KR102033405B1 - low bend loss optical fiber - Google Patents

Abstract

The present invention relates to an optical fiber, comprising a core, a first cladding surrounding the core, a second cladding surrounding the first clad, and a third cladding surrounding the second cladding, wherein the refractive index n12 (r) of the core is As the distance (r) from the center of the core toward the first cladding increases linearly, the refractive index (n34 (r)) of the first cladding is lower than that of the core and the center of the core (r = 0). As the distance from the direction toward the second cladding increases linearly decreases or has a constant refractive index irrespective of the distance change, the refractive index n56 (r) of the second cladding is lower than that of the first cladding. It has a constant refractive index regardless of the change in distance from the center of the core, and the refractive index of the third cladding is lower than the refractive index of the core and higher than the refractive index of the second clad, but is constant regardless of the change in distance from the center of the core. It has a structure having a refractive index (n _0). According to such an optical fiber, the core also provides an advantage that the loss due to bending can be further suppressed by adjusting the refractive index differently from the center along the radial direction.

Description

Low bend loss optical fiber

The present invention relates to an optical fiber, and more particularly, to an optical fiber having a low bending loss that can reduce the loss due to bending.

Recently, the FTTH (Fiber To The Home) subscriber transmission service network of 100Mbps or more is being established, and the demand for optical fiber with improved bend characteristics and broadband characteristics is rapidly increasing as the related service industry is activated.

In this regard, the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) under the International Telecommunication Union has established the G.657 fiber optic standard, which is insensitive to bending loss.

According to the minimum allowable radius of curvature, G.657 A1, A2 / B2, and B3 were divided into 10mm, 7.5mm, and 5mm, respectively. They are mainly used for long-haul networks, metro networks and access networks, respectively. On the other hand, G.657 optical fibers that are insensitive to bending loss not only improve the bending loss, but also consider other optical characteristics (mode field diameter, blocking) in consideration of compatibility with the existing optical fiber G.652.D. Wavelength, dispersion characteristics, etc.) are standardized according to G.652.D. As an example, Table 1 is the specification for G.657.B3 products in ITU-T.

In general, when the optical fiber is accommodated in the housing or laid during the construction of the communication network, bending may occur, and bending loss occurs in the bending portion. Therefore, much research has been conducted on the optical fiber in this regard.

Various measures have been proposed to suppress the loss caused by this bending.

In Korean Patent Registration Nos. 10-1591956 and Korean Patent Registration No. 162897, a structure capable of suppressing bending loss by applying different refractive indices of clad along radial directions is proposed.

However, the structure proposed in the above patents is limited in improving bending loss by considering only the cladding.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical fiber in which bending loss can be suppressed by extending a refractive index change pattern to a core.

In order to achieve the above object, an optical fiber having a low bending loss according to the present invention includes a core; A first cladding surrounding the core; A second cladding surrounding the first cladding; And a third cladding surrounding the second cladding, wherein the refractive index n12 (r) of the core is linearly increased as the distance r from the center of the core toward the first clad increases. The refractive index n34 (r) of the first clad is lower than the refractive index of the core and decreases linearly as the distance from the center of the core (r = 0) toward the second clad increases. Or a constant refractive index regardless of the distance change, the refractive index n56 (r) of the second cladding is lower than the refractive index of the first cladding, and has a constant refractive index regardless of the distance change from the center of the core. The refractive index of the third cladding is lower than the refractive index of the core and higher than the refractive index of the second clad, but has a constant reference refractive index (n ₀ ) regardless of a change in distance from the center of the core. The distance r1 from the center of the core to the start point of the first clad, the distance r2 from the center of the core to the start point of the second clad and the start of the third clad from the center of the core The distance r3 to the point satisfies the conditions of 1.75 × r1 ≦ r2 ≦ 2.8 × r1 and 1.15 × r2 ≦ r3 ≦ 4 × r1.

Preferably, the refractive index n12 (r) of the core is

_{1 ≤ C 1 ≤1.1, Reff =} C 2 × Rmin, Rmin is the minimum allowable bend radius of the optical fiber, wherein C ₂ is a constant related to the optical fiber core and the first to third elastic modulus of the clad material, n1 = n12 (0 )to be.

Preferably, the core and the first clad to the third clad are formed of an oxide-based glass composition.

The low bending loss optical fiber according to the present invention provides an advantage that the loss due to bending can be further suppressed while having optical characteristics similar to those of a conventional single mode optical fiber for application to an FTTH related communication network.

1 is a view showing the refractive index distribution of the optical fiber having a low bending loss in accordance with the present invention matched with a cross-sectional view,
FIG. 2 is a view for explaining a change in refractive index when bending occurs of the optical fiber of FIG. 1.

Hereinafter, an optical fiber having a low bending loss according to a preferred embodiment of the present invention with reference to the accompanying drawings will be described in more detail.

1 is a view showing matching of the refractive index distribution of the optical fiber having a low bending loss according to the present invention with a cross-sectional view.

Referring to FIG. 1, the optical fiber 10 having a low bending loss according to the present invention includes a core 11, a first clad 21, a second clad 22, and a third clad.

The core 11 is a portion formed to have a first radius in the center, and the first clad 21 is a portion formed to surround the core outside the core 11, and the second clad 22 is outside the first clad 21. In the first clad 21 is a portion formed to surround, the third clad 23 is a portion formed to surround the second clad 22 outside the second clad 22.

The core 11 and the first to third clads 21 to 23 are preferably formed by adding an additional element in accordance with the refractive index distribution characteristic described later using an oxide-based glass composition as a base material.

Preferably, the core 11 is formed by adding fluoride ions (F ⁻ ) to one of the oxide-based glass compositions belonging to the first group described below or to a composition belonging to the first group.

Oxide-based glass compositions belonging to the first group include germano silicates (SiO ₂ -GeO ₂ ), aluminogermanosilicates (SiO ₂ -GeO ₂ -Al ₂ O ₃ ), phosphorosilicates (SiO ₂ -P ₂ O ₅ ), Phosphorogermanosilicate (SiO ₂ -GeO ₂ -P ₂ O ₅ ), aluminosilicate (SiO ₂ -Al ₂ O ₃ ) phosphoroaluminosilicate (SiO ₂ -Al ₂ O ₃ -P ₂ O ₅ ), Titanosilicate (SiO ₂ -TiO ₂ ), phosphorotitanosilicate (SiO ₂ -TiO ₂ -P ₂ O ₅ ), alumino titanosilicate (SiO ₂ -TiO ₂ -Al ₂ O ₃ ).

Meanwhile, the first clad 21 is formed by adding fluoride ions (F ⁻ ) to any one of the oxide-based glass compositions belonging to the second group or the composition belonging to the second group.

Oxide-based glass compositions belonging to the second group include phosphorosilicates (SiO ₂ -P ₂ O ₅ ), aluminosilicates (SiO ₂ -Al ₂ O ₃ ), borosilicates (SiO ₂ -B ₂ O ₃ ), borofoss Porosilicates (SiO ₂ -P ₂ O ₅ -B ₂ O ₃ ) and boroaluminosilicates (SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ ).

The second cladding 22 is fluoride ion (F ^-), a silica (SiO _2), ^- the composition by addition of the application that the addition of, or fluoride ion (F) in the oxide-based glass compositions belonging to the second group described above do.

The third cladding 23 is applied to a silica (SiO ₂₎ or silica (SiO ₂₎ on a P ₂ O ₅ or a fluoride ion (F ^-) is the composition that was added.

As an example, the core 11 may be formed of GeO ₂ or GeO ₂ as an additive element to SiO ₂ . And fluoride ions (F-).

In addition, the first to third clads 21 and 22 and 23 are formed by adding P ₂ O ₅ or F − as an additive element to SiO ₂ .

Here, the addition amount of the element added to the core 11 and the first to third clads 21 and 22 and 23 may be added corresponding to the refractive index conversion pattern described later.

On the other hand, the refractive index of the core 11 is formed to decrease linearly as the distance r in the direction from the center r = 0 of the core 11 toward the first clad 21 increases.

Here, r represents the distance in the radial direction with respect to the center of the core 11.

In addition, the refractive index of the first clad 21 is lower than the refractive index of the core 11 and linearly increases as the distance from the center r = 0 of the core 11 toward the second clad 21 increases. It is formed to decrease.

Alternatively, the refractive index of the first clad 21 may be formed to have a constant refractive index regardless of the distance change.

The refractive index of the second clad 22 is lower than the refractive index of the first clad 21 and is formed to have a constant refractive index regardless of the change in distance from the center of the core 11.

The refractive index of the third clad 23 is lower than the refractive index of the core 11 and higher than the refractive index of the second clad 22, but has a constant reference refractive index n ₀ regardless of a change in distance from the center of the core 11. Formed.

That is, the refractive index of the core 11 and the refractive index of the first clad 21 have a discontinuous value at r1, which is the boundary point between the core 11 and the first clad 21, and the first clad 21 and the second clad. At r2, the boundary point of (22), the refractive index of the first clad 21 and the refractive index of the second clad 22 have discontinuous values.

In addition, the refractive index of the second clad 22 and the refractive index of the third clad 23 have a discontinuous value at r3, which is a boundary point between the second clad 22 and the third clad 23.

In this structure, the first clad 21 is formed to have a suitable thickness to suppress light loss based on the outer diameter of the core 11.

To this end, the distance r1 from the center of the core 11 to the start point of the first clad 21, the distance r2 from the center of the core 11 to the start point of the second clad 22 and the core The distance r3 from the center of (11) to the start point of the third clad 23 is applied to satisfy the condition of Equations 1 and 2 below.

<Equation 1>

1.75 × r1 ≤ r2 ≤2.8 × r1

<Equation 2>

1.15 × r2 ≤ r3 ≤4 × r1

If r2 is smaller than 1.75 times of r1, there is a problem (mode of tolerance) of MFD (Mode field diameter), and if r2 is larger than 2.8 times of r1, bending loss suppression effect is inferior.

In addition, when r3 is smaller than 1.15 times of r2, the effect of suppressing bending loss due to the second clad 22 region is reduced, and when r3 is larger than 4 times of r1, it is difficult to manufacture an optical fiber and does not have a large effect on manufacturing cost.

Here, the distance r1 from the core 11 to the start time of the first clad 21 is applied to be 3.9 μm to 4.1 μm.

On the other hand, the refractive index n12 (r) of the core 11 is formed under the condition of Equation 3 below.

_{Here, 1 ≤ C 1 ≤1.1, Reff} = C 2 × Rmin is, Rmin is the minimum allowable bend radius of the optical fiber, C ₂ of the core 11 and the first to third cladding 21 22 23 Material Constant associated with the elastic modulus of. If C ₁ is less than 1, the bending loss suppressing effect is lowered. If C ₁ is larger than 1.1, the MFD value is decreased.

In addition, n1 = n12 (0), that is, n1 is a refractive index at the core center r = 0.

Here, the optical fiber is applied that the minimum allowable bending radius (Rmin) is 5mm or more and 15mm or less.

In addition, the difference value (Δn1 = n12 (0) −n0) between the refractive index n12 (0) at the point where r = 0 of the core 11 and the reference refractive index n0 of the third clad 23 is 0.005 or more. Apply to be less than 0.0065.

If the difference between the core 11 and the reference refractive index n0 is less than 0.005, the bending loss suppression effect is inferior. If the difference is greater than 0.0065, the MFD value is reduced.

Further, the difference value Δn 3 = between the refractive index n 34 (r 1) at the point where r = r 1 of the refractive index n 34 (r) of the first clad 21 and the reference refractive index n 0 of the third clad 23. n34 (r1) -n0) is applied so that it is -0.002 or more and 0.001 or less.

Here, if Δn 3 is less than −0.002, there is a problem that the MFD value becomes small, and when Δn 3 is larger than 0.001, the blocking wavelength becomes larger than the allowable range.

Further, the difference value (Δn4 = n34 (r2) -n0) between the refractive index n34 (r2) and the reference refractive index n0 at the point where r = r2 of the first clad 21 is set to be -0.002 or more and Δn3 or less. Apply.

The difference between the refractive index n56 (r2) at the point where r = r2 of the refractive index n56 (r) of the second clad 22 and the reference refractive index n0 of the third cladding 23 is Δn5 = n56 (r2) -n0) is applied so that it is -0.01 or more and -0.0025 or less.

That is, the refractive index n56 (r) of the second clad 22 is applied such that the difference value (Δn5 = n56 (r) -n0) from the reference refractive index n0 becomes -0.01 or more and -0.0025 or less regardless of the distance. do.

Here, if Δn5 is less than -0.01, it is difficult to fabricate the optical fiber, and when Δn5 is larger than -0.0025, the bending loss suppressing effect is inferior.

As shown in FIG. 2, the optical fiber 10 has a refractive index of the core 11 center region r = 0 along the bending direction R when the bending deformation due to bending occurs in the core outer region (0 <r). The light loss is adjusted to be suppressed by always being made larger than the refractive index of <r1).

<Example 1>

Fabricated according to the conditions described above, the radius of the core 11 or the starting point of the first clad 21 r1 = 4㎛, the starting point of the second clad 22 r2 = 9㎛, the third clad 23 R3 = 16µm, radius r4 = 62.5µm to outermost part, Δn1 = 0.0062, Δn2 = 0.005, Δn3 = -0.0007, Δn4 = -0.0012, Δn5 = -0.006, C ₁ = 1, C ₂ = 1.28 (Silica-based glass), when R _min = 5 mm and the optical fiber having a refractive index of 1.457 of the third clad 23 was wrapped once in a bobbin with a 5 mm radius, the bending loss at a wavelength of 1.55 占 퐉 is shown as 8.9 x 10 ^-9 dB. The blocking wavelength is 1144 nm and the zero-dispersion wavelength, zero-dispersion slope, and MFD at 1310 nm are 1304 nm, 0.086 ps / nm ² / km, and 8.3 μm, respectively.

<Example 2>

Fabricated according to the conditions described above, the radius of the core 11 or the starting point of the first clad 21 r1 = 4㎛, the starting point of the second clad 22 r2 = 8㎛, the third clad 23 R3 = 10 μm, the radius to the outermost r4 = 62.5 μm, Δn1 = 0.0055, Δn2 = 0.0045, Δn3 = 0.001, Δn4 = -0.001, Δn5 = -0.003, C ₁ = 1, C ₂ = 1.28 ( Silica-based glass), when R _min = 5 mm and the optical fiber with a refractive index of 1.457 of the third clad 23 was wrapped once in a bobbin with a 5 mm radius, the bending loss at a wavelength of 1.55 μm was 0.011 dB, and the blocking wavelength was The zero-dispersion wavelength, zero-dispersion slope, and MFD at 1310 nm are 1306 nm, 0.089 ps / nm ² / km, and 8.2 μm, respectively.

<Example 3>

Fabricated according to the conditions described above, the radius of the core 11 or the starting point of the first clad 21 r1 = 4㎛, the starting point of the second clad 22 r2 = 11㎛, the third clad 23 R3 = 13 μm, the radius to the outermost r4 = 62.5 μm, Δn1 = 0.005, Δn2 = 0.004, Δn3 = 0.001, Δn4 = -0.001, Δn5 = -0.006, C ₁ = 1, C ₂ = 1.28 ( Silica-based glass), when R _min = 5 mm and the optical fiber having a refractive index of 1.457 of the third clad 23 was wrapped in a bobbin of 5 mm radius once, the bending loss at a wavelength of 1.55 μm was 1.1 × 10 ^-6 dB. The blocking wavelength is 1155nm and the zero-dispersion wavelength, zero-dispersion slope and MFD at 1310nm are 1315nm, 0.085ps / nm ² / km and 8.9㎛, respectively.

<Example 4>

Fabricated according to the conditions described above, the radius of the core 11 or the starting point of the first clad 21 r1 = 4㎛, the starting point of the second clad 22 r2 = 11㎛, the third clad 23 R3 = 13 μm, the radius to the outermost r4 = 62.5 μm, Δn1 = 0.005, Δn2 = 0.004, Δn3 = 0.001, Δn4 = -0.001, Δn5 = -0.003, C ₁ = 1, C ₂ = 1.28 ( Silica-based glass), when R _min = 5 mm and the optical fiber having a refractive index of 1.457 of the third clad 23 was wrapped in a bobbin of 5 mm radius once, the bending loss at a wavelength of 1.55 μm was 0.100 dB, and the blocking wavelength was The zero-dispersion wavelength, zero-dispersion slope, and MFD at 1310 nm are 1318 nm, 0.091 ps / nm ² / km, and 8.9 μm, respectively.

Example 5

Fabricated according to the conditions described above, the radius of the core 11 or the starting point of the first clad 21 r1 = 4㎛, the starting point of the second clad 22 r2 = 9㎛, the third clad 23 R3 = 16µm, the radius to the outermost r4 = 62.5µm, Δn1 = 0.0062, Δn2 = 0.005, Δn3 = -0.001, Δn4 = -0.001, Δn5 = -0.006, C ₁ = 1, C ₂ = 1.28 (Silica-based glass), when R _min = 5 mm and the optical fiber with a refractive index of 1.457 of the third clad 23 was wrapped once in a bobbin with a 5 mm radius, the bending loss at a wavelength of 1.55 占 퐉 was 6.95 x 10 ^-10 dB. The blocking wavelength is 1133nm and the zero-dispersion wavelength, zero-dispersion slope and MFD at 1310nm are 1305nm, 0.090ps / nm ² / km, and 8.6㎛, respectively.

<Example 6>

Fabricated according to the conditions described above, the radius of the core 11 or the starting point of the first clad 21 r1 = 4㎛, the starting point of the second clad 22 r2 = 8㎛, the third clad 23 R3 = 10 μm, the radius to the outermost r4 = 62.5 μm, Δn1 = 0.0055, Δn2 = 0.0045, Δn3 = 0, Δn4 = 0, Δn5 = -0.006, C ₁ = 1, C ₂ = 1.28 (silica System glass), when R _min = 5 mm and the optical fiber having a refractive index of 1.457 of the third clad 23 is wrapped once in a bobbin of 5 mm radius, the bending loss at a wavelength of 1.55 μm was found to be 4.27 × 10 ^-8 dB. The blocking wavelength is 1132 nm and the zero-dispersion wavelength, zero-dispersion slope, and MFD at 1310 nm are 1302 nm, 0.089 ps / nm ² / km, and 8.5 µm, respectively.

<Example 7>

Fabricated according to the conditions described above, the radius of the core 11 or the starting point of the first clad 21 r1 = 4㎛, the starting point of the second clad 22 r2 = 11㎛, the third clad 23 R3 = 16 μm, the radius to the outermost r4 = 62.5 μm, Δn1 = 0.0055, Δn2 = 0.0045, Δn3 = -0.001, Δn4 = -0.002, Δn5 = -0.006, C ₁ = 1, C ₂ = 1.28 (Silica-based glass), when R _min = 5 mm and the optical fiber having a refractive index of 1.457 of the third clad 23 was wrapped once in a bobbin with a 5 mm radius, the bending loss at a wavelength of 1.55 占 퐉 was 2.39 x 10 ^-7 dB. The blocking wavelength is 1061 nm and the zero-dispersion wavelength, zero-dispersion slope and MFD at 1310 nm are 1306 nm, 0.090 ps / nm ² / km, and 8.6 μm, respectively.

Comparative Example 1

As a comparative example for Example 1, in the case of a single mode optical fiber having a general step index structure (C ₁ = 0, r ₁ = r 2 = r 3), a radius r 1 = 4 μm of the core 11 and an outermost angle of the cladding When the optical fiber with a radius of r4 = 62.5 μm, the difference in refractive index between the center of the core 11 and the cladding is 0.005 and the refractive index of the clad is 1.457 is wrapped in a bobbin of 10 mm radius once, the bending loss at a wavelength of 1.55 μm is 1.60 dB. The blocking wavelength is 1230nm, the zero-dispersion wavelength, zero-dispersion slope and MFD at 1310nm are 1320nm, 0.083ps / nm ² / km, and 8.6㎛, respectively.

According to the optical fiber described above, the core also provides an advantage that the loss due to bending can be further suppressed by adjusting the refractive index differently from the center to the radial direction.

11: core 21: first cladding
22: second clad 23: third clad

Claims (7)

delete A core;
A first cladding surrounding the core;
A second cladding surrounding the first cladding; And
And a third cladding surrounding the second cladding.
The index of refraction n12 (r) of the core decreases linearly as the distance r from the center of the core toward the first clad increases.
The refractive index n34 (r) of the first clad is lower than the refractive index of the core and decreases linearly or changes with distance as the distance from the center of the core (r = 0) toward the second clad increases. Has a constant refractive index regardless of
The refractive index n56 (r) of the second clad is lower than the refractive index of the first clad and has a constant refractive index regardless of a change in distance from the center of the core.
The refractive index of the third cladding is lower than the refractive index of the core and higher than the refractive index of the second clad, but has a constant reference refractive index (n ₀ ) regardless of the change in distance from the center of the core,
The distance r1 from the center of the core to the start point of the first clad, the distance r2 from the center of the core to the start point of the second clad and the start of the third clad from the center of the core The distance to the point (r3)
1.75 × r1 ≤ r2 ≤2.8 × r1 and 1.15 × r2 ≤ r3 ≤4 × r1
To satisfy the conditions of
The index of refraction n12 (r) of the core is

_{1 ≤ C 1 ≤1.1, Reff =} C 2 × Rmin, Rmin is the minimum allowable bend radius of the optical fiber, wherein C ₂ is a constant related to the optical fiber core and the first to third elastic modulus of the clad material, n1 = n12 (0 Optical fiber having a low bending loss, characterized in that). The optical fiber having a low bending loss of claim 2, wherein the optical fiber bending allowable minimum radius Rmin is 5 mm or more and 15 mm or less. The difference value (Δn1 = n12 (0) −n0) between the refractive index n12 (0) and the reference refractive index n0 at the point at which r = 0 of the core is 0.005 or more and 0.0065 or less, The difference value (Δn3 = n34 (r1) −n0) between the refractive index n34 (r1) at the point where r = r1 of the refractive index n34 (r) of the first clad and the reference refractive index n0 is −0.002 The difference value (Δn4 = n34 (r2) -n0) between the refractive index n34 (r2) and the reference refractive index n0 at the point at which r = r2 of the first clad is 0.001 or less and Δn3 or less And wherein the difference between the refractive index of the second clad and the reference refractive index (n0) is -0.01 or more and -0.0025 or less. delete delete A core;
A first cladding surrounding the core;
A second cladding surrounding the first cladding; And
And a third cladding surrounding the second cladding.
The index of refraction n12 (r) of the core decreases linearly as the distance r from the center of the core toward the first clad increases.
The refractive index n34 (r) of the first clad is lower than the refractive index of the core and decreases linearly or changes with distance as the distance from the center of the core (r = 0) toward the second clad increases. Has a constant refractive index regardless of
The refractive index n56 (r) of the second clad is lower than the refractive index of the first clad and has a constant refractive index regardless of a change in distance from the center of the core.
The refractive index of the third cladding is lower than the refractive index of the core and higher than the refractive index of the second clad, but has a constant reference refractive index (n ₀ ) regardless of the change in distance from the center of the core,
The distance r1 from the center of the core to the start point of the first clad, the distance r2 from the center of the core to the start point of the second clad and the start of the third clad from the center of the core The distance to the point (r3)
1.75 × r1 ≤ r2 ≤2.8 × r1 and 1.15 × r2 ≤ r3 ≤4 × r1
To satisfy the conditions of
The core and the first clad to the third cladding is formed including an oxide-based glass composition,
The core is germanosilicate (SiO ₂ -GeO ₂ ), aluminogermanosilicate (SiO ₂ -GeO ₂ -Al ₂ O ₃ ), phosphorosilicate (SiO ₂ -P ₂ O ₅ ), phosphorogeranosilicate (SiO ₂ -GeO ₂ -P ₂ O ₅ ), aluminosilicate (SiO ₂ -Al ₂ O ₃ ) phosphoroaluminosilicate (SiO ₂ -Al ₂ O ₃ -P ₂ O ₅ ), titanosilicate (SiO ₂ Oxide composition belonging to the first group comprising -TiO ₂ ), phosphoro titanosilicate (SiO ₂ -TiO ₂ -P ₂ O ₅ ), alumino titanosilicate (SiO ₂ -TiO ₂ -Al ₂ O ₃ ) Fluoride ion (F ⁻ ) is added to any one or any one of the oxide glass compositions belonging to the first group,
The first cladding is phosphorosilicate (SiO ₂ -P ₂ O ₅ ), aluminosilicate (SiO ₂ -Al ₂ O ₃ ), borosilicate (SiO ₂ -B ₂ O ₃ ), borophosphosilicate (SiO ₂ Any one of the oxide-based glass compositions belonging to the second group including -P ₂ O ₅ -B ₂ O ₃ ) and boroaluminosilicate (SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ ) or the second group It is composed by adding fluoride ions (F ⁻ ) to the oxide-based glass composition belonging to,
The second cladding is fluoride ion (F ^-) in the silica (SiO ₂₎ ^- and the composition to be added with, applied to or by the addition of fluoride ion (F) in the oxide-based glass compositions belonging to the second group
And the third cladding is applied to a silica (SiO ₂₎ or silica (SiO ₂₎ on a P ₂ O ₅ or a fluoride ion (F ^-) optical fiber with low bending loss, characterized in that the composition by the addition of.

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