JP5383455B2 - Optical fiber communication system - Google Patents

Description

  The present invention relates to an optical fiber communication system using a predistortion method, and more particularly to a chromatic dispersion compensation control technique for setting an optimum compensation dispersion value for a transmission signal.

In general, in an all-optical network, there is a signal waveform distortion due to chromatic dispersion as a constraint condition when establishing a long-distance / broadband optical path, and it is necessary to compensate appropriately.
A conventional chromatic dispersion compensation technique in an optical fiber communication system uses a dispersion compensation fiber (DCF) having an optical fiber transmission line and dispersion of an opposite sign based on a detailed dispersion compensation design before the construction of a network. It was common to perform fixed dispersion compensation.

  However, in a high-speed communication system of 40 G [bit / sec] or more, a signal waveform is distorted due to a slight change in dispersion due to temperature, fiber interruption, or the like, and the optical path is switched to an alternative optical path when a failure occurs. Since the chromatic dispersion is different for each optical path, a tunable dispersion compensation technique is required.

Conventionally, a predistortion method has been proposed as an example of a variable dispersion compensation technique (see, for example, Patent Document 1 and Non-Patent Document 1).
This type of predistortion method is to electrically calculate an input optical data sequence in order to realize a transfer function opposite to the transfer function of the optical fiber transmission line as a convolution on the time axis.

  In this case, there are three calculation methods: a lookup table method in which a conversion table is stored in advance in a large-scale memory, a method in which calculation is performed sequentially using an FIR filter, and a method in which calculation is performed using an analog transversal filter.

  An optical fiber communication system using a predistortion system performs I / Q modulation of light using a pre-modulated signal generated by any of the above three systems, thereby reducing group delay due to dispersion after optical fiber transmission. An optical waveform having a complex electric field is generated.

JP 2006-522508 A

Shiro Kasa, Mikio Yagi, Shuichi Satomi, Shoichiro Asano, “Chromatic Dispersion Compensation in Ultrafast Wavelength Path Network”, 2004 IEICE Communication Society Conference, BSC-1-1

  The conventional optical fiber communication system can realize the tunable dispersion compensation by using the predistortion method. However, the chromatic dispersion amount of the optical path is measured in advance and the chromatic dispersion amount to be compensated is determined by the end node of the optical path. There is a problem that it is necessary to set the variable dispersion compensator of the above.

  In addition, as one method of setting the chromatic dispersion amount of the path set in the tunable dispersion compensator, an error correction circuit provided in a receiving-side optical fiber optical communication node (hereinafter simply referred to as “optical communication node”) A chromatic dispersion adjustment method is also known in which the number of bit errors to be corrected is fed back to the optical fiber optical communication node on the transmission side so that the number of bit errors is minimized (optimum). When a communication path is not established between the optical fiber transmission nodes at the optical path end points, a feedback signal cannot be transmitted, so that the chromatic dispersion amount to be set in the variable dispersion compensator cannot be notified. was there.

  The present invention has been made to solve the above-described problems. In an optical fiber transmission system to which a predistortion system is applied, a compensation dispersion value that needs to be set in a variable dispersion compensator on the transmission side is automatically set. It is an object of the present invention to obtain an optical fiber communication system that can be determined automatically.

  An optical fiber communication system according to the present invention is an optical fiber communication system comprising a first optical communication node and a second optical communication node connected to the first optical communication node via an optical fiber transmission line. The first and second optical communication nodes respectively include an input terminal and an output terminal connected to the client device, and a framer / deframer, precoder, compensation controller provided on the transmission side from the input terminal to the optical fiber transmission line And an optical transmitter, and an optical receiver and a framer / deframer provided on the receiving side from the optical fiber transmission line to the output terminal, the framer / deframer being connected to the input terminal and the output terminal, The output signal is framed / deframed, error correction and detection of the number of bit errors per unit time are performed. Performs convolution of the chromatic dispersion and inverse function of the optical path of the input signal through the deframer, the optical transmitter performs electrical / optical conversion and transmits the electrical signal through the precoder, and the optical receiver transmits the optical fiber. The optical signal received from the path is optically / electrically converted and input to the framer / deframer, and the compensation control unit optimizes and determines the compensation dispersion value set in the precoder. Set the compensation dispersion value that is changed at intervals, send the set compensation dispersion value in the main signal overhead, and on the receiving side, detect the number of bit errors per unit time and minimize the number of bit errors. The compensation dispersion value and the number of bit errors notified from the transmission side at this time are stored, and the optimum compensation dispersion value is notified to the transmission side using the main signal overhead in the reverse direction.

  According to the present invention, in the chromatic dispersion compensation system based on the predistortion method in the optical fiber communication system, it is not necessary to measure the chromatic dispersion amount of the optical path which is necessary for determining the compensation dispersion value set in the variable dispersion compensator. Thus, the optimum compensation dispersion value can be automatically determined without human intervention, and the optical path can be conducted.

It is a block diagram which shows the whole structure of the optical fiber communication system which concerns on Embodiment 1 of this invention. FIG. 2 is an explanatory diagram showing a main signal overhead of an optical signal transmitted and received between optical communication nodes in FIG. 1. 3 is a flowchart showing a processing procedure on the optical signal transmission side for determining a sub-optimal compensation dispersion value by each optical communication node in FIG. 1. 2 is a flowchart showing a processing procedure on the optical signal receiving side for determining a sub-optimal compensation dispersion value by each optical communication node in FIG. 1. FIG. 2 is an explanatory diagram illustrating a processing procedure for determining a sub-optimal compensation dispersion value to be set by each optical communication node in FIG. 1. It is a block diagram which shows a partial structure of the optical fiber communication system which concerns on Embodiment 2 of this invention.

Embodiment 1 FIG.
1 is a block diagram showing the overall configuration of an optical fiber communication system according to Embodiment 1 of the present invention.
In FIG. 1, an optical fiber communication system includes first and second optical communication nodes (hereinafter simply referred to as “optical communication nodes”) 10A and 10B and optical fiber transmission lines interconnecting the optical communication nodes 10A and 10B. 11 and 12.
Each of the optical communication node 10A and the optical communication node 10B is connected to a client device (IP router, L2 switch, etc.) not shown, and provides a bidirectional optical path to the client device.

  The optical communication node 10A includes an input terminal 1a, a framer / deframer 2a, a precoder 3a, an optical transmitter 4a, an optical receiver 5a, an output terminal 6a, and a compensation controller 7a. ing.

Similarly, the optical communication node 10B includes an input terminal 1b, a framer / deframer 2b, a precoder 3b, an optical transmitter 4b, an optical receiver 5b, an output terminal 6b, and a compensation control unit 7b. And.
In the optical communication node 10B, the same reference numerals as those in the optical communication node 10A with “b” denote functional blocks similar to those in the optical communication node 10A.

The input terminal 1a and the output terminal 6a of the optical communication node 10A are connected to the client apparatus. Similarly, the input terminal 1b and the output terminal 6b of the optical communication node 10B are connected to the client apparatus.
The optical transmitter 4a of the optical communication node 10A is connected to the optical receiver 5b of the optical communication node 10B via the optical fiber transmission line 11, and the optical transmitter 4b of the optical communication node 10B is connected to the optical fiber transmission line. 12 is connected to the optical receiver 5a of the optical communication node 10A.

In the optical communication node 10A, the input terminal 1a takes in an input signal from the client device, and the output terminal 6a sends out an output signal to the client device.
The framer / deframer 2a is connected to the input terminal 1a and the output terminal 6a. The input signal from the client apparatus and the output signal to the client apparatus are framed / deframed into an SDH (Synchronous Digital Hierarchy) signal and error correction is performed. And BER (number of bit errors per unit time) is detected.

The precoder 3a premodulates the input signal via the framer / deframer 2a, and the compensation controller 7a sets a compensation dispersion value for the precoder 3a.
The compensation control unit 7a has a memory (RAM) (not shown), manages the optimum compensation dispersion value of the variable dispersion amount, detects the optimum compensation dispersion value of the variable dispersion amount, and detects the main signal overhead. The sub-optimal compensation variance value inserted in the memory is associated with the detected BER observed by the own apparatus, and recording / update is performed in the memory.

The optical transmitter 4a performs electrical / optical conversion on the output signal of the precoder 3a, introduces it into the optical fiber transmission line 11, and transmits the optical signal to the optical communication node 10B. On the other hand, the optical receiver 5a optical / electrically converts an optical signal introduced from the optical communication node 10B via the optical fiber transmission line 12.
The output terminal 6a sends an electrical signal obtained by optical / electrical conversion as an output signal to the client device via the framer / deframer 2a.

  In the optical communication node 10A, a framer / deframer 2a, a precoder 3a, a compensation controller 7a, and an optical transmitter 4a are provided on the transmission side from the input terminal 1a to the optical fiber transmission line 11, and output from the optical fiber transmission line 12 On the receiving side up to the terminal 6a, an optical receiver 5a and a framer / deframer 2a are provided.

Similarly, in the optical communication node 10B, a framer / deframer 2b, a precoder 3b, a compensation controller 7b, and an optical transmitter 4b are provided on the transmission side from the input terminal 1b to the optical fiber transmission line 12, and the optical fiber transmission line On the receiving side from 11 to the output terminal 6b, an optical receiver 5b and a framer / deframer 2b are provided.
The optical communication nodes 10A and 10B operate in response to a path establishment command (described later) from the operator.

Next, a processing procedure performed by the optical communication node 10A and the optical communication node 10B for determining a sub-optimal compensation dispersion value for conducting an optical path will be described with reference to FIGS.
FIG. 2 is an explanatory diagram showing a main signal overhead of an optical signal transmitted and received by the optical communication nodes 10A and 10B.

For example, when the above-described SDH signal is applied, as shown in FIG. 2, each field 201 to 204 is additionally defined and used in an empty overhead area of a transmission frame.
In FIG. 2, a field 201 is for notifying the opposite device (optical communication node 10B) of the compensation dispersion value set in the precoder 3a of the own device (optical communication node 10A).

The field 202 is for notifying the opposite device (optical communication node 10B) of the current detection BER observed by the own device (optical communication node 10A).
The field 203 is for notifying the counter device (optical communication node 10B) of the sub-optimal compensation dispersion value recorded in the memory of the own device (optical communication node 10A).
The field 204 is a field for notifying the opposite device (optical communication node 10B) of the optimum BER recorded in the memory of the own device (optical communication node 10A).

FIGS. 3 and 4 are flowcharts showing a processing procedure for determining sub-optimal compensation dispersion values by the optical communication nodes 10A and 10B. FIG. 3 shows an optical signal transmission side for transmitting an optical signal to the opposite optical communication node. FIG. 4 shows a processing procedure, and FIG. 4 shows a processing procedure on the optical signal receiving side that receives an optical signal from the opposite optical communication node.
Since the optical communication nodes 10A and 10B have the same configuration and operation, only the optical communication node 10A will be described here.

First, the optical signal transmission process shown in FIG. 3 will be described.
The operator inputs a path establishment command serving as a trigger for the bidirectional optical path establishment operation to each of the optical communication nodes 10A and 10B, and the optical communication nodes 10A and 10B operate in response thereto.
The optical communication node 10A when a command that triggers the establishment of an optical path is executed performs the following processing at a constant time interval Ta.

  In FIG. 3, the compensation controller 7a checks whether or not the sub-optimal compensation variance value is recorded in the memory (RAM) (step 301), and the sub-optimal compensation variance value is recorded in the memory (step 301). In other words, if it is determined Yes), the recorded sub-optimal compensation variance value is set in the precoder 3a (step 302).

  On the other hand, if it is determined in step 301 that the sub-optimal compensation dispersion value is not recorded in the memory (that is, No), the compensation dispersion value determined as the default is set immediately after the command is input. . If the processing is periodic after the command is input, the compensation dispersion value to be set is set by changing the compensation dispersion amount from the designated maximum value to the minimum value (step 303).

  Finally, the compensation controller 7a observes the BER measured by the framer / deframer 2a, the detected BER, the compensation dispersion value set in the precoder 3a, and the optimum BER recorded in the memory. The sub-optimal compensation dispersion value is supplied to the framer / deframer 2a and inserted into the main signal overhead (see FIG. 2) (step 304).

That is, when the framer / deframer 2a frames the input signal from the client device, the compensation dispersion value, the detection BER, the sub-optimal compensation dispersion value and the optimum BER given from the compensation controller 7a are shown in FIG. Each is inserted into the main signal overhead shown (step 304).
Thereafter, returning to step 301, steps 301 to 304 are repeatedly executed at a constant time interval Ta.

As described above, the input signal from the client device input from the input terminal 1a is framed and error-corrected by the framer / deframer 2a and then input to the precoder 3a.
The precoder 3a performs convolution with the compensation dispersion value (the chromatic dispersion amount of the optical path) set by the compensation controller 7a and the inverse function, and the optical transmitter 4a performs electrical / optical conversion, and the optical fiber transmission line 11 Send an optical signal up.

  Also in the optical communication node 10B, the optical signal transmission processing similar to that in FIG. 3 is performed by the compensation control unit 7b, the framer / deframer 2b, the precoder 3b, and the optical transmitter 4b.

Next, the optical signal reception process shown in FIG. 4 will be described.
In the optical communication node 10A, when a path establishment command serving as a trigger for establishing an optical path is input, first, the optical signal propagated through the optical fiber transmission line 12 by the optical receiver 5a is converted into an electrical signal. Subsequently, the framer / deframer 2a corrects the bit error and deframes it, and then outputs it from the output terminal 6a to the client device.

  In FIG. 4, in order to obtain a sub-optimal compensation variance value, the compensation controller 7a first checks whether or not frame synchronization is established (step 401), and if frame synchronization cannot be established (ie, No). If determined, the process returns to step 401 without executing any processing.

  This is because in the opposite device (optical communication node 10B), when the compensation dispersion value set in the precoder 3b is greatly deviated from the optimum compensation dispersion value, the received signal is distorted and the frame synchronization is not achieved. This is because it is impossible to refer to the value written in the box and to observe the BER.

On the other hand, when it is determined in step 401 that frame synchronization can be achieved (that is, Yes), the compensation control unit 7a observes the BER and the value of the compensation variance value inserted in the received main signal overhead. Is read (step 402).
In this case, in the opposite device (optical communication node 10B), the compensation dispersion value set in the precoder 3b is a quasi-optimal compensation dispersion value close to the optimum compensation dispersion value, so that frame synchronization can be achieved and within the main signal overhead. It is possible to refer to recorded values and observe BER.

  Next, it is checked whether or not the detected detected BER is smaller than the optimum BER recorded in the memory (step 403), and if it is determined that the optimum BER in the memory ≦ the detected BER (ie, No). Return to step 401.

  On the other hand, if it is determined in step 403 that the optimum BER in the memory> the detected BER (that is, Yes), the compensation control unit 7a updates the optimum BER recorded in the memory to the detected BER and records it in the memory. The sub-optimal compensation dispersion value that has been set is updated to the compensation dispersion value (set compensation dispersion value) inserted in the reception main signal overhead (step 404), and the process returns to step 401 to repeat the above processing procedure. .

  Also in the optical communication node 10B, the optical signal transmission processing similar to that in FIG. 4 is performed by the optical receiver 5b, the compensation controller 7b, and the framer / deframer 2b.

FIG. 5 is an explanatory diagram showing a processing procedure for determining a sub-optimal compensation dispersion value to be set by the optical communication nodes 10A and 10B.
In FIG. 5, as a precondition, since the optical signal in the direction from the optical communication node 10A to the optical communication node 10B is conducted, the sub-optimal compensation dispersion value to be set in the precoder 3a of the optical communication node 10A is “A3”. "

Further, since the optical signal in the direction from the optical communication node 10B to the optical communication node 10A is conducted, the sub-optimal compensation dispersion value to be set in the precoder 3b of the optical communication node 10B is “B5”.
FIG. 5 shows a processing procedure for determining a sub-optimal compensation dispersion value to be set under the above preconditions.

In FIG. 5, the left side describes the optical signal direction from the optical communication node 10A to the optical communication node 10B, and the right side conversely describes the optical signal direction from the optical communication node 10B to the optical communication node 10A. ing.
Moreover, the arrow attached | subjected between each optical communication node 10A, 10B has shown the content inserted in the direction of a main signal, and a main signal overhead.

First, when a path establishment command is input, as shown on the right side in FIG. 5, the transmission side of the optical communication node 10B sets a default compensation dispersion value “B0” in the precoder 3b using the path establishment command as a trigger. The optical signal is sent to the optical communication node 10A via the optical transmitter 4b and the optical fiber transmission line 12.
At this time, the compensation dispersion value “B0” set in the precoder 3b of the own apparatus is inserted into the main signal overhead (field 201 in FIG. 2).

On the other hand, at this time, as shown on the left side in FIG. 5, on the receiving side of the optical communication node 10B, the compensation dispersion value “A0” set in the precoder 3a by the optical communication node 10A is obtained from the sub-optimal compensation dispersion value. Since the received waveform is so distorted that the frame synchronization cannot be performed, it is impossible to detect the BER (number of error frames) or the set compensation dispersion value in the reception overhead.
Therefore, in the fields 203 and 202 in the main signal overhead, invalid values “−−” and “∞ = undetectable” are set as sub-optimal compensation dispersion values and detection BER values.

Thereafter, every time the predetermined time interval Tb elapses, the optical communication node 10B sets values to be set in the precoder 3b of its own device to “B1”, “B2”, “B3”,. The compensation dispersion value set in the precoder 3b is inserted into the main signal overhead (field 201).
In the reception-side process, the compensation dispersion value in the BER and the reception main signal overhead is detected based on the reception signal from the optical communication node 10A.

  Also in the optical communication node 10A, as shown on the left side in FIG. 5, using the path establishment command as a trigger, processing equivalent to that of the optical communication node 10B described above is executed at a constant time interval Ta, and the precoder 3a of its own device Are changed to “A1”, “A2”, “A3”,...

  On the left side in FIG. 5, when a period “2 × Ta” has elapsed since the path establishment command was input to the optical communication node 10A, the optical communication node 10A sets the compensation dispersion value “A2” in the precoder 3a. “A2” is inserted into the set compensation dispersion value of the signal overhead (field 201).

  At this time, since the set compensation dispersion value “A2” is a sub-optimal compensation dispersion value, frame synchronization can be established in the optical communication node 10B (reception side), so that detection of BER and setting within the reception main signal overhead are performed. Detection of the compensation dispersion value (step 402 in FIG. 4) is possible.

Therefore, the compensation controller 7b of the optical communication node 10B records the minimum BER (optimum BER) as “E1”, and records the sub-optimal compensation dispersion value at that time as “A2”.
In addition, when changing the set compensation dispersion value of the own device (after the period “3 × Tb” has elapsed since the command was input), the optimum BER “E1” and the sub-optimal are used for the main signal overhead to be transmitted (fields 204 and 203) The compensation dispersion value “A2” is inserted.

  Subsequently, when a period “3 × Ta” elapses after the path establishment command is input to the optical communication node 10A, the optical communication node 10A sets the compensation dispersion value set in the precoder 3a to “A3”, and the main signal overhead ( “A3” is inserted into the set compensation dispersion value in the field 201).

  At this time, since the set compensation dispersion value “A3” is a sub-optimal compensation dispersion value, frame synchronization can be established in the optical communication node 10B, so that the BER of the BER is the same as when the period “2 × Ta” has elapsed. Detection and detection of the set compensation variance value within the received main signal overhead is possible.

  At the elapse of the period “3 × Ta”, the detected BER is “E2”, the set compensation dispersion value in the main signal overhead is “A3”, and the optimum BER “E1” recorded by the compensation control unit 7b, The comparison result of “E2” is “E1> E2”.

  Therefore, the compensation control unit 7b of the optical communication node 10B updates the recorded optimum BER and the sub-optimal compensation dispersion value at this time to “E2” and “A3”, respectively. Also, the main signal overhead (field) to be transmitted when the updated values “E2” and “A3” are changed next (after the period “4 × Tb” has elapsed since the command was input) is changed. 204, 203).

  Subsequently, when a period “4 × Ta” elapses after the path establishment command is input to the optical communication node 10A, the optical communication node 10A changes the compensation dispersion value set in the precoder 3a from “A3” to “A4”. Then, “A4” is inserted into the set compensation dispersion value of the main signal overhead.

  At this time, since the set compensation dispersion value “A4” deviates from the sub-optimal compensation dispersion value, in the optical communication node 10B, the received waveform is distorted to the extent that frame synchronization cannot be achieved. Further, it becomes impossible to detect the set compensation dispersion value in the reception main signal overhead.

  Therefore, the optical communication node 10B does not update the optimum BER “E2” and the sub-optimal compensation dispersion value “A3” recorded in the compensation control unit 7b, and next sets the set compensation dispersion value of the own device. The sub-optimal compensation variance value and the optimum BER value to be inserted into the main signal overhead to be transmitted at the time of changing (after the period “5 × Tb” has elapsed from the command input) are not changed.

  On the other hand, on the right side in FIG. 5, when the period “5 × Tb” has elapsed since the path establishment command was input to the optical communication node 10B, the optical communication node 10B sets the compensation dispersion value to be set in the precoder 3b to “B5”. And “B5” is inserted into the set compensation dispersion value in the main signal overhead (field 201).

  At this time, since the set compensation dispersion value “B5” in the optical communication node 10B is a sub-optimal compensation dispersion value, frame synchronization can be established in the optical communication node 10A (reception side). It is possible to detect the set compensation dispersion value in the main signal overhead.

When the period “5 × Tb” elapses, the detection BER is “E1”, the set compensation dispersion value in the main signal overhead is “B5”, and the detection BER is changed from “∞ = undetectable” to “E1”. Since it is changed, the compensation control unit 7b of the optical communication node 10B updates the pair value of the recorded optimum BER and the sub-optimal compensation variance value at the optimum BER to “E1” and “B5”.
Further, it detects that the sub-optimal compensation variance value in the main signal overhead is “A3”, and records the sub-optimal compensation variance value to be set in the precoder 3b of the own apparatus.

On the left side in FIG. 5, the optical communication node 10A next changes the setting compensation dispersion value of its own device (after the elapse of the period “5 × Ta” from the input of the command), the sub-optimal learned by the precoder 3a. The compensation dispersion value “A3” is set and inserted into the set compensation dispersion value in the main signal overhead (field 201).
Further, the optimum BER “E1” recorded in the compensation controller 7a and the sub-optimal compensation variance value “B5” at that time are set in the main signal overhead (fields 204 and 203), respectively. .

  At this time, since the setting compensation dispersion value “A3” is a sub-optimal compensation dispersion value, frame synchronization can be established in the optical communication node 10B. Therefore, detection of the BER and setting compensation dispersion value in the reception main signal overhead Detection is possible.

When the period “5 × Ta” elapses, the detection BER is “E2”, the set compensation dispersion value in the main signal overhead is “A3”, and the compensation control unit 7b of the optical communication node 10B records. Since there is no change in the comparison result between the optimum BER “E2” and the detected BER “E2”, no update is performed.
Further, the optical communication node 10B detects that the sub-optimal compensation dispersion value in the main signal overhead is “B5”, and records the sub-optimal compensation dispersion value to be set in the precoder 3b of the own apparatus.

In this final stage, the optical communication node 10A learns that the suboptimal compensation dispersion value is “A3”, and the optical communication node 10B learns that the suboptimal compensation dispersion value is “B5”. .
As a result, the main signal becomes conductive in both directions from the optical communication node 10A to the optical communication node 10B and from the optical communication node 10B to the optical communication node 10A.

  In this way, the detection BER can be fed back in real time, and the optical communication nodes 10A and 10B can set the set compensation dispersion value to a sub-optimal compensation dispersion value so that the fed back BER is minimized (optimum). Is searched in a narrow range in the vicinity of, and the optimum compensation dispersion value is determined.

  As described above, the optical fiber communication system according to Embodiment 1 (FIGS. 1 to 5) of the present invention is connected to the optical communication node 10A via the optical communication node 10A and the optical fiber transmission lines 11 and 12. The optical communication nodes 10A and 10B each include input terminals 1a and 1b and output terminals 6a and 6b connected to the client device.

  The optical communication node 10A (10B) includes a framer / deframer 2a (2b), a precoder 3a (3b), compensation control provided on the transmission side from the input terminal 1a (1b) to the optical fiber transmission line 11 (12). Unit 7a (7b) and optical transmitter 4a (4b), optical receiver 5a (5b) and framer / deframer 2a provided on the receiving side from optical fiber transmission line 12 (11) to output terminal 6a (6b) (2b).

  The framer / deframer 2a (2b) is connected to the input terminal 1a (1b) and the output terminal 6a (6b) to frame / deframe the input / output signal, and to perform error correction and the number of bit errors BER per unit time. The precoder 3a (3b) performs convolution of the chromatic dispersion amount and inverse function of the optical path of the input signal via the framer / deframer 2a (2b).

The optical transmitter 4a (4b) performs electrical / optical conversion of the electrical signal that has passed through the precoder 3a (3b) and transmits it.
The optical receiver 5a (5b) optically / electrically converts the optical signal received from the optical fiber transmission line 12 (11) and inputs it to the framer / deframer 2a (2b).

  In order to optimize and determine the compensation dispersion value set in the precoder 3a (3b), the compensation controller 7a (7b) sets a compensation dispersion value that is changed at a constant time interval Ta (Tb) on the transmission side. Set and transmit the set compensation dispersion value including the main signal overhead, and the receiving side detects the number of bit errors BER per unit time and notifies the transmitting side when the number of bit errors is minimized. The compensated dispersion value and the number of bit errors are stored, and the optimum compensation dispersion value is notified to the transmission side using the main signal overhead in the reverse direction.

  That is, in the optical path to which predistortion type chromatic dispersion compensation is applied, the transmission side includes the compensation dispersion value every moment in the main signal overhead while changing the compensation dispersion value at a constant time interval Ta (Tb). At the receiving side, the BER is measured and the compensation dispersion value when the number of errors is minimized is stored, and notified to the transmitting side using the overhead of the main signal in the reverse direction.

As a result, the optimal compensation dispersion value within the changed range can be notified to the transmission side, and there is no need to measure the dispersion amount of the path using a measuring instrument. Settings can be made automatically.
Further, even when the bidirectional conduction is not established, the compensation dispersion value can be automatically set.

  Therefore, according to the first embodiment of the present invention, in the chromatic dispersion compensation system using the predistortion method in the optical fiber communication system, the optical path required for determining the compensation dispersion value set in the variable dispersion compensator is determined. Measurement of the amount of chromatic dispersion is not required, and the optimum compensation dispersion value can be automatically determined without human intervention, and the optical path can be conducted.

Embodiment 2. FIG.
In the first embodiment, multiplex transmission with a plurality of wavelengths is not mentioned. However, as shown in FIG. 6, it may be applied to an optical fiber communication system that performs multiplex transmission with a plurality of wavelengths.
FIG. 6 is a block diagram showing an optical fiber communication system according to Embodiment 2 of the present invention. A plurality of optical transceivers (transponders) are mounted in optical communication nodes 60A and 60B, and a plurality of wavelengths are multiplexed and transmitted. A possible configuration example is shown.

  In FIG. 6, only the configuration for conducting the optical path from the optical communication node 60A to the optical communication node 60B is representatively shown to avoid complexity, but the optical communication node 60B to the optical communication node are representatively shown. Needless to say, a symmetrical configuration (not shown) for conducting the optical path to 60A is provided in parallel.

That is, the optical communication node 60A has the same configuration (left-right reversal) as the optical communication node 60B in parallel, and has an output terminal 66a (not shown) connected to the client device.
Similarly, the optical communication node 60B has the same configuration (horizontal inversion) as the optical communication node 60A in parallel, and has an input terminal 61b (not shown) connected to the client device.

  In FIG. 6, the optical communication node 60A includes an input terminal 61a connected to the client device, a MUX (multiplexer) unit 62a connected to the optical fiber transmission line 68, and a first connected to the input side of the MUX unit 62a. Optical switch (hereinafter simply referred to as “optical switch”) 63a, first 10G transponder (hereinafter simply referred to as “10G transponder”) 64a, and first 40G transponder (hereinafter simply referred to as “40G transponder”) 65a. And a first compensation controller (hereinafter simply referred to as “compensation controller”) 67a.

  Similarly, the optical communication node 60B includes an output terminal 66b connected to the client device, a DEMUX (demultiplexer) unit 62b connected to the optical fiber transmission line 68, and a second connected to the output side of the DEMUX unit 62b. Optical switch (hereinafter simply referred to as “optical switch”) 63b, second 10G transponder (hereinafter simply referred to as “10G transponder”) 64b, and second 40G transponder (hereinafter simply referred to as “40G transponder”) 65b. And a second compensation controller (hereinafter simply referred to as “compensation controller”) 67b.

  The 40G transponders 65a and 65b indicate optical signal transmission / reception boards having a transmission speed of 40G [bit / sec] (high-speed transmission rate), and the 10G transponders 64a and 64b have a transmission speed of 10G [bit / sec] (low-speed transmission rate). The optical signal transmission / reception board | substrate of FIG.

Each transponder collectively includes the framer / deframer 2a (2b), the precoder 3a (3b), the optical transmitter 4a (4b), and the optical receiver 5a (5b) described above (FIG. 1).
The 10G transponder 64a (64b) determines an optimum compensation dispersion value to be set in a precoder (not shown) in each transponder when establishing an optical path using a plurality of 40G transponders 65a (65b). It can be shared and used.

The MUX unit 62a in the optical communication node 60A wavelength-multiplexes the optical signal of the wavelength λx (x = 1, 2,..., N) and is adjacently connected via the optical fiber transmission line 68. To send.
On the other hand, the DEMUX unit 62b in the optical communication node 60B separates the received optical signal (wavelength multiplexed signal) via the optical fiber transmission line 68.

The optical switch 63a in the optical communication node 60A selects an optical signal transmitted from each of the transponders 64a and 65a and inputs it to the MUX unit 62a.
On the other hand, the optical switch 63b in the optical communication node 60B selects which of the transponders 64b and 65b is to transmit the optical signal separated by the DEMUX unit 62b.

In each of the optical communication nodes 60A and 60B, the compensation controllers 67a and 67b set compensation dispersion values in the precoders installed in the respective transponders in the device, and manage the optimum compensation dispersion values.
That is, the compensation control units 67a and 67b determine the optimum compensation dispersion value by executing the same processing procedure as described above (FIG. 5).

Next, a processing procedure for determining a sub-optimal compensation dispersion value according to the second embodiment of the present invention shown in FIG. 6 will be described.
Here, a processing procedure for opening a bidirectional optical path of wavelength λx using the 40G transponders 65a and 65b by the optical communication nodes 60A and 60B will be described. As a precondition, both 40G transponders 65a and 65b and 10G transponders 64a and 64b are unused.

  First, the operator inputs a path establishment command that triggers a bidirectional optical path establishment operation to each of the optical communication nodes 60A and 60B. At this time, a transponder and a wavelength (in this case, 40G transponder, wavelength λx) are designated as command parameters.

The optical communication nodes 60A and 60B that have received the command check whether there is an unused transponder (for example, 10G transponders 64a and 64b) that is slower than the 40G transponders 65a and 65b. Is present, an optimum compensation dispersion value for conducting the optical path of wavelength λx between the optical communication node 60A and the optical communication node 60B is derived using the low-speed transponder.
In FIG. 6, as indicated by solid arrows, an optical path of wavelength λx using unused 10G transponders 64a and 64b is established, and an optimum compensation dispersion value is determined.

  The optical communication node 60A to which the path establishment command is input controls the optical switch 63a and performs port switching so that the optical signal transmitted from the 10G transponder 64a is transmitted to the λx port of the MUX unit 62a.

  Similarly, the optical communication node 60B to which the path establishment command is input controls the optical switch 63b, and the optical signal of the wavelength λx separated by the DEMUX unit 62b is transmitted to the 10G transponder 64b. Switch (see solid arrow).

Thereafter, the optical communication nodes 60A and 60B execute the same processing procedure as described above (FIG. 5), and determine sub-optimal compensation dispersion values to be set in the precoders in the 10G transponders 64a and 64b.
Further, after the optical path is turned on, the optimum compensation dispersion value is determined by feeding back the detection BER to the adjacent optical communication node connected adjacently in real time.

  After determining the optimum compensation dispersion value, the optical communication node 60A switches the optical switch 63a and the 10G transponder 64a sends out the optical signal introduced to the λx port of the MUX unit 62a as indicated by the dashed arrow. The optical signal is switched to the optical signal transmitted by the 40G transponder 65a.

  Similarly, the optical communication node 60B switches the optical switch 63b to switch the transmission target of the optical signal from the λx port of the DEMUX unit 62b from the 10G transponder 64b to the 40G transponder 65b (see the broken line arrow).

  Thus, after the switching of the optical switches 63a and 63b is completed, each of the optical communication nodes 60A and 60B sets the wavelength set in the 40G transponders 65a and 65b to λx, and the optimum compensation dispersion value for the precoder in each transponder To open the optical path.

Even when the optical path from the optical communication node 60B to the optical communication node 60B is made conductive, the same processing procedure as described above is performed.
In the above description, the 40G transponders 65a and 65b are used as the high-speed transponders and the 10G transponders 64a and 64b are used as the low-speed transponders. A transponder can be used.

  As described above, the optical fiber communication system according to Embodiment 2 (FIG. 6) of the present invention includes the optical communication node 60A and the optical communication node 60B connected to the optical communication node 60A via the optical fiber transmission line 68. Each of the optical communication nodes 60A and 60B includes input terminals 61a and 61b and output terminals 66a and 66b connected to the client device.

  The optical communication node 60A includes a 40G transponder (high-speed transponder) 65a, a 10G transponder (low-speed transponder) 64a, a compensation control unit 67a, an optical switch 63a, and a MUX unit provided on the transmission side from the input terminal 61a to the optical fiber transmission line 68. 62a is provided.

The optical communication node 60B includes a DEMUX unit 62b, an optical switch 63b, a compensation control unit 67b, a 40G transponder (high-speed transponder) 65b, and a 10G transponder (low-speed) provided on the receiving side from the optical fiber transmission line 68 to the output terminal 66b. Transponder) 64b.
The 40G transponders 65a and 65b and the 10G transponders 64a and 64b include a framer / deframer, a precoder, and an optical transceiver, respectively.

When the path establishment command is input, the optical communication nodes 60A and 60B control the optical switches 63a and 63b to interconnect the 10G transponder 64a and the 10G transponder 64b via the MUX unit 62a and the DEMUX unit 62b.
At the same time, the second low-speed transponder in the optical communication node 60A and the first low-speed transponder in the optical communication node 60B are interconnected via the MUX unit and the DEMUX unit (both not shown).

  The framer / deframer in each transponder is connected to the input terminal and the output terminal in the same manner as in the first embodiment, and the input / output signal is framed / deframed to perform error correction and bit error per unit time. The number is detected, and the precoder in each transponder performs convolution of the chromatic dispersion amount and the inverse function of the optical path of the input signal from the client device via the framer / deframer.

  The compensation controllers 67a and 67b are compensations set in the precoder between the 10G transponder 64a and the 10G transponder 64b, and between the low-speed transponder in the optical communication node 60A and the low-speed transponder in the optical communication node 60B. In order to optimize and determine the dispersion value, as in the first embodiment, the transmission side sets a compensation dispersion value that is changed at regular time intervals, and sets the set compensation dispersion value as the main signal overhead. Include and send.

  Similarly to the first embodiment, the compensation controllers 67a and 67b detect the number of bit errors per unit time on the reception side, and from the transmission side when the number of bit errors is minimized. The notified compensation dispersion value and the number of bit errors are stored, and the optimum compensation dispersion value is notified to the transmission side using the main signal overhead in the reverse direction.

  The optical communication nodes 60A and 60B control the optical switches 63a and 63b to determine the 40G transponder 65a and the 40G transponder 65b, the MUX unit 62a, and the DEMUX unit after determining the optimum compensation dispersion value in the interconnection state of the low-speed transponders. Interconnected via 62b.

At the same time, the second high-speed transponder in the optical communication node 60A and the first high-speed transponder in the optical communication node 60B are interconnected via the MUX unit and the DEMUX unit (both not shown).
Finally, the compensation controllers 67a and 67b set the optimum compensation dispersion value after determination in the precoder.

  At this time, when the path establishment command is input, the 10G [bit / sec] 10G transponder with the first low transmission rate is compared with the 40G [bit / sec] 40G transponder with the higher transmission rate. Since the range of the optimum compensation dispersion value is wide, when the processing procedure for determining the optimum compensation dispersion value is used while changing the compensation dispersion value at the constant time interval Ta (Tb) described above (FIG. 5), the optimum compensation dispersion value is used. The time for determining the compensation dispersion value can be shortened.

  Further, when an optical path is established with a 40 Gbit / s 40 G transponder with a high transmission rate, an optimum compensation dispersion value is determined using an unused low speed 10 G transponder, and then the learned optimum compensation dispersion value is obtained. Is set as a high-speed 40G transponder used for the original optical path, it is possible to shorten the time until the optical path is established.

  1a, 1b input terminal, 2a, 2b framer / deframer, 3a, 3b precoder, 4a, 4b optical transmitter, 5a, 5b optical receiver, 6a, 6b output terminal, 7a, 7b compensation controller, 10A, 10B optical communication Node 11, 11 Optical fiber transmission line, 60A, 60B Optical communication node, 61b, 61a Input terminal, 62a MUX part, 62b DEMUX part, 63a, 63b Optical switch, 64a, 64b 10G transponder (low speed transponder), 65a, 65b 40G transponder (high-speed transponder), 66a, 66b Output terminal, 67a, 67b Compensation control unit, 68 Optical fiber transmission line, Ta, Tb Fixed time intervals.

Claims (2)

In an optical fiber communication system comprising a first optical communication node and a second optical communication node connected to the first optical communication node via an optical fiber transmission line,
The first and second optical communication nodes are respectively
An input terminal and an output terminal connected to the client device;
A framer / deframer, a precoder, a compensation controller and an optical transmitter provided on the transmission side from the input terminal to the optical fiber transmission line;
An optical receiver provided on the receiving side from the optical fiber transmission line to the output terminal and the framer and deframer,
The framer / deframer is connected to the input terminal and the output terminal to frame / deframe the input / output signal, perform error correction and detect the number of bit errors per unit time,
The precoder performs convolution of the chromatic dispersion amount and inverse function of the optical path of the input signal through the framer / deframer,
The optical transmitter transmits the electrical signal via the precoder by electrical / optical conversion,
The optical receiver optically / electrically converts an optical signal received from the optical fiber transmission line and inputs the optical signal to the framer / deframer,
The compensation control unit optimizes and determines a compensation dispersion value set in the precoder.
On the transmission side, a compensation dispersion value that is changed at regular time intervals is set, the set compensation dispersion value is included in the main signal overhead, and transmitted.
On the receiving side, the number of bit errors per unit time is detected, and the compensation variance value and the number of bit errors notified from the transmitting side when the number of bit errors is minimized are stored in the reverse direction. An optical fiber communication system characterized in that an optimal compensation dispersion value is notified to the transmission side using the main signal overhead. In an optical fiber communication system comprising a first optical communication node and a second optical communication node connected to the first optical communication node via an optical fiber transmission line,
The first and second optical communication nodes are respectively
An input terminal and an output terminal connected to the client device;
A first high-speed transponder, a first low-speed transponder, a first compensation control unit, a first optical switch and a multiplexer unit provided on the transmission side from the input terminal to the optical fiber transmission line;
A demultiplexer unit provided on the receiving side from the optical fiber transmission line to the output terminal, a second optical switch, a second compensation control unit, a second high-speed transponder and a second low-speed transponder,
The first and second high-speed transponders, the first and second low-speed transponders each include a framer / deframer, a precoder and an optical transceiver,
The first and second optical communication nodes are:
When the path establishment command is input, the first and second optical switches are controlled,
Interconnecting the first low-speed transponder in the first optical communication node and the second low-speed transponder in the second optical communication node via the multiplexer unit and the demultiplexer unit;
Interconnecting a second low-speed transponder in the first optical communication node and a first low-speed transponder in the second optical communication node via the multiplexer unit and the demultiplexer unit;
The framer / deframer is connected to the input terminal and the output terminal to frame / deframe the input / output signal, perform error correction and detect the number of bit errors per unit time,
The precoder performs convolution of the chromatic dispersion amount and inverse function of the optical path of the input signal from the client device via the framer / deframer,
The first and second compensation controllers are
Between a first low-speed transponder in the first optical communication node and a second low-speed transponder in the second optical communication node, and a second low-speed transponder in the first optical communication node; In order to optimize and determine the compensation dispersion value set in the precoder with the first low-speed transponder in the second optical communication node,
On the transmission side, a compensation dispersion value that is changed at regular time intervals is set, the set compensation dispersion value is included in the main signal overhead, and transmitted.
On the receiving side, the number of bit errors per unit time is detected, and the compensation variance value and the number of bit errors notified from the transmitting side when the number of bit errors is minimized are stored in the reverse direction. To notify the transmitting side of the optimal compensation dispersion value using the main signal overhead of
The first and second optical communication nodes are:
After determining the optimal compensation dispersion value, controlling the first and second optical switches,
Interconnecting the first high-speed transponder in the first optical communication node and the second high-speed transponder in the second optical communication node via the multiplexer unit and the demultiplexer unit;
Interconnecting the second high-speed transponder in the first optical communication node and the first high-speed transponder in the second optical communication node via the multiplexer unit and the demultiplexer unit;
The first and second compensation control units set the optimum compensation dispersion value after determination in the precoder.

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