JP2005197940A - Distributed compensation fiber module and fiber-optic transmission path - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distributed compensation fiber module capable of compensating the accumulated wavelength dispersion of an optical fiber having zero dispersion on the side of a wavelength longer than 1.55 μm collectively in a wide band, and a fiber-optic transmission path using the module. <P>SOLUTION: The distributed compensation fiber module is connected to a transmitting optical fiber having a wavelength dispersion of -10 to -1 ps/nm/km and a positive dispersion slope of +0.03 to +0.10 ps/nm<SP>2</SP>/km at a wavelength of 1.55 μm, and performs compensation so that its residual dispersion may become small. The module is provided with a fiber having positive wavelength dispersion, a negative dispersion slope, and an average wavelength dispersion of ≥+5 ps/nm/km at the wavelength of 1.55 μm, and a bending loss at a diameter of 20 mm of the fiber to be used is not larger than 20dB/m. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a dispersion compensating fiber module and an optical fiber transmission line for compensating the accumulated chromatic dispersion of an optical fiber having zero dispersion on the longer wavelength side than 1.55 μm, and in particular, dispersion capable of performing collective compensation in a wide band. The present invention relates to a compensation fiber module and an optical fiber transmission line configured by connecting the module to a transmission optical fiber.

  With the practical use of erbium-doped optical fiber amplifiers, systems using optical amplifiers such as ultra-long distance non-regenerative repeaters have already been commercialized at wavelengths of 1.53 μm to 1.63 μm. In addition, with the increase in communication capacity, development of wavelength multiplexing transmission has been rapidly advanced, and some transmission paths have already been commercialized. In the future, it is expected that the widening of the wavelength band and the increase in the number of wavelength multiplexing will proceed rapidly.

  Assuming high-speed transmission, these transmission lines are desirably optical fiber transmission lines that have as little chromatic dispersion as possible in the transmission band and that do not become zero in order to suppress nonlinear effects.

  In order to increase the transmission capacity in the wavelength division multiplexing transmission system, it is effective to widen the used wavelength region and increase the transmission rate per channel. In order to increase the transmission speed, it is necessary to reduce the cumulative dispersion of the transmission path. As the transmission speed increases, the allowable residual dispersion decreases. Therefore, dispersion compensation for each span becomes indispensable when the transmission distance becomes long and the transmission speed is increased. Since this is required over the entire wavelength band to be used, it is necessary to simultaneously compensate for the accumulated dispersion slope of the transmission line.

  Wavelength 1.3 μm band single-mode optical fiber networks have been widely used since early and are inexpensive and have been laid and used extensively. However, since the chromatic dispersion accumulated before dispersion compensation is large, it is not suitable for high-speed transmission. Therefore, as shown in FIG. 1, various non-zero dispersion shifted optical fibers (hereinafter referred to as NZ-DSF) having a dispersion of about several ps / nm / km in the used wavelength band by slightly shifting the zero dispersion wavelength from the used wavelength band. Abbreviated.) Is used all over the world. These optical fibers are used in C-band (wavelength 1.525 μm to 1.565 μm), L-band (wavelength 1.565 μm to 1.625 μm), U-band (1.625 μm to 1.675 μm) + / -It has a wavelength dispersion of about several ps / nm / km. By using this fiber and compensating the dispersion with the dispersion compensating fiber module, it becomes possible to transmit 10 Gb / s or 40 Gb / s.

As dispersion compensating fibers for compensating for the wavelength dispersion and dispersion slope of NZ-DSF, there are dispersion compensating fibers disclosed in Patent Documents 1 to 3 and Non-Patent Document 1, for example. By using the dispersion compensating fiber disclosed in these documents, it is possible to compensate the accumulated chromatic dispersion in the wavelength range from 1.525 μm to 1.625 μm of the NZ-DSF.
JP 2000-162462 A JP 2000-47048 A JP 9-318833 A Kazuhiko Aikawa et al., “High-performance, broadband dispersion compensating fiber module for NZ-DSF”, IEICE Technical Report, OCS 2002-7, April 2002, p35-p40

Here, the dispersion slope compensation will be briefly described. A value used when obtaining the performance of dispersion slope compensation is a ratio of dispersion slope to chromatic dispersion (RDS: Relative Dispersion Slope). If the chromatic dispersion is D and the dispersion slope is S, RDS can be expressed as the following equation (1).
RDS = S / D (1)

If the RDS of the dispersion compensating fiber is equal to the RDS of the transmission optical fiber, the dispersion slope can be completely compensated when the chromatic dispersion is compensated.
The dispersion slope compensation rate can be expressed as the following equation (2), where RDS of the transmission optical fiber is RDS _TMF and RDS of the dispersion compensation fiber is RDS _SC-DCF .
Dispersion slope compensation rate = RDS _SC-DCF / RDS _TMF (2)

  When the RDS of the dispersion compensating fiber is equal to the RDS of the transmission optical fiber, if the chromatic dispersion is completely compensated, the dispersion slope can be completely compensated at that wavelength. This is schematically shown in FIG.

  Conventional dispersion compensating fibers have been studied and put into practical use for transmission optical fibers having positive chromatic dispersion and positive dispersion slope. However, in the submarine laying optical fiber transmission line, NZ-DSF having a negative chromatic dispersion and a positive dispersion slope in the wavelength 1.55 μm band may be used as shown in FIG. In order to compensate the accumulated chromatic dispersion of NZ-DSF having such dispersion characteristics, it is desirable to have a positive dispersion in the wavelength band used and a negative dispersion slope, but the material dispersion of quartz glass is Since it has zero dispersion near the wavelength of 1.3 μm and has a positive dispersion slope, even if the refractive index distribution is controlled so as to have a negative dispersion slope due to material dispersion, negative chromatic dispersion and positive It is difficult to obtain a dispersion compensating fiber suitable for NZ-DSF having a dispersion slope.

  For example, Patent Document 3 has a zero dispersion wavelength in a wavelength range of 1500 nm to 1600 nm, an average dispersion slope from a wavelength of 1530 nm to 1560 nm is negative, and a dispersion from a wavelength of 1530 nm to 1560 nm is +1.5 to +4. A dispersion-shifted optical fiber that is 0.0 ps / nm / km is disclosed. However, when this dispersion-shifted optical fiber is used as a module, since the absolute value of chromatic dispersion is small, a long fiber is necessary, and while maintaining a bending loss that can be modularized, this is the case. It is difficult to maintain proper characteristics.

Therefore, dispersion compensation for a transmission line having a zero dispersion wavelength on the longer wavelength side than the 1.55 μm band is performed by modularizing a standard single mode fiber (hereinafter abbreviated as SMF) and performing dispersion compensation at each wavelength. It was. The dispersion characteristic of SMF is shown in FIG. Dispersion compensation can be achieved by dividing and winding an SMF having such characteristics in accordance with a required compensation amount. A schematic diagram of dispersion compensation when this SMF is used is shown in FIG.
However, when dispersion compensation is performed by such a method, a dispersion compensating fiber module is required for each wavelength as shown in FIG. 4, and there is a problem that a transmission system becomes very expensive.

  The present invention has been made in view of the above circumstances, and a dispersion compensation fiber module capable of collectively compensating the cumulative chromatic dispersion of an optical fiber having zero dispersion on the longer wavelength side than 1.55 μm in a wide band and an optical device using the module The purpose is to provide a fiber transmission line.

In order to achieve the above object, the present invention is for transmission having a chromatic dispersion of −10 to −1 ps / nm / km and a positive dispersion slope of +0.03 to +0.10 ps / nm ² / km at a wavelength of 1.55 μm. In a dispersion compensating fiber module that is connected to an optical fiber and compensates so that the residual dispersion becomes small, the chromatic dispersion at a wavelength of 1.55 μm is positive, the dispersion slope is negative, and the average chromatic dispersion is +5 ps / nm / km. A dispersion compensating fiber module comprising the above-described fiber and having a bending loss of 20 dB / m or less at a diameter of 20 mm of the fiber used is provided.

In the dispersion compensating fiber module of the present invention, the fiber used is a combination of a dispersion compensating fiber in which both chromatic dispersion and dispersion slope are negative, and an optical fiber in which both chromatic dispersion and dispersion slope are positive, and the wavelength. The ratio of the dispersion slope to chromatic dispersion at 1.55 μm is preferably in the range of −0.015 nm ⁻¹ to −0.005 nm ⁻¹ .

The dispersion compensating fiber includes at least a central core portion having a refractive index larger than the refractive index of the cladding, a depressed core portion provided on the outer periphery of the central core portion and having a refractive index smaller than the refractive index of the cladding, and the depressed core portion. A ring core having a refractive index greater than the refractive index of the cladding, a depressed cladding having a refractive index smaller than the refractive index of the cladding, and an outer periphery of the depressed cladding. And a clad provided in the
The ring core radius is in the range of 6.7 to 10.7 μm,
The ratio of the depressed core radius to the central core radius is in the range of 2.0 to 3.5;
The ratio of the ring core radius to the depressed core radius is in the range of 1.3 to 2.0;
The relative refractive index difference of the central core portion with respect to the cladding is in the range of 1.4 to 2.4%,
The relative refractive index difference of the depressed core portion with respect to the clad is in the range of -1.30 to -0.7%,
It is preferable that the relative refractive index difference of the ring core portion with respect to the clad is in the range of +0.3 to + 0.7%.

In the dispersion compensating fiber module of the present invention, the fiber used is a combination of a dispersion compensating fiber in which both chromatic dispersion and dispersion slope are negative, and an optical fiber in which both chromatic dispersion and dispersion slope are positive, and the wavelength. The ratio of the dispersion slope and wavelength dispersion at 1.55 μm is preferably in the range of −0.020 nm ⁻¹ to −0.010 nm ⁻¹ .

The dispersion compensating fiber includes at least a central core portion having a refractive index larger than the refractive index of the cladding, a depressed core portion provided on the outer periphery of the central core portion and having a refractive index smaller than the refractive index of the cladding, and the depressed core portion. A ring core portion provided on the outer periphery and having a refractive index larger than that of the cladding, a depressed cladding portion provided on the outer periphery of the ring core portion and having a refractive index smaller than that of the cladding, and an outer periphery of the depressed cladding portion. With a provided cladding,
The ring core radius is in the range of 6.7 to 10.7 μm,
The ratio of the depressed core radius to the central core radius is in the range of 2.0 to 3.5;
The ratio of the ring core radius to the depressed core radius is in the range of 1.3 to 2.0;
The relative refractive index difference of the central core portion with respect to the cladding is in the range of 1.4 to 2.4%,
The relative refractive index difference of the depressed core portion with respect to the clad is in the range of -1.50 to -1.0%,
It is preferable that the relative refractive index difference of the ring core portion with respect to the clad is in the range of +0.3 to + 0.7%.

In the present invention, an optical fiber having both positive chromatic dispersion and dispersion slope has a wavelength of 1.55 μm and a chromatic dispersion in the range of +15 to +22 ps / nm / km, and the ratio of the dispersion slope to the chromatic dispersion is 0.0028 nm ⁻ It is preferably in the range of ^{1 to} 0.0038 nm ⁻¹ .

  The present invention also provides an optical fiber transmission line configured by connecting the dispersion compensating fiber module of the present invention to a transmission optical fiber.

  According to the present invention, it is possible to provide a dispersion compensating fiber module for compensating the accumulated chromatic dispersion of NZ-DSF having zero dispersion on the longer wavelength side than the wavelength of 1.55 μm, so that a low-cost optical transmission system is provided. be able to.

  The first embodiment of the dispersion compensating fiber module of the present invention has a chromatic dispersion of −10 to −1 ps / nm / km and a positive dispersion slope of +0.03 to +0.10 ps / nm / km at a wavelength of 1.55 μm. In a dispersion compensating fiber module that is connected to a transmission optical fiber and compensates so that the residual dispersion becomes small, the chromatic dispersion at a wavelength of 1.55 μm is positive, the dispersion slope is negative, and the average chromatic dispersion is +5 ps / nm. It is characterized by including a fiber that is at least / km and the bending loss at a diameter of 20 mm of the fiber used is 20 dB / m or less.

This dispersion compensating fiber module is connected to a transmission optical fiber having a chromatic dispersion of −10 to −1 ps / nm / km and a positive dispersion slope of +0.03 to +0.10 ps / nm ² / km at a wavelength of 1.55 μm. As a result, the residual dispersion is compensated to be small. As such an optical fiber for transmission, NZ-DSF having a chromatic dispersion in a range of −10 to −1 ps / nm / km in C-band (wavelength 1.525 μm to 1.565 μm) can be mentioned. By using this NZ-DSF for transmission and compensating the dispersion with the dispersion compensating fiber module of the present invention, high-speed transmission of 10 Gb / s or 40 Gb / s becomes possible.

This dispersion compensating fiber module has a positive chromatic dispersion at a wavelength of 1.55 μm, a negative dispersion slope, an average chromatic dispersion of +5 ps / nm / km or more, and a bending loss at a diameter of 20 mm of 20 dB / m or less. Constructed using fiber. This fiber is used, for example, in a state where a dispersion compensating fiber module is wound around a small reel and one end thereof is connected to an optical fiber for transmission.
Here, the “average chromatic dispersion” is a value obtained by dividing the chromatic dispersion of the entire module by the fiber length using the module.

  This dispersion compensating fiber module can compensate the accumulated chromatic dispersion of NZ-DSF having zero dispersion on the longer wavelength side than 1.55 μm by one dispersion compensating fiber module, and is an optical fiber for high speed transmission at low cost. A transmission path can be configured. Further, by using a fiber having a bending loss of 20 dB / m or less at a diameter of 20 mm, the module can be miniaturized.

The second embodiment of the dispersion compensating fiber module of the present invention is a combination of a dispersion compensating fiber in which both chromatic dispersion and dispersion slope are negative and an optical fiber in which both chromatic dispersion and dispersion slope are positive at a wavelength of 1.55 μm. And the ratio of the dispersion slope to the wavelength dispersion at a wavelength of 1.55 μm is in the range of −0.015 nm ⁻¹ to −0.005 nm ⁻¹ .

In this dispersion compensation fiber module, a dispersion compensation fiber in which both chromatic dispersion and dispersion slope are negative, and an optical fiber in which both chromatic dispersion and dispersion slope are positive have appropriate lengths, and these are connected to each other. By appropriately setting the lengths of the dispersion compensation fiber and the optical fiber according to the chromatic dispersion and dispersion slope of the dispersion compensation fiber and the optical fiber to be used, the dispersion slope and chromatic dispersion at a wavelength of 1.55 μm are used. The ratio can be in the range of −0.015 nm ⁻¹ to −0.005 nm ⁻¹ .

This dispersion compensating fiber module compensates for NZ-DSF residual dispersion having a wavelength dispersion of around −4 ps / nm / km and a dispersion slope of +0.045 ps / nm ² / km in a wide wavelength range at a wavelength of 1.55 μm. It becomes possible.

  The third embodiment of the dispersion compensating fiber module of the present invention is characterized in that a dispersion compensating fiber having a refractive index profile as shown in FIG. 5 is used as the dispersion compensating fiber used in the dispersion compensating fiber module. The dispersion compensating fiber includes a core 1 and a clad 2, a central core portion 3 having a refractive index larger than that of the clad 2, and a refractive index smaller than the refractive index of the clad 2 provided on the outer periphery of the central core portion 3. A depressed core portion 4 having a refractive index, a ring core portion 5 having a refractive index larger than the refractive index of the cladding 2 provided on the outer periphery of the depressed core portion 4, and smaller than a refractive index of the cladding 2 provided on the outer periphery of the ring core portion 5. The structure includes a depressed cladding portion 6 having a refractive index and a cladding 2 provided on the outer periphery of the depressed cladding portion 4.

The dispersion compensating fiber has the following structural parameters.
The ring core radius is in the range of 6.7 to 10.7 μm,
The ratio of the depressed core radius to the central core radius is in the range of 2.0 to 3.5,
The ratio of the ring core radius to the depressed core radius is in the range of 1.3 to 2.0,
-The relative refractive index difference of the central core portion with respect to the cladding is in the range of 1.4 to 2.4%,
-The relative refractive index difference of the depressed core portion with respect to the cladding is in the range of -1.30 to -0.7%,
The relative refractive index difference of the ring core portion with respect to the clad is in the range of +0.3 to + 0.7%.

This dispersion compensating fiber module uses the dispersion compensating fiber, so that a NZ-DSF having a chromatic dispersion of about −4 ps / nm / km at 1.55 μm and a dispersion slope of about +0.045 ps / nm ² / km at 1.55 μm. Dispersion can be compensated in a wide wavelength range.

The fourth embodiment of the dispersion compensating fiber module of the present invention is a combination of a dispersion compensating fiber in which both chromatic dispersion and dispersion slope are negative and an optical fiber in which both chromatic dispersion and dispersion slope are positive at a wavelength of 1.55 μm. And the ratio of the dispersion slope to the wavelength dispersion at a wavelength of 1.55 μm is in the range of −0.020 nm ⁻¹ to −0.010 nm ⁻¹ .

This dispersion compensating fiber module compensates NZ-DSF residual dispersion having a chromatic dispersion of around −4 ps / nm / km and a dispersion slope of +0.08 ps / nm ² / km in a wide wavelength range at 1.55 μm. Is possible.

  In the fifth embodiment of the dispersion compensating fiber module of the present invention, a dispersion compensating fiber having a refractive index profile as shown in FIG. 5 is used as the dispersion compensating fiber used in the dispersion compensating fiber module of the fourth embodiment. It is a feature. The dispersion compensating fiber includes a core 1 and a clad 2, a central core portion 3 having a refractive index larger than that of the clad 2, and a refractive index smaller than the refractive index of the clad 2 provided on the outer periphery of the central core portion 3. A depressed core portion 4 having a refractive index, a ring core portion 5 having a refractive index larger than the refractive index of the cladding 2 provided on the outer periphery of the depressed core portion 4, and smaller than a refractive index of the cladding 2 provided on the outer periphery of the ring core portion 5. The structure includes a depressed cladding portion 6 having a refractive index and a cladding 2 provided on the outer periphery of the depressed cladding portion 4.

Further, this dispersion compensating fiber has the following structural parameters: the radius of the ring core part is in the range of 6.7 to 10.7 μm,
The ratio of the depressed core radius to the central core radius is in the range of 2.0 to 3.5,
The ratio of the ring core radius to the depressed core radius is in the range of 1.3 to 2.0,
-The relative refractive index difference of the central core portion with respect to the cladding is in the range of 1.4 to 2.4%,
The relative refractive index difference of the depressed core portion with respect to the cladding is in the range of −1.50 to −1.0%,
The relative refractive index difference of the ring core portion with respect to the clad is in the range of +0.3 to + 0.7%.

This dispersion compensating fiber module is a NZ-DSF having a chromatic dispersion of around −4 ps / nm / km and a dispersion slope of around +0.08 ps / nm ² / km at a wavelength of 1.55 μm by using the dispersion compensating fiber. Residual dispersion can be compensated over a wide wavelength range.

The sixth embodiment of the dispersion compensating fiber module of the present invention is the dispersion compensating fiber module according to any one of the second to fifth embodiments, wherein an optical fiber having both positive chromatic dispersion and dispersion slope is used at a wavelength of 1.55 μm. An optical fiber having a chromatic dispersion in the range of +15 to +22 ps / nm / km and a ratio of the dispersion slope to the chromatic dispersion in the range of 0.0028 nm ^{−1 to} 0.0038 nm ⁻¹ is used. An example of such an optical fiber is SMF.

  This dispersion compensating fiber module can compensate the accumulated chromatic dispersion of NZ-DSF having zero dispersion on the longer wavelength side than 1.55 μm by one dispersion compensating fiber module, and is an optical fiber for high speed transmission at low cost. A transmission path can be configured.

The seventh embodiment of the present invention is an optical fiber transmission line configured by connecting the dispersion compensating fiber module of the present invention to a transmission optical fiber.
By connecting the dispersion compensating fiber module of each of the above-described embodiments to a transmission optical fiber to form an optical fiber transmission line, the number of dispersion compensating fiber modules can be reduced, the transmission device itself can be reduced in size, and the cost can be reduced. Can be provided.

  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]
Dispersion compensating fibers A and B (hereinafter referred to as fibers A and B) having a refractive index profile as shown in FIG. 5 were produced by a known method such as VAD method or MCVD method. At this time, Δ1, Δ2, Δ3, Δ4, b / a, c / b, and d / c were manufactured so as to have the values shown in Table 1.
Table 2 shows the optical characteristics of these fibers A and B. The chromatic dispersion characteristics of the fibers A and B are shown in FIGS.
Characteristics of dispersion compensating fiber module A-1 of the present invention in which SMF 24.2 km is combined with fiber A 1.9 km, characteristics of cumulative chromatic dispersion of NZ-DSF 45 km having the characteristics shown in Table 3, and dispersion compensating fiber module of the present invention FIG. 7 shows the residual dispersion characteristics when compensated by A-1. The dispersion compensating fiber module A-1 had an RDS of −0.0114 nm ^{−1 at} a wavelength of 1.55 μm, a chromatic dispersion compensation of +209.9 ps / nm, and a module loss of 7.1 dB. From the graph shown in FIG. 7, in one dispersion compensating fiber module, the residual dispersion at wavelengths of 1530 nm to 1565 nm is suppressed to be small, and the maximum residual dispersion is suppressed to +/− 10 ps / nm or less in the wavelength range of 1530 nm to 1565 nm. I understand that
Further, the characteristics of the dispersion compensating fiber module B-1 of the present invention in which SMF 25.2 km is combined with the fiber B 3.2 km, the cumulative chromatic dispersion characteristics of the NZ-DSF 45 km having the characteristics shown in Table 3, and the dispersion compensation of the present invention FIG. 9 shows the residual dispersion characteristics when compensated by the fiber module B-1. The dispersion compensating fiber module B-1 had an RDS of -0.0052 nm ^{-1 at} a wavelength of 1.55 µm, a chromatic dispersion compensation of +208.9 ps / nm, and a module loss of 7.2 dB. From the graph shown in FIG. 9, in one dispersion compensating fiber module, the residual dispersion at wavelengths of 1530 nm to 1565 nm is suppressed to be small, and the maximum residual dispersion is suppressed to +/− 20 ps / nm or less in the wavelength range of 1530 nm to 1565 nm. I understand that

[Comparative Example 1]
Using SMF having the characteristics shown in Table 4, a dispersion compensating fiber module for compensating the residual dispersion of NZ-DSF 45 km having the characteristics shown in Table 3 was produced. Since dispersion slope compensation cannot be performed, a single dispersion compensation fiber module cannot reduce the residual dispersion over the entire wavelength range. Therefore, the module compensated the residual dispersion by dividing the wavelength range of 1530 nm to 1565 nm. When dispersion compensation is performed with the SMF in Table 4, the residual dispersion slope is about +2.7 ps / nm ^2, so in order to suppress the residual dispersion equivalent to that in Example 1 (+/− 20 ps / nm), every 14.8 nm It is necessary to compensate for dispersion by dividing into two. By performing dispersion compensation in this way, each dispersion compensation could be performed in the same way as in the first embodiment. However, the number of dispersion compensating fiber modules used was three, resulting in a high-cost optical transmission system. .

[Example 2]
Dispersion compensating fibers A and C (hereinafter referred to as fibers A and C) having a refractive index profile as shown in FIG. 5 were produced by a known method such as VAD method or MCVD method. At this time, Δ1, Δ2, Δ3, Δ4, b / a, c / b, and d / c were manufactured so as to have values shown in Table 5. The fiber A in Table 5 is the same as the fiber A manufactured in Example 1.
The optical characteristics of this fiber C are shown in Table 6. FIG. 11 shows the chromatic dispersion characteristics of the fiber C.
Characteristics of dispersion compensating fiber module A-2 of the present invention in which SMF 26.4 km is combined with fiber A 2.4 km, characteristics of cumulative chromatic dispersion of NZ-DSF 45 km having the characteristics shown in Table 7, and dispersion compensating fiber module of the present invention The residual dispersion characteristics when compensated by A-2 are shown together in FIG. The dispersion compensating fiber module A-2 had an RDS of −0.0170 nm ^{−1 at} a wavelength of 1.55 μm, a chromatic dispersion compensation of +192.5 ps / nm, and a module loss of 7.8 dB. From the graph shown in FIG. 10, in one dispersion compensating fiber module, the residual dispersion of wavelengths 1530 nm to 1565 nm is suppressed to a small value, and the maximum residual dispersion is suppressed to +/− 13 ps / nm or less in the wavelength range of 1530 nm to 1565 nm. I understand that
Further, the dispersion compensation fiber module B-2 of the present invention in which SMF 28.5 km is combined with the fiber C 4.0 km, the cumulative chromatic dispersion characteristic of NZ-DSF 45 km having the characteristics shown in Table 7, and the dispersion compensation of the present invention FIG. 12 shows the residual dispersion characteristics when compensated by the fiber module B-2. The dispersion compensating fiber module B-2 had an RDS of −0.0154 nm ^{−1 at} a wavelength of 1.55 μm, a chromatic dispersion compensation of +194.2 ps / nm, and a module loss of 9.0 dB. From the graph shown in FIG. 12, from one dispersion compensating fiber module B-2, the residual dispersion at wavelengths of 1530 nm to 1565 nm is suppressed to be small, and the maximum residual dispersion is +/− 17 ps / nm in the wavelength range of 1530 nm to 1565 nm. It can be seen that the following are suppressed.

[Comparative Example 2]
Using an SMF having the characteristics shown in Table 4, a dispersion compensating fiber module for compensating the residual dispersion of NZ-DSF 45 km having the characteristics shown in Table 7 was produced. Since dispersion slope compensation cannot be performed, a single dispersion compensation fiber module cannot reduce the residual dispersion over the entire wavelength range. Therefore, the module compensated the residual dispersion by dividing the wavelength range of 1530 nm to 1565 nm. When dispersion compensation is performed with the SMF in Table 4, the residual dispersion slope is about +4.2 ps / nm ^2, so in order to suppress the residual dispersion equivalent to that in Example 1 (+/− 17 ps / nm), every 8.1 nm. It is necessary to compensate for dispersion by dividing into two. By performing dispersion compensation in this way, each dispersion compensation could be performed in the same way as in the first embodiment, but the number of dispersion compensating fiber modules was five, resulting in a high-cost optical transmission system. .

It is a graph which illustrates the wavelength dispersion of various NZ-DSF. It is a schematic diagram for demonstrating the basic concept of the compensation of chromatic dispersion in an optical fiber transmission line. It is a graph which illustrates the wavelength dispersion of SMF. It is a schematic diagram of dispersion compensation when using SMF. It is a schematic diagram which illustrates the cross-sectional refractive index distribution of a dispersion compensation fiber. It is a graph which shows the wavelength dispersion characteristic of the fiber A used in the Example. It is a graph which shows the characteristic of the dispersion compensation fiber module A-1 used in the Example, the characteristic of the cumulative chromatic dispersion of NZ-DSF, and the residual dispersion characteristic when it compensates with the dispersion compensation fiber module A-1. It is a graph which shows the wavelength dispersion characteristic of the fiber B used in the Example. It is a graph which shows the characteristic of the dispersion compensation fiber module B-1 used in the Example, the characteristic of the cumulative chromatic dispersion of NZ-DSF, and the residual dispersion characteristic when it compensates with the dispersion compensation fiber module B-1. It is a graph which shows the characteristic of the dispersion compensation fiber module A-2 used in the Example, the characteristic of the cumulative chromatic dispersion of NZ-DSF, and the residual dispersion characteristic when it compensates with the dispersion compensation fiber module A-2. It is a graph which shows the wavelength dispersion characteristic of the fiber C used in the Example. It is a graph which shows the characteristic of the dispersion compensation fiber module B-2 used in the Example, the characteristic of the cumulative chromatic dispersion of NZ-DSF, and the residual dispersion characteristic when it compensates with the dispersion compensation fiber module B-2.

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 (7)

The residual dispersion is connected to a transmission optical fiber having a chromatic dispersion of −10 to −1 ps / nm / km and a positive dispersion slope of +0.03 to +0.10 ps / nm ² / km at a wavelength of 1.55 μm. In a dispersion compensating fiber module that compensates for smaller,
A fiber having a positive chromatic dispersion at a wavelength of 1.55 μm, a negative dispersion slope, an average chromatic dispersion of +5 ps / nm / km or more, and a bending loss at a diameter of 20 mm of the fiber used is 20 dB / m or less. A dispersion compensating fiber module, characterized in that The fiber used is a combination of a dispersion compensating fiber in which both chromatic dispersion and dispersion slope are negative, and an optical fiber in which both chromatic dispersion and dispersion slope are positive, and a dispersion slope and chromatic dispersion at a wavelength of 1.55 μm. The dispersion compensating fiber module according to claim 1, wherein the ratio is in the range of −0.015 nm ⁻¹ to −0.005 nm ⁻¹ . The dispersion compensating fiber includes at least a central core portion having a refractive index larger than the refractive index of the cladding, a depressed core portion provided on an outer periphery of the central core portion and having a refractive index smaller than the refractive index of the cladding, and the depressed core portion A ring core portion provided on the outer periphery and having a refractive index larger than that of the cladding, a depressed cladding portion provided on the outer periphery of the ring core portion and having a refractive index smaller than the refractive index of the cladding, and an outer periphery of the depressed cladding portion. With a provided cladding,
The ring core radius is in the range of 6.7 to 10.7 μm,
The ratio of the depressed core radius to the central core radius is in the range of 2.0 to 3.5;
The ratio of the ring core radius to the depressed core radius is in the range of 1.3 to 2.0;
The relative refractive index difference of the central core portion with respect to the cladding is in the range of 1.4 to 2.4%,
The relative refractive index difference of the depressed core portion with respect to the clad is in the range of -1.30 to -0.7%,
The dispersion compensating fiber module according to claim 2, wherein the relative refractive index difference of the ring core portion with respect to the clad is in the range of +0.3 to + 0.7%. The fiber used is a combination of a dispersion compensating fiber in which both chromatic dispersion and dispersion slope are negative, and an optical fiber in which both chromatic dispersion and dispersion slope are positive, and a dispersion slope and chromatic dispersion at a wavelength of 1.55 μm. The dispersion compensating fiber module according to claim 1, wherein the ratio is in the range of −0.020 nm ⁻¹ to −0.010 nm ⁻¹ . The dispersion compensating fiber includes at least a central core portion having a refractive index larger than the refractive index of the cladding, a depressed core portion provided on the outer periphery of the central core portion and having a refractive index smaller than the refractive index of the cladding, and the depressed core portion A ring core portion provided on the outer periphery and having a refractive index larger than that of the cladding, a depressed cladding portion provided on the outer periphery of the ring core portion and having a refractive index smaller than that of the cladding, and an outer periphery of the depressed cladding portion. With a provided cladding,
The ring core radius is in the range of 6.7 to 10.7 μm,
The ratio of the depressed core radius to the central core radius is in the range of 2.0 to 3.5;
The ratio of the ring core radius to the depressed core radius is in the range of 1.3 to 2.0;
The relative refractive index difference of the central core portion with respect to the cladding is in the range of 1.4 to 2.4%,
The relative refractive index difference of the depressed core portion with respect to the clad is in the range of -1.50 to -1.0%,
The dispersion compensating fiber module according to claim 4, wherein a relative refractive index difference of the ring core portion with respect to the clad is in a range of +0.3 to + 0.7%. An optical fiber having both positive chromatic dispersion and dispersion slope has a wavelength of 1.55 μm and a chromatic dispersion in the range of +15 to +22 ps / nm / km, and the ratio of the dispersion slope to the chromatic dispersion is 0.0028 nm ⁻¹ to 0.00. 6. The dispersion compensating fiber module according to claim 2, wherein the dispersion compensating fiber module is in a range of 0038 nm ⁻¹ . An optical fiber transmission line configured by connecting the dispersion compensating fiber module according to claim 1 to a transmission optical fiber.

Images