CN1198156C - Dispersion-compensating optical fiber with W-shaped index profile - Google Patents

Abstract

The invention is directed to a dispersion-compensating optical fiber which can compensate for the chromatic dispersion and dispersion slope of a non-zero dispersion-shifted optical fiber by a short length. The dispersion-shifted optical fiber constitutes an optical transmission line together with a dispersion-compensating optical fiber fusion-spliced thereto. The dispersion-compensating optical fiber has, at a wavelength of 1550 nm, a chromatic dispersion DDCF of -40 ps/nm/km or less and a ratio (DDCF/SDCF) of dispersion slope SDCF to the chromatic dispersion DDCF of 0.005/nm or more.

Description

Dispersion compensation optical fiber, module and optical transmission line

technical field

The invention relates to a dispersion compensating optical fiber for compensating the dispersion and dispersion slope of the dispersion-shifted optical fiber, an optical transmission line comprising the dispersion-shifted optical fiber and the dispersion-compensating optical fiber, and a dispersion compensation module formed by winding the dispersion-shifted optical fiber like a coil .

Background technique

In order to obtain further higher speed and larger capacity in an optical transmission system realizing wavelength division multiplexing (WDM) optical transmission, it is important that the absolute value of accumulated dispersion in a wide signal band be as small as possible. Generally, since this is difficult to achieve in an optical transmission line using only one type of optical fiber, multiple types of optical fibers are connected to construct an optical transmission line, thereby reducing the absolute value of the accumulated dispersion of the optical transmission line in a wide wavelength band.

For example, Japanese Patent Application Laid-Open No. HEI 6-11620 discloses a technique in which a standard single-mode fiber (SMF) having a zero-dispersion wavelength near a wavelength of 1.3 μm is compensated for the dispersion of the standard single-mode fiber at a wavelength of 1550 nm. A dispersion compensating fiber (DCF) of the above-mentioned fibers is connected to each other to reduce the absolute value of the accumulated dispersion in the 1.55-μm band of the optical fiber transmission line constructed by the optical fibers thus connected.

In addition, U.S. Patent No. 5,838,867 discloses a technique in which a non-zero dispersion-shifted fiber (NZDSF) having a small positive dispersion at a wavelength of 1550 nm is interconnected with a dispersion-compensating fiber that compensates for the dispersion and dispersion slope of the dispersion-shifted fiber , to reduce the absolute value of the accumulated dispersion in the 1.55-μm band of the optical fiber transmission line constructed through the optical fibers thus connected.

Here, the dispersion of a standard single-mode fiber (SMF) at a wavelength of 1550 nm is called D _SMF , and its dispersion slope is called S _SMF . The dispersion of a non-zero dispersion-shifted fiber (NZDSF) at a wavelength of 1550 nm is called D _DSF , and its dispersion slope is called S _DSF . The dispersion of a dispersion compensating fiber (DCF) at a wavelength of 1550 nm is called D _DCF , and its dispersion slope is called S _DCF . Therefore, in order to reduce the absolute value of the cumulative dispersion of an optical transmission line in a wide band including wavelength 1550nm, a dispersion compensating fiber (hereinafter referred to as "used for SMF) for compensating the dispersion and dispersion slope of the single-mode fiber In the dispersion compensating fiber"), it is required that the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) and the ratio of the dispersion slope S _SMF to the dispersion D _SMF of the single-mode fiber (S _SMF /D _SMF ) Basically equal. In addition, in a dispersion compensating fiber (hereinafter referred to as "dispersion compensating fiber for DSF") for compensating the dispersion and dispersion slope of the dispersion-shifted fiber, the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) is basically equal to the ratio of the dispersion slope S _DSF to the dispersion D _DSF (S _DSF /D _DSF ) of the dispersion-shifted fiber.

Contents of the invention

The inventors studied conventional optical transmission lines in detail, and as a result found the following problems.

Compared with standard single-mode fiber, dispersion-shifted fiber has a larger ratio (S _DSF /D _DSF ) at a wavelength of 1550nm. Therefore, the dispersion compensating fiber for DSF is required to have a larger ratio (S _DSF /D _DSF ) at a wavelength of 1550 nm than that for SMF.

The dispersion compensating optical fiber used for SMF disclosed in Japanese Patent Application Laid-Open No. HEI 6-11620 compensates the dispersion of a standard single-mode optical fiber, which has a zero dispersion wavelength near the wavelength of 1.3 μm, and a wavelength of zero dispersion at the wavelength of 1550 nm. Large dispersion, and negative dispersion with large absolute value. Therefore, the dispersion compensating fiber for SMF is suitable for compensating the dispersion of standard single-mode fiber. However, this dispersion compensating fiber for SMF is insufficient to compensate the dispersion slope.

On the other hand, the dispersion compensating fiber for DSF disclosed in US Pat. No. 5,838,867 can compensate the dispersion and dispersion slope of a non-zero dispersion shifted fiber having small positive dispersion at a wavelength of 1550 nm. Since the dispersion compensating fiber for DSF has a small absolute value of dispersion, a long dispersion compensating fiber for DSF is required to compensate the dispersion and the dispersion slope of the non-zero dispersion fiber.

For example, document 1 of people such as S.Bigo, " 150 channels are transmitted with 1.5Terabit/s WDM of 10Gbit/s on TeraLight ^TM optical fiber of 4 * 100km ", ECOC'99, the non-zero disclosed in PD (1999) Dispersion-shifted fiber has a dispersion of +0.8ps/nm/km and a dispersion slope of +0.06ps/nm ² /km at a wavelength of 1550nm. On the other hand, the non-zero dispersion-shifted fiber disclosed in the document 2 of DW Peckham et al., "Reduced dispersion slope, non-zero dispersion fiber", ECOC'98, pages 139-140 (1998), has + Dispersion of 4ps/nm/km and dispersion slope of +0.046ps/nm ² /km. In order to compensate the dispersion and dispersion slope of any non-zero dispersion-shifted fiber of length 80 km disclosed in these documents, a dispersion compensating fiber length of 8 km to 16 km is required for DSF.

At the same time, even if it is slightly bent, usually the fundamental mode light may leak from the dispersion compensating fiber used for DSF, so that the bending loss in the fundamental mode light is relatively large. Therefore, when a dispersion compensating optical fiber for DSF is placed like an optical cable or constitutes a dispersion compensating module wound like a coil, the transmission loss becomes larger. Therefore, in an optical transmission system realizing optical communication by signal propagation on an optical transmission line consisting of a dispersion-shifted optical fiber and a dispersion-compensating optical fiber for DSF connected to each other, the transmission loss in the optical transmission line is as follows It is so large that the relay part cannot be extended, so that higher speed and larger capacity cannot be further obtained in optical communication.

In order to overcome the above-mentioned problems, an object of the present invention is to provide a dispersion-compensating optical fiber capable of compensating the dispersion and the dispersion slope of a non-zero dispersion-shifted optical fiber with a short length, including a dispersion-shifted optical fiber and a dispersion-compensating optical fiber having a low transmission loss. The optical transmission line, and a dispersion compensating module having low transmission loss, wherein the dispersion compensating optical fiber is wound like a coil.

The dispersion compensating fiber according to the present invention has a dispersion D _DCF of -40 ps/nm/km or less at a wavelength of 1550 nm, and a ratio of dispersion slope S _DCF to dispersion D _DCF (S _DCF /D _DCF ) of 0.005/nm or more . With this structure, the occurrence of nonlinear phenomena can be effectively prevented because the effective area can be easily enlarged. Preferably, in the dispersion compensating optical fiber according to the present invention, the dispersion D _DCF is -100 ps/nm/km or more but -40 ps/nm/km or less, and the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) is 0.005/nm or more but 0.015/nm or less. Since the dispersion D _DCF is the negative value of the large absolute value, and the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) is within the above numerical range, the dispersion compensating fiber can be used in a wide band including a wavelength of 1550nm The dispersion and dispersion slope of a dispersion-shifted fiber is compensated with a short length.

The dispersion compensating fiber according to the present invention preferably has an effective area of 16 µm ² , more preferably 20 µm ² or more at a wavelength of 1550 nm. In this case, it can suppress the occurrence of four-wave mixing and suppress the degradation of the waveform of the optical signal propagating therethrough.

The dispersion compensating fiber according to the present invention preferably has a cutoff wavelength of 1.2 µm or more but 1.8 µm or less, more preferably 1.4 µm or more but 1.8 µm or less. Furthermore, the dispersion compensating optical fiber according to the present invention preferably has a transmission loss of 0.5 dB/km or less at a wavelength of 1550 nm. In this case, since the cutoff wavelength is longer than conventionally obtained, an increase in bending loss can be suppressed, and since the transmission loss is also within the above-mentioned numerical range, a lower loss.

The dispersion-shifted fiber according to the present invention preferably has a core region extending along a predetermined axis and having a first refractive index, and a cladding region surrounding the outer edge of the core region. The cladding region includes a first cladding surrounding the outer edge of the core region and having a second refractive index less than the first refractive index, a second cladding surrounding the outer edge of the first cladding and having a second refractive index greater than the first refractive index A third index of refraction of two, and a third cladding surrounds the outer edge of the second cladding and has a fourth index of refraction less than the third index of refraction. Regarding the fourth refractive index of the third cladding, the core region preferably has a relative refractive index difference of 0.8% or more but 2.0% or less, more preferably 0.8% or more but 1.5% or less. Regarding the fourth refractive index of the third cladding layer, the first cladding layer preferably has a relative refractive index difference of -0.4% or less. These circumstances are suitable for realizing a dispersion compensating optical fiber having the above-mentioned characteristics.

In the dispersion compensating fiber according to the present invention, when the outer diameter of the second cladding is changed by 2%, the ratio (S _DCF /D _DCF ) is preferably changed by 10% or less. In this case, a dispersion compensating optical fiber having desired dispersion characteristics can be easily manufactured.

On the other hand, in order to reduce the transmission loss by shortening the fiber length, the dispersion compensating fiber according to the present invention preferably has a dispersion D _DCF of -250 ps/nm/km or more but -120 ps/nm/km or less, 0.005/nm or above the ratio of dispersion slope S _DCF to dispersion D _DCF (S _DCF /D _DCF ), and 10 μm ² or above but 20 μm ² or below, preferably (20-|D _DCF |/25) or above but (23 - |D _DCF |/25) or less effective area. This is because it is necessary to reduce the size of the effective area at the curved fragile portion where the absolute value of dispersion becomes large. In addition, the dispersion compensating fiber preferably has a transmission loss of 1.0 dB/km or less. As described above, the dispersion compensating fiber has a core region, and a cladding region including first to third cladding layers. Also, preferably, the relative refractive index difference of the core region with respect to the third cladding is 0.2% or more but 3.0% or less, and the relative refractive index difference of the first cladding with respect to the third cladding is -0.4% or the following.

An optical transmission line according to the present invention has a relay section placed together with the above-mentioned dispersion compensating fiber; and a dispersion-shifted fiber fusion spliced to the dispersion compensating fiber. The dispersion-shifted fiber has a dispersion of +2 ps/nm/km or more but +10 ps/nm/km or less at a wavelength of 1550 nm, and +0.04 ps/nm ² /km or more but +0.12 ps/nm ² /km or The following dispersion slope. When the dispersion-shifted fiber and the dispersion-compensating fiber are connected to each other at an appropriate length ratio, the thus constituted optical transmission line is produced at a wavelength of 1550 nm, generally, with a small absolute value of the average dispersion and with a small absolute value of the average dispersion slope. Therefore, the optical transmission line has, in general, average dispersion with a small absolute value and small average transmission loss in a broad wavelength band including a wavelength of 1550 nm.

The optical transmission line according to the present invention preferably has, in general, a deviation (=maximum value-minimum value) of 0.2 ps/nm/km or less in a waveband (C-band) of 1535 nm or more but 1560 nm or less average dispersion. More preferably, the average dispersion generally has a deviation of 0.2 ps/nm/km or less in a band (C and L bands) of 1535 nm or more but 1600 nm or less. In an optical transmission system that realizes optical communication by propagating a signal through such an optical transmission line in this case, which produces low transmission loss, has a small absolute value of average dispersion, and has a wide range including a wavelength of 1550 nm Optical transmission with a high bit rate is possible in wavebands including at least the C-band and further including the L-band. Therefore, the optical transmission system can extend the relay section and achieve further higher speed and larger capacity in optical communication.

The dispersion compensating module according to the present invention is characterized in that the above-mentioned dispersion compensating optical fiber is wound like a coil to constitute a module. The dispersion compensation module in which the dispersion compensating fiber constitutes a module compensates the dispersion and the dispersion slope of a dispersion shifted fiber placed in a trunk section, and when there is an appropriate length ratio between the dispersion shifted fiber and the dispersion compensating fiber, at wavelength 1550 nm produces, in general, an average dispersion with a small absolute value and an average dispersion slope with a small absolute value. Therefore, the entire dispersion-shifted optical fiber and the dispersion compensation module have an average dispersion with a small absolute value and a small average transmission loss in a wide band including a wavelength of 1550 nm.

According to the dispersion compensation module of the present invention, when the dispersion compensation amount of -640ps/nm is generated at a wavelength of 1550nm, it preferably has a total loss of 7dB or less in a band of 1535nm or above but 1565nm or below, and more preferably at 1565nm or below. There is a total loss of 7 dB or less in a band of 1535 nm or more but 1610 nm or less. In the dispersion compensation module according to the present invention, when the dispersion compensation amount at the wavelength of 1550nm is -320ps/nm, the total loss is preferably 3dB or less in the band of 1535nm or above but 1565nm or below, more preferably at 3dB or less in the band of 1535nm or more but 1610nm or less. In an optical transmission system having the dispersion compensating module, its average transmission loss is small, its average dispersion has a small absolute value, and in a wide band including a wavelength of 1550nm (a band including at least the C band and further including the L band) Optical transmission with high bit rates is possible. Therefore, the optical transmission system can extend the relay section and achieve further higher speed and larger capacity in optical communication.

In addition, the dispersion compensating fiber according to the present invention preferably has a dispersion D _DCF of -40 ps/nm/km or less at a wavelength of 1550 nm, and a ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF / D _{DCF )} , and an effective area of 16 μm ² or more, more preferably 20 μm ² or more. In a wide band including a wavelength of 1550nm, the dispersion compensating fiber can not only compensate the dispersion and the dispersion slope of a dispersion shifted fiber with a short length, but also suppress the occurrence of four-wave mixing and the degradation of the waveform of the optical signal propagating therethrough .

Furthermore, the dispersion compensating fiber according to the present invention preferably has a dispersion D _DCF of -40 ps/nm/km or less at a wavelength of 1550 nm, and a ratio (S _DCF ) of a dispersion slope S _DCF to a dispersion D _DCF of 0.005/nm or more. /D _DCF ), and a transmission loss of 0.5dB/km or less. The dispersion compensating fiber not only can compensate the dispersion and the dispersion slope of a dispersion shifted fiber with a short length, but also produces low loss even when constituting an optical cable or module.

Specifically, the present invention provides a dispersion compensating optical fiber having a core region extending along a predetermined axis, and a cladding region surrounding the outer edge of the core region, wherein: the core region has a first a refractive index, and the cladding region has: a first cladding surrounding the outer edge of the core region and having a second refractive index less than the first refractive index; a second cladding surrounding the first an outer edge of the cladding and having a third index of refraction greater than the second index of refraction; and a third cladding surrounding the outer edge of the second cladding and having a fourth index of refraction less than the third index of refraction; The core region has a relative refractive index difference greater than or equal to 0.8% but less than or equal to 2.0% relative to the third cladding layer; the first cladding layer has a relative refractive index difference of -0.4% or less relative to the third cladding layer rate difference; the dispersion compensating fiber has the following characteristics at a wavelength of 1550nm: a dispersion greater than or equal to -100ps/nm/km but less than or equal to -40ps/nm/km; and a ratio of dispersion slope to dispersion greater than or equal to 0.005/nm .

The present invention also provides a dispersion compensating optical fiber having a core region extending along a predetermined axis, and a cladding region surrounding an outer edge of the core region, wherein: the core region has a first refractive index and the cladding region has: a first cladding surrounding the outer edge of the core region and having a second refractive index less than the first refractive index, a second cladding surrounding the first cladding an outer edge having a third index of refraction greater than the second index of refraction, and a third cladding surrounding the outer edge of the second cladding and having a fourth index of refraction less than the third index of refraction; the core region having a relative refractive index difference of 2.0% or more but 3.0% or less with respect to the third cladding; the first cladding having a relative refractive index difference of -0.4% or less with respect to the third cladding; The dispersion compensating fiber has the following characteristics at a wavelength of 1550 nm: a dispersion of -250 ps/nm/km or more but -120 ps/nm/km or less; a ratio of dispersion slope to dispersion of 0.005/nm or more; and 10 μm ² or above but with an effective area of 20 μm ² or less.

The present invention also provides an optical transmission line, comprising: a dispersion compensating optical fiber having a core region extending along a predetermined axis, and a cladding region surrounding the outer edge of the core region, wherein: the the core region has a first index of refraction, and the cladding region has: a first cladding surrounding the outer edge of the core region and having a second index of refraction less than the first index of refraction; a second cladding, surrounding the outer edge of the first cladding and having a third refractive index greater than the second refractive index; and a third cladding surrounding the outer edge of the second cladding and having a fourth refractive index less than the third refractive index Refractive index; the core region has a relative refractive index difference greater than or equal to 0.8% but less than or equal to 2.0% relative to the third cladding; the first cladding has -0.4% relative to the third cladding or below the relative refractive index difference; the dispersion compensating fiber has the following characteristics at a wavelength of 1550nm: a dispersion greater than or equal to -100ps/nm/km but less than or equal to -40ps/nm/km; and a dispersion greater than or equal to 0.005/nm Ratio of slope to dispersion; a dispersion-shifted fiber connected to said dispersion-compensating fiber, said dispersion-shifted fiber having the following characteristics at a wavelength of 1550 nm: +2 ps/nm/km or more but +10 ps/nm/km or less dispersion; and a dispersion slope of +0.04 ps/nm ² /km or more but +0.12 ps/nm ² /km or less.

The present invention also provides an optical transmission line, comprising: a dispersion compensating optical fiber having a core region extending along a predetermined axis, and a cladding region surrounding the outer edge of the core region, wherein: the the core region has a first index of refraction; and the cladding region has: a first cladding surrounding an outer edge of the core region and having a second index of refraction less than the first index of refraction, a second cladding, surrounding the outer edge of the first cladding and having a third refractive index greater than the second refractive index, and a third cladding surrounding the outer edge of the second cladding and having a fourth refractive index less than the third refractive index Refractive index; the core region has a relative refractive index difference of 2.0% or more but 3.0% or less with respect to the third cladding; the first cladding has -0.4% with respect to the third cladding or below the relative refractive index difference; the dispersion compensation fiber has the following characteristics at a wavelength of 1550nm: -250ps/nm/km or above but -120ps/nm/km or below the dispersion; 0.005/nm or above the dispersion slope and a ratio of dispersion; and an effective area of 10 μm ^or more but 20 μm or less; a dispersion-shifted fiber connected to said dispersion-compensating fiber, said dispersion-shifted fiber having the following characteristics at a wavelength of ¹⁵⁵⁰ nm: +2 ps/nm/km or more but +10 ps/nm/km or less dispersion; and +0.04 ps/nm ² /km or more but +0.12 ps/nm ² /km or less dispersion slope.

The present invention also provides a dispersion compensating module, comprising a dispersion compensating optical fiber in the state that said dispersion compensating optical fiber is wound like a coil to form a module, wherein: said dispersion compensating optical fiber has a length extending along a predetermined axis a core region, and a cladding region surrounding an outer edge of the core region, wherein: the core region has a first index of refraction, and the cladding region has a first cladding surrounding the an outer edge of the core region and having a second index of refraction less than the first index of refraction; a second cladding surrounding the outer edge of the first cladding and having a third index of refraction greater than the second index of refraction; and a first Triple cladding surrounding the outer edge of the second cladding and having a fourth refractive index less than the third refractive index; the core region has a ratio of 0.8% or more but 2.0% or less relative to the third cladding relative refractive index difference; the first cladding layer has a relative refractive index difference of -0.4% or less relative to the third cladding layer; the dispersion compensating fiber has the following characteristics at a wavelength of 1550nm: greater than or equal to -100ps /nm/km but less than or equal to -40ps/nm/km dispersion; and a ratio of dispersion slope to dispersion greater than or equal to 0.005/nm.

The present invention also provides a dispersion compensating module, comprising a dispersion compensating optical fiber in the state that said dispersion compensating optical fiber is wound like a coil to form a module, wherein: said dispersion compensating optical fiber has a length extending along a predetermined axis a core region, and a cladding region surrounding the outer edge of the core region, wherein: the core region has a first index of refraction; and the cladding region has: a first cladding surrounding the an outer edge of the core region and having a second index of refraction less than the first index of refraction, a second cladding surrounding the outer edge of the first cladding and having a third index of refraction greater than the second index of refraction, and a first Triple-cladding, surrounding the outer edge of the second cladding and having a fourth refractive index smaller than the third refractive index; the core region has 2.0% or more but 3.0% or less relative to the third cladding relative refractive index difference; the first cladding layer has a relative refractive index difference of -0.4% or less relative to the third cladding layer; the dispersion compensating fiber has the following characteristics at a wavelength of 1550nm: -250ps/nm/ km or more but -120 ps/nm/km or less; a dispersion slope-to-dispersion ratio of 0.005/nm or more; and an effective area of 10 ^μm2 or more but 20 ^μm2 or less.

Description of drawings

Fig. 1 is a view showing the schematic structure of an optical transmission system comprising an optical transmission line according to the present invention;

Fig. 2 is a view showing a schematic structure of an optical transmission system in which a dispersion-shifted optical fiber is placed as an optical transmission line, and a dispersion-compensating optical fiber is placed in a station as a dispersion compensation module;

3A and 3B are views showing, respectively, the cross-sectional structure of the dispersion compensating optical fiber and its refractive index distribution according to the present invention;

4 is a graph showing the relationship between the dispersion and the dispersion slope at a wavelength of 1550 nm of the dispersion compensating optical fiber according to the first to third embodiments;

Fig. 5 is a graph showing the relationship between bending loss and wavelength at a bending diameter of 140 mm of the dispersion compensating optical fiber according to the first to third embodiments;

Fig. 6 is a graph showing the relationship between dispersion and wavelength of dispersion compensating optical fibers according to the first to third embodiments;

FIG. 7 is a graph showing overall average dispersion versus wavelength for each assembly in which a dispersion compensating optical fiber and a dispersion shifted optical fiber according to each of the first to third embodiments are fusion spliced to each other ;

Fig. 8 is a view showing the schematic structure of the dispersion compensation module according to the present invention;

FIG. 9 is a graph showing the relationship between the dispersion and the dispersion slope of the dispersion compensating fiber at a wavelength of 1550 nm according to the fourth embodiment;

Fig. 10 is a graph showing the relationship between bending loss and wavelength at a bending diameter of 140 mm of the dispersion compensating optical fiber according to the fourth embodiment;

Fig. 11 is a graph showing the relationship between dispersion and wavelength of the dispersion compensating optical fiber according to the fourth embodiment;

FIG. 12 is a graph showing overall average dispersion versus wavelength for each assembly in which a dispersion-compensating optical fiber according to a fourth embodiment and a dispersion-shifted optical fiber are fusion spliced to each other;

FIG. 13 is a graph showing the relationship between the dispersion and the dispersion slope at a wavelength of 1550 nm of the dispersion compensating optical fiber according to the fifth to seventh embodiments;

Fig. 14 is a graph showing the relationship between bending loss and wavelength at a bending diameter of 140 mm of dispersion compensating optical fibers according to fifth to seventh embodiments;

Fig. 15 is a graph showing the relationship between dispersion and wavelength of dispersion compensating optical fibers according to fifth to seventh embodiments;

Fig. 16 is a graph showing overall average dispersion versus wavelength for each assembly in which a dispersion compensating optical fiber and a dispersion shifted optical fiber according to each of the fifth to seventh embodiments are fusion spliced to each other ;

17A and 17B are views showing, respectively, the cross-sectional structure of a dispersion compensating optical fiber and its refractive index distribution according to a comparative example; and

Fig. 18 is a graph showing the relationship between dispersion and dispersion slope at a wavelength of 1550 nm of a dispersion compensating fiber according to a comparative example.

Detailed ways

Hereinafter, means for realizing the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, components that are the same as each other will be denoted by the same numerals as each other, and overlapping descriptions thereof will not be repeated.

FIG. 1 is a view showing a schematic structure of an optical transmission system including an optical transmission line 30 according to the present invention. In this optical transmission system 1 , an optical transmission line 30 is placed in a relay section between a station (sending station or relay station) 10 and a station (receiving station or relay station) 20 . The optical transmission line 30 is composed of a dispersion-shifted optical fiber 31 and a dispersion-compensating optical fiber 32 which are fusion bonded to each other. In this optical transmission system 1, signals having a plurality of wavelengths in one 1.55-μm band transmitted from the station 10 arrive at the station 20 through the dispersion-shifted optical fiber 31 and the dispersion-compensating optical fiber 32 successively, and are received by the station 20 or are received by the station 20 The optical amplification is sent further downstream.

The dispersion-shifted fiber 31 is a silica-based fiber with small positive dispersion at a wavelength of 1550 nm. In the dispersion-shifted fiber 31, at a wavelength of 1550nm, the dispersion D _DSF is +2ps/nm/km to +10ps/nm/km, and the dispersion slope S _DSF is +0.04ps/nm ² /km to +0.12ps/nm ² /km, and the transmission loss is about 0.2dB/km.

The dispersion compensating fiber 32 according to the present invention is a silicon-based fiber, which compensates the dispersion and the dispersion slope of the dispersion-shifted fiber 31 at a wavelength of 1550 nm. In the dispersion compensating fiber 32, at a wavelength of 1550 nm, its dispersion D _DCF is -40 ps/nm/km or less, and the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) is 0.005/nm or more . Preferably, in the dispersion compensating fiber 32, at a wavelength of 1550 nm, the dispersion D _DCF is -100 ps/nm/km to -40 ps/nm/km, and the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) is 0.005/nm to 0.015/nm. In addition, the dispersion compensating fiber 32 has an effective area of 16 μm ² or more, preferably 20 μm ² or more at a wavelength of 1550 nm, a cutoff wavelength of 1.2 μm to 1.8 μm, preferably 1.4 μm to 1.8 μm, and a wavelength of 1550 nm Transmission loss of 0.5dB/km or less at .

In addition, the dispersion compensating fiber 32 may have a dispersion D _DCF of -250 ps/nm/km to -120 ps/nm/km at a wavelength of 1550 nm, and a ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF / D _DCF ), and an effective area of 10 μm ² to 20 μm ² at a wavelength of 1550 nm. In addition, the dispersion compensating fiber has a cutoff wavelength of 1.2 µm to 1.8 µm, preferably 1.4 µm to 1.8 µm, and a transmission loss of 1.0 dB/km or less at a wavelength of 1550 nm.

Since the dispersion D _DCF and the dispersion slope S _DCF are within the above numerical range, the dispersion compensating fiber 32 having these characteristics can compensate the dispersion and the dispersion slope of the dispersion shifted fiber 31 with a short length in a wide band including a wavelength of 1550 nm. Furthermore, since the dispersion compensating fiber 32 has dispersion within its numerical range described above and a sufficient effective area, it can suppress the occurrence of four-wave mixing and suppress the degradation of the waveform of a signal propagating therethrough. In addition, in the dispersion compensating fiber 32, since the cutoff wavelength is within the above-mentioned numerical range thereof, an increase in bending loss can be suppressed, and since the transmission loss is also within the above-mentioned numerical range, even when the optical transmission line 30 constitutes one optical cable Lower losses are also obtained.

The optical transmission line 30 in which the dispersion-shifted fiber 31 and the dispersion-compensating fiber 32 are fused to each other with an appropriate length ratio generally has a small absolute average dispersion and a small absolute average dispersion slope at a wavelength of 1550 nm. Therefore, the optical transmission line 30 has, in general, an average dispersion of a small absolute value in a wide wavelength band including a wavelength of 1550 nm. Furthermore, the optical transmission line 30 has a small average transmission loss as a whole. The deviation of the average dispersion of the entire optical transmission line 30 is preferably 0.2 ps/nm/km or less in a wave band (C band) from 1535 nm to 1560 nm, more preferably in a wave band (C and L bands) from 1535 nm to 1600 nm The ground is 0.2 ps/nm/km or less. In the optical transmission system 1, a signal propagated through the optical transmission line 30 is generated to realize optical communication, the average transmission loss of the optical transmission line 30 is small, the absolute value of the average dispersion is small, and it is available in a wide band including a wavelength of 1550nm (at least including the C band and Optical transmission with high bit rates is possible further including in the L-band). Therefore, the optical transmission system 1 can extend the relay section and obtain further higher speed and larger capacity in optical communication.

2 is a view showing a schematic structure of an optical transmission system 2 in which a dispersion-shifted optical fiber 31 is placed as an optical transmission line, and a dispersion-compensating optical fiber 32 is placed in the station 20 as a dispersion compensation module. In this optical transmission system 2 , a dispersion-shifted optical fiber 31 is placed in a relay section between a station (sending station or relay station) 10 and a station (receiving station or relay station) 20 . In this optical transmission system 2, a signal having a plurality of wavelengths in one 1.55-μm band transmitted from a station 10 reaches the station 20 through a dispersion-shifted optical fiber 31 as an optical transmission line. In station 20, the signal is optically amplified by optical amplifier 21, whose dispersion is compensated by dispersion compensating fiber 32, and the signal is optically amplified by optical amplifier 22 and then received or sent further downstream thereof.

The dispersion-shifted fiber 31 used as an optical transmission line in the optical transmission system 2 of FIG. 2 has similar characteristics to the dispersion-shifted fiber 31 used as a part of the optical transmission line in the optical transmission system 1 of FIG. 1 . In addition, the dispersion compensating fiber 32 used as a dispersion compensation module in the optical transmission system 2 of FIG. 2 has similar characteristics to the dispersion compensation module 32 used as a part of the optical transmission line in the optical transmission system 1 of FIG. 1 . However, in the optical transmission system 2 shown in FIG. 2, the dispersion compensating optical fiber 32 is located in the station 20 and is wound like a coil around a bobbin to form a module.

Since the dispersion D _DCF and the dispersion slope S _DCF are within the above numerical range, the dispersion compensating fiber 32 having the above characteristics can compensate the dispersion and the dispersion slope of the dispersion shifted fiber 31 with a short length in a wide band including a wavelength of 1550 nm. Furthermore, since the dispersion compensating fiber 32 has dispersion within its numerical range described above and a sufficient effective area, it can suppress the occurrence of four-wave mixing and suppress the degradation of the waveform of a signal propagating therethrough. In addition, since the cutoff wavelength is within the above-mentioned numerical range thereof, the dispersion compensating optical fiber 32 can suppress an increase in bending loss, and since the transmission loss is also within the above-mentioned numerical range thereof, a lower loss is obtained even when constituting one module .

The dispersion-shifted optical fiber 31 as an optical transmission line and the integral body of the dispersion-compensating optical fiber 32 as a dispersion-compensating module have when they have their respective appropriate lengths, at a wavelength of 1550 nm, generally speaking, the average dispersion of the small absolute value and Average dispersion slope with small absolute value. Therefore, the entirety of the dispersion-shifted fiber 31 and the dispersion-compensating fiber 32 has an average dispersion with a small absolute value and a small average transmission loss in a wide band including a wavelength of 1550 nm. The deviation of its total average dispersion is preferably 0.2 ps/nm/km or less in the band (C band) from 1535 nm to 1560 nm, and more preferably 0.2 ps/km in the band (C and L bands) from 1535 nm to 1600 nm. nm/km or less.

On the other hand, when the dispersion compensation fiber 32 as a dispersion compensation module produces a dispersion compensation amount of -640 ps/nm at a wavelength of 1550 nm, it is preferable to have a total of 7 dB or less in the band (C band) from 1535 nm to 1565 nm. Loss, preferably a total loss of 7dB or less in the band from 1535nm to 1610nm (C and L bands). In addition, when the dispersion compensation fiber 32 as a dispersion compensation module produces a dispersion compensation amount of -320ps/nm at a wavelength of 1550nm, it preferably has a total loss of 3dB or less in the band (C band) from 1535nm to 1565nm, It is better to have a total loss of 3 dB or less in the band (C and L bands) from 1535 nm to 1610 nm.

In the optical transmission system 2, the average transmission loss is small, the absolute value of the average dispersion is small, and optical transmission with a high bit rate is possible in a wide band (including at least the C band and further including the L band) including a wavelength of 1550 nm . Therefore, the optical transmission system 2 can extend the relay section and obtain further higher speed and larger capacity in optical communication.

3A and 3B are views respectively showing the cross-sectional structure of the dispersion compensating optical fiber and its refractive index distribution according to the present invention.

The optical fiber 100 shown in FIG. 3A corresponds to the dispersion compensating optical fiber 32 , and includes a core region 110 extending along a predetermined axis, and a cladding region 120 for surrounding the outer edge of the core region 110 . The core region 110 has a refractive index _n1 and an outer diameter 2a. In addition, the cladding region 120 includes a first cladding 121 having a second refractive index n ₂ (<n ₁ ) and an outer diameter 2b, a second cladding 122 for surrounding the outer edge of the first cladding 121 and having a second Three refractive indices n ₃ (>n ₂ , <n ₁ ) and outer diameter 2c, and the third cladding layer 123, used to surround the outer edge of the second cladding layer 122, has a fourth refractive index n ₄ (<n ₃ , > n ₂ ).

The refractive index distribution 150 shown in FIG. 3B represents the respective refractive indices at various parts on the line L1 in FIG. , the refractive index of each part on the centerline L1 of the second cladding layer 122 and the third cladding layer 123 .

In the dispersion compensating fiber 100 of FIGS. 3A and 3B, with respect to the third cladding 123 serving as a reference region, the relative refractive index difference Δn ₁ of the core region 110, the relative refractive index difference Δn ₂ of the first cladding 121, and the relative refractive index difference Δn ₃ of the second cladding layer 122 is given by the following respective expressions:

Δn ₁ =(n ₁ -n ₄ )/n ₄

Δn ₂ =(n ₂ −n ₄ )/n ₄

Δn ₃ =(n ₃ -n ₄ )/n ₄

where n ₁ is the refractive index of the core region 110, n ₂ is the refractive index of the first cladding 121, n ₃ is the refractive index of the second cladding 122, and n ₄ is the third cladding 123 used as a reference region the refractive index. In this specification, the relative refractive index difference of each part is expressed by percentage, and the various parameters in the above expressions can be placed in a fixed order. Therefore, the relative refractive index difference of a glass region having a lower refractive index than the third cladding layer 123 (reference region) is represented by a negative value.

Here, in the dispersion compensating fiber 100, the core region 110 has a relative refractive index difference Δn ₁ of 0.8% to 2.0%, more preferably 0.8% to 1.5%, with respect to the refractive index n ₄ of the third cladding 123, the first The cladding layer 121 has a relative refractive index difference Δn ₂ of -0.4% or less.

Since the dispersion compensating fiber 100 has such a refractive index distribution, its dispersion D _DCF , ratio (S _DCF /D _DCF ), effective area, cut-off wavelength, and transmission loss are within the above-mentioned numerical ranges. For the dispersion compensating optical fiber 100 having such a refractive index distribution, it is better to use silica glass as the base, its core region 110 is doped with GeO ₂ , its first cladding 121 is doped with F element, and its second cladding 122 Doped with GeO ₂ . Therefore, the refractive index profile shown in FIG. 3B can be realized, and the transmission loss of the dispersion compensating fiber 100 at a wavelength of 1550 nm can be reduced.

Next, an embodiment of the dispersion compensating optical fiber 32 according to the present invention will now be described. Each of the dispersion compensating fibers DCF1-DCF7 according to the first to seventh embodiments, which will be described below, has the cross-sectional structure of FIG. 3A and the refractive index profile 150 of FIG. 3B.

first embodiment

In the dispersion compensating fiber DCF1 according to the first embodiment, with respect to the third cladding 123, the relative refractive index difference Δn ₁ of the core region 110 is 1.2%, and the relative refractive index difference Δn ₂ of the first cladding 121 is -0.50 %, the relative refractive index difference Δn ₃ of the second cladding layer 122 is 0.20%, the ratio (2a/2c) of each outer diameter of the core region 110 and the second cladding layer 122 is 0.30, and the first cladding layer 121 and the second cladding layer 121 The ratio (2b/2c) of the respective outer diameters of the secondary cladding 122 was 0.60. When the outer diameter 2c of the second cladding 122 is 17.7 μm, at a wavelength of 1550 nm, the dispersion compensation fiber DCF1 of the first embodiment shows a dispersion D _DCF of -62.4 ps/nm/km, -0.44 ps/nm ² /km The dispersion slope S _DCF , an effective area of 24.4μm ² , a bending loss of 10dB/m at a bending diameter of 20mm, and a transmission loss of 0.30dB/km. In addition, its cutoff wavelength was 1224 nm, and the ratio (S _DCF /D _DCF ) at a wavelength of 1550 nm was 0.0071/nm.

second embodiment

In the dispersion compensating fiber DCF2 according to the second embodiment, with respect to the third cladding 123, the relative refractive index difference Δn ₁ of the core region 110 is 1.3%, and the relative refractive index difference Δn ₂ of the first cladding 121 is -0.50 %, the relative refractive index difference Δn ₃ of the second cladding layer 122 is 0.23%, the ratio (2a/2c) of each outer diameter of the core region 110 and the second cladding layer 122 is 0.27, and the first cladding layer 121 and the second cladding layer 121 The ratio (2b/2c) of the respective outer diameters of the secondary cladding 122 is 0.55. When the outer diameter 2c of the second cladding 122 is 19.0 μm, at a wavelength of 1550 nm, the dispersion compensating fiber DCF2 of the second embodiment shows a dispersion D _DCF of -80.4 ps/nm/km, -0.59 ps/nm ² /km The dispersion slope S _DCF , the effective area of 23.9μm ² , the bending loss of 4dB/m at a bending diameter of 20mm, and the transmission loss of 0.33dB/km. In addition, its cutoff wavelength was 1576 nm, and the ratio (S _DCF /D _DCF ) at a wavelength of 1550 nm was 0.0073/nm.

third embodiment

In the dispersion compensating fiber DCF3 according to the third embodiment, with respect to the third cladding 123, the relative refractive index difference Δn ₁ of the core region 110 is 1.7%, and the relative refractive index difference Δn ₂ of the first cladding 121 is -0.50 %, the relative refractive index difference Δn ₃ of the second cladding layer 122 is 0.25%, the ratio (2a/2c) of each outer diameter of the core region 110 and the second cladding layer 122 is 0.23, and the first cladding layer 121 and the second cladding layer 121 The ratio (2b/2c) of the respective outer diameters of the secondary cladding 122 was 0.53. When the outer diameter 2c of the second cladding 122 is 18.7 μm, at a wavelength of 1550 nm, the dispersion compensating fiber DCF3 of the third embodiment shows a dispersion D _DCF of -83.7 ps/nm/km, -0.66 ps/nm ² /km The dispersion slope S _DCF , the effective area of 17.2μm ² , the bending loss of 0.2dB/m at the bending diameter of 20mm, and the transmission loss of 0.39dB/km. In addition, its cutoff wavelength was 1696 nm, and the ratio (S _DCF /D _DCF ) at a wavelength of 1550 nm was 0.0079/nm.

Fig. 4 is a graph showing the relationship between the dispersion and the dispersion slope at a wavelength of 1550 nm in each of the dispersion compensating optical fibers of the first to third embodiments. In FIG. 4 , G110 indicates the curve of the first embodiment, G210 indicates the curve of the second embodiment, and G310 indicates the curve of the third embodiment. Shown here is the relationship between the dispersion D _DCF and the dispersion slope S _DCF in each dispersion compensating fiber of these embodiments when the outer diameter 2c of the second cladding 122 is changed. It can be seen from the graph of Fig. 4 that if the dispersion D _DCF is approximately in the range of -60ps/nm/km to -10ps/nm/km, even when the outer diameter 2c of the second cladding 122 changes, each dispersion compensating fiber The variation of the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) in DCF1 to DCF3 is also small. In the dispersion compensating fiber DCF1 of the first embodiment, when the outer diameter 2c of the second cladding 122 changes by 2%, the ratio (S _DCF /D _DCF ) changes by 2.5% or less, and furthermore the ratio (S _DCF /D _DCF ) is kept at or below 10% and the dispersion D _DCF ranges from -68 ps/nm/km to -17 ps/nm/km. In the dispersion compensating fiber DCF2 of the second embodiment, when the outer diameter 2c of the second cladding 122 is changed by 2%, the ratio (S _DCF /D _DCF ) changes by 9.0% or less, and furthermore the ratio (S _DCF /D _DCF ) is kept at or below 10% and the dispersion D _DCF ranges from -81 ps/nm/km to -30 ps/nm/km. In the dispersion compensating fiber DCF3 of the third embodiment, when the outer diameter 2c of the second cladding 122 changes by 2%, the ratio (S _DCF /D _DCF ) changes by 4.0% or less, and furthermore the ratio (S _DCF /D _DCF ) is kept at or below 10% and the dispersion D _DCF ranges from -115 ps/nm/km to -62 ps/nm/km. If the ratio (S _DCF /D _DCF ) varies by 10% or less when the outer diameter 2c of the second cladding 122 is similarly changed by 2%, a dispersion compensating fiber having desired dispersion characteristics can be easily manufactured.

Fig. 5 is a graph showing bend loss versus wavelength at a bend diameter of 140 mm in each of the dispersion compensating optical fibers of the first to third embodiments. In FIG. 5 , G120 indicates the curve of the first embodiment, G220 indicates the curve of the second embodiment, and G320 indicates the curve of the third embodiment. The outer diameter 2c of the second cladding 122 in the dispersion compensating fiber DCF1 of the first embodiment is 17.7 μm, the outer diameter 2c of the second cladding 122 in the dispersion compensating fiber DCF2 of the second embodiment is 19.0 μm, and the third embodiment The outer diameter 2c of the second cladding layer 122 in the dispersion compensating fiber DCF3 of the example is 18.7 μm. As can be seen from the graph of FIG. 5, each of the dispersion compensating fibers DCF1 to DCF3 has a low bending loss in the wavelength range of 1610 nm or less.

Therefore, each of the dispersion compensating fibers DCF1 to DCF3 is suitable not only as the dispersion compensating fiber 32 constituting a part of the optical transmission line 30 in the optical transmission system 1 shown in FIG. The dispersion compensating fiber 32 of the medium dispersion compensating module can thereby compensate for dispersion with low loss not only in the C-band but also in the L-band.

Fig. 6 is a graph showing the dispersion versus wavelength in each of the dispersion compensating optical fibers of the first to third embodiments. In Fig. 6, G130 represents the curve of the first embodiment, G230 represents the curve of the second embodiment, G330 represents the curve of the third embodiment, and G1000 represents the curve of a non-zero dispersion-shifted fiber NZDSF disclosed in the above document 1 . Here, also, the outer diameter 2c of the second cladding 122 in the dispersion compensating fiber DCF1 of the first embodiment is 17.7 μm, and the outer diameter 2c of the second cladding 122 in the dispersion compensating fiber DCF2 of the second embodiment is 19.0 μm, And the outer diameter 2c of the second cladding layer 122 in the dispersion compensating fiber DCF3 of the third embodiment is 18.7 μm.

Fig. 7 is a graph showing the overall average dispersion versus wavelength in each assembly formed by interconnecting each of the dispersion compensating fibers and the dispersion shifted fibers of the first to third embodiments. In Fig. 7, G140 represents the curve of the assembly where the dispersion compensating fiber DCF1 of the first embodiment and the dispersion-shifted fiber NZDSF of Fig. 6 are interconnected, and G240 represents wherein the dispersion compensating fiber DCF2 of the second embodiment and the dispersion-shifted fiber of Fig. 6 The curves of the interconnected components of the optical fiber NZDSF, and G340 represent the curves of the interconnected components of the dispersion compensating fiber DCF3 of the third embodiment and the dispersion shifted optical fiber NZDSF of FIG. 6 . In order to compensate the dispersion of the dispersion-shifted optical fiber NZDSF having the dispersion characteristics shown in Figure 6 and a length of 80 km at a wavelength of 1550 nm, the dispersion-compensating optical fiber DCF1 of the first embodiment needs a length of 10.3 km, and the dispersion-compensating optical fiber DCF2 of the second embodiment requires a length of 8.0 km. km, and the dispersion compensating fiber DCF3 of the third embodiment requires a length of 7.5 km.

In an assembly in which the dispersion compensating fiber DCF1 of the first embodiment and the dispersion shifting fiber NZDSF are interconnected, the total average dispersion has a deviation of 0.2 ps/nm/km or less in one band (C and L bands) from 1535 nm to 1600 nm . In an assembly in which the dispersion compensating fiber DCF2 of the second embodiment and the dispersion shifting fiber NZDSF are interconnected, the average dispersion generally has a value of 0.2 ps/nm/km or less in one band (C band) of 1535 nm to 1560 nm deviation. Furthermore, in an assembly in which the dispersion compensating fiber DCF3 of the third embodiment and the dispersion shifting fiber NZDSF are connected to each other, the average dispersion generally has 0.2 ps/nm/km or following deviations. Therefore, they are capable of optical transmission over a distance of 400km at a bit rate of 40Gb/s.

Fig. 8 is a view showing a schematic structure of a dispersion compensating module including the dispersion compensating optical fiber according to the present invention. The dispersion compensating fiber 100 (corresponding to the dispersion compensating fiber 32 ) is housed in a box 300 having an output and an output connector 310 . Both ends of the optical fiber 100 are respectively fused to the pigtail 320 to reduce connection loss. When the dispersion compensating optical fiber DCF1 of the first embodiment of the length 10.3km was wound with a bending diameter of 140mm to form a dispersion compensating module, the dispersion compensation amount at the wavelength 1550nm place was -640ps/nm, and the total loss was 4.1dB (wavelength 1550nm place). When the dispersion compensating fiber DCF2 of the second embodiment with a length of 8.0km is wound with a bending diameter of 140mm to form a dispersion compensating module, the dispersion compensation amount at the wavelength 1550nm place is -640ps/nm, and the total loss is 4.4dB (wavelength 1550nm place). In addition, when the dispersion compensating fiber DCF3 of the third embodiment with a length of 7.5 km is wound with a bending diameter of 140 mm to constitute a dispersion compensating module, the dispersion compensation amount at a wavelength of 1550 nm is -640 ps/nm, and the total loss is 4.1 dB ( at a wavelength of 1550nm).

In addition, when the dispersion compensation fiber DCF1 of the first embodiment is wound with a bending diameter of 140mm to form a dispersion compensation module, the amount of dispersion compensation at the wavelength of 1550nm is -320ps/nm, and the total loss is 2.3dB (at the wavelength of 1550nm) . When the dispersion compensation fiber DCF2 of the second embodiment is wound with a bending diameter of 140mm to form a dispersion compensation module, the dispersion compensation at a wavelength of 1550nm is -320ps/nm, and the total loss is 2.5dB (at a wavelength of 1550nm). In addition, when the dispersion compensation fiber DCF3 of the third embodiment is wound with a bending diameter of 140mm to form a dispersion compensation module, the amount of dispersion compensation at the wavelength of 1550nm is -320ps/nm, and the total loss is 2.7dB (at the wavelength of 1550nm) .

Therefore, each of the dispersion compensating fibers DCF1 to DCF3 can compensate the dispersion and the dispersion slope of the dispersion shifted fiber with a short length and low loss in a wide band including a wavelength of 1550 nm.

Fourth embodiment

In the dispersion compensating fiber DCF4 according to the fourth embodiment, with respect to the third cladding 123, the relative refractive index difference Δn ₁ of the core region 110 is 1.6%, and the relative refractive index difference Δn ₂ of the first cladding 121 is -0.50 %, the relative refractive index difference Δn ₃ of the second cladding layer 122 is 0.24%, the ratio (2a/2c) of each outer diameter of the core region 110 and the second cladding layer 122 is 0.23, and the first cladding layer 121 and the second cladding layer 121 The ratio (2b/2c) of the respective outer diameters of the secondary cladding 122 is 0.55. When the outer diameter 2c of the second cladding 122 is 19.2 μm, at a wavelength of 1550 nm, the dispersion compensating fiber DCF4 of the fourth embodiment shows a dispersion D _DCF of -85.1 ps/nm/km, -0.83 ps/nm ² /km The dispersion slope S _DCF , an effective area of 18.1μm ² , a bending loss of 0.9dB/m at a bending diameter of 20mm, and a transmission loss of 0.38dB/km. In addition, its cutoff wavelength is 1638 nm, and the ratio (S _DCF /D _DCF ) at a wavelength of 1550 nm is 0.0098/nm.

Fig. 9 is a graph showing the relationship between the dispersion and the dispersion slope at a wavelength of 1550 nm in the dispersion compensating fiber of the fourth embodiment. In FIG. 9, G410 represents the graph of the fourth embodiment. Shown here is the relationship between the dispersion D _DCF and the dispersion slope S _DCF in the dispersion compensating fiber of this embodiment when the outer diameter 2c of the second cladding 122 is changed. It can be seen from the graph of FIG. 9 that if the dispersion D _DCF is approximately in the range of -102 ps/nm/km to -71 ps/nm/km, even when the outer diameter 2c of the second cladding 122 changes, the dispersion compensating fiber DCF4 The variation of the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) is also kept at 10% or less. In the dispersion compensating fiber DCF4 of the fourth embodiment, when the outer diameter 2c of the second cladding 122 is changed by 2%, the ratio (S _DCF /D _DCF ) changes by 5.8% or less. If the ratio (S _DCF /D _DCF ) varies by 10% or less when the outer diameter 2c of the second cladding 122 is similarly changed by 2%, a dispersion compensating fiber having desired dispersion characteristics can be easily manufactured.

Fig. 10 is a graph showing bend loss versus wavelength at a bend diameter of 140 mm in the dispersion compensating optical fiber of the fourth embodiment. In FIG. 10, G420 represents the curve of the fourth embodiment. The outer diameter 2c of the second cladding layer 122 in the dispersion compensating fiber DCF4 of the fourth embodiment is 17.2 μm. As can be seen from the graph of FIG. 10, the dispersion compensating fiber DCF4 has low bending loss in the wavelength range of 1610 nm or less.

Therefore, the dispersion compensating fiber DCF4 is suitable not only as the dispersion compensating fiber 32 constituting a part of the optical transmission line 30 in the optical transmission system 1 shown in FIG. The dispersion compensating fiber 32 can thereby compensate for dispersion with low loss not only in the C-band but also in the L-band.

Fig. 11 is a graph showing dispersion versus wavelength in the dispersion compensating fiber of the fourth embodiment. In FIG. 11, G430 represents the curve of the fourth embodiment, and G1000 represents the curve of a non-zero dispersion-shifted fiber NZDSF disclosed in the above document 1, having a dispersion of 4 ps/nm/km or less and 0.046 ps/nm ² / A dispersion slope of km or less. Here, too, the outer diameter 2c of the second cladding 122 in the dispersion compensating fiber DCF4 of the fourth embodiment is 19.2 μm.

Fig. 12 is a graph showing overall average dispersion versus wavelength in a module in which the dispersion compensating fiber and the dispersion shifted fiber of the fourth embodiment are interconnected. In FIG. 12, G440 represents a curve of an assembly in which the dispersion compensating fiber DCF4 of the fourth embodiment and the dispersion shifted fiber NZDSF of FIG. 11 are interconnected. In order to compensate the dispersion of the dispersion-shifted fiber NZDSF having the dispersion characteristics shown in Figure 11 and the length of 80 km at a wavelength of 1550 nm, the dispersion-compensating fiber DCF1 of the first embodiment needs a length of 10.3 km, and the dispersion-compensating fiber DCF4 of the fourth embodiment needs a length of 4.4 km. km.

In an assembly in which the dispersion compensating fiber DCF4 of the fourth embodiment and the dispersion shifting fiber NZDSF are interconnected, the total average dispersion has a deviation of 0.2 ps/nm/km or less in one band (C and L bands) from 1535 nm to 1600 nm . Therefore, they are capable of optical transmission at a bit rate of 40Gb/s over a repeater distance of 400km.

When the dispersion compensating optical fiber DCF4 of the fourth embodiment of the length 4.4km is wound with a bending diameter of 140mm to form a dispersion compensating module, the dispersion compensation amount at the wavelength 1550nm place is -640ps/nm, and the total loss is 3.9dB (wavelength at 1550nm). In addition, when the dispersion compensation fiber DCF4 of the fourth embodiment is wound with a bending diameter of 140mm to form a dispersion compensation module, the amount of dispersion compensation at the wavelength of 1550nm is -320ps/nm, and the total loss is 2.5dB (at the wavelength of 1550nm ).

Therefore, the dispersion compensating fiber DCF4 can compensate the dispersion and the dispersion slope of the dispersion shifted fiber NZDSF with a short length and low loss in a wide band including a wavelength of 1550 nm.

fifth embodiment

In the dispersion compensating fiber DCF5 according to the fifth embodiment, with respect to the third cladding 123, the relative refractive index difference Δn ₁ of the core region 110 is 2.1%, and the relative refractive index difference Δn ₂ of the first cladding 121 is -0.50 %, the relative refractive index difference Δn ₃ of the second cladding layer 122 is 0.20%, the ratio (2a/2c) of each outer diameter of the core region 110 and the second cladding layer 122 is 0.18, and the first cladding layer 121 and the second cladding layer 121 The ratio (2b/2c) of the respective outer diameters of the secondary cladding 122 was 0.49. When the outer diameter 2c of the second cladding 122 is 19.4 μm, at a wavelength of 1550 nm, the dispersion compensating fiber DCF5 of the fifth embodiment shows a dispersion D _DCF of -160.7 ps/nm/km, -1.63 ps/nm ² /km The dispersion slope S _DCF , an effective area of 15.7μm ² , a bending loss of 1.8dB/m at a bending diameter of 20mm, and a transmission loss of 0.49dB/km. In addition, its cutoff wavelength was 1566 nm, and the ratio (S _DCF /D _DCF ) at a wavelength of 1550 nm was 0.0101/nm.

Sixth embodiment

In the dispersion compensating fiber DCF6 according to the sixth embodiment, with respect to the third cladding 123, the relative refractive index difference Δn ₁ of the core region 110 is 2.4%, and the relative refractive index difference Δn ₂ of the first cladding 121 is -0.50 %, the relative refractive index difference Δn ₃ of the second cladding layer 122 is 0.40%, the ratio (2a/2c) of each outer diameter of the core region 110 and the second cladding layer 122 is 0.20, and the first cladding layer 121 and the second cladding layer 121 The ratio (2b/2c) of the respective outer diameters of the secondary cladding 122 was 0.65. When the outer diameter 2c of the second cladding 122 is 16.0 μm, at a wavelength of 1550 nm, the dispersion compensating fiber DCF6 of the sixth embodiment shows a dispersion D _DCF of -181.6 ps/nm/km, -1.87 ps/nm ² /km The dispersion slope S _DCF , the effective area of 13.8μm ² , the bending loss of 0.5dB/m at the bending diameter of 20mm, and the transmission loss of 0.61dB/km. In addition, its cutoff wavelength is 1660 nm, and the ratio (S _DCF /D _DCF ) at a wavelength of 1550 nm is 0.0103/nm.

Seventh embodiment

In the dispersion compensating fiber DCF7 according to the seventh embodiment, with respect to the third cladding 123, the relative refractive index difference Δn ₁ of the core region 110 is 2.7%, and the relative refractive index difference Δn ₂ of the first cladding 121 is -0.50 %, the relative refractive index difference Δn ₃ of the second cladding layer 122 is 0.40%, the ratio (2a/2c) of each outer diameter of the core region 110 and the second cladding layer 122 is 0.19, and the first cladding layer 121 and the second cladding layer 121 The ratio (2b/2c) of the respective outer diameters of the secondary cladding 122 was 0.67. When the outer diameter 2c of the second cladding 122 is 15.2 μm, at a wavelength of 1550 nm, the dispersion compensating fiber DCF7 of the seventh embodiment shows a dispersion D _DCF of -215.8 ps/nm/km, -2.12 ps/nm ² /km The dispersion slope S _DCF , an effective area of 13.1μm ² , a bending loss of 1.3dB/m at a bending diameter of 20mm, and a transmission loss of 0.75dB/km. In addition, its cutoff wavelength was 1514 nm, and the ratio (S _DCF /D _DCF ) at a wavelength of 1550 nm was 0.0097/nm.

Fig. 13 is a graph showing the relationship between the dispersion and the dispersion slope at a wavelength of 1550 nm for each of the dispersion compensating fibers of the fifth to seventh embodiments. In FIG. 13 , G510 indicates the curve of the fifth embodiment, G610 indicates the curve of the sixth embodiment, and G710 indicates the curve of the seventh embodiment. Shown here is the relationship between the dispersion D _DCF and the dispersion slope S _DCF in each dispersion compensating fiber of these embodiments when the outer diameter 2c of the second cladding 122 is changed. It can be seen from the graph of FIG. 13 that if the dispersion D _DCF is approximately in the range of -200ps/nm/km to -120ps/nm/km, even when the outer diameter 2c of the second cladding 122 changes, each dispersion compensating fiber The variation of the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) is also small in DCF5 to DCF7. In the dispersion compensating fiber DCF5 of the fifth embodiment, when the outer diameter 2c of the second cladding 122 is changed by 2%, the ratio (S _DCF /D _DCF ) changes by 7.7% or less, and furthermore the ratio (S _DCF /D _DCF ) is kept at or below 10% and the dispersion D _DCF ranges from -192 ps/nm/km to -135 ps/nm/km. In the dispersion compensating fiber DCF6 of the sixth embodiment, when the outer diameter 2c of the second cladding 122 changes by 2%, the ratio (S _DCF /D _DCF ) changes by 4.6% or less, and furthermore the ratio (S _DCF /D _DCF ) is kept at or below 10% and the dispersion D _DCF ranges from -226 ps/nm/km to -146 ps/nm/km. In the dispersion compensating fiber DCF7 of the seventh embodiment, when the outer diameter 2c of the second cladding 122 is changed by 2%, the ratio (S _DCF /D _DCF ) changes by 4.9% or less, and furthermore the ratio (S _DCF /D _DCF ) is kept at or below 10% and the dispersion D _DCF ranges from -173 ps/nm/km to -269 ps/nm/km. If the ratio (S _DCF /D _DCF ) varies by 10% or less when the outer diameter 2c of the second cladding 122 is similarly changed by 2%, a dispersion compensating fiber having desired dispersion characteristics can be easily manufactured.

Fig. 14 is a graph showing bend loss versus wavelength at a bend diameter of 140 mm in each of the dispersion compensating optical fibers of the fifth to seventh embodiments. In FIG. 14 , G520 indicates the curve of the fifth embodiment, G620 indicates the curve of the sixth embodiment, and G720 indicates the curve of the seventh embodiment. The outer diameter 2c of the second cladding 122 in the dispersion compensating fiber DCF5 of the fifth embodiment is 19.4 μm, the outer diameter 2c of the second cladding 122 in the dispersion compensating fiber DCF6 of the sixth embodiment is 16.0 μm, and the seventh embodiment In the example dispersion compensating fiber DCF7, the outer diameter 2c of the second cladding layer 122 is 15.2 μm. As can be seen from the graph of FIG. 14, each of the dispersion compensating fibers DCF5 to DCF7 has a low bending loss in the wavelength range of 1610 nm or less.

Therefore, each of the dispersion compensating fibers DCF5 to DCF7 is suitable not only as the dispersion compensating fiber 32 constituting a part of the optical transmission line 30 in the optical transmission system 1 shown in FIG. The dispersion compensating fiber 32 of the medium dispersion compensating module can thereby compensate dispersion with low loss not only in the C-band but also in the L-band.

Fig. 15 is a graph showing the dispersion versus wavelength in each of the dispersion compensating optical fibers of the fifth to seventh embodiments. In FIG. 15 , G530 indicates the curve of the fifth embodiment, G630 indicates the curve of the sixth embodiment, and G730 indicates the curve of the seventh embodiment. Here, also, the outer diameter 2c of the second cladding 122 in the dispersion compensating fiber DCF5 of the fifth embodiment is 19.4 μm, and the outer diameter 2c of the second cladding 122 in the dispersion compensating fiber DCF6 of the sixth embodiment is 16.0 μm, And the outer diameter 2c of the second cladding layer 122 in the dispersion compensating fiber DCF7 of the seventh embodiment is 15.2 μm.

Fig. 16 is a graph showing that each of the dispersion compensating optical fibers passed through the fifth to seventh embodiments is the same as that disclosed in the above document 2 and has a dispersion of 4 ps/nm/km or less and 0.046 ps/nm ² /km or less The dispersion slope of a non-zero dispersion-shifted fiber interconnects each component of the overall average dispersion versus wavelength. In Fig. 16, G540 represents the curve of an assembly in which the dispersion compensating fiber DCF5 of the fifth embodiment is connected to the dispersion-shifted fiber NZDSF of Document 2, and G640 represents the dispersion compensating fiber DCF6 of the sixth embodiment and the dispersion-shifted fiber NZDSF of Document 2. A curve of an assembly in which dispersion-shifted fibers NZDSF are connected to each other, and G740 represents a curve in which dispersion-compensating fiber DCF7 of the seventh embodiment and dispersion-shifted fibers NZDSF of Document 2 are connected to each other. In order to compensate the dispersion of the dispersion-shifted optical fiber NZDSF with a length of 80 km at a wavelength of 1550 nm, the dispersion-compensating optical fiber DCF5 of the fifth embodiment needs a length of 2.2 km, the dispersion-compensating optical fiber DCF6 of the sixth embodiment needs a length of 1.9 km, and the length of the dispersion-compensating optical fiber DCF6 of the seventh embodiment The dispersion compensation fiber DCF7 needs to be 1.7km in length.

In an assembly in which the dispersion compensating fiber DCF5 of the fifth embodiment and the dispersion shifting fiber NZDSF are interconnected, the total average dispersion has a deviation of 0.2 ps/nm/km or less in a band (C band) of 1535 nm to 1560 nm. In an assembly in which the dispersion compensating fiber DCF6 of the sixth embodiment and the dispersion shifting fiber NZDSF are interconnected, the average dispersion generally has 0.2 ps/nm/km or following deviations. Furthermore, in an assembly in which the dispersion compensating fiber DCF7 of the seventh embodiment and the dispersion shifting fiber NZDSF are interconnected, the average dispersion in one band (C and L bands) from 1535 nm to 1600 nm generally has 0.2 ps/nm/ km or less. Therefore, they are capable of optical transmission at a bit rate of 40Gb/s over a repeater distance of 400km.

As shown in Figure 8, when the dispersion compensation optical fiber DCF5 of the fifth embodiment with a length of 2.2km is wound with a bending diameter of 140mm to form a dispersion compensation module, the dispersion compensation amount at a wavelength of 1550nm is -640ps/nm, and the total The loss is 3.0dB (at a wavelength of 1550nm). When the dispersion compensating fiber DCF6 of the sixth embodiment with a length of 1.9km is wound to form a dispersion compensating module with a bending diameter of 140mm, the dispersion compensation amount at the wavelength 1550nm place is -640ps/nm, and the total loss is 2.7dB (wavelength at 1550nm). Furthermore, when the dispersion compensating fiber DCF7 of the seventh embodiment having a length of 1.7 km is wound with a bending diameter of 140 mm to constitute a dispersion compensating module, the amount of dispersion compensation at a wavelength of 1550 nm is -640 ps/nm, and the total loss is 2.5 dB (Wavelength 1550nm).

In addition, when the dispersion compensating fiber DCF5 of the fifth embodiment is wound with a bending diameter of 140mm to form a dispersion compensating module, the amount of dispersion compensation at a wavelength of 1550nm is -320ps/nm, and the total loss is 2.0dB (at a wavelength of 1550nm ). When the dispersion compensating fiber DCF6 of the sixth embodiment is wound with a bending diameter of 140mm to form a dispersion compensating module, the amount of dispersion compensation at a wavelength of 1550nm is -320ps/nm, and the total loss is 1.9dB (at a wavelength of 1550nm). In addition, when the dispersion compensation fiber DCF7 of the seventh embodiment is wound with a bending diameter of 140mm to form a dispersion compensation module, the amount of dispersion compensation at the wavelength of 1550nm is -320ps/nm, and the total loss is 1.7dB (at the wavelength of 1550nm ).

Therefore, each of the dispersion compensating fibers DCF5 to DCF7 can compensate the dispersion and the dispersion slope of the dispersion shifted fiber NZDSF with a short length and low loss in a wide band including a wavelength of 1550 nm.

comparative example

In order to compare the dispersion compensating optical fibers of each of the above-mentioned first to seventh embodiments, a dispersion compensating optical fiber of a comparative example will now be explained. 17A and 17B are views respectively showing the cross-sectional structure of a dispersion compensating optical fiber and its refractive index distribution according to a comparative example. The comparative example 200 includes a core region 210 extending along a predetermined axis, and a cladding region 220 for surrounding the outer edge of the core region 210 . The core region 210 has a refractive index _n1 and an outer diameter 2a. In addition, the cladding region 220 includes a first cladding layer 221 having a second refractive index n ₂ (<n ₁ ) and an outer diameter 2b. And the second cladding layer 222, used to surround the outer edge of the first cladding layer 221, has a third refractive index n ₃ (>n ₂ , <n ₁ ).

The refractive index distribution 250 shown in FIG. 17B represents the respective refractive indices at various parts on the line L2 in FIG. The refractive index of each part on the center line L2 of the second cladding layer 222 .

In the comparative example 200 of FIGS. 17A and 17B , with respect to the second cladding 222 serving as one reference region, the relative refractive index difference Δn ₁ of the core region 210 and the relative refractive index difference Δn ₂ of the first cladding 221 are given by the following The individual expressions give:

Δn ₁ =(n ₁ -n ₃ )/n ₃

Δn ₂ =(n ₂ −n ₃ )/n ₃

where _n1 is the refractive index of the core region 210, _n2 is the refractive index of the first cladding layer 221, and _n3 is the refractive index of the second cladding layer 222 used as a reference region. In this specification, the relative refractive index difference of each part is expressed by percentage, and the various parameters in the above expressions can be placed in a fixed order. Therefore, the relative refractive index difference of a glass region having a lower refractive index than the second cladding layer 222 (reference region) is represented by a negative value.

Here, in the comparative example 200, with respect to the refractive index n ₃ of the second cladding 222, the core region 210 has a relative refractive index difference Δn ₁ of 1.2%, and the first cladding 221 has a relative refractive index difference Δn of -0.36%. ₂ . In addition, the ratio Ra (=2a/2b) of the outer diameter 2a of the core region 210 to the outer diameter 2b of the first cladding layer 221 was 0.50.

Fig. 18 is a graph showing the relationship between the dispersion and the dispersion slope at a wavelength of 1550 nm of a dispersion compensating fiber of a comparative example. Shown here is the relationship between the dispersion D _DCF and the dispersion slope S _DCF in the comparative example when the outer diameter 2b of the first cladding layer 221 is changed. In the range where the dispersion is -40 ps/nm/km or less, this comparative example has unfavorable bending characteristics to be unusable. If the outer diameter 2c of the second cladding layer 222 varies greatly, the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) will vary greatly. For example, when the outer diameter 2b of the first cladding layer 221 is 10.0 μm, then the dispersion D _DCF is -28ps/nm/km (corresponding to the condition of point A in Figure 18), thus the dispersion slope S _DCF is -0.081ps/km nm ² /km. In addition, when the outer diameter 2b of the first cladding layer 221 is 9.8 μm, the dispersion D _DCF is -22 ps/nm/km (corresponding to the condition of point B in Figure 18 ), thus the dispersion slope S _DCF is -0.056 ps/km nm ² /km. If the outer diameter 2b varies by 2% from this value, the ratio (S _DCF /D _DCF ) will vary by up to 17%. Therefore, it is difficult to manufacture a dispersion compensating optical fiber having desired dispersion characteristics.

Compared with the dispersion-compensating optical fiber of the comparative example, the dispersion-compensating optical fiber according to the embodiment (including the dispersion-compensating optical fiber of the first to seventh embodiments) has excellent bending characteristics and can be used for the above-mentioned dispersion-40 ps/nm/km or within the following range. In addition, if the dispersion D _DCF is within a predetermined range, even when the outer diameter 2c of the second cladding varies, the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _DCF ) in the dispersion compensating fiber according to the present invention changes are also small. Therefore, it is easy to manufacture a dispersion compensating optical fiber according to the present invention having desired dispersion characteristics.

Industrial Applicability

As previously described in detail, the dispersion compensating optical fiber according to the present invention has a wavelength of 1550nm at -40ps/nm/km or below (preferably -100ps/nm/km to -40ps/nm/km or -250ps/nm/km) km to -120ps/nm/km), the ratio of the dispersion slope S _DCF to the dispersion D _DCF (S _DCF /D _{DCF )} of 0.005/nm or above (preferably 0.005/nm to 0.015/nm). Since the dispersion compensating fiber according to the present invention has such characteristics, it can compensate the dispersion and the dispersion slope of the dispersion shifted fiber with a short length in a wide band including a wavelength of 1550 nm.

Claims (24)

1. a dispersion compensating fiber has a core region of extending along a predetermined shaft, and around the outer peripheral cladding regions of described core region, wherein:

Described core region has first refractive index, and described cladding regions has: one first covering, around described core region outward flange and have second refractive index less than first refractive index; One second covering is around the outward flange of described first covering and have third reflect rate greater than second refractive index; And a triple clad, around the outward flange of described second covering and have fourth reflect rate less than the third reflect rate;

Described core region has more than or equal to 0.8% with respect to described triple clad but smaller or equal to 2.0% refractive index contrast;

Described first covering has-0.4% or following refractive index contrast with respect to described triple clad;

Described dispersion compensating fiber has following characteristics at wavelength 1550nm place:

More than or equal to-100ps/nm/km but smaller or equal to the chromatic dispersion of-40ps/nm/km; And

More than or equal to the chromatic dispersion gradient of 0.005/nm and the ratio of chromatic dispersion.

2. according to the dispersion compensating fiber of claim 1, wherein, the ratio of described chromatic dispersion gradient and chromatic dispersion is more than or equal to 0.005/nm but smaller or equal to 0.015/nm.

3. according to the dispersion compensating fiber of claim 1, wherein said dispersion compensating fiber has 16 μ m at wavelength 1550nm place ²Or above useful area.

4. according to the dispersion compensating fiber of claim 3, wherein said dispersion compensating fiber has 20 μ m at wavelength 1550nm place ²Or above useful area.

5. according to the dispersion compensating fiber of claim 1, but wherein said dispersion compensating fiber has 1.2 μ m or above 1.8 μ m or following cutoff wavelength.

6. according to the dispersion compensating fiber of claim 5, but wherein said dispersion compensating fiber has 1.4 μ m or above 1.8 μ m or following cutoff wavelength.

7. according to the dispersion compensating fiber of claim 1, wherein said dispersion compensating fiber has 0.5dB/km or following loss at wavelength 1550nm place.

8. according to the dispersion compensating fiber of claim 1, wherein said core region have more than or equal to 0.8% with respect to described triple clad but smaller or equal to 1.5% refractive index contrast.

9. according to the dispersion compensating fiber of claim 1, wherein when the external diameter of described second covering changes 2%, the described ratio of chromatic dispersion gradient and chromatic dispersion change 10% or below.

10. a dispersion compensating fiber has a core region of extending along a predetermined shaft, and around the outer peripheral cladding regions of described core region, wherein:

Described core region has first refractive index; And described cladding regions has: one first covering, around described core region outward flange and have second refractive index less than first refractive index, one second covering, around the outward flange of described first covering and have third reflect rate greater than second refractive index, and a triple clad, around the outward flange of described second covering and have fourth reflect rate less than the third reflect rate;

But described core region has 2.0% or above 3.0% or following refractive index contrast with respect to described triple clad;

Described first covering has-0.4% or following refractive index contrast with respect to described triple clad;

Described dispersion compensating fiber has following feature :-250ps/nm/km or still above-120ps/nm/km or following chromatic dispersion at wavelength 1550nm place; 0.005/nm or the ratio of above chromatic dispersion gradient and chromatic dispersion; And 10 μ m ²But or above 20 μ m ²Or following useful area.

11. according to the dispersion compensating fiber of claim 10, wherein the ratio of chromatic dispersion gradient and chromatic dispersion is 0.015/nm or following.

12. according to the dispersion compensating fiber of claim 10, useful area is positioned at (20-| chromatic dispersion |/25) or above still (23-| chromatic dispersion |/25) or following scope.

13. according to the dispersion compensating fiber of claim 10, wherein said dispersion compensating fiber has 1.0dB/km or following loss at wavelength 1550nm place.

14. according to the dispersion compensating fiber of claim 10, wherein when the external diameter of described second covering changes 2%, the described ratio of chromatic dispersion gradient and chromatic dispersion change 10% or below.

15. an optical transmission line comprises:

A kind of dispersion compensating fiber has a core region of extending along a predetermined shaft, and around the outer peripheral cladding regions of described core region, wherein:

Described core region has first refractive index, and described cladding regions has: one first covering, around described core region outward flange and have second refractive index less than first refractive index; One second covering is around the outward flange of described first covering and have third reflect rate greater than second refractive index; And a triple clad, around the outward flange of described second covering and have fourth reflect rate less than the third reflect rate;

Described core region has more than or equal to 0.8% with respect to described triple clad but smaller or equal to 2.0% refractive index contrast;

Described first covering has-0.4% or following refractive index contrast with respect to described triple clad;

Described dispersion compensating fiber has following characteristics at wavelength 1550nm place:

More than or equal to-100ps/nm/km but smaller or equal to the chromatic dispersion of-40ps/nm/km; And

More than or equal to the chromatic dispersion gradient of 0.005/nm and the ratio of chromatic dispersion;

Be connected to a dispersion shifted optical fiber of described dispersion compensating fiber, described dispersion shifted optical fiber has following feature at wavelength 1550nm place:

+ 2ps/nm/km or still above+10ps/nm/km or following chromatic dispersion; And

+ 0.04ps/nm ²/ km or still above+0.12ps/nm ²/ km or following chromatic dispersion gradient.

16. according to the optical transmission line of claim 15, but the deviation of the mean dispersion of wherein said overall optical transmission line in 1535nm or above 1560nm or a following wave band is 0.2ps/nm/km or following.

17. according to the optical transmission line of claim 16, but the deviation of the mean dispersion of wherein said overall optical transmission line in 1535nm or above 1600nm or a following wave band is 0.2ps/nm/km or following.

18. an optical transmission line comprises:

A kind of dispersion compensating fiber has a core region of extending along a predetermined shaft, and around the outer peripheral cladding regions of described core region, wherein:

Described core region has first refractive index; And described cladding regions has: one first covering, around described core region outward flange and have second refractive index less than first refractive index, one second covering, around the outward flange of described first covering and have third reflect rate greater than second refractive index, and a triple clad, around the outward flange of described second covering and have fourth reflect rate less than the third reflect rate;

But described core region has 2.0% or above 3.0% or following refractive index contrast with respect to described triple clad;

Described first covering has-0.4% or following refractive index contrast with respect to described triple clad;

Described dispersion compensating fiber has following feature :-250ps/nm/km or still above-120ps/nm/km or following chromatic dispersion at wavelength 1550nm place; 0.005/nm or the ratio of above chromatic dispersion gradient and chromatic dispersion; And 10 μ m ²But or above 20 μ m ²Or following useful area; And

Be connected to a dispersion shifted optical fiber of described dispersion compensating fiber, described dispersion shifted optical fiber has following feature at wavelength 1550nm place:

+ 2ps/nm/km or still above+10ps/nm/km or following chromatic dispersion; And

+ 0.04ps/nm ²/ km or still above+0.12ps/nm ²/ km or following chromatic dispersion gradient.

19. a dispersion compensation module comprises a kind of dispersion compensating fiber, its state is that described dispersion compensating fiber is wound to constitute a module, wherein as coil:

Described dispersion compensating fiber has a core region of extending along a predetermined shaft, and around the outer peripheral cladding regions of described core region, wherein:

Described core region has first refractive index, and described cladding regions has: one first covering, around described core region outward flange and have second refractive index less than first refractive index; One second covering is around the outward flange of described first covering and have third reflect rate greater than second refractive index; And a triple clad, around the outward flange of described second covering and have fourth reflect rate less than the third reflect rate;

Described core region has more than or equal to 0.8% with respect to described triple clad but smaller or equal to 2.0% refractive index contrast;

Described first covering has-0.4% or following refractive index contrast with respect to described triple clad;

Described dispersion compensating fiber has following characteristics at wavelength 1550nm place:

More than or equal to-100ps/nm/km but smaller or equal to the chromatic dispersion of-40ps/nm/km; And

More than or equal to the chromatic dispersion gradient of 0.005/nm and the ratio of chromatic dispersion.

20. according to the dispersion compensation module of claim 19, wherein the chromatic dispersion compensation quantity when wavelength 1550nm place be-during 640ps/nm, but described dispersion compensation module has 7dB or following total losses in 1535nm or above 1565nm or a following wave band.

21. according to the dispersion compensation module of claim 20, but wherein in 1535nm or above 1610nm or a following wave band total losses be 7dB or following.

22. according to the dispersion compensation module of claim 19, wherein the chromatic dispersion compensation quantity when wavelength 1550nm place be-during 320ps/nm, but described dispersion compensation module has 3dB or following total losses in 1535nm or above 1565nm or a following wave band.

23. according to the dispersion compensation module of claim 22, but wherein in 1535nm or above 1610nm or a following wave band total losses be 3dB or following.

24. a dispersion compensation module comprises a kind of dispersion compensating fiber, its state is that described dispersion compensating fiber is wound to constitute a module, wherein as coil:

Described dispersion compensating fiber has a core region of extending along a predetermined shaft, and around the outer peripheral cladding regions of described core region, wherein:

Described core region has first refractive index; And described cladding regions has: one first covering, around described core region outward flange and have second refractive index less than first refractive index, one second covering, around the outward flange of described first covering and have third reflect rate greater than second refractive index, and a triple clad, around the outward flange of described second covering and have fourth reflect rate less than the third reflect rate;

But described core region has 2.0% or above 3.0% or following refractive index contrast with respect to described triple clad;

Described first covering has-0.4% or following refractive index contrast with respect to described triple clad;

Described dispersion compensating fiber has following feature :-250ps/nm/km or still above-120ps/nm/km or following chromatic dispersion at wavelength 1550nm place; 0.005/nm or the ratio of above chromatic dispersion gradient and chromatic dispersion; And 10 μ m ²But or above 20 μ m ²Or following useful area.

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