WO2023112968A1

WO2023112968A1 - Optical fiber

Info

Publication number: WO2023112968A1
Application number: PCT/JP2022/046080
Authority: WO
Inventors: 裕基井上; 圭省森田; 崇広斎藤
Original assignee: 住友電気工業株式会社
Priority date: 2021-12-14
Filing date: 2022-12-14
Publication date: 2023-06-22

Abstract

An optical fiber (1) is provided with: a core (10) having a maximum refractive index n₁; cladding (30) which is disposed around the core (10) and which has a refractive index n₀ lower than the maximum refractive index n₁; and a depressed part (20) which is disposed between the core (10) and the cladding (30) and which has a refractive index n₂ lower than the refractive index n₀. The relative refractive index difference between the maximum refractive index n₁ and the refractive index n₀ is denoted by Δ₁, the shape of the refractive index distribution n(r) of the core (10) is defined by equation (1) and equation (2) with respect to the radial distance r from the central axis of the core (10). The multiplier α in equation (1) is 1.5-10. The outer diameter 2a of the core (10) is 8-14 μm. The ratio b/a of the outer diameter 2b of the depressed part (20) to the outer diameter 2a of the core is 4.2-7.0.

Description

optical fiber

This disclosure relates to optical fibers. This application claims priority based on Japanese Application No. 2021-202601 filed on December 14, 2021, and incorporates all the descriptions described in the Japanese Application.

Patent document 1 describes ITU-T G. An optical fiber is disclosed that has a MAC value similar to that of a general-purpose single-mode optical fiber (SMF) conforming to Recommendation 652 and that can suppress bending loss. The MAC value is a value obtained by dividing the mode field diameter (MFD) [μm] at a wavelength of 1310 nm by the fiber cutoff wavelength λc [μm]. In this optical fiber, the refractive index distribution in the radial direction of the core is defined by the α multiplier.

Patent Document 2 discloses an optical fiber capable of minimizing bending loss and loss difference by wavelength and maintaining short cut-off wavelength characteristics. In this optical fiber, a trench layer is provided outside the core.

JP 2018-189914 A JP 2013-88818 A

The optical fiber of the present disclosure includes a core having a maximum refractive index _n1 , a clad provided around the core and having a refractive index _n0 lower than the maximum refractive index _n1 , and provided between the core and the clad, and a depressed having a refractive index _n2 lower than the refractive index _n0 . When the relative refractive index difference between the maximum refractive index _n1 and the refractive index _n0 is _Δ1 , the refractive index distribution n(r) of the core is expressed by the formula (1 ) and equation (2) define its shape. The α multiplier in Equation (1) is 1.5 or more and 10 or less. The outer diameter 2a of the core is 8 μm or more and 14 μm or less. The ratio b/a of the depressed outer diameter 2b to the core outer diameter 2a is 4.2 or more and 7.0 or less.

FIG. 1 is a diagram showing a cross section of an optical fiber according to an embodiment. FIG. 2 is a refractive index profile of an optical fiber. FIG. 3 is a graph showing the relationship between the ratio b/a and bending loss. FIG. 4 is a graph showing the relationship between the ratio b/a and the zero dispersion wavelength. FIG. 5 is a graph showing the relationship between the ratio b/a and chromatic dispersion at a wavelength of 1.55 μm.

[Problems to be Solved by the Present Disclosure]
In the optical fiber disclosed in Patent Document 1, the bending loss is suppressed by the core having an α-th power refractive index distribution, but this is not sufficient. In the optical fiber disclosed in Patent Document 2, although the trench layer improves the bending loss characteristics, the design of the refractive index profile becomes complicated because other optical characteristics such as the dispersion characteristics and the fiber cutoff wavelength λc change. .

An object of the present disclosure is to provide an optical fiber capable of further suppressing bending loss without affecting other optical properties.
[Effect of the present disclosure]

According to the present disclosure, it is possible to provide an optical fiber capable of further suppressing bending loss without affecting other optical properties.
[Description of embodiments of the present disclosure]
First, the embodiments of the present disclosure will be listed and described. An optical fiber according to an embodiment of the present disclosure includes a core having a maximum refractive index _n1 , a clad provided around the core and having a refractive index _n0 lower than the maximum refractive index _n1 , and and a depressed therebetween and having a refractive index _n2 lower than the refractive index _n0 . When the relative refractive index difference between the maximum refractive index _n1 and the refractive index _n0 is _Δ1 , the refractive index distribution n(r) of the core is expressed by the formula (1 ) and equation (2) define its shape. The α multiplier in Equation (1) is 1.5 or more and 10 or less. The outer diameter 2a of the core is 8 μm or more and 14 μm or less. A ratio b/a of the depressed outer diameter 2b to the core outer diameter 2a is 4.2 or more and 7.0 or less.

In this optical fiber, the core has an α power type refractive index distribution, and the α multiplier is 10 or less, so bending loss can be suppressed. Further, since the α multiplier is 1.5 or more, the dispersion characteristics can be adjusted. Since the ratio b/a of the depressed outer diameter 2b to the core outer diameter 2a is 4.2 or more, the bending loss can be further suppressed. In addition, since the ratio b/a is 7.0 or less, it is possible to suppress reduction in manufacturing efficiency due to shortening of the converted core length. Here, the equivalent core length is the length of the optical fiber obtained from the glass base material of the core portion having a predetermined length.

The ratio b/a may be greater than 6.0. In this case, bending loss can be further suppressed.

The relative refractive index difference _Δ1 represented by formula (2) may be 0.30% or more and 0.50% or less. By setting the relative refractive index difference _Δ1 to 0.30% or more, the zero dispersion wavelength can be set to 1300 nm or more. By setting the relative refractive index difference _Δ1 to 0.50% or less, the zero dispersion wavelength can be set to 1324 nm or less. With this, the ITU-T G. 657. The zero dispersion wavelength of 1300 nm or more and 1324 nm or less, which is the standard for the A series, can be satisfied.

The relative refractive index difference _Δ2 represented by formula (3) may be −0.12% or more and less than 0%. If it is -0.12% or more, the amount of additive added to the depressed layer can be small. Therefore, it is easy to manufacture, and the amount of gas used when adding can be reduced. Further, when the content is less than 0%, the effect of suppressing bending loss by the depressed layer can be reliably obtained.

The zero-dispersion wavelength may be 1300 nm or more and 1324 nm or less. In this case, the zero-dispersion wavelength specification is satisfied.

The chromatic dispersion at a wavelength of 1.55 μm may be 13.3 ps/nm/km or more and 18.6 ps/nm/km or less. In this case, the standard for chromatic dispersion at a wavelength of 1.55 μm is satisfied.

[Details of the embodiment of the present disclosure]
A specific example of the optical fiber of the present disclosure will be described below with reference to the drawings. The present invention is not limited to these exemplifications, but is indicated by the scope of the claims, and is intended to include all modifications within the meaning and scope of equivalents to the scope of the claims. In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted.

FIG. 1 is a diagram showing a cross section of an optical fiber according to an embodiment. As shown in FIG. 1, the optical fiber 1 comprises a core 10, a depressed 20 and a clad 30. As shown in FIG. The core 10 has a central axis 10a. The central axis 10 a coincides with the central axis of the optical fiber 1 . The core 10 has a maximum refractive index _n1 and an outer diameter 2a. The core 10 has a maximum refractive index _n1 at the central axis 10a. The outer diameter 2a is 8 μm or more and 14 μm or less. The core 10 is made of silica glass containing GeO ₂ , for example.

When the refractive index of the core 10 is increased, the optical energy confinement force is increased, resulting in improved bending loss characteristics. However, as the MFD becomes smaller, the MFD mismatch with the general purpose SMF becomes larger. Therefore, splice loss at the time of fusion splicing increases. In addition, increasing the Ge dopant concentration in core 10 increases transmission loss due to light scattering. Therefore, in the optical fiber 1, another method is used to suppress the bending loss.

A depressed portion 20 is provided around the core 10 . Depressed 20 is provided between core 10 and clad 30 . Depressed portion 20 is in contact with core 10 and clad 30 . Depressed 20 has a refractive index of _n2 and an outer diameter of 2b. The refractive index _n2 is lower than the maximum refractive index _n1 ( _n2 < _n1 ). The depressed 20 is made of silica glass containing fluorine, for example. By providing the depressed portion 20, bending loss characteristics can be improved.

A clad 30 is provided around the core 10 and the depressed portion 20 . The cladding 30 has a refractive index _n0 . The refractive index n ₀ is lower than the maximum refractive index n ₁ and higher than the refractive index n ₂ (n ₂ <n ₀ <n ₁ ). The clad 30 is made of pure silica glass, for example. The relative refractive index difference Δ ₁ represented by the above formula (2) is 0.30% or more and 0.55% or less (0.30%≦Δ ₁ ≦0.55%). The relative refractive index difference _Δ1 is the relative refractive index difference between the central axis 10 a of the core 10 and the clad 30 . The relative refractive index difference Δ ₂ represented by the above formula (3) is −0.12% or more and less than 0% (−0.12%≦Δ ₂ <0%). The relative refractive index difference _Δ2 is the relative refractive index difference between the depressed 20 and the clad 30 .

The zero-dispersion wavelength of the optical fiber 1 is, for example, 1300 nm or more and 1324 nm or less. The chromatic dispersion at a wavelength of 1.55 μm is 13.3 ps/nm/km or more and 18.6 ps/nm/km or less.

The optical fiber 1 is G.I. 657. It has a MAC value equivalent to a general-purpose SMF conforming to the A series. The MAC value of the optical fiber 1 is, for example, 6.7 or more and 7.5 or less (7.1±0.4). The MAC value may be 7.1 or less.

In general, bending loss characteristics can be organized by MAC value, and the larger the MAC value, the worse the bending loss characteristics. When the MAC value exceeds 7.5, the bending loss increases depending on the refractive index distribution. 657. There is a possibility that it will deviate from the standard of the A series. When the MAC value is less than 6.7, the fiber cutoff wavelength λc increases and the G.C. 657. It exceeds the A series standard (≦1260 nm), and the single mode operation of the signal light cannot be guaranteed.

The ratio b/a between the outer diameter 2b and the outer diameter 2a is 4.2 or more and 7.0 or less. The ratio b/a may be greater than 6.0. The longer the distance between the core/depressed interface and the depressed/cladding interface (interfacial distance), the stronger the optical energy confinement force. Therefore, leakage of light energy is suppressed when the optical fiber 1 is bent, and bending loss is improved. In the invention described in Patent Document 1, the ratio b/a is from 2.4 to 4.0. When the ratio b/a is small in this way, the interfacial distance becomes short, so the optical energy confinement force becomes weak. Therefore, the bending loss characteristic deteriorates.

On the other hand, if the ratio b/a is too large, the converted core length will be shortened, resulting in a decrease in manufacturing efficiency and an increase in manufacturing cost. Even if the MAC value is 7.5, which is the upper limit of the MAC value range (7.1±0.4) of the generic SMF, the G. 657. The ratio b/a that can satisfy the A2 standard is 7.0. Therefore, in the optical fiber 1, the upper limit of the ratio b/a is set to 7.0.

Fig. 2 is the refractive index profile of an optical fiber. The horizontal axis indicates the radial position, that is, the radial distance r from the central axis 10a. The vertical axis indicates the refractive index. The core has an α power type refractive index distribution with an α multiplier of 1.5 or more and 10 or less. That is, the shape of the refractive index distribution n(r) in the radial direction of the core 10 is defined by the α multiplier shown in Equation (1) with respect to the radial distance r from the central axis 10a. The α multiplier is 1.5 or more and 10 or less.

The preform base material to be the optical fiber 1 is any one of the VAD (Vapor-phase Axial Deposition) method, the OVD (Outside Vapor Deposition) method which is a multi-layer deposition method, and the MMD method which is a multi-layer deposition method using multiple burners. Manufactured using The α multiplier can be adjusted by changing the flow rate of SiCl ₄ and GeCl ₄ introduced during the fabrication of the core, the flow rate of the combustion supporting gas such as hydrogen and oxygen, the rotation speed, and the traverse speed.

In the optical fiber disclosed in Patent Document 2, the trench layer improves bending loss characteristics. However, in order to form the low refractive index portion by the VAD method or the OVD method, it is necessary to form a plurality of layers with different refractive indices. Also, in order to form a deep trench layer, it is necessary to add many additives. Therefore, the steps and manufacturing costs required to fabricate the preform base material are increased. In this embodiment, a shallow depressed portion is formed by flowing CF ₄ gas, so productivity can be improved. The optical fiber 1 can suppress bending loss by including the depressed 20 .

Next, experimental results obtained by simulation will be described. G. 657. The MFD and the fiber cutoff wavelength λc were set so as to satisfy the A series standard, and the behavior of each characteristic was calculated when the ratio b/a was changed.
rice field.

Table 1 is a table summarizing the specifications of the optical fibers of Experimental Examples 1 to 26. In Table 1, relative refractive index difference Δ ₁ [%], relative refractive index difference Δ ₂ [%], α multiplier, outer diameter 2a, outer diameter 2b, ratio b / a, MAC value, 10 turns with a bending radius of 10 mm Bending loss [dB/10 turn] at a wavelength of 1550 nm, zero dispersion wavelength [nm], and chromatic dispersion [ps/nm/km] at a wavelength of 1.55 μm are shown. The G.I. 657. A2 requires that the bending loss at a wavelength of 1550 nm is 1.0 dB/10 turns or less. Also, G657. A1 is required to have a bending loss of 7.5 dB/10 turns or less at a wavelength of 1550 nm.

FIG. 3 is a graph showing the relationship between the ratio b/a and bending loss. The horizontal axis indicates the ratio b/a. The vertical axis indicates the bending loss [dB/10turn] at a wavelength of 1550nm when winding 10 turns with a bending radius of 10mm. In FIG. 3, the results of Experimental Examples 1 to 16 are shown. In Examples 1 to 16, the relative refractive index difference Δ ₁ [%], relative refractive index difference Δ ₂ [%], MFD, and fiber cutoff wavelength λc are set to the same value. As shown in FIG. 3, the larger the ratio b/a, the lower the bending loss. When the ratio b/a is less than 4.2 (b/a<4.2), the bending loss is reduced to G. 657. It becomes larger than the A1 standard. If the ratio b/a is made larger than 6.0 (b/a>6.0), the bending loss will be reduced to G. 657. It can be made smaller than the A2 standard.

FIG. 4 is a graph showing the relationship between the ratio b/a and the zero dispersion wavelength. The horizontal axis indicates the ratio b/a. The vertical axis indicates the zero-dispersion wavelength [nm]. In FIG. 4, the results of Experimental Examples 1 to 16 are shown. As shown in FIG. 4, the zero-dispersion wavelength is almost constant regardless of the magnitude of the ratio b/a.

FIG. 5 is a graph showing the relationship between the ratio b/a and chromatic dispersion at a wavelength of 1.55 μm. The horizontal axis indicates the ratio b/a. The vertical axis represents chromatic dispersion [ps/nm/km] at a wavelength of 1.55 μm. In FIG. 5, the results of Experimental Examples 1 to 16 are shown. As shown in FIG. 5, the chromatic dispersion at a wavelength of 1.55 μm is almost constant regardless of the magnitude of the ratio b/a.

By comparing Experimental Examples 15 and 18 and comparing Experimental Examples 16 and 17, it can be confirmed that bending loss worsens as the MAC value increases.

From the results of Experimental Examples 17 and 18, when the MAC value is 7.5, by increasing the ratio b/a to greater than 6.8 (b/a>6.8), the G.I. 657. A2 standard can be met. As described above, if the ratio b/a is too large, the productivity decreases, so the upper limit of the ratio b/a was set to 7.0 for evaluation.

From the results of Experimental Examples 8 and 19 to 21, when the relative refractive index difference Δ ₁ is less than 0.3% (Δ ₁ <0.3%), the zero dispersion wavelength is shorter than the standard 1300 nm. I understand. It can be seen that when the relative refractive index difference Δ ₁ exceeds 0.5% (Δ ₁ >0.5%), the zero dispersion wavelength becomes longer than the standard 1324 nm. Therefore, the relative refractive index difference _Δ1 must satisfy 0.30% or more and 0.50% or less.

From the results of Experimental Examples 22 to 26, it can be seen that bending loss becomes larger than the standard when the α multiplier is large. It can be seen that when the α multiplier is small, the zero chromatic dispersion becomes longer than the standard.

　From these results, the G.I. 657. It was confirmed that the standard of the A series could be satisfied, and that the size of the ratio b/a had almost no effect on other optical characteristics such as zero dispersion wavelength and 1.55 μm dispersion.

DESCRIPTION OF SYMBOLS 1... Optical fiber 10... Core 10a... Central axis 20... Depressed 30... Clad

Claims

a core with a maximum refractive index n 1 ;
a clad provided around the core and having a refractive index n0 lower than the maximum refractive index n1 ;
a depressed layer provided between the core and the cladding and having a refractive index n2 lower than the refractive index n0 ;
with
When the relative refractive index difference between the maximum refractive index n1 and the refractive index n0 is Δ1 , the refractive index distribution n(r) of the core is The shape is defined by the formulas (1) and (2),
The α multiplier in formula (1) is 1.5 or more and 10 or less,
The outer diameter 2a of the core is 8 μm or more and 14 μm or less,
A ratio b/a of the depressed outer diameter 2b to the core outer diameter 2a is 4.2 or more and 7.0 or less.
fiber optic.
the ratio b/a is greater than 6.0;
The optical fiber according to claim 1.
The relative refractive index difference Δ1 represented by the formula (2) is 0.30% or more and 0.50% or less.
3. The optical fiber according to claim 1 or 2.
When the relative refractive index difference Δ2 between the refractive index n2 and the refractive index n0 is Δ2 , the relative refractive index difference Δ2 represented by the formula (3) is −0.12% or more and less than 0%. ,
4. The optical fiber according to any one of claims 1-3.
The zero dispersion wavelength is 1300 nm or more and 1324 nm or less,
5. The optical fiber according to any one of claims 1-4.
chromatic dispersion at a wavelength of 1.55 μm is 13.3 ps/nm/km or more and 18.6 ps/nm/km or less;
6. The optical fiber according to any one of claims 1-5.