JP2010034830A - Pre-equalized optical fiber communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a pre-equalized optical fiber communication system capable of compensating the dispersion of an optical transmission line precisely at a high speed. <P>SOLUTION: An optical communication node A on the transmission side includes: a precoder (variable dispersion compensation means) 4a for supplying a dispersion amount (dispersion compensation setting value) beforehand to input signals to be input to an input terminal 2a; an optimization means 21a for adjusting the dispersion amount; and an electric/optical converter (E/O) 5a for converting electric signals generated by supplying the dispersion amount to the input signals to optical signals to output them to the optical fiber transmission line 11. An optical communication node B on the reception side includes, an error correction circuit (FEC) 3 for detecting the number of bit errors of the optical signals propagated through the optical fiber transmission line 11; and a monitoring optical interface (OSC) 10 for returning the detected number of bit errors through the optical fiber transmission line 12 to the optimization means 21a of the optical communication node A on the transmission side. The optimization means of the optical communication node A on the transmission side adjusts the dispersion amount and controls it to an optimum value on the basis of the monitoring optical interface (OSC). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pre-equalized optical fiber communication system, and more particularly to a pre-equalized optical fiber communication system that compensates for dispersion of an optical fiber transmission line at high speed and precisely in an all-optical network and facilitates provisioning, protection, and restoration. It is about.

  In general, in an optical fiber communication system, it is necessary to compensate for signal waveform distortion due to chromatic dispersion in an optical fiber transmission line. As a dispersion compensation method, a method using a dispersion compensation fiber having dispersion opposite to that of an optical fiber transmission line is widely used. In recent high-speed optical fiber communication systems of 40 Gb / s or more, the waveform is easily distorted by a slight change in the dispersion amount due to temperature, fiber insertion, or the like. Introduction of variable dispersion compensators has begun. In particular, in an all-optical network in which an optical path (or Label Switch Path: LSP) is dynamically changed, the dispersion amount differs for each optical path, so a variable dispersion compensator is required.

  As a new tunable dispersion compensator, there is a predistortion method (see, for example, Non-Patent Document 1). A transfer function opposite to that of an optical fiber is realized as a convolution on the time axis, and an input data series is electrically calculated. An optical waveform having a complex electric field that compensates for group delay due to dispersion after optical fiber transmission is generated by performing quadrature modulation of light with a premodulation signal sequentially calculated by an FIR filter configured with a look-up table. Is.

  In the predistortion method, the value of the lookup table is set on the transmission side based on the dispersion of the transmission line that has been measured in advance, but as another conventional method, dispersion measurement at the measurement wavelength is performed. There is known a method of adaptively equalizing an optimum dispersion compensation amount in a short time even if a certain amount of error occurs (see, for example, Patent Document 1). Bit error number information is fed back to the transmitting end so that the number of bit errors observed at the receiving end is minimized, and the dispersion compensation amount at the transmitting end is increased / decreased based on this feedback control to adaptively control the optimum value.

M. M. El Said, J. Sitch and M. I. Elmasry, “An Electrically Pre-Equalized 10-Gb / s Duobinary Transmission System”, IEEE Journal of Lightwave Technology, Vol. 23, No. 1, pp. 388-400, Jan. 2005 JP 2007-259281 A

  In the method disclosed in Non-Patent Document 1, the value of the look-up table must be set on the transmission side based on the dispersion of the transmission line measured in advance, and the dispersion of the optical fiber transmission line Even when an error occurs in the measurement, there is a problem that it cannot be compensated for at high speed and accurately.

  Further, if the method disclosed in Patent Document 1 is used, dispersion of the optical fiber transmission line can be compensated at high speed and with precision, but the number of bit errors observed at the receiving end is placed on the overhead of the main signal. Therefore, dispersion compensation from the receiving end to the transmitting end must be completed, and the main signal needs to be conducted. That is, there is a problem in that the bit error number information cannot be transferred to the transmitting end when the main signal is not yet conducted as in construction.

  The present invention has been made to solve such a problem. Even when the main signal is not conducted as in construction, the dispersion compensation control information is accurately transferred from the receiving end to the transmitting end, and an optical fiber is provided. An object of the present invention is to obtain a pre-equalized optical fiber communication system capable of compensating for transmission path dispersion at high speed and with precision.

  The present invention relates to a pre-equalization optical fiber communication system including a plurality of optical communication nodes connected to each other via an optical fiber transmission line, and the transmission-side optical communication node itself is an optical communication on the reception side. Optimization means for controlling the amount of dispersion to be given to the input signal based on the received bit error number of the optical signal transmitted to the node from the receiving optical communication node; and A variable dispersion compensator for generating an electric signal which is input and given a predetermined dispersion amount for the first time and a dispersion amount from the optimizing device for the input signal thereafter, and the electric signal from the variable dispersion compensation unit. Electrical / optical conversion means for converting a signal into an optical signal and transmitting the optical signal to the reception-side optical communication node via the optical fiber transmission line, and the reception-side optical communication node includes the transmission-side optical communication node. From communication node An optical / electrical converter for receiving the optical signal and converting it into an electrical signal; an error correcting unit for detecting the number of bit errors in the optical signal based on the electrical signal from the optical / electrical converter; and a detection A reception-side supervisory optical interface that transmits the number of bit errors transmitted to the transmission-side optical communication node via the optical fiber transmission line, and the error correction means of the reception-side optical communication node The detected number of bit errors is transmitted to the optimization means of the transmission side optical communication node, and the optimization means determines the number of bit errors in the reception side optical communication node based on the received number of bit errors. In the pre-equalized optical fiber communication system, the dispersion amount is adjusted to an optimum value so as to be minimized.

  The present invention relates to a pre-equalization optical fiber communication system including a plurality of optical communication nodes connected to each other via an optical fiber transmission line, and the transmission-side optical communication node itself is an optical communication on the reception side. Optimization means for controlling the amount of dispersion to be given to the input signal based on the received bit error number of the optical signal transmitted to the node from the receiving optical communication node; and A variable dispersion compensator for generating an electric signal which is input and given a predetermined dispersion amount for the first time and a dispersion amount from the optimizing device for the input signal thereafter, and the electric signal from the variable dispersion compensation unit. Electrical / optical conversion means for converting a signal into an optical signal and transmitting the optical signal to the reception-side optical communication node via the optical fiber transmission line, and the reception-side optical communication node includes the transmission-side optical communication node. From communication node An optical / electrical converter for receiving the optical signal and converting it into an electrical signal; an error correcting unit for detecting the number of bit errors in the optical signal based on the electrical signal from the optical / electrical converter; and a detection A reception-side supervisory optical interface that transmits the number of bit errors transmitted to the transmission-side optical communication node via the optical fiber transmission line, and the error correction means of the reception-side optical communication node The detected number of bit errors is transmitted to the optimization means of the transmission side optical communication node, and the optimization means determines the number of bit errors in the reception side optical communication node based on the received number of bit errors. Since the pre-equalization optical fiber communication system is characterized in that the dispersion amount is adjusted to an optimum value so as to be minimized, even if the main signal is not conducted as in construction, the transmission is performed from the receiving end. The dispersion compensation controlling information transferred correctly to the end, the dispersion of the optical fiber transmission line can be fast and accurately compensated.

Embodiment 1 FIG.
A pre-equalized optical fiber communication system according to Embodiment 1 of the present invention will be described with reference to FIG. 1 is a diagram showing a configuration of a pre-equalized optical fiber communication system according to Embodiment 1 of the present invention. In the following, in each drawing, the same reference numerals indicate the same or corresponding parts.

  In FIG. 1, the pre-equalization optical fiber communication system according to the first embodiment is provided with an optical communication node A and an optical communication node B connected by optical fiber transmission lines 11 and 12, and these A control plane 100 for controlling the optical communication nodes A and B is also provided (see FIG. 2).

  The optical communication node A includes an input terminal 2a to which an input signal is input, and an error correction circuit that detects the number of bit errors of the optical signal transmitted from the optical communication node B that is the opposite station and propagated through the optical fiber transmission line 12. (FEC) 3a and the input signal are given a predetermined dispersion amount (dispersion compensation setting value) from the control plane 100 for the first time, and a dispersion amount (dispersion compensation setting value) from the optimization means 21a described later is given next time. Thus, a precoder 4a (variable dispersion compensation circuit) that performs pre-modulation, and an electrical / optical converter that converts an electrical signal from the precoder 4a (variable dispersion compensation circuit) into an optical signal and outputs the optical signal to the optical fiber transmission line 11 ( E / O) 5a, an optical / electrical converter (O / E) 6a that receives an optical signal transmitted from the optical communication node B and propagates through the optical fiber transmission line 12, and converts the optical signal into an electrical signal; Memory (RAM) A conversion table 7a (conversion table storage unit) for converting the amount of dispersion stored in a and the amount of dispersion from the optimization unit 21a described later into a precoded value (set value) and the control plane 100 are notified ( Based on the number of bit errors of the optical signal propagated through the optical fiber transmission line 12 detected and transmitted by the optical communication node B, and a memory (RAM) 8a for storing the predetermined dispersion amount to be compensated) Until the number of bit errors is minimized, the setting value of the dispersion amount of the precoder 4a (variable dispersion compensation circuit) is changed, and the optimization means 21a for detecting the optimum value of the dispersion amount and the output signal are output. An output terminal 9a and a monitoring optical interface (OSC) 10a that forms a monitoring channel between the optical communication nodes are provided. Here, the memory (RAM) 8a, the conversion table 7a, and the precoder (variable dispersion compensation circuit) 4a constitute variable dispersion compensation means for giving a predetermined dispersion amount to the input signal in advance.

  Among the configurations, the configuration used when the optical communication node A is the transmission side includes an optimization unit 21a, a memory (RAM) 8a, a conversion table 7a, a precoder (variable dispersion compensation circuit) 4a, An electric / optical converter (E / O) 5a. The configuration used when the optical communication node A is the transmission side is an optical / electrical converter (O / E) 6a, an error correction circuit (FEC) 3a, and a supervisory optical interface (OSC) 10a.

  In FIG. 1, in each configuration of the optical communication node B, the same number as that of each configuration of the optical communication node A and b in place of “a” at the end is the same as the optical communication node A in the optical communication node B. Indicates a similar functional block.

  That is, the optical communication node B includes an input terminal 2b for receiving an input signal, an error correction circuit (FEC) 3b, a precoder (variable dispersion compensation circuit) 4b for premodulation, and an electric / optical converter (E / O) 5b, an optical / electrical converter (O / E) 6b, a dispersion amount / precoding value (setting value) conversion table 7b, and a memory storing a predetermined dispersion amount notified from the control plane 100 (RAM) 8b, an optimization means 21b for detecting an optimum value of the dispersion amount, an output terminal 9b for outputting an output signal, and a monitoring optical interface (OSC) 10b are provided. Since these configurations are the same as those of the optical communication node A as described above, the description thereof is omitted here.

  FIG. 2 is a diagram showing an example of the relationship between the control plane 100 and each of the optical communication nodes A to F in the pre-equalized optical fiber communication system according to Embodiment 1 of the present invention.

  FIG. 1 shows an example in which only two optical communication nodes A and B are provided, but actually, a plurality of optical communication nodes are provided as shown in FIG. It is. Therefore, in the following description, when a common configuration is described, reference numerals such as a and b at the end of the numbers indicating the respective components are omitted and only numerical values are indicated (for example, input signals 2a and 2b). ,..., Simply shown as input signal 2).

  That is, each optical communication node has an input terminal 2 for receiving an input signal, an error correction circuit (FEC) 3, a precoder (variable dispersion compensation circuit) 4 for performing pre-modulation, and an electric / optical converter (E / O) 5, optical / electrical converter (O / E) 6, dispersion amount and precoded value (setting value) conversion table 7, and approximate dispersion amount to be compensated notified from the control plane 100 A stored memory (RAM) 8, an optimization means 21 for detecting an optimum value of variable dispersion compensation, an output terminal 9 from which an output signal is output, and a monitoring optical interface (OSC) 10 are provided.

  FIG. 3 is a diagram showing a specific example of the precoder (variable dispersion compensation circuit) 4 and the electrical / optical converter (E / O) 5 of the pre-equalized optical fiber communication system according to Embodiment 1 of the present invention.

  In FIG. 3, (a) uses a look-up table and a high-speed D / A converter (high-speed digital / analog converter) as a precoder (variable dispersion compensation circuit) 4, and an electric / optical converter (E / O). 5 shows an example using an optical quadrature modulator (I / Q modulator).

  (B) uses a digital FIR filter and a high-speed D / A converter as a precoder (variable dispersion compensation circuit) 4, and an optical quadrature modulator (I / Q modulation) as an electrical / optical converter (E / O) 5. An example using a container is shown.

  (C) uses a high-speed analog transversal filter as the precoder (variable dispersion compensation circuit) 4 and an optical quadrature modulator (I / Q modulator) as the electrical / optical converter (E / O) 5. An example is shown.

  The precoder (variable dispersion compensation circuit) 4 and the electrical / optical converter (E / O) 5 select and use one of the methods (a) to (c) as appropriate depending on the dispersion compensation amount and circuit scale. Further, the present invention is not limited to the three methods listed here, and other configurations may be used. The “parameter” shown in FIG. 3 corresponds to a pre-coded value that will be described later.

  Next, the operation of the pre-equalized optical fiber communication system according to the first embodiment will be described with reference to the drawings.

  In the optical communication node A, an input signal (electric signal) input from the input terminal 2a is framed and error correction encoded by an error correction circuit (FEC) 3a, and then input to a precoder (variable dispersion compensation circuit) 4a. Is done. On the other hand, a rough predetermined dispersion amount to be compensated is notified from the control plane 100 that controls the entire network.

  The notified amount of distribution is stored in the memory (RAM) 8a. The dispersion amount stored in the memory (RAM) 8a is converted into a precoded value by the conversion table 7a, and is supplied to the precoder (variable dispersion compensation circuit) 4a. A precoder (variable dispersion compensation circuit) 4a gives the precoded value to an input signal (electrical signal), and the electric / optical converter (E / O) 5a converts it into an optical signal. Convolution of the inverse function of the dispersion of the fiber transmission line 11 is performed (this compensates for the dispersion of the optical fiber transmission line 11).

  The optical signal output from the electrical / optical converter (E / O) 5a and propagated through the optical fiber transmission line 11 is received by the optical / electrical converter (O / E) 6b in the optical communication node B, and the electrical signal. The bit error is corrected by the error correction circuit (FEC) 3b and deframed to become an output signal from the output terminal 9b.

  The error correction circuit (FEC) 3b detects the number of bit errors in the optical signal propagated through the optical fiber transmission line 11 based on the electrical signal converted to the optical / electrical converter (O / E) 6b. . The detected number of bit errors is transmitted to the optical communication node A through the optical fiber transmission line 12 by the monitoring optical interface (OSC) 21b. In the optical communication node A, based on the number of transmitted bit errors, the dispersion amount setting value of the precoder 4a (variable dispersion compensation circuit) is changed until the number of bit errors is minimized, Find the optimal value. By doing so, the number of bit errors (dispersion compensation error) detected on the receiving side is transferred to the transmitting side by a supervisory control optical signal different from the main signal, and the dispersion of the optical fiber transmission line is compensated.

  The signal flow from the optical communication node B to the optical communication node A is the same as described above.

  FIG. 4 is a flowchart showing the operation of the pre-equalized optical fiber communication system according to Embodiment 1 of the present invention.

  In step 101, the control plane 100 first notifies each optical communication node of a predetermined dispersion amount roughly set for each LSP (Label Switch Path). The amount of dispersion is used at the first time.

  In step 201, each optical communication node writes the dispersion amount notified from the control plane 100 in the memory (RAM) 8.

  Next, in step 202, a transponder card that transmits and receives a main signal is inserted into each optical communication node, and an optical signal starts to be emitted. In the first time, as the initial value of the dispersion amount, a value obtained by converting the dispersion amount stored in the memory (RAM) 8 into the pre-coded value is used, but there is no compensation that the dispersion amount becomes the optimum value at this stage. The main signal is not always conducted. Further, it is assumed that the main signal from the optical communication node B to the optical communication node A has not been emitted yet. Thus, at the first time, a predetermined dispersion amount stored in the memory (RAM) 8 is given to the input signal, which is converted into an optical signal by the electrical / optical converter (E / O) 5a, and the optical signal is It is output to the fiber transmission line 11. Note that details of how to compensate for dispersion in the optical fiber transmission line by the precoded value are described in detail in, for example, Patent Document 1, so refer to that.

  In step 203, if the optical / electrical converter (O / E) 6b of the optical communication node B on the receiving side receives the optical signal, converts it into an electrical signal, and transfers it to the error correction circuit (FEC) 3b, an error occurs. The correction circuit (FEC) 3b detects the number of bit errors, and determines whether or not the detected number of bit errors is the minimum. In step 204, the information on the number of bit errors is transmitted toward the optical communication node A through the monitoring optical interface (OSC) 10b of the optical communication node B. In step 205, the monitoring optical interface (OSC) 10a of the optical communication node A receives this and transfers it to the optimization means 21a. In step 206, the optimization means 21a performs control for slightly increasing / decreasing the amount of dispersion (control for increasing / decreasing by a preset increase / decrease width) to the precoder 4a. Is repeated until the number of bit errors is determined to be minimum in the determination in step 203, and the set value of the dispersion amount of the precoder (variable dispersion compensation means) 4a is changed. Details of the control for minimizing the number of bit errors are described in detail in, for example, Patent Document 1, so refer to that. In step 203, when the number of bit errors is minimized, the process proceeds to step 207, where the main signal is opened.

  In step 208, the distribution amount in the memory (RAM) 8 is updated with the optimized distribution amount as the true distribution amount in the LSP. Simultaneously with the update of the memory (RAM) 8, the distribution amount is notified to the control plane 100.

  In step 209, the control plane 100 re-notifies all the optical communication nodes of the updated dispersion amount.

  Here, an example is shown in which the number of bit errors is used as a parameter for optimizing the dispersion amount. However, an alarm (for example, LOS OF SIGNAL, LOSS OF FRAME, etc.) generated on the receiving side due to a deviation from the optimum dispersion value is shown. It goes without saying that the same effect can be obtained even if the above is used.

  Further, as a parameter for optimizing the dispersion compensation set value, any signal is used as long as it is a parameter indicating a deviation from the optimum dispersion value (for example, the intensity of the clock component extracted on the receiving side). However, it goes without saying that the same effect can be obtained.

  Further, the example of the precoder 4 is shown as the variable dispersion compensator. However, if the dispersion compensator can be used on the transmission side, the same effect can be obtained by using an optical dispersion compensator such as a fiber grating. It goes without saying that it is obtained.

  As described above, in the first embodiment, a pre-equalized optical fiber communication system including a plurality of optical communication nodes connected to each other through an optical fiber transmission line, the transmitting optical communication node is: A precoder (variable dispersion compensation means) 4 for giving a predetermined dispersion amount to an input signal in advance, and an optimization means 21 for detecting an optimum value of the dispersion amount are provided, and the optical communication node on the receiving side includes an optical fiber transmission line And an error correction circuit (FEC) 3 for detecting the number of bit errors of the optical signal propagated through the optical signal, and the number of bit errors detected by the error correction circuit (FEC) 3 of the optical communication node on the receiving side is determined by the monitoring optical interface (OSC). ) 10 is transferred to the optimization means of the optical communication node on the transmission side, and based on this, the dispersion amount is adjusted and controlled to the optimum value. Spirit In addition to enabling high-speed provisioning, protection, and restoration, it is possible to efficiently control to the optimum value even in the system construction stage where the main signal is not conducted. .

It is a figure which shows the structure of the pre-equalization optical fiber communication system which concerns on Embodiment 1 of this invention. It is a figure which shows the relationship between the control plane of each pre-equalization optical fiber communication system which concerns on Embodiment 1 of this invention, and each optical communication node. It is a figure which shows the specific example of the precoder of the pre-equalization optical fiber communication system which concerns on Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the pre-equalization optical fiber communication system which concerns on Embodiment 1 of this invention.

Explanation of symbols

  2, 2a, 2b input terminals, 3, 3a, 3b error correction circuit (FEC), 4, 4a, 4b precoder (variable dispersion compensation circuit), 5, 5a, 5b electrical / optical converter (E / O), 6 , 6a, 6b Optical / electrical converter (O / E), 7, 7a, 7b conversion table, 8, 8a, 8b Memory (RAM), 9, 9a, 9b Output terminal 10, 10a, 10b Monitoring optical interface ( OSC), 11, 12 optical fiber transmission line, 21, 21a, 21b optimization means, 100 control plane, A, B, C, D, E, F optical communication nodes.

Claims (2)

A pre-equalized optical fiber communication system comprising a plurality of optical communication nodes connected to each other via an optical fiber transmission line,
The optical communication node on the transmission side
Optimization that performs control to increase or decrease the amount of dispersion to be given to the input signal based on the number of bit errors of the optical signal transmitted to the optical communication node on the receiving side from the receiving optical communication node Means,
A variable dispersion compensator for generating an electric signal to which the input signal is input and for which the input signal is given a predetermined dispersion amount for the first time and a dispersion amount from the optimization means thereafter;
An electrical / optical conversion means for converting the electrical signal from the variable dispersion compensation means into an optical signal and transmitting the optical signal to the optical communication node on the receiving side via the optical fiber transmission line;
The optical communication node on the receiving side
Optical / electrical conversion means for receiving the optical signal from the optical communication node on the transmitting side and converting it into an electrical signal;
Error correction means for detecting the number of bit errors in the optical signal based on the electrical signal from the optical / electrical conversion means;
A reception-side monitoring optical interface that transmits the detected number of bit errors to the transmission-side optical communication node via the optical fiber transmission line;
The number of bit errors detected by the error correction means of the receiving side optical communication node is transmitted to the optimization means of the transmitting side optical communication node, and the optimization means is based on the received number of bit errors. The dispersion amount is adjusted to an optimal value so that the number of bit errors in the optical communication node on the receiving side is minimized. The variable dispersion compensation means includes
A memory for storing the predetermined amount of dispersion used for the first time;
A conversion table for converting the predetermined amount of dispersion stored in the memory and the amount of dispersion from the optimization means into precoded values;
The pre-equalized optical fiber communication system according to claim 1, further comprising: a precoder that compensates for dispersion of the optical fiber transmission line based on the precoded value.

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