JP2004194153A - Optical wavelength multiplex transmission system - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、正分散光ファイバと負分散光ファイバを組み合わせた光ファイバ伝送路を介して波長多重信号光を伝送する光波長多重伝送システムに関する。
【０００２】
【従来の技術】
光通信システムにおいて、光信号の伝送距離を延ばすためには、光信号の減衰等を考慮すると光信号強度を増大させる必要がある。しかし、光伝送路として一般に用いられている光ファイバは、伝搬する光信号の強度および伝送距離の増加とともに、その非線形性による効果が顕著になることが知られている。この非線形性による効果は、一般的に次のような現象を引き起こして光信号の伝送可能距離を制限する要因になる（非特許文献１）。
【０００３】
(1) 光強度変化に応じた信号光自身の位相変化をもたらす自己位相変調。
(2) 異なる波長の信号光間、または信号光と雑音光間の相互作用を引き起こす四光波混合。
(3) 波長多重信号光間の光強度変化に応じて信号光自身の位相変化をもたらす相互位相変調。
【０００４】
自己位相変調効果は、信号光自身のスペクトルを拡大するため、光ファイバの波長分散による信号光波形劣化を増大させる。この波形劣化の原因となる光ファイバの波長分散は、一般的に２次以上の次数の分散を意味する。したがって、自己位相変調効果の低減または防止を図るには、信号光の波長を光ファイバの零分散波長に設定して伝送すればよい。
【０００５】
一方、四光波混合および相互位相変調は、異なる波長の信号光間または信号光と雑音光間の群速度差に依存し、この群速度差が大きいほど相互作用の大きさは小さくなる。この群速度差は２次分散値にほぼ比例するので、四光波混合および相互位相変調効果の低減を図るには、２次分散値が大きくなるようにすればよい。すなわち、自己位相変調効果の低減のための対応とはトレードオフの関係にある。
【０００６】
次に、３次分散が信号光に与える影響について考える。３次分散は２次分散の傾き（分散スロープ）であり、波長に応じて２次分散値が異なることになるので、例えば光伝送路中で２次分散値を補償しても特定の波長に対する２次分散値を補償できるだけで、他の波長に対する２次分散値を同時に零にすることは不可能である。その結果、補償できない波長の信号光が光伝送路を伝搬すると分散の影響を受け、しかも光伝送路中でこの分散が補償されないために２次分散がシステム全体にわたって累積し、信号光波形劣化を増大させることになる。
【０００７】
このような問題を解決するための従来技術としては、図３に示すように、信号波長における正の２次分散および３次分散を有する正分散光ファイバ１と、負の２次分散および３次分散を有する負分散光ファイバ２を１対とし、光増幅中継器３を介して２対以上接続し、全体の累積３次分散を減少させ、かつ周期的に累積２次分散値を零にする分散マネジメント法が提案されている（非特許文献２）。本方法は、光ファイバの非線形性の影響を強く受ける長距離光波長多重伝送システムに有効である。
【０００８】
【非特許文献１】
G.P.Agrawal 著, Nonlinear Fiber Optics, Academic Press, 1989
【非特許文献２】
村上誠、前田英樹、今井崇雅、ファイバ高次分散マネジメントによる16×10Gb/s長距離波長多重伝送、1998年電子情報通信学会通信ソサイエティ大会
【非特許文献３】
H.Maeda et al.,"Effectiveness of receiver-side compensation against FBG dispersion-induced SNR degradation in long-haul WDM optical networks",LEOS2001 Annual Meeting of the IEEE 2001, 2001
【非特許文献４】
M.Murakami et al.,"Long-haul WDM transmission with 20 Gb/s data channels using Raman assisted optical amplification", ECOC'01, 2001
【０００９】
【発明が解決しようとする課題】
図４〜図６は、累積２次分散と波長多重信号光の伝送可能波長帯域の関係を示す。
【００１０】
図４は、３次分散を補償することにより累積２次分散が大幅に低減し（破線から実線）、零分散波長を中心に累積２次分散値が小さい範囲で多くの信号光波長を配置できることを示す。
【００１１】
しかし、波長多重信号光の波長多重数を零分散波長を中心に増大していくと、図５に示すように零分散波長から離れた波長域ａ，ｂでは、３次分散に起因する累積２次分散が大きくなって信号波形劣化が生じ、波長多重数が制限されることになる。特に、短波長側ａで生じる負の累積２次分散は信号波形劣化を大きくする（非特許文献３）。
【００１２】
また、零分散波長で３次分散が零になるように光ファイバ伝送路を構成すると、図６のような凸型の曲線の分散特性が得られる。これは、４次以上の分散特性が影響しているためである（非特許文献４）。このため、波長多重数を増大していくと、図５に示した場合と同様に零分散波長から離れた波長域ａ，ｂでは、ともに負の累積２次分散による信号波形劣化により伝送可能な波長帯域が制限される問題があった。
【００１３】
本発明は、光ファイバ中の３次分散に起因する累積２次分散による信号波形劣化を回避し、システムのもつ伝送容量、伝送距離の制限要因を緩和することができる光波長多重伝送システムを提供することを目的とする。
【００１４】
【課題を解決するための手段】
本発明は、信号波長に対して正の２次分散および３次分散を有する正分散光ファイバと、負の２次分散および３次分散を有する負分散光ファイバで１対とし、それを２対以上接続して全体の累積３次分散値が周期的に零となり、かつ累積２次分散値が十分に小さくなるように設定された光ファイバ伝送路を介して波長多重信号光を伝送する光波長多重伝送システムにおいて、光ファイバ伝送路は累積３次分散値が零となる波長で累積２次分散値が正となるように構成し、波長多重信号光の波長帯域の中心波長が光ファイバ伝送路の３次分散値が零となる波長に設定する。
【００１５】
また、正分散光ファイバおよび負分散光ファイバの各長さが、各光ファイバの２次分散値と信号光のパルス幅と信号光波長から決まる２次分散長と、各光ファイバ内の信号光の平均電力と各光ファイバの光ファイバ非線形定数で決まる非線形長との積の平方根で定まる長さの１／２以下に設定する。
【００１６】
また、光ファイバ伝送路に信号光を増幅する光増幅器を配置し、その光増幅器の出力側に、正分散光ファイバおよび負分散光ファイバのうち非線形定数の小さい光ファイバを配置する。
【００１７】
【発明の実施の形態】
図１は、本発明の光波長多重伝送システムの構成例を示す。ここでは、システム構成と光ファイバ伝送路の累積２次分散の変化を示す。
【００１８】
図において、正の２次分散および３次分散を有する正分散光ファイバ１と、負の２次分散および３次分散を有する負分散光ファイバ２を１対とし、光増幅中継器３を介して２対以上接続して光ファイバ伝送路とする構成は、従来のものと同様である。本発明の特徴は、光ファイバ伝送路全体の累積３次分散値が周期的に零となり、かつ累積２次分散が十分に小さくなるように設定するときに、図２に示すように、累積３次分散値が零となる波長で累積２次分散値が正となるように構成し、波長多重信号光の波長帯域の中心波長を光ファイバ伝送路の３次分散値が零となる波長に設定するところにある。
【００１９】
これにより、波長多重信号光の伝送可能波長帯域は累積２次分散値が正となる波長域とともに、２つの零分散波長の外側にある累積２次分散が負かつ小である範囲にまで広げることができる。したがって、広帯域にわたって光ファイバの非線形効果による信号波形劣化、および負の累積２次分散による信号波形劣化を回避することができる。
【００２０】
また、光増幅中継器３の出力側に、正分散光ファイバ１および負分散光ファイバ２のうち非線形定数の小さい光ファイバ（ここでは正分散光ファイバ１）を配置することにより、光ファイバの非線形効果の影響を抑えることができる。
【００２１】
ここで、光ファイバ非線形係数をｋ、２次分散値をＤ、光ファイバ内の１波長信号あたりの平均電力をＰ、信号光のパルス幅（パルス波形の半値全幅または半値半幅、またはパルス波形ピーク値の１／ｅの値となるパルス幅）をＴ0 、信号光波長をλ（近似的に全信号波長に対して共通とする）、光速をｃとしたときに、光ファイバの非線形性の尺度となる非線形長ＬNLと、２次分散の大きさの尺度である２次分散長ＬD を
ＬNL＝１／(ｋＰ) …(1)
ＬD ＝Ｔ0 2／(λ2｜Ｄ｜／(2πｃ)) …(2)
と定義する。さらに、正分散光ファイバ１の２次分散長をＬDp、負分散光ファイバ２の２次分散長をＬDnと定義する。
【００２２】
このとき、正分散光ファイバ１の長さＬp と、負分散光ファイバ２の長さＬn は、
Ｌp <<（ＬDpＬNL)1/2 …(3)
Ｌn <<（ＬDnＬNL)1/2 …(4)
となるように設定する。例えば、
Ｌp ≦（ＬDpＬNL)1/2／２ …(5)
Ｌn ≦（ＬDnＬNL)1/2／２ …(6)
とすることにより、これらの区間で起こる光ファイバ非線形性と２次分散による信号波形劣化を効果的に抑えることができる（非特許文献４）。
【００２３】
なお、非特許文献３には、伝送速度10Ｇbit/s で伝送距離6000ｋｍの場合、累積２次分散の許容範囲（累積分散耐力Δ）は約−1000ps／nm〜＋2000ps／nmとあるので、正の２次分散値Ｄは約＋0.3 ps／nm／km（＝2000／6000）、負の２次分散値Ｄは約−0.16ps／nm／km（＝−1000／6000）がよいと考えられる。この値は、伝送速度の増加または伝送距離の増加により減少する。また、図６のａおよびｂの波長に対応する３次分散値が0.01ps／nmnm／kmおよび−0.01ps／nmnm／kmとすると、非特許文献３に示されている累積分散耐力から次のように見積もることができる。すなわち、伝送距離6000ｋｍとしたときに、図６の従来の場合では累積分散耐力Δは０〜−1000ps／nm（０〜−0.16ps／nm／km）の範囲を利用するので、伝送可能な波長帯域はおおよそ±15ｎｍとなる。一方、図２の本発明の場合では、累積分散耐力Δは−1000〜＋2000ps／nm（＋0.3 〜−0.16ps／nm／km）の範囲を利用することができ、伝送可能な波長帯域はおおよそ±45ｎｍとなって従来の３倍に広げることができる。
【００２４】
【発明の効果】
以上説明したように、本発明の光波長多重伝送システムは、累積３次分散値が零となる波長で累積２次分散値が正となるように光ファイバ伝送路を構成し、かつ波長多重信号光の波長帯域の中心波長が光ファイバ伝送路の３次分散値が零となる波長に設定することにより、広帯域にわたって光ファイバの非線形効果による信号波形劣化、および負の累積２次分散による信号波形劣化を回避することができる。
【図面の簡単な説明】
【図１】本発明の光波長多重伝送システムの構成例を示す図。
【図２】本発明の光波長多重伝送システムにおける波長多重信号光の伝送可能波長帯域を示す図。
【図３】従来の光波長多重伝送システムの構成例を示す図。
【図４】累積２次分散と波長多重信号光の伝送可能波長帯域の関係１を示す図。
【図５】累積２次分散と波長多重信号光の伝送可能波長帯域の関係２を示す図。
【図６】累積２次分散と波長多重信号光の伝送可能波長帯域の関係３を示す図。
【符号の説明】
１ 正分散光ファイバ
２ 負分散光ファイバ
３ 光増幅中継器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical wavelength division multiplexing transmission system for transmitting wavelength division multiplexed signal light via an optical fiber transmission line combining a positive dispersion optical fiber and a negative dispersion optical fiber.
[0002]
[Prior art]
In an optical communication system, in order to extend the transmission distance of an optical signal, it is necessary to increase the optical signal strength in consideration of attenuation of the optical signal and the like. However, it is known that the effect of the nonlinearity of an optical fiber generally used as an optical transmission line becomes more remarkable as the intensity and the transmission distance of a propagating optical signal increase. The effect due to this nonlinearity generally causes the following phenomenon, and is a factor that limits the transmittable distance of an optical signal (Non-Patent Document 1).
[0003]
(1) Self-phase modulation that changes the phase of the signal light itself according to the change in light intensity.
(2) Four-wave mixing that causes interaction between signal light of different wavelengths or between signal light and noise light.
(3) Cross-phase modulation that causes a phase change of the signal light itself according to a change in light intensity between the wavelength-multiplexed signal lights.
[0004]
The self-phase modulation effect enlarges the spectrum of the signal light itself, thereby increasing the signal light waveform deterioration due to the chromatic dispersion of the optical fiber. The chromatic dispersion of the optical fiber that causes the waveform deterioration generally means dispersion of the second or higher order. Therefore, in order to reduce or prevent the self-phase modulation effect, the wavelength of the signal light may be set to the zero dispersion wavelength of the optical fiber and transmitted.
[0005]
On the other hand, four-wave mixing and cross-phase modulation depend on the group velocity difference between signal lights of different wavelengths or between signal light and noise light, and the greater the group velocity difference, the smaller the magnitude of the interaction. Since this group velocity difference is almost proportional to the secondary dispersion value, the secondary dispersion value may be increased in order to reduce the four-wave mixing and cross-phase modulation effects. In other words, there is a trade-off relationship with measures for reducing the self-phase modulation effect.
[0006]
Next, the effect of third-order dispersion on signal light will be considered. The tertiary dispersion is the gradient of the secondary dispersion (dispersion slope), and the secondary dispersion value differs depending on the wavelength. For example, even if the secondary dispersion value is compensated in an optical transmission line, the tertiary dispersion for a specific wavelength may be compensated. Only the secondary dispersion value can be compensated, but it is impossible to make the secondary dispersion values for other wavelengths zero simultaneously. As a result, when the signal light of the wavelength that cannot be compensated propagates through the optical transmission line, it is affected by the dispersion, and since this dispersion is not compensated in the optical transmission line, the secondary dispersion accumulates over the entire system, thereby deteriorating the signal light waveform. Will increase.
[0007]
As a conventional technique for solving such a problem, as shown in FIG. 3, a positive dispersion optical fiber 1 having a positive second-order dispersion and a third-order dispersion at a signal wavelength, and a negative second-order dispersion and a third order dispersion One pair of negative dispersion optical fibers 2 having dispersion is connected to two or more pairs via an optical amplifier repeater 3 to reduce the total cumulative third-order dispersion and periodically reduce the cumulative secondary dispersion value to zero. A distributed management method has been proposed (Non-Patent Document 2). This method is effective for a long-distance optical wavelength division multiplexing transmission system that is strongly affected by nonlinearity of an optical fiber.
[0008]
[Non-patent document 1]
GPAgrawal, Nonlinear Fiber Optics, Academic Press, 1989
[Non-patent document 2]
Makoto Murakami, Hideki Maeda, Takamasa Imai, 16 × 10Gb / s long-distance wavelength division multiplexing transmission using fiber higher-order dispersion management, 1998 IEICE Communications Society Conference [Non-Patent Document 3]
H. Maeda et al., "Effectiveness of receiver-side compensation against FBG dispersion-induced SNR degradation in long-haul WDM optical networks", LEOS 2001 Annual Meeting of the IEEE 2001, 2001
[Non-patent document 4]
M. Murakami et al., "Long-haul WDM transmission with 20 Gb / s data channels using Raman assisted optical amplification", ECOC'01, 2001.
[0009]
[Problems to be solved by the invention]
4 to 6 show the relationship between the accumulated secondary dispersion and the transmittable wavelength band of the wavelength multiplexed signal light.
[0010]
FIG. 4 shows that the accumulated secondary dispersion is greatly reduced by compensating the third-order dispersion (from the broken line to the solid line), and many signal light wavelengths can be arranged in a range where the accumulated secondary dispersion value is small around the zero dispersion wavelength. Is shown.
[0011]
However, as the wavelength multiplexing number of the wavelength-division multiplexed signal light is increased with the zero dispersion wavelength as the center, as shown in FIG. The secondary dispersion increases and signal waveform deterioration occurs, and the number of multiplexed wavelengths is limited. In particular, the negative cumulative second-order dispersion generated on the short wavelength side a increases the signal waveform deterioration (Non-Patent Document 3).
[0012]
When the optical fiber transmission line is configured such that the third-order dispersion becomes zero at the zero dispersion wavelength, the dispersion characteristic of a convex curve as shown in FIG. 6 is obtained. This is because the dispersion characteristics of the fourth or higher order have an influence (Non-Patent Document 4). Therefore, as the number of multiplexed wavelengths is increased, transmission is possible due to signal waveform deterioration due to negative cumulative second-order dispersion in both wavelength regions a and b away from the zero dispersion wavelength as in the case shown in FIG. There is a problem that the wavelength band is limited.
[0013]
The present invention provides an optical wavelength division multiplexing transmission system capable of avoiding signal waveform deterioration due to cumulative secondary dispersion caused by tertiary dispersion in an optical fiber and alleviating the limiting factors of the transmission capacity and transmission distance of the system. The purpose is to do.
[0014]
[Means for Solving the Problems]
The present invention provides a pair of a positive dispersion optical fiber having positive second-order dispersion and third-order dispersion with respect to a signal wavelength and a negative dispersion optical fiber having negative second-order dispersion and third-order dispersion with two pairs. Optical wavelengths for transmitting wavelength-division multiplexed signal light through an optical fiber transmission line that is connected so that the cumulative third-order dispersion value becomes zero periodically and the cumulative second-order dispersion value becomes sufficiently small. In the multiplex transmission system, the optical fiber transmission line is configured such that the cumulative secondary dispersion value is positive at the wavelength where the cumulative tertiary dispersion value is zero, and the center wavelength of the wavelength band of the wavelength multiplexed signal light is the optical fiber transmission line. Is set to a wavelength at which the third-order dispersion value becomes zero.
[0015]
The lengths of the positive dispersion optical fiber and the negative dispersion optical fiber are determined by the secondary dispersion value of each optical fiber, the pulse width of the signal light, and the signal light wavelength. Is set to be equal to or less than の of the length determined by the square root of the product of the average power of the optical fiber and the nonlinear length determined by the optical fiber nonlinear constant of each optical fiber.
[0016]
Further, an optical amplifier for amplifying signal light is disposed on the optical fiber transmission line, and an optical fiber having a small nonlinear constant among the positive dispersion optical fiber and the negative dispersion optical fiber is disposed on the output side of the optical amplifier.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a configuration example of an optical wavelength multiplex transmission system of the present invention. Here, the change of the system configuration and the accumulated secondary dispersion of the optical fiber transmission line are shown.
[0018]
In the figure, a pair of a positive dispersion optical fiber 1 having a positive second-order dispersion and a third-order dispersion and a negative dispersion optical fiber 2 having a negative second-order dispersion and a third-order dispersion are provided via an optical amplifier repeater 3. A configuration in which two or more pairs are connected to form an optical fiber transmission line is the same as the conventional one. The feature of the present invention is that when the cumulative third-order dispersion value of the entire optical fiber transmission line is periodically set to zero and the cumulative second-order dispersion is set to be sufficiently small, as shown in FIG. The secondary dispersion value is configured to be positive at the wavelength at which the secondary dispersion value becomes zero, and the center wavelength of the wavelength band of the wavelength multiplexed signal light is set to the wavelength at which the tertiary dispersion value of the optical fiber transmission line becomes zero. Where you do it.
[0019]
Thereby, the transmittable wavelength band of the wavelength-division multiplexed signal light is expanded to a wavelength range where the cumulative secondary dispersion value is positive and a range where the cumulative secondary dispersion outside the two zero-dispersion wavelengths is negative and small. Can be. Therefore, it is possible to avoid signal waveform deterioration due to the nonlinear effect of the optical fiber and signal waveform deterioration due to negative cumulative second-order dispersion over a wide band.
[0020]
Further, by disposing an optical fiber having a small nonlinear constant (here, the positive dispersion optical fiber 1) of the positive dispersion optical fiber 1 and the negative dispersion optical fiber 2 on the output side of the optical amplification repeater 3, the nonlinearity of the optical fiber can be improved. The effect of the effect can be suppressed.
[0021]
Here, k is the nonlinear coefficient of the optical fiber, D is the second-order dispersion value, P is the average power per wavelength signal in the optical fiber, and pulse width of the signal light (full width at half maximum or half width at half maximum of pulse waveform, or peak of pulse waveform) Assuming that the pulse width of 1 / e of the value) is T 0 , the signal light wavelength is λ (approximately common to all signal wavelengths), and the light speed is c, the nonlinearity of the optical fiber is The non-linear length L NL as a measure and the second-order dispersion length L D as a measure of the magnitude of the second-order variance are represented by L NL = 1 / (kP) (1)
L D = T 0 2 / (λ 2 | D | / (2πc)) (2)
Is defined. Further, the secondary dispersion length of the positive dispersion optical fiber 1 is defined as L Dp , and the secondary dispersion length of the negative dispersion optical fiber 2 is defined as L Dn .
[0022]
At this time, the length Lp of the positive dispersion optical fiber 1 and the length Ln of the negative dispersion optical fiber 2 are:
Lp << (L Dp L NL ) 1/2 … (3)
Ln << (L Dn L NL ) 1/2 … (4)
Set so that For example,
Lp ≦ (L Dp L NL) 1/2 / 2 ... (5)
Ln ≦ (L Dn L NL) 1/2 / 2 ... (6)
By doing so, signal waveform deterioration due to optical fiber nonlinearity and second-order dispersion occurring in these sections can be effectively suppressed (Non-Patent Document 4).
[0023]
In Non-Patent Document 3, when the transmission speed is 10 Gbit / s and the transmission distance is 6000 km, the allowable range of the cumulative secondary dispersion (cumulative dispersion tolerance Δ) is about −1000 ps / nm to +2000 ps / nm. It is considered that the secondary dispersion value D should be about +0.3 ps / nm / km (= 2000/6000), and the negative secondary dispersion value D should be about -0.16 ps / nm / km (= -1000 / 6000). . This value decreases as the transmission speed or the transmission distance increases. Further, assuming that the third-order dispersion values corresponding to the wavelengths of a and b in FIG. 6 are 0.01 ps / nmnm / km and −0.01 ps / nmnm / km, the following formula is obtained from the cumulative dispersion tolerance shown in Non-Patent Document 3. It can be estimated as follows. That is, when the transmission distance is 6000 km, in the conventional case of FIG. 6, the accumulated dispersion tolerance Δ uses the range of 0 to −1000 ps / nm (0 to −0.16 ps / nm / km). The band is approximately ± 15 nm. On the other hand, in the case of the present invention shown in FIG. 2, the cumulative dispersion strength Δ can use a range of −1000 to +2000 ps / nm (+0.3 to −0.16 ps / nm / km), and the wavelength band that can be transmitted is It is approximately ± 45 nm, which can be expanded to three times the conventional value.
[0024]
【The invention's effect】
As described above, the optical wavelength division multiplexing transmission system of the present invention configures an optical fiber transmission line so that the cumulative secondary dispersion value becomes positive at the wavelength where the cumulative third dispersion value becomes zero, and By setting the center wavelength of the light wavelength band to a wavelength at which the third-order dispersion value of the optical fiber transmission line becomes zero, signal waveform deterioration due to nonlinear effects of the optical fiber and signal waveform due to negative cumulative second-order dispersion over a wide band. Deterioration can be avoided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration example of an optical wavelength multiplex transmission system of the present invention.
FIG. 2 is a diagram showing a transmittable wavelength band of wavelength multiplexed signal light in the optical wavelength multiplex transmission system of the present invention.
FIG. 3 is a diagram showing a configuration example of a conventional optical wavelength multiplex transmission system.
FIG. 4 is a diagram illustrating a first relationship between cumulative second-order dispersion and a transmittable wavelength band of wavelength multiplexed signal light.
FIG. 5 is a diagram illustrating a relationship 2 between the accumulated secondary dispersion and the transmittable wavelength band of the wavelength multiplexed signal light.
FIG. 6 is a diagram illustrating a relationship 3 between the accumulated secondary dispersion and the wavelength band in which the wavelength multiplexed signal light can be transmitted.
[Explanation of symbols]
1 Positive dispersion optical fiber 2 Negative dispersion optical fiber 3 Optical amplification repeater
Claims (3)
前記光ファイバ伝送路は累積３次分散値が零となる波長で累積２次分散値が正となるように構成し、前記波長多重信号光の波長帯域の中心波長が前記光ファイバ伝送路の３次分散値が零となる波長に設定されたことを特徴とする光波長多重伝送システム。A pair of a positive dispersion optical fiber having positive second-order dispersion and third-order dispersion with respect to the signal wavelength and a negative dispersion optical fiber having negative second-order dispersion and third-order dispersion are connected. In an optical wavelength division multiplexing transmission system for transmitting wavelength division multiplexed signal light through an optical fiber transmission line set so that the total cumulative third order dispersion value becomes zero periodically and the cumulative second order dispersion value becomes sufficiently small. ,
The optical fiber transmission line is configured such that the cumulative secondary dispersion value is positive at a wavelength where the cumulative tertiary dispersion value is zero, and the center wavelength of the wavelength band of the wavelength-division multiplexed signal light is the wavelength of the optical fiber transmission line. An optical wavelength division multiplexing transmission system characterized in that the wavelength is set to a value at which the secondary dispersion value becomes zero.
前記正分散光ファイバおよび前記負分散光ファイバの各長さが、各光ファイバの２次分散値と信号光のパルス幅と信号光波長から決まる２次分散長と、各光ファイバ内の信号光の平均電力と各光ファイバの光ファイバ非線形定数で決まる非線形長との積の平方根で定まる長さの１／２以下に設定された
ことを特徴とする光波長多重伝送システム。The optical wavelength division multiplexing transmission system according to claim 1,
The length of each of the positive dispersion optical fiber and the negative dispersion optical fiber is a secondary dispersion length determined by the secondary dispersion value of each optical fiber, the pulse width of the signal light, and the signal light wavelength, and the signal light within each optical fiber. The wavelength multiplex transmission system is set to be equal to or less than の of a length determined by a square root of a product of an average power of the optical fiber and a nonlinear length determined by an optical fiber nonlinear constant of each optical fiber.
前記光ファイバ伝送路に信号光を増幅する光増幅器を配置し、その光増幅器の出力側に、前記正分散光ファイバおよび前記負分散光ファイバのうち非線形定数の小さい光ファイバを配置する
ことを特徴とする光波長多重伝送システム。The optical wavelength division multiplexing transmission system according to claim 1 or 2,
An optical amplifier for amplifying signal light is disposed on the optical fiber transmission line, and an optical fiber having a small nonlinear constant among the positive dispersion optical fiber and the negative dispersion optical fiber is disposed on the output side of the optical amplifier. WDM transmission system.
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