JPH1039155A - Dispersion-compensated fiber and light transmission system including that - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the wavelength dispersion and dispersion slope of a whole transmission system applied in 1.55μm wavelength band. SOLUTION: The dispersion compensated fiber 100 is provided with at least a wavelength dispersion of -40ps/km/nm to 0ps/km/nm, and a dispersion slope of -0.5ps/km/nm<2> to -0.1ps/km/nm<2> for a light of 1.55μm wavelength band, and the wavelength dispersion and dispersion slope of the whole system containing the dispersion-compensated fiber 100 are improved in the 1.55μm wavelength band by cascade connecting the dispersion-compensated fiber 100 and a dispersion shift fiber 500 being a compensation object at a proper length ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion compensating fiber applied to an optical fiber transmission network which enables long-distance and large-capacity optical communication using a wavelength multiplexed signal light in a 1.55 .mu.m wavelength band, and a dispersion compensating fiber. The present invention relates to an optical transmission system including:

[0002]

2. Description of the Related Art Conventionally, research and development on large-capacity high-speed communication such as image communication using an optical fiber transmission line network and long-distance communication such as international communication have been actively conducted due to social needs due to the advent of an advanced information society. It has been done.

In an optical fiber transmission line network for realizing long-distance and large-capacity optical communication, first, the transmission line must be an optical fiber that allows only single-mode propagation. This is because in the case of multi-mode communication, mode dispersion (represented by dispersion due to the difference in group velocity for each propagation mode) inevitably occurs.

Therefore, a single-mode optical fiber that can be transmitted only in a single mode is first considered as a transmission line. However, although mode dispersion does not occur in a single mode optical fiber, material dispersion (dispersion due to the wavelength dependence of the refractive index inherent to the material of the optical fiber) and structural dispersion (wavelength dependence of the group velocity of the propagation mode). (Dispersion due to chromatic dispersion) limits the transmission capacity. That is, although the wavelength of the light output from the light source is singular, it has a strictly constant spectral width, so that an optical pulse having this spectral width is a single mode light having a predetermined chromatic dispersion characteristic. When propagating in the fiber, the width of the light pulse is widened and the pulse shape is broken. This chromatic dispersion is expressed in units (ps / km / nm) as a propagation delay time difference per unit spectral width (nm) and unit optical fiber length (km).

It is known that silica glass, which is generally used as a material for an optical fiber, has a material dispersion of zero around a wavelength of 1.26 to 1.29 μm. In addition, since the structural dispersion changes depending on the parameters of the optical fiber, when the parameters of the optical fiber are optimally designed, the material dispersion and the structural dispersion cancel each other around the wavelength of 1.3 to 1.32 μm, and the chromatic dispersion becomes zero. be able to. Therefore, if a single mode optical fiber is used, optical communication of a longer distance and a larger capacity can be performed in the vicinity of a wavelength of 1.3 μm as compared with a multimode optical fiber.
Actually, the communication distance is several hundred km and the communication capacity is several hundred Mbit.
/ Second optical communication.

However, the transmission loss of the optical fiber is the smallest in the 1.55 μm wavelength band.
It has been desired to perform optical communication using light in the 55 μm wavelength band. For this reason, a dispersion-shifted fiber has been developed in which the wavelength at which chromatic dispersion becomes zero (zero dispersion wavelength) is shifted to this wavelength band. Since the dispersion-shifted fiber cannot largely change the material dispersion, the zero-dispersion wavelength is set to around 1.55 μm by optimally designing the refractive index profile and changing the value of the structural dispersion. This dispersion-shifted fiber is made of erbium (E
r) Used in an optical transmission system having a long distance and a communication capacity of several Gbit / sec using a wavelength multiplexed signal light in a 1.55 μm wavelength band together with an added optical fiber amplifier.

On the other hand, a large number of single mode optical fibers have already been laid so far, and there is a need for performing optical communication in a 1.55 μm wavelength band using an existing single mode optical fiber transmission line network. There is. Therefore, 1.5
A dispersion compensating fiber having a negative chromatic dispersion and a negative dispersion slope is cascaded to a single-mode optical fiber having a positive chromatic dispersion in the 5 μm wavelength band, thereby canceling out the chromatic dispersion and the dispersion slope as the entire optical transmission line. Attempts have been made (for example, see Japanese Unexamined Patent Application Publication No.
No. 1620).

[0008] The dispersion slope is given by the slope of the chromatic dispersion graph.

[0009]

The above-mentioned dispersion-shifted fiber is designed so that its chromatic dispersion becomes zero at a predetermined wavelength around 1.55 μm. However, if the chromatic dispersion is not zero around the wavelength (zero dispersion wavelength) and the sign of the chromatic dispersion is positive, generally, the longer the wavelength, the greater the chromatic dispersion. In other words, the dispersion slope (the wavelength dependence of chromatic dispersion, expressed in units (ps /
km / nm ² ) is a positive sign. This is because wavelength division multiplexing (WDM: Wafer) for multiplexing signal light components having mutually different wavelengths in order to further increase the transmission capacity.
A problem arises in the case of communication using the “vehicle division multiplex” method. That is, of the wavelength multiplexed signal light (having a plurality of wavelengths) in the 1.55 μm wavelength band, the signal light component having a longer wavelength has a larger chromatic dispersion (positive value) and a signal light having a shorter wavelength. Since the chromatic dispersion tends to be smaller (negative value) (has a positive dispersion slope) with respect to the component, this limits the capacity of the WDM system to increase.

On the other hand, regarding research on dispersion flat optical fibers in which both the chromatic dispersion and the dispersion slope are substantially zero in the 1.55 μm wavelength band, for example, Kubo et al., “Characteristics of Double-Clad Low-Dispersion SM Fiber”, Proceedings of the 1990 IEICE Spring National Convention, C-374, and PK Bachmann et.al., "Dispersion-Flattened Si
ngle-Mode Fibers Prepared with PCVD: Performance,
Limitations, Design Optimization ", J. of Lightwave
Technol., Vol. LT-4, No. 2, pp. 858-863 (1986)). However, the dispersion flat fiber has not yet been put to practical use because its size and refractive index profile, such as the core diameter, need to be controlled very precisely and its production is difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the conventional optical fiber transmission line to be compensated and the dispersion compensating fiber according to the present invention are each made to have an appropriate length. By connecting them together,
Dispersion compensating fiber that improves the chromatic dispersion and dispersion slope of the entire optical transmission line in the 55 μm wavelength band (making the absolute values of chromatic dispersion and dispersion slope close to zero) and enables long-distance and large-capacity optical communication, and It is an object of the present invention to provide an optical transmission system including:

[0012]

The dispersion compensating fiber according to the present invention mainly has a zero dispersion wavelength of 1450-1650 n.
The dispersion-shifted fiber set in the range of m and the optical fiber transmission line including the dispersion-shifted fiber are to be compensated. Further preferably, the dispersion compensating fiber according to the present invention has a zero dispersion wavelength of 1450 to 1550 n.
The dispersion-shifted fiber set in the range of m and the optical fiber transmission line including the dispersion-shifted fiber are to be compensated. Each of these dispersion compensation targets has a positive dispersion slope.

Accordingly, the dispersion compensating fiber according to the present invention has a characteristic of -40 ps / km / nm or more and 0 ps / km / n as various characteristics with respect to light in the 1.55 μm wavelength band.
m, a dispersion slope of not less than -0.5 ps / km / nm ² and not more than -0.1 ps / km / nm ² , a transmission loss of not more than 0.5 dB / km and 0.7 ps ·
a polarization mode dispersion of less than km ^-1/2, a mode field diameter of more than 4.5 μm and less than 6.5 μm, a cutoff wavelength of more than 0.7 μm and less than 1.7 μm at a reference length of 2 m, and 20m diameter, less than 100dB / m
and a bending loss at m.

In this specification, 1.55 μm
The wavelength band means a band in a wavelength range of 1500 to 1600 nm.

When the dispersion compensating fiber and the optical fiber to be compensated (mainly, a dispersion-shifted fiber or a transmission system including the dispersion-shifted fiber) are optically connected at a predetermined length ratio, the dispersion compensating fiber has a length of 1.55 μm. It is possible to improve the chromatic dispersion and dispersion slope of the entire transmission line in the wavelength band. Furthermore, these characteristics, as well as transmission loss, polarization mode dispersion, mode field diameter,
From the conditions of the cutoff wavelength (cutoff wavelength at a reference length of 2 m) and the bending loss (bending loss at a diameter of 20 mm), long-distance and large-capacity optical communication becomes possible.

In the dispersion compensating fiber according to the present invention, the chromatic dispersion of the light in the 1.55 μm wavelength band is -20 ps / km / nm or more and -5 ps / km / nm.
nm and the dispersion slope is -0.4 ps / km /
More preferably, it is not less than nm ² and not more than -0.13 ps / km / nm ² . As described above, by setting the chromatic dispersion and the dispersion slope, the optical transmission system including the dispersion compensating fiber (the zero dispersion wavelength becomes 1450 to 1400).
The whole (including the dispersion-shifted fiber set in the range of 650 nm, preferably in the range of 1450 to 1550 nm) can be more suitably compensated (the absolute value of the entire chromatic dispersion and dispersion slope can be made closer to zero).

In order to obtain the above characteristics, the dispersion compensating fiber according to the present invention comprises at least a glass region having a predetermined refractive index and a core region having an outer diameter of not less than 3.5 μm and not more than 6.0 μm. An inner cladding region provided on the outer periphery of the core region and having a lower refractive index than the core region; and a refraction provided on the outer periphery of the inner cladding region and higher than the inner cladding region and lower than the core region. A single-mode optical fiber having silica glass as a main component and having an outer cladding region having a refractive index. In particular, the dispersion compensating fiber has a ratio of the outer diameter of the core region to the outer diameter of the inner cladding region of 0.3.
And the relative refractive index difference between the outer cladding region and the portion having the maximum refractive index in the core region is 0.6% or more and 1.4% or less, and the outer cladding is The relative refractive index difference between the region and the portion having the minimum refractive index in the inner cladding region is characterized by being 0.25% or more and 0.65% or less.

Further, when the dispersion compensating fiber has a triple clad structure, the dispersion compensating fiber has a refractive index higher than the outer cladding and lower than the core region between the inner cladding region and the outer cladding region. And an intermediate cladding region having The relative refractive index difference between the portion having the maximum refractive index in the intermediate cladding region and the outer cladding region is 0.2% or more and 0.5% or less.

In the dispersion compensating fiber according to the present invention having the above-mentioned structure, the germanium element is added to the core region, and the fluorine element is not added to the inner cladding region. It is preferable to obtain a sufficient relative refractive index difference with the concentration. In addition, a configuration in which elemental fluorine is added to the outer cladding region can also be realized.

Further, the dispersion compensating fiber according to the present invention constitutes an optical transmission system together with another optical fiber (object of compensation) which is optically connected to the dispersion compensating fiber and forms a part of an optical transmission line. (See FIG. 1). An optical transmission system including the dispersion compensating fiber has an optical transmission path of -0.02 ps / k with respect to light in a wavelength band of 1.5 μm.
It is preferable to have a dispersion slope of not less than m / nm ² and not more than 0.05 ps / km / nm ^{2. In} such an optical transmission system, long-distance and large-capacity optical transmission is possible. When realizing optical communication using multi-wavelength light, long-distance and large-capacity optical communication becomes possible.

The optical fiber transmission line to be dispersion-compensated, which constitutes the optical transmission line of the optical transmission system together with the dispersion compensating fiber, has a zero dispersion wavelength of 1560 nm.
Preferably, it is a dispersion shifted fiber shifted as follows. When the compensation target is a dispersion-shifted fiber having a zero-dispersion wavelength of 1.56 μm or less, the chromatic dispersion and the chromatic dispersion slope of the dispersion-shifted fiber are easily compensated by the dispersion compensation fiber according to the present invention.

In addition, as described above, the optical transmission system including the dispersion compensating fiber and the dispersion-shifted fiber to be compensated may further include an optical fiber amplifier forming a part of an optical transmission line. The optical fiber amplifier includes an amplification optical fiber having an erbium element added to a core region thereof, and an excitation light source for outputting excitation light for exciting the erbium element in the amplification optical fiber to the amplification optical fiber. And at least an optical coupler for optically coupling the pumping light source and the amplification optical fiber. The length of the amplification optical fiber inserted into the optical transmission system is compared with the length of the dispersion-shifted fiber or the entire optical transmission line including the dispersion-shifted fiber, which is the compensation target of the dispersion-compensating fiber. Therefore, since it is very short, the contribution to the chromatic dispersion and dispersion slope to be compensated for as a whole optical transmission line can be neglected.

On the other hand, the dispersion compensating fiber according to the present invention may have a configuration in which an erbium element is added to the core region. Thus, the dispersion compensating fiber containing the erbium element can function as an amplification optical fiber.

Therefore, the optical transmission system including the dispersion compensating fiber in which the erbium element is added to the core region includes a dispersion compensating fiber according to the present invention and an optical transmission line optically connected to the dispersion compensating fiber. Another optical fiber constituting a part (compensation target), an excitation light source for outputting excitation light for exciting the erbium element in the dispersion compensation fiber to the dispersion compensation fiber, and the excitation light source and the excitation light source. An optical coupler for optically coupling with the dispersion compensating fiber. With this configuration, the optical transmission system including the dispersion compensating fiber, as an entire optical transmission path,
For light in the 1.5 μm wavelength band, -0.02 ps / km /
It has a dispersion slope of at least nm ² and at most 0.05 ps / km / nm ² . In such an optical transmission system, long-distance, large-capacity, low-loss optical communication becomes possible.

In the optical transmission system including the optical fiber amplifier (having the dispersion compensating fiber according to the present invention), the object of the dispersion compensation is that the zero dispersion wavelength is 1
Preferably, the fiber is a dispersion shifted fiber shifted to 560 nm or less.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a dispersion compensating fiber according to the present invention and an optical transmission system including the same will be described with reference to FIGS.
This will be described with reference to FIG. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

The dispersion compensating fiber according to the present invention comprises:
It has the following characteristics in the 55 μm wavelength band. That is, the chromatic dispersion is in the range of -40 to 0 ps / km / nm, and the dispersion slope is -0.5 to -0.1 ps / km / n.
m ² , transmission loss is 0.5 dB / km or less, polarization mode dispersion (PMD) is 0.7 ps · km ^−1/2 or less, and mode field diameter (MFD) is 4.5 to 6.5 μm. The cut-off wavelength is in the range of 0.7 to 1.7 μm, and the bending loss at a diameter of 20 mm is 100 dB / m or less.

In the case of optical transmission in the 1.55 μm wavelength band, a cutoff wavelength of 1.55 μm or less, which is shorter than the signal light wavelength, is generally selected with a reference length of 2 m (measurement method according to CCITT-G.650). You. With a short length of 2 m, which is a standard for the general evaluation of the cutoff wavelength, in the case of the dispersion-shifted fiber, not only the fundamental mode but also higher-order modes of the transmission light may propagate (for example, with a reference length of 2 m). When the cut-off wavelength is 1.7 μm). However, since the higher-order mode has a higher attenuation factor in propagation in the dispersion-shifted fiber than the fundamental mode, a propagation length of several km is sufficiently smaller than the fundamental mode.
Therefore, when the propagation distance ranges from several hundred to several thousand km as in the case of a submarine communication cable, the problem due to the higher-order mode does not occur. The bending loss is 20 m in diameter.
It is the increase in transmission loss of the dispersion compensating fiber measured while it is wrapped around a m mandrel.
And in this specification, the 1.55 μm wavelength band is a band in the range of 1500 to 1600 nm.

As will be described later, the dispersion compensating fiber according to the present invention includes another optical fiber (for example,
It compensates not only the chromatic dispersion of the single mode optical fiber, the dispersion shift fiber, and the entire optical fiber transmission line including these fibers, but also the dispersion slope. Especially,
It is suitable for compensating for chromatic dispersion and dispersion slope of a dispersion shifted fiber. Further, chromatic dispersion is -20 to -5p
s / km / nm and the dispersion slope is −
It is more preferable to be in the range of 0.4 to -0.13 ps / km / nm ² in order to compensate for the chromatic dispersion and dispersion slope of the dispersion-shifted fiber.

Next, the configuration of the optical transmission system including the dispersion compensating fiber according to the present invention will be described with reference to FIGS.

FIG. 1 shows a dispersion compensating fiber 100 according to the present invention and a dispersion-shifting fiber 500 which is the main compensation target.
FIG. 1 is a diagram illustrating a configuration of an optical transmission system in which the optical transmission system is optically connected to the optical transmission system. In this optical transmission system, one end (incident end) of the dispersion compensating fiber 100 is connected to the optical fiber transmission line 10.
(Single-mode optical fiber) and optically connected to the transmitter TX, and the other end (outgoing end) is optically connected to one end (incident end) of the dispersion shift fiber 500. Further, the other end (outgoing end) of the dispersion shift fiber 500 is optically connected to the receiver RX via the optical fiber transmission line 10 (single mode optical fiber). In FIG. 1, the dispersion compensating fiber 100 is
Although arranged on the upstream side of the dispersion-shifted fiber 500, it may be arranged on the downstream side of the dispersion-shifted fiber 500. Further, the optical transmission line of the optical transmission system shown in FIG. 1 may be an optical transmission line network capable of two-way communication.

FIG. 2 shows an optical transmission system including the dispersion compensating fiber according to the present invention, in which an optical fiber amplifier 600 is arranged in the optical transmission line. In particular, the amplification optical fiber 610 of the optical fiber amplifier 600
(At least the erbium element is added to the core region) constitutes a part of the transmission line of the optical transmission system.

In the optical transmission line shown in FIG. 2, an optical fiber whose one end (incident end) is optically connected to the transmitter TX via the optical fiber transmission line 10 (single mode optical fiber) according to the present invention. A configuration similar to that of the optical fiber transmission line having the structure shown in FIG. 1 in which the dispersion compensating fiber 100 and the dispersion shift fiber 500 are cascaded can be used. On the other hand, the optical fiber amplifier 60 optically connected to the other end (outgoing end) of the optical fiber transmission line 700
The optical isolator 800 is disposed between the optical fiber amplifier 600 and one end (incident end) of the optical fiber amplifier 600. Excitation light for exciting the erbium element in the amplification optical fiber 610 of the optical fiber amplifier 600 propagates through the optical transmission line. Is prevented from doing so. The other end (output end) of the optical fiber amplifier 600 is optically connected to the receiver RX via the optical fiber transmission line 10 (single mode optical fiber). The positions of the optical fiber transmission line 700 and the optical fiber amplifier 600 are not particularly limited, and the optical transmission line in the optical transmission system may have a configuration capable of bidirectional optical communication.

As described above, the optical fiber amplifier 600 arranged in the optical transmission line of the optical transmission system includes an amplification optical fiber 610 having at least a core region doped with an erbium element, and an amplification optical fiber 610 in the amplification optical fiber 610. The excitation light for exciting the erbium element is supplied to the amplification optical fiber 610.
And an optical coupler 620 for optically coupling the pumping light source 640 and the amplifying optical fiber 610. In addition, 630 in FIG. 2 is a non-reflection terminal. The length of the amplification optical fiber 610 of the optical fiber amplifier 600 is sufficiently shorter than the length of the entire optical transmission line so that the contribution of chromatic dispersion and dispersion slope to the entire optical transmission line can be ignored.

Further, in the optical transmission system shown in FIG. 2, the amplifying optical fiber 610 of the optical fiber amplifier 600 can be constituted by the dispersion compensating fiber 100 according to the present invention. That is, by adding erbium to the core region of the dispersion compensating fiber 100 according to the present invention, the dispersion compensating fiber 100
Functions as an amplification optical fiber 610. In this configuration, the optical fiber transmission line 700 includes only the dispersion shift fiber 500 excluding the dispersion compensation fiber 100.

Next, compensation of chromatic dispersion and dispersion slope of the dispersion compensating fiber according to the present invention will be described. FIG. 3 is a graph for explaining chromatic dispersion compensation and dispersion slope compensation by the dispersion compensating fiber according to the present invention. In this graph, the horizontal axis is the wavelength of the signal light (unit is nm), and the vertical axis is the chromatic dispersion (unit is ps / km).
/ Nm)).

In the graph, the curve represented by the code DCF is
5 is a chromatic dispersion characteristic of the dispersion compensating fiber according to the present invention (hereinafter, the dispersion compensating fiber is indicated by DCF). Note that, as described above, the dispersion compensating fiber DCF according to the present invention has a chromatic dispersion of −1.55 μm in the wavelength band.
40~0ps / km / nm range, and the dispersion slope is in the range of ^{-0.5~-0.1ps / km / nm 2} .

In the graph, a curve represented by the symbol DSF-1 is a chromatic dispersion characteristic of the dispersion-shifted fiber (hereinafter, this dispersion-shifted fiber is represented by DSF-1). This dispersion-shifted fiber DSF-1 has an appropriately designed structural dispersion, has no chromatic dispersion near a wavelength of 1.5 μm, and has a positive dispersion slope in a 1.55 μm wavelength band. This dispersion-shifted fiber DSF-1
For example, at a wavelength of 1.55 μm, the chromatic dispersion is 3
ps / km / nm and the dispersion slope is 0.065p
s / km / nm ² .

An optical transmission line in which the dispersion compensating fiber DCF and the dispersion shifting fiber DSF-1 according to the present invention are connected in cascade at an appropriate length ratio. "DCF + DSF-
1 "), the overall chromatic dispersion is substantially zero and the overall dispersion slope is -0.
It is almost flat within the range of 02 to +0.05 ps / km / nm ² . As described above, the chromatic dispersion and the dispersion slope of the entire optical transmission line are respectively related to the dispersion compensating fiber
The absolute value of one of the CF and the dispersion-shifted fiber DSF-1 is smaller than the chromatic dispersion and the dispersion slope. That is, the dispersion-shifted fiber DSF-
1, both the chromatic dispersion and the dispersion slope are 1.55 μm
In the wavelength band, the dispersion compensation fiber DCF effectively compensates.

The dispersion compensating fiber D according to the present invention
When the CF and the dispersion-shifted fiber DSF-1 are connected, the transmission loss and the polarization mode dispersion (P
MD) does not cause any problem when performing long-distance and large-capacity optical communication. Further, the mode field diameter (MFD), the cutoff wavelength and the bending loss are respectively the dispersion compensation fiber DC according to the present invention.
F and the above-mentioned dispersion-shifted fiber DSF-1 are to be evaluated independently. However, even in an optical transmission line in which both are cascaded, no problem occurs when performing long-distance and large-capacity optical communication. Absent. Therefore, WDM
Even in communication by the system, chromatic dispersion is improved for each signal light component in the 1.55 μm wavelength band, and there is no problem in performing optical communication with other characteristic values. And large capacity optical communication becomes possible.

On the other hand, in the graph, the code DSF-2
The curve represented by represents the chromatic dispersion characteristic of the dispersion-shifted fiber such that the chromatic dispersion becomes zero around the wavelength of 1.6 μm (hereinafter, this dispersion-shifted fiber is referred to as DSF-2).
). An optical transmission line in which the dispersion-shifted fiber DSF-2 and the dispersion compensating fiber DCF according to the present invention are cascaded (the chromatic dispersion characteristic of the entire optical transmission line is represented by a curve represented by "DCF + DSF-2" in the graph). Indicated by
In the figure, in the 1.55 μm wavelength band, the overall chromatic dispersion slope is substantially flat, but the overall chromatic dispersion is a negative value and its absolute value is further increased.

(First Embodiment) FIG. 4 is a view showing a sectional structure and a refractive index profile of a first embodiment (having a double clad structure) of a dispersion compensating fiber according to the present invention.

As shown in FIG. 4, a dispersion compensating fiber 100a having a double clad structure (first embodiment)
Is a single mode optical fiber mainly composed of quartz glass, a core region 110 having a predetermined refractive index,
A glass region provided on the outer periphery of the core region 110, the inner cladding region 111 having a lower refractive index than the core region 110;
And an outer cladding region 112 having a refractive index higher than the inner cladding region 111 and lower than the core region 110.

The outer diameter 2b of the inner cladding region 111
Ratio of the outer diameter 2a of the core region 110 to Ra (= 2a /
2b) is 0.3 or more and 0.5 or less, and the outer diameter of the core region is 3.5 μm or more and 6.0 μm or less. The relative refractive index difference Δ ⁺ between the outer cladding region 112 and the portion having the maximum refractive index in the core region 110 is 0.6% or more and 1.4% or less. The relative refractive index difference Δ ⁻ from the portion having the minimum refractive index is 0.25% or more and 0.65%
It is as follows.

The refractive index profile 200 shown in FIG.
The horizontal axis of a corresponds to each position on the line L1 in the cross section of the dispersion compensating fiber 100a (the plane perpendicular to the traveling direction of the propagating signal light). Further, in the refractive index profile 200a, the region 210 is a refractive index (n _core ) at each portion on the line L1 of the core region 110, and the region 220 is a refractive index (n at each portion on the line L1 of the inner cladding 111). _clad1 ) and the region 230 correspond to the refractive index (n _clad2 ) at each portion of the outer cladding region 112 on the line L1. In this embodiment, the refractive index profile in the radial direction of the core region 110 is a graded index type, and the refractive index of the inner cladding region 111 is lower than that of the other glass regions. The dent A (depr) is formed in the refractive index profile 200a of the dispersion compensating fiber 100a.
ession) is formed. In particular, the refractive index profile provided with such a depression A is defined as a depressed cladding type profile.
profile).

In this embodiment, the relative refractive index difference Δ is defined as follows.

Δ ⁺ = (n _core −n _clad2 ) / n _clad2 Δ ⁻ = (n _clad2 −n _clad1 ) / n _clad2 n _core : maximum refractive index of the core region n _clad1 : minimum refractive index of the inner cladding region n _clad2 : Refractive index of outer cladding region Therefore, each parameter of the first embodiment (double cladding structure) is set as follows.

[0048] ^{Δ + = 0.6 ~1.4% ... (} 1) Δ - = 0.25~0.65% ... (2) 2a = 3.5 ~6.0 μm ... (3) Ra = 0 0.3 to 0.5 (4) In this specification, the relative refractive index difference between each glass region is:
It is displayed as a percentage.

In the case of an optical fiber mainly composed of quartz glass, the relative refractive index difference as shown in the above conditions (1) and (2) is, for example, germanium element (Ge) which is a refractive index increasing material. And the inner cladding region 111 to which elemental fluorine (F) as a refractive index lowering material is added. Further, the outer cladding region 112 may also contain elemental fluorine. The dispersion compensating fiber 100a of the first embodiment can be easily obtained by, for example, a VAD method (Vapour-phase Axial Deposition). In addition, since the allowable range of the above parameters is relatively wide, manufacturing is easy in this respect as well.

(Second Embodiment) FIG. 5 is a view showing a sectional structure and a refractive index profile of a second embodiment (having a triple clad structure) of a dispersion compensating fiber according to the present invention.

As shown in FIG. 5, a dispersion compensating fiber 100b having a triple clad structure (second embodiment).
Is a single mode optical fiber mainly composed of quartz glass, a core region 120 having a predetermined refractive index,
A glass region provided on the outer periphery of the core region 120, the inner cladding region 121 having a lower refractive index than the core region 120, and a glass region provided on the outer periphery of the inner cladding region 121, and An intermediate cladding region 122 having a higher refractive index than the core region 120; and an outer cladding region provided on the outer periphery of the intermediate cladding region 122 and having a lower refractive index than the intermediate cladding region 122 and a higher refractive index than the inner cladding region 121. And a cladding region 123.

The outer diameter 2b of the inner cladding region 121
Ratio of the outer diameter 2a of the core region 120 to Ra (= 2a /
2b) and the outer diameter of the core region 120 are in the range of the first embodiment described above (Ra = 0.3 to 0.5; 2a = 3.5 μm).
(Approximately 6.0 μm). And the outer diameter of the core region is 3.5 μm or more and 6.
0 μm or less. The relative refractive index difference Δ ⁺ between the outer cladding region 123 and the portion having the maximum refractive index in the core region 120 is 0.6% or more and 1.4% or less, and the minimum refractive index in the outer cladding region 123 and the inner cladding region 121 is smaller. The relative refractive index difference Δ ⁻ from the portion having the refractive index is 0.25% or more and 0.65% or less, which is similar to those of the first embodiment described above.

The refractive index profile 300 shown in FIG.
The horizontal axis of a corresponds to each position on the line L2 in the cross section of the dispersion compensating fiber 100b (the plane perpendicular to the traveling direction of the propagating signal light). Further, in the refractive index profile 300a, the region 310 is a refractive index (n _core ) at each portion on the line L2 of the core region 120, and the region 320 is a refractive index (n at each portion on the line L2 of the inner cladding 121). _clad1 ), area 33
0 corresponds to the refractive index (n _clad2 ) at each position on the line L2 of the intermediate cladding region 122, and the region 340 corresponds to the refractive index (n _clad3 ) at each position on the line L2 of the outer cladding region 123. . And in this embodiment, the refractive index profile in the radial direction of the core region 120 is:
It is a graded index type, in which the refractive index of the inner cladding region 121 is lower than the refractive index of the other glass region, and a concave A (depression) is formed in the refractive index profile 300a of the dispersion compensating fiber 100b. I have. In particular, a refractive index profile provided with such a depression A is referred to as a depressed cladding type profile.

In this embodiment, the relative refractive index difference Δ is defined as follows.

[0055] ^{_{Δ + = (n core -n clad3}} ) / n clad3 Δ - = (n clad3 -n clad1) / n clad3 Δ r = (n clad2 -n clad3) / n clad3 n core: maximum refractive core region Index n _clad1 : minimum refractive index of the inner cladding region n _clad2 : maximum refractive index of the intermediate cladding region n _clad3 : refractive index of the outer cladding region Accordingly, in the second embodiment (triple cladding structure), the relative refractive index difference delta _r between sites and the outer cladding region 123 having a maximum refractive index is given as follows.

[0056] _{Δ r = 0.2 ~0.5% ... (} 5) In addition, other relative refractive index difference delta ^+, delta ^- in the same range as the first embodiment described above (double cladding structure) The range of the outer diameter 2a and the outer diameter ratio Ra of the core region 120 is wider than the range of the first embodiment. In this specification, the relative refractive index difference between the respective glass regions is expressed in percentage.

The refractive index profile 300a as shown in FIG. 5 shows that the core region 120 and the intermediate cladding region 122 to which the germanium element as the refractive index increasing material is added.
This can be realized by the inner cladding region 121 to which elemental fluorine as a refractive index lowering material is added. Further, the outer cladding region 123 may also contain elemental fluorine.

(Third Embodiment) FIG. 6 is a view showing a sectional structure and a refractive index profile of a third embodiment (having a triple clad structure) of a dispersion compensating fiber according to the present invention. The third embodiment is different from the second embodiment in that the refractive index profile in the radial direction of the intermediate cladding region is of a graded index type (the second embodiment). The refractive index profile of the intermediate cladding region in the radial direction is a step index type).

As shown in FIG. 6, a dispersion compensating fiber 100c having a triple clad structure (third embodiment).
Is a single mode optical fiber mainly composed of quartz glass, and has a predetermined refractive index and a glass region provided on the outer periphery of the core region 130 as in the second embodiment described above. An inner cladding region 131 having a lower refractive index than the core region 130, and an intermediate cladding region 132 provided on the outer periphery of the inner cladding region 131 and having a higher refractive index than the inner cladding region 131. An outer cladding region 133 is provided on the outer periphery of the intermediate cladding region 132 and has a lower refractive index than the intermediate cladding region 132 and a higher refractive index than the inner cladding region 131.

The refractive index profile 400 shown in FIG.
The horizontal axis of a corresponds to each position on the line L3 in the cross section of the dispersion compensating fiber 100c (the plane perpendicular to the traveling direction of the propagating signal light). Further, in the refractive index profile 400a, the region 410 is a refractive index (n _core ) at each portion on the line L3 of the core region 130, and the region 420 is a refractive index (n) at each portion on the line L3 of the inner cladding 131. _clad1 ), area 43
0 corresponds to the refractive index (n _clad2 ) at each position on the line L3 of the intermediate cladding region 122, and the region 440 corresponds to the refractive index (n _clad3 ) at each position on the line L3 of the outer cladding region 133. . And in this embodiment, the refractive index profile in the radial direction of the core region 130 is:
It is a graded index type, in which the refractive index of the inner cladding region 131 is lower than the refractive index of the other glass region, and a concave A (depression) is formed in the refractive index profile 400a of the dispersion compensating fiber 100c. I have. In particular, a refractive index profile provided with such a depression A is referred to as a depressed cladding type profile.

Incidentally, the relative refractive index difference Δ ⁺ between each glass region,
Delta ^-, and delta _r, as well as other parameters Ra, for definitions and figures 2a is similar to the second embodiment described above.

The refractive index profiles 200a to 400a shown in FIGS. 4 to 6 are examples of the refractive index profile of the dispersion compensating fiber according to the present invention. The present invention is not limited to these, and may have a refractive index profile having a shape shown in FIGS. 7 to 9, for example.

That is, FIG. 7 is a diagram showing a modification of the refractive index profile 200a (first embodiment) of FIG.
The refractive index profile shown at the upper left in the figure is the refractive index profile 200a of FIG. Refractive index profile 2
Reference numeral 00b denotes a refractive index drop in the center of the core region 110 in the refractive index profile 200a of FIG.
It is said that this is likely to occur when manufacturing by the eposition method. Also, the refractive index profile 200c is:
In the refractive index profile 200a of FIG.
Is a step index type in which the refractive index in the radial direction is constant.

Further, the refractive index profiles 200d-2
00f is the refractive index profile 20 described above, respectively.
0a to 200c, the inner cladding region 11
The refractive index in the radial direction at 1 is not constant, but gradually decreases from the center toward the periphery. The refractive index profiles 200g to 200i correspond to the above-described refractive index profiles 200a to 200c, respectively, and the refractive index in the radial direction in the inner cladding region 111 is not constant, but is from the center to the peripheral portion. Once decreased and increased again. These inner cladding regions 111
Is easy to occur in actual manufacturing.

These refractive index profiles 200b-20
The dispersion compensating fiber having 0i has the same characteristics as the dispersion compensating fiber having the refractive index profile 200a shown in FIG.

FIG. 8 is a view showing a modified example of the refractive index profile 300a (second embodiment) shown in FIG. The upper left refractive index profile in the drawing is the refractive index profile 300a in FIG. In the refractive index profile 300b, the refractive index drops at the center of the core region 120 in the refractive index profile 300a of FIG. The refractive index profile 300c is shown in FIG.
In the refractive index profile 300a of the core region 12
It is of a step index type with a constant refractive index in the radial direction at 0.

Also, the refractive index profiles 300d-30
0f is the refractive index profile 300 described above, respectively.
a to 300c, the inner cladding region 121
Is not constant, but gradually decreases from the center toward the periphery. The refractive index profiles 300g to 300i correspond to the above-described refractive index profiles 300a to 300c, respectively.
The refractive index in the radial direction in the inner cladding region 121 is not constant, but once decreases from the center toward the peripheral portion and increases again.

These refractive index profiles 300b-30
The dispersion compensating fiber having 0i has the same characteristics as the dispersion compensating fiber having the refractive index profile 300a shown in FIG.

FIG. 9 is a diagram showing a modification of the refractive index profile 400a (third embodiment) of FIG. The upper left refractive index profile in the figure is the same as the refractive index profile 400a in FIG. Refractive index profile 40
0b is the refractive index profile 400a of FIG.
This is due to a drop in the refractive index at the center of the core region 130. The refractive index profile 400c is a step index type in which the refractive index in the radial direction in the core region 130 is constant in the refractive index profile 400a of FIG.

Further, the refractive index profiles 400d-40
0f is the refractive index profile 400 described above, respectively.
a to 400c, the inner cladding region 131
Is not constant, but gradually decreases from the center toward the periphery. The refractive index profiles 400g to 400i correspond to the above-described refractive index profiles 400a to 400c, respectively.
The refractive index in the radial direction in the inner cladding region 131 is not constant, but once decreases from the center toward the peripheral portion and increases again.

These refractive index profiles 400b-40
The dispersion compensating fiber having 0i has the same characteristics as the dispersion compensating fiber having the refractive index profile 400a shown in FIG.

Next, a description will be given of experimental results obtained by simulating various characteristics of the dispersion compensating fiber having the refractive index profile 200a shown in FIG. FIG. 10 is a table showing simulation results. Four parameters Δ ⁺ , Δ ⁻ , 2a and Ra (= 2a / 2b)
, 11 conditions were set, and the characteristic value of the optical fiber was obtained. Fibers (samples) prepared corresponding to the respective conditions are No. 1 to No. 11 is represented.

For light having a wavelength of 1.55 μm, the sample (optical fiber) No. 1 to No. 11 for each, chromatic dispersion (shown by Disp ＠ 1550 in the table, the unit is ps / km / nm), dispersion slope (shown by Slope ＠ 1550 in the table, and the unit is ps / km / n)
m ² ), the dispersion-shifted fiber that is the main compensation target and each of the optical fibers No. 1 to No. 11, the dispersion slope (indicated by Total Slope ＠ 1550 in the table, the unit is ps / km / nm ² ), and the transmission loss (indicated by Loss ＠ 1550 in the table) of the entire optical transmission line configured by cascade-connecting The unit is dB / km), the polarization mode dispersion (indicated by PMD in the table, the unit is ps · km ^-1/2 ), the cutoff wavelength at the reference length of 2 m (indicated by Cut-Off in the table,
The unit is μm) and the bending loss at a diameter of 20 mm (Ben in the table)
d Loss, and the unit is dB / m).

The dispersion-shifted fiber to be compensated assumed in this simulation has a wavelength of 1.50 μm.
m, the chromatic dispersion is zero, and the wavelength is 1.55 μm.
m, the chromatic dispersion and the dispersion slope are each 3p
s / km / nm and 0.065 ps / km / nm ² . In addition, the above-mentioned No. 1 to No. The dispersion slope of the entire optical transmission line composed of the dispersion compensating fiber No. 11 and the dispersion shift fiber is represented by the dispersion shift fiber and the fiber no. 1 to No. 11 is cascade-connected at a predetermined length ratio, and the value is when the total chromatic dispersion becomes zero at 1.55 μm.

As can be seen from the table of FIG.
o. 7 and No. 7 It is not preferable to apply 8 to a transmission system including the above compensation target (dispersion shift fiber having the above-described characteristics). In addition, the fiber No. In the case of 9, since the outer diameter 2a of the core region does not satisfy the condition (3), it cannot be realized as the dispersion compensating fiber according to the present invention.

However, other samples (fiber No. 1)
-No. 6, fiber No. 10 and fiber no.
Since 11) satisfies all of the conditions (1) to (4), the dispersion compensating fiber according to the present invention can be realized for these samples. Furthermore, the dispersion slope of the entire optical transmission line when any one of these samples and the above-mentioned dispersion-shifted fiber are cascaded is −0.02 to −0.02.
It is 0.05 ps / km / nm ² , which is almost flat. Therefore, when optical communication is performed with wavelength-division multiplexed signal light (including a plurality of wavelengths) in the 1.55 μm wavelength band by the WDM method, the dispersion slope is sufficiently reduced in the wavelength range of each signal light component. Optical communication of the capacity becomes possible.

In particular, the fiber No. 1 to No. 3
Has a wavelength dispersion in the range of -20 to -5 ps / km / nm and a dispersion slope of -0.4 to -0.13 ps / km.
/ Nm ² , and the dispersion slope of the entire optical transmission line when cascaded with the dispersion-shifted fiber is 0.01 to 0.02 ps / km / nm ² . WDM is more suitable for compensating chromatic dispersion and dispersion slope of each signal light component.
It can be more suitably used for communication by a system.

In addition, the inventors have proposed a dispersion compensating fiber (3) having a refractive index profile 300a shown in FIG.
Similar simulations were performed for various characteristics of the double clad structure. FIG. 11 is a table showing the simulation results. Five parameters Δ ^+, Δ ^-,
Delta _r, 2a and Ra (= 2a / 2b) to set conditions for triplicate for to determine the characteristic values of the optical fiber. Fibers (samples) prepared for each condition are N
o. 12-No. It is represented as 14.

The other parameters are the same as in the case of the double clad structure described above. The assumed dispersion-shifted fiber (compensation target) is the same as the above-described fiber.

As can be seen from the table of FIG. 11, each sample (optical fiber) No. 12-No. No. 14 has a chromatic dispersion in the range of −30 to −5 ps / km / nm and a dispersion slope in the range of −0.39 to −0.06 ps / km / nm ^2. When connected, the dispersion slope of the entire optical transmission line is 0.03 ps /
Since it is km / nm ² , it is more suitable for compensating the chromatic dispersion and dispersion slope of each signal light component generated in the dispersion-shifted fiber, and can be more suitably used for communication by the WDM method.

The dispersion compensating fiber 1 according to the present invention
2, the dispersion compensating fiber 100 and the dispersion shift fiber 500 are used in cascade connection as shown in FIG. 2, and for example, an optical fiber amplifier 600 is further connected in cascade. A different configuration is also possible. Further, the dispersion compensating fiber 1 according to the present invention
00, dispersion shift fiber 500 (dispersion compensation fiber 1
00 and the optical fiber amplifier 700) and the optical fiber amplifier 700 may be cascaded in any order. As the amplification optical fiber 610 of the optical fiber amplifier 600, a rare earth element (for example, Er element) is used.
-Doped optical fiber (EDF: Erbium Doped Fiber
r) Optical fiber amplifier (EDFA: Erbium Do)
If a ped fiber amplifier is used, it is suitable for optically amplifying the wavelength multiplexed signal light in the 1.55 μm wavelength band. The length of each of the dispersion compensating fiber 100 and the dispersion shift fiber 500, and the arrangement interval and the amplification factor of the optical fiber amplifier 600 are optimized based on the chromatic dispersion and the transmission loss of the dispersion compensation fiber 100 and the dispersion shift fiber 500, respectively. Is determined. With the above configuration, the chromatic dispersion and the dispersion slope of the entire optical transmission line in the optical transmission system are effectively improved (close to zero).
In addition to the above, it can be expected that transmission loss can be sufficiently reduced. Therefore, even in such a configuration, large-capacity signal light can be transmitted through a long-distance optical transmission line with low loss.

The Er element may be added to the core region of the dispersion compensating fiber itself according to the present invention. in this case,
The inversion distribution is formed by propagating the 1.48 μm wavelength pumping light output from the pumping light source 640 to the dispersion compensating fiber via the optical coupler 620, and the signal light propagating in the dispersion compensating fiber is amplified. . That is, the dispersion compensating fiber not only compensates for chromatic dispersion and dispersion slope but also functions as an amplification optical fiber. Therefore, this Er-doped dispersion compensating fiber is used as an amplifying optical fiber, a pumping light source 640 for outputting pumping light, an optical coupler for guiding pumping light to the dispersion compensating fiber, and an optical coupler only in the signal light propagation direction. (Signal light,
Optical isolator 80 that transmits excitation light and spontaneous emission light)
0 and a filter or the like that blocks excitation light and spontaneous emission light and transmits only signal light,
00 may be configured. In this case, the chromatic dispersion and the dispersion slope of the dispersion-shifted fiber are not only compensated by the dispersion-compensating fiber, but the transmission loss generated in the dispersion-shifted fiber can be offset by the optical amplification effect in the dispersion-compensating fiber.

The signal light may be amplified using Raman amplification. In other words, the pump light having a wavelength different from the wavelength of the signal light but close to the wavelength value and having a sufficiently large light amount is propagated through the optical coupler 620 to the dispersion compensating fiber, so that the signal light is emitted by the Raman effect. Is amplified. Also in this case, the chromatic dispersion and the dispersion slope of the dispersion-shifted fiber are not only compensated for by the dispersion-compensating fiber, but the transmission loss generated in the dispersion-shifted fiber can be offset by the optical amplification action in the dispersion-compensating fiber.

[0084]

As described above, the characteristics of the dispersion compensating fiber according to the present invention in the 1.55 μm wavelength band are as follows: chromatic dispersion is -40 ps / km / nm or more and 0 ps / km.
/ Nm or less, dispersion slope is -0.5 ps / km / nm
² or more and -0.1ps / km / nm ² or less, the transmission loss is 0.5 dB / miles or less, the polarization mode dispersion 0.7ps
Km- ^{1 / 2} or less, mode field diameter of 4.5 μm or more and 6.5 μm or less, cut-off wavelength of 0.7 μm or more and 1.7 μm or less, and bending loss at a diameter of 20 mm of 100 dB / m or less. (Especially, chromatic dispersion is -20.
ps / km / nm or more and is at -5ps / km / nm or less and a dispersion slope is -0.4ps / km / nm ² or more and -0.13ps / km / nm ² or less).

If this dispersion compensating fiber and another optical fiber (particularly, a dispersion-shifted fiber or an optical transmission line including the dispersion-shifted fiber) are optically connected at a predetermined length ratio, optical transmission in a 1.55 μm wavelength band is achieved. The chromatic dispersion of the entire path can be effectively reduced, and the overall dispersion slope is also improved. From these characteristics and the conditions of the transmission loss, the polarization mode dispersion, the mode field diameter, the cutoff wavelength, and the bending loss, long-distance and large-capacity optical communication becomes possible. In particular, in the optical communication based on the WDM method, the wavelength dispersion of the entire optical transmission line is improved for the wavelength of each component of the wavelength multiplexed signal light used, so that longer distance and larger capacity optical communication is possible. .

The dispersion compensating fiber according to the present invention may have any of a double clad structure and a triple clad structure. In each structure, a predetermined parameter condition (dimension ratio, ratio between glass regions) is used. (Difference in refractive index). Further, in the case of a dispersion compensating fiber mainly composed of quartz glass, a specific relative refractive index difference can be obtained by selectively adding germanium or fluorine to each glass region. Since the allowable range of the parameters is wide, the manufacturing is easy. Even if the parameters vary in the manufacturing, if the parameters are within the allowable range, there is no problem in performing long-distance and large-capacity optical communication. There is no.

Further, a configuration in which an erbium element is added to the core region of the dispersion compensating fiber can be realized. That is, by propagating the pumping light through the dispersion compensating fiber, not only the chromatic dispersion and the dispersion slope can be compensated, but also the signal light can be amplified.

Also, the optical transmission system according to the present invention
The dispersion compensating fiber according to the present invention is optically connected to another optical fiber (particularly, a dispersion shift fiber).
In the 55 μm wavelength band, the dispersion slope of the entire optical transmission line is −0.02 ps / km / nm ² or more and 0.05 ps /
km / nm ² or less. Therefore, in this optical transmission system, long-distance and large-capacity optical communication is possible. Particularly, when optical communication is performed using a plurality of wavelengths in the WDM system, longer-distance and large-capacity optical communication is possible. Becomes Furthermore, if the dispersion compensating fiber according to the present invention to which the erbium element is added is used, the optical transmission line can perform not only long distance and large capacity but also low loss optical communication.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical transmission system including a dispersion-shifted fiber provided with a dispersion compensation fiber according to the present invention.

FIG. 2 is a diagram showing a configuration of an optical transmission system including an optical fiber amplifier provided with a dispersion compensating fiber according to the present invention.

FIG. 3 is a graph for explaining chromatic dispersion compensation and dispersion slope compensation by the dispersion compensating fiber according to the present invention.

FIG. 4 is a diagram showing a cross-sectional structure and a refractive index profile of a first embodiment of the dispersion compensating fiber according to the present invention.

FIG. 5 is a diagram showing a sectional structure and a refractive index profile of a second embodiment of the dispersion compensating fiber according to the present invention.

FIG. 6 is a diagram showing a cross-sectional structure and a refractive index profile of a third embodiment of the dispersion compensating fiber according to the present invention.

FIG. 7 is a diagram showing various application examples of the refractive index profile (FIG. 4) applicable to the first embodiment of the dispersion compensating fiber according to the present invention.

FIG. 8 is a diagram showing various application examples of the refractive index profile (FIG. 5) applicable to the second embodiment of the dispersion compensating fiber according to the present invention.

FIG. 9 is a diagram showing various application examples of the refractive index profile (FIG. 6) applicable to the third embodiment of the dispersion compensating fiber according to the present invention.

FIG. 10 is a table showing experimental results of a dispersion compensating fiber having a double clad structure.

FIG. 11 is a table showing experimental results of a dispersion compensating fiber having a triple clad structure.

[Explanation of symbols]

100, 100a, 100b, 100c: dispersion compensating fiber; 110, 120, 130: core region, 111, 1
21, 131 ... inner cladding region, 122, 132 ... intermediate cladding region, 112, 123, 133 ... outer cladding region, 500 ... optical fiber transmission line (dispersion shift fiber), 600 ... optical fiber amplifier, 610 ... amplification optical fiber (Or dispersion compensating fiber containing erbium element), 700 ... optical fiber transmission line (dispersion shift fiber only, or dispersion shift fiber and dispersion compensating fiber).

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tomonori Kashiwada 1-chome Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Hirofumi Otani 1-chome Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Ki Kogyo Co., Ltd.

Claims (11)

[Claims] 1. As various characteristics for light in a 1.55 μm wavelength band, chromatic dispersion is -40 ps / km / nm or more and 0 ps / k.
m / nm or less, and the dispersion slope is -0.5 ps / km / nm ² or more and-
0.1 ps / km / nm ² or less, transmission loss is 0.5 dB / km or less, polarization mode dispersion is 0.7 ps · km ^-1/2 or less, and mode field diameter is 4.5 μm or more And a cut-off wavelength at a reference length of 2 m is not less than 0.7 μm and not more than 1.7 μm, and a bending loss at a diameter of 20 mm is not more than 100 dB / m. Compensating fiber. 2. Various characteristics for light in a 1.55 μm wavelength band include a wavelength dispersion of −20 ps / km / nm or more and −5 ps / km.
km / nm or less, and the dispersion slope is −0.4 ps / km / nm ² or more and −
0.13 ps / km / nm ² or less, transmission loss is 0.5 dB / km or less, polarization mode dispersion is 0.7 ps · km ^-1/2 or less, and mode field diameter is 4.5 μm or more And a cut-off wavelength at a reference length of 2 m is not less than 0.7 μm and not more than 1.7 μm, and a bending loss at a diameter of 20 mm is not more than 100 dB / m. Compensating fiber. 3. A glass region containing quartz glass as a main component and having at least a predetermined refractive index and having a refractive index of 3.5 μm
A core region having an outer diameter of not less than 6.0 μm and a glass region provided on the outer periphery of the core region and having a lower refractive index than the core region, An inner cladding region having an outer diameter of not less than twice and not more than 3.3 times, and glass provided on an outer periphery of the inner cladding region and having a refractive index higher than the inner cladding region and lower than the core region. A region having a relative refractive index difference of 0.6% or more and 1.4% or less with respect to a region having a maximum refractive index in the core region, and a region having a minimum refractive index in the inner cladding region. The relative refractive index difference is 0.2
3. The dispersion compensating fiber according to claim 1, further comprising an outer cladding region of 5% or more and 0.65% or less. 4. A glass region provided between the inner cladding region and the outer cladding region, further comprising an intermediate cladding region having a refractive index higher than the outer cladding region and lower than the core region. 4. The dispersion according to claim 3, wherein the relative refractive index difference between the portion having the maximum refractive index in the intermediate cladding region and the outer cladding region is 0.2% or more and 0.5% or less. Compensating fiber. 5. The element according to claim 3, wherein a germanium element is added to the core region, and a fluorine element is added to the inner cladding region.
The dispersion compensating fiber as described in the above. 6. The dispersion compensation fiber according to claim 3, wherein an erbium element is added to the core region. 7. The dispersion compensating fiber according to claim 5, wherein the outer cladding region is doped with a fluorine element. 8. The transmission line as a whole has a wavelength of -0.02 ps / km / nm ² or more and a light intensity of 1.5 μm wavelength band.
An optical transmission system having a dispersion slope of 05 ps / km / nm ² or less, wherein at least the dispersion compensating fiber according to claim 1 or 2, and the transmission line optically connected to the dispersion compensating fiber. An optical transmission system comprising: an optical fiber transmission line that forms a part of the optical transmission system. 9. A part of the transmission path,
At least, an amplification optical fiber in which an erbium element is added to a core region, an excitation light source for outputting excitation light for exciting the erbium element in the amplification optical fiber to the amplification optical fiber, and An optical fiber amplifier comprising an excitation light source and an optical coupler for optically coupling the amplification optical fiber,
The optical transmission system according to claim 8, further comprising: 10. An optical transmission system having a dispersion slope of not less than -0.02 ps / km / nm ² and not more than 0.05 ps / km / nm ² for 1.5 μm wavelength band light as a whole transmission line. And at least, the dispersion compensating fiber according to claim 6, an optical fiber transmission line optically connected to the dispersion compensating fiber and constituting a part of the transmission line, and an erbium element in the dispersion compensating fiber. A pump light source for outputting pump light to be pumped to the dispersion compensating fiber; and an optical coupler for optically coupling the pump light source and the dispersion compensating fiber. Optical transmission system. 11. The optical transmission system according to claim 8, wherein the optical fiber transmission line is a dispersion-shifted fiber whose zero dispersion wavelength is shifted to 1560 nm or less.