KR101965873B1 - low bend loss optical fiber - Google Patents

Abstract

The present invention relates to an optical fiber, which comprises a first clad surrounding a core and a second clad surrounding the first clad, wherein the refractive index of the core increases as the distance r from the center of the core toward the first clad increases , The refractive index of the first clad is lower than the refractive index of the core and linearly decreases as the distance from the center of the core (r = 0) toward the second clad increases, and the refractive index of the second clad The refractive index is lower than the refractive index of the core and is higher than the refractive index of the first cladding but has a constant refractive index (n ₀ ) regardless of the change in distance from the center of the core. The distance r 1 from the center of the core to the starting point of the first cladding ) And the distance r2 from the center of the core to the starting point of the second clad satisfy the condition of 2 x r1? R2? 3 x r1. According to such an optical fiber, the refractive index of the core can be adjusted along the radial direction from the center to provide a merit that the loss due to bending can be further suppressed.

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.

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.

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 the refractive index of the clad is applied differently along the radial direction to suppress the bending loss.

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 which is developed to solve the above-mentioned problems, and which can suppress a bending loss by extending a refractive index variation pattern 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; And a second clad surrounding the first clad, wherein the refractive index of the core linearly decreases as the distance r from the center of the core toward the first clad increases, Is lower than the refractive index of the core and linearly decreases as the distance from the center (r = 0) of the core toward the second cladding increases, and the refractive index of the second cladding decreases as the refractive index And has a constant refractive index (n ₀ ) higher than the refractive index of the first cladding, regardless of a change in distance from the center of the core, and a distance r 1 from the center of the core to the starting point of the first cladding, And the distance r2 from the center of the core to the starting point of the second clad satisfy the condition of 2 x r1? R2? 3 x r1.

,

이고 C₁ ≥1, C₂ ≥1, Reff=C₃×Rmin, Rmin은 광섬유 굴곡 허용 최소반경이고, 상기 C3는 광섬유 코어와 제1 및 제2클래드 소재의 탄성계수와 관련된 상수이고, n1=n12(0)이다.Preferably, the refractive index n12 (r) of the core and the refractive index n34 (r) of the first clad are

,

A _{C 1 ≥1, C 2 ≥1,} Reff = C 3 × Rmin, Rmin is the minimum allowable bend radius of the optical fiber, wherein C3 is a constant associated with the optical fiber core and the first and the modulus of elasticity of the second clad material, n1 = n12 (0).

The minimum allowable radius of curvature R of the optical fiber is 5 mm or more and 20 mm or less. The difference value (n1-n0) between n1 and n0 is 0.002 or more and 0.015 or less, Lt; / RTI >

More preferably, the core and the first clad and the second clad are formed by including an oxide-based glass composition.

The core may be selected from the group consisting of germanosilicate (SiO ₂ -GeO ₂ ), aluminogermannosilicate (SiO ₂ -GeO ₂ -Al ₂ O ₃ ), phosphorosilicate (SiO ₂ -P ₂ O ₅ ), phosphorogermannosilicate (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 Based glass composition belonging to the first group, which comprises phosphorus titanosilicate (SiO ₂ -TiO ₂ ), phosphorothiatosilicate (SiO ₂ -TiO ₂ -P ₂ O ₅ ), and aluminotitanosilicate (SiO ₂ -TiO ₂ -Al ₂ O ₃ ) of fluoride ions (F ^-) in either or any one of the oxide-based glass compositions belonging to the first group and the composition as the addition of the first cladding are phosphorothioate silicate _{(SiO 2 -P 2 O 5)} , aluminum Borosilicate (SiO ₂ -Al ₂ O ₃ ), borosilicate (SiO ₂ -B ₂ O ₃ ), borophosphorosilicate (SiO ₂ -P ₂ O ₅ -B ₂ O ₃ ), boroaluminosilicate (SiO _2- Al ₂ O ₃ -B ₂ O ₃ ) or an oxide-based glass composition belonging to the second group, wherein fluoride ion (F ^- ) is added to the oxide-based glass composition belonging to the second group And the second clad is formed by adding fluoride ion (F ^- ) to silica (SiO ₂ ) or silica (SiO ₂ ).

According to the optical fiber having a low bending loss according to the present invention, 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.

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.

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, and a second clad 22.

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 The first clad is formed to surround the first clad.

The core 11, the first clad 21 and the second clad 22 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 ) Based glass composition belonging to the second group comprising borosilicate (SiO ₂ -P ₂ O ₅ -B ₂ O ₃ ), boroaluminosilicate (SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ ).

The second clad 22 is formed by adding fluoride ion (F ^- ) to silica (SiO ₂ ) or silica (SiO ₂ ).

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 and second clads 21 and 22 are formed by adding P ₂ O ₅ or F- as an additive element to SiO ₂ .

Here, the addition amounts of the elements added to the core 11 and the first and second cladding layers 21 and 22 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 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 second clad 22 is lower than the refractive index of the core 11 and is higher than the refractive index of the first clad 21 but does not have a constant refractive index n ₀ regardless of the change in distance from the center of the core 11 Respectively.

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 are Is satisfied so as to satisfy the condition of Equation (1).

That is, the thickness of the first clad 21 is formed to be equal to or larger than the radius of the core 11 but less than twice the thickness of the core 11. If r2 is smaller than 2 times r1, the effect of the bending loss due to the first cladding region is deteriorated. If r2 is larger than 3 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 starting point of the first clad 21 is 2 占 퐉 to 10 占 퐉.

On the other hand, the refractive index n12 (r) of the core 11 and the refractive index n34 (r) of the first clad 21 are formed under the following conditions (2) and (3).

_{Here, C 1 ≥1, C 2 ≥1} , Reff = C 3 × Rmin is, Rmin is the minimum allowable bend radius of the optical fiber, C ₃ comprises a core 11 and the first and second clad 21, 22. Material Is a constant related to the modulus of elasticity.

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 20 mm or less.

Also, the difference value (n1-n0) between n1 and n0 is set to be 0.002 or more and 0.015 or less.

If the difference (n1-n0) between n1 and n0 is less than 0.002, the characteristics of the optical fiber core are greatly deteriorated. If it is larger than 0.015, the effect of reducing the bending loss due to the difference between n1 and n0 is greater than the effect of the present invention.

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 the refractive index of the region of the first clad 21 (r1? r <r2) is always equal to or larger than the refractive index of the region of the core 11 and the refractive index of the region of the second clad 22 (r2? r < r3) so that the optical loss is 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 = 8 占 퐉 which is the starting point of the second clad 22 and the second clad 22, And the refractive index difference value (n1-n0) between the center of the core 11 and the second clad 22 is 0.005, C ₁ = C ₂ = 1, and C ₃ = 1.28 based glass), R _min = 10mm, and the second case of the optical fiber refractive index of 1.457 for the clad 22 wrapped once around a bobbin of 10mm radius bending loss at the wavelength is represented by a 1.55㎛ 0.79dB.

&Lt; Example 2 >

The radius of the core 11 or the starting point of the first clad 21 r1 = 4 占 퐉 and the starting point of the second cladding 22 r2 = 12 占 퐉, the second cladding 22, And the refractive index difference value (n1-n0) between the center of the core 11 and the second clad 22 is 0.005, C ₁ = C ₂ = 1, and C ₃ = 1.28 When the optical fiber having the _Rmin = 5 mm and the refractive index of the second clad 22 is 1.457 is wrapped once on the bobbin having a radius of 7.5 mm, the bending loss at the wavelength of 1.55 m is 0.41 dB.

&Lt; Example 3 >

The radius of the core 11 or r1 = 4 탆 which is the starting point of the first cladding 21 and r2 = 10 탆 which is the starting point of the second cladding 22 and the second cladding 22, And the refractive index difference value (n1-n0) between the center of the core 11 and the second clad 22 is 0.005, C ₁ = C ₂ = 1, and C ₃ = 1.28 based glass), and R _min = 20mm, the second case of the optical fiber refractive index of 1.457 for the clad 22 wrapped 10,000 times around a bobbin of 20mm radius bending loss at the wavelength is represented by a 1.55㎛ 0.06dB.

<Example 4>

The radius of the core 11 or r1 = 2.5 占 퐉 which is the starting point of the first clad 21 and r2 = 7.5 占 퐉 which is the starting point of the second clad 22 and the second clad 22, The refractive index difference value (n1-n0) between the center of the core 11 and the second clad 22 is 0.01, C ₁ = C ₂ = 1, and C ₃ = 1.28 When the optical fiber having the _Rmin = 5 mm and the refractive index of the second clad 22 is 1.457 is wrapped once on the bobbin having a radius of 5 mm, the bending loss at the wavelength of 1.55 m is 0.24 dB.

&Lt; Example 5 >

The radius of the core 11 or r1 = 2.5 占 퐉 which is the starting point of the first clad 21 and r2 = 7.5 占 퐉 which is the starting point of the second clad 22 and the second clad 22, The refractive index difference value (n1-n0) between the center of the core 11 and the second clad 22 is 0.017, C ₁ = C ₂ = 1, C ₃ = 1.28 based glass), R _min = 5mm, and the second case of the optical fiber refractive index of 1.457 for the clad 22 wrapped 10,000 times around a bobbin a 5mm radius of the bending loss at the wavelength 1.55㎛ is represented by a 8.1 × 10 ^-8 dB.

&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 second clad 22, The refractive index difference value (n1-n0) between the center of the core 11 and the second clad 22 is 0.005, C ₁ = C ₂ = 2, C ₃ = 1.28 When the optical fiber having the _Rmin = 10 mm and the refractive index of the second clad 22 is 1.457 is wrapped once on the bobbin having a radius of 10 mm, the bending loss at the wavelength of 1.55 m is 0.37 dB.

&Lt; Comparative Example 1 &

By way of comparison to the example in 1, for single-mode optical fiber having a common index structure Step _{(C 1 = C 2 = 0} , r1 = r2) are the radius r1 = 4㎛, cladding 22 of the core 11 An optical fiber having a radius r3 = 62.5 占 퐉 from the center of the core 11 to the outermost edge and a refractive index difference value (n1-n0) between the center of the core 11 and the second clad 22 is 0.005 and a refractive index of the second clad 22 is 1.457, The bending loss at a wavelength of 1.55 탆 is 1.60 dB.

&Lt; Comparative Example 2 &

As Example 2 Comparative examples for the case of single-mode optical fiber having a common index structure Step _{(C 1 = C 2 = 0} , r1 = r2) are the radius r1 = 4㎛, cladding 22 of the core 11 An optical fiber having a radius r3 = 62.5 占 퐉 from the center of the core 11 to the outermost edge and a refractive index difference value (n1-n0) between the center of the core 11 and the second clad 22 is 0.005 and a refractive index of the second clad 22 is 1.457 is 7.5 mm The bending loss at a wavelength of 1.55 μm is 7.21 dB when wrapped once in a bobbin of radius.

&Lt; Comparative Example 3 &

(C ₁ = C ₂ = 0, r ₁ = r ₂ ) in the case of a single mode optical fiber having a general step index structure, the radius r 1 of the core 11 is 4 μm, The radius r3 = 62.5 占 퐉 from the center of the core 11 to the outermost edge and the refractive index difference value (n1-n0) between the center of the core 11 and the second clad 22 is 0.005 and the refractive index of the second clad 22 is 1.457. The bending loss at a wavelength of 1.55 μm is 16.8 dB.

&Lt; Comparative Example 4 &

As a comparative example to the fourth embodiment, in the case of an optical fiber having a step index structure (C ₁ = C ₂ = 0 and r ₁ = r ₂ ), the radius r 1 of the core 11 is 2.5 μm, An optical fiber having a radius r3 of 62.5 占 퐉 and a refractive index difference value n1-n0 between the center of the core 11 and the second cladding 22 of 0.01 and a refractive index of 1.457 of the second cladding 22, The bending loss at 1.55 μm wavelength is 0.79 dB when wrapped once.

&Lt; Comparative Example 5 &

As a comparative example to the fifth embodiment, in the case of an optical fiber having a step index structure (C ₁ = C ₂ = 0, r ₁ = r ₂ ), the radius r 1 of the core 11 is 2.5 μm, An optical fiber having a radius r3 of 62.5 占 퐉 and a refractive index difference value n1-n0 between the center of the core 11 and the second cladding 22 of 0.017 and a refractive index of 1.457 of the second cladding 22, Bending loss at 1.55 ㎛ wavelength is 1.4 × 10 ^-6 dB.

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 cladding

Claims (7)

delete A core;
A first clad surrounding the core;
And a second clad surrounding the first clad,
The refractive index of the core linearly decreases as the distance r from the center of the core toward the first clad increases,
The refractive index 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 of the second clad is lower than the refractive index of the core and is higher than the refractive index of the first clad but has a constant refractive index n ₀ irrespective 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 and the distance r2 from the center of the core to the start point of the second clad are
2 x r1? R2? 3 x r1
Is satisfied,
The refractive index n12 (r) of the core and the refractive index n34 (r) of the first clad are

ego
Wherein C _{1 is} C ₁ ≧ 1, C ₂ ≧ 1, Reff = C ₃ × Rmin, Rmin is a minimum allowable radius of the optical fiber, C3 is a constant related to the modulus of elasticity of the optical fiber core and the first and second clad materials, (0). &Lt; / RTI &gt; 3. The optical fiber according to claim 2, wherein the optical fiber bending allowable minimum radius (Rmin) is 5 mm or more and 20 mm or less. 3. The optical fiber according to claim 2, wherein the difference (n1-n0) between n1 and n0 is 0.002 or more and 0.015 or less. delete A core;
A first clad surrounding the core;
And a second clad surrounding the first clad,
The refractive index of the core linearly decreases as the distance r from the center of the core toward the first clad increases,
The refractive index 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 of the second clad is lower than the refractive index of the core and is higher than the refractive index of the first clad but has a constant refractive index n ₀ irrespective 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 and the distance r2 from the center of the core to the start point of the second clad are
2 x r1? R2? 3 x r1
Is satisfied,
Wherein the core and the first clad and the second clad 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 in the oxide-based fluoride ion (F ^-) as in any one of the oxide-based glass compositions belonging to the one or the first group of the glass composition is the composition that belong to the addition of the first cladding are phosphorothioate silicate (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 ) Aluminum ^A-silicate _{(SiO 2 -Al 2 O 3 -B} 2 O 3) The fluoride ion in the oxide-based glass compositions belonging to the one or the second group of oxide-based glass compositions belonging to the second group comprising the (F) Wherein the second cladding is formed by adding fluoride ion (F ^- ) to silica (SiO ₂ ) or silica (SiO ₂ ).

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