JP2000286800A - Carrier level deviation correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a carrier level deviation at the time of multistage connection by correcting the levels of all the plurality of carriers installed and inputted between arbitrary local stations. SOLUTION: In a sub-carrier multiplex system optical network, a center station 16, local stations 17a-17f and a level correction device 18 are connected in a circle through optical fiber cables 13a-13j. The level correction device 18 is connected between the local stations 17c and 17d. The center station 16 outputs signal light containing a pilot carrier to the local station 17a of a next stage through the optical fiber cable 13a. The local station 17a has a function for synthesizing a signal from the previous stage with the carrier taken in by a self-station and outputting signal light to the next stage and the other local stations have the same functions. All the carriers are contained in signal light which the local station 17f of the final stage outputs, and the center station 16 can receive the whole carriers. The level correction device 18 arranged between the local stations corrects each carrier level in the input signals to be constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier level deviation correcting device, and more particularly to an optical transmission terminal and an optical transmission system of a system in which signals from a plurality of points are multiplexed and transmitted through an optical fiber. The present invention relates to a carrier level deviation correction device for controlling a level deviation of a signal from a carrier signal.

[0002]

2. Description of the Related Art Conventionally, as shown in, for example, Japanese Patent Application Laid-Open No. 7-123072, this type of optical transmission terminal has the same signal level in a system for multiplexing and transmitting signals from a plurality of points. It is used for multiplexing.

FIG. 6 is a configuration diagram of an example of a conventional optical transmission system. Referring to FIG. 6, a conventional optical transmission system includes a center station 16 and n (n is a positive integer) local stations 1.
7a to 17f are optical fibers 13a, 13b, 13c,
It is connected in a ring through 13j. Center station 16
Converts the reference signal into an optical signal and outputs it to the local station 17a via the optical fiber 13a. Local station 17a
Converts an electric signal input from the outside into an optical signal, multiplexes the signal light with the input signal light, and outputs the multiplexed signal light to the next local station 17b via the optical fiber 13b. Similarly, after the n local stations are connected, the signal light output from the local station 17f is input to the center station 16. The signal light input to the center station 16 is output after being converted into an electric signal.

FIG. 8 is a configuration diagram of an example of a conventional optical transmission terminal. Referring to FIG. 8, a conventional optical transmission terminal, for example, a local station 17a includes an optical multiplexer 14 and an optical distributor 15
, A light source unit 6, an electric signal level setting unit 3a, a modulation unit 10, a control unit 9, a detection unit 8a, an optical fiber 13a, and the like. The optical fiber 13a is connected to the input side of the optical multiplexer 14. An optical fiber 13m is connected between the output side of the optical multiplexer 14 and the input side of the optical distributor 15, and an optical fiber 13p is connected between the other input side of the optical multiplexer 14 and the output side of the light source unit 6, An optical fiber 13n is connected between an output side of the optical distributor 15 and an input side of the detection unit 8a, and an optical fiber 13b is connected to another output side of the optical distributor 15.

Each signal output from the center station 16 at the preceding stage is transmitted by the optical fiber 13a and input to one input terminal of the optical multiplexer 14 as signal light. The signal light output from the light source unit 6 is input to the other input terminal of the optical multiplexer 14 via the optical fiber 13p. The optical multiplexer 14 multiplexes the two input signal lights and outputs the multiplexed signal light.
The multiplexed signal light is input to the optical splitter 15 via the optical fiber 13m, and is split into two signal lights. One of the divided signal lights is transmitted to the next-stage optical terminal via the optical fiber 13b. The other distributed signal light is input to the detection unit 8a via the optical fiber 13m. The detection unit 8a detects a signal level of a predetermined frequency in the input signal light and outputs the result to the control unit 9a. The control unit 9a controls the gain or the loss of the electric signal level setting unit 3a based on the detection result. The electric signal input to the optical transmission terminal is input from the electric signal input 24,
Is output to the light source unit 6 via the electric signal level setting unit 3a as a signal obtained by modulating a carrier having a frequency different from the carrier signal frequency from the previous stage. The light source unit 6 outputs a new signal light having the same optical modulation degree as the signal light transmitted from the previous stage to the optical multiplexer 14 via the optical fiber 13p by the function of the electric signal level setting unit 3a.

The operation of the conventional optical transmission system configured as described above will be described with reference to FIG. FIG. 7 shows a frequency spectrum of a signal in a conventional optical transmission system. The signal light output from the center station 16 includes FIG.
(A), a reference signal such as a pilot signal fp is included. This signal may be at a level that does not affect other transmission signals. Next, the local station 17a converts the newly input signal and the signal light transmitted from the previous stage into an optical multiplexer 1
The signal is multiplexed at 4. At this time, the optical modulation degrees of the signal light transmitted from the previous stage and the newly input signal are controlled to be equal by the detection unit 8a, the control unit 9a, and the electric signal level setting unit 3a. The signal light output from the local station 17a includes a pilot signal fp and a new input signal f1, as shown in FIG. 7B. Similarly, the signal light output from the local station 17b includes FIG.
(C), the pilot signal fp transmission signal f
1 and a new input signal f2. In this way, the signal light transmitted through the n local stations includes the pilot signal fp and the n transmission signals as shown in FIG. 7D. By receiving this signal light at the center station 16, signals from a plurality of points are transmitted.

[0007]

However, despite the fact that the center station and each local station individually control the level of signal light, the serial multistage connection of the local stations deteriorates the frequency level deviation. There was a disadvantage.

This is because only the pilot carrier or the carrier level of the own station is monitored and controlled, and the deterioration is not corrected. Even if the number per station is small, it becomes remarkable in multiple stages. The frequency level deviation degradation is considered to have little effect if it is limited to an extremely narrow band, but it becomes more problematic as the frequency band becomes wider and the number of local stations and carriers increases. I can not cope.

There is also a drawback that the carrier frequency that can be used in each local station is determined by the number of local stations, the number of carriers, and the local station frequency level deviation characteristics. For this reason, it is necessary to construct a system limited for each application, and it is not possible to flexibly respond.

The reason is due to the shape of the local station frequency level characteristic, and the level deviation of the normal carrier with respect to the pilot carrier becomes larger at the time of multistage connection. At this time, when the pilot is high, the distortion characteristic deterioration is remarkable, and when the pilot characteristic is low, the noise characteristic deterioration is remarkable. In either case, the electric signal level at the time of demodulation may fall outside the dynamic range of the demodulator.

An object of the present invention is to provide a subcarrier multiplexing system in which a plurality of local stations transmitting signal light modulated by one or a plurality of carriers and a center station receiving the signal light are connected by an optical fiber network. In a system optical network, it is to suppress a carrier level deviation at the time of multistage connection.

[0012]

According to the present invention, a plurality of local stations for transmitting signal light modulated by one or a plurality of carriers and a center station for receiving the signal light are provided. An apparatus for correcting carrier level deviation in a subcarrier multiplexing optical network connected by an optical fiber network, comprising a level correcting means provided between any local stations and correcting the level of all of the plurality of carriers inputted. It is characterized by the following.

According to the present invention, since the levels of a plurality of carriers on an optical fiber cable are corrected, it is possible to suppress a carrier level deviation at the time of multistage connection.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The above problem can be solved by always monitoring all bands and all carriers in each local station and performing control. However, a great deal of adjustment is required for each station, and the cost and the external dimensions increase due to the increase in the size of the circuit. Therefore, the present invention solves the problem by disposing a device having a carrier level correction function between arbitrary local stations at the time of multistage connection.

First, the overall configuration of a subcarrier multiplexing optical network according to the present invention will be described. FIG. 1 is an overall configuration diagram of a subcarrier multiplexing optical network according to the present invention. In the subcarrier multiplexing optical network, a center station 16, n local stations 17a to 17f, and a level correction device 18 are composed of optical fiber cables 13a to 13j.
Are connected to each other in a ring. And local station 1
The level correction device 18 is connected between 7c and 17d.

The center station 16 outputs the signal light including the pilot carrier to the next local station 17a via the optical fiber cable 13a. The local station 17a has a function of multiplexing the carrier taken by the own station into the signal from the previous stage and outputting the signal light to the next stage, and the same applies to other local stations. The signal light output by the local station 17f at the last stage (n-th stage) includes all carriers, and the center station 16 can receive all carriers. The level correction device 18 disposed between the local stations has a function of correcting each carrier level in the input signal to a constant.

Hereinafter, embodiments and examples of the level correcting device 18 will be described. First, a first embodiment will be described. FIG. 3 is a configuration diagram of the first embodiment. In the first embodiment, a light receiving unit 1, amplifiers 2a to 2a,
2e, distributors 4a to 4h, and signal selectors 7a to 7d
And electric signal level setting units 3a to 3d, and control unit 9a
And comparison control units 19a to 19c and detection units 8a to 8d
, The multiplexers 5a to 5d, the light source unit 6, the automatic temperature control unit 11, the automatic optical output level control unit 12, the optical fiber cable 13e, and the like.

An optical fiber cable 13e is connected to the input side of the light receiving unit 1, and the light receiving unit 1, the amplifier 2a, and the distributor 4a
Are connected in series. Further, a distributor 4a, a signal selector 7a, an amplifier 2b, an electric signal level setting unit 3a, a distributor 4e, and a multiplexer 5a are connected in series. The distributor 4a, the detector 8a, and the electric signal level setting unit 3a are connected in a ring.

The other output side of the distributor 4a is connected to the distributors 4b to 4b.
4d are connected in series. On the other output side of the distributor 4b, a signal selector 7b, an amplifier 2c, an electric signal level setting unit 3b, a distributor 4f, and a multiplexer 5b are connected in series. The distributor 4f, the detection unit 8b, and the comparison control unit 19a are connected in a ring. The same components are connected to the distributors 4c and 4d.

A multiplexer 5a, a multiplexer 5b, and a multiplexer 5c connected to the distributor 4g and a multiplexer 5d connected to the distributor 4h are connected in series. The multiplexer 5a and the light source unit 6 are connected, and an output side of the light source unit 6 is connected to an optical fiber cable 13f. Further, an automatic temperature control unit 11 and an automatic light output level control unit 12 are connected to the light source unit 6.

Next, an outline of the operation of the first embodiment will be described. The signal light containing the carrier up to the preceding local station 17c is converted into an electric signal by the light receiving unit 1 and then amplified, separated by the signal selecting unit 7 into separate circuits for each carrier, and the respective levels are detected. At this time, all carriers are level-adjusted based on the pilot carrier level already detected. Thereafter, all the carriers are multiplexed, converted into an optical signal by the light source unit 6, and then transmitted to the next local station 17d.
Output to

Next, the operation of the first embodiment will be described in detail. The signal light output from the preceding local station 17 is input to the light receiving unit 1 via the optical fiber cable 13a. The signal light is converted into an electric signal by the light receiving unit 1, then amplified by the amplifier 2a and distributed to a pilot carrier system and a carrier system by the distributor 4a. From the signal distributed to the pilot carrier system, only the pilot carrier is extracted by the signal selector 7a and amplified by the amplifier 2b.
It is controlled to a constant level by the electric signal level setting section 3a. Thereafter, the signal is divided into two parts by a distributor 4e into a main signal system and an AGC system. The signal distributed to the main signal system is multiplexed with another carrier by the multiplexer 5a, converted into an optical signal by the light source unit 6, and then transmitted to the next local station 17 by the optical fiber cable 13f.
Output to The automatic temperature control unit 11 is a general circuit that keeps the light source unit 6 at a constant temperature, and the automatic light output level control unit 12 is a general circuit that keeps the light output constant.

The level of the signal distributed to the AGC system by the distributor 4e is detected by the detector 8a, and the detected data is input to the controller 9a. In the control unit 9a, the detection unit 8a
Is compared with a certain reference level to control the electric signal level setting section 3a.

The signal distributed to the carrier system from distributor 4a is further distributed by distributor 4b. On the other hand, only one arbitrary carrier is extracted by the signal selector 7b, amplified by the amplifier 2c, and then controlled to a constant level by the electric signal level setting unit 3b. After that, the signal is distributed to the signal system and the AGC system by the distributor 4f. The signal distributed to the signal system is multiplexed with another carrier by the multiplexer 5b, and then multiplexed with the pilot carrier by the multiplexer 5a. The signal distributed to the AGC system by the distributor 4f is carrier level detected by the detection unit 8b, and the detected data is input to the comparison control unit 19a. The comparison control unit 19a compares the data from the detection unit 8b with the data from the detection unit 8a, and controls the electric signal level setting unit 3b.

The operation of the stage subsequent to the distributors 4c and 4d is the same as the operation of the stage subsequent to the distributor 4b, and a description thereof will be omitted. That is, the levels of the carriers received by the light receiving unit 1 are controlled to be equal, and the carriers after the control are multiplexed and output from the light source unit 6.

The comparison control section 19a also has a function of discriminating the presence or absence of a carrier. When the carrier is below a certain level value (extremely low), it is determined that there is no carrier, and the attenuation of the electric signal level setting section 3b is reversed. To the maximum. This function suppresses the noise of the amplifier when there is no carrier.

As a situation, it is conceivable that an accident such as a signal from a certain local station does not arrive due to the disconnection of the optical fiber cable, or that only a part of the carrier is used due to the system configuration. Other carriers are similarly extracted and level-controlled for each carrier, and then combined and output together. At this time, each carrier level is controlled in consideration of the loss of the multiplexer.

Next, a second embodiment will be described. FIG. 4 is a configuration diagram of the second embodiment. In the second embodiment, the light receiving unit 1, the amplifiers 2a to 2e, and the distributor 4
a to 4d, signal selection units 7a to 7c, and detection units 8a to 8
c, frequency level deviation correction unit 21 and comparison control unit 19
a, a light source unit 6, an automatic temperature control unit 11, an automatic light output level control unit 12, an optical fiber cable 13e, and the like.

An optical fiber cable 13e is connected to the input side of the light receiving unit 1, and the light receiving unit 1, the amplifier 2a, and the distributor 4a
Are connected in series. Further, the distributor 4a, the amplifier 2b, the frequency level deviation correction unit 21, the light source unit 6, and the optical fiber cable 13f are connected in series.

The other output side of the distributor 4a is connected to the distributors 4b to 4b.
4d are connected in series. On the other output side of the distributor 4b, a signal selector 7a, an amplifier 2c, and a detector 8a are connected in series. Note that the distributors 4c and 4d are also provided with the distributor 4c.
The same components as those in b are connected. The outputs of the detection units 8a to 8c are input to the comparison control unit 19a. The output of the comparison control section 19a is input to another input side of the frequency level deviation correction section 21.

Next, the operation of the second embodiment will be described. The signal light containing the carrier up to the preceding local station 17c is converted into an electric signal by the light receiving unit 1 and then amplified, separated into separate circuits for each carrier by the signal selecting units 7a to 7c, and the respective levels are detected. Thereafter, the comparison control unit 19a receives the detected values of all carriers, and controls the frequency level deviation correction unit 21. The frequency level characteristic of the main signal system is corrected by the frequency level deviation correction unit 21 so that all carriers are constant. Thereafter, the light is converted into an optical signal by the light source unit 6 and output to the next local station 17d.

[0032]

Next, an embodiment of the present invention will be described. First, the first embodiment will be described. The first example is an example of the first embodiment. Referring to FIG. 1, a signal light including a pilot carrier output from a center station 16 is transmitted to a local station 17 via an optical fiber cable 13a.
a. In the local station 17a, the signal light is converted into an electric signal, a new carrier is taken in, and then converted into an optical signal and output to the next-stage local station 17b via the optical fiber cable 13b. Here, a configuration example of the local station will be described with reference to FIG.

FIG. 5 is a configuration diagram of an example of the local station.
FIG. 5 shows the configuration of the local station 17a as an example, but the configurations of the other local stations 17b to 17f are the same.
Referring to FIG. 5, local station 17a includes light receiving unit 1, amplifier 2, electric signal level setting units 3a and 3b, distributor 4a, multiplexer 5, light source unit 6, and signal selecting unit 7. , Detectors 8a and 8b, controllers 9a and 9b, and modulator 1
0, an automatic temperature control unit 11, and an automatic light output level control unit 12.

An optical fiber cable 13a is connected to the input side of the light receiving unit 1, and the light receiving unit 1, the amplifier 2, the electric signal level setting units 3a and 3b, the distributor 4a, the multiplexer 5, and the light source unit 6 are connected in series. It is connected to the. Further, an optical fiber cable 13b is connected to the output side of the light source unit 6. or,
The distributor 4a, the signal selector 7, the detector 8a, the controller 9a, and the electric signal level setting unit 3a are connected in a ring, and the distributor 4a, the signal selector 7, the detector 8a, the controller 9b, and the electric signal level are connected. The setting unit 3b and the multiplexer 5 are connected in a ring shape, and the electric signal level setting unit 3b, the distributor 4b, and the detection unit 8
b and the control unit 9b are connected in a ring shape. The modulator 10 and the distributor 4b are connected in series, and the light source 6 is connected with an automatic temperature controller 11 and an automatic light output level controller 12.

Next, the operation of the local station 17a will be described. Referring to FIG. 5, the signal light output from the center station 16 at the preceding stage is input to the light receiving unit 1 via the optical fiber cable 13a. The signal light is converted into an electric signal by the light receiving unit 1, then amplified by the amplifier 2, and controlled to a constant level by the electric signal level setting unit 3a. Thereafter, the signal is distributed to the main signal system, the AGC system, and the output system by the distributor 4a.
In the main signal system, the new carrier is thereafter multiplexed by the multiplexer 5, converted into an optical signal by the light source unit 6, and outputted to the next local station 17b by the optical fiber cable 13b. The automatic temperature control unit 11 is a general circuit that controls the Peltier element in the LD of the light source unit 6 and maintains the LD element at a constant temperature.
The automatic light output level controller 12 is a general circuit for keeping the LD light output constant.

From the signal distributed to the AGC system by the distributor 4a, only the pilot carrier is extracted by the signal selector 7 and input to the detector 8a. The detection unit 8a converts the input pilot carrier into a voltage corresponding to the carrier level and outputs the voltage to the control units 9a and 9b. The control unit 9a compares the voltage from the detection unit 8a with the reference voltage and controls the electric signal level setting unit 3a. The signal distributed to the output system by the distributor 4a is an external output, and a carrier output input before the previous stage is possible.

The input electric signal is modulated into a carrier by the modulating unit 10, and then divided by the distributor 4b into a signal system and an AGC system. Thereafter, the signal system is controlled to have a constant level by the electric signal level setting unit 3b, and is multiplexed with the main signal by the multiplexer 5.

The signal distributed to the AGC system by the distributor 4b is converted into a voltage by the detector 8b and input to the controller 9b. The control section 9b compares the voltage from the detection section 8b with reference to the voltage from the detection section 8a to control the electric signal level setting section 3b.

As described above, the local station controls the pilot carrier so that the carrier level from the previous stage and the new input carrier level are constant, and then combines and transmits the signals. The optical signal output from the local station 17c is input to the level correction device 18 via the fiber 13e.

The operation of the level correction device 18 will now be described with reference to FIG. The signal light output from the local station 17c at the preceding stage is input to the light receiving section 1 (photodiode) via the optical fiber cable 13e. The signal light is converted into an electric signal by the light receiving unit 1, then amplified by the amplifier 2a and distributed to a pilot carrier system and a carrier system by the distributor 4a. From the signal distributed to the pilot carrier system, only the pilot carrier is extracted by the signal frequency selection unit 7a (bandpass filter) and amplified by the amplifier 2b, and then the electric signal level setting unit 3a (voltage control variable attenuator)
Is controlled to a constant level. Thereafter, the signal is divided into two parts by a distributor 4e into a main signal system and an AGC system.

The signal distributed to the main signal system is multiplexed with another carrier by the multiplexer 5a, converted into an optical signal by the light source section 6 (laser diode), and then converted into an optical fiber cable 13f.
Is output to the next-stage local station 17d. The automatic temperature control unit 11 (ATC circuit) is a general circuit that feedback-controls the Peltier element current in the laser diode module of the light source unit 6 and maintains the LD element at a constant temperature. The automatic light output level control unit 12 (APC circuit) ) Is a general circuit for feedback-controlling the drive current so as to keep the laser light output constant.

The signal distributed to the AGC system by the distributor 4e is converted into a voltage corresponding to the pilot carrier level by the detection unit 8a (full-wave rectifier) and input to the control unit 9a (operational amplifier). The control unit 9a compares the voltage from the detection unit 8a with the reference voltage and outputs a corresponding voltage, and feedback-controls the attenuation of the electric signal level setting unit 3a so that the carrier level is constant.

The signal distributed to the carrier system from distributor 4a is further distributed by distributor 4b. On the other hand, only an arbitrary carrier is extracted by the signal selection unit 7b (band-pass filter), amplified by the amplifier 2c, and then controlled to a constant level by the electric signal level setting unit 3b (voltage-controlled variable attenuator). Thereafter, the signal system, AG
It is divided into two in the C system. The signal distributed to the signal system is multiplexed with another carrier by the multiplexer 5b, and then multiplexed with the pilot carrier by the multiplexer 5a.

The signal distributed to the AGC system by the distributor 4f is converted into a voltage corresponding to the carrier level by the detection unit 8b (full-wave rectifier) and input to the comparison control unit 19a (operational amplifier). The comparison control unit 19a compares the voltage from the detection unit 8b with reference to the voltage from the pilot carrier detection unit 8a, and performs feedback control so that the attenuation of the electric signal level setting unit 3b is constant at the carrier level.

The comparison control section 19a also has a function of discriminating the presence or absence of a carrier. When the carrier is below a certain level value (extremely low), it is determined that there is no carrier, and the attenuation of the electric signal level setting section 3b is reversed. To the maximum. With this function, when there is no carrier, the attenuation of the electric signal level setting unit 3b is prevented from being minimized, and the noise of the amplifier 2c is suppressed. Specifically, the comparison control unit 19a sets the electric signal level setting unit 3b in accordance with the two types of reference voltages (threshold voltages).
Control.

As a situation, it is conceivable that an accident such as a signal from one local station does not arrive due to disconnection of the optical fiber cable, or that only a part of the carrier is used due to the system configuration. Other carriers are similarly extracted and level-controlled for each carrier, and then combined and output together. At this time, each carrier level is controlled in consideration of the loss of the multiplexer.

In this embodiment, two distributors (4a to 4a) are used for distribution.
Although a plurality of d) is used, the same effect can be obtained by using a plurality of 1: n distributors. This is a multiplexer (5a ~
The same applies to 5d). In addition, the signal selection unit (7a-
The circuit scale can be reduced by selecting one to a plurality of waves (appropriately up to two or three waves) depending on the number of carriers used and the carrier frequency interval for the carriers extracted in d). This is because the closer the adjacent carrier frequency is, the less the influence of the frequency level characteristic is. Since the adjacent carrier frequency depends on the demodulation bandwidth of the baseband signal modulated on the carrier, the number of carriers that can be selected varies according to required specifications.

Here, the description returns to FIG. The signal light output from the level correction device 18 is
The signal is input to the next-stage local station 17d via f. As described above, the local station fetches a new carrier and transmits it to the next stage. Similarly, the signal light transmitted to the local station 17f is input to the center station 16. The center station 16 receives all carriers.

Next, each carrier level in the system of FIG. 1 will be described with reference to FIG. FIG. 2 is a frequency spectrum of a signal in the optical transmission system of the present invention. The center station 16 outputs a signal light including the pilot carrier fp (see FIG. 2A). In this example, the pilot carrier level is lower than other carriers, but the purpose is to be a reference, and the level difference has no particular meaning. Carrier f1 captured by local station 17a
Is level-controlled based on the pilot carrier fp and transmitted (see FIG. 2B). The level of the carrier f2 captured by the local station 17b is also controlled in the same manner. However, since only the pilot carrier and the new carrier are monitored in the local station, the input carrier before the preceding stage is the frequency level characteristic of the transmission path. Affected by Where f1
If the nearby frequency characteristic has a deviation on the high level side, f1 becomes higher than the desired level (see FIG. 2C). Similarly, the carrier level at the local station 17c after passing through several stages deviates from the desired level except for the carrier fm and the pilot carrier taken in at that station. Assuming that the frequency level characteristics of all the local stations have the same tendency, the carrier taken in the preceding stage is more affected by the frequency level characteristics (see FIG. 2D).

Next, the carrier levels are all controlled to be constant by the level correction device 18 and output to the next-stage local station 17d (see FIG. 2E).

Since the local stations 17e and 17f in the succeeding stages are affected by the frequency level characteristics of the local stations as in the preceding stage, the carrier level varies as the stages are increased, but the number of stages before the level corrector 18 is affected. Is not performed (see FIGS. 2F and 2G).

In this embodiment, the level correcting device 18 is arranged near the middle stage, but the effect changes depending on the location. For example, the last stage (between the center station 16 and the local station 17f)
By arranging the present device 18 in the first stage, it is possible to make all carrier levels constant, but the noise and distortion characteristics in the level deviation up to the immediately preceding stage greatly deteriorate. Thus, the optimum position changes depending on the required characteristics and the system configuration.

Next, a second embodiment will be described. Second
The example is an example for the second embodiment. FIG.
, The signal light output from the local station 17c at the preceding stage is input to the light receiving unit 1 via the optical fiber cable 13e. The signal light is converted into an electric signal by the light receiving unit 1 and then amplified by the amplifier 2a.
Distributed to the carrier level detection system. After the signal distributed to the main signal system is amplified by the amplifier 2b, the frequency level deviation correction unit 21 corrects the in-band frequency level deviation. Thereafter, the light signal is converted into an optical signal by the light source unit 6 and output to the next-stage local station 17d via the optical fiber cable 13f. The automatic temperature control unit 11 is a general circuit that controls the Peltier element in the LD of the light source unit 6 and keeps the LD element at a constant temperature, and the automatic light output level control unit 12 is a general circuit that keeps the LD light output constant. Circuit.

The signal distributed from the distributor 4a to the carrier level detection system is further distributed by the distributor 4b. On the other hand, only an arbitrary carrier is extracted by the signal selector 7a, amplified by the amplifier 2c, and input to the detector 8a. The detection unit 8a converts the input carrier into a voltage corresponding to the carrier level and outputs the voltage to the comparison control unit 19a. The comparison control unit 19a similarly receives the information on the level values of a plurality of carriers, and controls the frequency level deviation correction unit 21 according to the current in-band frequency level deviation. At this time, the comparison controller 19a compares the given voltage conversion value of each carrier level with the reference voltage, and if it is higher, performs control such that only the band near the carrier is attenuated. As an example of the frequency level deviation correction unit 21, a circuit having an active filter function combining a diode and a transistor can be considered.

The comparison control section 19a also has a function of discriminating the presence or absence of a carrier.
Judgment is made that there is no carrier, and the band near this is controlled to be a reference value from the level of the pilot carrier. With this function, it is possible to prevent a part of band gain without a carrier from being increased unnecessarily, and to prevent deterioration of noise characteristics, crosstalk, isolation characteristics, and the like. Specifically, it is controlled by two types of reference voltages (threshold voltages). As a situation, an accident such as a signal from a certain local station not reaching due to a cut of an optical fiber cable, and a case where only a part of a carrier is used due to a system configuration are considered.

It should be noted that in this embodiment, two distributors (4a
4d), a similar effect can be obtained by using a 1: n multiple distributor. Further, the extracted carrier may have various patterns such as full wave, every other wave, or arbitrary number of waves according to the frequency level deviation characteristic of the local station, the carrier frequency interval, and the like.

[0057]

According to the present invention, a plurality of local stations for transmitting signal light modulated by one or more carriers and a center station for receiving the signal light are connected to a subcarrier by an optical fiber network. A carrier level deviation correcting device in a multiplex optical network, the device comprising a level correcting means provided between any of the local stations and correcting the level of all of the plurality of carriers inputted, so that multi-stage connection is possible. It is possible to suppress the carrier level deviation at the time.

If the level correction means is arranged effectively, the upper limit (the number of node stations, etc.) of the current system can be increased. The reason is that the in-band carriers are individually extracted, the level is individually monitored, and the control is performed. Further, the level correcting means can be introduced without affecting the center station and the local station, and can be easily added to an existing system, so that an inexpensive system can be provided. The reason is that only the carrier level is controlled and the baseband signal is not affected.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a subcarrier multiplexing optical network according to the present invention.

FIG. 2 is a frequency spectrum of a signal in the optical transmission system of the present invention.

FIG. 3 is a configuration diagram of the first embodiment.

FIG. 4 is a configuration diagram of a second embodiment.

FIG. 5 is a configuration diagram of an example of a local station.

FIG. 6 is a configuration diagram of an example of a conventional optical transmission system.

FIG. 7 is a frequency spectrum of a signal in a conventional optical transmission system.

FIG. 8 is a configuration diagram of an example of a conventional optical transmission terminal.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light receiving section 2 amplifying section 3 electric signal setting section 4 distributor 5 multiplexer 6 light source section 7 signal selecting section 8 detecting section 9 control section 16 center station 17 local station 18 level correction device 19 comparison control section 21 frequency level deviation correction Department

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04J 1/00

Claims (7)

[Claims] 1. A carrier in a subcarrier multiplexing optical network in which a plurality of local stations transmitting signal light modulated by one or more carriers and a center station receiving the signal light are connected by an optical fiber network. A carrier level deviation correcting device, comprising a level correcting means provided between any local stations and correcting the level of all of the plurality of carriers inputted. 2. A level divider comprising: a distributor for distributing the plurality of carriers inputted to individual carriers; a comparator for comparing the level of each carrier distributed by the distributor with a reference level; A level setting unit that sets the level of the carrier to a constant level in accordance with a result of the comparison by the comparator; and a multiplexer that multiplexes the individual carriers set to a constant level by the level setting unit. The carrier level deviation correction device according to claim 1, wherein: 3. The carrier level deviation correction device according to claim 2, wherein the reference level is a level value of a pilot carrier output from the center station. 4. The comparator has a function of determining the presence or absence of a carrier to be compared, and when the comparator determines that there is no carrier, the level setting unit sets the attenuation to a maximum. The carrier level deviation correction device according to claim 2 or 3, wherein: 5. A level divider for distributing the input plurality of carriers to a main signal system and a carrier level detection system, and a level divider for the main signal system distributed by the first distributor. A level corrector for correcting a plurality of carrier levels; a second distributor for distributing the plurality of carriers of the carrier level detection system distributed by the first distributor to individual carriers; 2. A comparison control unit, comprising: comparing the level of each individual carrier obtained with a reference level, and making the level correction unit correct each individual carrier level of the main signal system according to the comparison result. The carrier level deviation correction device as described in the above. 6. The comparison control unit has a function of determining the presence or absence of a carrier to be compared, and when determining that there is no carrier, controls the carrier level of the frequency band to be a constant reference value. The carrier level deviation correction device according to claim 5. 7. The carrier level deviation correcting device according to claim 6, wherein the fixed reference value is a level value of a pilot carrier output from the center station.