optical receivers 1a and 11b, respectively. Further, in FIG. 10 (b), each optical amplifier 13 is located at a substantially intermediate position in each optical fiber 12a, 12b.
a and 13b are inserted.

Although not shown, each transmitting / receiving base 11
Each optical fiber 1 near each transmitter / receiver in a and 11b
It is also possible to insert the optical amplifiers 13a and 13b into the optical amplifiers 2a and 12b. The amplification factors of the optical amplifiers 13a and 13b are large, and the optical signals of the amplified optical signals output from the optical amplifiers 13a and 13b are output. The strength is very large as described above. Therefore, if it is incident on each receiving unit of each transmitting / receiving base 11a, 11b as it is, the light receiver of the receiving unit will be damaged. It is adjusted so that an optical signal having a light intensity is not input.

[0017]

However, the optical fibers 12a and 12b connected to the receivers of the transmission / reception bases 11a and 11b are removed to replace the optical fibers 12a and 12b shown in FIG. When connected to the optical signal analyzers 2 and 2a shown in FIG. 9, whether or not the optical amplifiers 13a and 13b are inserted in the optical fibers 12a and 12b, and if they are inserted, amplification is performed. In many cases, the information such as the rate and the position of insertion is unknown.

Therefore, the optical fibers 12a,
If 12b is connected to the optical signal analyzers 2 and 2a, P
There is a concern that an optical signal exceeding the allowable upper limit light intensity may be incident on a photodetector such as IN-PD4 or APD9 and damage the photodetector.

The present invention has been made in view of the above circumstances, and always uses the optical branching device, the variable optical attenuator, and the optical monitoring photodetector to control the optical intensity of the optical signal incident on the main photodetector. An object of the present invention is to provide an optical signal receiving device capable of maintaining an optimum value, preventing an excessively high light intensity signal from being input to the main light receiver, and capable of always receiving an optical signal in the best state. .

[0020]

In order to solve the above problems, an optical signal receiving apparatus of the present invention is an optical branching device for branching an optical signal input from the outside in two directions and a branching by this optical branching device. A receiver for monitoring that receives one optical signal and converts it into a light intensity signal, a variable optical attenuator that attenuates the other optical signal branched by the optical splitter, and an optical attenuator that is attenuated by the variable optical attenuator. The main photodetector that receives the received optical signal and converts it into an electrical signal, and the attenuation amount of the variable optical attenuator is changed based on the optical intensity signal output from the monitor photodetector, and then input to the main photodetector. And a control unit for controlling the light intensity of the optical signal to an optimum value.

According to another aspect of the present invention, the control unit of the above-mentioned invention is used to calculate the light intensity by using each optical loss amount and the optical branching ratio of the optical branching device when light passes through the optical branching device and the variable optical attenuator. A light intensity conversion means for obtaining the light intensity of the optical signal output from the variable optical attenuator from the signal value of the signal and the attenuation amount of the variable optical attenuator, and the variable optical attenuator in response to the input start command. Using the attenuation amount initial setting means for initializing the attenuation amount to the maximum attenuation amount and the light intensity signal and the attenuation amount in the state where the optical signal is input from the outside, the variable light in this state is used by the light intensity conversion means. Light intensity calculation means for obtaining the light intensity of the output signal of the attenuator, and if the obtained light intensity is smaller than the optimum light intensity obtained by subtracting a predetermined grace light intensity from the allowable input light intensity for the main light receiver Make the light intensity closer to the optimum light intensity And attenuation reducing means for decreasing the attenuation sequentially, when the light intensity obtained is greater than the optimum light intensity, the light intensity obtained optimum light intensity in the near Nuisance so on,
The attenuation amount increasing means is configured to gradually increase the attenuation amount.

Further, in another invention, as a concrete method of the light intensity converting means in the above invention, a corresponding combination is obtained for each combination of each signal value of the light intensity signal and each attenuation amount of the variable optical attenuator. The light intensity corresponding to the combination is read from the conversion table that stores the light intensity of the optical signal output from the variable optical attenuator when set.

[0023]

In the optical signal receiving device thus constructed, the optical signal input to the optical signal receiving device is incident on the main light receiving device via the optical branching device and the variable optical attenuator. The light split by the optical splitter is input to the monitor light receiver. Then, the optical attenuation amount of the variable optical attenuator is controlled on the basis of the optical intensity signal output from the monitor optical receiver so that the optical intensity of the optical signal input to the main optical receiver has an optimum value.

Therefore, even if an optical signal having an excessive light intensity is input, it is immediately attenuated to the optimum value by the variable optical attenuator, so that the main light receiver is not damaged.

In another invention, when a start command for this device such as power-on is input, the attenuation is unconditionally set to the maximum attenuation regardless of the light intensity of the input optical signal. To be done. After that, the light intensity of the optical signal input by the monitor light receiver is measured, and based on this light intensity and the attenuation amount of the variable light attenuator at the present time, the light is output from the variable light attenuator and is incident on the main light receiver. The light intensity of the optical signal is required. Then, the attenuation amount of the variable optical attenuator is automatically changed so that the light intensity of the optical signal matches the optimum light intensity obtained by subtracting a predetermined delay light intensity from the allowable input light intensity of the main light receiver.

According to the present invention, since the attenuation amount of the variable optical attenuator is the maximum when the apparatus is started, the light intensity of the optical signal incident on the main photodetector is initially the minimum value. , Then, this light intensity starts to increase and approaches the optimum light intensity. Therefore, it is possible to prevent an optical signal exceeding the allowable input light intensity from being input to the main light receiver even in a short time.

Further, in another invention, each optical loss in the passage of light in the optical branching device and the variable optical attenuator and the optical branching ratio of the optical branching device are fixed values depending on individual optical parts.
Therefore, if the light intensity and the amount of attenuation obtained by the monitor light receiver are determined, the light intensity of the optical signal output from the variable optical attenuator is also uniquely determined. Therefore, the light intensity of the optical signal output from the variable optical attenuator when the corresponding combination is set for each combination of each signal value of the optical intensity signal and each attenuation amount of the variable optical attenuator is stored in the conversion table. Therefore, the light intensity of the input light signal of the main light receiver can be immediately grasped by the monitor light receiver.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the schematic arrangement of an optical signal analyzing apparatus incorporating the optical signal receiving apparatus of the embodiment.
The same parts as those of the conventional optical signal analyzer shown in FIG. 8 are designated by the same reference numerals.

The optical signal a input into the optical signal analysis device 23 via the optical fiber connector 22 connected to the optical fiber 21 introduced from another transmission / reception base is first incident into the optical signal reception device 24. The optical signal a that has entered the optical signal receiving device 24 is branched in two directions by the optical branching device 25.
One optical signal b branched by the optical branching device 25 is converted into a light intensity signal d by a monitor PIN-PD (pin photodiode) 26 as a monitor light receiver, and is input to the next control unit 27. It

The other optical signal c branched by the optical branching device 25
Is incident on the variable optical attenuator 28. The variable optical attenuator 28 attenuates the light intensity of the incident optical signal c by the attenuation amount A set by the setting signal g from the control unit 27, and then outputs it.
The attenuated optical signal e output from the variable optical attenuator 28
Is a main signal APD (or PIN-P) as a main light receiver.
D) is input to 29. This main signal APD (or PI
The N-PD) 29 converts the incident optical signal e into an electric signal f.

The electric signal f is amplified to a predetermined signal level by the next amplifier 30, and then output from the optical signal receiving device 24 and input to the decoding circuit 6 and the clock recovery circuit 7. The clock reproduction circuit 7 reproduces the clock signal CLK from the received signal, and the decoding circuit 6 and the next signal analysis unit 8
Send to. The decoding circuit 6 demodulates the input electric signal using the clock signal CLK into digital data D and sends it to the signal analysis unit 8. The signal analyzer 8 analyzes the corresponding digital data D and determines whether the received optical signal a is normal or not.

As shown in FIG. 2, the control unit 27 is composed of a kind of computer. For the bus 31, a CPU 32 that performs various information processing, a ROM 33 that stores fixed data such as a control program, a RAM 34 that stores a conversion table 34a, a set value memory 35 that stores various set values such as the maximum attenuation Am, a power supply An operation unit 36 provided with various operation keys such as switches, the monitor PIN-PD
An input circuit 37 to which the light intensity signal d is input from 26, an output circuit 38 for transmitting the setting signal g of the attenuation amount A to the variable optical attenuator 28, and the like are connected.

The input circuit 37 is a monitor PIN-P.
The light intensity signal d input from D26 is A / D converted,
The value is the optical intensity I of the optical signal b branched by the optical branching device 25.
_Capture as _M. On the other hand, the output circuit 38 includes the variable attenuator 2
The attenuation amount A to be set to 8 is D / A converted and sent to the variable optical attenuator 28 as a setting signal g.

Next, the conversion table 34a formed in the RAM 34 will be described.

The optical splitter 25 splits the optical signal a input via the optical fiber 21 and the optical fiber connector 22 into a splitting ratio α.
Although the light is branched in two directions, a constant light intensity loss Ia occurs in the process of the light passing through the light branching device 25. Therefore,
The light intensity I _N of the optical signal c incident on the variable optical attenuator 28 is I _N = (I-Ia) α. Further, the light intensity I _M of the optical signal b which is incident to the monitor PIN-PD 26 becomes _{= I M (I-Ia)} (1-α). The branching ratio α is a value close to 1, and most of the input optical signal a is input to the variable optical attenuator 28.

Similarly, in the variable optical attenuator 28, a constant light intensity loss Ib occurs even if the attenuation amount A is set to zero (A = 0). Therefore, the light intensity I _S of the optical signal e output from the variable optical attenuator 28 becomes _{I S = I N -A-Ib} .

Here, the relationship between the optical intensity I _M obtained by the monitor PIN-PD 26 and the optical intensity I _S of the optical signal e output from the variable optical attenuator 28 is as follows. Since the light intensity losses Ia and Ib are constant values, they are uniquely determined if the attenuation amount A is determined.

In the conversion table 34a, each light intensity I _S obtained for each combination of each light intensity I _M1 , I _M2 , ... And each attenuation amount A ₁ , A ₂ ,. There is. Therefore, the monitor PIN-PD 26 provides the light intensity I.
_{When M} is obtained, the light intensity I _S of the optical signal e output from the variable optical attenuator 28 is immediately obtained from the attenuation amount A at that time using this conversion table 34a.

Since the branching ratio α and the light intensity loss Ia of the optical branching device 25 are constant values, the monitor PIN-PD 26 is used.
The light intensity I _{M of the} optical signal a input to the optical signal receiving device 24 is also uniquely determined from the light intensity I _M obtained in step a.

I = { _IM / (1-α)} + Ia In the set value memory 35, the variable optical attenuator 28 is used.
In addition to the maximum attenuation Am of the input optical signal
Lower limit optical intensity I _ML of optical intensity I _M of optical signal b obtained by monitor PIN-PD 26 corresponding to _LL , variable optical attenuator 28
The allowable upper limit light intensity I _{US of} the optical signal e output from the optical signal e, and the delay light intensity ΔI. Various setting values such as lower light intensity I _MS of the light intensity I _M of the optical signal b obtained by the monitor PIN-PD 26 corresponding to the lower limit starting light intensity I _LS of the input optical signal a is stored.

When the power switch of the operation unit 36 is turned on and the system reset state is released, the control unit 27 executes the flow chart shown in FIG.

When the flow chart starts, P (program
In step 1), the attenuation amount A of the variable optical attenuator 28 is initialized to the maximum attenuation amount Am (A = Am). Next, the light intensity I _M of the monitor PIN-PD 25 is read (P2). When the read light intensity I _M is equal to or higher than the lower limit light intensity I _ML (P3), the optical fiber 21 is the optical fiber connector 22.
Since it is connected to (P
In 4), the light intensity I _M is measured again.

When the light intensity I _M becomes less than the lower limit light intensity I _ML , it is judged that the optical fiber 21 is detached from the optical fiber connector 22.

Next, in the process of P5 to P7, the light intensity I _M read wait for exceeding the lower limit starting light intensity I _MS.
When the read light intensity I _M exceeds the lower limit start light intensity I _MS ,
It is determined that the optical fiber 21 is connected to the optical fiber connector 22.

Then, the process proceeds to P8, where the present variable optical attenuator 2
The optical intensity I _S of the output optical signal e of the variable optical attenuator 28 corresponding to the combination of the attenuation amount A set to 8 and the optical intensity I _M read this time is read from the conversion table 34a. The light intensity I _S obtained this time is based on the allowable upper limit light intensity I _US and the postponed light intensity ΔI.
If it is smaller than the optimum light intensity (I _us −ΔI) (P
In 9), at P10, the attenuation A set in the variable optical attenuator 28 is decreased by a minute amount ΔA (A = A−ΔA). Then, the light intensity I _M is read again (P11), the process returns to P8, and the light intensity I _S of the output optical signal e is obtained again.

At P9, when the light intensity I _S obtained this time becomes equal to or higher than the optimum light intensity (I _us −ΔI), A for main signal is used.
Since the light intensity I _S of the optical signal e input to the PD (or PIN-PD) 29 has reached the vicinity of the optimum light intensity, this flow chart is ended.

Further, when the control section 27 shifts to the normal operation state, it executes the control processing shown in FIG.

That is, when the flow chart is started, the light intensity I _M of the monitor PIN-PD 26 is read (Q1), and then the output of the variable optical attenuator 28 is determined from the light intensity I _M and the current attenuation amount A. The light intensity I _S of the optical signal e is converted into the conversion table 34a.
(Q2). If the obtained light intensity I _S exceeds the optimum light intensity (I _us −ΔI) obtained by subtracting the delay light intensity ΔI from the allowable upper limit light intensity I _US (Q3), the attenuation amount A
Increase (Q4) and return to the original.

The obtained light intensity I _S is the optimum light intensity (I _us
When the difference is equal to (ΔI) including a predetermined error range (Q3, Q5), the main signal APD (or PIN)
Since the light intensity I _S of the optical signal e input to the (-PD) 29 is near the optimum light intensity, the process returns to Q1 again after a certain period of time (Q6).

The obtained light intensity I _S is the optimum light intensity (I _us
If it is less than −ΔI) (Q5), the attenuation amount A is reduced by a small amount (A = A−ΔA), and if it is confirmed that the limit amount A after reduction has not reached 0, the process returns to Q1 again. .

When the attenuation amount A after reduction reaches 0, the light intensity I _M of the monitor PIN-PD 26 is read (Q
9), it is determined whether or not this light intensity I _M has dropped below the lower limit light intensity I _ML (Q10). When the light intensity I _M has not dropped below the lower limit light intensity I _ML , the input optical signal a
Since the light intensity I itself is low, the process proceeds to Q6 without doing anything, and returns to Q1 again after a lapse of a certain time (Q6).

When the light intensity I _M drops below the lower limit light intensity I _{ML, the} light intensity I of the input optical signal a drops below the lower limit light intensity I _LL . , Or it is determined that the optical signal a itself is cut off (Q1
1). Then, in this case, the attenuation amount A of the variable optical attenuator 28 is once set to the maximum value (A = Am). Then, this flow chart is ended.

The optical signal receiving device 24 configured as described above
In the above, when the power is turned on, the attenuation amount A of the variable optical attenuator 28 is automatically set to the maximum attenuation amount Am. Therefore, even if the optical fiber 21 through which the optical signal a having the unknown optical intensity I is transmitted is connected to the optical fiber connector 22, the main signal APD (or PIN-PD) 29 has a large allowable input optical intensity I _US . No optical signal that exceeds it is incident.

The branching ratio α in the optical branching device 25 is 1
Since it is set to a value close to, even if the optical signal a having excessive light intensity is input, the monitor PIN-P
Since the light intensity I _M of the optical signal b is incident on the D26 will not greatly exceed the allowable value, PIN-PD for the monitor
26 is not damaged.

As described above, in the optical signal receiving device 23, the variable optical attenuator 2 is temporarily turned on when the power is turned on.
The attenuation amount A of 8 is set to the maximum attenuation amount Am, and it is confirmed that the optical fiber 21 is removed or the optical signal a is blocked.

When the optical fiber 21 is connected to the optical fiber connector 22 and the light intensity I of the optical signal a exceeds the lower limit start light intensity I _LS which is slightly larger than the lower limit light intensity I _LL , the control unit 27 and the variable optical attenuation are set. Control by the device 28 is started,
The attenuation amount A gradually decreases so that the light intensity I _S of the optical signal e input to the main signal APD (or PIN-PD) 29 approaches the optimum light intensity (I _us −ΔI) from below. .

Therefore, the main signal APD (or PIN-P)
D) In the process of controlling the optical intensity I _S of the optical signal e input to 29 to the optimum optical intensity (I _us −ΔI), the excessive optical intensity is input to the main signal APD (or PIN-PD) 29. Is prevented in advance.

After the optical signal receiving device 24 has once entered the operating state, as shown in the flow chart of FIG.
When the light intensity I of the input optical signal a fluctuates, the attenuation amount A changes according to this fluctuation, and the main signal APD (or PIN-
The optical intensity I _S of the optical signal e input to the PD) 29 is controlled to the optimal optical intensity (I _us −ΔI). Therefore, A for main signal
The PD (or PIN-PD) 29 always works in optimum condition.

Then, as shown in FIG. 5, the input optical signal a
When the light intensity I of the input light signal is _less than the lower limit light intensity I _LL , the input optical signal a
Is determined to have been cut off, and the attenuation amount A is automatically set to the maximum attenuation amount Am. Therefore, even if the optical signal a having an excessively high light intensity that exceeds the allowable limit is carelessly incident next, damage to the main signal APD (or PIN-PD) 29 is prevented in advance.

The lower limit light intensity I _LL indicating the stop of the control operation
Since the hysteresis is provided between the lower limit start light intensity I _LS indicating the start of the control operation and the lower limit start light intensity I _LS , the chattering phenomenon in the attenuation amount A control is prevented.

[0062] The variable optical attenuator 28 when applicable combination is set for each each combination of the respective attenuation A of the light intensity I _M and the variable optical attenuator 28 obtained by monitoring PIN-PD 26 I remember the light intensity I _S of the optical signal e is output to the conversion table 34a from so immediately the light intensity I _S of the input optical signal e of the main signal APD (or PIN-PD) 29 is obtained, Control response performance can be improved.

As described above, a high-power optical amplifier is inserted in the path of the optical fiber 21 connected to the optical signal receiving device 24, and the optical intensity I of the input optical signal a is +.
Even if it is 20 dBm or more, the optical signal receiving device 24 operates normally. Moreover, the operator need not consider the light intensity I of the input optical signal a at all.

FIG. 6 is a block diagram showing the schematic arrangement of an optical signal analysis device 23 incorporating an optical signal receiving device 24 according to another embodiment of the present invention. The same parts as those in the embodiment shown in FIG. 1 are designated by the same reference numerals. Therefore, detailed description of the overlapping portions is omitted.

In this embodiment system, the variable optical attenuator 4 is used.
0 indicates an attenuator 40a having an attenuation amount A of 0 and an attenuation amount A of 1
0 dB attenuator 40b. Attenuation A selects switched by designating signal g ₁ of the attenuation A of the three attenuators 40a~40c the control unit 27a of the attenuator 40c is 20 dB.

When the control section 27a sends the designation signal g ₁ to switch the attenuation amount A according to the detected light intensity I _M of the optical signal b, as shown in FIG. A hysteresis range is provided to prevent the occurrence of chattering at the time of switching.

Also in the optical signal receiving device configured as described above, it is possible to prevent the optical signal e having an excessive optical intensity from being input to the main signal APD (or PIN-PD) 29. It is possible to obtain substantially the same effect as that of the above-described embodiment.

[0068]

As described above, in the optical signal receiving device of the present invention, the optical intensity of the optical signal incident on the main photodetector using the optical branching device, the variable optical attenuator, and the optical monitoring photodetector. Is always maintained at the optimum value. Further, it is possible to prevent the input of an excessive light intensity signal to the main light receiver by interposing an attenuator in advance at the time of connection, and always receive the optical signal in the best condition.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an optical signal receiving apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a control unit incorporated in the apparatus of the embodiment.

FIG. 3 is a flowchart showing the operation of the control unit when the power is turned on.

FIG. 4 is a flowchart showing the operation of the control unit during normal operation.

FIG. 5 is a time chart showing the operation of the apparatus of the embodiment.

FIG. 6 is a block diagram showing a schematic configuration of an optical signal receiving device according to another embodiment of the present invention.

FIG. 7 is a time chart showing the operation of the apparatus of the embodiment.

FIG. 8 is a block diagram showing a schematic configuration of a general optical signal analysis device.

FIG. 9 is a block diagram showing a schematic configuration of the same general optical signal analysis device.

FIG. 10 is a diagram showing a general optical communication system incorporating an optical amplifier.

[Explanation of symbols]

21 ... Optical fiber, 22 ... Optical fiber connector, 23 ...
Optical signal analyzing device, 24 ... Optical signal receiving device, 25 ... Optical branching device, 26 ... Monitor PN-PD, 27 ... Control unit, 28,
40 ... Variable optical attenuator, 29 ... Main signal APD (or PI)
N-PD), 34a ... Conversion table

Claims (3)

[Claims] 1. An optical branching device (25) for branching an optical signal input from the outside in two directions, and a monitor for receiving one optical signal branched by this optical branching device and converting it into an optical intensity signal. A light receiver (26), a variable optical attenuator (28, 40) for attenuating the other optical signal split by the optical splitter, and an optical signal attenuated by the variable optical attenuator for receiving the optical signal. A main photoreceiver (29) for converting into an electric signal, and changing the attenuation amount of the variable optical attenuator based on the light intensity signal output from the monitor photoreceiver, the light input to the main photoreceiver. Control unit that controls the light intensity of the signal to an optimum value
(27) An optical signal receiving device comprising: 2. The control unit (27) uses the optical loss of each of the optical branching device and the variable optical attenuator at the time of light passage and the optical branching ratio of the optical branching device to obtain a signal of the optical intensity signal. Optical intensity conversion means (32a) for obtaining the optical intensity of the optical signal output from the variable optical attenuator from the value and the attenuation amount of the variable optical attenuator, and the variable optical attenuation in response to the input start command. Attenuation initial setting means (P1) for initializing the attenuation of the reactor to the maximum attenuation
And an optical intensity for obtaining the optical intensity of the output signal of the variable optical attenuator in this state by using the optical intensity conversion means from the optical intensity signal and the attenuation amount in the state where the optical signal is input from the outside. When calculating means (Q2) and the obtained light intensity is smaller than the optimum light intensity obtained by subtracting a predetermined grace light intensity from the allowable input light intensity for the main light receiver, the obtained light intensity is the optimum light intensity. Attenuation amount reduction means (Q7) that gradually decreases the attenuation amount so that the obtained light intensity is larger than the optimum light intensity, and the obtained light intensity is the optimum light intensity. Attenuation amount increasing means (Q
4) The optical signal receiving device according to claim 1, further comprising: 3. The light intensity conversion means outputs from the variable optical attenuator when a corresponding combination is set for each combination of each signal value of the light intensity signal and each attenuation amount of the variable optical attenuator. 3. The optical signal receiving device according to claim 2, wherein the light intensity corresponding to the combination is read from the conversion table (34a) storing the light intensity of the output optical signal.