WO2000052507A1

WO2000052507A1 - Optical fiber

Info

Publication number: WO2000052507A1
Application number: PCT/JP2000/001237
Authority: WO
Inventors: Takatoshi Kato; Yuji Kubo; Yuji Takahashi; Michifumi Yoneda
Original assignee: Sumitomo Electric Industries, Ltd.
Priority date: 1999-03-03
Filing date: 2000-03-02
Publication date: 2000-09-08
Also published as: AU2825800A; TW419603B

Abstract

An optical fiber having a sufficiently large effective cross sectional area while suppressing an increase of the dispersion slope in the 1.55 νm wavelength band. The optical fiber comprises an inner core where a core region extends along a predetermined axis and an outer core provided on the periphery of the inner core and having a refractive index lower than that of the inner core. Specifically, the relative index difference Δn1 of the inner core to the reference region in the clad region provided on the periphery of the core region, the relative index difference Δn2 of the outer core to the reference region, the ratio a/b of the outside diameter (2b) of the outer core to the outside diameter (2a) of the inner core, outside, and the outside diameter (2b) of the outer core are all adequately determined according to the structure of the clad region.

Description

Satsuki Itoda

Technical field

The present invention relates to an optical fiber applicable to an optical transmission line in an optical communication system or the like. Background art

Generally, an optical fiber based on silica glass is applied to an optical transmission line in an optical communication system. Silica glass has low transmission loss in the 1.55 m wavelength band, so light in this wavelength band is used as signal light. In recent optical communications, wavelength division multiplexing (WDM), which multiplexes signal light of multiple wavelengths in the 1.55 m wavelength band, is being performed to enable large-capacity optical communications. Will be In order to reduce the cumulative dispersion, it is desirable that the optical fiber applied to WDM transmission has a small dispersion and a small dispersion slope in the 1.55〃m wavelength band, and suppresses the occurrence of nonlinear optical phenomena. Therefore, it is desired that the effective area is large in the wavelength band.

For example, the optical fiber disclosed in U.S. Pat. No. 5,327,516 (first conventional example) has a dispersion slope in the 1.55 m wavelength band of not more than 0.4 OQ SpsZnm ² / km. Further, Yanming Liu, et al "" Single-mode dispersion-shifted fibers with effective area larger than 80 m 2 and good bending performance ", ECOC'95, Tu丄.2.4 (1995) comprising an optical fiber described in the literature ( The second conventional example) has an effective area of 80 / m ² or more.

The inventors have studied the conventional optical fiber described above, and as a result, Problem was discovered. That is, although the optical fiber according to the first conventional example has a small dispersion slope, it also has a small effective cross-sectional area of 53 、 m ² , so that the occurrence of the nonlinear optical phenomenon cannot be sufficiently suppressed. On the other hand, although the optical fiber according to the second conventional example has a large effective area, the dispersion slope is also as large as 0.11 ps / nmS / km, so that the accumulated dispersion cannot be sufficiently reduced.

The present invention has been made to solve the above-described problems, and the effective cross-sectional area is reduced in a state in which the dispersion slope is suppressed to a small value in the 1.55 μm wavelength band, which is a frequently used signal light wavelength band. The purpose is to provide an optical fiber with a structure that can be sufficiently expanded.

An optical fiber according to the present invention includes a core region extending along a predetermined axis, and a cladding region provided on an outer periphery of the core region. The core region further includes an inner core and an outer core provided on an outer periphery of the inner core and having a smaller refractive index than the inner core. In the optical fiber according to the first embodiment, the cladding region is provided on the outer periphery of the outer core and has a lower refractive index than the outer core. It is composed of an outer cladding having a higher refractive index than the cladding, and the refractive index profile of the optical fiber in which the cladding region is composed of the inner cladding having a lower refractive index and the outer cladding having a higher refractive index. Is called a depressed cladding type refractive index profile. Further, in the optical fiber according to the second embodiment, the cladding region is composed of a single layer, and the refractive index profile of the optical fiber in which the cladding region is composed of a single layer is a matched cladding type refractive index profile. Called.

In particular, the optical fiber according to the first embodiment includes a depressed cladding type refractive index profile in which the cladding region surrounding the core region is composed of an inner cladding and an outer cladding, and the outer cladding (the cladding region surrounding the core region). the relative refractive index difference of the inner core with respect to a region) and the reference area and delta gamma ^ and (%) of the relative refractive index difference of the outer core and delta eta ₂ (%) with respect to the outer clad, outside of the inner core Diameter 2 a (ju m) and the outer diameter of the outer core region is 2 b (jm),

0.55≤Δπ! ≤ 0.75,

0.02≤Δη ₂ ≤ 0.12,

0.18≤a / b≤0.24,

25≤2 b≤33

It is characterized by satisfying the following conditions. Furthermore, when the relative refractive index difference between the outer cladding and the inner cladding is Δη ₃ (), the optical fiber according to the first embodiment

- 0. 1 5≤Δη ₃ ≤- 0. 03

It is preferable to satisfy the following conditions.

Further, the optical fiber according to the second embodiment has a matched clad type refractive index profile in which the clad region surrounding the core region is constituted by a single layer, and the relative refractive index difference of the inner core with respect to the clad region is ΔΓ ^. (), The relative refractive index difference of the outer core to the cladding region is Δη ₂ (%), the outer diameter of the inner core is 2 a (jum), and the outer diameter of the outer core is 2 b (〃m). When

0.60≤Δη! ≤ 0.80,

0.05≤Δη ₂ ≤ 0.15,

0.2 1≤a / b≤0.27,

20≤ 2 b≤27

It is characterized by satisfying the following conditions.

Each of the optical fibers according to the first and second embodiments having the above-described structure has a sufficiently small dispersion slope and a sufficiently large effective area in the 1.55 μm wavelength band. In addition, other optical characteristics are good in such a wavelength band.

The effective area A _eif is given by the following equation, as shown in JP-A- _8-248251 (EP0724171 A2).

Here, E is the electric field associated with the propagating light, and r is the radial distance from the core center. The dispersion slope is given by the slope of a graph showing the wavelength dependence of dispersion. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a sectional view showing the structure of a first embodiment of the optical fiber according to the present invention, and FIG. 1B is a refractive index profile of the optical fiber shown in FIG.

FIG. 2 is a graph showing the optical characteristics of the optical fiber according to the first embodiment, where the relative refractive index difference Δη ₂ (%) of the outer core with respect to the outer cladding and the outer diameter 2 b (JUL m) of the outer layer core are shown. The cut-off wavelength on a two-dimensional plane with (〃M), effective area A _eff (〃m), dispersion (ps / nm / km, dispersion slope (psZn mVkm), and bending loss (dB / m). 5 is a graph showing a relationship between an effective area A _efi (urn) and a bending loss (dB / m) at a diameter of 20 mm for the optical fiber according to the first example.

FIG. 4 is a refractive index profile of a second embodiment of the optical fiber according to the present invention. FIG. 5 is a graph showing the optical characteristics of the optical fiber according to the second embodiment, wherein the relative refractive index difference Δη ₂ (%) of the outer core with respect to the cladding region and the outer diameter 2 b (um ) On the two-dimensional plane, with the cutoff wavelength λ. (M), effective area A eff 'dispersion value (psZnm / km) 分散 dispersion slope (ps / nmkm) and bending loss (dB / m). BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the optical fiber according to the present invention will be described with reference to FIGS. 1A, 1B, and FIGS. In the description of the drawings, the same elements are denoted by the same reference numerals. And duplicate explanations are omitted.

(First embodiment)

FIG. 1A is a sectional view showing the structure of an optical fiber according to a first embodiment of the present invention, and FIG. 1B is a refractive index profile of the optical fiber 100 according to the first embodiment. As shown in FIG. 1B, the optical fiber 100 according to the first embodiment has a refractive index profile 150 of a double core / depressed clad type.

The optical fiber 100 according to the first embodiment includes, as shown in FIG. 1A, a core region 110 and a cladding region 120 surrounding the core region. The core region 1 10 includes an inner core 1 1 1 having an outer diameter 2 a having a refractive index including the center of the optical axis and an outer diameter 2 b surrounding the inner core 1 1 1 and having a refractive index n ₂ (<n!). And an outer core 1 1 2. The cladding region 1 20 surrounds the outer core 1 12 and has an outer cladding 1 2 1 having an outer diameter 2 c having a refractive index n ₃ (<n ₂ ), and an inner cladding 1 2 1 surrounding the inner cladding 1 2 1 and having a refractive index n ₄ (> n ₃ , <n ₂ ). An optical fiber having a structure like this, for example, silica glass as a base, respectively inner side core 1 1 1 and the outer core 1 1 2 was added an appropriate amount of Ge_〇 _2, the inner cluster head 12 1 It is obtained by adding element F.

Note that the refractive index profile 150 shown in FIG. 1B is represented by the refractive index of each portion on the line L in FIG. 1A, and the region 151 is the inner core 111 on the line L. The refractive index of each part, the area 152 is the refractive index of each part in the outer core 112 on the line L, the area 153 is the refractive index of each part in the inner cladding 121 on the line L, and the area 154 is the line L This corresponds to the refractive index of each portion in the upper outer cladding 122. Further, in this specification, when the outer clad 122 is used as a reference region, the relative refractive index difference Δη ^ of the inner core 111 and the relative refractive index difference Δη _{2 of the} outer core 112 and the inner clad 1 The relative refractive index difference Δη ₃ of 21 is given as follows.

Δ n! _{= (N -! Η 4)} / η 4 Δ n ₂ = (n ₂ -n ₄ ) / n ₄

Δ n ₃ = (n ₃ -n ₄ ) / n ₄

However, the refractive index of the inner core 1 1 1, n ₂ is the refractive index of the outer core 1 1 2, n ₃ is the inner cladding 1 2 1 having a refractive index, n ₄ is the refractive index of the outer cladding 1 2 2. Also, in this specification, these relative refractive index differences are expressed as percentages, and the refractive indices of the respective regions in the above equation are not in any order (the same applies hereinafter). Therefore, it is considered that a region where the relative refractive index difference has a negative value with respect to the reference region has a lower refractive index than the reference region.

In the optical fiber 100 according to the first embodiment having the above-described structure, the relative refractive index difference ΔΓ ^ (%) of the inner core 1 1 1 with respect to the outer clad 1 2 2 and the outer core 1 1 2 Relative index difference Δη ₂ (%), ratio of outer diameter 2 a (jum) of inner core 1 1 1 to outer diameter 2 b (jum) of outer core 1 1 2 (2 / b), and outer core 1 1 The outer diameter 2 b (〃m) of 2 satisfies the following conditions.

0.5 5≤Δη! ≤ 0.7 5-(1)

0.0 2 ≤ Δ η _¾ ≤ 0.1 2-(2)

0.18≤a / b≤ 0.24 '' • (3)

2 5≤ 2 b≤ 3 3

In particular, in the optical fiber 100 according to the first embodiment, the relative refractive index difference Διι ₃ (%) of the inner cladding 122 with respect to the outer cladding 122 preferably satisfies the following condition.

-0.15≤Δη ₃ ≤- 0.03-(5)

Next, FIG. 2 is a graph showing optical characteristics of the optical fiber 1 0 0 according to the first embodiment, the outer clad 1 2 relative refractive index of the outer core 1 1 2 difference with respect to 2 delta eta ₂ (%) And the outer diameter 2 b (urn) of the outer core 1 1 2 on a two-dimensional plane with the parameters being parallel, the cutoff wavelength c (1.1 1.πι, 1.6 jm) Area A _ef _f (56〃m ² , 66〃m ² ), dispersion (+1.0 ps / nm / km, +6 O ps / nm / km) ヽ Dispersion slope (0.06 ps / nm ² / km _s 0.08 ps / nm ² / km) and bending loss at 20 mm diameter (S dBZm) FIG. The characteristics shown in these graphs were calculated for a sample having the cross-sectional structure shown in FIG. 1A and having a refractive index profile as shown in FIG. 1B. Specifically, supposed sample is the specific refractive index difference Δ Γ ^ 0. 6 5% of the inner core with respect to the outer cladding, the inner clad relative refractive index difference .DELTA..eta ₃ with respect to the outer clad - 0.05 % Is set. The ratio (a / b) of the outer diameter 2a of the inner core to the outer diameter 2b of the outer core (a / b) is 0.21, and the ratio (c / c) of the outer diameter 2c of the inner clad to the outer diameter 2b of the outer core. b) is set to 2.0. Under the above conditions, various optical properties in the 1.55 1.πι wavelength band were calculated. The cutoff wavelength c (urn) refers to the LPu mode cutoff wavelength measured when a 2 m long optical fiber is wrapped around a mandrel only once loosely to a radius of 140 mm ( The same applies to the following).

In FIG. 2, a hatched area is a preferable area. This hatch ring range, under the conditions described above, the specific refraction index difference .DELTA..eta ₂ is 0.03% of the outer core to 0 with respect to the outer cladding. A 09%, the outer diameter 2 b of the outer core 2 5. 7〃M～29. when a 8〃M, cutoff wavelength input c (〃M), the effective area a _{ef f} (〃M ^2), dispersion (ps / nm / miles), dispersion slope (ps / nm ² / km) _s and bending loss (dB / m) at a diameter of 20 mm.

Furthermore, according to the results of various calculations with the conditions changed, the cutoff wavelength c (〃m) and the effective area A _eff (jm ² ) within the range where the above equations (1) to (4) are satisfied. ), Dispersion (ps / nm / km) ヽ Dispersion slope (ps / nm ² / km) and bending loss (dB / m) at a diameter of 20 mm were confirmed to be favorable values. That is, the optical fiber according to the first embodiment has various characteristics at a wavelength of 1.55 μm. As sex, 5 6-6 6〃M ² of effective area _{A ef f, + 1~ + 6} ps / nm / km in dispersion, 0. 06~0. 08 ps / nm 2 / km dispersion slope, and 0.1 5 ps · km—Polarization mode dispersion of less than ^1/2 , 20 mm diameter with bending loss of less than 5 dB / m. The cutoff wavelength c is 1.1 to 1. Conventionally, in order to suppress the increase in loss due to the use of cables, one guideline is that the bending loss at 20 mm should be 5 dB / km or less.

Next, FIG. 3 is a graph showing the relationship between the effective area A _eif (JLL m ² ) and the bending loss (dB / m) at a diameter of 20 mm in the optical fiber according to the first embodiment. Note that a graph G100 in this figure shows the above relationship for the conventional optical fiber, and a graph G200 shows the above relationship for the optical fiber according to the first embodiment. These graphs G 1 00, as can be seen from the G 200, both the bending as effective area A _{ef f} (〃M ²⁾ is greater loss (dB / m) is increased. For conventional optical fiber, the effective area A _{ef f} becomes 5 6〃M ² or more, the bending loss becomes 5 dB / m or more, it is likely that loss due to cable manufacturing is increased. On the other hand, in the case of the optical fiber according to the first embodiment, the bending loss is 5 dB / m or less if the effective area A _efi is 56 zm ² or more and ₆₆ m ² or less. The increase in loss due to the cable is effectively suppressed.

Next, various characteristics of the sample manufactured as the optical fiber according to the first embodiment will be described. The manufactured sample has an inner core outer diameter 2a of 5.4 2m, an outer core outer diameter 2b of 27.2〃m, an inner cladding outer diameter 2c of 47.0〃m, and an outer diameter of 27.0〃m. The ratio (a / b) of the outer diameter 2a of the inner core to the outer diameter 2a of the side core was 0.20. The ratio of this sample, the relative refractive index difference delta gamma ^ is 0.62% of the inner core with respect to the outer cladding, the relative refractive index difference of the outer core with respect to the outer cladding .DELTA..eta ₂ is 0.05%, the inner cladding with the outer cladding The refractive index difference Δη ₃ was one 0.08%. The sample with the above structure has various characteristics at a wavelength of 1.55 m, an effective area A _{ef f} of ₆₁ m ² , a dispersion of +4.6 ps / nm / km, and ps It has a dispersion slope of / nm ² / km, a polarization mode dispersion of 0.1 1 ps · km—1 / ² , and a bending loss of 0.4 dB / m at a diameter of 20 mm. The cutoff wavelength c was 1.34 m.

As described above, the optical fiber according to the first embodiment has a refractive index profile of a so-called “double core” depressed clad type and satisfies the above expressions (1) to (4). In the / m wavelength band, a larger effective area A _eff can be obtained with the dispersion slope kept low.

(Second embodiment)

FIG. 4 is a refractive index profile of a second embodiment of the optical fiber according to the present invention. The optical fiber according to the second embodiment has a matched clad type refractive index profile in which the clad region is composed of a single layer. Note that, also in the second embodiment, the structure of the core region has a double core structure as in the first embodiment shown in FIG. 1A. The optical fiber according to the second embodiment includes an inner core having an outer diameter 2 a having a refractive index including the center of the optical axis, and an outer core having an outer diameter 2 b surrounding the inner core and having a refractive index η ₂ (<η!). A core and a cladding region surrounding the outer core and having a refractive index n ₃ (<n ₂ ).

Note that the refractive index profile 250 of the optical fiber according to the second embodiment shown in FIG. 4 is the same as that of the first embodiment shown in FIG. Represent. In the refractive index profile 250, the region 251 is a refractive index of each portion on the line L of the inner core, the region 252 is a refractive index of each portion on the line L of the outer core, and the region 253 is This corresponds to the refractive index of each part on the line L of the cladding region. The relative refractive index difference Δι ^ (%) of the inner core and the relative refractive index difference Δη ₂ (%) of the outer core with the cladding region as a reference region are given as follows.

Here, is the refractive index of the inner core, η ₂ is the refractive index of the outer core, and η ₃ is the refractive index of the cladding region. An optical fiber having such a structure, for example, as a base a Shirikagara scan, an appropriate amount of G e 0 ₂ is added to each inner and outer cores obtained by Rukoto.

The optical fiber having the structure described above, the relative refractive index difference of the inner co § respect to the cladding region .DELTA..eta ₂ (%), the relative refractive index difference of the outer core with respect to the cladding region △ eta and ₂ (), the inner core region It is preferable that the following conditions are satisfied when the outer diameter of the outer layer is 2 a (〃m) and the outer diameter of the outer layer core region is 2 b (ju).

0.6 0≤Δη! ≤ 0.80

0.0 5≤Δη ₂ ≤ 0.15-(7)

0.2 1≤a / b≤ 0.27…)

2 0≤ 2 b≤ 2 7 '(9)

Next, FIG. 5 is a graph showing the optical characteristics of the optical fiber according to the second embodiment. The relative refractive index difference Δη ₂ (%) of the outer core with respect to the cladding region and the outer diameter 2 b ( the 〃M) and on two-dimensional plane and parameter Isseki force Dzutoofu wavelength e c (1. 1 urn, 1. 6〃M), the effective area _{^{a eff (5 6 / m 2}} , 6 6〃M ²⁾ dispersion (+ 1. 0 ps / nm / km, + 6. O ps / nm / km) N dispersion slope ^{(0. 0 6 ps / nm 2} Zkm, 0. 0 8 ps / nm 2 / km) , And a graph showing the respective contour lines of the bending hole at a diameter of 20 mm (5 dB / m). The characteristics shown in these graphs are that the relative refractive index difference Δι ^ of the inner core to the cladding region is 0.70%, and the ratio of the outer diameter 2a of the inner core to the outer diameter 2b of the outer core (a / b) Calculated at a wavelength of 1.55〃m for a sample set to 0.24. In FIG. 5, the hatched area is a suitable area. From this hatched range, under this condition, the relative refractive index difference n ₂ of the outer core to the cladding region is 0.05% to 0.13%, and the outer diameter of the outer core 2 b Is 2 1.l〃m to 25.3〃m, the cutoff wavelength c (〃m), the effective area A _{ef f} (〃M ^2), dispersion (ps / nm / km), the dispersion slope ^{(ps / nm 2 / km)} , and the bending loss (dB / m), respectively can be seen to be preferred value.

Furthermore, calculation under various conditions shows that within the range where the above equations (6) to (9) are satisfied, the cutoff wavelength c (/ m), the effective area A _eif (〃m ² ), and the dispersion (ps / nm / km) _N dispersion slope (ps / nm ² / km) ヽ and bending loss (d

B / m) It was confirmed that each was a preferable value. That is, engagement Ru optical fiber to the second embodiment has, as characteristics at a wavelength of 1. 55〃M, the 56～66〃M ² effective area A _{ef f,} +. 1 to ten 6 ps / nm / km in Dispersion, 0.06 to 08 ps / nm ² / km Dispersion slope, 0.15 pskm-Polarization mode dispersion of ^1/2 or less, Bending loss of 5 dB / m or less for 20 mm diameter Have. The cut-off wavelength c is 1.1 to L. 6 zm.

Next, various characteristics of the sample manufactured as the optical fiber according to the second embodiment will be described. The manufactured sample had an inner core outer diameter 2a of 6.0 / m, an outer core outer diameter 2b of 24.0 m, and an inner core outer diameter 2b of the outer core outer diameter 2b. The ratio (a / b) of the outer diameter 2a was 0.25. In this sample, the relative refractive index difference ΔΓ ^ of the inner core with respect to the cladding region was 0.72%, and the relative refractive index difference Δη ₂ of the outer core with respect to the cladding region was 0.08%. According to the evaluation results of this sample, at a wavelength of 1.55 m, the effective area A _eff is 60 / m ² s, the dispersion is +2.8 ps / nm / km, and the dispersion slope is 0.072 ps / nm ² / km, the polarization mode dispersion was 0.09 ps' km— ^{1 / 2} , and the bend diameter at a diameter of 20 mm was 0.5 dB / m. The cutoff wavelength c was 1.38 m.

As described above, according to the optical fiber according to the second embodiment having the so-called double-core / matched-clad refractive index profile, by designing to satisfy the above equations (6) to (9), 1 In the 55 m wavelength band, the effective area can be made sufficiently large while effectively suppressing the increase of the dispersion slope. Also, Other optical properties are also good. Industrial applicability

As described above, according to the present invention, an optical fiber having a dual-core Daveless-Trade-type refractive index profile is designed so as to satisfy the above equations (1) to (4). An optical fiber having a heavy-core / matched-clad refractive index profile was designed to satisfy the above equations (6) to (9), thereby suppressing the increase in dispersion slope in the 1.55-m wavelength band. In this state, the effective area can be increased sufficiently. As a result, the optical fiber according to the present invention can effectively suppress the occurrence of nonlinear optical phenomena and reduce the accumulated dispersion, so that it can be used in an optical transmission line in an optical communication system such as a WDM transmission system. Are suitable.

Claims

Speculation of Word

1. an inner core extending along a predetermined axis and having a predetermined refractive index;

An outer core provided on the outer periphery of the inner core and having a lower refractive index than the inner core;

An inner cladding provided around the outer core and having a lower refractive index than the outer core;

An outer cladding provided on the outer periphery of the inner cladding and having a higher refractive index than the inner cladding;

The relative refractive index difference of the inner core with respect to the outer cladding is ΔΓ ^ (%), the relative refractive index difference of the outer core with respect to the outer cladding is Δη ₂ (%), and the outer diameter of the inner core is 2 a (jm) and the outer diameter of the outer core is 2 b (^ m),

0.5 5 ≤ Anj ≤ 0.75,

0.0 ₂ ≤ Δη ₂ ≤ 0.1 2

0.18≤a / b≤0.24,

2 5≤ 2 b≤ 3 3

An optical fiber that meets certain conditions.

2. When the relative refractive index difference between the inner cladding and the outer cladding is Δη ₃ (%),

_{- 0. 1 5≤Δη 3 ≤- 0. 0} 3

2. The optical fiber according to claim 1, wherein the optical fiber satisfies the following conditions.

3. an inner core extending along a predetermined axis and having a predetermined refractive index;

A cladding provided around the outer core and having a lower refractive index than the outer core; And a storage area.

The relative refractive index difference of the inner core with respect to the cladding region is Δι ^ (%), the relative refractive index difference of the outer core with respect to the cladding region is Δη ₂ (%), and the outer diameter of the inner core is 2 a (jum), and the outer diameter of the outer core is 2 b (〃m).

0.6 0≤ΔΠ! ≤ 0.80,

0.0 5 ≤ Δη ₂ ≤ 0.15,

0.2 1 ≤a / b≤ 0.27,

2 0≤ 2 b≤ 2 7

An optical fiber that meets certain conditions.