JP2007259281A - Optical fiber communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber communication system capable of precisely compensating the dispersion of an optical fiber transmission line at a high speed. <P>SOLUTION: A transmission-side optical communication node A includes an error correcting circuit 3a which frames an input signal, corrects an error, and encodes the signal, a memory 8a which stores a dispersion quantity reported from a control plane 100, an optimizing means 20a which adjusts the dispersion quantity to an optimum dispersion quantity so that the number of corrected bit errors from the error correcting circuit 3b becomes minimum, a conversion table 7a for converting the dispersion quantities from the memory 8a and optimizing means 20a into precode values, a precoder 4a which compensates the dispersion of the optical fiber transmission line 11 based upon the precode values, and an electrooptic converter 5a which converts an electric signal from the precoder 4a into an electric signal. A reception-side optical communication node B includes an optoelectric converter 6b which converts the optical signal propagated through the optical fiber transmission line 11 into an electric signal, and an error correcting circuit 3b which corrects a bit error of the signal from the optoelectric converter 6b, deframes the signal, and outputs an output signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an 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.

  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 breakage, etc., so the dispersion amount is not a dispersion compensation fiber with a fixed dispersion amount. Introduction of variable dispersion compensators has begun. Alternatively, even in the case of 10 Gb / s, in an all-optical network that dynamically replaces an optical path (or Label Switch Path: LSP), the dispersion amount differs for each optical path, so a variable dispersion compensator is required. .

  As a method of controlling the optimum value of the dispersion amount of the tunable dispersion compensator, there is a method of controlling so that the number of bit errors corrected by an error correction circuit provided in the optical transmission apparatus on the receiving side is minimized (for example, patents) Reference 1). In order to make the residual dispersion zero by this method, feedback for minimizing the number of bit errors is necessary, and a certain control time is inevitably required.

  On the other hand, as a method for shortening the control time of the tunable dispersion compensator, a method using a GMPLS RSVP-TE message has been proposed (for example, see Non-Patent Document 1). The dispersion value of the optical fiber constituting each link starting from each optical communication node on the optical fiber communication network is set in advance as a database in each optical communication node. When a message requesting the setting of an optical path is actually issued, the residual dispersion value at the receiving end is finally obtained by taking the cumulative value of the chromatic dispersion values of the links constituting the optical path.

  As a tunable dispersion compensator suitable for the above method, there is a predistortion method (for example, see Non-Patent Document 2). 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. As a calculation method, there are a look-up table method in which a conversion table is previously stored in a large-scale memory, a method of sequentially calculating with an FIR filter, a method of calculating with an analog transversal filter, and the like. By performing quadrature modulation of light with a premodulation signal generated by either of them, an optical waveform having a complex electric field that compensates for group delay due to dispersion after optical fiber transmission is generated.

  A method for measuring the amount of dispersion in advance has been proposed (see, for example, Patent Document 2). In this method, the dispersion value of each optical path is measured based on the propagation delay time difference between the signal light and another measurement wavelength.

JP 2002-208992 A JP 2003-121303 A Co-authored by Shiro Kasa, Mikio Yagi, Shuichi Satomi, and Shoichiro Asano “Chromatic Dispersion Compensation in Ultra-High-Speed Wavelength Path Networks” 2004 IEICE Communication Society Conference, BSC-1-1 M. M. El Said, J. Sitch and M. I. Elmasry, “An Electrically Pre-equalized 10-Gb / s Duobinary Transmission System” IEEE J. Lightwave Technol. , Vol. 23, no. 1, pp. 388-400, Jan. 2005

  Although the dispersion compensation optimization control time is expected to be shortened by using the above-described conventional method, not only does a certain amount of error occur in dispersion measurement at the measurement wavelength, but also the distribution of connected optical paths. There is a problem that it is difficult to instantly start a desired operation with zero residual dispersion only by accumulating errors and simply giving a dispersion value of a database prepared in advance to a variable dispersion compensator.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain an optical fiber communication system capable of compensating for dispersion of an optical fiber transmission line at high speed and with precision.

  An optical fiber communication system according to the present invention is an optical fiber communication system comprising a plurality of optical communication nodes connected to each other through an optical fiber transmission line, and a control plane for controlling the plurality of optical communication nodes, The optical communication node on the transmission side detects the optimum value of the dispersion amount, the first error correction circuit that frames the input signal and performs error correction coding, the memory that stores the dispersion amount notified from the control plane, and An optimization unit that performs the conversion, a conversion table that converts the dispersion amount stored in the memory and the dispersion amount from the optimization unit into a precoded value, and the dispersion of the optical fiber transmission line is compensated based on the precoded value. A variable dispersion compensator; and an electric / optical converter that converts an electric signal from the variable dispersion compensator into an optical signal and outputs the optical signal to the optical fiber transmission line. Thus, the optical communication node on the receiving side corrects the bit error of the signal from the optical / electrical converter that converts the optical signal propagated through the optical fiber transmission path into an electrical signal, and the signal from the optical / electrical converter. And at least a second error correction circuit that outputs a framed output signal.

  The optical fiber communication system according to the present invention can compensate for dispersion of the optical fiber transmission line at high speed and precisely, and has the effect of enabling high-speed provisioning, protection, and restoration.

Embodiment 1 FIG.
An optical fiber communication system according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 is a diagram showing a configuration of an optical fiber communication system according to Embodiment 1 of the present invention. In the following, in each figure, the same reference numerals indicate the same or corresponding parts.

  1, the optical fiber communication system according to the first embodiment includes a control plane 100 that controls the entire network (each optical communication node), an optical communication node A connected by optical fiber transmission lines 11 and 12, and An optical communication node B is provided.

  The optical communication node A has an input terminal 2a for receiving an input signal, an error correction circuit (FEC) 3a, a precoder (variable dispersion compensation means) 4a for premodulation, and an electric / optical converter (E / O). ) 5a, optical / electrical converter (O / E) 6a, conversion table 7a of dispersion amount and precoded value (set value), and rough dispersion amount to be compensated notified from the control plane 100 are stored A memory (RAM) 8a, an optimization means 20a for detecting the optimum value of the variable dispersion amount, and an output terminal 9a from which an output signal is output are provided.

  Those assigned b with the same number indicate similar functional blocks in the optical communication node B.

  That is, the optical communication node B has an input terminal 2b for receiving an input signal, an error correction circuit (FEC) 3b, a precoder 4b for premodulation, an electric / optical converter (E / O) 5b, Optical / electrical converter (O / E) 6b, dispersion amount and precoded value (set value) conversion table 7b, and a memory (RAM) storing the approximate dispersion amount notified from the control plane 100 to be compensated 8b, an optimization means 20b for detecting the optimum value of variable dispersion compensation, and an output terminal 9b from which an output signal is output.

  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 optical fiber communication system according to the first embodiment of the present invention.

  FIG. 3 is a diagram showing a specific example of the precoder and the electrical / optical converter of the optical fiber communication system according to Embodiment 1 of the present invention.

  3A shows an example in which a look-up table and a high-speed D / A converter are used as the precoder 4, and an optical quadrature modulator (I / Q modulator) is used as the electrical / optical converter 5. In FIG. .

  (B) shows an example in which a digital FIR filter and a high-speed D / A converter are used as the precoder 4 and an optical quadrature modulator (I / Q modulator) is used as the electrical / optical converter 5.

  (C) shows an example in which a high-speed analog transversal filter is used as the precoder 4 and an optical quadrature modulator (I / Q modulator) is used as the electrical / optical converter 5.

  Either method is selected and used depending on the amount of dispersion compensation and circuit scale. Also, the present invention is not limited to the three methods listed here. The parameter corresponds to a precoded value that will be described later.

  Next, the operation of the 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 input from the input terminal 2a is framed and error correction encoded by the error correction circuit 3a, and then input to the precoder 4a. On the other hand, a rough 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 8a. The amount of dispersion stored in the memory 8a is converted into a precoded value by the conversion table 7a and given to the precoder 4a. The precoder 4a and the electrical / optical converter 5a perform dispersion of the optical fiber transmission line 11 and convolution of the inverse function.

  In the optical communication node B, the optical signal propagated through the optical fiber transmission line 11 is converted into an electric signal by the optical / electrical converter 6b, the bit error is corrected by the error correction circuit 3b, deframed, and output. This is an output signal from the terminal 9b. The signal flow from the optical communication node B to the optical communication node A is the same as described above.

  FIG. 5 is a diagram showing a compensation amount and precoded value conversion table of the optical fiber communication system according to Embodiment 1 of the present invention.

  FIG. 5 shows an example of the relationship between the dispersion amount that can be compensated and the precode value given to the precoder 4a from the conversion table 7a. A certain amount of dispersion can be compensated for a certain precoded value. In this example, the upper limit that can be compensated is 20,000 ps / nm. Since the pre-coded value is a quantized discrete value, the amount of dispersion that can be compensated is also stepped. For example, when the precoded values are set to X, Y, and Z, dispersions of 9,900 ps / nm, 10,100 ps / nm, and 10,000 ps / nm can be compensated, respectively.

  FIG. 6 is a diagram showing how the amount of dispersion is adjusted (optimization procedure) by the optimization means of the optical fiber communication system according to Embodiment 1 of the present invention.

  It is assumed that the dispersion amount of the optical fiber transmission line 11 is notified in advance from the control plane 100 to the optical communication node A on the transmission side as 9,900 ps / nm and stored in the memory 8a. Assume that the actual dispersion amount of the actual optical fiber transmission line 11 is 10,000 ps / nm.

  When the power is turned on, the precoder 4a starts the operation with the precode value (X in FIG. 5) obtained by converting the dispersion amount stored in the memory 8a in advance by the conversion table 7a, but compensates with the precode value given in advance. Due to an error (10,000-9,900 = 100 ps / nm) between the dispersion amount that can be generated and the dispersion amount that the actual optical fiber transmission line 11 has, a large amount of bit errors occur in the error correction circuit 3b of the optical communication node B on the receiving side. Is observed.

  The observed bit error number is added to the signal from the optical communication node B to the optical communication node A as the bit error correction number, and is notified to the optical communication node A again. As shown in FIG. 6, the optimization unit 20a sweeps the dispersion amount from X → Y → Z so that the number of bit error corrections notified via the error correction circuit 3a is minimized, and the optimum value Z, that is, the optimum Adjust the amount of dispersion. The conversion table 7a converts the amount of dispersion from the optimization means 20a into a precoded value and gives it to the precoder 4a. The precoder 4a, together with the electrical / optical converter 5a, performs dispersion and inverse function convolution on the optical fiber transmission line 11 based on the given precoded value. The optimization unit 20a rewrites the dispersion amount originally stored in the memory 8a in accordance with the adjusted optimum value Z, and notifies the control plane 100 of the true dispersion amount.

  Here, a method for minimizing the number of bit error corrections on the receiving side has been shown as an optimal method for the amount of dispersion, but the present invention is not limited to this.

  FIG. 4 is a flowchart showing the operation of the 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 an approximate dispersion amount for each LSP (Label Switch Path).

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

  Next, in step 202, when each optical communication node is powered on or a card is inserted, the optical signal starts to be conducted. However, the dispersion amount stored in the memory 8 is set as an initial value. used.

  Thereafter, in steps 203 to 205, optimization control is performed to minimize the number of bit error corrections detected by the receiving optical communication node, and the optimized dispersion amount is set as the true dispersion amount in the LSP. Update the distribution amount. Simultaneously with the update of the memory 8, the distribution amount is notified to the control plane 100.

  In step 102, the control plane 100 notifies all the optical communication nodes of the updated dispersion amount.

Embodiment 2. FIG.
An optical fiber communication system according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 7 is a diagram showing a configuration of an optical fiber communication system according to Embodiment 2 of the present invention.

  In FIG. 7, optical communication nodes A and B are newly provided with optical dispersion compensators (variable dispersion compensation means) 10a and 10b, respectively, and the precoders 4a and 4b are deleted instead. The other parts having the same numbers as those in FIG. 1 have the same functions.

  Next, the operation of the optical fiber communication system according to the second embodiment will be described with reference to the drawings.

  In the first embodiment, the transmission-side precoder 4 is used as the dispersion compensation method, but in the second embodiment, the reception-side optical dispersion compensator 10 is used. The optical dispersion compensator 10 generally uses a grating or a system using an etalon.

  In the optical communication node A, the input signal is framed and error correction encoded by the error correction circuit 3a, and then converted into an optical signal by the electrical / optical converter 5a.

  The dispersion of the optical signal propagated through the optical fiber transmission line 11 is compensated by the dispersion compensator 10b in the optical communication node B. A rough 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 8b. The dispersion amount stored in the memory 8b is converted into the set value of the dispersion compensator 10b by the conversion table 7b, and given to the dispersion compensator 10b. The dispersion-compensated optical signal is converted into an electrical signal by the optical / electrical converter 6b, the bit error is corrected by the error correction circuit 3b, deframed, and an output signal is obtained. The signal flow from the optical communication node B to the optical communication node A is the same as described above.

  Also in the second embodiment, the conversion table 7b is used. In FIG. 5, if “precoded value” is replaced with “dispersion compensator setting value”, the operation is the same. A specific amount of dispersion can be compensated for a set value of a certain dispersion compensator. In the example of FIG. 5, the upper limit that can be compensated is 20,000 ps / nm. Since the set value of the dispersion compensator 10 is a quantized discrete value, the amount of dispersion that can be compensated is also stepped. For example, when the set values of the dispersion compensator 10 are set to X, Y, and Z, dispersions of 9,900 ps / nm, 10,100 ps / nm, and 10,000 ps / nm can be compensated, respectively.

  FIG. 6 illustrates how the amount of dispersion of the optimization means is adjusted as described above. It is assumed that the dispersion amount of the optical fiber transmission line 11 is notified in advance from the control plane 100 to the optical communication node B on the receiving side as 9,900 ps / nm and stored in the memory 8b. Assume that the actual dispersion amount of the actual optical fiber transmission line 11 is 10,000 ps / nm.

  When the power is turned on, the dispersion compensator 10b starts to operate with the set value (X in FIG. 5) converted by the conversion table 7b using the dispersion amount stored in the memory 8b in advance. Due to the error (10,000-9,900 = 100 ps / nm) between the dispersion amount that can be compensated and the dispersion amount that the actual optical fiber transmission line 11 has, a large amount of bit errors are observed in the error correction circuit 3b on the reception side. .

  The observed bit error count is fed back to the optimization means 20b as the bit error correction count. As shown in FIG. 6, the optimization unit 20b sweeps the dispersion amount from X → Y → Z so as to minimize the number of bit error corrections, and adjusts to the optimum value Z, that is, the optimum dispersion amount. The conversion table 7b converts the amount of dispersion from the optimization unit 20b into a set value and gives it to the dispersion compensator 10b. The dispersion compensator 10b compensates for the dispersion of the optical fiber transmission line 11 based on the given set value. The optimization unit 20b rewrites the dispersion amount originally stored in the memory 8b according to the adjusted optimum value Z, and notifies the control plane 100 of the true dispersion amount.

  Here, an example of the optical dispersion compensators 10a and 10b is shown as the dispersion compensator 10. However, the dispersion compensator is not limited to the optical type as long as it is a dispersion compensator that can be used on the reception side, but is not limited to the optical type. ) And MLSE (Maximum Likelihood Sequence Estimation), it goes without saying that the same effect can be obtained by using an electric adaptive equalizer.

It is a figure which shows the structure of the 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 the 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 and electrical / optical converter of the optical fiber communication system which concerns on Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the optical fiber communication system which concerns on Embodiment 1 of this invention. It is a figure which shows the conversion table of the dispersion | distribution amount which can be compensated for the optical fiber communication system which concerns on Embodiment 1 of this invention, and a precode value (setting value). It is a figure which shows the mode (optimization procedure) of adjustment of the dispersion amount of the optimization means of the optical fiber communication system which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the optical fiber communication system which concerns on Embodiment 2 of this invention.

Explanation of symbols

  2a, 2b input terminal, 3a, 3b error correction circuit, 4, 4a, 4b precoder, 5, 5a electrical / optical converter, 6b optical / electrical converter, 7a, 7b conversion table, 8, 8a, 8b memory, 9a , 9b Output terminal, 10, 10a, 10b Dispersion compensator, 11, 12 Optical fiber transmission line, 20a, 20b Optimization means, 100 Control plane, A, B Optical communication node.

Claims (4)

An optical fiber communication system comprising a plurality of optical communication nodes connected to each other through an optical fiber transmission line, and a control plane for controlling the plurality of optical communication nodes,
The optical communication node on the transmission side
A first error correction circuit for framing the input signal and for error correction encoding;
A memory for storing a distribution amount notified from the control plane;
An optimization means for detecting the optimum value of the dispersion amount;
A conversion table for converting the amount of dispersion stored in the memory and the amount of dispersion from the optimization means into a precoded value;
Variable dispersion compensation means for compensating dispersion of the optical fiber transmission line based on the precoded value;
An electrical / optical converter that converts an electrical signal from the tunable dispersion compensation means into an optical signal and outputs the optical signal to the optical fiber transmission line;
The optical communication node on the receiving side
An optical / electrical converter that converts an optical signal propagated through the optical fiber transmission line into an electrical signal;
An optical fiber communication system comprising at least a second error correction circuit that corrects a bit error of a signal from the optical / electrical converter and deframes the signal to output an output signal. 2. The optical fiber communication system according to claim 1, wherein the variable dispersion compensation unit is a precoder that performs convolution of an inverse function and dispersion of the optical fiber transmission line based on the precoded value. An optical fiber communication system comprising a plurality of optical communication nodes connected to each other through an optical fiber transmission line, and a control plane for controlling the plurality of optical communication nodes,
The optical communication node on the transmission side
A first error correction circuit for framing the input signal and for error correction encoding;
An electrical / optical converter that converts an electrical signal from the first error correction circuit into an optical signal and outputs the optical signal to the optical fiber transmission line;
The optical communication node on the receiving side
Variable dispersion compensation means for compensating for dispersion of an optical signal propagated through the optical fiber transmission line based on a set value;
An optical / electrical converter for converting an optical signal from the tunable dispersion compensating means into an electrical signal;
A second error correction circuit for correcting a bit error of the signal from the optical / electrical converter and deframed to output an output signal;
A memory for storing a distribution amount notified from the control plane;
An optimization means for detecting the optimum value of the dispersion amount;
An optical fiber communication system comprising at least a conversion table for converting a dispersion amount stored in the memory and a dispersion amount from the optimization unit into a set value. 4. The optical fiber communication system according to claim 3, wherein the tunable dispersion compensation means is an optical dispersion compensator that compensates for dispersion of an optical signal propagated through the optical fiber transmission line based on the set value. .

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