JPH06160240A - Estimation system for optical transmission characteristics - Google Patents

Abstract

PURPOSE:To obtain an estimation system for optical transmission characteristics in which operation is stabilized for a long time by facilitating gain control during single circulation of an optical fiber loop. CONSTITUTION:The estimation system for optical transmission characteristics comprises an optical transmitter 1 for converting an electric signal into an optical signal, an optical fiber loop 6 for transmitting optical signal, an optical amplifier 4 included in the optical fiber loop 6, an optical receiver 7 for converting an optical signal circulated through the optical fiber loop 6 into an electric signal, and a controller 10a for controlling gain of the optical amplifier based on an optical signal circulated through the optical fiber loop 6 or an output from a light receiver provided, as required, in order to demultiplex optical signal in the optical fiber loop 6 and convert into an electric signal. The estimation system further comprises, as required, an optical switch or a polarization controller inserted into the optical fiber loop 6, a pulse generator for providing the electric signal with a pulse pattern, and control means for pulse generator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system and a device evaluation apparatus in an optical communication system.

[0002]

2. Description of the Related Art In recent years, with the progress of optical amplification technology, a long distance optical transmission system using an optical amplification transmission method has been actively developed. The optical amplification transmission method has a problem that noise of an optical amplifier and deterioration of a transmission optical signal are accumulated because an optical signal is transmitted without being regenerated and relayed. In the regenerative repeater transmission system, it was sufficient to test each repeater section, whereas in the optical amplification transmission system, it is necessary to perform a system test in the entire system.

As a method of performing and evaluating a system test of the whole long-distance optical transmission system so far, for example, N. Edagawa et al .: “12300ps, 2.4Gb / s” is used.
Nonregenerative Optical Fiber Transmission Experi
ment and Effect of Transmitter Phase Noise ”Photo
nics Technolgy Letters, Vol.2, No.4, pp.274-276. It connects a number of optical amplifiers in cascade with an optical fiber having the same length as the distance over which light is transmitted. However, since a long-distance optical fiber and a large number of optical amplifiers are required, the test system becomes extremely large. Therefore, as a method to perform a simple system test,
NSBergano: ”Bit ErrorRate Measurements of 14000
km 5Gbit / s Fiber-Amplifier Transmission Systemusin
g Circulating Loop ”, Elecronics Letters, 27, pp.188
The method shown in 9-1890 has been proposed. FIG. 13 is a block diagram of the long-distance optical transmission system test system shown in the above document.

In FIG. 13, the optical signal output by the optical transmitter 1 is cut out by the optical switch 2 for a time period that fills the optical fiber loop once without excess or deficiency. The cut out optical signal is introduced into the optical fiber loop by the optical multiplexer / demultiplexer 3. The optical fiber loop, the optical amplifier 4, and the optical switch 5 are included in the optical fiber loop, and the gain of the optical amplifier is set to a value that compensates for the loss in the optical fiber loop. After the optical signal circulates the optical fiber loop a specified number of times, the optical signal output from the optical multiplexer / demultiplexer 3 is converted into an electric signal by the optical receiver 7 and evaluated. Optical switch 5
Is opened after the optical signal has circulated the optical fiber loop a specified number of times, clears the optical signal and noise light remaining in the optical fiber loop, and prepares for the next measurement.

In the above system, the gain setting of the optical amplifier is fixed, so that it cannot be operated for a long time. It is known that the optical amplifier detects the light on the output side and feeds it back to the set value to control its own gain.

[0006]

Since the conventional evaluation apparatus for an optical transmission system is configured as described above, when trying to evaluate characteristics by a small-scale loop, unless the loop gain is completely set to 1, The light signal either extinguished or diverged and was allowed to operate for only a short time. For example, trying to verify an error rate of 10 ^-11 for a 400 ps signal requires 10 ¹² observations, which takes 10 to 20 minutes. Conventionally, there has been a problem that a characteristic evaluation device with a stable loop cannot be obtained for such a long time. In addition, in the conventional evaluation device, additional components for measuring the characteristics are incorporated in the loop, and the method of removing this effect is not considered, so there is also the problem that evaluation by a system equivalent to the actual system cannot be performed. there were.

The present invention has been made to solve the above problems, and provides an optical transmission characteristic evaluation apparatus capable of easily controlling the loop gain in an optical fiber loop and thus capable of operating for a long time. The purpose is to get. It is also an object of the present invention to provide an evaluation device capable of easily giving variations to the system or giving a limit value to evaluate the characteristics. Furthermore, another object is to obtain an evaluation device capable of evaluating characteristics by forming a loop close to an actual system.

[0008]

An optical transmission characteristic evaluation apparatus according to the present invention includes an optical transmitter for converting an electric signal into an optical signal, an optical fiber loop for transmitting the optical signal, and an optical fiber loop in the optical fiber loop. An optical amplifier included in the optical fiber loop, an optical receiver that converts the optical signal after circulating the optical fiber loop into an electrical signal, and an electrical signal that demultiplexes the optical signal in the optical fiber loop as necessary. And a control means for controlling the gain of the optical amplifier by an optical signal output from the loop or after the optical fiber loop is circulated around the optical fiber loop. An optical transmission characteristic evaluation apparatus according to the invention of claim 2 is an optical transmitter for converting an electric signal into an optical signal, an optical fiber loop for transmitting the optical signal, and an optical amplifier included in the optical fiber loop. An optical receiver for converting an optical signal after going around the optical fiber loop into an electric signal, and an optical switch or an optical polarization controller provided in the optical fiber loop if necessary, and the optical signal if necessary. A light receiver for demultiplexing the optical signal in the fiber loop to convert it into an electric signal is provided, and a control means for controlling the gain of the optical amplifier or the polarization controller by the output of the optical receiver or the light receiver is provided.

The optical transmission characteristic evaluation apparatus according to the invention of claim 3 is
An optical transmitter for converting an electric signal into an optical signal, an optical fiber loop for transmitting the optical signal, an optical amplifier included in the optical fiber loop, and an optical signal after circulating the optical fiber loop. An optical receiver for converting to an electric signal, and a receiver for demultiplexing the optical signal in the optical fiber loop and converting it into an electric signal as necessary are provided, and a pulse generator for giving a pulse pattern to the electric signal and the outside of the loop. And a control means for controlling the gain of the optical amplifier or the pulse generator by the output of the optical receiver or the optical receiver.

[0010]

In the optical transmission characteristic evaluation device according to the present invention, the optical signal from the optical transmitter is stably gain-controlled in the optical loop,
After circling the loop for a predetermined time, it reaches the receiver. The gain of the optical signal of the optical loop is controlled by the optical signal after it goes out of the loop, or a part of the optical signal is demultiplexed and goes out of the loop, and the gain is controlled by this signal. An additional component having the opposite property is added to the additional component for measuring the characteristic, and the optical components are canceled and the optical signal flows in the loop.

[0011]

【Example】

Example 1. FIG. 1 is a block diagram showing the configuration of an embodiment of the optical transmission characteristic evaluation apparatus according to the first aspect of the invention. In the figure,
Reference numeral 1 is an optical transmitter, 2 is an optical switch that cuts out an optical signal for a time period sufficient to fill the optical fiber loop without excess or deficiency, and 3 is an optical coupling device that introduces the cut out optical signal into the optical fiber loop and that extracts the optical signal from the optical fiber loop. It is a duplexer. Reference numeral 4 is an optical amplifier, 5 is an optical switch, and 6 is an optical fiber, which is included in an optical fiber loop. A novel part is a control device for controlling the gain of the optical receiver 7; the pulse pattern generator 8; the error rate measuring device 9; and the optical amplifier 10a. Reference numeral 19 denotes a timing control device, which is an optical switch 2,
5 and the operation timing of the error rate measuring device 9 are controlled.
As the above-mentioned optical switch, various optical switches utilizing electro-optical effect, acousto-optical effect, magneto-optical effect, etc. can be used. The optical switch 5 may be omitted if a switching operation by gain control of an optical amplifier or an optical multiplexer / demultiplexer that switches the optical path is used. As the optical amplifier, a rare earth-doped optical fiber amplifier or a semiconductor optical amplifier can be used.

The novel part of this evaluation apparatus is to control the gain of the optical amplifier by the optical signal output from the loop by the above configuration. Next, the operation will be described. The optical signal output by the optical transmitter 1 is cut out by the optical switch 2 for a time T that fills the optical fiber loop by one round without excess or deficiency. A part of the optical signal cut out in this way is introduced into the optical fiber loop by the optical multiplexer / demultiplexer 3. An optical fiber 6, an optical amplifier 4, and an optical switch 5 are included in the optical fiber loop. The optical signal introduced into the optical fiber loop passes through the optical fiber 6, the optical amplifier 4, and the optical switch 5, and is input to the optical multiplexer / demultiplexer 3 again. A part of the optical signal is input to the optical fiber loop again, and a part of the optical signal is output to the outside of the optical fiber loop. After the optical signal goes around the optical fiber loop a specified number of times (N times) (after NT time), the optical signal output from the optical multiplexer / demultiplexer 3 to the outside of the optical fiber loop is converted into an electrical signal by the optical receiver 7. Then, the error rate measuring device 9 measures the code error rate. The optical switch 5 is opened after the optical signal has circulated the optical fiber loop a specified number of times (time T or more), clears the optical signal and noise light remaining in the optical fiber loop, and prepares for the next measurement. The timing control device 19 controls the operation timings of the optical switches 2 and 5 and the error rate measuring device 9 described above.

When the gain of the optical amplifier 4 is equal to the value that compensates for the loss in the optical fiber loop, the code error rate becomes the minimum. At the time of the next evaluation, that is, when the optical signal for one round is cut out and looped around, the gain of the optical amplifier is also changed and set. Therefore, the gain of the optical amplifier can be easily set by controlling the gain of the optical amplifier by the cut-and-try method several times by the controller 10a so as to minimize the measurement result of the error rate measuring device. After several attempts,
Loop gain becomes stable. To control the gain of the optical amplifier,
There are methods such as control of pumping light power and control of variable attenuator. As described above, in this embodiment, the loop gain is stabilized for the evaluation device through several error rate measurements.

Example 2. FIG. 2 is a block diagram showing the configuration of another embodiment of the optical transmission characteristic evaluation apparatus according to the first aspect of the present invention. In the figure, the following are new parts different from FIG. Reference numeral 11 is an optical demultiplexer, 12 is a light receiver, 14 is an oscilloscope, and 15 is an optical switch that cuts out only the optical signal that has circulated the optical fiber loop a specified number of times. A timing control device 19 controls the operation timings of the optical switches 2 and 5 and the oscilloscope 14 in this case.

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. The optical signal output from the optical multiplexer / demultiplexer 3 to the outside of the optical fiber loop is demultiplexed by the optical demultiplexer 11, one output is input to the optical receiver, and the clock is regenerated. The other output is input to the optical switch and circulates the optical fiber loop a specified number of times, for example, 100 times, after which only the optical signal is cut out and converted into an electric signal by the photodetector 12. The oscilloscope 14 observes the waveform with the clock regenerated by the optical receiver 7 and the signal converted into the electric signal by the light receiver 12 as inputs. The change in characteristics can be evaluated by comparing the transmitted light power after the circulation. Therefore, it is also possible to cut out the optical signal after orbiting to a measuring instrument other than the oroscope and compare it with the initial value.

Embodiment 3. FIG. 3 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus according to the first aspect of the present invention. In the figure, as a new part different from FIG.
There is a control device for controlling the gain of the optical amplifier of b, 11 is an optical demultiplexer, and 12 is a light receiver. In the present embodiment, while the amplifier gain is made constant for each cyclic test and the gain is changed based on the previous result in the long run to finally obtain the stable gain, the present embodiment is cyclic. The feature is that the gain is controlled inside.

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. The optical signal output from the optical multiplexer / demultiplexer 3 to the outside of the optical fiber loop is demultiplexed by the optical demultiplexer 11, one output is converted into an electrical signal by the photodetector 12, and the other output is an optical receiver. Or input to the measuring device. When the gain of the optical amplifier 4 is equal to the value that compensates for the loss in the optical fiber loop, the optical signal level output from the optical fiber loop is a constant value. Therefore, by measuring the optical signal level by the light receiver 12 and continuously controlling the gain of the optical amplifier by the controller 10b so that the optical signal level becomes a constant value, the gain of the optical amplifier can be easily set.

Example 4. FIG. 4 is a block diagram showing the configuration of another embodiment of the optical transmission characteristic evaluation apparatus according to the first aspect of the invention. In the figure, as a new part different from FIG. 1, there is an optical multiplexer / demultiplexer that introduces the cut out optical signal 3a into the optical fiber loop and takes out the optical signal from the optical fiber loop. The purpose of this embodiment is to improve the simulation accuracy for an actual system.

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. One of the problems in constructing an optical transmission characteristic evaluation device using an optical fiber loop is that there is extra loss that is not available in an actual system. Optical multiplexer / demultiplexer 3
If an optical coupler with a branching ratio of 1: 1 is used as a, the loss is 3 dB. Therefore, by using an optical multiplexer / demultiplexer with a branching ratio of 1: N, the extra loss in the optical fiber loop is reduced, and an optical transmission characteristic evaluation device closer to an actual system is constructed. Although the configuration of the gain control of the optical amplifier is not described, it is clear that either the first embodiment or the third embodiment can be expressed.

Example 5. FIG. 5 is a block diagram showing the configuration of another embodiment of the optical transmission characteristic evaluation apparatus according to the first aspect of the invention. In the figure, as a part different from FIG.
In synchronization with the cycle that the optical signal goes around the optical fiber loop,
Alternatively, there is a controller that asynchronously changes the gain of the optical amplifier. The present embodiment is characterized in that the amplifier gain is changed for each cyclic test and the simulation accuracy of the actual system is improved, while the embodiment 1 controls the widening amplifier in which the loop gain is stable in the long term. .

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. One of the problems in constructing an optical transmission characteristic evaluation device using an optical fiber loop is that the characteristics of optical amplifiers through which optical signals pass are all the same. Therefore, if the gain of the optical amplifier is changed in synchronization with the cycle in which the optical signal goes around the optical fiber loop, it is possible to give arbitrary variations to the characteristics of the optical amplifier through which the optical signal passes, and it is closer to the actual system. A long-distance optical transmission characteristic evaluation device can be configured. Of course, a similar effect can be obtained by changing the gain of the optical amplifier asynchronously with the cycle of the optical signal circulating in the optical fiber loop.

Embodiment 6. FIG. 6 is a block diagram showing the configuration of another embodiment of the optical transmission characteristic evaluation apparatus according to the first aspect of the invention. The transmission controller 17 includes an optical transmitter 1, an optical switch 1,
5, an optical multiplexer / demultiplexer 4, an optical receiver 7, and a controller 10f are included, and the optical amplifier 4 is connected between the output terminals 18a and 18b, and the optical fiber 6 is connected between the output terminals 18c and 18d. Thus, a transmission characteristic evaluation device similar to that of the fifth embodiment can be configured to evaluate the characteristics of the optical amplifier 4 and the optical fiber 6. Reference numeral 10f is a controller that changes the gain of the optical amplifier in synchronism with or asynchronously with the cycle of the optical signal circulating in the optical fiber loop. A timing control device 19 controls the operation timing of the optical switches 2 and 5. In this way, a simulation close to that of an actual system can be stably performed, and various evaluations can be performed.

Example 7. FIG. 7 is a configuration block diagram showing an embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 2. In the figure, the following are new parts different from FIG.
A polarization controller 15 is included in the optical fiber loop. Reference numeral 10d is a control device for controlling the polarization controller. While the first embodiment controls the gain of the optical amplifier, the present embodiment controls the polarization controller.

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. Since the transmittance of the optical components in the optical fiber loop depends on the polarization, fluctuations in the polarization of the optical fiber cause fluctuations in the signal level. Since the code error rate is minimized when the optical signal level is kept constant, the polarization controller is controlled by the controller 1 so that the measurement value of the error rate measuring device is minimized.
By controlling with 0d, the fluctuation of the signal level caused by the fluctuation of the polarization of the optical fiber can be suppressed. Of course, the gain control of the optical amplifier can be used together.

Example 8. FIG. 8 is a block diagram showing the configuration of another embodiment of the optical transmission characteristic evaluation apparatus according to the present invention. In the figure, the following parts are different from those in FIG. Reference numeral 11 is an optical demultiplexer, 12 is a light receiver, 10e is a control device for controlling the polarization controller, and 15 is a polarization controller. While the third embodiment controls the gain of the optical width increaser, the present embodiment controls the polarization controller.

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. The optical signal output from the optical multiplexer / demultiplexer 3 to the outside of the optical fiber loop is demultiplexed by the optical demultiplexer 11, one output is converted into an electrical signal by the photodetector 12, and the other output is an optical receiver. Or input to the measuring device. Since the transmittance of the optical components in the optical fiber loop depends on the polarization, fluctuations in the polarization of the optical fiber cause fluctuations in the signal level.
The optical signal level is monitored by the light receiver 12, and the polarization controller is controlled by the controller 10e so that the optical signal level becomes constant, thereby suppressing the fluctuation of the signal level caused by the polarization fluctuation of the optical fiber. You can

Example 9. FIG. 9 is a block diagram showing the configuration of another embodiment of the optical transmission characteristic evaluation apparatus according to the present invention. In the figure, a part different from that shown in FIG. 7 is a controller that changes the polarization state in synchronization with the period in which an optical signal of 10 g goes around the optical fiber loop or asynchronously. The purpose of this embodiment is to improve the simulation accuracy for an actual system.

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. In an optical transmission characteristic evaluation device using an optical fiber loop, the characteristics of all optical components are the same, so we will improve it and obtain an evaluation device close to an actual system. Controls the polarization controller in synchronization with the loop cycle to change the polarization state and gives an arbitrary variation to the characteristics of the optical components through which the optical signal passes, thus providing a long-distance optical transmission characteristic that is closer to that of an actual system. Configure an evaluation device. Of course, a similar effect can be obtained by changing the gain of the optical amplifier asynchronously with the cycle of the optical signal circulating in the optical fiber loop.

Example 10. FIG. 10 is a block diagram showing the configuration of another embodiment of the optical transmission characteristic evaluation device according to the present invention. In the figure, the following points are different from those in FIG. Reference numeral 10h is a controller that changes the polarization state in synchronization with the cycle of the optical signal circulating in the optical fiber loop. 11
Reference numerals a and 11b are optical demultiplexers, and reference numerals 15a and 15b are polarization controllers, which are included in the optical fiber loop. Reference numerals 16a and 16b are polarization state measuring instruments, and 7 is an optical receiver. A timing control device 19 controls the operation timing of the optical switches 2 and 5. The purpose of this embodiment is to obtain an apparatus capable of stably confirming a limit value during simulation.

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. A part of the outputs of the polarization controllers 15a and 15b are taken out by the optical demultiplexers 11a and 11b, and 16a and
The polarization state monitor 16b monitors the polarization state. One of the advantages in constructing a long-distance optical transmission characteristic evaluation device using an optical fiber loop is that the propagation characteristics can be evaluated by changing the state of the system. At that time, the worst and best possible states of the system are often the states where there is no variation in the characteristics of the optical components through which the optical signal passes and the characteristics of the amplifier. Therefore, if the polarization controller is controlled in synchronism with the cycle of the optical signal circulating in the optical fiber loop so that the polarization state does not change even if it circulates in the optical fiber loop, the worst case of the system is considered. A long-distance optical transmission characteristic evaluation device capable of monitoring the state can be configured.

Example 11. FIG. 11 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 2. In the figure, a new part different from FIG. 1 is 5a,
5b optical switch. The purpose of this embodiment is to insert a component having a characteristic that cancels out the characteristic of the component inserted for the evaluation test so that the characteristic of the evaluation device can be brought close to that of an actual system.

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. An optical switch in the optical fiber loop is required to have a high extinction ratio and a high operation speed, and a typical example thereof is an acousto-optical switch. However, the optical signal undergoes a frequency shift when it passes through the acousto-optical switch. There are two types of acousto-optic switches, one using + 1st order diffracted light and the other using −1st order diffracted light, and the frequency shift due to these is in the opposite direction. Therefore, by connecting the two types of acousto-optic optical switches in cascade, an optical switch having a high extinction ratio and no optical frequency shift can be configured.

Example 12 FIG. 12 is a configuration block diagram showing an embodiment of the optical transmission characteristic evaluation device of the invention of claim 3. In the figure, the following are new parts different from those in FIG. Reference numeral 10c is a control device for controlling the oscillation frequency of the synthesizer 13, and 13 is a pulse pattern generator 8
It is a synthesizer that gives a reference clock to. The embodiment aims at reliably reproducing the timing signal which is essential for the evaluation device.

Next, the operation will be described. Even if the optical switch 2 is controlled by the timing control device,
In some cases, the time for one round of the optical signal loop cannot be controlled. In such a case, instead of finely adjusting the on / off time of the optical switch 2, the synthesizer is controlled to slightly change the oscillation frequency of the original pulse pattern generator 8. The time it takes for an optical signal to make one round in an optical fiber loop
When the time is an integral multiple of the time of one time slot of the optical signal, the clock recovery is easiest in the optical receiver, close to the actual system, and the code error rate becomes the minimum. Therefore, by controlling the oscillation frequency of the synthesizer 13 by the controller 10c so that the measurement result of the error rate measuring device is minimized, the time taken for the optical signal to make one round in the optical fiber loop can be set to 1 time of the optical signal. It can be set to an integer multiple of the slot time.

Example 13. If an optical switch using an acousto-optic effect is used as the optical switch in the optical fiber loop in the above embodiment, the optical frequency can be shifted each time the optical switch transmits, and the influence of detuning of the optical signal is investigated. be able to. Further, the number of optical amplifiers in the optical fiber loop in the above embodiment may be two or more.
Further, the arrangement of the optical switch, the optical amplifier, and the optical fiber in the optical fiber loop may be different from that in the embodiment. The length of the optical signal cut out by the optical switch between the optical transmitter and the optical fiber loop may be shorter than the time T for filling the optical fiber loop without excess or deficiency, but if it is short, the time required for measurement becomes long. Become.

[0036]

As described above, according to the present invention, in the optical transmission characteristic evaluation apparatus, after the loop is circulated for a predetermined number of times, it is output by a receiver that receives an optical signal that has exited the loop or by another light receiver. Since the optical amplifier is controlled, or the optical switch, the optical polarization controller, and the pulse generation control means are further provided, a stable device can be obtained even for long-term transmission characteristic evaluation. is there. Furthermore, there is an effect that a simulation close to an actual system can be performed and an arbitrary deviation can be stably given.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of an optical transmission characteristic evaluation apparatus of the invention of claim 1;

FIG. 2 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 1;

FIG. 3 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 1;

FIG. 4 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 1;

FIG. 5 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 1;

FIG. 6 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 1;

FIG. 7 is a configuration block diagram showing an embodiment of an optical transmission characteristic evaluation device of the invention of claim 2;

FIG. 8 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 2;

FIG. 9 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 2;

FIG. 10 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 2;

FIG. 11 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 2;

FIG. 12 is a configuration block diagram showing an embodiment of an optical transmission characteristic evaluation apparatus of the invention of claim 3;

FIG. 13 is a block diagram of a conventional long-distance optical transmission characteristic evaluation device.

[Explanation of symbols]

1 Optical transmitter 2 Optical switch 3, 3a Optical multiplexer / demultiplexer 4 Optical amplifier 5, 5a, 5b Optical switch 6 Optical fiber 7 Optical receiver 8 Pulse pattern generator 9 Error rate measuring device 10a, 10b, 10c, 10d, 10e , 10f, 1
0g, 10h Controller 11, 11a, 11b Optical demultiplexer 12 Light receiver 13 Synthesizer 14 Oscilloscope 15, 15a, 15b Polarization controller 16a, 16b Polarization state measuring instrument 17 Transmission controller 19 Timing controller

[Procedure amendment]

[Submission date] August 31, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

[Correction content]

In the above method, the setting of the gain of the optical amplifier is fixed, so that there is a problem in long-term operation stability. It is known that the optical amplifier detects the light on the output side and feeds it back to the set value to control its own gain.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

[0006]

Since the conventional evaluation apparatus for an optical transmission system is configured as described above, when trying to evaluate characteristics by a small-scale loop, unless the loop gain is completely set to 1, The light signal either extinguished or diverged and was allowed to operate for only a short time. For example, an optical fiber loop 10 for signals with a pulse width of 800 ps
If you try to verify the error rate of 10 ^-9 after 0 laps, 10 ¹⁰
It is necessary to observe a pulse of about 10 to 20.
I have a minute. Conventionally, there has been a problem that a characteristic evaluation device with a stable loop cannot be obtained for such a long time. In addition, in the conventional evaluation device, additional components for measuring the characteristics are incorporated in the loop, and the method of removing this effect is not considered, so there is also the problem that evaluation by a system equivalent to the actual system cannot be performed. there were.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

[0008]

An optical transmission characteristic evaluation apparatus according to the present invention includes an optical transmitter for converting an electric signal into an optical signal, an optical fiber loop for transmitting the optical signal, and an optical fiber loop in the optical fiber loop. An optical amplifier included in the optical fiber loop, an optical receiver that converts the optical signal after circulating the optical fiber loop into an electrical signal, and an electrical signal that demultiplexes the optical signal in the optical fiber loop as necessary. And a control means for controlling the gain of the optical amplifier by an optical signal output from the loop or after the optical fiber loop is circulated around the optical fiber loop. An optical transmission characteristic evaluation apparatus according to the invention of claim 2 is an optical transmitter for converting an electric signal into an optical signal, an optical fiber loop for transmitting the optical signal, and an optical amplifier included in the optical fiber loop. An optical receiver for converting an optical signal after circulating the optical fiber loop into an electric signal, and an optical polarization controller in the optical fiber loop are provided, and the optical fiber A light receiver for demultiplexing the optical signal in the loop into an electric signal is provided, and a control means for controlling the gain of the optical amplifier or the polarization controller by the output of the optical receiver or the light receiver is provided.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

[0011]

EXAMPLES Example 1. FIG. 1 is a block diagram showing the configuration of an embodiment of the optical transmission characteristic evaluation apparatus according to the first aspect of the invention. In the figure,
Reference numeral 1 is an optical transmitter, 2 is an optical switch that cuts out an optical signal for a time period sufficient to fill the optical fiber loop without excess or deficiency, and 3 is an optical coupling device that introduces the cut out optical signal into the optical fiber loop and that extracts the optical signal from the optical fiber loop It is a duplexer. Reference numeral 4 is an optical amplifier, 5 is an optical switch, and 6 is an optical fiber, which is included in an optical fiber loop. Further, there are provided an optical receiver 7; a pulse pattern generator 8; an error rate measuring device 9; and a control device for controlling the gain of an optical amplifier 10a. A timing control device 19 controls the operation timings of the optical switches 2 and 5 and the error rate measuring device 9. As the above-mentioned optical switch, various optical switches utilizing electro-optical effect, acousto-optical effect, magneto-optical effect, etc. can be used. The optical switch 5 may be omitted if a switching operation by gain control of an optical amplifier or an optical multiplexer / demultiplexer that switches the optical path is used. As the optical amplifier, a rare earth-doped optical fiber amplifier or a semiconductor optical amplifier can be used.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

When the gain of the optical amplifier 4 is equal to the value that compensates for the loss in the optical fiber loop , in many cases
The error rate is minimum. At the next evaluation, that is, the specified lap
Sometimes cut out the light signal of only one round, to measure the error rate,
As a result, when looping through the next loop, the gain of the optical amplifier is also changed and set. Therefore, the gain of the optical amplifier is adjusted to the controller 10a so that the measurement result of the error rate measuring device is minimized.
The gain of the optical amplifier can be easily set by controlling the cut-and-try method several times. After several attempts, the loop gain becomes stable. For controlling the gain of the optical amplifier, there are methods such as control of pumping light power and control of a variable attenuator. As described above, the evaluation device is used in this embodiment.
On the other hand, the loop gain is stabilized by measuring the error rate .

[Procedure Amendment 7]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. The optical signal output from the optical multiplexer / demultiplexer 3 to the outside of the optical fiber loop is demultiplexed by the optical demultiplexer 11, one output is input to the optical receiver, and the clock is regenerated. The other output is input to the optical switch, and only the optical signal that has circulated the optical fiber loop a specified number of times, for example 100 times, is cut out,
The light receiver 12 converts the electric signal. The oscilloscope 14 observes the waveform with the clock regenerated by the optical receiver 7 and the signal converted into the electric signal by the light receiver 12 as inputs.
The change in characteristics can be evaluated by comparing the transmitted light power after the circulation. Therefore, it is also possible to cut out the optical signal after orbiting to a measuring instrument other than the oroscope and compare it with the initial value.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

Embodiment 3. FIG. 3 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus according to the first aspect of the present invention. In the figure, as a new part different from FIG.
There is a control device for controlling the gain of the optical amplifier of b, 11 is an optical demultiplexer, and 12 is a light receiver. This example is based on Example 1.
The amplifier gain is made constant for each fixed cycle test, and the gain is changed based on the previous result in the long term, and finally stable gain was obtained, but the gain is controlled continuously. There is a feature in doing it.

[Procedure Amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

Example 5. FIG. 5 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 4 . In the figure, as a part different from FIG.
In synchronization with the cycle that the optical signal goes around the optical fiber loop,
Alternatively, there is a controller that asynchronously changes the gain of the optical amplifier. The present embodiment is characterized in that the amplifier gain is changed for each cyclic test and the simulation accuracy of the actual system is improved, while the embodiment 1 controls the widening amplifier in which the loop gain is stable in the long term. .

[Procedure Amendment 10]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

Embodiment 6. FIG. 6 is a configuration block diagram showing another embodiment of the optical transmission characteristic evaluation apparatus of the invention of claim 4 . The transmission controller 17 includes an optical transmitter 1, an optical switch 2 ,
5, an optical multiplexer / demultiplexer 3 , an optical receiver 7, and a controller 10f are included. An optical amplifier 4 is connected between the output terminals 18a and 18b, and an optical fiber 6 is connected between the output terminals 18c and 18d. Thus, a transmission characteristic evaluation device similar to that of the fifth embodiment can be configured to evaluate the characteristics of the optical amplifier 4 and the optical fiber 6. Reference numeral 10f is a controller that changes the gain of the optical amplifier in synchronism with or asynchronously with the cycle of the optical signal circulating in the optical fiber loop. A timing control device 19 controls the operation timing of the optical switches 2 and 5. In this way, a simulation close to that of an actual system can be stably performed, and various evaluations can be performed.

[Procedure Amendment 11]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

Example 9. FIG. 9 is a block diagram showing the configuration of another embodiment of the optical transmission characteristic evaluation apparatus according to the invention of claim 4 . In the figure, a part different from that shown in FIG. 7 is a controller that changes the polarization state in synchronization with the period in which an optical signal of 10 g goes around the optical fiber loop or asynchronously. The purpose of this embodiment is to improve the simulation accuracy for an actual system.

[Procedure Amendment 12]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

Next, the operation will be described. Basic operations such as the passage of the signal light and the operation of the optical switch are the same as those in the first embodiment. An optical switch in the optical fiber loop is required to have a high extinction ratio and a high operation speed, and a typical example thereof is an acousto-optical switch. However, the optical signal undergoes a frequency shift when it passes through the acousto-optical switch. +1 order as transmitted light of acousto-optic switch
There are two types, one using the diffracted light of No. 1 and the other using the diffracted light of the -1st order, and the frequency shift due to these is in the opposite direction. Therefore, by connecting the two types of acousto-optic optical switches in cascade, an optical switch having a high extinction ratio and no optical frequency shift can be configured. Well
Also, one of the optical switches connected in cascade is always
It may be turned on.

[Procedure Amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction content]

Next, the operation will be described. Even if the optical switch 2 is controlled by the timing control device, the optical transmitter 1
The optical signal train obtained by cutting out the optical signals from
It cannot be controlled to be continuous with the signal train. Give continuity
The only way to get it is to adjust the length of the optical loop, but of course
I couldn't do this, instead I controlled the synthesizer,
The oscillation frequency of the original pulse pattern generator 8 is slightly changed. When the time taken for the optical signal to make one round in the optical fiber loop is an integral multiple of the time of one time slot of the optical signal, the clock recovery is easiest in the optical receiver, and it is close to the actual system, and , The code error rate is the minimum. Therefore, the oscillation frequency of the synthesizer 13 is set to the controller 10c so that the measurement result of the error rate measuring device is minimized.
By controlling with, the time for the optical signal to make one round in the optical fiber loop can be easily set to an integral multiple of the time of one time slot of the optical signal.

[Procedure Amendment 14]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

Example 13. If an optical switch using an acousto-optic effect is used as the optical switch in the optical fiber loop in the above embodiment, the optical frequency can be shifted each time the optical switch transmits, and the influence of detuning of the optical signal is investigated. be able to. Further, the number of optical amplifiers in the optical fiber loop in the above embodiment may be two or more.
Further, the arrangement of the optical switch, the optical amplifier, and the optical fiber in the optical fiber loop may be different from that in the embodiment. The length of the optical signal cut out by the optical switch between the optical transmitter and the optical fiber loop may be shorter than the time T for filling the optical fiber loop without excess or deficiency. The time required increases.

[Procedure Amendment 15]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

[0036]

As described above, according to the present invention, in the optical transmission characteristic evaluation apparatus, after the loop is circulated for a predetermined number of times, it is output by a receiver that receives an optical signal that has exited the loop or by another light receiver. Since the optical amplifier or the like is controlled, or the optical polarization controller and the pulse generation control means are further provided, there is an effect that a stable device can be obtained even for long-term transmission characteristic evaluation. Furthermore, there is an effect that a simulation close to an actual system can be performed and an arbitrary deviation can be stably given.

[Procedure Amendment 16]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

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Claims (3)

[Claims] 1. An optical transmitter for converting an electrical signal into an optical signal, an optical fiber loop for transmitting the optical signal, an optical amplifier included in the optical fiber loop, and a loop for the optical fiber loop. An optical receiver for converting the subsequent optical signal into an electrical signal and a receiver for converting the optical signal in the optical fiber loop into an electrical signal by demultiplexing the optical signal in the optical fiber loop are provided, and the optical fiber loop is circulated. Then, an optical transmission characteristic evaluation device comprising: a control means for controlling the gain of the optical amplifier by the optical signal output from the loop or by the output of the photodetector. 2. An optical transmitter for converting an electric signal into an optical signal, an optical fiber loop for transmitting the optical signal, an optical amplifier included in the optical fiber loop, and a loop for the optical fiber loop. An optical receiver for converting the latter optical signal into an electric signal and an optical switch or optical polarization controller in the optical fiber loop as needed, and demultiplexing the optical signal in the optical fiber loop. Optical transmission characteristics provided with a photoreceiver for converting into an electric signal as necessary, and a control means for controlling the gain of the optical amplifier or the optical polarization controller by the output of the optical receiver or the optical receiver. Evaluation device. 3. An optical transmitter for converting an electrical signal into an optical signal, an optical fiber loop for transmitting the optical signal, an optical amplifier included in the optical fiber loop, and a loop for the optical fiber loop. An optical receiver for converting the latter optical signal into an electric signal and a light receiver for demultiplexing the optical signal in the optical fiber loop into an electric signal if necessary, and providing the electric signal as necessary And a pulse generator control means for controlling the gain of the optical amplifier or the pulse generator by the output of the optical receiver or the photodetector. And an optical transmission characteristic evaluation device.