JP6736504B2 - Optical amplifier - Google Patents

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JP6736504B2
JP6736504B2 JP2017043038A JP2017043038A JP6736504B2 JP 6736504 B2 JP6736504 B2 JP 6736504B2 JP 2017043038 A JP2017043038 A JP 2017043038A JP 2017043038 A JP2017043038 A JP 2017043038A JP 6736504 B2 JP6736504 B2 JP 6736504B2
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高橋　英憲
英憲 高橋
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KDDI Corp
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Description

本発明は、偏波多重光通信システムにおける光増幅装置に関する。 The present invention relates to an optical amplification device in a polarization multiplexing optical communication system.

通信システムにおいては、１つの通信媒体の有効利用のため、例えば、多重化技術を使用して、１つの通信媒体で複数の信号を伝送することが行われる。特許文献１は、互いに直交する偏波の光信号を１つの光ファイバコアで伝送する偏波多重光通信システムを開示している。また、光通信システムにおいては、光信号を電気信号に変換することなく、光信号のままで増幅を行う光増幅装置が使用される。特許文献２は、偏波保持光ファイバを用いた光増幅装置を開示している。特許文献２によると、光増幅装置の増幅部として機能するエルビウム添加ファイバ（ＥＤＦ）で生じる自然放出光（ＡＳＥ光）のうち、光信号の偏波面に直交する成分を除去するため、偏光子を使用している。 In a communication system, in order to effectively use one communication medium, for example, a multiplexing technique is used to transmit a plurality of signals on one communication medium. Patent Document 1 discloses a polarization multiplexing optical communication system in which optical signals of mutually orthogonal polarized waves are transmitted by one optical fiber core. Further, in an optical communication system, an optical amplification device is used that amplifies an optical signal as it is without converting the optical signal into an electric signal. Patent Document 2 discloses an optical amplifier using a polarization maintaining optical fiber. According to Patent Document 2, in a spontaneous emission light (ASE light) generated in an erbium-doped fiber (EDF) functioning as an amplification unit of an optical amplification device, a polarizer is used to remove a component orthogonal to a polarization plane of an optical signal. I'm using it.

特開２０１４−２２０８２２号公報JP, 2014-220822, A 特開２００３−０３１８７５号公報JP, 2003-031875, A

特許文献２が開示する光増幅装置は、信号光と直交する成分を偏光子により阻止するため、直交する２つの偏波の信号光を含む光信号の増幅のために使用することはできない。 The optical amplifying device disclosed in Patent Document 2 cannot be used for amplifying an optical signal containing signal light of two polarizations orthogonal to each other, because the polarizer blocks the component orthogonal to the signal light.

本発明は、直交する２つの偏波の信号光を含む偏波多重光信号を増幅できる光増幅装置を提供するものである。 The present invention provides an optical amplifier capable of amplifying a polarization multiplexed optical signal including signal lights of two polarizations that are orthogonal to each other.

本発明の一態様によると、偏波多重光信号を増幅する光増幅装置は、制御手段と、入力される光信号の偏波面を前記制御手段から通知された回転量だけ回転させる第１回転手段と、前記第１回転手段からの光信号を第１偏波と、前記第１偏波とは直交する第２偏波とに偏波分離して、第１偏波の第１光信号と第２偏波の第２光信号と、を出力する分離手段と、前記第１光信号を光増幅する第１増幅手段と、前記第２光信号を光増幅する第２増幅手段と、前記第１増幅手段が出力する第１光信号に含まれる前記第２偏波の成分を抑制する第１抑制手段と、前記第２増幅手段が出力する第２光信号に含まれる前記第１偏波の成分を抑制する第２抑制手段と、前記第１抑制手段が出力する光信号と前記第２抑制手段が出力する光信号とを偏波多重して出力する多重手段と、前記多重手段からの光信号の偏波面を前記制御手段から通知された回転量だけ回転させる第２回転手段と、を備え、前記第１増幅手段及び前記第２増幅手段は、入力される光信号の偏波面を保持して出力し、前記制御手段は、前記第１回転手段の回転量の絶対値と前記第２回転手段の回転量の絶対値が等しく、前記第１回転手段による偏波面の回転方向と前記第２回転手段による偏波面の回転方向が互いに逆となる様に、前記第１回転手段及び前記第２回転手段を制御することを特徴とする。 According to one aspect of the present invention, an optical amplifier for amplifying a polarization multiplexed optical signal includes a control means and a first rotation means for rotating a polarization plane of an input optical signal by a rotation amount notified from the control means. And polarization-separating the optical signal from the first rotating means into a first polarized wave and a second polarized wave orthogonal to the first polarized wave. Demultiplexing means for outputting a second optical signal of two polarizations, first amplifying means for optically amplifying the first optical signal, second amplifying means for optically amplifying the second optical signal, and the first First suppressing means for suppressing the component of the second polarized wave included in the first optical signal output by the amplifying means, and component of the first polarized wave included in the second optical signal output by the second amplifying means Suppressing means, a multiplexing means for polarization-multiplexing and outputting the optical signal output by the first suppressing means and the optical signal output by the second suppressing means, and an optical signal from the multiplexing means. Second rotation means for rotating the plane of polarization of the optical signal by the rotation amount notified from the control means , wherein the first amplification means and the second amplification means hold the polarization plane of the input optical signal. The control means outputs the absolute value of the rotation amount of the first rotation means and the absolute value of the rotation amount of the second rotation means are equal to each other, and the rotation direction of the polarization plane by the first rotation means and the second rotation. It is characterized in that the first rotating means and the second rotating means are controlled so that the directions of rotation of polarization planes by the means are opposite to each other .

本発明によると、直交する２つの偏波の信号光を含む偏波多重光信号を増幅することができる。 According to the present invention, it is possible to amplify a polarization multiplexed optical signal including signal lights of two polarizations orthogonal to each other.

一実施形態による光増幅装置の構成図。The block diagram of the optical amplifier by one Embodiment. 一実施形態による光増幅装置の構成図。The block diagram of the optical amplifier by one Embodiment. 一実施形態による光増幅装置の構成図。The block diagram of the optical amplifier by one Embodiment. 一実施形態による光増幅装置の構成図。The block diagram of the optical amplifier by one Embodiment.

以下、本発明の例示的な実施形態について図面を参照して説明する。なお、以下の実施形態は例示であり、本発明を実施形態の内容に限定するものではない。また、以下の各図においては、実施形態の説明に必要ではない構成要素については図から省略する。 Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. The following embodiments are exemplifications, and the present invention is not limited to the contents of the embodiments. Further, in each of the following drawings, components that are not necessary for explaining the embodiment are omitted from the drawings.

＜第一実施形態＞
図１は、本実施形態による光増幅装置の構成図である。光増幅装置に入力される偏波多重光信号は、Ｘ偏波の信号光と、Ｘ偏波とは直交する偏波であるＹ偏波の信号光とを含んでいる。分離部１は、偏波多重光信号を偏波分離して、Ｘ偏波の信号光とＹ偏波の信号光とをそれぞれ出力する。偏波保持型増幅部２１は、エルビウム添加ファイバ（ＥＤＦ）を有し、図示しない励起光源からの励起光により、Ｘ偏波の信号光を増幅する。同様に、偏波保持型増幅部２２は、ＥＤＦを有し、図示しない励起光源からの励起光により、Ｙ偏波の信号光を増幅する。なお、偏波保持型増幅部２１及び偏波保持型増幅部２２は、増幅する光信号の偏波面を維持／保持する。したがって、偏波保持型増幅部２１は、増幅されたＸ偏波の信号光を出力し、偏波保持型増幅部２２は、増幅されたＹ偏波の信号光を出力する。なお、偏波保持型増幅部２１及び偏波保持型増幅部２２は、増幅された信号光のみならず、ＥＤＦで生じる自然放出光（ＡＳＥ光）も出力する。つまり、偏波保持型増幅部２１及び偏波保持型増幅部２２は、増幅された信号光とＡＳＥ光を含む光信号を出力する。
なお、ＡＳＥ光の偏波面は、一意ではなく、ＡＳＥ光は、様々な方向の偏波面の成分を含んでいる。 <First embodiment>
FIG. 1 is a configuration diagram of the optical amplification device according to the present embodiment. The polarization multiplexed optical signal input to the optical amplifier device includes an X-polarized signal light and a Y-polarized signal light that is a polarization orthogonal to the X-polarized light. The demultiplexing unit 1 demultiplexes the polarization multiplexed optical signal and outputs the X-polarized signal light and the Y-polarized signal light, respectively. The polarization-maintaining amplification unit 21 has an erbium-doped fiber (EDF) and amplifies the X-polarized signal light by pumping light from a pumping light source (not shown). Similarly, the polarization-maintaining amplification unit 22 has an EDF and amplifies the Y-polarized signal light by pumping light from a pumping light source (not shown). The polarization maintaining amplifier 21 and the polarization maintaining amplifier 22 maintain/maintain the polarization plane of the optical signal to be amplified. Therefore, the polarization-maintaining amplifier 21 outputs the amplified X-polarized signal light, and the polarization-maintaining amplifier 22 outputs the amplified Y-polarized signal light. The polarization-maintaining amplifier 21 and the polarization-maintaining amplifier 22 output not only the amplified signal light but also spontaneous emission light (ASE light) generated in the EDF. That is, the polarization maintaining amplifier 21 and the polarization maintaining amplifier 22 output an optical signal including the amplified signal light and ASE light.
The polarization plane of the ASE light is not unique, and the ASE light contains polarization plane components in various directions.

偏光子３１は、Ｙ偏波の光成分を阻止する様に設けられ、増幅されたＸ偏波の信号光と、ＡＳＥ光を含む光信号のうち、Ｙ偏波の光成分を阻止する。したがって、偏光子３１でＸ偏波の信号光は減衰されず、偏光子３１は、Ｙ偏波のＡＳＥ光、つまり、雑音成分を阻止・抑制して、Ｘ偏波の信号光とＸ偏波のＡＳＥ光を含む光信号を出力する。同様に、偏光子３２は、Ｘ偏波の光成分を阻止する様に設けられる。したがって、偏光子３２でＹ偏波の信号光は減衰されず、偏光子３２は、Ｘ偏波のＡＳＥ光、つまり、雑音成分を阻止して、Ｙ偏波の信号光とＹ偏波のＡＳＥ光を含む光信号を出力する。合波部４は、偏光子３１が出力するＸ偏波の光信号と、偏光子３２が出力するＹ偏波の光信号を偏波多重して出力する。 The polarizer 31 is provided so as to block the Y-polarized light component, and blocks the Y-polarized light component of the amplified X-polarized signal light and the amplified optical signal containing the ASE light. Therefore, the X-polarized signal light is not attenuated by the polarizer 31, and the polarizer 31 blocks and suppresses the Y-polarized ASE light, that is, the noise component, and the X-polarized signal light and the X-polarized signal light are blocked. The optical signal including the ASE light is output. Similarly, the polarizer 32 is provided so as to block the light component of the X polarization. Therefore, the Y-polarized signal light is not attenuated by the polarizer 32, and the polarizer 32 blocks the X-polarized ASE light, that is, the noise component, and the Y-polarized signal light and the Y-polarized ASE light. Outputs an optical signal including light. The multiplexing unit 4 polarization-multiplexes the X-polarized optical signal output from the polarizer 31 and the Y-polarized optical signal output from the polarizer 32 and outputs the multiplexed signal.

以上、本実施形態によると、偏波多重光信号の光増幅を行うことができる。また、偏光子３１、３２により、不要な雑音成分を抑制でき、よって、信号対雑音比（ＳＮ比）を改良できる。 As described above, according to this embodiment, the optical amplification of the polarization multiplexed optical signal can be performed. Further, the polarizers 31 and 32 can suppress unnecessary noise components, and thus can improve the signal-to-noise ratio (SN ratio).

＜第二実施形態＞
続いて、第二実施形態について、第一実施形態との相違点を中心に説明する。図２は、本実施形態による光増幅装置の構成図である。なお、第一実施形態の光増幅装置と同様の構成要素には同じ参照符号を付与してその説明は省略する。本実施形態において、偏波コントローラ５１及び偏波コントローラ５２は、入力される光信号の偏波面を４５度だけ回転させて出力する。なお、偏波コントローラ５１及び偏波コントローラ５２の偏波面の回転方向は同じ方向であっても互いに異なる方向であってもよい。したがって、偏波コントローラ５１は、Ｘ偏波の信号光の偏波面を４５度だけ回転させ、Ｚ１偏波の信号光として出力する。同様に、偏波コントローラ５２は、Ｙ偏波の信号光の偏波面を４５度だけ回転させ、Ｚ２偏波の信号光として出力する。なお、偏波コントローラ５１及び偏波コントローラ５２の偏波面の回転方向が同じ方向であると、Ｚ１とＺ２の偏波面は互いに直交する。一方、偏波コントローラ５１及び偏波コントローラ５２の偏波面の回転方向が互いに異なる方向であると、Ｚ１とＺ２の偏波面は同じである。 <Second embodiment>
Next, the second embodiment will be described focusing on the differences from the first embodiment. FIG. 2 is a configuration diagram of the optical amplification device according to the present embodiment. The same components as those of the optical amplifying device of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. In the present embodiment, the polarization controller 51 and the polarization controller 52 rotate the polarization plane of the input optical signal by 45 degrees and output it. The polarization directions of the polarization planes of the polarization controller 51 and the polarization controller 52 may be the same direction or different directions. Therefore, the polarization controller 51 rotates the polarization plane of the X-polarized signal light by 45 degrees and outputs it as the Z1-polarized signal light. Similarly, the polarization controller 52 rotates the polarization plane of the Y-polarized signal light by 45 degrees and outputs it as Z2-polarized signal light. If the polarization planes of the polarization controller 51 and the polarization controller 52 have the same rotation direction, the polarization planes of Z1 and Z2 are orthogonal to each other. On the other hand, when the polarization planes of the polarization controller 51 and the polarization controller 52 have different rotation directions, the polarization planes of Z1 and Z2 are the same.

したがって、本実施形態の偏波保持型増幅部２１は、増幅されたＺ１偏波の信号光と、ＡＳＥ光を含む光信号を出力し、本実施形態の偏波保持型増幅部２２は、増幅されたＺ２偏波の信号光と、ＡＳＥ光を含む光信号を出力する。偏波コントローラ５３は、入力される光信号の偏波面を偏波コントローラ５１とは逆方向に４５度だけ回転させて出力する。同様に、偏波コントローラ５４は、入力される光信号の偏波面を偏波コントローラ５２とは逆方向に４５度だけ回転させて出力する。したがって、偏波コントローラ５３は、増幅されたＸ偏波の信号光と、ＡＳＥ光を含む光信号を出力し、偏波コントローラ５４は、増幅されたＹ偏波の信号光と、ＡＳＥ光を含む光信号を出力する。その後は、第一実施形態と同様である。 Therefore, the polarization-maintaining amplification unit 21 of the present embodiment outputs the amplified Z1 polarized signal light and the optical signal including the ASE light, and the polarization-maintenance amplification unit 22 of the present embodiment amplifies The optical signal including the Z2 polarized signal light and the ASE light is output. The polarization controller 53 rotates the polarization plane of the input optical signal in the direction opposite to that of the polarization controller 51 by 45 degrees and outputs it. Similarly, the polarization controller 54 rotates the polarization plane of the input optical signal by 45 degrees in the direction opposite to that of the polarization controller 52 and outputs it. Therefore, the polarization controller 53 outputs an optical signal including the amplified X polarization signal light and the ASE light, and the polarization controller 54 includes the amplified Y polarization signal light and the ASE light. Output an optical signal. After that, it is similar to the first embodiment.

ＥＤＦでは、信号光のない偏波のＡＳＥ光の増幅に、増幅のためのエネルギーがとられ、その結果、信号光のゲインが低下する。本実施形態において偏波保持型増幅部２１及び偏波保持型増幅部２２には、Ｘ偏波とＹ偏波の両方の成分を有する信号光が入力されるため、増幅のためのエネルギーを信号光の増幅に効率よく利用でき、よって、Ｓ／Ｎ比をさらに改良することができる。なお、本実施形態では、各偏波コントローラ５１、５２、５３及び５４での偏波面の回転量を４５度としたが、９０度、１８０度及び２７０度を除く任意の他の量とすることができる。この場合、偏波保持型増幅部２１及び偏波保持型増幅部２２に入力されるＸ偏波とＹ偏波のいずれか一方の成分は他方の成分に比べて弱くなるが、信号光が入力されることには変わりなく、Ｓ／Ｎ比を改善することができる。なお、偏波コントローラ５１、５２、５３及び５４での偏波面の回転量を９０度、１８０度及び２７０度のいずれかとすると、第一実施形態と同様になる。 In the EDF, energy for amplification is taken to amplify the polarized ASE light without signal light, and as a result, the gain of the signal light decreases. In the present embodiment, the polarization-maintaining amplifier 21 and the polarization-maintaining amplifier 22 are supplied with signal light having both X-polarized and Y-polarized components, so that the energy for amplification is signaled. It can be efficiently used for amplification of light, so that the S/N ratio can be further improved. In the present embodiment, the rotation amount of the plane of polarization in each polarization controller 51, 52, 53 and 54 is 45 degrees, but it may be any other amount except 90 degrees, 180 degrees and 270 degrees. You can In this case, one component of the X polarization and the Y polarization input to the polarization maintaining amplifier 21 and the polarization maintaining amplifier 22 is weaker than the other component, but the signal light is input. However, the S/N ratio can be improved. If the amount of rotation of the plane of polarization in the polarization controllers 51, 52, 53, and 54 is 90 degrees, 180 degrees, or 270 degrees, the same as in the first embodiment.

また、偏波保持型増幅部２１及び２２のＸ偏波とＹ偏波が感じる屈折率に差（複屈折）がある場合、偏波保持型増幅部２１及び２２の出力の偏波状態が入力の偏波状態と異なる場合がある。この場合、各偏波コントローラ５３、５４を調節することで、直線偏波に変換し、且つ各偏光子３１及び３２の軸に一致させることで解決できる。 Further, when there is a difference (birefringence) in the refractive index between the X polarization and the Y polarization of the polarization maintaining amplifiers 21 and 22, the polarization state of the output of the polarization maintaining amplifiers 21 and 22 is input. It may be different from the polarization state of. In this case, it can be solved by adjusting the polarization controllers 53 and 54 to convert the polarization into linear polarization and to match the axes of the polarizers 31 and 32.

＜第三実施形態＞
続いて、第三実施形態について、第二実施形態との相違点を中心に説明する。図３は、本実施形態による光増幅装置の構成図である。なお、第二実施形態の光増幅装置と同様の構成要素には同じ参照符号を付与してその説明は省略する。本実施形態においては、光増幅部として、偏波を保持しない、偏波無依存型増幅部６１及び６２を使用する。このため、偏波コントローラ７１及び偏波コントローラ７２は、入力される直線偏波の光信号を、円偏波の光信号に変換して出力する。なお、円偏波の回転方向は、右回転であっても左回転であっても良い。したがって、偏波コントローラ７１は、Ｘ偏波の信号光を円偏波の信号光に変換して出力する。同様に、偏波コントローラ７２は、Ｙ偏波の信号光を円偏波の信号光に変換して出力する。 <Third embodiment>
Next, the third embodiment will be described focusing on the differences from the second embodiment. FIG. 3 is a configuration diagram of the optical amplification device according to the present embodiment. The same components as those of the optical amplifying device of the second embodiment are designated by the same reference numerals, and the description thereof will be omitted. In the present embodiment, the polarization-independent amplifiers 61 and 62 that do not maintain polarization are used as the optical amplifiers. Therefore, the polarization controller 71 and the polarization controller 72 convert the input linearly polarized optical signal into a circularly polarized optical signal and output it. The rotation direction of the circularly polarized wave may be right rotation or left rotation. Therefore, the polarization controller 71 converts the X polarization signal light into the circular polarization signal light and outputs the signal light. Similarly, the polarization controller 72 converts the signal light of Y polarization into the signal light of circular polarization and outputs the signal light.

本実施形態の偏波無依存型増幅部６１及び６２は、それぞれ、増幅された円偏波の信号光と、ＡＳＥ光を含む光信号を出力する。偏波コントローラ７３は、入力される円偏波の光信号をＸ偏波の光信号に変換して出力し、偏波コントローラ７４は、入力される円偏波の光信号をＹ偏波の光信号に変換して出力する。したがって、偏波コントローラ７３は、増幅されたＸ偏波の信号光と、ＡＳＥ光を含む光信号を出力し、偏波コントローラ７４は、増幅されたＹ偏波の信号光と、ＡＳＥ光を含む光信号を出力する。その後は、第二実施形態と同様である。 The polarization independent amplifiers 61 and 62 of the present embodiment output an amplified circularly polarized signal light and an optical signal including the ASE light, respectively. The polarization controller 73 converts the input circular polarization optical signal into an X polarization optical signal and outputs it. The polarization controller 74 converts the input circular polarization optical signal into a Y polarization optical signal. Convert to a signal and output. Therefore, the polarization controller 73 outputs an optical signal including the amplified X polarization signal light and the ASE light, and the polarization controller 74 includes the amplified Y polarization signal light and the ASE light. Output an optical signal. After that, it is the same as the second embodiment.

上記構成により、偏波面を保持しないＥＤＦを使用して偏波多重光信号の光増幅を行うことができる。また、偏光子３１、３２により、不要な雑音成分を抑制でき、よって、信号対雑音比（ＳＮ比）を改良できる。 With the above configuration, it is possible to perform optical amplification of the polarization multiplexed optical signal using the EDF that does not maintain the plane of polarization. Further, the polarizers 31 and 32 can suppress unnecessary noise components, and thus can improve the signal-to-noise ratio (SN ratio).

＜第四実施形態＞
続いて、第四実施形態について、第一実施形態との相違点を中心に説明する。図４は、本実施形態による光増幅装置の構成図である。なお、第一実施形態の光増幅装置と同様の構成要素には同じ参照符号を付与してその説明は省略する。本実施形態の光増幅装置は、第一実施形態の光増幅装置の分離部１の上流側に可変偏波コントローラ８１を設け、第一実施形態の光増幅装置の合波部４の下流側に可変偏波コントローラ８２を設け、さらに、可変偏波コントローラ８１及び可変偏波コントローラ８２による偏波面の回転角度が互いに逆方向で同じ量となる様に同期制御する制御部９を追加した点で、第一実施形態の光増幅装置とは異なる。 <Fourth Embodiment>
Next, the fourth embodiment will be described focusing on the differences from the first embodiment. FIG. 4 is a configuration diagram of the optical amplification device according to the present embodiment. The same components as those of the optical amplifying device of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. The optical amplification device of the present embodiment is provided with a variable polarization controller 81 on the upstream side of the separation unit 1 of the optical amplification device of the first embodiment, and on the downstream side of the multiplexing unit 4 of the optical amplification device of the first embodiment. The variable polarization controller 82 is provided, and the variable polarization controller 81 and the control unit 9 for synchronously controlling the rotation angles of the polarization planes by the variable polarization controller 82 in the opposite directions are the same amount. It is different from the optical amplification device of the first embodiment.

たとえば、可変偏波コントローラ８１は、制御部９の制御のもと、光信号の偏波面の回転量を徐々に変化させる。たとえば、所定期間で、偏波面の回転量が０から２πになる様に可変偏波コントローラ８１は制御される。なお、回転量が２π、つまり、０になると、再度、２πに向けて回転量を増加させることを繰り返し行う。可変偏波コントローラ８２は、制御部９の制御のもと、光信号の偏波面の回転量を徐々に変化させる。なお、可変偏波コントローラ８２の偏波面の回転量の絶対値は、可変偏波コントローラ８１での回転量の絶対値と同じで、かつ、その方向は、可変偏波コントローラ８１とは逆向きとする。たとえば、可変偏波コントローラ８１が右回りで４５度の回転量を与えていると、可変偏波コントローラ８１は左回りで４５度の回転量を与えているように、可変偏波コントローラ８１及び可変偏波コントローラ８２は制御部９により制御される。したがって、可変偏波コントローラ８１及び可変偏波コントローラ８２の全体では、偏波面の回転は相殺され、よって、光増幅装置に入力されたＸ偏波の信号光とＹ偏波の信号光を含む偏波多重光信号は、同じくＸ偏波の信号光とＹ偏波の信号光（及びＡＳＥ光）を含む偏波多重光信号として光増幅装置から出力される。 For example, the variable polarization controller 81 gradually changes the rotation amount of the polarization plane of the optical signal under the control of the control unit 9. For example, the variable polarization controller 81 is controlled so that the rotation amount of the polarization plane changes from 0 to 2π in a predetermined period. When the rotation amount becomes 2π, that is, 0, the rotation amount is increased again toward 2π again. Under the control of the control unit 9, the variable polarization controller 82 gradually changes the rotation amount of the polarization plane of the optical signal. The absolute value of the rotation amount of the polarization plane of the variable polarization controller 82 is the same as the absolute value of the rotation amount of the variable polarization controller 81, and its direction is opposite to that of the variable polarization controller 81. To do. For example, when the variable polarization controller 81 gives a rotation amount of 45 degrees clockwise, the variable polarization controller 81 gives a rotation amount of 45 degrees counterclockwise. The polarization controller 82 is controlled by the control unit 9. Therefore, in the variable polarization controller 81 and the variable polarization controller 82 as a whole, the rotations of the polarization planes are canceled out, so that the polarization light including the X polarization signal light and the Y polarization signal light input to the optical amplifying device is cancelled. The wave-multiplexed optical signal is output from the optical amplifier device as a polarization-multiplexed optical signal that also includes X-polarized signal light and Y-polarized signal light (and ASE light).

続いて、本実施形態による光増幅装置の利点について説明する。偏波多重光信号に含まれるＸ偏波の信号光とＹ偏波の信号光が同じ変調方式を使用し、かつ、同じデータが連続していると、Ｘ偏波及びＹ偏波のそれぞれと４５度だけその偏波面が異なる直線偏波となり得る。また、光信号の偏波面は、光伝送路での複屈折の影響を受けて変化し得る。仮に上述したように、各信号光が搬送するデータにより、Ｘ偏波及びＹ偏波のそれぞれと４５度だけその偏波面が異なる直線偏波となり、かつ、その偏波面が、光伝送路での複屈折の影響を受けてＸ偏波に一致すると、第一実施形態の構成では、偏波保持型増幅器２２には信号光が入力されない。したがって、偏波保持型増幅器２２は、強いＡＳＥ光のみを出力することになりＳ／Ｎ比が劣化し得る。本実施形態では、可変偏波コントローラ８１が回転量を変化させるため、偏波保持型増幅器２１及び偏波保持型増幅器２２のいずれか一方に光信号が入力されない状態が継続することを防ぐことができ、よって、Ｓ／Ｎ比の劣化を抑えることができる。 Next, the advantages of the optical amplification device according to the present embodiment will be described. When the X-polarized signal light and the Y-polarized signal light included in the polarization multiplexed optical signal use the same modulation method and the same data are continuous, the X-polarized signal light and the Y-polarized signal light are respectively transmitted. It may be a linearly polarized wave whose polarization planes differ by 45 degrees. Further, the polarization plane of the optical signal may change under the influence of birefringence in the optical transmission line. As described above, depending on the data carried by each signal light, the polarization planes of the X polarization and the Y polarization are different from each other by 45 degrees, and the polarization plane is different from that of the optical transmission line. When the X polarization coincides with the influence of birefringence, no signal light is input to the polarization maintaining amplifier 22 in the configuration of the first embodiment. Therefore, the polarization maintaining amplifier 22 outputs only strong ASE light, and the S/N ratio may deteriorate. In the present embodiment, since the variable polarization controller 81 changes the rotation amount, it is possible to prevent the state in which the optical signal is not input to one of the polarization maintaining amplifier 21 and the polarization maintaining amplifier 22 from continuing. Therefore, deterioration of the S/N ratio can be suppressed.

１：分離部、２１、２２：偏波保持型増幅部、３１、３２：偏光子、４：合波部 1: Separation unit, 21, 22: Polarization-maintaining amplification unit, 31, 32: Polarizer, 4: Multiplexing unit

Claims (7)

偏波多重光信号を増幅する光増幅装置であって、
制御手段と、
入力される光信号の偏波面を前記制御手段から通知された回転量だけ回転させる第１回転手段と、
前記第１回転手段からの光信号を第１偏波と、前記第１偏波とは直交する第２偏波とに偏波分離して、第１偏波の第１光信号と第２偏波の第２光信号と、を出力する分離手段と、
前記第１光信号を光増幅する第１増幅手段と、
前記第２光信号を光増幅する第２増幅手段と、
前記第１増幅手段が出力する第１光信号に含まれる前記第２偏波の成分を抑制する第１抑制手段と、
前記第２増幅手段が出力する第２光信号に含まれる前記第１偏波の成分を抑制する第２抑制手段と、
前記第１抑制手段が出力する光信号と前記第２抑制手段が出力する光信号とを偏波多重して出力する多重手段と、
前記多重手段からの光信号の偏波面を前記制御手段から通知された回転量だけ回転させる第２回転手段と、
を備え、
前記第１増幅手段及び前記第２増幅手段は、入力される光信号の偏波面を保持して出力し、
前記制御手段は、前記第１回転手段の回転量の絶対値と前記第２回転手段の回転量の絶対値が等しく、前記第１回転手段による偏波面の回転方向と前記第２回転手段による偏波面の回転方向が互いに逆となる様に、前記第１回転手段及び前記第２回転手段を制御することを特徴とする光増幅装置。 An optical amplifier for amplifying a polarization multiplexed optical signal,
Control means,
First rotation means for rotating the plane of polarization of the input optical signal by the rotation amount notified from the control means;
The optical signal from the first rotating means is polarization-separated into a first polarized wave and a second polarized wave orthogonal to the first polarized wave, and the first optical signal of the first polarized wave and the second polarized wave are separated. Separating means for outputting the second optical signal of the wave,
First amplification means for optically amplifying the first optical signal;
Second amplification means for optically amplifying the second optical signal;
First suppressing means for suppressing a component of the second polarized wave included in the first optical signal output from the first amplifying means,
Second suppressing means for suppressing the component of the first polarized wave included in the second optical signal output by the second amplifying means,
Multiplexing means for polarization-multiplexing and outputting the optical signal output by the first suppressing means and the optical signal output by the second suppressing means,
Second rotation means for rotating the polarization plane of the optical signal from the multiplexing means by the rotation amount notified from the control means;
Equipped with
The first amplifying means and the second amplifying means hold and output the polarization plane of the input optical signal,
The control means is such that the absolute value of the rotation amount of the first rotation means and the absolute value of the rotation amount of the second rotation means are equal, and the rotation direction of the plane of polarization by the first rotation means and the polarization direction by the second rotation means. An optical amplifying device, characterized in that the first rotating means and the second rotating means are controlled so that the rotation directions of the wavefronts are opposite to each other . 前記制御手段は、前記第１回転手段の回転量を時間とともに変化させることを特徴とする請求項１に記載の光増幅装置。 Wherein, the optical amplifier according to claim 1, characterized in that changing the amount of rotation of said first rotating means over time. 偏波多重光信号を増幅する光増幅装置であって、
入力される光信号を第１偏波と、前記第１偏波とは直交する第２偏波とに偏波分離して、第１偏波の第１光信号と第２偏波の第２光信号と、を出力する分離手段と、
前記第１光信号の偏波面を第１所定量だけ回転させて第３光信号を出力する第１回転手段と、
前記第２光信号の偏波面を第２所定量だけ回転させて第４光信号を出力する第２回転手段と、
前記第３光信号を光増幅する第１増幅手段と、
前記第４光信号を光増幅する第２増幅手段と、
前記第１増幅手段が出力する第３光信号の偏波面を前記第１所定量だけ、前記第１回転手段とは逆方向に回転させた第５光信号を出力する第３回転手段と、
前記第２増幅手段が出力する第４光信号の偏波面を前記第２所定量だけ、前記第２回転手段とは逆方向に回転させた第６光信号を出力する第４回転手段と、
前記第５光信号に含まれる前記第２偏波の成分を抑制する第１抑制手段と、
前記第６光信号に含まれる前記第１偏波の成分を抑制する第２抑制手段と、
前記第１抑制手段が出力する光信号と前記第２抑制手段が出力する光信号とを偏波多重して出力する多重手段と、
を備え、
前記第１増幅手段及び前記第２増幅手段は、入力される光信号の偏波面を保持して出力することを特徴とする光増幅装置。 An optical amplifier for amplifying a polarization multiplexed optical signal,
The input optical signal is split into a first polarized wave and a second polarized wave orthogonal to the first polarized wave, and the first optical signal of the first polarized wave and the second polarized wave of the second polarized wave are separated. Separation means for outputting an optical signal,
First rotating means for outputting a third optical signal by rotating the polarization plane of the first optical signal by a first predetermined amount;
Second rotating means for outputting a fourth optical signal by rotating the polarization plane of the second optical signal by a second predetermined amount;
First amplifying means for optically amplifying the third optical signal,
Second amplifying means for optically amplifying the fourth optical signal;
Third rotating means for outputting a fifth optical signal obtained by rotating the polarization plane of the third optical signal output by the first amplifying means in the direction opposite to the first rotating means by the first predetermined amount;
Fourth rotating means for outputting a sixth optical signal obtained by rotating the polarization plane of the fourth optical signal output by the second amplifying means in the direction opposite to the second rotating means by the second predetermined amount;
First suppressing means for suppressing a component of the second polarized wave included in the fifth optical signal,
Second suppressing means for suppressing the component of the first polarized wave included in the sixth optical signal;
Multiplexing means for polarization-multiplexing and outputting the optical signal output by the first suppressing means and the optical signal output by the second suppressing means,
Equipped with
It said first amplifying means and the second amplifying means, an optical amplifier, wherein also be output from holding the polarization plane of the input optical signal. 前記第１所定量及び前記第２所定量は、９０度、１８０度及び２７０度以外の値であることを特徴とする請求項３に記載の光増幅装置。 The optical amplification device according to claim 3 , wherein the first predetermined amount and the second predetermined amount are values other than 90 degrees, 180 degrees, and 270 degrees. 前記第１所定量及び前記第２所定量は、４５度であることを特徴とする請求項３に記載の光増幅装置。 The optical amplification device according to claim 3 , wherein the first predetermined amount and the second predetermined amount are 45 degrees. 偏波多重光信号を増幅する光増幅装置であって、
入力される光信号を第１偏波と、前記第１偏波とは直交する第２偏波とに偏波分離して、第１偏波の第１光信号と第２偏波の第２光信号と、を出力する分離手段と、
前記第１光信号を円偏波の第３光信号に変換して出力する第１変換手段と、
前記第２光信号を円偏波の第４光信号に変換して出力する第２変換手段と、
前記第３光信号を光増幅する第１増幅手段と、
前記第４光信号を光増幅する第２増幅手段と、
前記第１増幅手段が出力する前記円偏波の第３光信号を前記第１偏波の第５光信号に変換して出力する第３変換手段と、
前記第２増幅手段が出力する前記円偏波の第４光信号を前記第２偏波の第６光信号に変換して出力する第４変換手段と、
前記第５光信号に含まれる前記第２偏波の成分を抑制する第１抑制手段と、
前記第６光信号に含まれる前記第１偏波の成分を抑制する第２抑制手段と、
前記第１抑制手段が出力する光信号と前記第２抑制手段が出力する光信号とを偏波多重して出力する多重手段と、
を備えていることを特徴とする光増幅装置。 An optical amplifier for amplifying a polarization multiplexed optical signal,
The input optical signal is split into a first polarized wave and a second polarized wave orthogonal to the first polarized wave, and the first optical signal of the first polarized wave and the second polarized wave of the second polarized wave are separated. Separation means for outputting an optical signal,
First conversion means for converting the first optical signal into a circularly polarized third optical signal and outputting the third optical signal,
Second conversion means for converting the second optical signal into a circularly polarized fourth optical signal and outputting the fourth optical signal;
First amplifying means for optically amplifying the third optical signal,
Second amplifying means for optically amplifying the fourth optical signal;
Third converting means for converting the circularly polarized third optical signal output by the first amplifying means into a fifth optical signal for the first polarized wave, and outputting the fifth optical signal.
Fourth conversion means for converting the circularly polarized fourth optical signal output from the second amplifying means into the sixth polarized light sixth optical signal, and outputting the sixth optical signal.
First suppressing means for suppressing a component of the second polarized wave included in the fifth optical signal,
Second suppressing means for suppressing the component of the first polarized wave included in the sixth optical signal;
Multiplexing means for polarization-multiplexing and outputting the optical signal output by the first suppressing means and the optical signal output by the second suppressing means,
An optical amplification device comprising: 前記第１増幅手段及び前記第２増幅手段は、入力される光信号の偏波面を保持しないことを特徴とする請求項６に記載の光増幅装置。 The optical amplifying device according to claim 6 , wherein the first amplifying unit and the second amplifying unit do not hold the polarization plane of the input optical signal.
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