KR20190057939A - low bend loss optical fiber - Google Patents

Abstract

The present invention relates to an optical fiber comprising: a core; a first clad surrounding the core; a second clad surrounding the first clad; and a third cladding surrounding the second clad, wherein a refractive index (n12(r)) of the core decreases linearly as a distance (r) from the center of the core toward the first clad increases, a refractive index (n34(r)) of the first clad is lower than that of the core and decreases linearly as the distance from the center (r=0) of the core toward the second clad increases or has a constant refractive index irrespective of a change in distance, a refractive index (n56(r)) of the second clad is lower than that of the first clad and has a constant refractive index irrespective of a change in distance from the center of the core, and a refractive index of the third clad is lower than that of the core and higher than that of the second clad but has a constant reference refractive index (n_0) irrespective of the change in the distance from the center of the core. According to the optical fiber, the refractive index can be adjusted differently along a radial direction from the center of the core, thereby providing a merit of further suppressing the loss due to bending.

Description

Low bend loss optical fiber < RTI ID = 0.0 >

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber, and more particularly, to an optical fiber having a low bending loss capable of reducing loss due to bending.

Recently, the FTTH (Fiber To The Home) subscriber transmission service network has been established, and as the related service industry is activated, the demand for optical fiber with improved broadband transmission and bending characteristics is rapidly increasing.

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

G.657 A1, A2 / B2, and B3 were defined according to the minimum allowable radius of curvature, and values of 10 mm, 7.5 mm, and 5 mm were specified, respectively. They are mainly used for long-haul networks, Metro networks and access networks. On the other hand, G.657 optical fibers that are insensitive to bending loss can not only improve bending loss, but also consider other optical properties except for bending loss (mode field diameter, blocking Wavelength, dispersion characteristics, etc.) are standardized in accordance with G.652.D. For example, Table 1 is a specification for the G.657.B3 product in ITU-T.

Generally, in the process of establishing a communication network, the optical fiber may be accommodated in the housing, flexing may occur at the time of installation, and bending loss may occur at the flexing portion. Therefore, researches on optical fibers have been carried out in this regard.

Various measures have been proposed to suppress the loss due to such bending.

Korean Patent No. 10-1591956 and Korean Patent No. 162897 disclose a structure in which bending loss can be suppressed by applying a refractive index of a clad differently along a radial direction.

However, the structures proposed in the above patents have limitations in improving the bending loss by considering only the clad.

It is an object of the present invention to provide an optical fiber capable of suppressing bending loss by expanding a refractive index change pattern up to a core.

According to an aspect of the present invention, there is provided an optical fiber having a low bending loss, comprising: a core; A first clad surrounding the core; A second clad surrounding the first clad; And a third clad surrounding the second clad, wherein a 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 , And 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 (r = 0) of the core toward the second clad increases 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 a change in distance from the center of the core , The refractive index of the third clad 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, (R1) from the center of the core to the start point of the first clad, a distance (r2) from the center of the core to the start point of the second clad, and a distance The distance r3 to the point is 1.75 x r1? R2? 2.8 r1 and 1.15 x r2? R3? 4 x 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 to third clads are formed to include an oxide-based glass composition.

According to the optical fiber having a low bending loss according to the present invention, an optical characteristic similar to that of a conventional single mode optical fiber is applied to an FTTH related communication network, and the loss due to bending can be further suppressed.

1 is a view showing a refractive index distribution of an optical fiber having a low bending loss according to the present invention,
FIG. 2 is a view for explaining the refractive index change at the time of occurrence of bending 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 will be described in more detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a refractive index distribution of an optical fiber having a low bending loss according to the present invention, together with a cross-sectional view. FIG.

Referring to FIG. 1, an 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 first clad 21 is a portion formed outside the core 11 so as to surround the core and the second clad 22 is a portion formed outside the first clad 21 And the third cladding 23 is a portion formed to surround the second cladding 22 from the outside of the second cladding 22. The second cladding 22 is formed to surround the first cladding 21,

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

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

The oxide belonging to the first group of glass compositions germanosilicide silicate (SiO ₂ -GeO _2), alumino-silicate germanosilicide _{(SiO 2 -GeO 2 -Al 2 O} 3), phosphorothioate silicate (SiO ₂ -P ₂ O ₅ ), Phosphorous germano silicate (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 ), phosphorothiatosilicate (SiO ₂ -TiO ₂ -P ₂ O ₅ ), and aluminotitanosilicate (SiO ₂ -TiO ₂ -Al ₂ O ₃ ).

On the other hand, the first clad 21 is formed by adding fluoride ion (F ^- ) to any composition of the oxide-based glass composition belonging to the second group or composition belonging to the second group.

The oxide-based glass composition belonging to the second group is selected from the group consisting of phosphorosilicate (SiO ₂ -P ₂ O ₅ ), aluminosilicate (SiO ₂ -Al ₂ O ₃ ), borosilicate (SiO ₂ -B ₂ O ₃ ) (SiO ₂ -P ₂ O ₅ -B ₂ O ₃ ), boroaluminosilicate (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.

In one example, the core 11 is GeO ₂ or GeO ₂ as an additive element in the SiO ₂ And fluoride ion (F-).

Further, the first to third clads 21, 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 elements added to the core 11 and the first to third clads 21, 22, and 23 may be added corresponding to a 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 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.

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 to the second clad 21 increases .

The refractive index of the first clad 21 may be formed to have a constant refractive index irrespective of a change in distance.

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 irrespective 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 is 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 Respectively.

That is, the refractive index of the core 11 and the refractive index of the first clad 21 have discontinuous values at the boundary point r1 between the core 11 and the first clad 21, and the refractive indexes of the first clad 21 and the second clad 21, The refractive index of the first clad 21 and the refractive index of the second clad 22 at the boundary point r2 of the first clad layer 22 have discontinuous values.

The refractive index of the second cladding 22 and the refractive index of the third cladding 23 have discontinuous values at r3 which is the boundary point between the second cladding 22 and the third cladding 23. [

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

The distance r1 from the center of the core 11 to the starting point of the first clad 21 and the distance r2 from the center of the core 11 to the starting point of the second clad 22, The distance r3 from the center of the first clad 11 to the starting point of the third clad 23 is applied so as to satisfy the following equations (1) and (2).

&Quot; (1) "

1.75 占 r1? R2? 2.8 占 r1

&Quot; (2) "

1.15 x r2? R3? 4 x r1

When r2 is smaller than 1.75 times r1, there is a problem that the MFD (Mode field diameter) becomes small (based on the allowable range), and when r2 is larger than 2.8 times r1, the bending loss suppressing effect is reduced.

If r3 is smaller than 1.15 times r2, the effect of suppressing the bending loss due to the region of the second clad 22 is lowered. If r3 is larger than 4 times r1, fabrication of the optical fiber is difficult and the effect on fabrication cost is not significant.

Here, the distance r1 from the core 11 to the start point of the first clad 21 is 3.9 mu m to 4.1 mu m.

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

_{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 Is a constant related to the modulus of elasticity. When C ₁ is less than 1, the bending loss suppressing effect is lowered, and when it is larger than 1.1, the MFD value becomes smaller (on the basis of the allowable range).

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

Here, the optical fiber has a bending allowable minimum radius (Rmin) of 5 mm or more and 15 mm or less.

The difference value? N1 = 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 cladding 23 is 0.005 or more 0.0065 or less.

When the difference between the core 11 and the reference refractive index n0 is less than 0.005, the effect of suppressing the bending loss is deteriorated. When the difference is larger than 0.0065, the MFD value is reduced.

The difference (? N3) between the refractive index n34 (r1) at the point where r = r1 of the refractive index n34 (r) of the first clad 21 and the reference refractive index n0 of the third cladding 21, n34 (r1) -n0) is set to be not less than -0.002 and not more than 0.001.

Here, when? N3 is less than -0.002, there is a problem that the MFD value becomes small. When it is larger than 0.001, there is a problem that the cutoff wavelength becomes larger than the allowable range.

The difference (? N4 = n34 (r2) -n0) between the refractive index n34 (r2) at the point where r = r2 of the first clad 21 and the reference refractive index n0 is equal to or more than -0.002 and? To be applied.

(N56 (r2)) of the refractive index n56 (r) of the second cladding 22 to the refractive index n56 (r2) of the point r = r2 and the reference refractive index n0 of the third cladding 22 n56 (r2) -n0) is applied so as to be -0.01 or more and -0.0025 or less.

That is, the refractive index n56 (r) of the second clad 22 is applied so that the difference (? N5 = n56 (r) -n0) from the reference refractive index n0 is -0.01 or more and -0.0025 or less irrespective of the distance do.

If? N5 is less than -0.01, fabrication of the optical fiber is difficult, and if it is larger than -0.0025, the bending loss suppressing effect is inferior.

2, the refractive index of the core region 11 (r = 0) along the bending direction R is smaller than the refractive index of the core outer region (0 < r < r1), the optical loss is adjusted to be suppressed.

&Lt; Example 1 >

The radius of the core 11 or r1 = 4 占 퐉 which is the starting point of the first clad 21 and r2 = 9 占 퐉 which is the starting point of the second clad 22 and the third clad 23, the starting point r3 = 16㎛, the radius to the outermost r4 = 62.5㎛, Δn1 = 0.0062, Δn2 = 0.005, Δn3 = -0.0007, Δn4 = -0.0012, Δn5 = -0.006, C 1 = 1, C 2 = 1.28 (Silica glass), _Rmin = 5 mm, and the refractive index of the third clad 23 is 1.457, the bending loss at a wavelength of 1.55 μm is 8.9 × 10 ^-9 dB when the optical fiber is once wrapped around a bobbin of radius 5 mm The cut-off wavelength is 1144 nm, the zero dispersion wavelength and zero dispersion slope, and the MFD at 1310 nm are 1304 nm, 0.086 ps / nm ² / km, and 8.3 μm, respectively.

&Lt; Example 2 >

The radius of the core 11 or r1 = 4 占 퐉 which is the starting point of the first clad 21 and r2 = 8 占 퐉 which is the starting point of the second clad 22 and the third clad 23, to the radius of r3 = 10㎛, the starting point of the outermost r4 = 62.5㎛, Δn1 = 0.0055, Δn2 = 0.0045, Δn3 = 0.001, Δn4 = -0.001, Δn5 = -0.003, C 1 = 1, C 2 = 1.28 ( and silica-based glass), R _min = 5mm, the third case of the optical fiber refractive index of 1.457 in the cladding (23) wrapped once around a bobbin a 5mm radius of the bending loss at the wavelength 1.55㎛ appeared to 0.011dB, cut-off wavelength is And the zero dispersion wavelength and zero dispersion slope and the MFD at 1310 nm are 1306 nm, 0.089 ps / nm ² / km, and 8.2 μm, respectively.

&Lt; Example 3 >

The radius of the core 11 or r1 = 4 占 퐉 which is the starting point of the first clad 21 and r2 = 11 占 퐉 which is the starting point of the second clad 22 and the third clad 23, R4 = 62.5 mu m,? N1 = 0.005,? N2 = 0.004,? N3 = 0.001,? N4 = -0.001,? N5 = -0.006, C ₁ = 1, C ₂ = 1.28 Silica glass), _Rmin = 5 mm, and the refractive index of the third clad 23 was 1.457, the bending loss at a wavelength of 1.55 μm was 1.1 × 10 ^-6 dB when the optical fiber was once wrapped around a bobbin having a radius of 5 mm , The blocking wavelength is 1155 nm, the zero dispersion wavelength and zero dispersion slope, and the MFD at 1310 nm are 1315 nm, 0.085 ps / nm ² / km, and 8.9 μm, respectively.

<Example 4>

The radius of the core 11 or r1 = 4 占 퐉 which is the starting point of the first clad 21 and r2 = 11 占 퐉 which is the starting point of the second clad 22 and the third clad 23, to the radius of r3 = 13㎛, the starting point of the outermost r4 = 62.5㎛, Δn1 = 0.005, Δn2 = 0.004, Δn3 = 0.001, Δn4 = -0.001, Δn5 = -0.003, C 1 = 1, C 2 = 1.28 ( and silica-based glass), R _min = 5mm, the third case of the optical fiber refractive index of 1.457 in the cladding (23) wrapped once around a bobbin a 5mm radius of the bending loss at the wavelength 1.55㎛ appeared to 0.100dB, cut-off wavelength is The zero dispersion wavelength and the zero dispersion slope, and the MFD at 1310 nm are 1318 nm, 0.091 ps / nm ² / km, and 8.9 μm, respectively.

&Lt; Example 5 >

The radius of the core 11 or r1 = 4 占 퐉 which is the starting point of the first clad 21 and r2 = 9 占 퐉 which is the starting point of the second clad 22 and the third clad 23, the starting point r3 = 16㎛, the radius to the outermost r4 = 62.5㎛, Δn1 = 0.0062, Δn2 = 0.005, Δn3 = -0.001, Δn4 = -0.001, Δn5 = -0.006, C 1 = 1, C 2 = 1.28 (Silica glass), _Rmin = 5 mm, and the refractive index of the third clad 23 is 1.457, the bending loss at a wavelength of 1.55 μm is 6.95 × 10 ^-10 dB when the optical fiber is once wrapped around a bobbin of radius 5 mm The cut-off wavelength is 1133 nm, the zero dispersion wavelength and zero dispersion slope, and the MFD at 1310 nm are 1305 nm, 0.090 ps / nm ² / km, and 8.6 μm, respectively.

&Lt; Example 6 >

The radius of the core 11 or r1 = 4 占 퐉 which is the starting point of the first clad 21 and r2 = 8 占 퐉 which is the starting point of the second clad 22 and the third clad 23, to the radius of r3 = 10㎛, the starting point of the outermost r4 = 62.5㎛, Δn1 = 0.0055, Δn2 = 0.0045, Δn3 = 0, Δn4 = 0, Δn5 = -0.006, C 1 = 1, C 2 = 1.28 ( silica based glass), and R _min = 5mm, when the third optical fiber of a refractive index of 1.457 in the cladding (23) wrapped once around a bobbin a 5mm radius of the bending loss at the wavelength 1.55㎛ appeared to 4.27 × 10 ^-8 dB, The cut-off wavelength is 1132 nm, the zero dispersion wavelength and zero dispersion slope, and the MFD at 1310 nm are 1302 nm, 0.089 ps / nm ² / km, and 8.5 μm, respectively.

&Lt; Example 7 >

The radius of the core 11 or r1 = 4 占 퐉 which is the starting point of the first clad 21 and r2 = 11 占 퐉 which is the starting point of the second clad 22 and the third clad 23, the starting point r3 = 16㎛, the radius to the outermost r4 = 62.5㎛, 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), _Rmin = 5 mm, and the refractive index of the third clad 23 is 1.457, the bending loss at a wavelength of 1.55 μm is 2.39 × 10 ^-7 dB when the optical fiber is once wrapped around a bobbin having a radius of 5 mm The cut-off wavelength is 1061 nm, the zero-dispersion wavelength and zero dispersion slope, and the MFD at 1310 nm are 1306 nm, 0.090 ps / nm ² / km, and 8.6 μm, respectively.

&Lt; Comparative Example 1 &

In the case of the single mode optical fiber having a general step index structure (C ₁ = 0, r ₁ = r 2 = r 3), the radius r 1 of the core 11 is 4 μm, When the optical fiber having the radius r4 = 62.5 占 퐉, the refractive index difference value between the center of the core 11 and the clad is 0.005, and the refractive index of the clad is 1.457, the bending loss at 1.55 占 퐉 wavelength is 1.60 dB It appeared, the cutoff wavelength is 1230nm and the MFD of the zero-dispersion wavelength and the zero-dispersion slope is represented by a and 1310nm respectively ^{1320nm, 0.083ps / nm 2 / km} , and 8.6㎛.

According to the optical fiber described above, the refractive index of the core can be adjusted along the radial direction from the center, thereby further reducing the loss due to the bending.

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

Claims (7)

A core;
A first clad surrounding the core;
A second clad surrounding the first clad; And
And a third clad surrounding the second clad,
The refractive index n12 (r) of the core linearly decreases 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 the distance And has a constant refractive index,
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 irrespective of a change in distance from the center of the core,
The refractive index of the third cladding were lower than the refractive index of the core has a constant reference refractive index (n _0), regardless of the changes in distance from the center of the core nopdoe than the refractive index of the second cladding,
(R1) from the center of the core to the start point of the first clad, a distance (r2) from the center of the core to the start point of the second clad, and a distance The distance (r3) to the point
1.75 占 r1? R2? 2.8 占 r1 and 1.15 占 r2? R3? 4 占 r1
Wherein the optical fiber has a low bending loss. The method of claim 1, wherein 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 ). &Lt; / RTI &gt; The optical fiber according to claim 2, wherein the optical fiber bending allowable minimum radius (Rmin) is 5 mm or more and 15 mm or less. The optical fiber according to claim 2, wherein the difference (? N1 = n12 (0) -n0) between the refractive index (n12 (0)) at the point where r = 0 of the core and the reference refractive index (n0) The difference (? N3 = n34 (r1) -n0) between the refractive index n34 (r1) at the point where r = r1 of the refractive index n34 (r) of the first cladding and the reference refractive index n0 is -0.002 Of the first clad and the difference (? N4 = n34 (r2) -n0) between the refractive index (n34 (r2)) at the point of r = r2 of the first cladding and the reference refractive index (n0) And the difference between the refractive index of the second cladding and the reference refractive index n0 is -0.01 or more and -0.0025 or less. 2. The optical fiber according to claim 1, wherein r1 is 3.9 to 4.1 mu m, and a distance (r4) from the center of the core to an end point of the third clad is 50 to 100 mu m. . The optical fiber according to claim 1, wherein the core and the first to third clads are formed to include an oxide-based glass composition. The method of claim 6, wherein the core is germanosilicide silicate (SiO ₂ -GeO _2), alumino-silicate germanosilicide _{(SiO 2 -GeO 2 -Al 2 O} 3), phosphorothioate silicate (SiO ₂ -P ₂ O ₅₎ (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 ), phosphorous germanosilicate (SiO ₂ -TiO ₂ -Al ₂ O ₃ ), and a first group comprising a titanosilicate (SiO ₂ -TiO ₂ ), a phosphorothiatosilicate (SiO ₂ -TiO ₂ -P ₂ O ₅ ), and an aluminothitannosilicate (F &lt; ^- &gt;) is added to any one of the oxide-based glass compositions belonging to the first group or the oxide-based glass compositions belonging to the first group,
The first cladding may be made of phosphorosilicate (SiO ₂ -P ₂ O ₅ ), aluminosilicate (SiO ₂ -Al ₂ O ₃ ), borosilicate (SiO ₂ -B ₂ O ₃ ), borophosphorosilicate (SiO ₂ -P ₂ O ₅ -B ₂ O ₃ ), and an oxide-based glass composition belonging to a second group comprising boroaluminosilicate (SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ ) (F &lt; ^- &gt;) is added to an oxide-based glass composition belonging to the formula
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
Wherein the third cladding is made of silica (SiO ₂ ) or silica (SiO ₂ ) added with P ₂ O ₅ or fluoride ion (F ^- ).

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