JP3274817B2 - Fiber for WDM transmission - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength multiplex transmission fiber, and more particularly to a wavelength multiplex transmission fiber for performing wavelength multiplex transmission using eight or more optical signals in a wavelength range of 1.53 to 1.56 .mu.m. .

[0002]

2. Description of the Related Art With the advent of optical fiber amplifiers, long-distance, large-capacity transmission systems for transmitting large-capacity information over long distances at high speed have been receiving attention. As this long-distance, large-capacity transmission system, a wavelength multiplexing transmission system for transmitting a large number of optical signals having different wavelengths in one optical fiber is considered promising. As the wavelength multiplexing transmission method, wavelength 1.
1 nm or 0.5 from the range of 53 to 1.57 μm
It has been considered that several tens of optical signals are used at nm intervals, and information is superimposed on the optical signals of the respective wavelengths and transmitted through an optical fiber.

FIGS. 6, 7, 8, and 9 show conventional wavelength division multiplexing transmission fibers used in such a transmission system. The fiber shown in FIG.
Mode fiber (SM
A dispersion compensating fiber (DCF: Dispersion) having a refractive index distribution shown in FIG. 4B having a dispersion of the opposite sign to cancel the dispersion of the SMF in the transmission line of F: Single Mode Fiber.
Compensating Fiber) to show the total dispersion characteristics
(c). The fiber shown in FIG. 7 has a step-shaped refractive index distribution shown in FIG.
The dispersion characteristic of the dispersion-shifted fiber (DSF) having a segmented refractive index distribution is shifted from the 1.3 μm band to the 1.55 μm band toward the longer wavelength side, and the dispersion characteristics are as shown in FIG. It is to become. The sum of the material dispersion and the structural dispersion is the wavelength dispersion in FIG. The fiber shown in FIG.
(Large Effective Area Shifted Fiber)
It has a refractive index distribution as shown in FIG. 2 (a), and as shown in a light intensity distribution diagram in FIG. 2 (b), the effective core diameter is increased to about 10 μm to suppress the induction of nonlinear phenomena. It is. The fiber shown in FIG. 9 is a triple-clad dispersion flat fiber (D) having the refractive index distribution shown in FIG.
As shown in the dispersion characteristic diagram of FIG. 2B, the dispersion is reduced by using FF (Dispersion Flattened Fiber) to reduce the dispersion in a wide wavelength range of 1.3 to 1.55 μm. The aim of these fibers is 1.53 ~
Small chromatic dispersion over a wide wavelength range of 1.57 μm,
And dispersion slope (variation of dispersion per unit wavelength)
Is also to make it smaller.

[0004]

However, according to the conventional wavelength division multiplexing transmission fiber, there are advantages and disadvantages when attempting to wavelength division multiplex transmission of ten to several tens of optical signals. (1) In the fiber in which the SMF and the DCF are combined as shown in FIG. 6, the chromatic dispersion and the dispersion slope can be reduced, but if the dispersion amount is to be compensated for using a short DCF,
There is a drawback that the transmission loss of the DCF increases and a dedicated optical fiber amplifier must be added to compensate for the transmission loss. In addition, the effective core diameter is small (4 to 6
μm), there is also a disadvantage that a nonlinear phenomenon is induced by an increase in the optical energy density in the core with an increase in the number of wavelength multiplexes, and the transmission waveform is deteriorated. (2) In the DSF of FIG. 7, the transmission loss is very low (0.2
(5 dB / km or less), but it is difficult to make the effective core diameter 8.5 μm or more, and there is a drawback that a nonlinear phenomenon is induced. (3) In the LEAF of FIG. 8, the effective core diameter can be increased to near 10 μm, but there is a disadvantage that transmission loss due to bending or the like may increase. (4) The DFF of FIG. 9 has low chromatic dispersion and low dispersion slope, but has a drawback that the effective core diameter is small (7.5 μm or less).

Accordingly, an object of the present invention is to provide a wavelength of 1.53 to 1.53.
An object of the present invention is to provide a wavelength division multiplexing transmission fiber capable of performing long-distance and large-capacity transmission by wavelength division multiplexing using eight or more optical signals in the range of 1.56 μm. Another object of the present invention is to provide a wavelength division multiplexing transmission fiber which has a small transmission loss, does not induce a nonlinear phenomenon even when the number of wavelength division multiplexes increases, and does not deteriorate the transmission waveform.

[0006]

In order to achieve the above object, the present invention provides a first core having a diameter D and a refractive index n ₁ and a thickness S.
₁ , a first intermediate layer having a refractive index n _i (n _i <n ₁ ), a thickness W, a second core having a refractive index n ₂ (n ₂ ≧ n ₁ ), and a thickness S
_2, the second refractive index _{n j (n j ≦ n i} ) an intermediate layer, and a cladding provided concentrically in order from the center to the refractive index _{n c (n 1> n c} ≧ n j), the first The diameter D of the core and the thickness W of the second core are set to 0.7 to 2.4 μm, and the relative refractive index difference between the second core and the second intermediate layer is set to 1.3 to 2 0.5%, and the thickness s1 of the _first intermediate layer and the thickness s2 of the _second intermediate layer are 0.5 to 0.5%.
By setting the diameter to 1.5 μm, the effective core diameter in the 1.55 μm band is set to 9 μm or more, and the zero dispersion wavelength is set to 1.
Provided is a fiber for wavelength division multiplexing transmission, which is shifted to a shorter wavelength side than 53 μm . According to the above Symbol configuration,
The diameter D of the first core and the thickness W of the second core are 0.7
To 2.4 μm, the relative refractive index difference between the second core and the second intermediate layer is 1.3 to 2.5%, and the thicknesses s ₁ and s ₂ of the first and second intermediate layers are with 0.5 to 1.5 [mu] m, since the effective core diameter of the wave length 1.55μm band can be more than 9 .mu.m, 8 waves the number of multiplexed wavelengths, 16
Even if the number of waves increases, such as 32 waves, non-linear phenomena hardly occur, and distortion of the transmission waveform hardly occurs. Further, the zero dispersion wavelength λ _{0 is set} to 1.53 while the effective core diameter is kept at 9 μm or more.
By setting the wavelength shorter than μm,
In the range of 1.56 μm, the values of chromatic dispersion and dispersion slope become small. As a result, the wavelength 1.53 to 1.56 μm
It is possible to perform long-distance and large-capacity transmission by wavelength multiplexing using eight or more optical signals in the range described above.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.
This will be described in detail with reference to FIG. FIG. 1 shows an embodiment of the present invention.
Wavelength multiplexing transmission fiber (hereinafter simply referred to as
Ba ". FIG. This fiber 10
Diameter D, refractive index n₁SiO_Two-GeO_TwoFrom system glass
First core 11, thickness S₁, Refractive index n_i(N_i<N
₁), The first intermediate layer 12, the thickness W, and the refractive index n_Two(N_Two≧
n₁) SiO _Two-GeO_TwoSecond glass made of base glass
A13, thickness S_Two, Refractive index n_j(N_j≤n_iThe second of
Intermediate layer 14, and refractive index n_c(N₁> N_c≧ n_j)of
SiO_TwoCladding 15 made of glass
Provided in a concentric shape, parameters D and S ₁, S_Two, W, n₁,
n_Two, N_i, N_j, N_cBy setting
The effective core diameter in the 1.55 μm band is 9 μm or less.
It is the one above. The effective core diameter is calculated by the following equation.
It is obtained from the effective core area obtained in (1). A = (πk / 4) · (MFD)^Two (1) where A is the effective core area, and k is the proportional coefficient (0.96
Hereinafter, MFD indicates a mold field diameter.

FIGS. 2A and 2B are diagrams according to the first and second embodiments. FIG. 2A is a sectional view, and FIG. 2B is a refractive index distribution diagram of the first embodiment. (c) is a refractive index distribution diagram of the second embodiment. In FIGS. 2 (a) and 2 (b), Δ
₊ Is the relative refractive index difference between the first and second cores 11 and 13 and the clad 15, Δ _- is the relative refractive index difference between the clad 15 and the first and second intermediate layers 12 and 14, and Δ is the first And the second
Cores 11 and 13 and first and second intermediate layers 12 and 14
And the relative refractive index difference between the two. The relative refractive index difference Δ is Δ = Δ ₊ + Δ
_- it can be represented by.

The fiber 10 according to the first embodiment
The first and second intermediate layers 12 and 14 are made of SiO ₂ glass, and the fiber 10 according to the second embodiment is
The first and second intermediate layers 12, 14 are made of SiO ₂ glass to which fluorine (F) is added.

The effective core diameter and the zero-dispersion wavelength λ ₀ are determined by the structural parameters of the diameter D, the thickness W, S ₁ , S ₂ , and the relative refractive index differences Δ ₊ , Δ. Under the condition that the effective core diameter in the 1.55 μm band becomes 9 μm or more, the zero dispersion wavelength λ
_{In order to make 0} smaller than 1.53 μm, the inventor conducted various experiments and found that the following parameter values should be adopted. That is, the relative refractive index difference Δ is 1.3 to
2.5%, diameter D and thickness W are 0.7 to 2.4 μ
m, and thicknesses S ₁ and S ₂ are 0.5 to 1.5 μm. Additionally, delta ₊ 1.5% in FIG. 2 (b), Δ _- 0%
When Δ is 1.5%, the thicknesses S ₁ and S ₂ are 0.5 to 1.
The diameter D and the thickness W are set to values smaller than 2.0 μm. Further, the delta ₊ in FIG. 2 (c) 1.5
%, Δ _- is 0.7%, and Δ is 2.2%, the diameter D and the thickness W are set to values smaller than the above values.
It is set to 1.2 μm or less. In order to reduce the zero dispersion wavelength λ ₀ , it is better to increase the relative refractive index difference Δ as shown in FIG. Conversely, to increase the effective core diameter, use Fig. 2
The structure of (b) is more advantageous.

FIGS. 3A and 3B are views according to the third and fourth embodiments. FIG. 3A is a sectional view, and FIG. 3B is a refractive index distribution chart of the third embodiment. (c) is a refractive index distribution diagram of the fourth embodiment. Note that in FIGS. 3B and 3C, Δ
₁ is a relative refractive index difference between the first core 11 and the clad 15, and Δ
₂ is a relative refractive index difference between the second core 13 and the clad 15, and Δ
_- The cladding 15 first and second intermediate layers 12, 14
And Δ is the second core 13 and the first and second cores 13.
Is the relative refractive index difference with the intermediate layers 12 and 14. The relative refractive index difference Δ can be represented by Δ = Δ ₂ + Δ ₋ .

The fiber 10 according to the third embodiment
The first and second intermediate layers 12 and 14 are made of SiO ₂ glass, and the fiber 10 according to the fourth embodiment is
The first and second intermediate layers 12, 14 are made of Si doped with F.
It is composed of O ₂ glass. Further, the fiber 10 according to the third and fourth embodiments is different from the fiber 10 shown in FIG.
(c), the refractive index of the first core 11 is slightly smaller than the refractive index of the second core 13, the delta ₁ from delta ₂ 0. It is set to be several percent smaller.

As a result, the confinement of the optical power in the second core 13 is enhanced, and the effective core diameter can be increased. As a modification of FIG. 3, the diameter D may be set to a value smaller than the thickness W by several percent to ten and several percent in order to obtain the above-described effect.

FIGS. 4A and 4B are diagrams according to the fifth and sixth embodiments. FIG. 4A is a sectional view, and FIG. 4B is a refractive index distribution diagram of the fifth embodiment. (c) is a refractive index distribution diagram of the sixth embodiment. 4 (a) and 4 (b), Δ
₊ Is a relative refractive index difference between the first and second cores 11 and 13 and the cladding 15, and Δ _- is a cladding 15 and the second intermediate layer 14.
And Δ are the first and second cores 11 and 13.
And the relative refractive index difference between the second intermediate layer 14 and the second intermediate layer 14. The relative refractive index difference Δ can be represented by Δ = Δ ₊ + Δ ₋ .

The fiber 10 according to the fifth embodiment
In the fiber according to the sixth embodiment, the refractive index of the first intermediate layer 12 is made equal to that of the clad 15, the refractive index of the second intermediate layer 14 is made smaller than that of the first intermediate layer 12. 1
0 indicates that the refractive index of the first intermediate layer 12 is smaller than that of the cladding 15 and the refractive index of the second intermediate layer 14 is
Is smaller than the refractive index.

Thus, the amount of light propagating to the second core 13 becomes substantially equal to the amount of light propagating to the first core 11,
Alternatively, the power distribution in the fiber 10 is increased, and as a result, the effective core diameter can be increased.

FIGS. 5A and 5B are views according to the seventh and eighth embodiments. FIG. 5A is a sectional view, and FIG. 5B is a refractive index distribution chart of the seventh embodiment. (c) is a refractive index distribution diagram of the eighth embodiment. Note that in FIGS. 5B and 5C, Δ
₁ is a relative refractive index difference between the first core 11 and the clad 15, and Δ
₂ is a relative refractive index difference between the second core 13 and the clad 15, and Δ
_- The relative refractive the cladding 15 relative refractive index difference between the first intermediate layer 12 or the second intermediate layer 14, delta and the second core 13 and the first intermediate layer 12 or the second intermediate layer 14 The rate difference. The relative refractive index difference Δ can be represented by Δ = Δ ₂ + Δ ₋ .

In the fibers 10 according to the seventh and eighth embodiments, the refractive index of the first core 11 is made slightly smaller than the refractive index of the second core 13 as in the structure of FIG.
In the fiber 10 according to the seventh embodiment, the refractive index of the first intermediate layer 12 is smaller than the refractive index of the clad 15, and the fiber 10 according to the eighth embodiment is different from the second intermediate layer. 14 is smaller than the refractive index of the cladding 15.

[0019] Thus, the relative refractive index difference between the first intermediate layer 12 or the second intermediate layer 14 and the cladding 15 delta _- zero dispersion wavelength lambda ₀ is added as the adjustment parameter of the zero dispersion wavelength lambda ₀ It can be adjusted more freely.

As described above, according to the present fiber 10, the following effects can be obtained. (1) A large number of structural parameters (D, W, S ₁ ,
S ₂ , Δ ₊ and Δ), the wavelength 1.55
With the effective core diameter in the μm band kept at 9 μm or more, the zero dispersion wavelength λ ₀ can be set to a shorter wavelength side than 1.53 μm. (2) The effective core diameter in the 1.55 μm band is 9
μm or more, so that the
Even if the number is increased to 16 waves, 32 waves,..., A nonlinear phenomenon hardly occurs, and a transmission waveform distortion is hardly caused. (3) Further, since the zero dispersion wavelength λ ₀ can be set to a shorter wavelength side than 1.53 μm while maintaining the effective core diameter at 9 μm or more, the wavelength in the wavelength range of 1.53 to 1.56 μm Dispersion and dispersion slope values can be significantly reduced. In addition, the generation of interference noise due to four-wave mixing can be prevented. (4) Accordingly, long-distance, large-capacity transmission by wavelength division multiplexing becomes possible. (5) Further, it has a structure that can be easily manufactured by various methods such as a VAD method, an OVD method, an MCVD method, a rod-in-tube method, and can realize a large-diameter optical fiber preform. Therefore, cost reduction is possible. Also, due to the symmetrical structure, there is little increase in fiber loss, and a low-loss fiber can be obtained.

[0021]

As described above, according to the present invention, the diameter D of the first core and the thickness W of the second core are 0.7 to 0.7.
2.4 μm, the relative refractive index difference between the second core and the second intermediate layer is 1.3 to 2.5%, and the thicknesses s ₁ and s ₂ of the first and second intermediate layers are 0. with .5～1.5Myuemu, since the effective core diameter of the wave length 1.55μm band can be more than 9 .mu.m, 8 waves the number of multiplexed wavelengths, 16
Even if the number of waves is increased, such as 32 waves, non-linear phenomena are unlikely to occur, and distortion of the transmission waveform is unlikely to occur. Further, the zero dispersion wavelength λ _{0 is set} to 1.53 while the effective core diameter is kept at 9 μm or more.
Since the wavelength can be set shorter than μm, the wavelength 1.53
The wavelength dispersion and the value of the dispersion slope become smaller in the range of 1.56 μm. As a result, the wavelength 1.53 to 1.56 μm
Long-distance, large-capacity transmission can be performed by wavelength multiplexing using eight or more optical signals in the range of m. VAD
It is a structure that can be easily manufactured by various methods such as an OVD method, an MCVD method, and a rod-in-tube method, and a large-diameter optical fiber preform can be realized. It is possible. Also, due to the symmetrical structure, there is little increase in fiber loss, and a low-loss fiber can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a wavelength division multiplexing transmission fiber according to the present invention.

FIGS. 2A and 2B are diagrams of a wavelength division multiplexing transmission fiber according to first and second embodiments, wherein FIG. 2A is a cross-sectional view and FIG. 2B is a refractive index distribution of the first embodiment; FIG. 3C is a refractive index distribution diagram of the second embodiment.

FIGS. 3A and 3B are diagrams relating to a wavelength division multiplexing transmission fiber according to third and fourth embodiments, wherein FIG. 3A is a cross-sectional view and FIG. 3B is a refractive index distribution of the third embodiment; FIG. 13C is a refractive index distribution diagram of the fourth embodiment.

FIGS. 4A and 4B are diagrams illustrating a wavelength division multiplexing transmission fiber according to fifth and sixth embodiments, wherein FIG. 4A is a cross-sectional view and FIG. 4B is a refractive index distribution of the fifth embodiment; FIG. 13C is a refractive index distribution diagram of the sixth embodiment.

FIGS. 5A and 5B are diagrams illustrating wavelength division multiplexing transmission fibers according to seventh and eighth embodiments, wherein FIG. 5A is a cross-sectional view and FIG. 5B is a refractive index distribution of the seventh embodiment; FIG. 13C is a refractive index distribution diagram of the eighth embodiment.

FIG. 6 is a diagram related to a conventional optical fiber, and FIG.
Is a refractive index profile of a single mode fiber (SMF),
FIG. 3B shows a refractive index distribution diagram of the dispersion compensating fiber (DCF), and FIG. 3C shows a total dispersion characteristic diagram.

FIG. 7 is a diagram related to a conventional dispersion-shifted fiber (DSF), wherein FIG. 7A shows a step-shaped refractive index distribution diagram, and FIG.
Is a segment type refractive index distribution diagram, and FIG.

8A and 8B are diagrams relating to a conventional LEAF, wherein FIG. 8A is a refractive index distribution diagram, and FIG. 8B is a light intensity distribution diagram.

9A and 9B are diagrams relating to a conventional dispersion flat fiber (DFF), in which FIG. 9A shows a refractive index distribution diagram, and FIG. 9B shows a dispersion characteristic diagram.

[Explanation of symbols]

Reference Signs List 10 wavelength multiplexing transmission fiber 11 first core 12 first intermediate layer 13 second core 14 second intermediate layer 15 clad D diameter of _first core S ₁ thickness of first intermediate layer S ₂ Thickness of intermediate layer 2 W Thickness of second core

──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazuo Kamiya 2-13-1 Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd.Precision Functional Materials Research Laboratory (72) Inventor Jun Abe Isobe, Annaka-shi, Gunma No. 2-13-1 Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Laboratory (56) References JP-A-62-215206 (JP, A) JP-A-62-215207 (JP, A) JP-A-58-104040 (JP, A) JP-A-59-226301 (JP, A) JP-A-7-168046 (JP, A) JP-A 8-304655 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ G02B 6/00 G02B 6/10 G02B 6/16-6/22 G02B 6/44

Claims (1)

(57) [Claims] _1. A first core having a diameter D and a refractive index n ₁ , and a thickness S.
₁ , a first intermediate layer having a refractive index n _i (n _i <n ₁ ), a thickness W, a second core having a refractive index n ₂ (n ₂ ≧ n ₁ ), and a thickness S
_2, the second refractive index _{n j (n j ≦ n i} ) an intermediate layer, and a cladding provided concentrically in order from the center to the refractive index _{n c (n 1> n c} ≧ n j), the first The diameter D of the core and the thickness W of the second core are set to 0.7 to 2.4 μm, and the relative refractive index difference between the second core and the second intermediate layer is set to 1.3 to 2 0.5%, and the thickness s1 of the _first intermediate layer and the thickness s2 of the _second intermediate layer are 0.5 to 1.5 μm, so that the effective wavelength in the 1.55 μm band is improved. 9μ core diameter
m, and the zero dispersion wavelength is shifted to a shorter wavelength side than 1.53 μm.