JP2005156944A - Dispersion compensating fiber and dispersion compensating fiber module for raman amplification - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dispersion compensating fiber suited to various kinds of transmitting optical fibers by reducing transmission loss near a band of 1,430nm which is used for Raman amplification of a band of 1.55μm wavelength. <P>SOLUTION: In a quartz glass dispersion compensating fiber provided with a center core part 3 which consists of a core 1 and a clad 2 formed on the outer periphery of the core 1 and in which the core 1 has the refractive index higher than that of the clad 2 and an intermediate core part 4 which is arranged on the outer periphery of the center core part 3 and has a refractive index lower than that of the clad, a specific refractive index difference with respect to the clad of the center core part 3 is 1.2 to 2.0%, the fluorine addition concentration of the center core part 3 is in a range of 0.02 to 0.3 mass%, and the maximum transmission loss in a band of 1.38μm wavelength is ≤1.5dB/km. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a dispersion compensating fiber used for Raman amplification, and particularly to dispersion compensation for Raman amplification suitable for various transmission optical fibers by reducing transmission loss near a wavelength of 1430 nm used for Raman amplification at a wavelength of 1.55 μm. The present invention relates to a fiber and a dispersion compensation fiber module for Raman amplification using the fiber.

  For long-distance optical communications, a standard single mode optical fiber (hereinafter referred to as SMF) or a non-zero dispersion shifted optical fiber is mainly used to suppress cumulative chromatic dispersion and four-wave mixing (hereinafter referred to as FWM). (Hereinafter referred to as NZ-DSF) uses a transmission line in which a dispersion compensating fiber is combined. In addition, an optical amplifier using a rare earth-doped optical fiber such as an erbium-doped optical fiber (hereinafter referred to as EDF) is also used at the same time in order to compensate for the optical loss generated in the transmission line or the dispersion compensating fiber.

  However, when the distance is further increased, the loss of the dispersion compensating fiber used for compensating the chromatic dispersion is large, so that the optical signal-to-noise ratio (OSNR) is deteriorated. Therefore, a method of using the dispersion compensating fiber itself as an amplification medium has been proposed (for example, see Patent Document 1). The Raman amplifier disclosed in Patent Document 1 performs optical amplification using a highly nonlinear fiber or dispersion compensating fiber as a Raman amplification optical fiber.

On the other hand, proposals have been made for highly nonlinear optical fibers that are nonlinear in the signal wavelength band and optical fibers that are suitable for Raman amplification against dispersion compensating fibers that have a large absolute value of chromatic dispersion with a small degree of design freedom for Raman amplification. (For example, refer to Patent Document 2).
Further, as a dispersion compensation fiber suitable for Raman amplification, Patent Document 3 discloses a refractive index distribution and the like (see Patent Document 3).

  As main transmission optical fibers, the types of optical fibers shown in Table 1 are known.

RDS in Table 1 is a ratio of dispersion slope to chromatic dispersion (RDS; Relative Dispersion Slope), and when chromatic dispersion is D and dispersion slope is S, RDS can be expressed as the following equation (1). it can.
RDS = S / D (1)

  RDS is a value used when expressing the performance of dispersion slope compensation. If the RDS of the dispersion compensation fiber is equal to the RDS of the transmission optical fiber, the dispersion slope can be completely compensated when the chromatic dispersion is compensated. .

For these dispersion compensating fibers, many dispersion compensating fibers have been proposed from the viewpoint of dispersion slope compensation. For example, a dispersion compensating fiber for completely compensating the accumulated chromatic dispersion of SMF in a wide wavelength region while increasing the effective core area has been proposed (see, for example, Patent Document 4).
JP-A-11-84440 JP 2002-277911 A JP 2003-241001 A JP 2002-221632 A

However, these dispersion compensation fibers are insufficient as dispersion compensation fibers suitable for Raman amplification, and there is a strong demand for providing a dispersion compensation fiber for Raman amplification with higher efficiency.
In particular, transmission loss in the vicinity of 1430 nm, which is a wavelength band in which an excitation light source is used in actual Raman amplification, is likely to deteriorate due to the tail of the OH absorption band generated in the vicinity of a wavelength of 1.38 μm. This is because the dispersion compensation fiber having a large relative refractive index difference of the central core increases the amount of GeO _{2 to be} added, and the degree of deterioration increases. The Raman gain coefficient increases as the amount of GeO ₂ added to the core increases. However, if the loss in the excitation wavelength band increases, the excitation efficiency deteriorates.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a dispersion compensating fiber suitable for various transmission optical fibers by reducing transmission loss in the vicinity of a wavelength of 1430 nm, particularly used for wavelength 1.55 μm band Raman amplification.

In order to achieve the above object, the present invention comprises a core and a clad provided on the outer periphery thereof, and the core is provided on a central core portion having a higher refractive index than the clad, and on the outer periphery of the central core portion. A dispersion compensation fiber based on silica glass comprising an intermediate core portion having a refractive index lower than that of the cladding, wherein a relative refractive index difference of the central core portion relative to the cladding is 1.2 to 2.0%. The dispersion compensating fiber is characterized in that the concentration of fluorine added to the central core is in the range of 0.02 to 0.3% by mass, and the maximum transmission loss in the wavelength band of 1.38 μm is 1.5 dB / km or less. I will provide a.
In the dispersion compensating fiber of the present invention, it is preferable that the maximum transmission loss in the wavelength band of 1.38 μm is 1.0 dB / km or less.
Moreover, it is preferable that the loss increase in the wavelength 1.38 micrometer band by OH absorption is 0.5 dB / km or less.
Here, the absorption loss due to OH groups in the optical fiber will be described.
The absorption loss due to the OH group causes an increase in transmission loss in the wavelength band of 1.38 μm. The absorption loss due to this OH group is that the moisture remaining in the optical fiber in the manufacturing process becomes a bonded state called OH group, and vibration absorption of this OH group exists in a wavelength band centered on 1.38 μm. This is a loss due to the phenomenon of light absorption at the center.
Conventionally, in the manufacture of optical fiber preforms, particularly in the VAD method, dehydration work using a chlorine-based gas has been performed in order to suppress absorption loss due to OH groups. However, in particular, in the MCVD method and the PCVD method in which vitrification proceeds almost simultaneously with the reaction, unlike the VAD method in which OH groups are generated during the reaction, no dehydration work is performed. In the present invention, since a small amount of fluorine is added to the central core portion together with germanium, absorption loss due to OH groups can be suppressed without depending on the manufacturing method of the optical fiber preform.

In the dispersion compensating fiber of the present invention, the core includes a central core portion having a refractive index higher than that of the cladding, an intermediate core portion provided on an outer periphery of the central core portion and having a refractive index lower than that of the cladding, and the intermediate core portion. A ring core portion provided on the outer periphery of the core portion and having a refractive index higher than that of the clad and lower than that of the central core can be provided.
Further, in the dispersion compensating fiber of the present invention, the core has a central core portion having a higher refractive index than the cladding, an intermediate core portion provided on the outer periphery of the central core portion and having a lower refractive index than the cladding, A ring core portion provided on the outer periphery of the intermediate core portion and having a refractive index higher than that of the cladding and lower than that of the central core; and provided on an outer periphery of the ring core portion and having a refractive index lower than that of the cladding and higher than that of the intermediate core portion. It can also be set as the structure provided with the depressed core part.
In these dispersion compensating fibers, the effective area at a wavelength of 1.55 μm is 17 to 25 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, and the chromatic dispersion is in the range of −150 to −65 ps / nm / km. And the ratio of the dispersion slope to the chromatic dispersion is preferably in the range of 0.0027 to 0.0041 nm ⁻¹ .
In these dispersion compensating fibers, the effective cross-sectional area at a wavelength of 1.59 μm is 17 to 25 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, and the chromatic dispersion is −150 to −65 ps / nm / km. It is preferable that the ratio of the dispersion slope to the chromatic dispersion is in the range of 0.0022 to 0.0034 nm ⁻¹ .
In these dispersion compensating fibers, the radius of the central core portion, the intermediate core portion, the ring core portion, and the depressed core portion, and the relative refractive index difference of each portion with respect to the clad are respectively (a, Δ1), ( b, Δ2), (c, Δ3), (d, Δ4),
c is 6-9 μm,
Δ1 is 1.2 to 2.0%,
Δ2 is −0.45 to −0.25%,
Δ3 is 0.3 to 0.6%,
Δ4 is −0.1 to −0.005%,
b / a is 2.5 to 4.0,
It is preferable that c / b is in the range of 1.1 to 1.5 and d / c is in the range of 1.5 to 2.0.

In the dispersion compensating fiber of the present invention, the effective area at a wavelength of 1.55 μm is 15 to 20 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, and the chromatic dispersion is −120 to −40 ps / nm / km. The ratio of the dispersion slope to the chromatic dispersion may be in the range of 0.005 to 0.012 nm ⁻¹ .
In the dispersion compensating fiber of the present invention, the effective cross-sectional area at a wavelength of 1.59 μm is 15 to 22 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, and the chromatic dispersion is −130 to −40 ps / nm / km. And the ratio of the dispersion slope to the chromatic dispersion may be in the range of 0.004 to 0.009 nm ⁻¹ .
In these dispersion compensating fibers, the radius of the central core portion, the intermediate core portion, the ring core portion, and the depressed core portion, and the relative refractive index difference of each portion with respect to the clad are respectively (a, Δ1), ( b, Δ2), (c, Δ3), (d, Δ4),
c is 6-9 μm,
Δ1 is 1.2 to 2.0%,
Δ2 is −0.8 to −0.5%,
Δ3 is 0.3 to 0.6%,
Δ4 is −0.1 to −0.005%,
b / a is 2.0 to 3.5,
It is preferable that c / b is in the range of 1.1 to 2.0 and d / c is in the range of 1.4 to 2.0.

In the dispersion compensating fiber of the present invention, the effective area at a wavelength of 1.55 μm is 11 to 16 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, and the chromatic dispersion is −170 to −40 ps / nm / km. The dispersion slope ratio with respect to chromatic dispersion may be within a range of 0.016 to 0.024 nm ⁻¹ .
In the dispersion compensating fiber of the present invention, the effective cross-sectional area at a wavelength of 1.59 μm is 14 to 19 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, and the chromatic dispersion is −140 to −40 ps / nm / km. The ratio of the dispersion slope to the chromatic dispersion may be in the range of 0.008 to 0.012 nm ⁻¹ .
In these dispersion compensating fibers, the radius of the central core portion, the intermediate core portion, the ring core portion, and the depressed core portion, and the relative refractive index difference of each portion with respect to the clad are respectively (a, Δ1), ( b, Δ2), (c, Δ3), (d, Δ4),
c is 6-9 μm,
Δ1 is 1.5 to 2.0%,
Δ2 is −1.3 to −0.8%,
Δ3 is 0.3 to 0.6%,
Δ4 is −0.15 to −0.03%,
b / a is 2.0 to 3.5,
It is preferable that c / b is in the range of 1.1 to 2.0 and d / c is in the range of 1.4 to 2.0.

  In addition, the present invention provides a dispersion compensation fiber module for Raman amplification, wherein the dispersion compensation fiber is used as a Raman amplification medium.

ADVANTAGE OF THE INVENTION According to this invention, the transmission loss of 1430 nm band vicinity used for wavelength 1.55 micrometer band Raman amplification can be reduced, and the dispersion compensation fiber suitable for various optical fibers for transmission can be provided.
Furthermore, the present invention can provide a dispersion compensation fiber module for Raman amplification with low loss and high Raman amplification efficiency by using the dispersion compensation fiber as a Raman amplification medium.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a graph showing a first embodiment of a dispersion compensating fiber of the present invention and showing a refractive index distribution of the dispersion compensating fiber. The dispersion compensating fiber according to the present embodiment includes a core 1 at the center and a clad 2 provided on the outer periphery thereof. The core 1 includes a central core 3 having a higher refractive index than the clad 2 and the central core 3. And an intermediate core portion 4 having a lower refractive index than that of the clad 2.

The central core portion 3 is made of quartz glass doped with GeO ₂ and fluorine, and the relative refractive index difference Δ1 with respect to the cladding 2 of the central core portion 3 is in a range of 1.2 to 2.0%. The concentration of fluorine added to the central core portion 3 is in the range of 0.02 to 0.3% by mass. The intermediate core portion 4 having a lower refractive index than the clad 2 is made of quartz glass to which fluorine is added, and the clad 2 is made of quartz glass or quartz glass to which fluorine is added. This dispersion compensating fiber is characterized in that the maximum transmission loss in a wavelength band of 1.38 μm is 1.5 dB / km or less.

  The inventors added a small amount of fluorine to the core together with germanium, thereby having an OH absorption loss reducing effect that causes transmission loss deterioration in the wavelength 1.38 μm band, and suppressing Raman loss while suppressing transmission loss deterioration. It has been found that an effective amount of germanium can be increased.

  When the fluorine addition concentration of the central core portion 3 is less than 0.02 mass%, the effect of fluorine addition is small, the maximum transmission loss in the wavelength 1.38 μm band is high, and the germanium addition amount is also a relative refractive index difference Δ In terms of conversion, the increase is only about 0.06%, and the effect of improving the Raman gain efficiency by addition becomes small. On the other hand, when the fluorine addition concentration of the central core portion 3 exceeds 0.3 mass%, the efficiency of Raman amplification is degraded due to the degradation of Rayleigh scattering and structural irregularity loss.

  In addition, by suppressing the maximum transmission loss in the wavelength 1.38 μm band to 1.5 dB / km or less, it is possible to perform Raman amplification without reducing efficiency. When the maximum transmission loss in the wavelength 1.38 μm band due to OH absorption exceeds 1.5 dB / km, the transmission loss in the excitation wavelength band of Raman amplification (near 1430 nm) deteriorates and the Raman amplification efficiency decreases.

The second embodiment of the dispersion compensating fiber of the present invention is characterized in that the maximum transmission loss in a wavelength band of 1.38 μm is 1.0 dB / km or less.
In the present embodiment, the Raman amplification efficiency can be further increased by further reducing the transmission loss in the excitation wavelength band of Raman amplification.

The third embodiment of the dispersion compensating fiber of the present invention is characterized in that an increase in loss in a wavelength band of 1.38 μm due to OH absorption is 0.5 dB / km or less.
The main cause of transmission loss deterioration in the wavelength 1.38 μm band is due to OH groups contained in quartz glass. In a dispersion compensating fiber in which a large amount of germanium is added to the core as compared with a normal SMF, the residual OH group concentration also increases. In the present embodiment, by suppressing this OH group concentration, it is possible to reduce deterioration of transmission loss in the 1.38 μm band and increase Raman amplification efficiency.

  FIG. 2 is a graph showing a fourth embodiment of the dispersion compensating fiber of the present invention and showing a refractive index distribution of the dispersion compensating fiber. The dispersion compensating fiber according to the present embodiment includes a core 1 at the center and a clad 2 provided on the outer periphery thereof. The core 1 includes a central core 3 having a higher refractive index than the clad 2 and the central core 3. An intermediate core portion 4 having a refractive index lower than that of the clad 2 and a ring core portion 5 having a refractive index higher than that of the clad 2 and lower than that of the central core portion 3. It has a configuration with.

As in the case of the first embodiment described above, the central core portion 3 is made of quartz glass to which GeO ₂ and fluorine are added. The relative refractive index difference Δ1 of the central core portion 3 with respect to the cladding 2 is 1. The concentration of fluorine added to the central core portion 3 is set to a range of 0.02 to 0.3% by mass. The intermediate core portion 4 having a refractive index lower than that of the clad 2 is made of quartz glass to which fluorine is added, and the clad 2 is made of quartz glass.

  The dispersion compensating fiber of the present embodiment can obtain the same effect as the dispersion compensating fiber of the first embodiment, and has a refractive index higher than that of the cladding 2 and lower than that of the central core portion 3 on the outer periphery of the intermediate core portion 4. By providing the ring core portion 5 having the chromatic dispersion and dispersion slope compensation performance required for the dispersion compensating fiber together with the effect of Raman amplification, the low bending loss and the low transmission loss are maintained. be able to.

  FIG. 3 is a graph showing a fifth embodiment of the dispersion compensating fiber of the present invention and showing a refractive index distribution of the dispersion compensating fiber. FIG. 4 is a graph showing the fluorine concentration distribution of the dispersion compensating fiber according to the third embodiment. In FIG. 4, the same refractive index distribution as that of FIG. 3 is shown for reference. The dispersion compensating fiber according to the present embodiment includes a core 1 at the center and a clad 2 provided on the outer periphery thereof. The core 1 includes a central core 3 having a higher refractive index than the clad 2 and the central core 3. An intermediate core portion 4 having a refractive index lower than that of the clad 2 and a ring core portion having a refractive index higher than that of the clad 2 and lower than that of the central core portion 3. 5 and a depressed core portion 6 provided on the outer periphery of the ring core portion 5 and having a refractive index lower than that of the clad 2 and higher than that of the intermediate core portion 4.

  The dispersion compensating fiber of the present embodiment can obtain the same effect as the dispersion compensating fiber of the first embodiment, and has a refractive index higher than that of the cladding 2 and lower than that of the central core portion 3 on the outer periphery of the intermediate core portion 4. The ring core portion 5 and the depressed core portion 6 having a refractive index lower than that of the cladding 2 and higher than that of the intermediate core portion 4 are provided on the outer periphery of the ring core portion 5. The chromatic dispersion and dispersion slope compensation performance required for the compensation fiber can be shortened in particular while maintaining low bending loss and low transmission loss.

A sixth embodiment of the dispersion compensating fiber of the present invention, 17μm ² ~25μm ² is an effective area at a wavelength of 1.55 .mu.m, the bending loss when wound at a diameter 20mm below 20 dB / m, the chromatic dispersion is -150 It is in the range of −65 ps / nm / km, and the ratio of the dispersion slope to the chromatic dispersion is 0.0027 nm ^{−1 to} 0.0041 nm ⁻¹ .
By obtaining the chromatic dispersion and the ratio of the dispersion slope to the chromatic dispersion as described above, the chromatic dispersion accumulated by the SMF can be compensated in a wide wavelength region including 1.55 μm.

Seventh embodiment of the dispersion compensating fiber of the present invention, an effective area at a wavelength of 1.59μm is 17μm ² ~25μm ^2, less bending loss 20 dB / m when wound at a diameter 20 mm, the wavelength dispersion -150～- It is in the range of 65 ps / nm / km, and the ratio of the dispersion slope to the chromatic dispersion is 0.0022 nm ^{−1 to} 0.0034 nm ⁻¹ .
By obtaining the chromatic dispersion and the ratio of the dispersion slope to the chromatic dispersion as described above, the chromatic dispersion accumulated by the SMF can be compensated in a wide wavelength region including 1.59 μm.

The eighth embodiment of the dispersion compensating fiber of the present invention is the dispersion compensating fiber having the characteristics of the sixth or seventh embodiment, wherein the central core portion 3, the intermediate core portion 4, the ring core portion 5, and the depressed core portion 6 are used. And the relative refractive index difference of each part with respect to the cladding 2 were (a, Δ1), (b, Δ2), (c, Δ3), and (d, Δ4), respectively. When
c is 6-9 μm,
Δ1 is 1.2 to 2.0%,
Δ2 is −0.45 to −0.25%,
Δ3 is 0.3 to 0.6%,
Δ4 is −0.1 to −0.005%,
b / a is 2.5 to 4.0,
c / b is in the range of 1.1 to 1.5, and d / c is in the range of 1.5 to 2.0.
By adopting such a refractive index distribution structure, the dispersion compensating fiber of the sixth or seventh embodiment can be obtained.
Note that not all dispersion compensating fibers having a refractive index distribution structure in this range have the characteristics described in the sixth or seventh embodiment. Within this range, the desired characteristics can be obtained by checking and adjusting various optical characteristics while changing the refractive index difference of each part and the ratio of the layer thickness.

The ninth embodiment of the dispersion compensating fiber of the present invention has an effective area of 15 to 20 μm ^{2 at} a wavelength of 1.55 μm, a bending loss of 20 dB / m or less when wound at a diameter of 20 mm, and a wavelength dispersion of −120 to − The range is 40 ps / nm / km, and the ratio of the dispersion slope to the chromatic dispersion is 0.005 to 0.012 nm ⁻¹ .
Compensating the chromatic dispersion accumulated by the low dispersion slope type NZ-DSF and the middle dispersion type NZ-DSF in a wide wavelength range including 1.55 μm by taking the ratio of the chromatic dispersion and the dispersion slope to the chromatic dispersion. Is possible.

The tenth embodiment of the dispersion compensating fiber of the present invention has an effective area of 15 to 22 μm ^{2 at} a wavelength of 1.59 μm, a bending loss of 20 dB / m or less when wound at a diameter of 20 mm, and a wavelength dispersion of −130 to −40 ps. The dispersion slope ratio is in the range of 0.004 to 0.009 nm ^{−1 in} the range of / nm / km.
Compensating the chromatic dispersion accumulated by the low dispersion slope type NZ-DSF and the medium dispersion type NZ-DSF in a wide wavelength range including 1.59 μm by taking the ratio of the chromatic dispersion and the dispersion slope to the chromatic dispersion. Is possible.

The eleventh embodiment of the dispersion compensating fiber of the present invention is the dispersion compensating fiber having the characteristics described in the ninth or tenth embodiment, wherein the central core portion 3, the intermediate core portion 4, the ring core portion 5, and the depressed core. The radius of the part 6 (1/2 of the outer diameter of each part) and the relative refractive index difference of each part with respect to the clad 2 are (a, Δ1), (b, Δ2), (c, Δ3), (d, Δ4), respectively. When
c is 6-9 μm,
Δ1 is 1.2 to 2.0%,
Δ2 is −0.8 to −0.5%,
Δ3 is 0.3 to 0.6%,
Δ4 is −0.1 to −0.005%,
b / a is 2.0 to 3.5,
c / b is in the range of 1.1 to 2.0, and d / c is in the range of 1.4 to 2.0.
By adopting such a refractive index distribution structure, the dispersion compensating fiber of the ninth or tenth embodiment can be obtained.
Note that not all dispersion compensating fibers having a refractive index distribution structure in this range have the characteristics described in the ninth or tenth embodiment. Within this range, the desired characteristics can be obtained by checking and adjusting various optical characteristics while changing the refractive index difference of each part and the ratio of the layer thickness.

The twelfth embodiment of the dispersion compensating fiber of the present invention has an effective area of 11 to 16 μm ^{2 at} a wavelength of 1.55 μm, a bending loss of 20 dB / m or less when wound at a diameter of 20 mm, and a wavelength dispersion of −170 to −40 ps. The dispersion slope ratio is in the range of 0.016 to 0.024 nm ^{−1 in} the range of / nm / km.
By taking the ratio of the chromatic dispersion and the dispersion slope to the chromatic dispersion, a wide wavelength range including 1.55 μm of the chromatic dispersion accumulated by the effective area (Aeff) expansion type NZ-DSF and the medium dispersion type NZ-DSF. It becomes possible to compensate with.

The thirteenth embodiment of the dispersion compensating fiber of the present invention has an effective area of 14 to 19 μm ^{2 at} a wavelength of 1.59 μm, a bending loss of 20 dB / m or less when wound at a diameter of 20 mm, and a wavelength dispersion of −140 to −40 ps. / Nm / km and the ratio of the dispersion slope to the chromatic dispersion is in the range of 0.008 to 0.012 nm- ¹ .
By taking the ratio of the chromatic dispersion and the dispersion slope to the chromatic dispersion, a wide wavelength range including 1.59 μm of the chromatic dispersion accumulated by the effective area (Aeff) expansion type NZ-DSF and the medium dispersion type NZ-DSF. It becomes possible to compensate with.

The fourteenth embodiment of the dispersion compensating fiber of the present invention is the dispersion compensating fiber having the characteristics described in the twelfth or thirteenth embodiment, wherein the central core portion 3, the intermediate core portion 4, the ring core portion 5, and the depressed core. The radius of the part 6 (1/2 of the outer diameter of each part) and the relative refractive index difference of each part with respect to the clad 2 are (a, Δ1), (b, Δ2), (c, Δ3), (d, Δ4), respectively. When
c is 6-9 μm,
Δ1 is 1.5 to 2.0%,
Δ2 is −1.3 to −0.8%,
Δ3 is 0.3 to 0.6%,
Δ4 is −0.15 to −0.03%,
b / a is 2.0 to 3.5,
c / b is in the range of 1.1 to 2.0, and d / c is in the range of 1.4 to 2.0.
By adopting such a refractive index distribution structure, the dispersion compensating fiber of the twelfth or thirteenth embodiment can be obtained.
Note that not all dispersion compensating fibers having a refractive index distribution structure in this range have the characteristics described in the twelfth or thirteenth embodiment. Within this range, the desired characteristics can be obtained by checking and adjusting various optical characteristics while changing the refractive index difference of each part and the ratio of the layer thickness.

The present invention also provides a dispersion compensation fiber module for Raman amplification, wherein any of the dispersion compensation fibers according to the present invention described above is used as a Raman amplification medium.
The dispersion compensation fiber module for Raman amplification may use the dispersion compensation fiber of the present invention as the dispersion compensation fiber, and the other structure can be configured as a conventionally known dispersion compensation fiber module for Raman amplification. For example, a module can be configured by winding the dispersion compensating fiber of the present invention having a length necessary for dispersion compensation around a small bobbin or the like.
The dispersion compensation fiber module for Raman amplification of the present invention uses the dispersion compensation fiber as described above, so that the insertion loss is low and the Raman amplification efficiency can be improved.

  Hereinafter, the effects of the present invention will be demonstrated by examples, but the present invention is not limited to the following examples.

[Example 1]
Two types of dispersion compensating fibers (referred to as “fiber A” and “fiber B” in Tables 2 and 3) having a refractive index profile as shown in FIG. 3 were prepared using the MCVD method.
The refractive index distribution parameters of the manufactured fibers A and B are shown in Table 2, and the fluorine concentration distribution is shown in FIG. In these fibers A and B, 0.15% by mass of fluorine is added to the central core portion 3, which is 0.05% in terms of relative refractive index difference.
The optical characteristics of these fibers A and B are summarized in Table 3. FIG. 5 shows the loss wavelength characteristic of the optical fiber A, FIG. 6 shows the Raman gain coefficient, FIG. 7 shows the loss wavelength characteristic of the fiber B, and FIG. 8 shows the Raman gain coefficient.

In the fibers A and B, since fluorine is added to the central core portion 3, the absorption in the wavelength band of 1.38 μm is reduced and the Raman efficiency is also increased. Maximum Raman gain efficiency, fiber A is ^{3.9 W} -1 ^{miles -1,} the fiber B was ^{4.9W -1 km} -1.

[Example 2]
Two types of dispersion compensating fibers (referred to as “fiber C” and “fiber D” in Tables 4 and 5) having a refractive index profile as shown in FIG. 3 were prepared using the MCVD method.
The refractive index distribution parameters of the produced fibers C and D are shown in Table 4, and the fluorine concentration distribution is shown in FIG. In these fibers C and D, 0.15% by mass of fluorine is added to the central core portion 3, which is 0.05% in terms of relative refractive index difference.
The optical characteristics of these fibers C and D are summarized in Table 5. FIG. 9 shows the loss wavelength characteristic of the optical fiber C, FIG. 10 shows the Raman gain coefficient, FIG. 11 shows the loss wavelength characteristic of the fiber D, and FIG. 12 shows the Raman gain coefficient.

In the fibers C and D, since fluorine is added to the central core portion 3, the absorption in the 1.38 μm wavelength band is reduced and the Raman efficiency is also increased. Maximum Raman gain efficiency, the fiber C is ^{6.5 W} -1 ^{miles -1,} the fiber D was ^{7.1W -1 km} -1.

[Example 3]
Two types of dispersion compensating fibers (referred to as “fiber E” and “fiber F” in Tables 6 and 7) having a refractive index profile as shown in FIG. 3 were prepared using the MCVD method.
The refractive index distribution parameters of the manufactured fibers E and F are shown in Table 6, and the fluorine concentration distribution is shown in FIG. In these fibers E and F, 0.10% by mass of fluorine is added to the central core portion 3, which is 0.03% in terms of relative refractive index difference.
The optical characteristics of these fibers E and F are summarized in Table 7. FIG. 13 shows the loss wavelength characteristic of the optical fiber E, FIG. 14 shows the Raman gain coefficient, FIG. 15 shows the loss wavelength characteristic of the fiber F, and FIG. 16 shows the Raman gain coefficient.

In the fibers E and F, since fluorine is added to the central core portion 3, the absorption in the 1.38 μm wavelength band is also reduced, and the Raman efficiency is also increased. Maximum Raman gain efficiency, the fiber E is ^{8.2 W} -1 ^{miles -1,} the fiber F was ^{7.1W -1 km} -1.

[Comparative Example 1]
Two types of dispersion compensating fibers (referred to as “fiber G” and “fiber H” in Tables 8 and 9) having a refractive index profile as shown in FIG. 3 were prepared using the MCVD method. However, these fibers G and H did not add fluorine to the central core portion. Table 8 shows the refractive index distribution parameters of the manufactured fibers G and H.
Table 9 summarizes the optical characteristics of the fibers G and H. The loss wavelength characteristics of the optical fibers G and H are collectively shown in FIG.

Although the Raman gain profiles of these fibers G and H were similar to those of the fibers A to F according to the present invention in which fluorine was added to the central core portion, the maximum Raman gain efficiency was 3.7 W ^{−1 for} the fiber G. km ⁻¹ and fiber F were 3.5 W ⁻¹ km ⁻¹ , which were lower than fiber A having similar characteristics.

It is a graph which shows 1st Embodiment of the dispersion compensation fiber of this invention, and shows the refractive index distribution of a dispersion compensation fiber. It is a graph which shows 4th Embodiment of the dispersion compensation fiber of this invention, and shows the refractive index distribution of a dispersion compensation fiber. It is a graph which shows 5th Embodiment of the dispersion compensation fiber of this invention, and shows the refractive index distribution of a dispersion compensation fiber. It is a graph which similarly shows the fluorine addition density | concentration of the dispersion compensation fiber of 5th Embodiment. It is a graph which shows the loss wavelength characteristic of the fiber A of the Example which concerns on this invention. It is a graph which shows the Raman gain coefficient of the same fiber A. It is a graph which shows the loss wavelength characteristic of the fiber B of the Example which concerns on this invention. It is a graph which shows the Raman gain coefficient of the same fiber B. It is a graph which shows the loss wavelength characteristic of the fiber C of the Example which concerns on this invention. 4 is a graph showing a Raman gain coefficient of the same fiber C. It is a graph which shows the loss wavelength characteristic of the fiber D of the Example which concerns on this invention. 6 is a graph showing Raman gain coefficients of the same fiber D. It is a graph which shows the loss wavelength characteristic of the fiber E of the Example which concerns on this invention. 6 is a graph showing a Raman gain coefficient of the same fiber E. It is a graph which shows the loss wavelength characteristic of the fiber F of the Example which concerns on this invention. 3 is a graph showing a Raman gain coefficient of the same fiber F. It is a graph which shows the loss wavelength characteristic of the fibers G and H of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Cladding, 3 ... Center core part, 4 ... Intermediate core part, 5 ... Ring core part, 6 ... Depressed core part.

Claims (15)

A core having a refractive index higher than that of the clad, and an intermediate core having a refractive index lower than that of the clad. A quartz glass-based dispersion compensating fiber having a portion,
The relative refractive index difference of the central core portion relative to the cladding is 1.2 to 2.0%, the fluorine addition concentration of the central core portion is in the range of 0.02 to 0.3% by mass, and the wavelength is 1.38 μm band. A dispersion compensating fiber characterized by having a maximum transmission loss at 1.5 dB / km or less.   2. The dispersion compensating fiber according to claim 1, wherein a maximum transmission loss in a wavelength band of 1.38 [mu] m is 1.0 dB / km or less.   The dispersion compensation fiber according to claim 1 or 2, wherein an increase in loss in a wavelength band of 1.38 µm due to OH absorption is 0.5 dB / km or less.   The core is provided on the outer periphery of the central core portion having a higher refractive index than the cladding, the outer periphery of the central core portion, the intermediate core portion having a lower refractive index than the cladding, and provided on the outer periphery of the intermediate core portion, The dispersion compensating fiber according to claim 1, further comprising a ring core portion having a refractive index higher than that of the clad and lower than that of the central core.   The core is provided on the outer periphery of the central core portion having a higher refractive index than the cladding, the outer periphery of the central core portion, the intermediate core portion having a lower refractive index than the cladding, and provided on the outer periphery of the intermediate core portion, A ring core portion having a refractive index higher than that of the cladding and lower than that of the central core; and a depressed core portion provided on an outer periphery of the ring core portion and having a refractive index lower than that of the cladding and higher than that of the intermediate core portion. The dispersion compensating fiber according to any one of claims 1 to 4. The effective area at a wavelength of 1.55 μm is 17 to 25 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, the chromatic dispersion is in the range of −150 to −65 ps / nm / km, and 6. The dispersion compensating fiber according to claim 1, wherein a dispersion slope ratio is in a range of 0.0027 to 0.0041 nm ⁻¹ . The effective cross-sectional area at a wavelength of 1.59 μm is 17 to 25 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, the chromatic dispersion is in the range of −150 to −65 ps / nm / km, and the chromatic dispersion is The dispersion compensating fiber according to any one of claims 1 to 5, wherein the ratio of the dispersion slope is in the range of 0.0022 to 0.0034 nm- ¹ . The radii of the central core portion, the intermediate core portion, the ring core portion, and the depressed core portion, and the relative refractive index differences of the respective portions with respect to the clad are respectively (a, Δ1), (b, Δ2), (c , Δ3), (d, Δ4),
c is 6-9 μm,
Δ1 is 1.2 to 2.0%,
Δ2 is −0.45 to −0.25%,
Δ3 is 0.3 to 0.6%,
Δ4 is −0.1 to −0.005%,
b / a is 2.5 to 4.0,
The dispersion compensating fiber according to claim 6 or 7, wherein c / b is in a range of 1.1 to 1.5, and d / c is in a range of 1.5 to 2.0. The effective area at a wavelength of 1.55 μm is 15 to 20 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, the chromatic dispersion is in the range of −120 to −40 ps / nm / km, and The dispersion compensating fiber according to any one of claims 1 to 5, wherein a ratio of the dispersion slope is in a range of 0.005 to 0.012 nm- ¹ . The effective area at a wavelength of 1.59 μm is 15 to 22 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, the chromatic dispersion is in the range of −130 to −40 ps / nm / km, and The dispersion compensating fiber according to any one of claims 1 to 5, wherein the ratio of the dispersion slope is in the range of 0.004 to 0.009 nm- ¹ . The radii of the central core portion, the intermediate core portion, the ring core portion, and the depressed core portion, and the relative refractive index differences of the respective portions with respect to the clad are respectively (a, Δ1), (b, Δ2), (c , Δ3), (d, Δ4),
c is 6-9 μm,
Δ1 is 1.2 to 2.0%,
Δ2 is −0.8 to −0.5%,
Δ3 is 0.3 to 0.6%,
Δ4 is −0.1 to −0.005%,
b / a is 2.0 to 3.5,
11. The dispersion compensating fiber according to claim 9, wherein c / b is in a range of 1.1 to 2.0, and d / c is in a range of 1.4 to 2.0. The effective area at a wavelength of 1.55 μm is 11 to 16 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, the chromatic dispersion is in the range of −170 to −40 ps / nm / km, and the chromatic dispersion is 6. The dispersion compensating fiber according to claim 1, wherein a dispersion slope ratio is in a range of 0.016 to 0.024 nm ⁻¹ . The effective area at a wavelength of 1.59 μm is 14 to 19 μm ² , the bending loss when wound at a diameter of 20 mm is 20 dB / m or less, the chromatic dispersion is in the range of −140 to −40 ps / nm / km, and the chromatic dispersion is The dispersion compensating fiber according to any one of claims 1 to 5, wherein the ratio of the dispersion slope is in the range of 0.008 to 0.012 nm- ¹ . The radii of the central core portion, the intermediate core portion, the ring core portion, and the depressed core portion, and the relative refractive index differences of the respective portions with respect to the clad are respectively (a, Δ1), (b, Δ2), (c , Δ3), (d, Δ4),
c is 6-9 μm,
Δ1 is 1.5 to 2.0%,
Δ2 is −1.3 to −0.8%,
Δ3 is 0.3 to 0.6%,
Δ4 is −0.15 to −0.03%,
b / a is 2.0 to 3.5,
14. The dispersion compensating fiber according to claim 12, wherein c / b is in a range of 1.1 to 2.0, and d / c is in a range of 1.4 to 2.0. 15. A dispersion compensation fiber module for Raman amplification, wherein the dispersion compensation fiber according to claim 1 is used as a Raman amplification medium.

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