JP2004251986A - Dispersion compensation fiber and dispersion compensation fiber module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dispersion compensation fiber which has a large wavelength dispersion value and is capable of compensating negative cumulative wavelength dispersion of an optical transmission path with a short pathway length, and a small and lightweight dispersion compensation fiber module using this dispersion compensation fiber. <P>SOLUTION: The dispersion compensation fiber is configured so that the radius r<SB>1</SB>of a 1st core part 11 is 3μm ≤ r<SB>1</SB>≤6μm, and the relative refractive-index difference D<SB>1</SB>of the 1st core part 11 is +1.4% ≤ D<SB>1</SB>≤ +2.4%; a ratio r<SB>2</SB>/r<SB>1</SB>of the radius r<SB>2</SB>of a 2nd core part 12 to the radius r<SB>1</SB>of the 1st core part 11 is 1.1 ≤ r<SB>2</SB>/r<SB>1</SB>≤ 2.0, and the relative refractive-index difference D<SB>2</SB>of the radius r<SB>2</SB>of the 2nd core part 12 is -0.2% ≤ D2 ≤ +0.2%; the radius r<SB>3</SB>of a 3rd core part 13 is 10μm ≤ r<SB>3</SB>≤20μm, and the relative refractive-index difference D<SB>3</SB>of the 3rd core part 13 is +0.2% ≤ D<SB>3</SB>≤ +0.6%; and the D<SB>1</SB>, D<SB>2</SB>, D<SB>3</SB>are in the relation of D<SB>1</SB>> D<SB>2</SB>> D<SB>3</SB>, and the wavelength dispersion in LP<SB>03</SB>mode is not less than +50ps/nm/km in 1.55μm band. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２６】
【表２】

【００２７】
図３は、分散補償ファイバＡの波長分散と光の波長との関係を示す図である。１．５５μｍ帯の広い波長領域において正の大きな波長分散が得られる。１．５５μｍにおける波長分散は＋１４８．７ｐｓ／ｎｍ／ｋｍであり、従来の１．３μｍ帯シングルモード光ファイバ（以下、ＳＭＦと言う。）の１．５５μｍにおける波長分散（約＋１７ｐｓ／ｎｍ／ｋｍ）の９倍であり、正の大きな波長分散が得られることがわかる。
【００２８】
図４は、分散補償ファイバＢ，Ｃの波長分散と光の波長との関係を示す図である。また、図５は、分散補償ファイバＤの波長分散と光の波長との関係を示す図である。
１．５５μｍ帯の広い波長領域において正の大きな波長分散が得られる。１．５５μｍにおける波長分散は＋１８４〜＋２７７ｐｓ／ｎｍ／ｋｍであり、従来のＳＭＦの波長分散の１０〜１６倍であり、正の大きな波長分散が得られることがわかる。
【００２９】
更に、分散補償ファイバＢ〜Ｄは、負の分散スロープを有する。通常、ＮＺ−ＤＳＦなどを用いた光ファイバ伝送路は、正の分散スロープを持つ。このため、この分散補償ファイバＢ〜Ｄを用いることによって、前記光ファイバ伝送路の正の分散スロープも補償することができ、光ファイバ伝送路の累積波長分散を広い波長範囲において補償することができる。
また、表２に示されたように、伝送損失は１．２ｄＢ／ｋｍ以下と低損失であり、また曲げ損失にも優れ、比較的小径のリールに巻くことが可能である。
【００３０】
次に、本実施形態と同様に、上記分散補償ファイバを用いて、波長分散を有する分散補償ファイバモジュールを作製した。ここで、分散補償ファイバの長さは、分散補償ファイバモジュールの経路全体の波長分散が＋１０００ｐｓ／ｎｍとなるように調整した。
表３は、この分散補償ファイバモジュールの光学特性を示す。
【００３１】
【表３】

【００３２】
表４は、従来のＳＭＦやＣＳＦを用いて作製した分散補償ファイバモジュールの光学特性を示す。
【００３３】
【表４】

【００３４】
分散補償ファイバＡ〜Ｄは前記したように正の大きな波長分散を持つため、ＳＭＦやＣＳＦに比べて分散補償ファイバの伝送路の長さを１／１６〜１／９まで短くすることができ、小型で軽量の分散補償ファイバモジュールが実現できる。
また、分散補償ファイバの伝送路の長さを短くすることができるため、分散補償ファイバモジュールの伝送損失や非線形効果を低減できる。
【００３５】
【発明の効果】
以上詳細に説明したように、本発明によれば、屈折率分布形状の構造パラメータを定めることによって、１５２５ｎｍ〜１６２５ｎｍの波長領域において、信号光を高次モードで伝搬させ、これ以外のモードでは伝搬させないようにすることができる。これにより異なる伝搬モード間の信号光の干渉もほとんど無く、この高次モードにおける正の大きな波長分散を得ることができる。
従って、短い長さで光ファイバ伝送路の負の累積波長分散を補償できる。
【００３６】
また、前記本発明の分散補償ファイバを用い、この分散補償ファイバの入力端と出力端にそれぞれモード変換器を接続し、分散補償ファイバ内を信号光がＬＰ_０３モードの伝搬モードで伝搬するようにすることによって、正の大きな波長分散が得られる。このため、光ファイバ伝送路の負の累積波長分散を補償する場合、必要となる分散補償ファイバの長さを短くすることができ、小型で、軽量な分散補償ファイバモジュ−ルが実現できる。
【図面の簡単な説明】
【図１】本実施形態の分散補償ファイバの屈折率分布の一例を示す概略図である。
【図２】本実施形態の分散補償ファイバモジュールと光ファイバ伝送路とが接続されて構成された光通信システムの概略図である。
【図３】分散補償ファイバＡの波長分散と光の波長との関係を示す図である。
【図４】分散補償ファイバＢ，Ｃの波長分散と光の波長との関係を示す図である。
【図５】分散補償ファイバＤの波長分散と光の波長との関係を示す図である。
【図６】ＮＺ−ＤＳＦの波長分散と信号光の波長との関係の一例を示す図である。
【符号の説明】
２‥‥クラッド，３‥‥分散補償ファイバモジュール，５‥‥分散補償ファイバ，１１‥‥第１のコア部，１２‥‥第２のコア部，１３‥‥第３のコア部，６１‥‥信号光の伝搬モードをＬＰ_０１モードからＬＰ_０３モードに変換するモード変換器，６２‥‥信号光の伝搬モードをＬＰ_０３モードからＬＰ_０１モードに変換するモード変換器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dispersion compensating fiber and a dispersion compensating fiber module for compensating for negative cumulative chromatic dispersion of an optical fiber transmission line in a 1.55 μm band.
[0002]
[Prior art]
In recent years, a non-zero dispersion-shifted optical fiber (hereinafter, referred to as NZ-DSF) has been used as a long-distance optical transmission line for wavelength-division multiplexing optical communication in the 1.55 μm band. The NZ-DSF has its zero-dispersion wavelength shifted outside the signal light wavelength band so that four-wave mixing does not occur due to the nonlinear optical effect at the zero-dispersion wavelength. As the NZ-DSF, as shown in the optical fiber (No. 1) in FIG. 6, a fiber having a negative chromatic dispersion in a 1.55 μm band may be used. Therefore, the optical transmission line using the NZ-DSF has a negative cumulative chromatic dispersion in the 1.55 μm band, and it is necessary to compensate for this chromatic dispersion.
In particular, when the transmission speed increases, the value of the allowable chromatic dispersion becomes extremely small. Therefore, in order to realize a high-speed transmission system, it is necessary to compensate for the chromatic dispersion.
[0003]
As the dispersion compensating fiber in this case, as shown in the optical fiber (No. 2) of FIG. 6, a 1.3 μm band single mode optical fiber having a positive chromatic dispersion or a 1.3 μm band single mode optical fiber. A cutoff shifted optical fiber (hereinafter, referred to as CSF) in which the cutoff wavelength is shifted to the longer wavelength side may be used.
The chromatic dispersion of the CSF in the 1.55 μm band is about +17 ps / nm / km. For example, when compensating for the accumulated chromatic dispersion of −1000 ps / nm, the CSF of 58.8 km is required. When a dispersion compensating fiber module is formed using such a long-distance CSF, the module becomes very large and heavy. Further, the manufacturing cost of the CSF is also high.
[0004]
In addition, in order to compensate for the chromatic dispersion of the optical transmission line having the negative chromatic dispersion, a dispersion compensating fiber having a positive chromatic dispersion of +20 to +21 ps / nm / km in a 1.55 μm band has been proposed (Patent). Reference 1).
Further, by using a holey fiber having holes around the core, dispersion compensation having a chromatic dispersion of +34 ps / nm / km in a 1.55 μm band and a low loss of 0.82 dB / km in a propagation loss is achieved. A fiber has also been proposed (see Non-Patent Document 1).
[0005]
However, even with the dispersion compensating fibers proposed in Patent Document 1 and Non-Patent Document 1, chromatic dispersion is about 1.2 to 2 times that of CSF. Therefore, in order to compensate for the negative cumulative chromatic dispersion of the optical transmission line, a long-range dispersion compensating fiber is required. If the dispersion compensating fiber module is used, the module becomes very large and heavy, and the manufacturing cost is high. It becomes.
[0006]
[Patent Document 1]
JP 2001-159721 A [Non-Patent Document 1]
Hasegawa, Proceedings of Optical Fiber Communication Conference 2001, Optical Society of America, Optical Society of America, United States
[0007]
[Problems to be solved by the invention]
Therefore, an object of the present invention has been made in view of the above circumstances. That is, a dispersion compensating fiber having a large positive chromatic dispersion value and capable of compensating for the negative cumulative chromatic dispersion of the optical transmission line with a short length, and a small and lightweight dispersion compensating fiber module using the dispersion compensating fiber. The purpose of providing
[0008]
[Means for Solving the Problems]
The invention according to claim 1 is a dispersion compensating fiber that propagates a higher-order mode than the fundamental mode, comprising: a clad; a first core having a higher refractive index than the clad; A second core portion provided on the outer periphery of the portion and having a lower refractive index than the first core portion; and a third core portion provided on the outer periphery of the second core portion and having a higher refractive index than the clad. has a core portion, the radius _{r 1} of the first core portion is 3 [mu] m ≦ _{r 1} ≦ 6 [mu] m, the first relative refractive index difference _{D 1} with respect to the cladding of the core portion is _{+ 1.4% ≦ D 1 ≦ +} 2 a .4%, the ratio _r 2 / _{r 1} and the radius _{r 1} of radius _{r 2} and the first core portion of the second core portion be 1.1 ≦ _r 2 / _{r 1} ≦ 2.0 The relative refractive index difference D _{2 of} the second core portion with respect to the cladding is −0.2% ≦ D ₂ ≦ + 0.2%, and the third core portion Has a radius r ₃ of 10 μm ≦ r ₃ ≦ 20 μm, a relative refractive index difference D _{3 of} the third core portion with respect to the cladding is + 0.2% ≦ D ₃ ≦ + 0.6%, and a relative refractive index with respect to the cladding. The differences D ₁ , D ₂ , and D ₃ satisfy D ₁ > D ₃ > D ₂ , and the chromatic dispersion of the higher-order mode is +50 ps / nm / km or more in the wavelength range of 1525 nm to 1625 nm. Compensating fiber.
The invention according to claim 2 is the dispersion compensating fiber according to claim 1, wherein the chromatic dispersion of the higher-order mode is +100 ps / nm / km or more in a wavelength range of 1525 nm to 1625 nm.
The dispersion compensating fiber according to claim 1 or 2, wherein the dispersion slope of the higher-order mode is negative in at least the range of +30 nm or more in the wavelength range of 1525 nm to 1625 nm. It is.
The invention according to claim 4 is the dispersion compensating fiber according to any one of claims 1 to 3, wherein the higher-order mode is an _LP03 mode.
[0009]
The invention according to claim 5, the dispersion compensating fiber according to any one of claims 1 to 4, is connected to an input end of the dispersion compensating fiber, converting the propagation mode of the signal light from the LP ₀₁ mode to the LP ₀₃ mode a mode converter which is connected to the output end of the dispersion compensating fiber has a mode converter for converting a propagation mode of the signal light from the LP ₀₃ mode to the LP ₀₁ mode, the dispersion compensation in the fiber the signal light LP A dispersion compensating fiber module characterized in that the fiber propagates in a ₀₃ mode propagation mode.
The invention according to claim 6 is the dispersion compensating fiber module according to claim 5, wherein the mode converter is a long-period fiber grating.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
[Dispersion compensating fiber]
FIG. 1 is a schematic diagram illustrating an example of a refractive index distribution shape of the dispersion compensating fiber of the present embodiment. The core 1 of the dispersion compensating fiber includes a first core portion 11 provided at the center, a second core portion 12 provided concentrically on the outer periphery thereof, and an outer periphery of the second core portion 12. The third core portion 13 is provided concentrically.
As shown in FIG. 1A, a step index type having a constant refractive index in each layer, or as shown in FIG. 1B, linearly as the refractive index of the first core goes to the outer periphery. And those that decrease.
Also, the actual refractive index distribution shape is often such that the boundary of each layer is not clear as shown in FIG. 1 and is a gentle curve, but it is sufficient that the refractive index distribution shape is substantially provided.
[0011]
The first core portion 11, the second core portion 12, the third core portion 13, and the clad 2 are each formed of pure quartz glass or quartz glass to which germanium, fluorine, or the like is added as an essential dopant.
This dispersion compensating fiber can be manufactured by drawing a fiber preform obtained by a known method such as a VAD method, an MCVD method, or a PCVD method by a conventional method.
[0012]
In this dispersion compensating fiber, structural parameters such as a relative refractive index difference and a radius of each layer are set as shown below.
The first core portion 11 has a higher refractive index than the cladding 2, and the radius r ₁ of the first core portion 11 is 3 μm ≦ r ₁ ≦ 6 μm, preferably 3.5 μm ≦ r ₁ ≦ 5.0 μm. It is. Also, the relative refractive index difference _{D 1} with respect to the cladding 2 of the first core portion 11 is _{+ 1.4% ≦ D 1 ≦ +} 2.4%, preferably from _{+ 1.8% ≦ D 1 ≦ +} 2.0% .
[0013]
The radius _{r 2} of the second core portion 12 the ratio _r 2 / _{r 1} and the radius _{r 1} of the first core portion 11 is _{1.1 ≦ r 2 / r 1 ≦} 2.0, preferably 1. 2 ≦ r ₂ / r ₁ ≦ 2.0. Also, the relative refractive index difference _{D 2} with respect to the cladding 2 of the second core part 12 is _{-0.2% ≦ D 2 ≦ + 0.2} %, preferably _{-0.1% ≦ D 2 ≦ + 0.1} % It is.
[0014]
The third core portion 13 has a higher refractive index than the cladding 2, and the radius r3 of the _third core portion 13 is 10 μm ≦ r ₃ ≦ 20 μm, preferably 12 μm ≦ r ₃ ≦ 16 μm. Also, the relative refractive index difference _{D 3} with respect to the cladding 2 of the third core portion 13 is _{+ 0.2% ≦ D 3 ≦ +} 0.6%, preferably from _{+ 0.3% ≦ D 3 ≦ +} 0.6% .
[0015]
Thus, it is possible to propagate signal light in LP ₀₃ mode of the high-order mode, the signal light further propagates in propagation modes other than the LP ₀₃ mode is adapted to radiation loss by the mode converter, LP Signal light can be propagated only in the ₀₃ mode. Therefore, a signal light propagating in the LP ₀₃ mode, it is not the signal light interfere with propagating at other propagation modes.
As described in U.S. Pat. No. 5,802,234, a dispersion compensating fiber using a higher-order mode can provide essentially large chromatic dispersion. In this embodiment, LP ₀₃ mode only can propagate signal light, almost without interference of the signal light between different propagation modes, it is possible to obtain a large positive wavelength dispersion in the LP ₀₃ mode.
[0016]
Accordingly, the dispersion compensating fiber of the present embodiment, in the wavelength range of 1525Nm～1625nm, and the chromatic dispersion in the _{LP 03} mode is + 50ps / nm / km or more, preferably to + 100ps / nm / km or more.
Since a large positive chromatic dispersion is obtained as described above, it is possible to compensate for the negative cumulative chromatic dispersion of the optical transmission line with a short length. Further, since the length of the transmission line of the dispersion compensating fiber can be shortened, the transmission loss and the nonlinear effect of the dispersion compensating fiber module can be reduced.
[0017]
Further, in the present embodiment, in addition to the above-described preferable structural parameters, it is preferable that r ₂ / r ₁ is set to be 1.4 to 2.0, whereby the wavelength range of at least 30 nm or more in the range of 1525 nm to 1625 nm. In the above, a dispersion compensating fiber having a negative dispersion slope in a higher-order mode can be obtained.
Usually, an optical fiber transmission line using NZ-DSF or the like has a positive dispersion slope. Therefore, by using the dispersion compensating fiber having the negative dispersion slope of the present embodiment, the positive dispersion slope of the optical fiber transmission line can also be compensated, and the accumulated chromatic dispersion of the optical fiber transmission line can be reduced over a wide wavelength range. Can be compensated for.
[0018]
[Dispersion compensation fiber module]
FIG. 2 is a schematic diagram of an optical communication system in which the dispersion compensating fiber module 3 of the present embodiment and the optical fiber transmission lines 41 and 42 are connected.
Dispersion compensating fiber module 3 of this embodiment, the dispersion compensating fiber 5 of the present embodiment described above, an input mode converter 61 for converting a propagation mode of the signal light from the LP ₀₁ mode to the LP ₀₃ mode, the signal light The output mode converter 62 converts the propagation mode from the LP ₀₃ mode to the LP ₀₁ mode.
[0019]
The optical fiber transmission lines 41 and 42 are non-zero dispersion shifted optical fibers (hereinafter, referred to as NZ-DSF) having negative chromatic dispersion.
The dispersion compensating fiber 5 has a positive chromatic dispersion as described above, and the dispersion compensating fiber 5 is adjusted so that the absolute value of the chromatic dispersion of the entire path coincides with the absolute value of the accumulated chromatic dispersion of the optical fiber transmission line 41. The length of the fiber 5 is adjusted. Thereby, the negative cumulative chromatic dispersion of the optical fiber transmission line 41 can be compensated, and the residual dispersion can be made almost zero.
Both the input mode converter 61 and the output mode converter 62 are long-period fiber gratings. The long-period fiber grating converts the propagation mode of the incident light into a mode and emits the reflected light as a reflected light.
[0020]
On the signal input side of the dispersion compensating fiber module 3, the input mode converter 61 and the input end of the dispersion compensating fiber 5 are connected via the optical circulator 7. This optical circulator 7 can be connected to an optical fiber transmission line 41 on the signal transmission side.
On the signal output side of the dispersion compensating fiber module 3, the output mode converter 62 and the output end of the dispersion compensating fiber 5 are connected via the optical circulator 7. The optical circulator 7 can be connected to an optical fiber transmission line 42 on the signal receiving side.
[0021]
The _LP01- mode signal light propagated through the optical fiber transmission line 41 on the signal transmission side enters the input mode converter 61 via the optical circulator 7. The signal light is converted by the input mode converter 61 from the LP ₀₁ mode to the LP ₀₃ mode, reflected, and emitted to the optical circulator 7.
Next, the signal light converted into the _LP03 mode enters the dispersion compensating fiber 5 via the optical circulator 7, and propagates through the dispersion compensating fiber 5 in the _LP03 mode. By propagating the dispersion compensating fiber 5 in the _LP03 mode, the signal light can obtain a large positive chromatic dispersion, and the negative cumulative chromatic dispersion of the optical fiber transmission line 41 is compensated.
[0022]
The signal light enters the output mode converter 62 via the optical circulator 7, and its propagation mode is converted from the LP ₀₃ mode to the LP ₀₁ mode, reflected, and transmitted through the optical circulator 7 to the signal receiving side. The light is emitted to the optical fiber transmission line 42.
[0023]
In the present embodiment, the dispersion compensating fiber 5 of the above-described embodiment is used. Since the dispersion compensating fiber 5 has a large positive chromatic dispersion as described above, the optical fiber transmission line 41 has a short length. Can be compensated for. Thus, the dispersion compensating fiber module 3 can be reduced in size and weight.
[0024]
Next, specific examples of the present invention will be described below.
A dispersion compensating fiber having the refractive index distribution shape shown in FIG.
Table 1 shows the values of the respective structural parameters of the refractive index distribution of the manufactured dispersion compensating fiber. Table 2 shows the optical characteristics of this dispersion compensating fiber at 1550 nm. Here, the bending loss is a value measured under the condition that the bending diameter is 20 mm.
[0025]
[Table 1]

[0026]
[Table 2]

[0027]
FIG. 3 is a diagram illustrating the relationship between the chromatic dispersion of the dispersion compensating fiber A and the wavelength of light. A large positive chromatic dispersion is obtained in a wide wavelength region of the 1.55 μm band. The chromatic dispersion at 1.55 μm is +148.7 ps / nm / km, and the chromatic dispersion at 1.55 μm (about +17 ps / nm / km) of a conventional 1.3 μm band single mode optical fiber (hereinafter referred to as SMF). This is nine times that of the above, and it can be seen that a large positive chromatic dispersion can be obtained.
[0028]
FIG. 4 is a diagram showing the relationship between the wavelength dispersion of the dispersion compensating fibers B and C and the wavelength of light. FIG. 5 is a diagram showing the relationship between the chromatic dispersion of the dispersion compensating fiber D and the wavelength of light.
A large positive chromatic dispersion is obtained in a wide wavelength region of the 1.55 μm band. The chromatic dispersion at 1.55 μm is +184 to +277 ps / nm / km, which is 10 to 16 times the chromatic dispersion of the conventional SMF, and it can be seen that a large positive chromatic dispersion can be obtained.
[0029]
Further, the dispersion compensating fibers BD have a negative dispersion slope. Usually, an optical fiber transmission line using NZ-DSF or the like has a positive dispersion slope. Therefore, by using the dispersion compensating fibers B to D, the positive dispersion slope of the optical fiber transmission line can be compensated, and the accumulated chromatic dispersion of the optical fiber transmission line can be compensated in a wide wavelength range. .
Further, as shown in Table 2, the transmission loss is as low as 1.2 dB / km or less, and the bending loss is excellent, so that it can be wound on a relatively small-diameter reel.
[0030]
Next, similarly to the present embodiment, a dispersion compensating fiber module having chromatic dispersion was manufactured using the dispersion compensating fiber. Here, the length of the dispersion compensating fiber was adjusted such that the chromatic dispersion of the entire path of the dispersion compensating fiber module was +1000 ps / nm.
Table 3 shows the optical characteristics of the dispersion compensating fiber module.
[0031]
[Table 3]

[0032]
Table 4 shows the optical characteristics of the dispersion compensating fiber module manufactured using the conventional SMF or CSF.
[0033]
[Table 4]

[0034]
Since the dispersion compensating fibers A to D have a large positive chromatic dispersion as described above, the length of the transmission line of the dispersion compensating fiber can be reduced to 1/16 to 1/9 as compared with SMF or CSF. A small and lightweight dispersion compensating fiber module can be realized.
Further, since the length of the transmission line of the dispersion compensating fiber can be shortened, the transmission loss and the nonlinear effect of the dispersion compensating fiber module can be reduced.
[0035]
【The invention's effect】
As described above in detail, according to the present invention, by determining the structural parameters of the refractive index distribution shape, the signal light propagates in the higher order mode in the wavelength region of 1525 nm to 1625 nm, and propagates in other modes. Can be prevented. As a result, there is almost no signal light interference between different propagation modes, and a large positive chromatic dispersion in the higher-order mode can be obtained.
Therefore, it is possible to compensate for the negative cumulative chromatic dispersion of the optical fiber transmission line with a short length.
[0036]
Moreover, the use of a dispersion compensating fiber of the present invention, to connect each mode converter to the input and output ends of the dispersion compensating fiber, as the dispersion compensation fiber within the signal light propagates in the LP ₀₃ mode propagation mode By doing so, a large positive chromatic dispersion can be obtained. Therefore, when compensating for the negative cumulative chromatic dispersion of the optical fiber transmission line, the required length of the dispersion compensating fiber can be shortened, and a small and lightweight dispersion compensating fiber module can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of a refractive index distribution of a dispersion compensating fiber according to an embodiment.
FIG. 2 is a schematic diagram of an optical communication system in which the dispersion compensating fiber module of the present embodiment is connected to an optical fiber transmission line.
FIG. 3 is a diagram showing a relationship between the wavelength dispersion of the dispersion compensating fiber A and the wavelength of light.
FIG. 4 is a diagram showing the relationship between the wavelength dispersion of dispersion compensation fibers B and C and the wavelength of light.
FIG. 5 is a diagram showing the relationship between the wavelength dispersion of the dispersion compensating fiber D and the wavelength of light.
FIG. 6 is a diagram illustrating an example of a relationship between chromatic dispersion of NZ-DSF and wavelength of signal light.
[Explanation of symbols]
2 ‥‥ clad, 3 ‥‥ dispersion compensating fiber module, 5 ‥‥ dispersion compensating fiber, 11 ‥‥ first core, 12 ‥‥ second core, 13 ‥‥ third core, 61 ‥‥ mode converter for converting a propagation mode of the signal light from the _{LP 01} mode to the _{LP 03} mode, 62 mode of propagation ‥‥ signal light mode converter for converting the _{LP 03} mode to the _{LP 01} mode

Claims (6)

A dispersion compensating fiber that propagates a higher-order mode than the fundamental mode,
A clad, a first core having a higher refractive index than the clad, and a second core provided on an outer periphery of the first core and having a lower refractive index than the first core. A third core portion provided on the outer periphery of the second core portion and having a higher refractive index than the cladding;
The radius r ₁ of the first core portion is 3 μm ≦ r ₁ ≦ 6 μm, the relative refractive index difference D _{1 of} the first core portion with respect to the cladding is + 1.4% ≦ D ₁ ≦ + 2.4%,
It said second ratio _r 2 / _{r 1} and the radius _{r 2} of the core portion and the radius _{r 1} of the first core portion is _{1.1 ≦ r 2 / r 1 ≦} 2.0, the second core portion The relative refractive index difference D ₂ with respect to the cladding is −0.2% ≦ D ₂ ≦ + 0.2%,
A radius r ₃ of the third core portion is 10 μm ≦ r ₃ ≦ 20 μm, and a relative refractive index difference D _{3 of} the third core portion to the cladding is + 0.2% ≦ D ₃ ≦ + 0.6%;
The relative refractive index differences D ₁ , D ₂ , D ₃ with respect to the cladding satisfy D ₁ > D ₃ > D ₂ ,
A dispersion compensating fiber, wherein the chromatic dispersion of a higher mode is +50 ps / nm / km or more in a wavelength range of 1525 nm to 1625 nm. 2. The dispersion compensating fiber according to claim 1, wherein the chromatic dispersion of the higher-order mode is +100 ps / nm / km or more in a wavelength range of 1525 nm to 1625 nm. The dispersion compensating fiber according to claim 1, wherein a dispersion slope of a higher-order mode is negative in at least a range of +30 nm or more in a wavelength range of 1525 nm to 1625 nm. 4. 4. The dispersion compensating fiber according to claim 1, wherein the higher-order mode is an _LP03 mode. A dispersion compensating fiber according to any one of claims 1 to 4, is connected to an input end of the dispersion compensating fiber, a mode converter for converting a propagation mode of the signal light from the LP ₀₁ mode to the LP ₀₃ mode, the dispersion is connected to the output end of the compensating fiber has a mode converter for converting a propagation mode of the signal light from the LP ₀₃ mode to the LP ₀₁ mode,
Dispersion compensating fiber module, wherein the dispersion compensating fiber for signal light to be propagated in LP ₀₃ mode propagation mode. The dispersion compensating fiber module according to claim 5, wherein the mode converter is a long-period fiber grating.

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