JP2009296290A - Pmd compensator - Google Patents

Pmd compensator Download PDF

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JP2009296290A
JP2009296290A JP2008147691A JP2008147691A JP2009296290A JP 2009296290 A JP2009296290 A JP 2009296290A JP 2008147691 A JP2008147691 A JP 2008147691A JP 2008147691 A JP2008147691 A JP 2008147691A JP 2009296290 A JP2009296290 A JP 2009296290A
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pmd
optical fiber
optical
path
dop
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Takeshi Kawasaki
岳 川崎
Toshiya Matsuda
俊哉 松田
Akira Naga
明 那賀
Shinji Matsuoka
伸治 松岡
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Nippon Telegraph and Telephone Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To adaptively control EDC based on an optical fiber DGD value that is estimated from a received optical signal DOP and stably compensate waveform degradation by PMD for a long period. <P>SOLUTION: A PMD compensator inputs optical signals that transmit on an optical fiber transmission path and are waveform degraded by PMD, converts them to electric signals and compensates the waveform degradation using EDC. The PMD compensator has one EDC which has PMD compensation characteristics based on a differential group delay DGD of the optical fiber transmission path, or two or more EDCs, the PMD compensation characteristics of which are different from each other, a path to output electric signals without passing through the EDC, a path selection means for selecting a path to output electric signals with passing either one of the EDCs, and a control means for monitoring the polarized DOP of optical signals and generating control signals for path selection of the path selection means to control the path selection means so that the optimum PMD compensation characteristics are achieved based on the differential group delay DGD value of an optical fiber transmission path to the polarized DOP. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

本発明は、光伝送システムにおいて、光ファイバ伝送路の偏波モード分散（Polarization Mode Dispersion：ＰＭＤ) に起因する波形劣化を補償するＰＭＤ補償装置に関する。   The present invention relates to a PMD compensation device that compensates for waveform degradation caused by polarization mode dispersion (PMD) in an optical fiber transmission line in an optical transmission system.

波長多重光伝送システムは、１本の光ファイバに複数の波長を多重して伝送する。伝送容量を向上させるためにはより多くの波長を多重する必要があり、広帯域の中でより均一で安定した伝送品質を保つことが不可欠である。伝送品質を制限する要因の一つとして光ファイバのＰＭＤがあり、特に伝送速度が40Gbit/s以上の高速な光伝送システムでは、このＰＭＤをいかに補償できるかが重要な課題となっている。   The wavelength division multiplexing optical transmission system multiplexes and transmits a plurality of wavelengths on one optical fiber. In order to improve the transmission capacity, it is necessary to multiplex more wavelengths, and it is indispensable to maintain more uniform and stable transmission quality in a wide band. One of the factors that limit transmission quality is PMD of an optical fiber. Particularly in a high-speed optical transmission system with a transmission speed of 40 Gbit / s or more, how to compensate for this PMD is an important issue.

ＰＭＤは、光ファイバへの入射偏波の状態によって伝搬速度が異なる現象で、光ファイバの複屈折特性に起因するものである。理想的な光ファイバコアは完全な円心構造をしており複屈折は生じない。しかし、光ファイバの製造過程や、光ファイバの敷設条件による曲げや張力など、種々の応力が加わることにより光ファイバコアの円心構造が崩れると、偏波モードの縮退が解けてＰＭＤが生じる。ＰＭＤの大きさは上記の条件によって大きく左右されるが、一般的にファイバ長に依存する。   PMD is a phenomenon in which the propagation speed varies depending on the state of polarized light incident on the optical fiber, and is caused by the birefringence characteristics of the optical fiber. An ideal optical fiber core has a perfect center structure, and birefringence does not occur. However, when the core structure of the optical fiber core is broken by applying various stresses such as bending and tension depending on the optical fiber manufacturing process and the optical fiber laying condition, the degeneration of the polarization mode is solved and PMD is generated. The size of PMD greatly depends on the above conditions, but generally depends on the fiber length.

ＰＭＤの大きさを示す指標として、群遅延差（Differential Group Delay：ＤＧＤ）がある。ＤＧＤは、直交する２つの偏波状態の伝搬遅延差に相当し、図５に示すように、波長ごとに異なる値をとるとともに時間的にもランダムに変動する。図５では、測定期間約１ヶ月の間に、波長1570ｎｍと波長1610ｎｍにおけるＤＧＤがそれぞれランダムに変動する様子を示す。   As an index indicating the size of PMD, there is a differential group delay (DGD). DGD corresponds to a propagation delay difference between two orthogonal polarization states, and takes a different value for each wavelength and randomly varies with time as shown in FIG. FIG. 5 shows how the DGD at the wavelength of 1570 nm and the wavelength of 1610 nm fluctuate randomly during the measurement period of about one month.

一般的に、光ファイバについて全波長帯域に渡ってＤＧＤ値をサンプリングした場合、ＤＧＤ値の分布はマクスウェル分布に従うことが知られている。ここで、ＤＧＤ値の分布の平均をＰＭＤ値と呼ぶ。したがって、ＰＭＤ値が大きい光ファイバほど大きなＤＧＤ値をとる確率が高く、かつＤＧＤ値の変動幅が大きくなる確率が高い。   In general, when DGD values are sampled over the entire wavelength band for an optical fiber, it is known that the distribution of DGD values follows the Maxwell distribution. Here, the average of the distribution of DGD values is referred to as PMD value. Therefore, an optical fiber having a larger PMD value has a higher probability of taking a larger DGD value, and has a higher probability of increasing the fluctuation range of the DGD value.

ここで、光ファイバのＤＧＤの測定（推定）方法について説明する（非特許文献１）。まず、光ファイバを伝搬した光信号の各偏光成分の光強度を検出してストークスパラメータを測定し、さらにストークスパラメータから光信号の偏光度（Degree of Polarization：ＤＯＰ）を算出する。   Here, a method for measuring (estimating) DGD of an optical fiber will be described (Non-Patent Document 1). First, the Stokes parameter is measured by detecting the light intensity of each polarization component of the optical signal propagated through the optical fiber, and the degree of polarization of the optical signal (Degree of Polarization: DOP) is calculated from the Stokes parameter.

一般に、任意の偏波状態はストークスパラメータＳ0 ，Ｓ1 ，Ｓ2 ，Ｓ3 を用いて次式のように定義される。
Ｓ0 ＝Ｉ1＋Ｉ2
Ｓ1 ＝Ｉ1−Ｉ2
Ｓ2 ＝２Ｉ3 −（Ｉ1＋Ｉ2 ）
Ｓ3 ＝２Ｉ4 −（Ｉ1＋Ｉ2 ） In general, an arbitrary polarization state is defined as follows using Stokes parameters S 0 , S 1 , S 2 , S 3 .
S 0 = I 1 + I 2
S 1 = I 1 −I 2
S 2 = 2I 3 − (I 1 + I 2 )
S 3 = 2I 4 − (I 1 + I 2 )

ここで、Ｉ1 は０°直線偏光成分、Ｉ2 は90°直線偏光成分、Ｉ3 は45°直線偏光成分、Ｉ4 は右回り円偏光成分の各光強度を示し、これらを検出することによりストークスパラメータを測定することができる。ＤＯＰは、ストークスパラメータＳ0 ，Ｓ1 ，Ｓ2 ，Ｓ3 から次式のように算出することができる。
ＤＯＰ＝ (Ｓ1 2＋Ｓ2 2＋Ｓ3 2)1/2／Ｓ0 Where I 1 is a 0 ° linearly polarized light component, I 2 is a 90 ° linearly polarized light component, I 3 is a 45 ° linearly polarized light component, and I 4 is a clockwise circularly polarized light component. Can measure the Stokes parameters. The DOP can be calculated from the Stokes parameters S 0 , S 1 , S 2 , S 3 as follows:
DOP = (S 1 2 + S 2 2 + S 3 2 ) 1/2 / S 0

図６は、ＤＯＰ測定系の構成例を示す。
図において、入力光信号は、ビームスプリッタ（ＢＳ，ＰＢＳ）により４つの成分に分岐して各受光器４１−１〜４１−４に受光される。0 °直線偏光成分と90°直線偏光成分は、偏光ビームスプリッタ（ＰＢＳ）４２で互いに直交する直線偏光に分離して受光器４１−１，４１−２に受光される。45°直線偏光成分は、偏光子（ＰＯＬ）４３−１を通過して受光器４１−３に受光される。右回り円偏光成分は、１／４波長板（ＱＷ）４４および偏光子（ＰＯＬ）４３−２を通過して受光器４１−４に受光される。この４つの成分に対応する各受光器４１−１〜４１−４の出力Ｉ1 〜Ｉ4 は、Ａ／Ｄ変換器４５を介して演算部４６に入力し、上式に基づいてストークスパラメータが算出され、さらにＤＯＰ値が算出される。 FIG. 6 shows a configuration example of the DOP measurement system.
In the figure, an input optical signal is branched into four components by a beam splitter (BS, PBS) and received by each of the light receivers 41-1 to 41-4. The 0 ° linearly polarized light component and the 90 ° linearly polarized light component are separated into linearly polarized light orthogonal to each other by a polarization beam splitter (PBS) 42 and received by the light receivers 41-1 and 41-2. The 45 ° linearly polarized light component passes through the polarizer (POL) 43-1 and is received by the light receiver 41-3. The clockwise circularly polarized light component passes through the quarter wave plate (QW) 44 and the polarizer (POL) 43-2 and is received by the light receiver 41-4. The outputs I 1 to I 4 of the light receivers 41-1 to 41-4 corresponding to these four components are input to the calculation unit 46 via the A / D converter 45, and the Stokes parameter is calculated based on the above equation. And the DOP value is further calculated.

次に、ＤＯＰとＤＧＤ（ＰＭＤ）は、非特許文献１，２，３に示されるように相関関係があることが知られており、ＤＯＰの大きさからＤＧＤを推定することができる。   Next, it is known that DOP and DGD (PMD) have a correlation as shown in Non-Patent Documents 1, 2, and 3, and DGD can be estimated from the size of DOP.

図７は、光信号のＤＯＰと伝送品質（Ｑ値）との関係の実測値を示す。ＤＧＤが大きな光ファイバでは、偏波状態の変化によってＤＯＰが著しく変化する。伝送品質（Ｑ値）は、ＤＯＰの時間変化に追従するように変化していることがわかる。このことから、光信号のＤＯＰを正しくモニタすることができれば、光ファイバのＤＧＤによる伝送品質劣化を推定し、効果的なＰＭＤ補償を行うことが可能になる。   FIG. 7 shows measured values of the relationship between DOP of optical signals and transmission quality (Q value). In an optical fiber having a large DGD, the DOP changes significantly due to a change in the polarization state. It can be seen that the transmission quality (Q value) changes so as to follow the time change of DOP. Therefore, if the DOP of the optical signal can be correctly monitored, it is possible to estimate the transmission quality deterioration due to the DGD of the optical fiber and perform effective PMD compensation.

ＰＭＤ補償は、光ファイバのＤＧＤによって発生した波形劣化を補償することであるが、ＰＭＤ補償器としては、(1) 光学補償器、(2) 電気分散補償器（Electronic Dispersion Compensator ：ＥＤＣ）などがある。光学補償器は、光ファイバのＰＭＤを相殺するために、光ファイバと同等のＰＭＤ値をもつＰＭＤ媒質と、入力偏波を制御する偏波制御部からなり、偏波制御部の入力偏波状態を制御することにより光ファイバのＰＭＤを補償する。波長多重光伝送システムでは、このような光学補償器が波長数に応じて必要になることから、伝送装置の小型化および低コスト化の実現が困難である。一方、ＥＤＣは、光学補償器に比べて小型化および低コスト化が容易であることから、波長多重光伝送システムに適しているが、光学補償器に比べて補償範囲が狭い。   PMD compensation is to compensate for waveform degradation caused by DGD of optical fiber. PMD compensators include (1) optical compensator and (2) electric dispersion compensator (EDC). is there. The optical compensator includes a PMD medium having a PMD value equivalent to that of the optical fiber and a polarization controller for controlling the input polarization in order to cancel the PMD of the optical fiber, and the input polarization state of the polarization controller. The PMD of the optical fiber is compensated by controlling. In a wavelength division multiplexing optical transmission system, such an optical compensator is required according to the number of wavelengths, and thus it is difficult to realize downsizing and cost reduction of the transmission apparatus. On the other hand, EDC is suitable for wavelength multiplexing optical transmission systems because it can be easily reduced in size and cost as compared with an optical compensator, but its compensation range is narrower than that of an optical compensator.

図８は、ＥＤＣの構成例を示す。ここでは、ＦＦＥ（Feed-Forword Equalizer) による構成例を示す。図において、入力電気信号を複数の遅延回路９１を介して順次遅延させ、入力電気信号および各遅延回路の出力を加算回路９２で順次加算する構成である。加算回路９２におけるタップ係数を調整して加算の重み付けを行うことにより、波形を最適化することができる。
特開２００７−３２９５５８号公報 畑野達也、他、「高精度ＤＯＰ測定器の開発」、古河電工時報、第111 号、平成15年１月 Nobuhiko Kikuchi,"Analysis of Signal Degree of Polarization Degradation Used as Control Signal for Optical Polarization Mode Dispersion Compensation", J.Lightwave.Technol., Vol.19, No.4, April 2001 波平宜敬、「偏波モード分散の測定技術動向」、OPTRONICS(2003), No.10, pp.112-120 FIG. 8 shows a configuration example of EDC. Here, a configuration example by FFE (Feed-Forword Equalizer) is shown. In the figure, an input electrical signal is sequentially delayed through a plurality of delay circuits 91, and the input electrical signal and the output of each delay circuit are sequentially added by an adder circuit 92. The waveform can be optimized by adjusting the tap coefficient in the adder circuit 92 and weighting the addition.
JP 2007-329558 A Tatsuya Hatano, et al., "Development of high-precision DOP measuring instrument", Furukawa Electric Times, No. 111, January 2003 Nobuhiko Kikuchi, "Analysis of Signal Degree of Polarization Degradation Used as Control Signal for Optical Polarization Mode Dispersion Compensation", J.Lightwave.Technol., Vol.19, No.4, April 2001 Yoshihei Namihira, “Trends in Polarization Mode Dispersion Measurement Technology”, OPTRONICS (2003), No.10, pp.112-120

ＰＭＤ値は光ファイバによって異なる値をとる。また、光ファイバのＤＧＤは、上述したように時間的にランダムに変動する特性をもつことから、ＰＭＤ値の大きな光ファイバではＤＧＤの変動幅も大きく、ＥＤＣの補償範囲を大きく逸脱する可能性がある。また、光ファイバのＤＧＤは波長ごとに異なる値をとることから、波長ごとのＤＧＤに対応した最適なＥＤＣが必要になる。   The PMD value varies depending on the optical fiber. In addition, since the DGD of the optical fiber has a characteristic that varies randomly with time as described above, an optical fiber having a large PMD value has a large fluctuation range of the DGD, and may greatly deviate from the EDC compensation range. is there. In addition, since the DGD of the optical fiber has a different value for each wavelength, an optimum EDC corresponding to the DGD for each wavelength is required.

このように光ファイバのＤＧＤは時間変動し、また波長に応じて異なる値をとることから、１種類のＥＤＣを用いたＰＭＤ補償器では光ファイバのＤＧＤがＥＤＣの補償範囲から外れることが想定される。また、後述するように、光ファイバのＤＧＤの値によってはＥＤＣを用いることによって却って光信号波形が劣化することがある。このような場合、光信号は波形劣化により伝送品質が低下し、長期間に渡って伝送品質を安定に保つことが困難になる。   Thus, since the DGD of the optical fiber varies with time and takes different values depending on the wavelength, it is assumed that the PMD compensator using one type of EDC deviates from the EDC compensation range. The As will be described later, depending on the DGD value of the optical fiber, the optical signal waveform may be deteriorated by using EDC. In such a case, the transmission quality of the optical signal is lowered due to waveform deterioration, and it becomes difficult to keep the transmission quality stable for a long period of time.

本発明は、受信した光信号のＤＯＰをモニタし、ＤＯＰから推定する光ファイバのＤＧＤ値に基づいてＥＤＣを適応制御し、ＰＭＤによる波形劣化を長期間にわたって安定に補償することができるＰＭＤ補償装置を提供することを目的とする。   The present invention monitors a DOP of a received optical signal, adaptively controls an EDC based on a DGD value of an optical fiber estimated from the DOP, and can stably compensate for waveform deterioration due to PMD over a long period of time. The purpose is to provide.

第１の発明は、光ファイバ伝送路を伝搬してＰＭＤに起因する波形劣化が生じた光信号を入力し、電気信号に変換し、ＥＤＣを用いて波形劣化を補償するＰＭＤ補償装置において、光ファイバ伝送路の群遅延差ＤＧＤに応じたＰＭＤ補償特性を有する１つのＥＤＣまたは互いにＰＭＤ補償特性が異なる２以上のＥＤＣと、電気信号をＥＤＣを通過させずに出力する経路と、いずれか１つのＥＤＣを通過して出力する経路を選択する経路選択手段と、光信号の偏光度ＤＯＰをモニタし、その偏光度ＤＯＰに対応する光ファイバ伝送路の群遅延差ＤＧＤ値に応じて最良のＰＭＤ補償特性が得られるように、経路選択手段の経路の選択する制御信号を生成して経路選択手段を制御する制御手段とを備える。   A first invention is a PMD compensation device that inputs an optical signal that has propagated through an optical fiber transmission line and has undergone waveform degradation caused by PMD, converts the optical signal into an electrical signal, and compensates the waveform degradation using EDC. One EDC having PMD compensation characteristics corresponding to the group delay difference DGD of the fiber transmission line, two or more EDCs having different PMD compensation characteristics, and a path for outputting an electrical signal without passing through the EDC, Path selection means for selecting a path to output through the EDC, and the degree of polarization DOP of the optical signal are monitored, and the best PMD compensation is performed according to the group delay difference DGD value of the optical fiber transmission line corresponding to the degree of polarization DOP Control means for generating a control signal for selecting a route of the route selection means to control the route selection means so as to obtain characteristics.

第２の発明は、光ファイバ伝送路を伝搬してＰＭＤに起因する波形劣化が生じた波長多重光信号を入力し、各波長の光信号に分波してそれぞれ電気信号に変換し、各波長対応にＥＤＣを用いて波形劣化を補償するＰＭＤ補償装置において、各波長の光信号に対応して、第１の発明のＰＭＤ補償装置と同様のＥＤＣと、経路選択手段と、制御手段とを備える。   According to a second aspect of the present invention, a wavelength-division multiplexed optical signal that has propagated through an optical fiber transmission line and has undergone waveform degradation due to PMD is input, demultiplexed into optical signals of each wavelength, converted into electrical signals, and Correspondingly, a PMD compensation device that compensates for waveform degradation using EDC includes an EDC similar to the PMD compensation device of the first invention, a path selection unit, and a control unit, corresponding to the optical signal of each wavelength. .

第１および第２の発明における制御手段は、光信号の各偏光成分の光強度を検出してストークスパラメータを測定し、さらにストークスパラメータから光信号の偏光度ＤＯＰを算出するＤＯＰモニタ部と、光信号のＤＯＰから光ファイバ伝送路の群遅延差ＤＧＤを推定し、その群遅延差ＤＧＤ値に応じた制御信号を経路選択手段に出力する制御部とを備える。   The control means in the first and second inventions includes a DOP monitor that detects the light intensity of each polarization component of the optical signal, measures the Stokes parameter, and calculates the polarization degree DOP of the optical signal from the Stokes parameter; A control unit that estimates the group delay difference DGD of the optical fiber transmission line from the DOP of the signal and outputs a control signal corresponding to the group delay difference DGD value to the path selection unit.

本発明は、ＰＭＤの大きな光ファイバ伝送路でも、また光ファイバ伝送路のＤＧＤの時間変動が大きい場合でも、常に伝送品質劣化を最小化する最適なＥＤＣ選択が可能となり、光ファイバ伝送路のＰＭＤによる伝送品質劣化を最小限に抑えるＰＭＤ補償が可能となる。   The present invention makes it possible to select an optimal EDC that always minimizes the degradation of transmission quality, even in an optical fiber transmission line with a large PMD or when the time variation of the DGD in the optical fiber transmission line is large. PMD compensation that minimizes degradation of transmission quality due to transmission is possible.

図１は、本発明のＰＭＤ補償装置の実施形態を示す。
図において、光ファイバ伝送路１を介して伝送された受信光信号は光カプラ２を介して２分岐され、それぞれ光受信部１０およびＤＯＰモニタ部３に入力する。光受信部１０は、受信光信号を電気信号に変換する光／電変換器（Ｏ／Ｅ）１１、Ｏ／Ｅ１１から出力される電気信号の波形等化を行う波形等化器（ＥＱ）１２、ＥＱ１２で波形等化された電気信号を受信処理して後段回路に出力する受信器（Ｒｘ）１３を備える。ＥＱ１２は、バッファ１２１、スイッチ１２２、それぞれ異なる波形等化特性を有するＥＤＣ１２３−１〜１２３−ｍ（ｍは１以上の整数）、スイッチ１２４により構成される。なお、スイッチ１２２，１２４は、いずれか一方のみとし、他方は分岐／合流器でもよい。ＥＱ１２に入力する電気信号は、スイッチ１２２，１２４の同期した切り替えにより、ＥＤＣ１２３−１〜１２３−ｍのいずれか１つを通過する経路またはＥＤＣをスルーする経路を介してＲｘ１３に出力される。 FIG. 1 shows an embodiment of a PMD compensation device of the present invention.
In the figure, the received optical signal transmitted via the optical fiber transmission line 1 is branched into two via the optical coupler 2 and is input to the optical receiver 10 and the DOP monitor 3 respectively. The optical receiver 10 includes an optical / electrical converter (O / E) 11 that converts a received optical signal into an electrical signal, and a waveform equalizer (EQ) 12 that performs waveform equalization of an electrical signal output from the O / E11. And a receiver (Rx) 13 for receiving and processing the electrical signal waveform-equalized by the EQ 12 and outputting it to a subsequent circuit. The EQ 12 includes a buffer 121, a switch 122, EDCs 123-1 to 123-m (m is an integer of 1 or more) and a switch 124 having different waveform equalization characteristics. Note that only one of the switches 122 and 124 may be provided, and the other may be a branching / merging device. The electrical signal input to the EQ 12 is output to the Rx 13 via a path that passes through any one of the EDCs 123-1 to 123-m or a path that passes through the EDC by the synchronized switching of the switches 122 and 124.

ＤＯＰモニタ部３は、図６に示すＤＯＰ測定系の構成を用い、受信光信号の各偏光成分の光強度を検出してストークスパラメータを測定し、さらにストークスパラメータから光信号のＤＯＰ値をモニタし、制御部４に出力する。制御部４は、光信号のＤＯＰ値から一意の関係にある光ファイバ伝送路１のＤＧＤ値を推定し、ＤＧＤ値に基づく制御信号をＥＱ１２に出力し、ＥＤＣ１２３−１〜１２３−ｍのいずれか１つを通過する経路またはＥＤＣをスルーする経路を選択するようにスイッチ１２２，１２４を切り替える。以下、光ファイバ伝送路１のＤＧＤ値に基づくＥＤＣの選択アルゴリズムについて説明する。   The DOP monitor unit 3 uses the configuration of the DOP measurement system shown in FIG. 6, detects the light intensity of each polarization component of the received optical signal, measures the Stokes parameter, and further monitors the DOP value of the optical signal from the Stokes parameter. To the control unit 4. The control unit 4 estimates the DGD value of the optical fiber transmission line 1 having a unique relationship from the DOP value of the optical signal, outputs a control signal based on the DGD value to the EQ 12, and any one of the EDCs 123-1 to 123-m The switches 122 and 124 are switched so as to select a path through one or a path through the EDC. Hereinafter, an EDC selection algorithm based on the DGD value of the optical fiber transmission line 1 will be described.

受信光信号は、光ファイバ伝送路１のＤＧＤにより２つの偏波モード間に遅延差が生じており、これをＯ／Ｅ１０１で光電変換することで、２つの電気信号として出力されることになる。ＥＱ１２の各ＥＤＣは図８に示す構成であり、この電気信号を複数の遅延回路９１および加算回路９２を用いて処理することにより、元の波形に整形する機能を有する。なお、各ＥＤＣの波形等化特性（補償範囲）は異なる。   The received optical signal has a delay difference between the two polarization modes due to the DGD of the optical fiber transmission line 1, and is photoelectrically converted by the O / E 101 to be output as two electrical signals. . Each EDC of the EQ 12 has the configuration shown in FIG. 8, and has a function of shaping this electric signal into an original waveform by processing it using a plurality of delay circuits 91 and adder circuits 92. The waveform equalization characteristics (compensation range) of each EDC are different.

図２は、ＤＧＤ値に対するＱペナルティ特性を示す。Ｑペナルティが大きいほど伝送品質は低下する。図中の曲線Ａは、ＥＤＣで波形等化を行わなかった場合のＱペナルティ特性を示す。ＤＧＤが大きくなるに従いＱペナルティが増加している。図中の曲線Ｂは、ＥＤＣを適用した場合のＱペナルティ特性を示す。曲線Ａ，Ｂが交差するＤＧＤ19[ps]付近を境にして、ＤＧＤが19[ps]以下では曲線Ａが曲線Ｂに比べてＱペナルティが小さく、ＤＧＤが19[ps]を超えると曲線Ｂが曲線Ａに比べてＱペナルティが小さくなる。   FIG. 2 shows the Q penalty characteristic with respect to the DGD value. The transmission quality decreases as the Q penalty increases. Curve A in the figure shows the Q penalty characteristic when waveform equalization is not performed by EDC. The Q penalty increases as the DGD increases. Curve B in the figure shows the Q penalty characteristic when EDC is applied. When the DGD is 19 [ps] or less at the vicinity of the DGD 19 [ps] where the curves A and B intersect, the curve A has a smaller Q penalty than the curve B, and when the DGD exceeds 19 [ps], the curve B Compared to curve A, the Q penalty is smaller.

ＤＧＤが小さい領域（19[ps]以下）では、ＥＤＣを適用するとＥＤＣを適用しない場合に比べてＱペナルティが大きくなる。これはＥＤＣとして用いているＦＦＥの特性であり、大きなＤＧＤに対してＱペナルティを減少させるため、波形を歪ませることによって残存するペナルティである。このため、ＤＧＤが大きな領域ではＱペナルティを減少させるものの、ＤＧＤが小さい領域では過剰なペナルティとなり、両者はトレードオフの関係になる。したがって、光信号波長におけるＤＧＤが十分に小さいときはＥＤＣを適用しない方が伝送品質を高く保つことができ、ＤＧＤが十分に大きいときはＥＤＣを適用することにより伝送品質劣化を最小限に保つことが可能になる。   In the region where the DGD is small (19 [ps] or less), when EDC is applied, the Q penalty is larger than when EDC is not applied. This is a characteristic of the FFE used as the EDC, and is a penalty remaining by distorting the waveform in order to reduce the Q penalty for a large DGD. For this reason, although the Q penalty is reduced in the region where the DGD is large, the penalty is excessive in the region where the DGD is small, and both are in a trade-off relationship. Therefore, when the DGD at the optical signal wavelength is sufficiently small, it is possible to keep the transmission quality higher without applying the EDC, and when the DGD is sufficiently large, the transmission quality deterioration is kept to a minimum by applying the EDC. Is possible.

本発明はこの事象に着目し、光信号のＤＯＰをモニタし、ＤＯＰから推定する光ファイバのＤＧＤ値に基づいて、Ｑペナルティを最小化するＥＤＣを選択する、あるいはＥＤＣをスルーするようにＥＱ１２を制御することを特徴とする。   The present invention pays attention to this phenomenon, monitors the DOP of the optical signal, selects the EDC that minimizes the Q penalty based on the DGD value of the optical fiber estimated from the DOP, or sets the EQ 12 to pass through the EDC. It is characterized by controlling.

図３は、本発明のＰＭＤ補償装置の実施形態の制御例を示す。
図において、曲線ＡはＥＤＣで波形等化を行わなかった場合のＱペナルティ特性を示し、曲線ＢはＥＤＣ１２３−１を適用した場合のＱペナルティ特性を示し、曲線ＣはＥＤＣ１２３−２を適用した場合のＱペナルティ特性を示す。すなわち、ＥＤＣ１２３−２は、ＥＤＣ１２３−１に比べて大きなＤＧＤ値でＱペナルティを減少される効果が高いものの、小さなＤＧＤ値では逆にＱペナルティが大きくなる特性がある。 FIG. 3 shows a control example of the embodiment of the PMD compensation apparatus of the present invention.
In the figure, curve A shows the Q penalty characteristic when waveform equalization is not performed by EDC, curve B shows the Q penalty characteristic when EDC 123-1 is applied, and curve C shows the case when EDC 123-2 is applied. The Q penalty characteristic is shown. That is, the EDC 123-2 has a higher effect of reducing the Q penalty with a large DGD value than the EDC 123-1, but has a characteristic that the Q penalty is increased with a small DGD value.

ここで、曲線Ａと曲線Ｂが交差するときのＤＧＤ値をＤＧＤ１、曲線Ｂと曲線Ｃが交差するときのＤＧＤ値をＤＧＤ２とする。制御部４は、光ファイバ伝送路１のＤＧＤ値が閾値ＤＧＤ１以下の領域では、ＥＱ１２のスイッチ１２２，１２４に対して、ＥＤＣをスルーする経路を選択するように制御する。また、光ファイバ伝送路１のＤＧＤ値が閾値ＤＧＤ１を超え、閾値ＤＧＤ２以下の領域では、ＥＱ１２のスイッチ１２２，１２４に対して、ＥＤＣ１２３−１を通過する経路を選択するように制御する。また、光ファイバ伝送路１のＤＧＤ値が閾値ＤＧＤ２を超える領域では、ＥＱ１２のスイッチ１２２，１２４に対して、ＥＤＣ１２３−２を通過する経路を選択するように制御する。これにより、ＥＱ１２は、光ファイバ伝送路１のＤＧＤ値に応じて常にＱペナルティを最小化するように制御され、光ファイバ伝送路１のＰＭＤによる伝送品質劣化を最小限に抑えるＰＭＤ補償が可能となる。ＥＤＣを３つ以上用いる場合でも同様である。   Here, it is assumed that the DGD value when the curve A and the curve B intersect is DGD1, and the DGD value when the curve B and the curve C intersect is DGD2. In the region where the DGD value of the optical fiber transmission line 1 is equal to or less than the threshold value DGD1, the control unit 4 controls the switches 122 and 124 of the EQ 12 so as to select a path through the EDC. Further, in a region where the DGD value of the optical fiber transmission line 1 exceeds the threshold value DGD1 and is equal to or less than the threshold value DGD2, the switches 122 and 124 of the EQ12 are controlled so as to select a route passing through the EDC 123-1. Further, in a region where the DGD value of the optical fiber transmission line 1 exceeds the threshold value DGD2, the switches 122 and 124 of the EQ 12 are controlled so as to select a route passing through the EDC 123-2. As a result, the EQ 12 is controlled so as to always minimize the Q penalty according to the DGD value of the optical fiber transmission line 1, and PMD compensation that minimizes transmission quality degradation due to PMD of the optical fiber transmission line 1 is possible. Become. The same applies when three or more EDCs are used.

図４は、本発明のＰＭＤ補償装置を波長多重光伝送システムに適用した構成例を示す。
図において、クライアント装置５から出力される複数の送信信号はそれぞれ光送信部６に入力され、互いに異なる波長λ１〜λｎの光信号に変換して送信される。各波長の光信号は光合波器７で波長多重され、光ファイバ伝送路１に送出される。光ファイバ伝送路１を介して伝送された波長多重光信号は、光分波器８で各波長の光信号に分波され、それぞれ光カプラ２を介して光受信部１０およびＤＯＰモニタ部３に入力する。光受信部１０を構成するＯ／Ｅ１１、ＥＱ１２、Ｒx １３、ＤＯＰモニタ部３、制御部４の構成は、図１に示したものと同じであり、各波長に対応する光受信部１０で同様にＥＤＣを選択するＰＭＤ補償が行われ、各光受信部１０のＲx １３の出力信号がクライアント装置９に出力される。このような構成により、波長ごとに異なるＤＧＤ値に基づいて個別に波形等化処理が可能となる。 FIG. 4 shows a configuration example in which the PMD compensation device of the present invention is applied to a wavelength division multiplexing optical transmission system.
In the figure, a plurality of transmission signals output from the client device 5 are respectively input to the optical transmission unit 6, converted into optical signals having different wavelengths λ1 to λn, and transmitted. The optical signals of the respective wavelengths are wavelength multiplexed by the optical multiplexer 7 and sent to the optical fiber transmission line 1. The wavelength multiplexed optical signal transmitted through the optical fiber transmission line 1 is demultiplexed into optical signals of respective wavelengths by the optical demultiplexer 8, and is respectively transmitted to the optical receiver 10 and the DOP monitor 3 via the optical coupler 2. input. The configurations of the O / E 11, EQ 12, Rx 13, DOP monitor unit 3, and control unit 4 constituting the optical receiving unit 10 are the same as those shown in FIG. 1, and the same applies to the optical receiving unit 10 corresponding to each wavelength. PMD compensation for selecting EDC is performed, and an output signal of Rx 13 of each optical receiver 10 is output to the client device 9. With such a configuration, it is possible to individually perform waveform equalization processing based on different DGD values for each wavelength.

本発明のＰＭＤ補償装置の実施形態を示す図。The figure which shows embodiment of the PMD compensation apparatus of this invention. ＤＧＤ値に対するＱペナルティ特性を示す図。The figure which shows the Q penalty characteristic with respect to a DGD value. 本発明のＰＭＤ補償装置の実施形態の制御例を示す図。The figure which shows the example of control of embodiment of the PMD compensation apparatus of this invention. 本発明のＰＭＤ補償装置を波長多重光伝送システムに適用した構成例を示す図。The figure which shows the structural example which applied the PMD compensation apparatus of this invention to the wavelength division multiplexing optical transmission system. 光ファイバのＤＧＤ変動特性を示す図。The figure which shows the DGD fluctuation | variation characteristic of an optical fiber. ＤＯＰ測定系の構成例を示す図。The figure which shows the structural example of a DOP measurement system. 光信号のＤＯＰと伝送品質（Ｑ値）との関係の実測値を示す図。The figure which shows the measured value of the relationship between DOP of an optical signal, and transmission quality (Q value). ＥＤＣの構成例を示す図。The figure which shows the structural example of EDC.

符号の説明Explanation of symbols

１ 光ファイバ伝送路
２ 光カプラ
３ ＤＯＰモニタ部
４ 制御部
５，９ クライアント装置
６ 光送信部（Ｔx ）
７ 光合波器
８ 光分波器
１０ 光受信部
１１ 光／電変換器（Ｏ／Ｅ）
１２ 波形等化器（ＥＱ）
１３ 受信器（Ｒx ）
１２１ バッファ
１２２，１２４ スイッチ（ＳＷ）
１２３ ＥＤＣ DESCRIPTION OF SYMBOLS 1 Optical fiber transmission line 2 Optical coupler 3 DOP monitor part 4 Control part 5,9 Client apparatus 6 Optical transmission part (Tx)
7 Optical multiplexer 8 Optical demultiplexer 10 Optical receiver 11 Optical / electrical converter (O / E)
12 Waveform equalizer (EQ)
13 Receiver (Rx)
121 Buffer 122, 124 Switch (SW)
123 EDC

Claims (3)

光ファイバ伝送路を伝搬してＰＭＤに起因する波形劣化が生じた光信号を入力し、電気信号に変換し、電気分散補償器を用いて波形劣化を補償するＰＭＤ補償装置において、
前記光ファイバ伝送路の群遅延差ＤＧＤに応じたＰＭＤ補償特性を有する１つの電気分散補償器または互いにＰＭＤ補償特性が異なる２以上の電気分散補償器と、
前記電気信号を前記電気分散補償器を通過させずに出力する経路と、いずれか１つの電気分散補償器を通過して出力する経路を選択する経路選択手段と、
前記光信号の偏光度ＤＯＰをモニタし、その偏光度ＤＯＰに対応する前記光ファイバ伝送路の群遅延差ＤＧＤ値に応じて最良の前記ＰＭＤ補償特性が得られるように、前記経路選択手段の前記経路の選択する制御信号を生成して前記経路選択手段を制御する制御手段と
を備えたことを特徴とするＰＭＤ補償装置。 In a PMD compensation device that inputs an optical signal that has propagated through an optical fiber transmission line and has undergone waveform degradation due to PMD, converts the optical signal into an electrical signal, and compensates for the waveform degradation using an electrical dispersion compensator.
One electrical dispersion compensator having PMD compensation characteristics corresponding to the group delay difference DGD of the optical fiber transmission line, or two or more electrical dispersion compensators having different PMD compensation characteristics;
Path selection means for selecting a path for outputting the electric signal without passing through the electric dispersion compensator, and a path for outputting the electric signal through any one electric dispersion compensator;
The degree of polarization DOP of the optical signal is monitored, and the PMD compensation characteristic of the path selection means is obtained so that the best PMD compensation characteristic is obtained according to the group delay difference DGD value of the optical fiber transmission line corresponding to the degree of polarization DOP. A PMD compensation apparatus comprising: a control unit that generates a control signal for selecting a path and controls the path selection unit. 光ファイバ伝送路を伝搬してＰＭＤに起因する波形劣化が生じた波長多重光信号を入力し、各波長の光信号に分波してそれぞれ電気信号に変換し、各波長対応に電気分散補償器を用いて波形劣化を補償するＰＭＤ補償装置において、
前記各波長の光信号に対応して、
前記光ファイバ伝送路の群遅延差ＤＧＤに応じたＰＭＤ補償特性を有する１つの電気分散補償器または互いにＰＭＤ補償特性が異なる２以上の電気分散補償器と、
前記電気信号を前記電気分散補償器を通過させずに出力する経路と、いずれか１つの電気分散補償器を通過して出力する経路を選択する経路選択手段と、
前記光信号の偏光度ＤＯＰをモニタし、その偏光度ＤＯＰに対応する前記光ファイバ伝送路の群遅延差ＤＧＤ値に応じて最良の前記ＰＭＤ補償特性が得られるように、前記経路選択手段の前記経路の選択する制御信号を生成して前記経路選択手段を制御する制御手段と
を備えたことを特徴とするＰＭＤ補償装置。 Wavelength multiplexed optical signal that has propagated through an optical fiber transmission line and has undergone waveform degradation due to PMD is input, demultiplexed into optical signals of each wavelength, converted into electrical signals, and an electrical dispersion compensator for each wavelength In a PMD compensation device that compensates for waveform deterioration using
In response to the optical signal of each wavelength,
One electrical dispersion compensator having PMD compensation characteristics corresponding to the group delay difference DGD of the optical fiber transmission line, or two or more electrical dispersion compensators having different PMD compensation characteristics;
Path selection means for selecting a path for outputting the electric signal without passing through the electric dispersion compensator, and a path for outputting the electric signal through any one electric dispersion compensator;
The degree of polarization DOP of the optical signal is monitored, and the PMD compensation characteristic of the path selection means is obtained so that the best PMD compensation characteristic is obtained according to the group delay difference DGD value of the optical fiber transmission line corresponding to the degree of polarization DOP. A PMD compensation apparatus comprising: a control unit that generates a control signal for selecting a path and controls the path selection unit. 請求項１または請求項２に記載のＰＭＤ補償装置において、
前記制御手段は、
前記光信号の各偏光成分の光強度を検出してストークスパラメータを測定し、さらにストークスパラメータから前記光信号の偏光度ＤＯＰを算出するＤＯＰモニタ部と、
前記光信号のＤＯＰから前記光ファイバ伝送路の群遅延差ＤＧＤを推定し、その群遅延差ＤＧＤ値に応じた前記制御信号を前記経路選択手段に出力する制御部と
を備えたことを特徴とするＰＭＤ補償装置。 The PMD compensator according to claim 1 or 2,
The control means includes
A DOP monitor unit that detects a light intensity of each polarization component of the optical signal to measure a Stokes parameter, and further calculates a polarization degree DOP of the optical signal from the Stokes parameter;
A controller that estimates a group delay difference DGD of the optical fiber transmission line from the DOP of the optical signal, and outputs the control signal corresponding to the group delay difference DGD value to the path selection unit. PMD compensation device.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012109871A1 (en) * 2011-08-01 2012-08-23 华为技术有限公司 Coherent receiver device and chromatic dispersion compensation method
CN103614377A (en) * 2013-10-28 2014-03-05 华大基因杨凌创新研究院有限公司 Promoter OsP001, and preparation method and application thereof

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012109871A1 (en) * 2011-08-01 2012-08-23 华为技术有限公司 Coherent receiver device and chromatic dispersion compensation method
US8861979B2 (en) 2011-08-01 2014-10-14 Huawei Technologies Co., Ltd. Coherent receiver apparatus and chromatic dispersion compensation method
CN103614377A (en) * 2013-10-28 2014-03-05 华大基因杨凌创新研究院有限公司 Promoter OsP001, and preparation method and application thereof

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