JP2009177237A - Dispersion compensation device - Google Patents

Dispersion compensation device Download PDF

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JP2009177237A
JP2009177237A JP2008010619A JP2008010619A JP2009177237A JP 2009177237 A JP2009177237 A JP 2009177237A JP 2008010619 A JP2008010619 A JP 2008010619A JP 2008010619 A JP2008010619 A JP 2008010619A JP 2009177237 A JP2009177237 A JP 2009177237A
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dispersion compensation
error rate
code error
dispersion
chromatic dispersion
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JP5025503B2 (en
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Hiroaki Shintaku
宏彰 新宅
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Mitsubishi Electric Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To perform dispersion compensation by finding the smallest value regardless of presence of a local minimal value of a code error rate and calculating a compensation amount for real suitable wavelength dispersion. <P>SOLUTION: When the code error rate judged based on the number of error corrections detected by an error detecting means becomes equal to or larger than a preset threshold A during operation, a control means varies a compensation amount for wavelength dispersion in a direction wherein the code error rate decreases and sets it to a point where the code error rate becomes smallest for the first time, and when the code error rate is equal to or less than a certain threshold B (<A) at this time, the control means allows temporary slight code error deterioration and searches for a point where the code error rate reaches the smallest value without falling into the local minimal value, and when there is the point where the code error rate reaches the smallest value, resets compensation amount for wavelength dispersion at the point. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

この発明は、長距離、大容量伝送を行う光伝送システムで起こる光信号の波形劣化の補償を行う分散補償装置に関するものである。   The present invention relates to a dispersion compensator that compensates for waveform degradation of an optical signal that occurs in an optical transmission system that performs long-distance and large-capacity transmission.

光ファイバ伝送路における波長分散は、外界の温度や応力などによって時間的に変動し、伝送される光信号に影響を及ぼす。光の伝搬時間は伝送路の波長分散特性により波長成分によって異なるため、矩形のパルス波形である光信号が光ファイバ伝送路を伝搬すると、伝送後の波形が時間軸上で広がったり圧縮したりするという劣化を引き起こす。特に、超高速光伝送システムにおいては、光ファイバ伝送路を伝送される光信号の波長分散に対する耐力が著しく低下するため、僅かな波長分散の変動によっても伝送信号品質が劣化する。そのため、超高速光伝送システムでは、光ファイバ伝送路の波長分散の変動に応じて随時適切な分散補償を行う必要がある。このような時間変動を伴う波長分散の補償を可能にする一つの方法として、自動分散補償技術が知られている。自動分散補償技術を用いた超高速光伝送システムの構築には、実装が容易で、かつ容易な制御手法の確立が不可欠である。   The chromatic dispersion in the optical fiber transmission line fluctuates with time due to external temperature, stress, etc., and affects the transmitted optical signal. Since the propagation time of light varies depending on the wavelength component due to the wavelength dispersion characteristics of the transmission line, when an optical signal with a rectangular pulse waveform propagates through the optical fiber transmission line, the waveform after transmission spreads or compresses on the time axis Cause deterioration. In particular, in an ultrahigh-speed optical transmission system, the tolerance to chromatic dispersion of an optical signal transmitted through an optical fiber transmission line is significantly reduced, so that transmission signal quality is deteriorated even by slight fluctuations in chromatic dispersion. For this reason, in an ultrahigh-speed optical transmission system, it is necessary to perform appropriate dispersion compensation as needed according to changes in chromatic dispersion in the optical fiber transmission line. An automatic dispersion compensation technique is known as one method that makes it possible to compensate for such chromatic dispersion accompanied by time variation. In order to construct an ultra-high-speed optical transmission system using automatic dispersion compensation technology, it is essential to establish a control method that is easy to implement and easy to implement.

このような自動分散補償技術に用いられる可変分散補償器の制御方法としては、例えば、受信光信号の抽出クロック成分の大きさによる制御方法の提案がある（例えば特許文献１参照）。また、伝送されてきた光信号の誤りモニタ結果をもとに可変分散補償器の制御を行う方法（例えば特許文献２参照）、エラー率を算出し、そのエラー率が小さくなるように分散補償器を制御する技術（例えば特許文献３参）も提案されている。   As a control method of the tunable dispersion compensator used in such an automatic dispersion compensation technique, for example, there is a proposal of a control method based on the size of the extracted clock component of the received optical signal (see, for example, Patent Document 1). Also, a method of controlling the tunable dispersion compensator based on the error monitoring result of the transmitted optical signal (see, for example, Patent Document 2), a dispersion compensator so that the error rate is calculated and the error rate is reduced. A technique for controlling the above has also been proposed (for example, see Patent Document 3).

光伝送路で起きる波長の分散値とＢＥＲ（Bit Error Rate：以下、「符号誤り率」と呼ぶ）の関係は一般的に図６のようになっている。例えば特許文献３に開示された、波長分散特性により発生する光信号の波形劣化を補償する制御方法の場合、最適な波長分散の補償量を見つけるために、図７のように符号誤り率が、ある閾値以下となるように波長分散の補償量を変動させ、設定した閾値以下に在る符号誤り率が最も少なくなる点に達成した時点の波長分散の補償量を最適値として設定し制御を終了する。あるいは符号誤り率が減少から増加へ転じた際の波長分散の補償量を最適値として設定し制御を終了する。   The relationship between the dispersion value of the wavelength occurring in the optical transmission line and the BER (Bit Error Rate: hereinafter referred to as “code error rate”) is generally as shown in FIG. For example, in the case of the control method disclosed in Patent Document 3 that compensates for waveform degradation of an optical signal caused by chromatic dispersion characteristics, in order to find an optimal compensation amount of chromatic dispersion, a code error rate as shown in FIG. The amount of compensation for chromatic dispersion is varied so that it is below a certain threshold, and the amount of compensation for chromatic dispersion at the point where the code error rate below the set threshold is minimized is set as the optimal value, and control is terminated. To do. Alternatively, the compensation amount of chromatic dispersion when the code error rate is changed from decrease to increase is set as an optimum value, and the control is terminated.

特開平１１−６８６５７号公報JP 11-68657 A 特開平９−３２６７５５号公報JP-A-9-326755 特開２００２−２０８８９２号公報JP 2002-208992 A

しかし、、波長分散補償器の特性、回線状況等により、分散値と符号誤り率の関係で、図８に示すような符号誤り率の極小値が発生するような状態が起こることがある。この場合、従来の制御方法だと、波長分散の補償量の掃引で最初に出会った符号誤り率の極小値を最適な分散補償点と勘違いして制御を終了してしまうことになる。つまり、図８のように、後に最適な分散補償点、すなわち符号誤り率が最小となる点が存在するにもかかわらず局所的に存在する符号誤り率の極小値の点に波長分散の補償量を設定して分散補償制御を終了してしまうため、真に最適な波長分散の補償量が得られないという問題がある。   However, depending on the characteristics of the chromatic dispersion compensator, the line condition, etc., there may occur a state in which the minimum value of the code error rate as shown in FIG. 8 occurs due to the relationship between the dispersion value and the code error rate. In this case, with the conventional control method, the minimum value of the code error rate first encountered by sweeping the compensation amount of chromatic dispersion is mistaken for the optimum dispersion compensation point, and the control is terminated. That is, as shown in FIG. 8, the amount of compensation for chromatic dispersion is at a point where the optimum dispersion compensation point, that is, the point at which the code error rate is minimized, exists at a local minimum point of the code error rate. Since the dispersion compensation control is terminated by setting the above, there is a problem that a truly optimum chromatic dispersion compensation amount cannot be obtained.

この発明は、上記問題点を解決するためになされたもので、局所的に符号誤り率の極小値の存在に拘わらず最小値を見つけだして真の最適な波長分散の補償量を算出して分散補償を行う分散補償装置を得ることを目的とする。   The present invention has been made in order to solve the above-mentioned problems, and finds the minimum value locally regardless of the presence of the minimum value of the code error rate and calculates the true optimum chromatic dispersion compensation amount. It is an object of the present invention to obtain a dispersion compensation device that performs compensation.

この発明に係る分散補償装置は、誤り訂正符号で符号化され、光ファイバ伝送路を伝送された光信号の誤り訂正符号による誤り訂正個数を検出する誤り検出手段と、誤り検出手段の前段に設けられ、波長分散の補償量を変更しながら光ファイバ伝送路の波長分散を補償する可変分散補償手段と、この可変分散補償手段に対して、誤り検出手段で検出された誤り訂正個数の変動に基づいて最適分散補償制御を行う制御手段を備えた分散補償装置において、制御手段は、初期設定時には、可変分散補償手段における波長分散の補償量を予め設定した範囲で掃引して、誤り検出手段で検出された誤り訂正個数を基に判断した符号誤り率が最も少なくなる点に波長分散の補償量を設定し、運用時には、誤り検出手段で検出された誤り訂正個数を基に判断した符号誤り率が予め設定した閾値Ａ以上になった場合には波長分散の補償量を符号誤り率が減少する方向に変化させて符号誤り率が最初に最も少なくなる点に再設定し、その際にある閾値Ｂ（＜Ａ）以下であれば、一時的な若干の符号誤り劣化を許容して符号誤り率の極小値に陥ることなく最小値となる点を探索し、最小値となる点があった場合に当該点に波長分散の補償量を再々設定するものである。   A dispersion compensation apparatus according to the present invention is provided with an error detection means for detecting the number of error corrections by an error correction code of an optical signal encoded with an error correction code and transmitted through an optical fiber transmission line, and provided before the error detection means. A variable dispersion compensation means for compensating the chromatic dispersion of the optical fiber transmission line while changing the compensation amount of the chromatic dispersion, and the variable dispersion compensation means based on the variation in the number of error corrections detected by the error detection means. In the dispersion compensation apparatus having the control means for performing the optimum dispersion compensation control, the control means sweeps the chromatic dispersion compensation amount in the variable dispersion compensation means within a preset range and detects it by the error detection means at the initial setting. The amount of chromatic dispersion compensation is set at the point where the code error rate determined based on the number of error corrections is minimized, and is determined based on the number of error corrections detected by the error detection means during operation. When the code error rate exceeds a preset threshold A, the chromatic dispersion compensation amount is changed in the direction in which the code error rate decreases, and the code error rate is reset to the lowest point first. If the threshold value is less than or equal to a certain threshold value B (<A), a point that becomes the minimum value is searched without allowing a slight code error degradation temporarily and falling into the minimum value of the code error rate. If there is, the compensation amount of chromatic dispersion is set again at that point.

この発明によれば、波長分散の補償量の掃引において、閾値Ａを達成する符号誤り率の極小値を見つけた後も、閾値Ｂまで符号誤り率が若干悪化するのを許容して現在の最適分散補償点の周辺探索を実行し、現在の分散補償点より良い点が無いかを探索する。すなわち、最適な分散補償点がある場合には、その前に存在する、波長分散補償器の特性、回線状況等に起因した局所的な符号誤り率の極小値で分散補償制御を終了させることなく探索を行って、真に最適な波長分散の補償量を設定するようにしたので、符号誤り率が真に最小となる状態での光通信を可能にする。   According to the present invention, even after finding the minimum value of the code error rate that achieves the threshold A in the sweep of the compensation amount of chromatic dispersion, the code error rate is allowed to slightly deteriorate up to the threshold B, and the current optimum A search for the periphery of the dispersion compensation point is executed to search for a better point than the current dispersion compensation point. In other words, when there is an optimum dispersion compensation point, the dispersion compensation control is not terminated at the local minimum value of the code error rate due to the characteristics of the chromatic dispersion compensator, the line condition, etc. existing before that point. Since a search is performed to set a truly optimal chromatic dispersion compensation amount, optical communication is possible in a state where the code error rate is truly minimized.

実施の形態１．
図１は、この発明の実施の形態１である分散補償装置の機能構成を示すブロック図である。
図１において、この分散補償装置は、可変分散補償器（可変分散補償手段）２、光受信器３、ＦＥＣ（Forward Error Correction）復号化器／符号誤り情報モニタ（誤り検出手段）４および制御回路（制御手段）５を備えている。
可変分散補償器２には、送信側から光ファイバ伝送路１を介して伝送されてきた光信号が入力される。この光信号は、送信側において、ＦＥＣ方式の誤り訂正符号で符号化した送信データにより光変調された信号である。可変分散補償器２は、入力された光信号に対して、後述する可変分散補償を行って光受信器３に出力する。光受信器３では、可変分散補償器２で補償された光信号を電気信号に変換し、周知の処理による識別再生を行い、識別後のフレーム信号をＦＥＣ復号化器／符号誤り情報モニタ４に出力する。ＦＥＣ復号化器／符号誤り情報モニタ４では、ＦＥＣ復号化器機能により、誤り検出および前段で識別再生されたフレーム信号を分解し、クライアント信号について誤り検出および誤り訂正を行う。その際に、誤り情報モニタにより、ビットエラーカウント機能によって伝送誤り情報の一つである誤り訂正個数を取得して制御回路５に出力する。誤り訂正個数は、誤り訂正前の誤り個数に対応している。 Embodiment 1 FIG.
FIG. 1 is a block diagram showing a functional configuration of a dispersion compensation apparatus according to Embodiment 1 of the present invention.
In FIG. 1, this dispersion compensation apparatus includes a variable dispersion compensator (variable dispersion compensation means) 2, an optical receiver 3, an FEC (Forward Error Correction) decoder / code error information monitor (error detection means) 4, and a control circuit. (Control means) 5 is provided.
The tunable dispersion compensator 2 receives an optical signal transmitted from the transmission side via the optical fiber transmission line 1. This optical signal is a signal optically modulated on the transmission side by transmission data encoded with an FEC error correction code. The tunable dispersion compensator 2 performs tunable dispersion compensation, which will be described later, on the input optical signal and outputs it to the optical receiver 3. In the optical receiver 3, the optical signal compensated by the tunable dispersion compensator 2 is converted into an electrical signal, identification reproduction is performed by a known process, and the identified frame signal is sent to the FEC decoder / code error information monitor 4. Output. In the FEC decoder / symbol error information monitor 4, the FEC decoder function is used to perform error detection and error correction and error correction for the client signal by decomposing the frame signal identified and reproduced in the previous stage. At that time, the error information monitor acquires the number of error corrections, which is one of transmission error information, by the bit error count function and outputs it to the control circuit 5. The number of error corrections corresponds to the number of errors before error correction.

制御回路５では、光受信器３、ＦＥＣ復号化器／符号誤り情報モニタ４のそれぞれから制御に用いる誤り訂正個数の情報を収集し、それらの情報に基づいて可変分散補償器２は光ファイバ伝送路１の伝送距離を制限するパラメータを調整する。このことにより、光信号が光ファイバ伝送路１や可変分散補償器２の特性で受けた波長分散の逆特性（波長分散の補償量）を入力光信号に与えることにより、光信号が光ファイバ伝送路１の波長分散によって受けた波形歪みを補償する。
ここで、可変分散補償器２で作り出す波長分散の補償量は、光ファイバ伝送路１が有する波長分散に応じて自由に可変できるものである。その結果、光ファイバ伝送路１の波長分散が応力や環境温度変化などによって変化した場合でも、可変分散補償器２で作り出す逆特性の波長分散特性、すなわち波長分散の補償量を制御して最適な分散補償を可能にする。
なお、可変分散補償器２が調整する光ファイバ伝送路１の伝送距離を制限するパラメータとしては、光ファイバ伝送路の波長分散の他に、例えば偏波モード分散、偏波依存性損失、非線形光学、送信光信号の状態（信号レベル、消光比、チャーピング等）などが挙げられる。 The control circuit 5 collects information on the number of error corrections used for control from the optical receiver 3 and the FEC decoder / code error information monitor 4, and the tunable dispersion compensator 2 transmits the optical fiber based on the information. A parameter that limits the transmission distance of the path 1 is adjusted. As a result, the optical signal is transmitted through the optical fiber by giving the input optical signal an inverse characteristic of chromatic dispersion (amount of compensation for chromatic dispersion) that the optical signal received by the characteristics of the optical fiber transmission line 1 and the variable dispersion compensator 2. The waveform distortion received by the chromatic dispersion of the path 1 is compensated.
Here, the compensation amount of the chromatic dispersion created by the tunable dispersion compensator 2 can be freely varied according to the chromatic dispersion of the optical fiber transmission line 1. As a result, even when the chromatic dispersion of the optical fiber transmission line 1 changes due to stress, environmental temperature change, or the like, the chromatic dispersion characteristic of the reverse characteristic created by the tunable dispersion compensator 2, that is, the compensation amount of chromatic dispersion is controlled to be optimal Allows dispersion compensation.
Parameters that limit the transmission distance of the optical fiber transmission line 1 adjusted by the tunable dispersion compensator 2 include, for example, polarization mode dispersion, polarization dependent loss, and nonlinear optics in addition to the chromatic dispersion of the optical fiber transmission line. And the state of the transmitted optical signal (signal level, extinction ratio, chirping, etc.).

次に、この実施の形態１による分散補償装置の動作について説明する。
上述したように、制御回路５には、ＦＥＣ復号化器／符号誤り情報モニタ４で得られた誤り訂正個数が伝送誤り情報として入力されるが、この誤り訂正個数に基づいて伝送誤りが小さくなるように可変分散補償器２の波長分散の補償量を制御し、誤り訂正個数が規定値以下になった時点で可変分散補償器２が用いる波長分散の補償量を固定する。
図２は、制御回路５による可変分散補償器２に対する制御アルゴリズムを示すフローチャートで、図２（ａ）は制御回路５のメインルーチンである。また、図３は、この実施の形態１に係る分散補償量制御の方法を示す説明図である。
定常時において誤り率の小さな領域では、不必要に可変分散補償器２の波長分散の補償量を変化させて伝送誤りを増加させることがないように現状の符号誤り率を確認し（ステップＳＴ１）、閾値Ａ以下の誤り率であるかの判定を行う（ステップＳＴ２）。符号誤り率が所定の閾値Ａ以下の誤り率であればその設定値を維持する。 Next, the operation of the dispersion compensation apparatus according to the first embodiment will be described.
As described above, the number of error corrections obtained by the FEC decoder / code error information monitor 4 is input to the control circuit 5 as transmission error information, but the transmission error is reduced based on the number of error corrections. Thus, the compensation amount of the chromatic dispersion of the tunable dispersion compensator 2 is controlled, and the compensation amount of the chromatic dispersion used by the tunable dispersion compensator 2 is fixed when the number of error corrections becomes equal to or less than the specified value.
FIG. 2 is a flowchart showing a control algorithm for the tunable dispersion compensator 2 by the control circuit 5, and FIG. 2A is a main routine of the control circuit 5. FIG. 3 is an explanatory diagram showing a dispersion compensation amount control method according to the first embodiment.
In a region where the error rate is small at regular times, the current code error rate is checked so as not to increase the transmission error by unnecessarily changing the compensation amount of the chromatic dispersion of the tunable dispersion compensator 2 (step ST1). Then, it is determined whether the error rate is equal to or less than the threshold A (step ST2). If the code error rate is an error rate below a predetermined threshold A, the set value is maintained.

ステップＳＴ２において、現在の符号誤り率が閾値Ａより高くＦＥＣでの誤り訂正能力の限界を超えるような値である領域では、波長分散の補償量が大幅に適正値からずれていると考えられるため、図２（ｂ）に示す初期設定の処理を行う（ステップＳＴ５）。まず、可変分散補償器２が可変できる全補償量範囲を掃引し（ステップＳＴ４１）、符号誤り率が閾値Ａ以下となる点があるかどうかを判定する（ステップＳＴ４２）。符号誤り率が閾値Ａ以下で無ければ波長分散の補償量を掃引前の値に戻して処理を終了する（ステップＳＴ４３）。一方、ステップＳＴ４２において、符号誤り率が閾値Ａ以下となる点が発見できた場合、波長分散の補償量を符号誤り率が最小となる点に設定し（ステップＳＴ４４）、図２（ａ）のメインルーチンへ戻る。   In step ST2, in the region where the current code error rate is higher than the threshold value A and exceeds the limit of the error correction capability in FEC, it is considered that the compensation amount of chromatic dispersion is significantly deviated from the appropriate value. Then, the initial setting process shown in FIG. 2B is performed (step ST5). First, the entire compensation amount range that can be varied by the tunable dispersion compensator 2 is swept (step ST41), and it is determined whether or not there is a point where the code error rate is equal to or less than the threshold A (step ST42). If the code error rate is not less than or equal to the threshold A, the chromatic dispersion compensation amount is returned to the value before the sweep, and the process is terminated (step ST43). On the other hand, when a point where the code error rate is equal to or lower than the threshold A can be found in step ST42, the compensation amount of chromatic dispersion is set to a point where the code error rate is minimized (step ST44), and FIG. Return to the main routine.

次に、ステップＳＴ２において符号誤り率が閾値Ａ以下である場合、その誤り率がさらに設けた閾値Ｂ（＜Ａ）以下となる点が存在するかを判定する（ステップＳＴ３）。ＦＥＣ訂正能力の許容範囲内だが、符号誤り率が比較的高い領域であると判定された場合、すなわちＢ＜ＢＥＲ＜Ａにある場合、図２（ｃ）に示す運用制御を行う（ステップＳＴ４）。
運用制御（ステップＳＴ４）においては、波長分散の補償量の最適点を探索する際に、エラー訂正限界となるような符号誤り率の閾値を越えて、受信データでのエラー発生、さらにはサービス中断といった事態を起こさぬよう、波長分散の補償量の掃引に伴う符号誤り率の変化が悪化傾向となった場合は掃引を中止し、直前の、波長分散の補償量の地点を最適値とする。そのため、可変分散補償器２の波長分散の補償量をある方向へ移動させる（ステップＳＴ５１）。その結果、符号誤り率が改善されたかどうかを判定する（ステップＳＴ５２）。符号誤り率が減少している場合、ステップＳＴ５１に戻り、同じ方向へ波長分散の補償量を再び変化させ、より符号誤り率の低い点を探索する。また、ステップＳＴ５２で符号誤り率が増加したと判定された場合には、符号誤り率が、ある一定の閾値Ｂ以下に収まっているかの判定を行い（ステップＳＴ５３）、収まっていた場合、ステップＳＴ５１に戻り、引き続き同方向へ波長分散の補償量を変化させて符号誤り率の変化を見る。これにより、受信データでのエラー発生あるいはサービスの停止を起こさない範囲での符号誤り率の悪化（閾値Ｂとする）を許容して、符号誤り率が増加する傾向となる方向へも波長分散の補償量を変化させることで、局所的な符号誤り率の極小点にとらわれることなく、真の最適な分散補償点を発見でき、精度の良い分散補償を行うことができる。 Next, when the code error rate is equal to or less than the threshold value A in step ST2, it is determined whether or not there is a point where the error rate is equal to or less than the provided threshold value B (<A) (step ST3). If it is determined that the FEC correction capability is within the allowable range but the code error rate is relatively high, that is, if B <BER <A, operation control shown in FIG. 2C is performed (step ST4). .
In the operation control (step ST4), when searching for the optimum point of the chromatic dispersion compensation amount, an error occurs in the received data exceeding the threshold of the code error rate that becomes the error correction limit, and further, the service is interrupted. In order to prevent such a situation, when the change of the code error rate accompanying the sweep of the chromatic dispersion compensation amount tends to deteriorate, the sweep is stopped, and the point of the chromatic dispersion compensation amount immediately before is made the optimum value. Therefore, the chromatic dispersion compensation amount of the tunable dispersion compensator 2 is moved in a certain direction (step ST51). As a result, it is determined whether or not the code error rate has been improved (step ST52). If the code error rate is decreasing, the process returns to step ST51, the chromatic dispersion compensation amount is changed again in the same direction, and a point with a lower code error rate is searched. If it is determined in step ST52 that the code error rate has increased, it is determined whether the code error rate is below a certain threshold B (step ST53). Returning to FIG. 3, the change in the chromatic dispersion is changed in the same direction, and the change in the code error rate is observed. As a result, the chromatic dispersion is also improved in a direction in which the code error rate tends to increase by allowing the deterioration of the code error rate (threshold B) within the range where no error occurs in the received data or the service is stopped. By changing the compensation amount, the true optimum dispersion compensation point can be found without being caught by the local minimum point of the code error rate, and accurate dispersion compensation can be performed.

一方、ステップＳＴ５３において、符号誤り率が閾値Ｂを超えたと判定された場合、分散補償量の変更方向の反転処理の有無を判定し（ステップＳＴ５４）、未だ反転処理をいていない場合には、可変分散補償器２の波長分散の補償量の変更方向を反転させ（ステップＳＴ５６）、再び前述のステップＳＴ５１〜ＳＴ５３の処理を行う。なお、ステップＳＴ５４において、１度反転も行った上で閾値Ｂ以下の範囲を探索したと判断された場合は、この運用制御の処理中で符号誤り率が最小となった点へ波長分散の補償量を設定して処理を終了する（ステップＳＴ５５）。
制御回路５は、ある閾値以下を達成した時点での掃引中止、あるいは符号誤り率が増加に転じた時点での掃引中止という従来のような処理は行わず、図３に示すように、エラーを発生させない範囲での符号誤り率の劣化を許容し、最適な分散補償点と思われる近傍を掃引することにより、局所的な符号誤り率の極小点にとらわれることなく、真に最適な分散補償点を発見できるようにしたので、精度の良い分散補償を行うことができる。 On the other hand, if it is determined in step ST53 that the code error rate has exceeded the threshold value B, it is determined whether or not the dispersion compensation amount changing direction is reversed (step ST54). The direction of changing the compensation amount of chromatic dispersion of the dispersion compensator 2 is reversed (step ST56), and the processes of steps ST51 to ST53 described above are performed again. If it is determined in step ST54 that a range equal to or smaller than the threshold value B has been searched after performing inversion once, the chromatic dispersion compensation is made to the point where the code error rate is minimized during the operation control process. The amount is set and the process is terminated (step ST55).
The control circuit 5 does not perform a conventional process of canceling the sweep when it reaches a certain threshold or less, or stopping the sweep when the code error rate starts to increase, as shown in FIG. By allowing the degradation of the code error rate in the range where it does not occur and sweeping the neighborhood that seems to be the optimal dispersion compensation point, the truly optimal dispersion compensation point is not caught by the local minimum point of the code error rate. Therefore, it is possible to perform dispersion compensation with high accuracy.

以上のように、この実施の形態１によれば、制御回路（制御手段）５が、初期設定時に、可変分散補償器（可変分散補償手段）２における波長分散の補償量を予め設定した範囲で掃引して、ＦＥＣ復号化器／符号誤り情報モニタ（誤り検出手段）４で検出された誤り訂正個数を基に判断した符号誤り率が最も少なくなる点に波長分散の補償量を設定し、運用時には、ＦＥＣ復号化器／符号誤り情報モニタ（誤り検出手段）４で検出された誤り訂正個数を基に判断した符号誤り率が予め設定した閾値Ａ以上になった場合には波長分散の補償量を符号誤り率が減少する方向に変化させて符号誤り率が最初に最も少なくなる点に再設定し、その際にある閾値Ｂ（＜Ａ）以下であれば一時的な若干の符号誤り劣化を許容して、符号誤り率の極小値に陥ることなく符号誤り率が最小値となる点を探索し、最小値となる点があった場合に当該点に波長分散の補償量を再々設定するようにしている。したがって、最適な分散補償点がある場合には、その前にある局所的な符号誤り率の極小値で分散補償制御を終了させることなく探索を行って、真に最適な波長分散の補償量を設定するようにしたので、符号誤り率が真に最小となる状態での光通信を可能にする。また、インサービス中に光伝送路の分散値が変動した場合、最適な波長分散の補償量を求めて可変分散補償器が変動可能な波長分散の補償量の全範囲を掃引すると、最適な分散補償点の探索に時間がかかるほか、波長分散の補償量を変化させることによる符号誤り率の悪化により回線断等の影響が出てしまうが、この実施の形態１の場合は、最適な分散補償点と思われる近傍を掃引するので探索時間や回線断に影響を及ぼすことは回避できる。   As described above, according to the first embodiment, the control circuit (control means) 5 is within a range in which the compensation amount of chromatic dispersion in the tunable dispersion compensator (variable dispersion compensation means) 2 is set in advance at the time of initial setting. Sweep and set the amount of chromatic dispersion compensation at the point where the code error rate judged based on the number of error corrections detected by the FEC decoder / code error information monitor (error detection means) 4 is minimized Sometimes, the amount of chromatic dispersion compensation when the code error rate determined based on the number of error corrections detected by the FEC decoder / code error information monitor (error detection means) 4 exceeds a preset threshold A. Is changed to a direction in which the code error rate decreases, and the code error rate is reset to the lowest point first, and if the threshold value B (<A) is not exceeded, temporary slight code error degradation is caused. Allow and fall into minimum value of code error rate Bit error rate is to explore the point having the minimum value, re-re set the compensation amount of chromatic dispersion to the point when there is a point having the minimum value without. Therefore, if there is an optimum dispersion compensation point, a search is performed without ending dispersion compensation control at the local minimum local code error rate, and a truly optimum chromatic dispersion compensation amount is obtained. Since it is set, optical communication is enabled in a state where the code error rate is truly minimized. If the dispersion value of the optical transmission line fluctuates during in-service, the optimum dispersion can be obtained by obtaining the optimum compensation amount of chromatic dispersion and sweeping the entire range of compensation amount of chromatic dispersion that the variable dispersion compensator can vary. In addition to the time required for searching for a compensation point, the code error rate is deteriorated by changing the compensation amount of chromatic dispersion, which may cause an effect such as line disconnection. In the case of the first embodiment, optimum dispersion compensation is performed. Since the neighborhood that seems to be a point is swept, it is possible to avoid affecting the search time and line disconnection.

実施の形態２．
図４は、この発明の実施の形態２である分散補償装置の機能構成を示すブロック図である。
この実施の形態２は、１本のファイバケーブル２１に異なる波長の光信号を重ねて伝送する光多重伝送システム、いわゆるＷＤＭ（Wavelength Division Multiplexing；波長分割多重）システムに上記実施の形態１の構成を適用したものである。ＷＤＭ通信システムは送信側の光合波器１２と受信側光分波器６は光ファイバで結ばれている。
周知のように、ｎ個のチャネルの情報は、それぞれ対応するＦＥＣ符号化器１０1 ，…，１０n でＦＥＣ符号化され、それぞれ対応する光通信機１１1 ，…，１１n に与えられて異なる波長の光信号に変換される。光合波器１２は、光通信機１１1 ，…，１２n で変換された各チャネルの光信号を合波して波長多重光信号を生成し、光ファイバ２１に入力して受信側に光伝送する。受信側の光分波器６では、光ファイバ２１から受信した波長多重光信号を各チャネルの波長の光信号に分波して取り出し、それぞれ対応するチャネルの可変分散補償器（可変分散補償手段）２1 ，…，２n に入力する。各チャネルにおいて、光受信器３1 ，…，３n 、ＦＥＣ復号化器／符号誤り情報モニタ（誤り検出手段）４1 ，…，４n の動作は実施の形態１のものと同様である。 Embodiment 2. FIG.
FIG. 4 is a block diagram showing a functional configuration of a dispersion compensation apparatus according to Embodiment 2 of the present invention.
In the second embodiment, the configuration of the first embodiment is applied to a so-called WDM (Wavelength Division Multiplexing) system in which optical signals of different wavelengths are transmitted by being superimposed on a single fiber cable 21. It is applied. In the WDM communication system, the transmission-side optical multiplexer 12 and the reception-side optical demultiplexer 6 are connected by an optical fiber.
As is well known, information of n channels, FEC encoder 10 1 corresponding, ..., are FEC encoded by 10 n, the corresponding optical transceiver 11 1, ..., given the 11 n It is converted into an optical signal of a different wavelength. The optical multiplexer 12 multiplexes the optical signals of the respective channels converted by the optical communication devices 11 1 ,..., 12 n to generate a wavelength multiplexed optical signal, and inputs it to the optical fiber 21 for optical transmission to the receiving side. To do. In the optical demultiplexer 6 on the receiving side, the wavelength multiplexed optical signal received from the optical fiber 21 is demultiplexed into optical signals having the wavelengths of the respective channels, and the variable dispersion compensators (variable dispersion compensating means) of the corresponding channels are extracted. Input to 2 1 ,..., 2 n . In each channel, the optical receiver 3 1, ..., 3 n, FEC decoder / code error information monitor (error detecting means) 4 1, ..., 4 n operation is the same as that of the first embodiment.

可変分散補償器２1 ，…，２n の分散補償量を制御する制御回路（制御手段）５は各チャネルで共用できるように設けられている。制御回路５では、ＦＥＣ復号化器／符号誤り情報モニタ４1 ，…，４n から得られる誤り訂正個数の情報を用いて、より伝送誤りが小さくなるように、実施の形態１と同様な方法により、各可変分散補償器２1 ，…，２n を制御する。この場合の制御では、例えば、初期設定時には、最適化制御を行う可変分散補償器２1 ，…，２n を順次切り替えるようにし、該当するチャネルの誤り訂正個数に基づいてそれぞれ対応する可変分散補償器の設定を行うようにする。一方、サービス運用時には、すべてのチャネルについて誤り訂正個数をＦＥＣ復号化器／符号誤り情報モニタ４1 ，…，４n で常時モニタし、再設定動作開始閾値を超える符号誤り率が発生したチャネルに対応する可変分散補償器について、実施の形態１と同様な方法で波長分散の補償量の最適制御を行うようにする。また、複数のチャネルの誤り率が同時に再設定動作開始閾値を超えた場合には、符号誤り率のより高いチャネルに対応する可変分散補償器について優先的に最適制御を行うようにする。
なお、上記動作において、制御回路５が行っている制御対象とするチャネルの選択処理は、例えば特許文献３に開示されている例などを用いて行えばよい。 A control circuit (control means) 5 for controlling the dispersion compensation amount of the variable dispersion compensators 2 1 ,..., 2 n is provided so as to be shared by each channel. In the control circuit 5, FEC decoder / code error information monitor 4 1, ..., 4 by using the information of the number of error corrections obtained from n, as more transmission errors is reduced, the same as the first embodiment method Thus, the variable dispersion compensators 2 1 ,..., 2 n are controlled. The control of the case, for example, the initial setting, variable dispersion compensator 2 1 for optimizing control, ..., to sequentially switched as the 2 n, the corresponding variable dispersion compensation corresponding respectively based on the number of error corrections of the channel Set the instrument. On the other hand, during service operation, all channels FEC decoder / code error information monitor 4 1 error correction number for, ..., and constantly monitored by 4 n, the channel bit error rate exceeding the re-setting operation start threshold has occurred For the corresponding tunable dispersion compensator, optimal control of the compensation amount of chromatic dispersion is performed in the same manner as in the first embodiment. In addition, when the error rates of a plurality of channels simultaneously exceed the resetting operation start threshold, optimal control is preferentially performed for the variable dispersion compensator corresponding to the channel with a higher code error rate.
In the above operation, the selection process of the channel to be controlled performed by the control circuit 5 may be performed using, for example, the example disclosed in Patent Document 3.

以上のように、この実施の形態２によれば、ＷＤＭシステムについても、各波長のチャネルにそれぞれ対応させて可変分散補償器２1 ，…，２n を設け、一つの制御回路５により、各可変分散補償器の波長分散の補償量を、ＦＥＣ復号化器／符号誤り情報モニタ４1 ，…，４n の各々の伝送誤り情報に基づいて一括して行うようにしたので、各チャネルの波長分散および偏波分散に伴う波形劣化を自動的に補償可能となる。これにより、分散補償部分のサイズおよびコストを大幅に軽減できるようになる。 As described above, according to the second embodiment, the WDM system is also provided with the variable dispersion compensators 2 1 ,..., 2 n corresponding to the channels of the respective wavelengths. Since the chromatic dispersion compensation amount of the tunable dispersion compensator is collectively performed based on the transmission error information of each of the FEC decoder / code error information monitors 4 1 ,..., 4 n , the wavelength of each channel Waveform deterioration due to dispersion and polarization dispersion can be automatically compensated. As a result, the size and cost of the dispersion compensation portion can be greatly reduced.

実施の形態３．
図５は、この発明の実施の形態３である分散補償装置の機能構成を示すブロック図である。
この実施の形態３では、上記実施の形態１で述べた構成に加え、光伝送システムの送信側にも可変波長分散補償器（第２の可変分散補償手段）２２と制御回路（第２の制御手段）２５を設けている。
受信側のＦＥＣ復号化器／符号誤り情報モニタ４で得られる誤り訂正個数の情報は、実施の形態１で説明した制御回路５に与えられるが、さらに監視制御系を介して伝送され、送信側の制御回路２５にも与えられる。可変分散補償器２２の波長分散の補償量は、受信側のＦＥＣ復号化器／符号誤り情報モニタ４から送られてくる誤り訂正個数の情報に従い受信側の分散補償状態に応じて随時制御される。この場合の制御回路２５による可変分散補償器２２の波長分散の補償量の制御方法は、実施の形態１で述べた受信側の制御回路５と同様な方法で行われる。
この光伝送システムの場合は、受信側の可変分散補償器２における波長分散の補償量との組み合わせにより光波形の劣化が最も小さくなるように、送信側の光送信機１１の出力段に設けられた可変分散補償器２２の波長分散の補償量が設定される。 Embodiment 3 FIG.
FIG. 5 is a block diagram showing a functional configuration of a dispersion compensation apparatus according to Embodiment 3 of the present invention.
In the third embodiment, in addition to the configuration described in the first embodiment, a variable wavelength dispersion compensator (second variable dispersion compensation means) 22 and a control circuit (second control) are also provided on the transmission side of the optical transmission system. Means) 25 is provided.
The information on the number of error corrections obtained by the FEC decoder / code error information monitor 4 on the reception side is given to the control circuit 5 described in the first embodiment, but is further transmitted via the monitoring control system, and is transmitted to the transmission side. The control circuit 25 is also provided. The compensation amount of the chromatic dispersion of the tunable dispersion compensator 22 is controlled at any time according to the dispersion compensation state on the receiving side according to the information on the number of error corrections sent from the FEC decoder / code error information monitor 4 on the receiving side. . In this case, the control method of the compensation amount of the chromatic dispersion of the tunable dispersion compensator 22 by the control circuit 25 is performed by the same method as the control circuit 5 on the receiving side described in the first embodiment.
In the case of this optical transmission system, it is provided at the output stage of the optical transmitter 11 on the transmission side so that the degradation of the optical waveform is minimized by the combination with the compensation amount of the chromatic dispersion in the variable dispersion compensator 2 on the reception side. The compensation amount of chromatic dispersion of the tunable dispersion compensator 22 is set.

以上のように、この実施の形態３によれば、波長分散に伴う光信号波形の劣化が、受信側だけでなく送信側でも補償できるようにしたことで、より広い範囲の分散補償が可能になる。
なお、この実施の形態３では、単一波長の光信号が伝送される光伝送システムに適用した例について示したが、実施の形態２に挙げたＷＤＭ伝送システムの例で、送信側にも制御回路２５と各チャネルの可変分散補償器を設け、制御回路２５によりそれぞれの可変分散補償器の波長分散の補償量を実施の形態２と同様に一括制御するようにしてもよい。 As described above, according to the third embodiment, since the deterioration of the optical signal waveform due to chromatic dispersion can be compensated not only on the reception side but also on the transmission side, dispersion compensation in a wider range is possible. Become.
In the third embodiment, an example in which the present invention is applied to an optical transmission system in which an optical signal having a single wavelength is transmitted has been described. However, in the example of the WDM transmission system described in the second embodiment, the transmission side is also controlled. A circuit 25 and a tunable dispersion compensator for each channel may be provided, and the control circuit 25 may collectively control the chromatic dispersion compensation amount of each tunable dispersion compensator as in the second embodiment.

この発明の実施の形態１である分散補償装置の機能構成を示すブロック図である。It is a block diagram which shows the function structure of the dispersion compensation apparatus which is Embodiment 1 of this invention. この発明の実施の形態１に係る制御回路による分散補償器に対する制御アルゴリズムを示すフローチャートである。It is a flowchart which shows the control algorithm with respect to the dispersion compensator by the control circuit which concerns on Embodiment 1 of this invention. この発明の実施の形態１に係る分散補償量制御の方法を示す説明図である。It is explanatory drawing which shows the method of the dispersion compensation amount control which concerns on Embodiment 1 of this invention. この発明の実施の形態２である分散補償装置の機能構成を表すブロック図である。It is a block diagram showing the function structure of the dispersion compensation apparatus which is Embodiment 2 of this invention. この発明の実施の形態３である分散補償装置の機能構成を表すブロック図である。It is a block diagram showing the function structure of the dispersion compensation apparatus which is Embodiment 3 of this invention. 残留分散値に対する符号誤り率の関係を表す説明図である。It is explanatory drawing showing the relationship of the code error rate with respect to a residual dispersion value. 符号誤り率を利用して分散補償の最適化を行う従来の方法を示す説明図である。It is explanatory drawing which shows the conventional method of optimizing dispersion compensation using a code error rate. 極小値を持つ場合の分散値と符号誤り率の関係を示す説明図である。It is explanatory drawing which shows the relationship between the variance value in the case of having a minimum value, and a code error rate.

符号の説明Explanation of symbols

１，２１ 光ファイバ伝送路、２，２1 ，…，２n 可変分散補償器、３，３1 ，…，３n 光受信器、４，４1 ，…，４n ＦＥＣ復号化器／符号誤り情報モニタ、５，２５ 制御回路、６ 光分波器、１０，１０1 ，…，１０n， ＦＥＣ符号化器、１１，１１1 ，…，１１n 光送信機、１２ 光合波器。 1, 21 optical fiber transmission line, 2, 2 1 ,..., 2 n tunable dispersion compensator, 3, 3 1 ,..., 3 n optical receiver, 4, 4 1 , ..., 4 n FEC decoder / code Error information monitor, 5, 25 control circuit, 6 optical demultiplexer, 10, 10 1 ,..., 10 n , FEC encoder, 11, 11 1 ,..., 11 n optical transmitter, 12 optical multiplexer.

Claims (3)

誤り訂正符号で符号化され、光ファイバ伝送路を伝送された光信号の誤り訂正符号による誤り訂正個数を検出する誤り検出手段と、
前記誤り検出手段の前段に設けられ、波長分散の補償量を変更しながら前記光ファイバ伝送路の波長分散を補償する可変分散補償手段と、
前記可変分散補償手段に対して、前記誤り検出手段で検出された誤り訂正個数の変動に基づいて最適分散補償制御を行う制御手段を備えた分散補償装置において、
前記制御手段は、
初期設定時には、前記可変分散補償手段における波長分散の補償量を予め設定した範囲で掃引して、前記誤り検出手段で検出された誤り訂正個数を基に判断した符号誤り率が最も少なくなる点に波長分散の補償量を設定し、
運用時には、前記誤り検出手段で検出された誤り訂正個数を基に判断した符号誤り率が予め設定した閾値Ａ以上になった場合には波長分散の補償量を符号誤り率が減少する方向に変化させて符号誤り率が最初に最も少なくなる点に再設定し、その際にある閾値Ｂ（＜Ａ）以下であれば、一時的な若干の符号誤り劣化を許容して符号誤り率の極小値に陥ることなく最小値となる点を探索し、最小値となる点があった場合に当該点に波長分散の補償量を再々設定することを特徴とする分散補償装置。 An error detection means for detecting the number of error corrections by an error correction code of an optical signal encoded with an error correction code and transmitted through an optical fiber transmission line;
Variable dispersion compensation means provided in the preceding stage of the error detection means, for compensating the chromatic dispersion of the optical fiber transmission line while changing the compensation amount of chromatic dispersion,
In the dispersion compensation apparatus comprising control means for performing optimal dispersion compensation control on the basis of variation in the number of error corrections detected by the error detection means with respect to the variable dispersion compensation means,
The control means includes
At the initial setting, the chromatic dispersion compensation amount in the tunable dispersion compensation unit is swept within a preset range, and the code error rate determined based on the number of error corrections detected by the error detection unit is minimized. Set the amount of chromatic dispersion compensation,
During operation, when the code error rate determined based on the number of error corrections detected by the error detection means is greater than or equal to a preset threshold A, the chromatic dispersion compensation amount is changed in a direction in which the code error rate decreases. Then, the code error rate is reset to the lowest point first, and if it is less than a certain threshold B (<A) at that time, a slight code error deterioration is allowed and a minimum value of the code error rate is allowed. A dispersion compensation device that searches for a point that has a minimum value without falling into the range and sets a compensation amount of chromatic dispersion again at that point when there is a point that has the minimum value. 光ファイバ伝送路を介して入力される光信号が、波長の異なる複数のチャネル光を含んだ波長多重光信号である場合、制御手段は、分波された各チャネルの波長の光信号にそれぞれ対応して設けられた可変分散補償手段の波長分散の補償量の制御を一括して行うことを特徴とする請求項１記載の分散補償装置。   If the optical signal input via the optical fiber transmission line is a wavelength multiplexed optical signal containing multiple channel lights with different wavelengths, the control means will respond to the optical signals of each demultiplexed wavelength. 2. The dispersion compensation apparatus according to claim 1, wherein the chromatic dispersion compensation amount of the tunable dispersion compensation means provided in a controlled manner is collectively controlled. 光伝送システムの送信側の光送信機の出力段に設けられ、波長分散の補償量を変更しながら光ファイバ伝送路の波長分散を補償する第２の可変分散補償手段と、
前記光送信機の出力側に設けられ、誤り検出手段から監視制御系を介して伝送された誤り訂正個数の変動に基づいて、受信側の制御手段と同様な方法により前記第２の可変分散補償手段に対して最適分散補償制御を行う第２の制御手段を備えたことを特徴とする請求項１記載の分散補償装置。 A second variable dispersion compensation means provided at the output stage of the optical transmitter on the transmission side of the optical transmission system, for compensating the chromatic dispersion of the optical fiber transmission line while changing the compensation amount of the chromatic dispersion;
The second variable dispersion compensation is provided on the output side of the optical transmitter, based on the variation in the number of error corrections transmitted from the error detection means via the supervisory control system, in the same manner as the control means on the reception side. 2. The dispersion compensation apparatus according to claim 1, further comprising second control means for performing optimum dispersion compensation control on the means.
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