JP2001311848A - Optical fiber and optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber or the like permitting a large capacity and long distance transmission using multiple wavelength signal light of a signal light wavelength band covering a 1.31 μm-1.58 μm wavelength band. SOLUTION: The optical fiber relating to this invention has a spectrum spread of >=-20 ps/nm/km and <=-3 ps/nm/km (more preferably, >=-12 ps/nm/ km and <=-4 ps/nm/km) in the full range of a 1.30 μm-1.60 μm wavelength band. Moreover, it is more preferable to be >=-20 ps/nm/km and <=-3 ps/nm/ km in the full range of a 1.25 μm-1.65 μm wavelength band broader than the above wavelength band. Since the spectrum spread is of a value within the above numeric values in the broader signal light wavelength band covering a 1.30 μm-1.60 μm wavelength band, both of waveform deterioration of the signal light due to a non-linear optical phenomenon and that due to accumulated spectrum spread are controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wavelength division multiplexing (WDM) for multiplexing multi-wavelength signal light for optical transmission.
The present invention relates to a division multiplexing transmission system and an optical fiber used as an optical transmission line in the optical transmission system.

[0002]

2. Description of the Related Art A WDM transmission system using an optical fiber network is capable of transmitting a large amount of information, a transmitter for transmitting multi-wavelength signal lights, an optical fiber for transmitting these signal lights, It is configured to include a receiver for receiving these signal lights, an optical amplifier for optically amplifying the signal lights, and the like. In such WDM transmission systems, attempts have been made to increase the width of the wavelength band of signal light in order to increase the transmission capacity.

Further, nonlinear optical phenomena (particularly four-wave mixing)
It is important that the absolute value of the chromatic dispersion of the optical fiber in the signal light wavelength band is not too small in order to suppress the waveform deterioration of the signal light due to the above. On the other hand, in order to suppress the waveform deterioration of the signal light due to the accumulated chromatic dispersion, it is also important that the absolute value of the chromatic dispersion of the optical fiber is not too large in the signal light wavelength band.

The wavelength band where the gain of the optical fiber amplifier has a gain is about 1.53 μm to 1.61 μm, whereas the zero dispersion wavelength of the conventional dispersion-shifted optical fiber is in the range of 1.56 μm to 1.60 μm. It is in. Therefore, in an optical transmission system including such an optical fiber amplifier and a dispersion-shifted optical fiber, even in a wavelength band where the optical fiber amplifier has a gain, a wavelength near the zero dispersion wavelength of the dispersion-shifted optical fiber is used. Since nonlinear optical phenomena are likely to occur, long-distance transmission cannot be performed using signal light of this wavelength.

An optical fiber intended to solve such a problem is disclosed in International Publication WO99 / 30194. This optical fiber has a zero dispersion wavelength of 1.
61 μm or more and 1.67 μm or less, and a wavelength of 1.55 μm
The chromatic dispersion slope at m is 0.15 ps / nm ² /
km or less. The optical fiber has a wavelength band of 1.53 μm to 1.6 in which the optical fiber amplifier has a gain.
At 1 μm, the absolute value of chromatic dispersion becomes an appropriate value, and both the deterioration of the signal light waveform due to the nonlinear optical phenomenon and the deterioration of the signal light waveform due to the accumulated chromatic dispersion can be suppressed. It is. The chromatic dispersion slope of the optical fiber shown as an example in this publication is 0.07.
ps / nm ² /km~0.15ps/nm is a ² / km.

[0006]

In order to further increase the transmission capacity in the WDM transmission system, it is desired to further increase the width of the wavelength band of the signal light. However, the optical fiber disclosed in the above publication has a wavelength of 1.55.
It is intended to be used in a wavelength band of 1.53 μm to 1.61 μm including a μm band (C band) and a wavelength band of 1.58 μm (L band).
No consideration is given to use in the 45 μm band (S band). That is, the optical fiber disclosed in the above publication is
At a wavelength of 1.31 μm, chromatic dispersion is −20 ps / n.
m / km and the absolute value of the chromatic dispersion is large, so that the signal light waveform is likely to be degraded due to the accumulated chromatic dispersion. Therefore, long-distance transmission should be performed using the 1.31 μm band signal light. Can not.

The present invention has been made to solve the above problems, and has a wavelength band of 1.31 μm and a wavelength of 1.45 μm.
Optical fiber capable of large-capacity long-distance transmission using multi-wavelength signal light in a wide signal light wavelength band including the m band, the wavelength 1.55 μm band, and the wavelength 1.58 μm band, and light including the optical fiber It is an object to provide a transmission system.

[0008]

SUMMARY OF THE INVENTION An optical fiber according to the present invention has a chromatic dispersion of -20 ps / nm / km or more and -3 ps / m over the entire wavelength band of 1.30 .mu.m to 1.60 .mu.m.
nm / km or less. More preferably, the chromatic dispersion is −12 ps / nm / km or more in the entire wavelength band of 1.30 μm to 1.60 μm.
It is characterized by being not more than ps / nm / km. Also,
More preferably, a wavelength band 1.2 wider than the above-mentioned wavelength band.
The wavelength dispersion is −2 in the entire range of 5 μm to 1.65 μm.
It is not less than 0 ps / nm / km and not more than -3 ps / nm / km. More preferably, the chromatic dispersion is -16 ps / nm / km or more and -4 ps / nm / km or less in the whole wavelength range of 1.25 μm to 1.65 μm.

According to this optical fiber, the wavelength is 1.31 μm.
Wide signal light wavelength band (1.3 band including m band, 1.45 μm band, 1.55 μm band and 1.58 μm band)
0 μm to 1.60 μm, more preferably 1.25 μm to
(1.65 μm), the chromatic dispersion is a value within the above numerical range, so that both the deterioration of the signal light waveform due to the nonlinear optical phenomenon and the deterioration of the signal light waveform due to the accumulated chromatic dispersion are suppressed. Therefore, if this optical fiber is used as an optical transmission line, large-capacity long-distance transmission is possible using multi-wavelength signal light in this wide signal light wavelength band. The absolute value of the chromatic dispersion of the optical fiber according to the present invention is 20 ps / n.
m / km or less means that although the sign is different,
The chromatic dispersion at a wavelength of 1.55 μm of a single mode optical fiber specified in ITU G.654 is about the same or less, and there is no problem in transmitting signal light.

The optical fiber according to the present invention is characterized in that the effective area at a wavelength of 1.55 μm is 40 μm ² or more. In this case, since the effective area is sufficiently large, the waveform deterioration of the signal light due to the nonlinear optical phenomenon is further suppressed, which is suitable for performing long-distance transmission. The optical fiber according to the present invention has an effective area of 40.
The value of “μm ² or more” is equal to or more than the effective area of the conventional dispersion-shifted optical fiber.

The optical fiber according to the present invention has a loss increase of 0.1 dB due to an OH group at a wavelength of 1.38 μm.
/ Km or less. In this case, since a wavelength near the wavelength of 1.38 μm can be used as the signal light wavelength, a larger capacity transmission is possible.

Further, the optical fiber according to the present invention comprises: (1) a central core region including the optical axis center and having a first refractive index;
(2) a second core region surrounding the central core region and having a second refractive index less than the first refractive index; and (3) the second core region.
A third core region surrounding the core region and having a third refractive index larger than the second refractive index; and (4) a cladding region surrounding the third core region and having a fourth refractive index smaller than the third refractive index. And characterized in that: More preferably, the cladding region includes (4a) an inner cladding region having a refractive index smaller than the third refractive index, and (4b) an outer cladding region having a refractive index larger than the refractive index of the inner cladding. It is characterized by. More preferably, the relative refractive index difference of the central core region is 0.4% or more and 0.7% or less based on the refractive index of the outermost layer of the cladding region. In any of these cases, an optical fiber having the above wavelength dispersion range in the above wavelength range can be realized.

The optical transmission system according to the present invention transmits (1) signal light of each wavelength within a wavelength band of 1.30 μm to 1.60 μm (more preferably, 1.25 μm to 1.65 μm). A plurality of transmitters; (2) an optical fiber according to the present invention for transmitting the signal light transmitted from each of the plurality of transmitters; and (3) receiving the signal light arriving after transmitting the optical fiber. And a receiver that performs the operation. Since this optical transmission system uses the optical fiber according to the present invention as an optical transmission line, the wavelength is 1.3.
A wide signal light wavelength band including the 1 μm band, the wavelength 1.45 μm band, the wavelength 1.55 μm band, and the wavelength 1.58 μm band (1.30 μm to 1.60 μm, more preferably 1.25 μm)
(μm-1.65 μm), both the signal light waveform deterioration due to the nonlinear optical phenomenon and the signal light waveform deterioration due to the accumulated chromatic dispersion are suppressed, and the multi-wavelength signal light in this wide signal light wavelength band is suppressed. , Large-capacity long-distance transmission is possible.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a diagram for explaining the chromatic dispersion characteristics of the optical fiber according to the present embodiment. The optical fiber according to the present embodiment has a chromatic dispersion of −20 ps / nm / km or more and −3 ps / in the entire wavelength band of 1.30 μm to 1.60 μm (hereinafter referred to as “signal light wavelength band A”).
nm / km or less. This signal light wavelength band A has a wavelength of 1.31 μm, a wavelength of 1.45 μm, and a wavelength of 1.55 μm.
m band and a 1.58 μm wavelength band. Further, the chromatic dispersion is −20 in the entire range of the signal light wavelength band A.
Since it is not less than ps / nm / km and not more than -3 ps / nm / km, both the deterioration of the signal light waveform due to the nonlinear optical phenomenon and the deterioration of the signal light waveform due to the accumulated chromatic dispersion are suppressed. Therefore, if this optical fiber is used as an optical transmission line, large-capacity long-distance transmission is possible using multi-wavelength signal light in this wide signal light wavelength band A.

More preferably, the optical fiber according to the present embodiment has a chromatic dispersion of -12 ps / nm / km or more and -4 ps / nm / km over the entire range of the signal light wavelength band A. In this case, the chromatic dispersion is -12 ps / nm /
km or more, the waveform deterioration of the signal light due to the accumulated chromatic dispersion is further suppressed, and the chromatic dispersion becomes -4 ps / nm.
By being equal to or less than / km, the waveform deterioration of the signal light due to the nonlinear optical phenomenon is further suppressed. Therefore, long-distance transmission with a larger capacity is possible using the signal light of multiple wavelengths in the signal light wavelength band A.

More preferably, the optical fiber according to the present embodiment has a wavelength band of 1.25 μm to 1.65 μm wider than the signal light wavelength band A (hereinafter, referred to as “signal light wavelength band B”). Is -20 in the entire range of
It is not less than ps / nm / km and not more than -3 ps / nm / km. In this case, even larger capacity long-distance transmission is possible using multi-wavelength signal light in the signal light wavelength band B wider than the signal light wavelength band A.

More preferably, the optical fiber according to the present embodiment has a chromatic dispersion of -16 ps / nm / km or more and -4 ps / nm / km in the entire range of the signal light wavelength band B. In this case, the chromatic dispersion is -16 ps / nm /
km or more, the waveform deterioration of the signal light due to the accumulated chromatic dispersion is further suppressed, and the chromatic dispersion becomes -4 ps / nm.
By being equal to or less than / km, the waveform deterioration of the signal light due to the nonlinear optical phenomenon is further suppressed. Therefore, long-distance transmission with a larger capacity is possible using multi-wavelength signal light in the signal light wavelength band B.

It is preferable that the optical fiber according to the present embodiment has an effective sectional area of 40 μm ² or more at a wavelength of 1.55 μm. In this case, since the effective area is sufficiently large, the waveform deterioration of the signal light due to the nonlinear optical phenomenon is further suppressed, which is suitable for performing long-distance transmission.

In the optical fiber according to this embodiment, the loss increase due to the OH group at the wavelength of 1.38 μm is 0.1 d.
It is preferably at most B / km. In this case, since a wavelength near the wavelength of 1.38 μm can be used as the signal light wavelength, a larger capacity transmission is possible.

Next, a refractive index profile suitable for realizing the optical fiber according to the present embodiment will be described.
FIG. 2 is a diagram illustrating a preferred example of the refractive index profile of the optical fiber according to the present embodiment. The refractive index profile shown in this figure includes a center core region (refractive index n ₁ , outer diameter 2a), a second core region (refractive index n ₂ ,
It has an outer diameter 2b), a third core region (refractive index n ₃ , outer diameter 2c) and a cladding region (refractive index n ₄ ). The magnitude relation of each refractive index is n ₁ > n ₂ , and n ₂ <n ₃ ,
n ₃ > n ₄ . More preferably, the relative refractive index difference Δ ₁ of the central core region with reference to the refractive index of the outermost layer of the cladding region.
Is 0.4% or more and 0.7% or less. An optical fiber having such a refractive index profile is based on quartz glass, for example, by adding GeO ₂ to each of the central core region and the third core region, and / or
This can be realized by adding an F element to each of the second core region and the cladding region.

FIG. 3 is a view for explaining a preferred example of the refractive index profile of the optical fiber according to this embodiment. The refractive index profile shown in this figure is, in order from the optical axis center,
Central core region (refractive index n ₁ , outer diameter 2a), second core region (refractive index n ₂ , outer diameter 2b), third core region (refractive index n ₃ ,
Outer diameter 2c), inner cladding region (refractive index n ₄ , outer diameter 2
d) and an outer cladding region (refractive index n ₅ ). The magnitude relationship between the refractive indices is n ₁ > n ₂ , and n ₂ <n ₃
And n ₃ > n ₄ and n ₄ <n ₅ . More preferably, the relative refractive index difference delta ₁ of the central core region refractive index of the outermost layer of the outer cladding region as a reference of 0.4% to 0.7%
It is as follows. An optical fiber having such a refractive index profile is based on quartz glass, for example, by adding GeO ₂ to each of a central core region and a third core region, and / or by adding a second core region and an inner cladding region. By adding the F element to each,
Can be realized.

Next, four specific examples of the optical fiber according to this embodiment will be described. Each of the optical fibers of the embodiments has the refractive index profile shown in FIG.
FIG. 4 is a table summarizing the specifications and characteristics of the optical fibers of the four embodiments. FIG. 5 is a graph showing the wavelength dispersion characteristics of the optical fibers of the four examples.

The specifications of the optical fiber of the first embodiment are as follows. The outer diameter 2a of the central core region is 5.7 μm, the outer diameter 2b of the second core region is 14.7 μm, the outer diameter 2c of the third core region is 22.6 μm, and the outer diameter of the inner cladding region. 2d is 45.2 μm. Furthermore, 0.50% is the refractive index difference delta ₁ of the central core region, the refractive index difference delta ₂ of the second core region is -0.20%, the refractive index difference delta ₃ of the third core region 0 was .25%, the refractive index difference delta ₄ of the inner cladding region is -0.20%.

The characteristics of the optical fiber of the first embodiment are as follows. The wavelength dispersion characteristics are as follows.
It is −11.98 ps / nm / km at 25 μm, −9.22 ps / nm / km at 1.31 μm, −8.07 ps / nm / km at 1.55 μm,
It is -3.81 ps / nm / km at a wavelength of 1.65 μm. At a wavelength of 1.55 μm, the chromatic dispersion slope is 0.016 ps / nm ² / km, and the effective area is 5 μm.
2.1 μm ² and a mode field diameter of 7.95 μm
m, and the bending loss at a bending diameter of 32 mmΦ is 2.4 dB.
/ Turn. The zero dispersion wavelength is 1.694 μm,
The cable cutoff wavelength is 1.29 μm. Also,
Loss increase Δα _{1.38 due} to OH group at wavelength 1.38 μm
Is 0.01 dB / km.

The specifications of the optical fiber of the second embodiment are as follows. The outer diameter 2a of the central core region is 5.5 μm, the outer diameter 2b of the second core region is 14.5 μm, the outer diameter 2c of the third core region is 21.3 μm, and the outer diameter of the inner cladding region. 2d is 42.6 μm. Furthermore, a 0.55% a refractive index difference delta ₁ of the central core region, the refractive index difference delta ₂ of the second core region is -0.20%, the refractive index difference delta ₃ of the third core region 0 was .30%, the refractive index difference delta ₄ of the inner cladding region is -0.20%.

The characteristics of the optical fiber of the second embodiment are as follows. The wavelength dispersion characteristics are as follows.
It is −11.82 ps / nm / km at 25 μm, −8.81 ps / nm / km at a wavelength of 1.31 μm, −6.28 ps / nm / km at a wavelength of 1.55 μm,
It is -3.32 ps / nm / km at a wavelength of 1.65 μm. At a wavelength of 1.55 μm, the chromatic dispersion slope is 0.011 ps / nm ² / km, and the effective area is 4
6.6 μm ² and mode field diameter 7.44 μm
m and the bending loss at a bending diameter of 32 mmΦ is 0.2 dB.
/ Turn. The zero dispersion wavelength is 1.700 μm,
The cable cutoff wavelength is 1.31 μm. Also,
Loss increase Δα _{1.38 due} to OH group at wavelength 1.38 μm
Is 0.06 dB / km.

The specifications of the optical fiber of the third embodiment are as follows. The outer diameter 2a of the central core region is 5.2 μm, the outer diameter 2b of the second core region is 15.1 μm, the outer diameter 2c of the third core region is 21.6 μm, and the outer diameter of the inner cladding region. 2d is 43.2 μm. Furthermore, 0.57% is the refractive index difference delta ₁ of the central core region, the refractive index difference delta ₂ of the second core region is -0.20%, the refractive index difference delta ₃ of the third core region 0 was .29%, the refractive index difference delta ₄ of the inner cladding region is -0.20%.

The characteristics of the optical fiber according to the third embodiment are as follows. The wavelength dispersion characteristics are as follows.
It is −12.60 ps / nm / km at 25 μm, −9.42 ps / nm / km at a wavelength of 1.31 μm, −7.99 ps / nm / km at a wavelength of 1.55 μm,
It is −7.10 ps / nm / km at a wavelength of 1.65 μm. At a wavelength of 1.55 μm, the chromatic dispersion slope is −
0.008 ps / nm ² / km, and the effective area is 4
2.1 μm ² and a mode field diameter of 7.15 μm
m and the bending loss at a bending diameter of 32 mmΦ is 1.5 dB.
/ Turn. The zero dispersion wavelength is 1.757 μm,
The cable cutoff wavelength is 1.22 μm. Also,
Loss increase Δα _{1.38 due} to OH group at wavelength 1.38 μm
Is 0.03 dB / km.

The specifications of the optical fiber of the fourth embodiment are as follows. The outer diameter 2a of the central core region is 5.0 μm, the outer diameter 2b of the second core region is 14.3 μm, the outer diameter 2c of the third core region is 21.6 μm, and the outer diameter of the inner cladding region. 2d is 43.2 μm. Furthermore, 0.59% is the refractive index difference delta ₁ of the central core region, the refractive index difference delta ₂ of the second core region is -0.15%, the refractive index difference delta ₃ of the third core region 0 was .27%, the refractive index difference delta ₄ of the inner cladding region is -0.15%.

The optical fiber of the fourth embodiment is
The characteristics are as follows. The wavelength dispersion characteristics are as follows.
It is -16.40 ps / nm / km at 25 μm, and the wavelength is
-14.30 ps / nm / km at 1.31 μm,
-14.70 ps / nm / km at a wavelength of 1.55 μm
At -8.60 ps / nm / km at a wavelength of 1.65 μm
is there. At a wavelength of 1.55 μm, the chromatic dispersion slope is
0.027ps / nm ^Two/ Km, and the effective area is 4
9.3 μm^TwoAnd the mode field diameter is 7.75 μm.
m, and the bending loss at a bending diameter of 32 mmΦ is 0.8 dB.
/ Turn. The zero-dispersion wavelength is 1.724 μm,
The cable cutoff wavelength is 1.33 μm. Also,
Loss increase Δα due to OH group at a wavelength of 1.38 μm_1.38
Is 0.03 dB / km.

Each of the optical fibers of the first to fourth embodiments described above has a chromatic dispersion of −20 ps / nm in the entire range of the signal light wavelength band A (wavelength band 1.30 μm to 1.60 μm). / Km or more-3ps / nm / k
m or less, and the signal light wavelength band B (wavelength band 1.
Even in the entire range of 25 μm to 1.65 μm), the chromatic dispersion is −20 ps / nm / km or more and −3 ps / nm / km.
It is as follows. Each of the optical fibers of the first to fourth embodiments has an effective sectional area of 40 μm ² or more at a wavelength of 1.55 μm and an O ² at a wavelength of 1.38 μm.
The loss increase due to the H group is 0.1 dB / km or less. First
Each of the optical fibers of the third to third embodiments has a chromatic dispersion of −12 ps / nm / k in the entire range of the signal light wavelength band A.
m or more and -4 ps / nm / km or less. The optical fiber of the third embodiment has a chromatic dispersion of -16 ps / nm / km or more and -4 ps / in the entire range of the signal light wavelength band B.
nm / km or less.

Next, a first embodiment of an optical transmission system using the optical fiber according to the present embodiment as an optical transmission line will be described. FIG. 6 is a schematic configuration diagram of the optical transmission system 1 according to the first embodiment. This optical transmission system 1
Is an optical fiber 1 between the transmitting station 110 and the receiving station 120.
Numeral 30 is laid as an optical transmission line.

The transmitting station 110 includes N (N ≧ 2) transmitters 111 _{1 to} 111 _N and a multiplexer 112. Transmitter 1
11 _n (where n is an integer of 1 or more and N or less; the same applies hereinafter) outputs the signal light of the wavelength λ _{n in} the signal light wavelength band A (or the signal light wavelength band B). Of the wavelengths λ _{1 to} λ _N , any wavelength is in the 1.31 μm band, any other wavelength is in the 1.45 μm band, and any other wavelength is the 1.55 μm band. And the other wavelengths are in the 1.58 μm band. Multiplexer 112 multiplexes enter the signal light sent out from the transmitter 111 ₁ - 111 _N wavelength lambda ₁ to [lambda] _N, and sends the signal light of the multiplexed multi-wavelength to the optical fiber 130 .

The optical fiber 130 transmits the signal light of the wavelengths λ _{1 to} λ _N multiplexed by the multiplexer 112 of the transmitting station 110 and transmitted to the receiving station 120. This optical fiber 13
0 indicates that the chromatic dispersion is − in the entire range of the signal light wavelength band A.
It is 20 ps / nm / km or more and -3 ps / nm / km or less. The optical fiber 130 is more preferably
The chromatic dispersion is -12p in the entire range of the signal light wavelength band A.
s / nm / km or more and -4 ps / nm / km or less;
Alternatively, the chromatic dispersion is −20 ps / nm / km or more and −3 ps / nm / km or less over the entire range of the signal light wavelength band B, and more preferably −16 ps over the entire range of the signal light wavelength band B. / Nm / km or more -4ps /
nm / km or less. The optical fiber 130
More preferably, the effective area at a wavelength of 1.55 μm is 40 μm ² or more, and the increase in loss due to OH groups at a wavelength of 1.38 μm is 0.1 dB / km or less.

The receiving station 120 has N receivers 121 ₁ to 121 ₁ .
121 _N and a duplexer 122. The demultiplexer 122
Wavelengths λ _{1 to} λ _N arriving after transmission through optical fiber 130
Is input and demultiplexed, and the demultiplexed signal light of each wavelength is output. The receiver 121 _n receives the signal light of the wavelength λ _n output from the duplexer 122.

In the optical transmission system 1, the transmitting station 110
And the multiplexers 1 output from the transmitters 111 _{1 to} 111 _N
The signal lights of wavelengths λ _{1 to} λ _N multiplexed by 12 reach the receiving station 120 via the optical fiber 130. At the receiving station 120, the signal light of wavelengths λ _{1 to} λ _N is
22 and is received by the receivers 121 _{1 to} 121 _N. Since the optical transmission system 1 uses the above-described optical fiber 130 according to the present embodiment as an optical transmission path between the transmitting station 110 and the receiving station 120, the wavelength is 1.31 μm and the wavelength is 1.45 μm. Band, wavelength 1.55μ
Signal light wavelength band A including m band and wavelength 1.58 μm band
In the entire range of (or the signal light wavelength band B), both the signal light waveform deterioration due to the nonlinear optical phenomenon and the signal light waveform deterioration due to the accumulated chromatic dispersion are suppressed. Therefore, the optical transmission system 1 uses the multi-wavelength signal lights λ ₁ to λ of the wide signal light wavelength band A (or the signal light wavelength band B).
Large-capacity long-distance transmission is possible using λ _N.

Next, a description will be given of a second embodiment of the optical transmission system using the optical fiber according to the present embodiment as an optical transmission line. FIG. 7 is a schematic configuration diagram of the optical transmission system 2 according to the second embodiment. This optical transmission system 2
Is an optical fiber 2 between the transmitting station 210 and the relay station 240.
31 is laid as an optical transmission line, and an optical fiber 232 is laid between the relay station 240 and the receiving station 220 as an optical transmission line.

The transmitting station 210 includes N transmitters 211 ₁ to 211 ₁ .
211 _N , multiplexers 212 ₁ , 212 ₂ , optical amplifier 213 ₁ ,
213 ₂ , and a multiplexer 214. Transmitter 211 _n
Outputs the signal light of the wavelength lambda _n of the signal light wavelength band A (or signal wavelength band B) within. Of the wavelengths λ _{1 to} λ _N , any wavelength is in the 1.31 μm band, any other wavelength is in the 1.45 μm band, and any other wavelength is the 1.55 μm band. And the other wavelengths are in the 1.58 μm band. The multiplexer 212 ₁ is connected to the transmitter 21
Multiplexes enter the signal light of the wavelength lambda ₁ to [lambda] _M included in the first wavelength band sent out from ₁ 1 ~211 _M, the optical amplifier 2
13 ₁ collectively optically amplifies and outputs the combined signal light of wavelengths λ _{1 to} λ _M (where 1 <M <N). Multiplexer 21
2 _2, transmitter ₂₁₁ M + 1 second sent from ～211 _N
Multiplexes to input of the signal light of the wavelength λ _{M + 1} ~λ _N included in the wavelength band, the optical amplifier 213 _2, the wavelength lambda that this combined
Collectively optical amplifying signal light of _{M + 1} to [lambda] _N outputs. Multiplexer 2
Reference numeral 14 denotes signal light of wavelengths λ _{1 to} λ _M optically amplified and output by the optical amplifier 213 ₁ , and signal light of wavelengths λ _{M + 1 to} λ _N optically amplified and output by the optical amplifier 213 ₂ Are input and multiplexed, and the multiplexed multi-wavelength signal light is transmitted to the optical fiber 231.

The optical fiber 231 transmits the signal light of wavelengths λ _{1 to} λ _N multiplexed by the multiplexer 214 of the transmitting station 210 and transmitted to the relay station 240. This optical fiber 23
1 indicates that chromatic dispersion is − in the entire range of the signal light wavelength band A.
It is 20 ps / nm / km or more and -3 ps / nm / km or less. The optical fiber 231 is more preferably
The chromatic dispersion is -12p in the entire range of the signal light wavelength band A.
s / nm / km or more and -4 ps / nm / km or less;
Alternatively, the chromatic dispersion is −20 ps / nm / km or more and −3 ps / nm / km or less over the entire range of the signal light wavelength band B, and more preferably −16 ps over the entire range of the signal light wavelength band B. / Nm / km or more -4ps /
nm / km or less. Also, this optical fiber 231
More preferably, the effective area at a wavelength of 1.55 μm is 40 μm ² or more, and the increase in loss due to OH groups at a wavelength of 1.38 μm is 0.1 dB / km or less.

The relay station 240 includes a demultiplexer 241, optical amplifiers 242 ₁ and 242 ₂ and a multiplexer 243. Duplexer 2
Reference numeral 41 denotes a signal light having wavelengths λ _{1 to} λ _N arriving after being transmitted through the optical fiber 231, and a _first signal including wavelengths λ _{1 to} λ _M.
And a second wavelength band including the wavelengths λ _{M + 1 to} λ _N. The optical amplifier 242 _1, batch optical amplifying signal light of the wavelength lambda ₁ to [lambda] _M included in the first wavelength band outputted from the demultiplexer 241, optical amplifier 242 _2, demultiplexer 241
Wavelength λ _{M + 1} included in the second wavelength band output from
Bulk optical amplifying signal light of the lambda _N. And the multiplexer 243
Is a signal light of wavelengths λ _{1 to} λ _M optically amplified and output by the optical amplifier 242 ₁ and a signal light of wavelengths λ _{M + 1 to} λ _N optically amplified and output by the optical amplifier 242 _2. The multiplexed signal light is input, and the multiplexed signal light of multiple wavelengths is transmitted to the optical fiber 232.

The optical fiber 232 transmits the signal light of wavelengths λ _{1 to} λ _N multiplexed by the multiplexer 243 of the relay station 240 and transmitted to the receiving station 220. This optical fiber 23
2 indicates that the chromatic dispersion is − in the entire range of the signal light wavelength band A.
It is 20 ps / nm / km or more and -3 ps / nm / km or less. The optical fiber 232 is more preferably
The chromatic dispersion is -12p in the entire range of the signal light wavelength band A.
s / nm / km or more and -4 ps / nm / km or less;
Alternatively, the chromatic dispersion is −20 ps / nm / km or more and −3 ps / nm / km or less over the entire range of the signal light wavelength band B, and more preferably −16 ps over the entire range of the signal light wavelength band B. / Nm / km or more -4ps /
nm / km or less. Also, this optical fiber 232
More preferably, the effective area at a wavelength of 1.55 μm is 40 μm ² or more, and the increase in loss due to OH groups at a wavelength of 1.38 μm is 0.1 dB / km or less.

The receiving station 220 has N receivers 221 ₁ to 221 ₁ .
221 _N , demultiplexers 222 ₁ , 222 ₂ , optical amplifiers 223 ₁ ,
223 ₂ and a duplexer 224. Duplexer 224
Is the wavelength λ ₁ that has arrived after being transmitted through the optical fiber 232.
To λ _N are input and demultiplexed into a first wavelength band including wavelengths λ _{1 to} λ _M and a second wavelength band including wavelengths λ _{M + 1 to} λ _N. Wavelength optical amplifier 223 _1, batch optical amplifying signal light of the wavelength lambda ₁ to [lambda] _M included in the first wavelength band outputted from the demultiplexer 224, the demultiplexer 222 _1, which is the optical amplifier The signal light of λ _{1 to} λ _M is split and output for each wavelength. The optical amplifier 223 ₂ collectively optically amplifies the signal light of the wavelengths λ _{M + 1 to} λ _N included in the second wavelength band output from the demultiplexer 224, and the demultiplexer 222 ₂ performs the optical amplification. Wavelength λ _{M + 1} ~
lambda _N and outputs demultiplexed for each wavelength signal light. Receiver 22
1 _n receives the signal light of wavelength λ _n output from the duplexer 222 ₁ or 222 ₂ .

In this optical transmission system 2, the transmitting station 210
, The first output from the transmitters 211 _{1 to} 211 _M
The signal light of the wavelength lambda ₁ to [lambda] _M wavelength band multiplexer 212 ₁
And are collectively optically amplified by the optical amplifier 213 ₁ . The signal light of wavelength λ _{M +} 1 ~λ _N of the second wavelength band which is output from the transmitter ₂₁₁ M + 1 _{~211 N} is multiplexer 21
Are multiplexed by the 2 _2, it is collectively light amplified by the optical amplifier 213 _2. Then, the signal light of wavelengths λ _{1 to} λ _M output after being optically amplified by the optical amplifier 213 ₁ and the optical amplifier 2
13 signal light of a wavelength λ _{M + 1} ~λ _N which is optically amplified output by ₂ is further multiplexed by multiplexer 214, which is output to an optical fiber 231. The signal light of the wavelengths λ _{1 to} λ _N transmitted from the transmitting station 210 is transmitted through the optical fiber 231 and reaches the relay station 240.

In the relay station 240, the optical fiber 23
Wavelength λ arrived after transmitting 1₁~ Λ_NThe signal light is
To the first wavelength band and the second wavelength band
It is split. Wavelength λ included in the first wavelength band₁~ Λ_Mof
The signal light is supplied to the optical amplifier 242 ₁Is collectively optically amplified by the
Wavelength λ included in wavelength band 2_{M + 1}~ Λ_NThe signal light is light
Amplifier 242_TwoThese are collectively optically amplified by
Multiplexed by the optical coupler 243 and transmitted to the optical fiber 232
Is done. Wavelength λ transmitted from relay station 240 ₁~ Λ_NNo faith
The optical signal is transmitted through the optical fiber 232 to the receiving station 220.
To reach.

In the receiving station 220, the optical fiber 23
Wavelength λ arrived after transmitting 2₁~ Λ_NThe signal light is
To the first wavelength band and the second wavelength band by the wave filter 224.
It is split. Wavelength λ included in the first wavelength band₁~ Λ_Mof
The signal light is supplied to the optical amplifier 223. ₁Collectively optically amplified by
Corrugator 222₁Are demultiplexed for each wavelength. Second wavelength band
Wavelength λ included in the range_{M + 1}~ Λ_NIs transmitted to the optical amplifier 22
3_TwoCollectively optically amplified by the_TwoBy wavelength
It is split into waves. And the wavelength λ₁~ Λ_NThe signal light is received
Vessel 221₁~ 221_NIs received by

The optical transmission system 2 includes an optical transmission line between the transmitting station 210 and the relay station 240,
Since the optical fibers 231 and 232 according to the above-described embodiment are used as an optical transmission line between the receiving station 220 and the receiving station 220, a wavelength of 1.31 μm, a wavelength of 1.45 μm, a wavelength of 1.55 μm, In the entire range of the signal light wavelength band A (or the signal light wavelength band B) including the 1.58 μm band, the deterioration of the signal light waveform caused by the nonlinear optical phenomenon and the deterioration of the signal light waveform caused by the accumulated chromatic dispersion. Both are suppressed. Therefore, the optical transmission system 2 can perform large-capacity long-distance transmission using the multi-wavelength signal light λ _{1 to} λ _N of the wide signal light wavelength band A (or the signal light wavelength band B).

In the optical transmission system 2, the signal light of wavelengths λ _{1 to} λ _M included in the first wavelength band is
13 _1, the 242 ₁ and 223 ₁ and optical batch amplification, also optical batch amplifying signal light of the wavelength lambda _{M +} 1 to [lambda] _N included in the second wavelength band by the optical amplifier 213 _2, 242 ₂ and 223 ₂ Therefore, long-distance transmission is also possible at this point.
For example, the first wavelength band includes a wavelength band of 1.55 μm and a wavelength of 1.58 μm, and an Er element is added to the optical waveguide region as an optical amplifier that collectively optically amplifies signal light in the first wavelength band. Element doped optical fiber amplifier (EDFA: Erbium-Dop
ed Fiber Amplifier) is preferably used. On the other hand, the second
Wavelength bands are 1.31 μm band and 1.45 μm.
A semiconductor optical amplifier or a Raman amplifier is preferably used as an optical amplifier that includes the m-band and collectively optically amplifies the signal light in the second wavelength band.

Note that, in the configuration shown in FIG.
Although the optical amplifier is divided into three wavelength bands and optically amplified by each optical amplifier, the whole may be optically amplified by one optical amplifier or may be divided into three or more wavelength bands and optically amplified by each optical amplifier. Is also suitable. For example, the wavelength 1.3
The wavelength band may be divided into four wavelength bands of 1 μm band, 1.45 μm wavelength band, 1.55 μm wavelength band, and 1.58 μm wavelength band. For the optical amplification of the signal light in the 1.31 μm band, a Pr element-doped fiber amplifier (PDFA: Praseodymium-Doped Fiber Amplifier) using an optical fiber in which Pr element is added to the optical waveguide region as an optical amplification medium. Is preferably used. For the optical amplification of signal light in the wavelength band of 1.45 μm, a Tm element-doped optical fiber amplifier (TDFA) using an optical fiber in which a Tm element is added to an optical waveguide region as an optical amplification medium is preferable. Used. An EDFA is suitably used for optical amplification of signal light in the wavelength band of 1.55 μm. An EDFA is also suitably used for optical amplification of signal light in a wavelength band of 1.58 μm. Further, a semiconductor optical amplifier or a Raman amplifier is suitably used for optical amplification of signal light in any wavelength band.

[0050]

As described above in detail, the optical fiber according to the present invention has a wavelength band of 1.30 μm to 1.60 μm.
m, the chromatic dispersion is -20 ps / nm / k
m or more and -3 ps / nm / km or less (more preferably, -1
2 ps / nm / km or more and -4 ps / nm / km or less). More preferably, in the entire wavelength range of 1.25 μm to 1.65 μm wider than the above wavelength band,
Chromatic dispersion is -20 ps / nm / km or more and -3 ps / nm
/ Km or less (more preferably, -16 ps / nm / km or more and -4 ps / nm / km or less). According to this optical fiber, a wavelength of 1.31 μm band, a wavelength of 1.45 μm band,
In a wide signal light wavelength band including the wavelength 1.55 μm band and the wavelength 1.58 μm band, the chromatic dispersion is a value within the above numerical range, so that the waveform deterioration and the accumulated chromatic dispersion of the signal light due to the nonlinear optical phenomenon are prevented. Both of the resulting signal light waveform deterioration are suppressed. Therefore, if this optical fiber is used as an optical transmission line, large-capacity long-distance transmission is possible using multi-wavelength signal light in this wide signal light wavelength band.

The optical fiber according to the present invention has a wavelength of 1.55.
40 μm effective area at μm ^TwoIf it is more than
Further suppresses signal light waveform deterioration due to nonlinear optical phenomena
This is suitable for performing long-distance transmission. In addition, the present invention
Is an OH group at a wavelength of 1.38 μm.
If the loss increase due to is less than 0.1 dB / km,
A wavelength near 1.38 μm is also used as a signal light wavelength.
Therefore, even larger capacity transmission is possible.

Since the optical transmission system according to the present invention uses the optical fiber according to the present invention as an optical transmission line, it has a wavelength band of 1.31 μm, a wavelength of 1.45 μm, a wavelength of 1.55 μm, and a wavelength of 1. In a wide signal light wavelength band including the .58 μm band (1.30 μm to 1.60 μm, more preferably 1.25 μm to 1.65 μm), it is possible to prevent the signal light waveform deterioration and the cumulative chromatic dispersion caused by the nonlinear optical phenomenon. Both of the resulting signal light waveform degradation are suppressed, and large-capacity long-distance transmission is possible using multi-wavelength signal light in this wide signal light wavelength band.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating chromatic dispersion characteristics of an optical fiber according to an embodiment.

FIG. 2 is a diagram illustrating a preferred example of a refractive index profile of the optical fiber according to the embodiment.

FIG. 3 is a diagram illustrating another preferred example of the refractive index profile of the optical fiber according to the embodiment.

FIG. 4 is a table summarizing the specifications and characteristics of each of the optical fibers of the four examples.

FIG. 5 is a graph showing chromatic dispersion characteristics of optical fibers of four examples.

FIG. 6 is a schematic configuration diagram of an optical transmission system according to the first embodiment.

FIG. 7 is a schematic configuration diagram of an optical transmission system according to a second embodiment.

[Description of Signs] 1, 2,... Optical transmission system, 110, transmitting station, 111 _1-
111 _N : transmitter, 112: multiplexer, 120: receiving station,
121 _{1 to} 121 _N ... receiver, 122 ... duplexer, 130 ...
Optical fiber, 210: transmitting station, 211 _{1 to} 211 _N : transmitter, 212 ₁ , 212 ₂ : multiplexer, 213 ₁ , 213 ₂ ... optical amplifier, 214: multiplexer, 220: receiving station, 221 ₁ to
221 _N ... receiver, 222 ₁ , 222 ₂ ... duplexer, 22
3 _1, 223 ₂ ... optical amplifier, 224 ... demultiplexer, 231,2
32: optical fiber, 240: relay station, 241: duplexer
242 ₁ , 242 ₂ ... optical amplifier, 243 ... multiplexer.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H050 AC14 AC15 AC28 AC71 AC73 AC76 5K002 AA01 AA03 AA06 BA04 BA05 CA01 DA02 FA02

Claims (11)

[Claims] 1. An optical fiber having a chromatic dispersion of not less than -20 ps / nm / km and not more than -3 ps / nm / km in a whole wavelength band of 1.30 μm to 1.60 μm. 2. The optical fiber according to claim 1, wherein the chromatic dispersion is -12 ps / nm / km or more and -4 ps / nm / km in the entire wavelength band of 1.30 μm to 1.60 μm. 3. The optical fiber according to claim 1, wherein the chromatic dispersion is -20 ps / nm / km or more and -3 ps / nm / km in the entire wavelength band of 1.25 μm to 1.65 μm. 4. The optical fiber according to claim 1, wherein the chromatic dispersion is -16 ps / nm / km or more and -4 ps / nm / km in the entire wavelength band of 1.25 μm to 1.65 μm. 5. The optical fiber according to claim 1, wherein the effective area at a wavelength of 1.55 μm is 40 μm ² or more. 6. The optical fiber according to claim 1, wherein an increase in loss due to OH groups at a wavelength of 1.38 μm is 0.1 dB / km or less. 7. A central core region including a center of the optical axis and having a first refractive index; a second core region surrounding the central core region and having a second refractive index smaller than the first refractive index; A third core region surrounding the second core region and having a third refractive index larger than the second refractive index; and a cladding surrounding the third core region and having a fourth refractive index smaller than the third refractive index. The optical fiber according to claim 1, comprising a region. 8. The cladding region includes an inner cladding region having a refractive index smaller than the third refractive index, and an outer cladding region having a refractive index larger than the refractive index of the inner cladding. The optical fiber according to claim 7. 9. The light according to claim 7, wherein a relative refractive index difference of the center core region is 0.4% or more and 0.7% or less based on a refractive index of an outermost layer of the cladding region. fiber. 10. A wavelength band of 1.30 μm to 1.60 μm.
A plurality of transmitting stations for multiplexing and transmitting the signal lights of the respective wavelengths in the optical fiber; an optical fiber according to claim 1 for transmitting the multi-wavelength signal light transmitted from the transmitting station; and transmitting the optical fiber. An optical transmission system comprising: a receiving station that demultiplexes multi-wavelength signal light that has arrived and receives signal light of each wavelength. 11. A wavelength band of 1.25 μm to 1.65 μm.
A plurality of transmitting stations for multiplexing and transmitting the signal lights of the respective wavelengths within the optical fiber; an optical fiber according to claim 3 for transmitting the multi-wavelength signal light transmitted from the transmitting station; and transmitting the optical fiber. An optical transmission system comprising: a receiving station that demultiplexes multi-wavelength signal light that has arrived and receives signal light of each wavelength.