JP2005234192A - Dispersion compensating fiber and Raman amplification transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersion compensating fiber suitable for a high-speed and Raman amplification transmission system and a Raman amplification transmission system using a 1.3 μm band zero-dispersion single mode optical fiber.
A dispersion compensating fiber F ₂ is connected to the end of a 1.3 μm band zero-dispersion single mode optical fiber F ₁ to constitute a high-speed Raman amplification transmission system. In this case, the length L ₁ of the 1.3μm band zero-dispersion single-mode optical fiber F _1, the length L ₂ of the ratio of the dispersion compensating fiber F ₂ (L ₂ / L _1), and the dispersion compensating fiber F ₂ The signal-to-noise ratio characteristic is improved by suitably designing the Raman gain factor.
[Selection] Figure 1

Description

  The present invention is applied to a Raman amplification transmission system using a 1.3 μm-band zero-dispersion single-mode optical fiber, and improves the signal-to-noise ratio characteristics of the transmission system for signal light of a wavelength of 1.55 μm. The present invention relates to a dispersion compensating fiber and a transmission path configuration method (Raman amplification transmission system).

  In a high-speed and long-distance transmission system using a 1.3 μm-band zero-dispersion single-mode optical fiber, in order to maintain good transmission characteristics, chromatic dispersion and dispersion slope in the 1.3-μm-band zero-dispersion single-mode optical fiber are maintained. Compensation technology is required. For this reason, Patent Document 1 proposes a dispersion compensating fiber that compensates for the chromatic dispersion and dispersion slope characteristics of a 1.3 μm band zero-dispersion single mode optical fiber.

  On the other hand, in Raman amplification transmission using a single-mode optical fiber, the signal-to-noise ratio characteristics are improved and the signal light intensity is reduced, thereby reducing the degradation of transmission characteristics due to various nonlinear phenomena in wavelength division multiplex transmission. it can. In general, the Raman amplification effect in a single-mode optical fiber depends on the characteristics of the glass material forming the optical fiber core and the amount added, for example, using a highly nonlinear medium with an increased amount of germanium in the core. Thus, it is known that a high Raman amplification effect can be obtained. For this reason, Patent Document 2 proposes a Raman amplification transmission system using a highly nonlinear medium including a single mode optical fiber for transmission and a dispersion compensating fiber for the purpose of realizing large capacity, wavelength division multiplexing transmission. .

Japanese Patent Application No. 2000-571291 JP 2000-349716 (Japanese Patent Application No. 11-158509) R. J. et al. Essiambre, P.M. Winzer, J .; Bromage, and C.I. H. Kim, “Design of bidirectionally pumped fiber amplifiers generating double Rayleigh backscattering,” IEEE Photon. Technol. Lett. , Vol. 14, pp. 914-916, 2002. C. Fukai, K .; Nakajima, and M.M. Ohashi, “Dopper dependency of Raman gain in effluent doped silica fiber,” in Proc. OECC2002, 10D2-6, pp. 186-187, 2002. M.M. Ohashi, K .; Shiraki, and K.K. Tajima, "Optical loss property of silica-based single-mode fibers," J. Lightwave Technol. , Vol. 10, pp. 539-543, 1992. E. Brinkmeyer, "Analysis of the backscattering method for single-mode optical fibers," J. Opt. Soc. Am, vol. 70, pp. 1010-1012, 1980. S. Ramachandran, “Higher-Order-Mode Dispersion Compensation for Broadband Dispersion and Non-linearity Management in Transmission System,” in Proc. OFC2002, pp. 333-335, 2002.

  However, in Raman amplification transmission using a highly nonlinear medium, transmission loss also increases with increasing Raman amplification effect in a single mode optical fiber, and the improvement effect of signal-to-noise ratio characteristics in Raman amplification transmission cannot be used effectively. There was a problem.

  In addition, the Raman amplification transmission using the dispersion compensation fiber has a problem that the improvement effect of the signal-to-noise ratio characteristic by the Raman amplification transmission varies depending on the length of the dispersion compensation fiber to be used and the Raman amplification characteristic. It was.

  The present invention has been made in view of such problems, and an object of the present invention is to provide signal-to-noise at a light receiving unit in a Raman amplification transmission system using a 1.3 μm band zero-dispersion single mode optical fiber. It is an object of the present invention to provide a dispersion compensating fiber having a suitable ratio characteristic and a transmission path configuration method (Raman amplification transmission system).

In order to achieve such an object, in the optical fiber used in the distributed Raman amplification optical transmission system, in the invention according to claim _1, a 1.3 μm-band zero-dispersion single mode optical fiber having a length L ₁ of A dispersion compensating fiber having a length L ₂ that compensates for chromatic dispersion and dispersion slope in a 1.55 μm wavelength band, wherein the ratio of length L ₁ to L ₂ (L ₂ / L ₁ ) is 0.25 or less, wavelength The Raman gain factor of 1.55 μm is 4.8 Wkm ⁻¹ to 9.0 Wkm ⁻¹ .

Further, in the invention according to claim 2, in the invention according to claim 1, the first core part having a higher refractive index than the cladding part, and the second core part having a lower refractive index than the cladding part, radius a ₁ and a second ratio of the radius a ₂ of the core portion Ra = a ₁ / a ₂ is 0.16 0.24 of the first core part, the relative refractive index difference with respect to the cladding portion of the first core portion 1. A dispersion compensating fiber designed in a range of 7% to 2.5% is used.

  Further, in the invention described in claim 3, in the Raman amplification transmission system, the 1.3 μm band zero-dispersion single mode optical fiber is connected to the end of the 1.3 band zero dispersion single mode optical fiber. A transmission path configuration comprising: the dispersion compensating fiber according to claim 1; and a Raman pumping light source that is disposed behind the dispersion compensating fiber and injects pumping light propagating in a direction opposite to the propagation direction of the signal light. And

  Furthermore, in the invention according to claim 4, in the Raman amplification transmission system, the 1.3 μm band zero-dispersion single mode optical fiber is connected to the rear of the 1.3 μm band zero dispersion single mode optical fiber. The pumping light that is disposed between the dispersion compensating fiber according to claim 1, the 1.3 μm-band zero-dispersion single-mode optical fiber, and the dispersion compensating fiber and that propagates in a direction opposite to the propagation direction of the signal light A transmission path configuration having a Raman excitation light source for injecting a liquid crystal.

According to the present invention, in the Raman amplification optical transmission system using the length L ₁ miles of 1.3μm band zero-dispersion single-mode optical fiber and the length L ₂ miles dispersion compensating fiber, the length L ₁ and L ₂ By suitably designing the ratio (L ₂ / L ₁ ) and the Raman gain factor of the dispersion compensating fiber, the effect of optimizing the signal-to-noise ratio improvement in Raman amplification transmission can be achieved.

In addition, according to the dispersion compensating fiber of the present invention, in addition to the design conditions for the L ₂ / L ₁ and the Raman gain factor, the radial shape of the refractive index distribution and the relative refractive index difference are suitably designed. Also, there is an effect that the dependency on the length ratio L ₂ / L ₁ of the optimum pumping light power in Raman amplification transmission can be reduced or the stability with respect to L ₂ / L ₁ can be improved.

  Furthermore, according to the dispersion compensating fiber of the present invention, the effect of improving the SNR characteristic can be obtained only by changing only the excitation light intensity, regardless of the insertion position of the excitation light.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram of a Raman amplification transmission system according to claim 3 using the dispersion compensating fiber of the present invention. Here, F _1, F _2, Pump, and EDFA are respectively the length L ₁ miles 1.3 .mu.m band zero-dispersion single-mode optical fiber, the length L ₂ miles dispersion compensating fiber, the pumping light source for Raman amplification, And an erbium-doped fiber amplifier. It is assumed that the excitation light from the Raman amplification excitation light source Pump is incident in the direction opposite to the signal light propagation direction and is connected to the dispersion compensation phi F ₂ bar via a circulator OC or the like. R is a light receiving portion.

Here, the 1.3 μm-band zero dispersion single relative to the signal-to-noise ratio SNR _F1 in the transmission using only the dispersion-compensating fiber F ₂ and the 1.3 μm-band zero-dispersion single-mode optical fiber F ₁ not adapted to Raman amplification. The improvement effect of the signal-to-noise ratio SNR _{F1 + F2} in the transmission in which the dispersion compensation fiber F ₂ is connected to the single-mode optical fiber F ₁ and the Raman amplification is applied is defined as the SNR improvement rate R _SNR in the equation (1). (Non-Patent Document 1).

Here, R _NL, and NF _F are respectively nonlinearity in the Raman amplification optical transmission line, and the noise figure of the optical fiber transmission line F (F = F ₁ or F ₁ + F _2,), equation (2), It can be expressed by equation (3).

Here, γ _F , P (z), and L are nonlinear coefficients in the optical fiber transmission line F (F = F ₁ or F ₁ + F ₂ ), the signal light power at the position z of the optical fiber transmission line, and the optical fiber It represents the transmission path length of the transmission path F (F = F ₁ + F ₂ ). Hν, Bc, Bs, and NF _EDFA represent photon energy, electrical filter band, optical filter band, and noise figure of erbium-doped fiber amplifier, respectively, and G _RF and T _FF represent optical fiber transmission lines, respectively. The Raman gain and transmission loss of F (F = F ₁ + F ₂ ) from position z _A to z _B , and N _ASEF and P _DRSF are the Raman amplification in the optical fiber transmission line F (F = F ₁ + F ₂ ), respectively. The optical power density by the spontaneous emission of the noise component to be generated and the noise power by double Rayleigh scattering are represented by equations (4) to (7), respectively.

Here, P _B and P _in represent pumping light power and incident signal light power, respectively. C _RF , α _PF , α _SF , and R _F are the Raman gain factor, the loss factor at the pumping light wavelength, and the loss factor at the signal light wavelength, respectively, in the optical fiber transmission line F (F = F ₁ or F ₂ ). , And the Rayleigh scattering coefficient, which are respectively represented by Expression (8) (Non-Patent Document 2), Expression (9) (Non-Patent Document 3), and Expression (10) (Non-Patent Document 4).

Here, λ represents the wavelength, and A _effF and n _coreF represent the effective cross-sectional area of the optical fiber transmission line F (F = F ₁ or F ₁ + F ₂ ) and the refractive index of the optical fiber core, respectively. Also, delta _F represents the relative refractive index difference between the optical fiber transmission line F (F = F ₁ or F _2,) core refractive index n _CoreF and pure silica having a refractive index n _SiO2 of, defined in formula (11) Is done.

Therefore, using the transmission path length of the optical fiber transmission line, the relative refractive index difference of the optical fiber core obtained from the refractive index distribution, and the effective cross-sectional area, the dispersion compensation fiber and the 1.3 μm band zero dispersion that does not apply Raman amplification for the signal-to-noise ratio SNR _F1 in the transmission of a single mode optical fiber F _1, connect the dispersion compensating fiber F ₂ to 1.3μm band zero-dispersion single-mode optical fiber F _1, signal-in transmission adapted Raman amplification The effect of improving the noise ratio SNR _{F1 + F2} can be obtained.

Hereinafter, Example 1 of the present invention will be described using a dispersion compensating fiber having a refractive index distribution according to claim 2 of the present invention. In the following examples, the Raman gain factor, transmission loss, and fiber length L ₁ of the 1.3 μm band zero-dispersion single mode optical fiber F ₁ are 0.44 Wkm ⁻¹ , 0.2 dB / km, and 80 km.

The configuration of the first embodiment is the same as that shown in FIG. That is, the dispersion compensating fiber F ₂ is connected to the end of the 1.3 μ-band zero-dispersion single mode optical fiber F ₁ , and the Raman amplification pumping light source Pump is arranged behind the dispersion compensating fiber F ₂ via the circulator OC. This constitutes a Raman amplification transmission system. Further, an erbium-doped fiber amplifier EDFA and a light receiving part R are provided. In this case the length L ₁ of 1.3μ band zero-dispersion single-mode optical fiber F _1, the length L ₂ of the ratio dispersion compensating fiber F ₂ (L ₂ / L ₁₎ is 0.25 or less, the dispersion compensating fiber The Raman gain factor of the F ₂ wavelength 1.55 μm band was adjusted from 4.8 Wkm ⁻¹ to 9.0 Wkm ⁻¹ .

FIG. 2 is a conceptual diagram showing the refractive index distribution in the cross-sectional direction of the dispersion compensating fiber F _{2 according} to claim 2 of the present invention. In this dispersion compensating fiber F ₂ , there is a first core portion at the center of the fiber cross section, a _second core portion is provided surrounding the first core portion, and a cladding is formed surrounding the second core portion. There is a department. Here, Δ ₁ and Δ ₂ , and a ₁ and a ₂ represent the relative refractive index difference between the first core portion and the second core portion with respect to the cladding portion, and the radii of the first core portion and the second core portion, respectively. In the following description, the ratio of the first core radius a _{1 to} the second core radius a ₂ is defined as Ra. In this example, the relative refractive index difference Δ ₂ of the second core portion was set to −0.5%.

FIG. 3 shows the relative refraction of the first core portion and the cladding portion when the dispersion-to-slope ratio (RDS) is 0.0033 nm ⁻¹ in the dispersion compensating fiber F ₂ having the refractive index distribution shown in FIG. This represents the relationship between the rate difference Δ ₁ and the second core radius a ₂ . Here, RDS at an arbitrary wavelength λ is defined by Equation (12) using the chromatic dispersion Dλ and the dispersion slope Sλ at the wavelength λ (Non-patent Document 5).

The RDS values used in FIG. 3 are the chromatic dispersion at the wavelength of 1.55 μm and the typical values of the dispersion slope of the 1.3 μm band zero-dispersion single mode optical fiber F ₁ , 17 ps / nm · km and 0.056 ps, respectively. / Nm ² · km. Therefore, by using the dispersion compensating fiber F ₂ having the relationship between Δ ₁ and a ₂ shown in FIG. 3, the dispersion characteristics of the 1.3 μm band zero-dispersion single mode optical fiber in the wavelength 1.55 μm band can be efficiently compensated. It becomes possible to do.

Figure 4 is the design satisfies the dispersion compensating fiber F ₂ shown in FIG. 3, the 1.3μm band zero-dispersion single-mode optical fiber F ₁ of the length L ₁ and the dispersion compensating fiber F ₂ of length L ₂ for the ratio (L ₂ / L _1), a diagram showing the relationship between the relative refractive index difference delta ₁ of the first core and the clad.

5, FIG. 3, and in the design satisfies the dispersion compensating fiber F ₂ shown in FIG. 4, the 1.3μm band zero-dispersion single-mode optical fiber F ₁ of the length L ₁ and the dispersion compensating fiber F ₂ length is for the ratio (L ₂ / L ₁₎ with L _2, is a diagram showing the relationship between the Raman gain factor C _R.

FIG. 6 is a diagram illustrating an example of a calculation result of the SNR improvement rate R _{SNR with} respect to the pumping light power in the Raman amplification transmission system illustrated in FIG. 1. Here, the Raman gain factor, transmission loss, and length ratio (L ₂ / L ₁ ) of the dispersion compensating fiber F _{2 to} the 1.3 μm band zero-dispersion single mode optical fiber F ₁ are shown in FIGS. As an example, the results were set to 6.3 Wkm ⁻¹ , 0.3 dB / km, and 0.15, respectively. The signal light wavelength λ _S and the excitation light wavelength λ _P were 1.55 μm and 1.45 μm, respectively, and the incident signal light power P _in and the transmission speed B were −10 dBm and 10 Gbit / s, respectively.

In FIG. 6, it can be seen that when the pumping light power is 80 mW, the SNR improvement rate becomes maximum at about 2.4 dB. Here, the maximum SNR improvement rate is defined as R _SNR-max , and the pumping light power at that time is defined as the optimum pumping light power P _B-opt .

FIG. 7 shows the maximum SNR improvement rate R _SNR-max and the 1.3 μm band zero dispersion unit in the Raman amplification transmission system shown in FIG. 1 having the dispersion compensating fiber F ₂ satisfying the design conditions shown in FIGS. it is a diagram showing a relationship between one mode optical fiber F ₁ and the length ratio of the dispersion compensating fiber _{F 2 (L 2 / L 1} ). From FIG. 7, it can be seen that by setting L ₂ / L ₁ to 0.25 or less, R _SNR-max becomes 0 dB or more in any Ra, and an effect of improving SNR can be obtained.

FIG. 8 shows the optimum pumping light power P _B-opt when the SNR improvement rate is maximized, the length L _{1 of the} 1.3 μm-band zero-dispersion single mode optical fiber F ₁ , and the length of the dispersion compensating fiber F ₂ . shows the relationship between the ratio (L ₂ / L ₁₎ with L _2. From FIG. 8, it can be seen that by designing Ra from 0.16 to 0.24, the amount of fluctuation of the optimum pumping light power with respect to L ₂ / L ₁ can be suppressed to ± 10 mW or less. Therefore, by reducing L ₂ / L ₁ to 0.25 or less and Ra from 0.16 to 0.24, the dependency on the pumping light power of the Raman amplification transmission system can be reduced or the stability can be improved. I understand.

Here, it can be seen from FIG. 4 that the lower limit of Δ ₁ satisfying Ra = 0.16 to 0.24 and L ₂ / L ₁ ≦ 0.25 is 1.7%. On the other hand, when a high concentration of germanium is added to the core, the Rayleigh scattering loss and the structural irregularity loss are increased, and the transmission loss at a wavelength of 1.55 μm is 0 at an addition amount of about 30 mol% where the relative refractive index difference is 3%. .5 dB / km or more. Further, as described in Patent Document 3, in the fiber in which fluorine is added to the clad, loss due to structural improperness can be reduced, but Rayleigh scattering loss cannot be reduced. For this reason, about 2.5% is considered desirable for the upper limit of Δ ₁ . Therefore, from FIG. 5, the Raman gain factors satisfying the conditions of Ra = 0.16 to 0.24, L ₂ / L ₁ ≦ 0.25, and Δ ₁ = 1.7% to 2.5% are satisfied. It can be seen that the design range is 4.8 Wkm ⁻¹ to 9.0 Wkm ⁻¹ .

Next, a second embodiment according to the present invention will be described. FIG. 9 is a diagram for explaining an embodiment of the dispersion compensating fiber of the present invention, and is a configuration diagram of the Raman amplification transmission system according to claim 4 using the dispersion compensating fiber of the present invention. Here, F _1, F _2, Pump, and EDFA are respectively the length L ₁ miles 1.3 .mu.m band zero-dispersion single-mode optical fiber, the length L ₂ miles dispersion compensating fiber, the pumping light source for Raman amplification, And an erbium-doped fiber amplifier. The pump light from the Raman amplification pump light source Pump is incident in the direction opposite to the signal light propagation direction, and is installed between the 1.3 μm-band zero-dispersion single mode optical fiber F ₁ and the dispersion compensation fiber F _2. It is assumed that the connection is made via the circulator OC or the like. R is a light receiving portion. In the second embodiment, a Raman amplification pumping light source Pump is arranged between the 1.3 μm-band zero-dispersion single mode optical fiber F ₁ and the dispersion compensating fiber F ₂ to constitute a Raman amplification transmission system.

FIG. 10 shows the maximum SNR improvement rate R _SNR-max and 1.3 μm-band zero-dispersion single mode optical fiber F _{1 in} the Raman amplification transmission system of FIG. 9 having the dispersion compensating fiber described in the first embodiment. and is a diagram showing the relationship between the length ratio of the dispersion compensating fiber _{F 2 (L 2 / L 1} ). From FIG. 10, it can be seen that, when L ₂ / L ₁ is 0.25 or less, R _SNR-max is 3 dB or more for any Ra, and a high SNR improvement effect is obtained.

FIG. 11 shows the optimum pumping light power P _B-opt that realizes the maximum SNR improvement rate of FIG. 10, the length L _{1 of the} 1.3 μm-band zero-dispersion single mode optical fiber F ₁ , and the length of the dispersion compensating fiber F ₂ . is shows the relationship of the ratio of _{L 2 (L 2 / L 1} ). From FIG. 11, it can be seen that the fluctuation amount of the optimum pumping light power can be reduced to ± 10 mW or less by setting L ₂ / L ₁ to 0.25 or less and Ra to the range of 0.16 to 0.24. Therefore, as in the case of Example 1, L ₂ / L ₁ ≦ 0.25, Ra = 0.16 to 0.24, C _R = 4.8 Wkm ^{−1 to} 9.0 Wkm ⁻¹ , and Δ By using a dispersion compensating fiber satisfying the condition of ₁ = 1.7% to 2.5%, the SNR improvement effect of the Raman amplification system having the configuration shown in FIG. 9 is preferable, and the excitation light of the Raman amplification transmission system is obtained. It can be seen that reduction in storage stability against power or improvement in stability can be realized.

  In addition, although Example 1 and Example 2 are the examples using the dispersion compensation fiber of Claim 2, you may make it use the dispersion compensation fiber of Claim 1 in Example 1,2. Good.

It is a block diagram which shows the structural example of the Raman amplification transmission system of Example 1 using the dispersion compensation fiber of this invention. It is explanatory drawing which shows the conceptual diagram showing the refractive index distribution of the cross-sectional direction in the dispersion compensation fiber of this invention. In the dispersion compensating fiber obtained from the refractive index profile shown in FIG. 2, the dispersion-to-slobe ratio (RDS) matches the RDS 0.0033 nm ^{−1 of the} 1.3 μm band zero-dispersion single mode optical fiber. parts and the relative refractive index difference between the clad portion delta ₁ and is a characteristic diagram showing the relationship between the second core radius a _2. In the design satisfies the dispersion compensating fiber shown in FIG. 3, the ratio of the 1.3μm band zero-dispersion single-mode optical fiber length L _1, the length L ₂ of the dispersion compensating fiber (L ₂ / L ₁₎ FIG. 6 is a characteristic diagram showing the relationship between the relative refractive index difference Δ ₁ between the first core portion and the cladding portion. 3, and in the design satisfies the dispersion compensating fiber shown in FIG. 4, the ratio of the 1.3μm band zero-dispersion single-mode optical fiber length L _1, the length L ₂ of the dispersion compensating fiber (L ₂ / L ₁₎ and is a characteristic diagram showing the relationship between the Raman gain constant C _R. It is a characteristic view showing an example of the calculation result of SNR improvement rate R _{SNR with} respect to pump light power in the Raman amplification transmission system of the present invention. In the Raman amplification transmission system shown in FIG. 1 having the dispersion compensating fiber that satisfies the design conditions shown in FIGS. 3 to 5, the maximum SNR improvement rate R _SNR-max , the 1.3 μm band zero-dispersion single mode optical fiber and the dispersion it is a characteristic diagram showing the relationship between the ratio of the length of the compensating fiber (L ₂ / L _1). The ratio (L ₂₎ between the optimum pumping light power P _B-opt when the conditions shown in FIG. 7 are satisfied, the length L _{1 of the} 1.3 μm-band zero-dispersion single-mode optical fiber, and the length L ₂ of the dispersion-compensating fiber / L ₁ ) is a characteristic diagram showing a relationship with. It is a block diagram which shows the structural example of the Raman amplification transmission system of Example 2 corresponding to Claim 4 using the dispersion compensation fiber of this invention. 9 shows the relationship between the maximum SNR improvement rate R _SNR-max and the length ratio (L ₂ / L ₁ ) between the 1.3 μm-band zero-dispersion single-mode optical fiber and the dispersion-compensating fiber in the Raman amplification system of FIG. FIG. The optimum pumping light power P _B-opt when the conditions shown in FIG. 10 are satisfied, and the ratio of the length of the 1.3 μm-band zero-dispersion single-mode optical fiber to the length of the dispersion-compensating fiber (L ₂ / L ₁ ) The characteristic view which shows a relationship.

Explanation of symbols

F ₁ 1.3 μm-band zero-dispersion single-mode optical fiber F ₂ dispersion-compensating fiber Pump Excitation light source OC for Raman amplification Circulator EDFA Erbium-doped fiber amplifier R Receiver

Claims (4)

Connected to the end of a 1.3 μm band zero-dispersion single mode optical fiber of length L ₁ to compensate for the chromatic dispersion and dispersion slope in the wavelength 1.55 μm band of the 1.3 μm band zero dispersion single mode optical fiber. A dispersion compensating fiber having a length L ₂ , wherein the ratio of the lengths L ₁ and L ₂ (L ₂ / L ₁ ) is 0.25 or less, and the Raman gain factor in the 1.55 μm wavelength band is 4.8 Wkm ^−1. To 9.0 Wkm ⁻¹ , a dispersion compensating fiber. A first core portion having a higher refractive index than the cladding portion and a second core portion having a lower refractive index than the cladding portion, and a ratio Ra between the radius a ₁ of the first core portion and the radius a ₂ of the second core portion; The relative refractive index difference with respect to the cladding portion of the first core portion is from 1.7% to 2.5%, wherein = a ₁ / a ₂ is 0.16 to 0.24. Dispersion compensating fiber.   A dispersion compensating fiber according to claim 1 or 2, connected to the end of the 1.3 band zero-dispersion single mode optical fiber, and the end of the 1.3 band zero dispersion single mode optical fiber, and the dispersion compensating fiber And a Raman pumping light source for injecting pumping light propagating in a direction opposite to the propagation direction of the signal light.   The dispersion compensating fiber according to claim 1 or 2, connected to the rear of the 1.3 μm band zero-dispersion single mode optical fiber, and the 1.3 μm band zero dispersion single mode optical fiber, and the 1.3 μm band A Raman amplification transmission system comprising: a band-zero-dispersion single-mode optical fiber; and a Raman pump light source that is disposed between the dispersion compensation fiber and injects pump light propagating in a direction opposite to the propagation direction of signal light. .

Images