JP2009043849A - Optical fiber amplifier - Google Patents

Optical fiber amplifier Download PDF

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JP2009043849A
JP2009043849A JP2007205783A JP2007205783A JP2009043849A JP 2009043849 A JP2009043849 A JP 2009043849A JP 2007205783 A JP2007205783 A JP 2007205783A JP 2007205783 A JP2007205783 A JP 2007205783A JP 2009043849 A JP2009043849 A JP 2009043849A
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light
input signal
optical fiber
fiber amplifier
gain
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Hirotaka Ono
浩孝 小野
Koji Masuda
浩次 増田
Makoto Yamada
誠 山田
Makoto Shimizu
誠 清水
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NTT Electronics Corp
Nippon Telegraph and Telephone Corp
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Nippon Telegraph and Telephone Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber amplifier which is reduced in gain control error due to scattered light of a rare earth added fiber and holds a gain at a fixed value. <P>SOLUTION: The optical fiber amplifier 100 according to an embodiment 1 reduces the influence of scattered light by adding an offset amount corresponding to input signal light power to a reference voltage used by a control circuit 109 for gain control. As the input signal light power increases, scattered light included in light passed through an optical filter 107 increases. Therefore, when such light is converted into a voltage to perform control so that the difference from the reference voltage becomes 0, since excitation light power becomes smaller than a value for imparting a desired gain, a plus offset corresponding to the increase of the input signal light power is added to the reference voltage. When the input signal light power decreases, on the other hand, a negative offset is only added to the contrary. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、光ファイバ増幅器に関し、より詳細には、利得を一定値に保持する光ファイバ増幅器に関する。   The present invention relates to an optical fiber amplifier, and more particularly to an optical fiber amplifier that maintains a gain at a constant value.

利得を一定値に保持する機能を有する光ファイバ増幅器の利得制御方法には種々の方式があるが、その１つとして、増幅媒体である希土類添加ファイバの側方向に放射される自然放出光（Ｓｐｏｎｔａｎｅｏｕｓ Ｅｍｉｓｓｉｏｎ光：ＳＥ光）の強度を光検出器により検出し、その検出結果に基づいて希土類添加ファイバへの励起光パワーを調整する方法がある（特許文献１参照）。   There are various methods for controlling the gain of an optical fiber amplifier having a function of holding a gain at a constant value. One of them is spontaneous emission light (Spontaneous) emitted in the lateral direction of a rare earth-doped fiber as an amplification medium. There is a method in which the intensity of the emission light (SE light) is detected by a photodetector and the excitation light power to the rare earth-doped fiber is adjusted based on the detection result (see Patent Document 1).

希土類添加ファイバを増幅媒体とする光ファイバ増幅器の利得Ｇは、希土類添加ファイバの側方向に放射される自然放出光を光検出器で検出して得られる光電流ＩSEと
Ｇ＝ａＩSE＋ｂ（ａおよびｂは定数） （１）
の関係にあり、利得を一定値に保持する機能を有する光ファイバ増幅器では光電流ＩSEが所望の一定値となるように制御が行われる。 The gain G of the optical fiber amplifier to amplify medium rare-earth doped fiber, an optical current obtained by detecting the spontaneous emission light emitted to the side direction of the rare earth-doped fiber optical detector I SE and G = aI SE + b ( a and b are constants) (1)
In the optical fiber amplifier having the function of maintaining the gain at a constant value, control is performed so that the photocurrent I SE becomes a desired constant value.

特開平４−３５６９８４号公報JP-A-4-356984 特許第３２３０７０８号公報Japanese Patent No. 3230708

しかしながら、この利得制御方法では、光検出器による検出に希土類添加ファイバにおいてレイリー過程等により散乱された励起光、入力信号光、および自然放出増幅光（Ａｍｐｌｉｆｉｅｄ Ｓｐｏｎｔａｎｅｏｕｓ Ｅｍｉｓｓｉｏｎ光：ＡＳＥ光）が含まれ、これらの散乱光が制御誤差となって利得制御精度を著しく低下させてしまう（特許文献２の段落０００４等を参照）。   However, in this gain control method, detection by the photodetector includes excitation light, input signal light, and spontaneous emission amplified light (Amplified Spontaneous Emission Light: ASE light) scattered by a Rayleigh process or the like in the rare earth-doped fiber. These scattered light becomes a control error and remarkably lowers the gain control accuracy (see paragraph 0004 of Patent Document 2).

すなわち、希土類添加ファイバの側方向に放射される光を検出して得られる光電流ＩDetを用いて制御を行うと、
ＩDet＝ＩSE＋ＩSct （２）
であり光電流ＩDetに散乱光による成分ＩSctが含まれるため、ＩDetが一定になるように励起光を制御すると光電流ＩSEが所望値からずれて利得に誤差が生じる。散乱光による光電流ＩSctが大きいほど、光電流ＩSEが所望値に比べて小さくなってしまう。 That is, when control is performed using the photocurrent I Det obtained by detecting the light emitted in the lateral direction of the rare earth-doped fiber,
I Det = I SE + I Sct (2)
Since the photocurrent I Det includes a component I Sct due to scattered light, if the excitation light is controlled so that I Det is constant, the photocurrent I SE deviates from a desired value and an error occurs in the gain. The greater the photocurrent I Sct due to scattered light, the smaller the photocurrent I SE compared to the desired value.

特に、入力信号光のパワーの変化に応じて光電流ＩSctが変動すると、散乱光に起因して生じた利得の誤差も変動することとなる。光電流ＩSEが非常に小さくＩSctとＩSEが同程度となる場合、入力信号光パワーが変化した際の利得の誤差が大きい。 In particular, when the photocurrent I Sct varies according to the change in power of the input signal light, the gain error caused by the scattered light also varies. If the photocurrent I SE is very small I Sct and I SE are comparable, a large error in the gain when the input signal light power is changed.

図７は、従来の利得制御方法により利得を一定値に保持する機能を有する光ファイバ増幅器の利得制御の結果を示す図である。この例では入力信号として１２チャネルの信号を使用しており、１２チャネル合計の光パワーがそれぞれ−５ｄＢｍ、０ｄＢｍおよび＋５ｄＢｍのときの利得スペクトルを示している。入力信号光パワーが−５ｄＢｍから＋５ｄＢｍに１０ｄＢだけ増加すると、利得スペクトルが最大で２．５ｄＢ程度減少してしまうことが分かる。これは、入力信号光パワーの増加により散乱光による光電流ＩSctが増加し、光電流ＩDetを用いて制御を行うことにより光電流ＩSEが所望値に比べて小さくなっているためである。 FIG. 7 is a diagram showing a result of gain control of an optical fiber amplifier having a function of maintaining a gain at a constant value by a conventional gain control method. In this example, a 12-channel signal is used as an input signal, and the gain spectrum is shown when the total optical power of the 12 channels is −5 dBm, 0 dBm, and +5 dBm, respectively. It can be seen that when the input signal light power is increased by -10 dBm from -5 dBm to +5 dBm, the gain spectrum is reduced by about 2.5 dB at the maximum. This is because the photocurrent I Sct due to the scattered light increases due to the increase of the input signal light power, and the photocurrent I SE becomes smaller than the desired value by performing the control using the photocurrent I Det. .

本発明は、このような問題点に鑑みてなされたものであり、その目的は、希土類添加ファイバにおける散乱光に起因する利得制御誤差が低減された、利得を一定値に保持する光ファイバ増幅器を提供することにある。   The present invention has been made in view of such problems, and an object of the present invention is to provide an optical fiber amplifier that maintains a gain at a constant value in which a gain control error caused by scattered light in a rare earth-doped fiber is reduced. It is to provide.

このような目的を達成するために、請求項１に記載の発明は、利得を一定値に保持する光ファイバ増幅器であって、入力信号光に励起光を合波する合波器と、前記合波器の出力を増幅し、出力信号光を出力する希土類添加ファイバと、前記希土類添加ファイバの側方向に放射される光から前記励起光の散乱光を抑制する光フィルタと、前記光フィルタを通過した光のパワーを検出して第１の電気信号に変換する第１の光検出器と、前記励起光のパワーを制御して、前記第１の電気信号を前記一定値の利得に対応する電気信号に調整する制御回路とを備え、前記一定値の利得に対応する電気信号は、前記入力信号光のパワーに応じたオフセット量を加えてオフセットされることを特徴とする。   In order to achieve such an object, an invention according to claim 1 is an optical fiber amplifier that maintains a gain at a constant value, a multiplexer that multiplexes pumping light to input signal light, and the multiplexer. A rare earth-doped fiber that amplifies the output of the waver and outputs output signal light, an optical filter that suppresses the scattered light of the excitation light from the light emitted in the lateral direction of the rare earth-doped fiber, and passes through the optical filter A first photodetector for detecting the power of the generated light and converting it to a first electrical signal; and controlling the power of the pumping light to cause the first electrical signal to correspond to the gain of the constant value. A control circuit for adjusting the signal, and the electrical signal corresponding to the constant gain is offset by adding an offset amount corresponding to the power of the input signal light.

また、請求項２に記載の発明は、請求項１において、前記オフセット量は、前記入力信号光を分岐し、分岐された前記入力信号光を第２の光検出器により第２の電気信号に変換し、前記第２の電気信号に予め定めた演算を施して算出されることを特徴とする。   According to a second aspect of the present invention, in the first aspect, the offset amount is obtained by branching the input signal light and converting the branched input signal light into a second electric signal by a second photodetector. Conversion is performed, and the second electric signal is calculated by performing a predetermined calculation.

また、請求項３に記載の発明は、請求項２において、前記予め定めた演算は、線形演算であることを特徴とする。   According to a third aspect of the present invention, in the second aspect, the predetermined calculation is a linear calculation.

また、請求項４に記載の発明は、利得を一定値に保持する光ファイバ増幅器であって、等しい周波数間隔で多重された入力信号光に励起光を合波する合波器と、前記合波器の出力を増幅し、出力信号光を出力する希土類添加ファイバと、前記希土類添加ファイバ近傍に配置され、櫛状の透過スペクトルを有し、光遮断波長が前記入力信号光の波長と一致する第１の光フィルタと、前記第１の光フィルタの入力側または出力側のいずれかに配置され、前記励起光の散乱光を抑制する第２の光フィルタと、前記第１および第２の光フィルタを通過した光のパワーを検出して電気信号に変換する光検出器と、前記励起光のパワーを制御して、前記電気信号を前記一定値の利得に対応する電気信号に調整する制御回路とを備えることを特徴とする。   According to a fourth aspect of the present invention, there is provided an optical fiber amplifier that maintains a gain at a constant value, a multiplexer that multiplexes pumping light with input signal light multiplexed at equal frequency intervals, and the multiplexing A rare earth-doped fiber that amplifies the output of the detector and outputs output signal light; and a rare earth-doped fiber that is disposed in the vicinity of the rare earth-doped fiber, has a comb-like transmission spectrum, and has a light cutoff wavelength that matches the wavelength of the input signal light. 1 optical filter, a second optical filter disposed on either the input side or the output side of the first optical filter, and suppressing scattered light of the excitation light, and the first and second optical filters A photodetector that detects the power of light that has passed through and converts it into an electrical signal; and a control circuit that controls the power of the pumping light to adjust the electrical signal to an electrical signal corresponding to the gain of the constant value; It is characterized by providing.

本発明によれば、制御目標である利得に対応する電気信号を入力信号光のパワーに応じたオフセット量を加えてオフセットすることにより、希土類添加ファイバにおける散乱光に起因する利得制御誤差が低減された、利得を一定値に保持する光ファイバ増幅器を提供することができる。   According to the present invention, the gain control error due to the scattered light in the rare earth-doped fiber is reduced by offsetting the electrical signal corresponding to the gain that is the control target by adding an offset amount corresponding to the power of the input signal light. In addition, it is possible to provide an optical fiber amplifier that maintains the gain at a constant value.

また、本発明によれば、櫛状の透過スペクトルを有し、光遮断波長が入力信号光の波長と一致している希土類添加ファイバ近傍に配置された光フィルタを備えることにより、希土類添加ファイバにおける散乱光に起因する利得制御誤差が低減された、利得を一定値に保持する光ファイバ増幅器を提供することができる。   In addition, according to the present invention, the optical filter disposed in the vicinity of the rare earth-doped fiber having a comb-like transmission spectrum and having the light blocking wavelength that matches the wavelength of the input signal light is provided. It is possible to provide an optical fiber amplifier in which a gain control error caused by scattered light is reduced and the gain is maintained at a constant value.

以下、図面を参照して実施形態を詳細に説明する。   Hereinafter, embodiments will be described in detail with reference to the drawings.

（実施形態１）
図１は、実施形態１に係る光ファイバ増幅器の構成を示している。光ファイバ増幅器１００は、希土類添加ファイバ１０５を増幅媒体として入力信号光が増幅されて出力信号光となるものであり、希土類添加ファイバ１０５の側方向に放射される自然放出光および散乱光を検出して利得の制御に利用している。光ファイバ増幅器１００の構成および機能を以下に説明する。 (Embodiment 1)
FIG. 1 shows a configuration of an optical fiber amplifier according to the first embodiment. The optical fiber amplifier 100 uses the rare earth doped fiber 105 as an amplifying medium to amplify the input signal light to become output signal light, and detects spontaneous emission light and scattered light emitted in the lateral direction of the rare earth doped fiber 105. It is used for gain control. The configuration and function of the optical fiber amplifier 100 will be described below.

入力信号光が、光分岐回路１０１で分岐される。光分岐回路１０１で分岐された一方の光が、光アイソレータ１０２を通過して合波器１０３に入力される。合波器１０３において、励起光源１０４からの励起光が入力信号光に合波される。合波器１０３の出力が希土類添加ファイバ１０５で増幅され、出力信号光が光アイソレータ１０６を通過して出力される。   The input signal light is branched by the optical branch circuit 101. One light branched by the optical branch circuit 101 passes through the optical isolator 102 and is input to the multiplexer 103. In the multiplexer 103, the excitation light from the excitation light source 104 is combined with the input signal light. The output of the multiplexer 103 is amplified by the rare earth doped fiber 105, and the output signal light passes through the optical isolator 106 and is output.

希土類添加ファイバ１０５からは、その側方向に自然放出光および散乱光が放出されており、自然放出光および散乱光が、希土類添加ファイバ１０５の近傍に配置された光フィルタ１０７を通過する。光フィルタ１０７は、散乱光のうち、励起光に起因する成分を抑制するものである。光フィルタ１０７が励起光を遮断し、自然放出光を透過させるバンドパスフィルタとすれば、励起光の散乱光は容易除去することができるが、信号光に起因する散乱光は主にレイリー散乱光であって信号光波長と一致し、且つ信号光波長は自然放出光が強く放出される波長帯と一致するため信号光に起因する散乱光をバンドパスフィルタで除去することは困難である。ＡＳＥ光に起因する散乱光は通常無視しうる程度のものであり、ここでは考慮しない。   Spontaneously emitted light and scattered light are emitted in the lateral direction from the rare earth-doped fiber 105, and the spontaneously emitted light and scattered light pass through an optical filter 107 disposed in the vicinity of the rare earth-doped fiber 105. The optical filter 107 suppresses components caused by excitation light in the scattered light. If the optical filter 107 is a bandpass filter that blocks the excitation light and transmits the spontaneous emission light, the scattered light of the excitation light can be easily removed, but the scattered light caused by the signal light is mainly Rayleigh scattered light. Since the signal light wavelength matches the wavelength band in which spontaneous emission light is strongly emitted, it is difficult to remove the scattered light caused by the signal light with a band-pass filter. Scattered light resulting from ASE light is normally negligible and is not considered here.

光検出器１０８が、光フィルタ１０７を通過した光のパワーを検出して電流に変換する。制御回路１０９が、その電流を電流−電圧変換して基準電圧との差分を求め、差分に応じた制御信号を励起光源１０４に入力する。制御信号により励起光源１０４が発生する励起光パワーが調整されて、差分が０に近づく。   The photodetector 108 detects the power of the light that has passed through the optical filter 107 and converts it into a current. The control circuit 109 obtains a difference from the reference voltage by current-voltage conversion of the current and inputs a control signal corresponding to the difference to the excitation light source 104. The pumping light power generated by the pumping light source 104 is adjusted by the control signal, and the difference approaches zero.

ここで基準電圧は、所望の利得Ｇを与える光検出器１０８の出力電流に対応する電圧である。入力信号光パワーを一定としておき励起光パワーを変化させることで、光ファイバ増幅器１００の利得と光検出器１０８の出力電流との関係を測定することができる。所望の利得Ｇを与える光検出器１０８の出力電流を制御回路１０９において電流−電圧変換した値が基準電圧である。増幅器１００の利得と光検出器１０８の出力電流との関係は、数式（１）のように一次関数近似をしてもよいし、より高い制御精度を得るために高次関数近似をしてもよい。予め求めた基準電圧は、制御回路１０９内の記憶装置に格納してもよいし、外部の記憶装置から読み出してもよい。   Here, the reference voltage is a voltage corresponding to the output current of the photodetector 108 that gives a desired gain G. By changing the pumping light power while keeping the input signal light power constant, the relationship between the gain of the optical fiber amplifier 100 and the output current of the photodetector 108 can be measured. A value obtained by performing current-voltage conversion on the output current of the photodetector 108 that gives a desired gain G in the control circuit 109 is a reference voltage. The relationship between the gain of the amplifier 100 and the output current of the photodetector 108 may be approximated by a linear function as shown in Formula (1), or may be approximated by a high-order function to obtain higher control accuracy. Good. The reference voltage obtained in advance may be stored in a storage device in the control circuit 109 or read from an external storage device.

このように光ファイバ増幅器１００は利得を一定値に保持する機能を有するが、本実施形態に係る光ファイバ増幅器１００は、基準電圧に入力信号光パワーに応じたオフセット量を加えて散乱光の影響を低減している。入力信号光パワーが増加すると、光フィルタ１０７を通過した光に含まれる散乱光が増加する。したがって、そのような光を電圧に変換して基準電圧との差分が０になるように制御を行うと、励起光パワーが所望の利得を与える値よりも小さくなってしまうので、入力信号光パワーの増加に応じた正のオフセットを基準電圧に加えている。入力信号光パワーが減少した場合は逆に負のオフセットを加えればよい。   As described above, the optical fiber amplifier 100 has a function of maintaining the gain at a constant value. However, the optical fiber amplifier 100 according to the present embodiment adds the offset amount corresponding to the input signal light power to the reference voltage and affects the scattered light. Is reduced. When the input signal light power increases, the scattered light included in the light that has passed through the optical filter 107 increases. Therefore, if such light is converted into a voltage and control is performed such that the difference from the reference voltage becomes zero, the pumping light power becomes smaller than a value giving a desired gain. A positive offset corresponding to the increase in the reference voltage is added to the reference voltage. If the input signal light power decreases, a negative offset may be added.

具体的には、光分岐回路１０１で分岐された入力信号光の他方を、光検出器１１０により電流に変換する。制御回路１０９においてその電流を電圧に変換し、そして予め定めた演算を施して基準電圧に加えるオフセット量を算出する。予め定めた演算は、上述のように入力信号光パワーが増加した場合には正、減少した場合には負のオフセット量を与えるものであるが、たとえば一次関数近似を行い、オフセット量を、ｃ×（光検出器１１０の出力電流に対応する電圧値）＋ｄ（ｃ，ｄは測定により得られる定数）のように求めることができる。より高い制御精度を得るために高次関数近似をしてもよい。   Specifically, the other of the input signal light branched by the optical branch circuit 101 is converted into a current by the photodetector 110. The control circuit 109 converts the current into a voltage, and performs a predetermined calculation to calculate an offset amount to be added to the reference voltage. The predetermined calculation gives a positive offset amount when the input signal light power increases as described above, and gives a negative offset amount when the input signal light power decreases. For example, a linear function approximation is performed, and the offset amount is expressed as c. × (Voltage value corresponding to the output current of the photodetector 110) + d (c and d are constants obtained by measurement). In order to obtain higher control accuracy, higher-order function approximation may be performed.

図２は、実施形態１に係る光ファイバ増幅器の利得制御の結果を示す図である。この例では入力信号として１２チャネルの信号を使用しており、１２チャネル合計の光パワーがそれぞれ−５ｄＢｍ、０ｄＢｍおよび＋５ｄＢｍのときの利得スペクトルを示している。オフセット量の算出には一次関数近似を用いた。入力信号光パワーが−５ｄＢｍから＋５ｄＢｍに１０ｄＢだけ増加しても、利得スペクトルの変化が０．５ｄＢ以下であり、従来技術（図７）と比較して大幅な制御精度の改善が得られている。   FIG. 2 is a diagram illustrating a result of gain control of the optical fiber amplifier according to the first embodiment. In this example, a 12-channel signal is used as an input signal, and the gain spectrum is shown when the total optical power of the 12 channels is −5 dBm, 0 dBm, and +5 dBm, respectively. A linear function approximation was used to calculate the offset amount. Even if the input signal light power is increased from −5 dBm to +5 dBm by 10 dB, the gain spectrum change is 0.5 dB or less, and a significant improvement in control accuracy is obtained compared to the conventional technique (FIG. 7). .

なお、入力信号光パワーに対応する光電流値（その電流−電圧変換後の電圧）に一次関数の演算を行い基準電圧を変化させても結果はほぼ同じである。   It should be noted that the result is almost the same even when a linear function is calculated for the photocurrent value corresponding to the input signal light power (voltage after the current-voltage conversion) and the reference voltage is changed.

また、本実施形態では、制御回路１０９において電流−電圧変換を行い電圧を用いて利得を制御したが、電流を用いて利得制御を行うことができることに留意されたい。すなわち、電圧または電流のいずれかを電気信号として使用することができる。   In the present embodiment, the control circuit 109 performs current-voltage conversion and the gain is controlled using the voltage. However, it should be noted that the gain control can be performed using the current. That is, either voltage or current can be used as an electrical signal.

（実施形態２）
図３は、実施形態２に係る光ファイバ増幅器の構成を示している。光ファイバ増幅器３００は、希土類添加ファイバ１０５を増幅媒体として入力信号光が増幅されて出力信号光となるものであり、希土類添加ファイバ１０５の側方向に放射される光を検出して利得の制御に利用している点で実施形態１に係る光ファイバ増幅器１００と同一だが、光ファイバ増幅器３００では、入力信号光パワーに応じた基準電圧のオフセットではなく、光フィルタ３０７の構成により散乱光に起因する利得制御誤差を低減している。なお本実施形態では、入力信号として波長多重信号を用いている。実施形態１においては、１波のみでもよい。 (Embodiment 2)
FIG. 3 shows the configuration of the optical fiber amplifier according to the second embodiment. The optical fiber amplifier 300 uses the rare earth-doped fiber 105 as an amplification medium to amplify input signal light to become output signal light. The optical fiber amplifier 300 detects light emitted in the lateral direction of the rare earth-doped fiber 105 and controls gain. Although it is the same as the optical fiber amplifier 100 according to the first embodiment in that it is used, the optical fiber amplifier 300 is not caused by the offset of the reference voltage according to the input signal light power but is caused by scattered light by the configuration of the optical filter 307. Gain control error is reduced. In this embodiment, a wavelength multiplexed signal is used as an input signal. In the first embodiment, only one wave may be used.

光フィルタ３０７は、希土類添加ファイバ１０５の近傍に配置されたファブリ・ペロー・エタロンフィルタであり、その透過スペクトルが櫛状になっている。光フィルタ３０７を透過させて光検出器１０８で検出した、希土類添加ファイバ１０５であるＥｒ添加ファイバの放出光の検出スペクトルは図４のようになり、その包絡線は図５に示したＥｒ添加ファイバの自然放出光スペクトルにほぼ一致する。したがって、光フィルタ３０７は自然放出光パワーの波長依存性を損なうことなく検出することができるものである。   The optical filter 307 is a Fabry-Perot etalon filter disposed in the vicinity of the rare earth-doped fiber 105, and its transmission spectrum is comb-shaped. The detection spectrum of the emitted light of the Er-doped fiber, which is the rare earth-doped fiber 105, transmitted through the optical filter 307 and detected by the photodetector 108 is as shown in FIG. 4, and the envelope is the Er-doped fiber shown in FIG. It almost coincides with the spontaneous emission light spectrum. Therefore, the optical filter 307 can detect without spoiling the wavelength dependence of the spontaneous emission light power.

光フィルタ３０７のこの特性は、散乱光の波長が入力信号光の波長と一致することを利用して、光フィルタ３０７の光遮断波長と入力信号光の波長とを一致させることにより、等しい周波数間隔で多重された波長多重信号による散乱光を一括して遮断することで得られる。なお、希土類添加ファイバ１０５と光フィルタ３０７の間に挿入された光フィルタ１０７は励起光に起因する散乱光を抑制するものであり、励起光波長の光を遮断し、自然放出光の波長帯の光を透過させるバンドパスフィルタである。励起光波長は、通常９８０ｎｍ近傍、あるいは１４８０ｎｍ近傍である。光フィルタの配置は図３に示したように希土類添加ファイバ１０５と光フィルタ１０７の間に限定されるものではなく、光フィルタ３０７と光検出器１０８の間に挿入しても効果は同じである。   This characteristic of the optical filter 307 uses the fact that the wavelength of the scattered light matches the wavelength of the input signal light, and makes the optical cutoff wavelength of the optical filter 307 match the wavelength of the input signal light, thereby equal frequency intervals. It is obtained by collectively blocking scattered light due to the wavelength multiplexed signal multiplexed by. The optical filter 107 inserted between the rare earth-doped fiber 105 and the optical filter 307 suppresses scattered light caused by the excitation light, blocks light of the excitation light wavelength, and emits light in the wavelength band of spontaneous emission light. It is a band pass filter that transmits light. The excitation light wavelength is usually around 980 nm or around 1480 nm. The arrangement of the optical filter is not limited between the rare earth-doped fiber 105 and the optical filter 107 as shown in FIG. 3, and the same effect can be obtained by inserting the optical filter between the optical filter 307 and the photodetector 108. .

図６は、実施形態２に係る光ファイバ増幅器の利得制御の結果を示す図である。この例では入力信号として８０チャネル波長多重信号を使用しており、８０チャネル合計の光パワーがそれぞれ−５ｄＢｍ、０ｄＢｍおよび＋５ｄＢｍのときの利得スペクトルを示している。入力信号光パワーが−５ｄＢｍから＋５ｄＢｍに１０ｄＢだけ増加しても、利得スペクトルの変化が０．５ｄＢ以下であり、従来技術（図７）と比較して大幅な制御精度の改善が得られている。   FIG. 6 is a diagram illustrating a result of gain control of the optical fiber amplifier according to the second embodiment. In this example, an 80 channel wavelength multiplexed signal is used as an input signal, and the gain spectrum is shown when the total optical power of the 80 channels is -5 dBm, 0 dBm, and +5 dBm, respectively. Even if the input signal light power is increased from −5 dBm to +5 dBm by 10 dB, the gain spectrum change is 0.5 dB or less, and a significant improvement in control accuracy is obtained compared to the conventional technique (FIG. 7). .

なお、本実施形態に係る光ファイバ増幅器３００は、特許文献２に記載されているような、入力信号光の波長帯外の自然放出光を光フィルタで透過させて光検出器により検出する従来の光ファイバ増幅器とは異なり、入力信号光の波長帯が自然放出光の波長帯に広く分布している場合にも精度良く自然放出光を検出することができる。実際、波長多重伝送システムの信号波長帯はＣ帯でおおよそ１５３０−１５６５ｎｍ、Ｌ帯でおおよそ１５７０−１６０５ｎｍであり、これらのシステムにおいて入力信号光の波長帯外の自然放出光を検出すると、強度が大きい波長帯の自然放出光を遮断することとなり、自然放出光パワーの検出精度が劣化する。一方、本発明の構成においては、精度良く自然放出光パワーを検出できる。   The optical fiber amplifier 300 according to the present embodiment is a conventional optical fiber amplifier 300 as described in Patent Document 2, in which spontaneous emission light outside the wavelength band of input signal light is transmitted through an optical filter and detected by a photodetector. Unlike an optical fiber amplifier, spontaneous emission light can be detected with high accuracy even when the wavelength band of input signal light is widely distributed in the wavelength band of spontaneous emission light. Actually, the wavelength band of the wavelength division multiplexing transmission system is approximately 1530 to 1565 nm in the C band and approximately 1570 to 1605 nm in the L band. When spontaneous emission light outside the wavelength band of the input signal light is detected in these systems, the intensity is increased. The spontaneous emission light in the large wavelength band is blocked, and the detection accuracy of the spontaneous emission light power is deteriorated. On the other hand, in the configuration of the present invention, the spontaneous emission light power can be detected with high accuracy.

実施形態１に係る光ファイバ増幅器の構成を示す図である。1 is a diagram illustrating a configuration of an optical fiber amplifier according to a first embodiment. 実施形態１に係る光ファイバ増幅器の利得制御の結果を示す図である。It is a figure which shows the result of the gain control of the optical fiber amplifier which concerns on Embodiment 1. FIG. 実施形態２に係る光ファイバ増幅器の構成を示す図である。6 is a diagram illustrating a configuration of an optical fiber amplifier according to a second embodiment. FIG. 希土類添加ファイバの放出光の、実施形態２に係る光フィルタ透過後の検出スペクトルを示すグラフである。It is a graph which shows the detection spectrum after the optical filter which concerns on Embodiment 2 of the emitted light of a rare earth addition fiber. 希土類添加ファイバの自然放出光スペクトルを示すグラフである。It is a graph which shows the spontaneous emission light spectrum of a rare earth addition fiber. 実施形態２に係る光ファイバ増幅器の利得制御の結果を示す図である。It is a figure which shows the result of the gain control of the optical fiber amplifier which concerns on Embodiment 2. FIG. 従来の利得制御方法により利得を一定値に保持する機能を有する光ファイバ増幅器の利得制御の結果を示す図である。It is a figure which shows the result of the gain control of the optical fiber amplifier which has the function to hold | maintain a gain to a constant value by the conventional gain control method.

符号の説明Explanation of symbols

１００、３００ 光ファイバ増幅器
１０１ 光分岐器
１０２、１０６ 光アイソレータ
１０３ 合波器
１０４ 励起光源
１０５ 希土類添加ファイバ
１０７、３０７ 光フィルタ
１０８ 光検出器
１０９ 制御回路
１１０ 光検出器（第２の光検出器に相当） 100, 300 Optical fiber amplifier 101 Optical splitter 102, 106 Optical isolator 103 Multiplexer 104 Excitation light source 105 Rare earth doped fiber 107, 307 Optical filter 108 Photo detector 109 Control circuit 110 Photo detector (into the second photo detector) Equivalent)

Claims (4)

利得を一定値に保持する光ファイバ増幅器であって、
入力信号光に励起光を合波する合波器と、
前記合波器の出力を増幅し、出力信号光を出力する希土類添加ファイバと、
前記希土類添加ファイバの側方向に放射される光から前記励起光の散乱光を抑制する光フィルタと、
前記光フィルタを通過した光のパワーを検出して第１の電気信号に変換する第１の光検出器と、
前記励起光のパワーを制御して、前記第１の電気信号を前記一定値の利得に対応する電気信号に調整する制御回路と
を備え、
前記一定値の利得に対応する電気信号は、前記入力信号光のパワーに応じたオフセット量を加えてオフセットされることを特徴とする光ファイバ増幅器。 An optical fiber amplifier that maintains a constant gain,
A multiplexer that combines the excitation light with the input signal light;
A rare earth-doped fiber that amplifies the output of the multiplexer and outputs output signal light;
An optical filter that suppresses the scattered light of the excitation light from the light emitted in the lateral direction of the rare earth-doped fiber;
A first photodetector that detects the power of the light that has passed through the optical filter and converts it into a first electrical signal;
A control circuit for controlling the power of the excitation light to adjust the first electric signal to an electric signal corresponding to the gain of the constant value;
An optical fiber amplifier, wherein an electrical signal corresponding to the constant gain is offset by adding an offset amount corresponding to the power of the input signal light. 前記オフセット量は、前記入力信号光を分岐し、分岐された前記入力信号光を第２の光検出器により第２の電気信号に変換し、前記第２の電気信号に予め定めた演算を施して算出されることを特徴とする請求項１に記載の光ファイバ増幅器。   The offset amount is determined by branching the input signal light, converting the branched input signal light into a second electric signal by a second photodetector, and performing a predetermined calculation on the second electric signal. The optical fiber amplifier according to claim 1, wherein the optical fiber amplifier is calculated by: 前記予め定めた演算は、線形演算であることを特徴とする請求項２に記載の光ファイバ増幅器。   The optical fiber amplifier according to claim 2, wherein the predetermined calculation is a linear calculation. 利得を一定値に保持する光ファイバ増幅器であって、
等しい周波数間隔で多重された入力信号光に励起光を合波する合波器と、
前記合波器の出力を増幅し、出力信号光を出力する希土類添加ファイバと、
前記希土類添加ファイバ近傍に配置され、櫛状の透過スペクトルを有し、光遮断波長が前記入力信号光の波長と一致する第１の光フィルタと、
前記第１の光フィルタの入力側または出力側のいずれかに配置され、前記励起光の散乱光を抑制する第２の光フィルタと、
前記第１および第２の光フィルタを通過した光のパワーを検出して電気信号に変換する光検出器と、
前記励起光のパワーを制御して、前記電気信号を前記一定値の利得に対応する電気信号に調整する制御回路と
を備えることを特徴とする光ファイバ増幅器。 An optical fiber amplifier that maintains a constant gain,
A multiplexer that multiplexes pumping light to input signal light multiplexed at equal frequency intervals;
A rare earth-doped fiber that amplifies the output of the multiplexer and outputs output signal light;
A first optical filter disposed in the vicinity of the rare earth-doped fiber, having a comb-like transmission spectrum, and having a light blocking wavelength that matches the wavelength of the input signal light;
A second optical filter disposed on either the input side or the output side of the first optical filter to suppress scattered light of the excitation light;
A photodetector that detects the power of the light that has passed through the first and second optical filters and converts it into an electrical signal;
An optical fiber amplifier comprising: a control circuit that controls the power of the pumping light to adjust the electrical signal to an electrical signal corresponding to the constant gain.
JP2007205783A 2007-08-07 2007-08-07 Optical fiber amplifier Pending JP2009043849A (en)

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Citations (8)

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JPS62245740A (en) * 1986-04-17 1987-10-27 Nec Corp Wavelength multiplex optical transmission system
JPH04241328A (en) * 1991-01-16 1992-08-28 Nec Corp Control method for optical amplifier and optical amplifier
JPH06268305A (en) * 1993-03-15 1994-09-22 Nippon Telegr & Teleph Corp <Ntt> Optical amplifier
JPH09326520A (en) * 1996-06-06 1997-12-16 Oki Electric Ind Co Ltd Optical filter module and optical amplifier using thereof
JP2000232433A (en) * 1999-02-08 2000-08-22 Fujitsu Ltd Wavelength multiplex optical communication system and optical amplifier
JP2005260013A (en) * 2004-03-12 2005-09-22 Fujitsu Ltd Light transmission system having noise eliminating function
JP2005277044A (en) * 2004-03-24 2005-10-06 Fujitsu Ltd Method and device for monitoring gain of optical amplifier
JP2007532005A (en) * 2004-03-31 2007-11-08 アイシン精機株式会社 High power short pulse fiber laser

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS62245740A (en) * 1986-04-17 1987-10-27 Nec Corp Wavelength multiplex optical transmission system
JPH04241328A (en) * 1991-01-16 1992-08-28 Nec Corp Control method for optical amplifier and optical amplifier
JPH06268305A (en) * 1993-03-15 1994-09-22 Nippon Telegr & Teleph Corp <Ntt> Optical amplifier
JPH09326520A (en) * 1996-06-06 1997-12-16 Oki Electric Ind Co Ltd Optical filter module and optical amplifier using thereof
JP2000232433A (en) * 1999-02-08 2000-08-22 Fujitsu Ltd Wavelength multiplex optical communication system and optical amplifier
JP2005260013A (en) * 2004-03-12 2005-09-22 Fujitsu Ltd Light transmission system having noise eliminating function
JP2005277044A (en) * 2004-03-24 2005-10-06 Fujitsu Ltd Method and device for monitoring gain of optical amplifier
JP2007532005A (en) * 2004-03-31 2007-11-08 アイシン精機株式会社 High power short pulse fiber laser

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