KR100826053B1 - Optical fiber for WDM transmission system, Optical transmission line and Optical transmission system using the same - Google Patents

Abstract

The present invention discloses an optical fiber for a wavelength division multiplexing optical transmission system, an optical transmission line and an optical communication system using the same. In the optical fiber according to the present invention, an optical fiber comprising a core region and a clad region, wherein the core region is located on the optical center axis (A), the radius is r ₁ , and the specific refractive index difference is Δ1 including Δ1a and Δ1b. Core region; (B) a second core region surrounding the first core region, having a radius r ₂ and a specific refractive index difference Δ2; And (C) a third core region surrounding the second core region and having a radius r ₃ and a specific refractive index difference Δ3, wherein each of the radii satisfies a relationship of r ₁ <r ₂ <r ₃ , and has a specific refractive index. The difference satisfies the relationship Δ1a≥Δ1b> Δ2, Δ2 <Δ3 and Δ1a≥Δ1b> Δ3, and each of the refractive index differences satisfies the following equation, wherein the radius r ₁ of the first core region is 3.38 ± 0.6 Μm, Δ1a is at least 0.474 ± 0.03%, Δ1b is 0.474 ± 0.03%; The radius r ₂ of the second core region is 6.77 ± 0.6 μm and Δ2 is no greater than −0.075 ± 0.03%; The radius r ₃ of the third core region is 9.59 ± 0.6 μm, and Δ3 is 0.233 ± 0.03%.

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(Where r in the equation satisfies a relation of -r ₁ <r <0 and 0 <r <r ₁ , respectively).

Wavelength Division Multiplexing (WDM), Optical Fiber, Effective Cross-sectional Area, Dispersion, Raman Amplification

Description

Optical fiber for WDM transmission system, Optical transmission line and Optical transmission system using the same}

The following drawings, which are attached to this specification, illustrate exemplary embodiments of the present invention, and together with the detailed description of the present invention, serve to further understand the technical spirit of the present invention. It should not be construed as limited to.

1 is a cross-sectional view schematically showing a configuration region of an optical fiber according to the prior art.

FIG. 2 is a structure diagram of a refractive index profile according to a configuration region of the optical fiber of FIG. 1; FIG.

3 is a cross-sectional view schematically showing a configuration region of an optical fiber according to an embodiment of the present invention.

4 is a structural diagram of the refractive index according to the configuration region of the optical fiber according to the embodiment of the present invention.

<Description of Major Reference Marks in Drawing>

100 ... optical fiber 10 ... core area

11 ... first core region 12 ... second core region

13 ... third core area 20 ... clad area

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical fibers suitable for wavelength division multiplexing (WDM) optical transmission systems. More specifically, Raman amplification efficiency is provided to enable high-speed large-capacity signal transmission over a wide range of wavelength bands. An optical fiber for a maximized WDM optical transmission system, and an optical transmission line and an optical communication system using the same.

The WDM optical transmission method is an optical transmission method capable of high-speed, high-capacity signal transmission by improving communication capacity and speed, and a system to which the WDM optical transmission method is applied can multiply transmit multiple channels having different wavelength bands.

The optical fiber applied to the WDM optical transmission system has to take into account the nonlinear phenomena caused by phase matching of several channels, unlike when operating in a single channel. (Non-Zero Dispersion Shifted Fibe, NZDSF hereinafter) applies.

The NZDSF satisfies standard specification G.655, as specified by the International Telecommunication Union (TTU) standardization sector (ITU-T).

The G.655 standard of ITU-T is G.655.A, which is a standard of NZDSF based on WDM optical transmission, and G.655.A, which is a standard of NZDSF based on Dense Wavelength Division Multiplexing (DWDM) transmission. Includes 655.B. Here, G.655.A defines a dispersion range of 0.1 to 6.0 ps / nm / km in the C-band in the 1530-1565nm region, and G.655.B defines 1.0 to 10.0 ps / nm / km. have.

Recently, the transmission speed of the optical transmission system has increased from 2.5Gb / s to 10Gb / s, and the optical transmission system of 40Gb / s will be commercialized after several years due to the demand for high speed and high capacity of information transmission.

NZDSF for high-speed transmission of 40Gb / s should consider the ease of dispersion compensation and the use of the S-band in the 1460 to 1530nm range. That is, since high dispersion requires sufficient dispersion, zero dispersion should not exist in the S-band, and dispersion should be 3 ps / nm / km or more in the 1460 to 1530 nm region. Therefore, for the use of the S-band, NZDSF that satisfies G.655.B rather than G.655.A is applied.

On the other hand, when the channel spacing is narrowed to increase the transmission capacity, the nonlinear phenomenon of NZDSF due to Four-Wave Mixing (hereinafter referred to as FWM) should be considered. FWM is caused by the third-order nonlinear phenomena due to the Kerr effect, and is maximized when there is phase matching with other channels during optical transmission.

In order to suppress the FWM, the dispersion must be large so that a phase mismatch occurs. That is, the zero variance value should not be placed in the communication band. Accordingly, ITU-T proposed G.656 as a new standard optimized for communication of wavelength bands including S-, C- and L-bands. It is a new standard and stipulates that the dispersion value in the wavelength band including S-, C- and L-bands in the 1460 to 1625 nm range satisfies 2 to 14 nm / ps / km.

However, in using the S-band for optical transmission, there is a problem that signal amplification cannot be performed with an Erbium Doped Fiber Amplifier (hereinafter referred to as EDFA). That is, signal amplification is possible with EDFA in C-band and L-band, but there is no special alternative except for Raman amplification for long-distance transmission of S-band.

Unlike EDFA, Raman amplification is an unlimited method of amplification band and active research is being conducted as various pump light sources are developed. The optical amplification is possible even in the wavelength range of 1100 to 1700 nm that EDFA cannot amplify. In addition, the smaller the effective cross-sectional area of the NZDSF, which represents the intensity of light per unit area, is more efficient. Therefore, when the transmission capacity is increased by using the S-band wavelength band, the effective cross-sectional area due to Raman amplification should be considered.

On the other hand, if the transmission capacity is increased by using a wavelength band other than the S-band, the mechanical stress and the bending loss due to the cabling of the NZDSF should be considered. In other words, when the NZDSF is used in an optical transmission system, it is coated with a steel wire to coat with a polymer or withstand tension, and a compact cabling with cost reduction acts as a mechanical stress on the NZDSF and the bending of the NZDSF. Increase the loss. This bending loss is sensitive in the L-band, which is a long wavelength region of 1565 to 1625nm, and the U-band, which is the region of 1625 to 1675nm, so stability due to bending loss for L-band and U-band should be considered. .

Various techniques for increasing the transmission capacity of the optical transmission system have been proposed.

U.S. Patent No. 5,835,655 proposes an optical fiber having an effective cross sectional area of 70 µm ² or more, but as the effective cross sectional area becomes larger, Raman amplification in the S-band cannot be maximized, the dispersion slope becomes larger, and the dispersion slope becomes longer, Since the variance value in s increases, the wavelength band that can be transmitted without dispersion compensation becomes narrow.

Korean Patent Publication No. 485889 proposes an optical fiber for a WDM type optical transmission system. As shown in FIGS. 1 and 2, a refractive index profile of an optical fiber composed of a core region 1 and a clad region 2 is stepped. Has a structure in which the dispersion is in the wavelength range of 1460 to 1625 is 2 to 14 ps / nm / km, the dispersion slope in the 1550 nm region is 0.073 ps / nm ² / km or less, and the effective cross-sectional area is 60 μm ² or more And an optical fiber having a zero dispersion wavelength of 1450 nm or less.

However, the optical fiber of No. 485889 has a low dispersion value in the S-band due to Raman amplification to increase the transmission capacity of the optical transmission system, resulting in increased nonlinearity resulting in degradation of transmission characteristics due to signal distortion caused by FWM, and Raman amplification. There is a problem that the efficiency is lowered. In addition, the stress is applied to the L-band and U-band when cabling has a problem that the bending loss increases.

The present invention was devised in consideration of the above problems, and improves the structure of the optical fiber to satisfy the dispersion characteristics of G.655.B and G.656, which are the standards of ITU-T, simultaneously, the dispersion slope is low, S It is an object of the present invention to provide an optical fiber for a wavelength division multiple optical transmission system having improved efficiency due to Raman amplification in a band and stability due to bending loss in an L-band and a U-band, and an optical transmission line and an optical communication system using the same.

The optical fiber for a wavelength division multiplexed optical transmission system according to the present invention for achieving the above object comprises a core region and a cladding region that compactly surrounds the core region, and includes wavelength division multiplexing, WDM) A single mode optical fiber suitable for an optical transmission system, wherein the core region is located at the optical center axis (A), the radius from the optical center axis is r ₁ , and the specific refractive index difference is Δ1 including Δ1a and Δ1b. 1 core region; (B) a second core region compactly surrounding the first core region, having a radius from the optical central axis of r ₂ and a specific refractive index difference of Δ2; And (C) a third core region that compactly surrounds the second core region, the radius from the optical central axis is r ₃ , and the specific refractive index difference is Δ3. The radius of the first to third core regions. Each satisfies a relationship of r ₁ <r ₂ <r ₃ , and each of the non-refractive index differences satisfies a relationship of Δ1a≥Δ1b> Δ2, Δ2 <Δ3 and Δ1a≥Δ1b> Δ3, and each of the non-refractive index differences Satisfying Equations 1 to 3, wherein the radius r ₁ of the first core region is 3.38 ± 0.6 μm, Δ1a is 0.474 ± 0.03% or more, and Δ1b is 0.474 ± 0.03%; The radius r ₂ of the second core region is 6.77 ± 0.6 μm and Δ2 is no greater than −0.075 ± 0.03%; The radius r ₃ of the third core region is 9.59 ± 0.6 μm, and Δ3 is 0.233 ± 0.03%.

Equation  One

Equation  2

Equation  3

(Where n _1a and n _1b in Equation 1 are the refractive indices of the first core region, and n ₂ and n ₃ are the refractive indices of the second and third core regions. In addition, r in Equation 2 is -r ₁ < satisfies r <0 the relational expression, and r of equation (3) satisfies 0 <r <r ₁ of equations.)

According to the present invention, the wavelength band used of the optical fiber satisfies the range of 1460 to 1675 nm.

Preferably, Δ1 of the first core region is increased toward the optical center axis such that the center of the shortest portion has a tapered tip-shaped refractive index profile structure.

In the present invention, as the Δ1 increases and the Δ2 decreases, the effective cross-sectional area of the optical fiber decreases, the Raman gain efficiency in the 1420 nm pump wavelength band is increased, and the dispersion slope in the 1550 nm wavelength band is decreased, Bend loss in the 1625 nm wavelength band is reduced.

Preferably, the effective cross-sectional area is 60 μm ² or less, the Raman gain efficiency is 0.6W ⁻¹ km ⁻¹ or more, and the dispersion slope is 0.05 ps / nm ² / km or less.

More preferably, the bending loss is 0.3 dB / km or less, and the zero dispersion wavelength band of the optical fiber is shifted to 1390 nm or less.

Still more preferably, the dispersion in the 1460-1530 nm wavelength band of the optical fiber is at least 3 ps / nm / km.

According to the present invention, when the refractive index difference Δ1 including Δ1a and Δ1b of the first core region is Δ1a = Δ1b, the specific refractive index difference Δ1 has a refractive index profile structure with the shortest flat portion.

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According to the present invention, the dispersion in the wavelength band of 1460 to 1625 nm of the optical fiber satisfies the range of 2 to 14 nm / ps / km prescribed by ITU-T G.656.

Further, the dispersion in the wavelength band of 1530 to 1565 nm of the optical fiber satisfies the range of 0.1 to 10 nm / ps / km prescribed by ITU-T G.655.B.

According to still another aspect of the present invention, there is provided an optical transmission line including the optical fiber and a wavelength division multiplex optical transmission system including the optical transmission line.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, which can be replaced at the time of the present application It should be understood that there may be various equivalents and variations.

The optical fiber according to the present invention is a fiber suitable for wavelength division multiplexing (WDM) optical transmission system, and can be used in wavelength bands including S-, C-, L- and U-bands. It is easy to maximize the Raman amplification efficiency in the S-band, the configuration of the optical fiber according to an embodiment of the present invention with reference to Figures 3 and 4 as follows. 3 is a cross-sectional view schematically showing a configuration area of an optical fiber according to an embodiment of the present invention, and FIG. 4 is a structure diagram of a refractive index profile according to a configuration area of an optical fiber according to an embodiment of the present invention.

Referring to the drawings, the optical fiber 100 according to the embodiment of the present invention is composed of a cladding region 20 formed to have a refractive index n _cl on the outer periphery of the core region 10, and the core region 10 again has a radius. a first core region 11 having a refractive index n _1a formed at r ₁ and having a radius 0 and a refractive index n _1b at a radius r ₁ and a radius surrounding the first core region 11. and a second core region 12 having r ₂ and a refractive index n ₂ , and a third core region 13 having a radius r ₃ and a refractive index n ₃ to surround the second core region 12. .

In an embodiment of the invention, the first core region 11 is configured to have a constant value with respect to the radius r ₁ , or the center thereof is increased to a tapered tip shape, and the refractive indices n _1a and n _1b are n _1a Satisfies the relation ≥ n _1b .

In addition, the refractive index n _1a of the first core region 11. And the specific refractive index difference according to n _1b is Δ1 including Δ1a and Δ1b, and the specific refractive index difference according to the refractive index n ₂ of the second core region 12 is Δ2, and the refractive index n ₃ of the third core region 13 is The specific refractive index difference is Δ3.

In addition, each of the refractive index differences satisfies a relational expression of Δ1a≥Δ1b, 1b> Δ2, Δ2 <Δ3 and Δ1a≥Δ1b> Δ3, and each of the non-refractive index differences satisfies Equation (1).

In addition, when the specific refractive index difference Δ1 of the first core region 11 increases, the dispersion slope decreases, the effective area decreases, and the increase of the refractive index and the blocking wavelength can be suppressed. The specific refractive index difference Δ1 of is configured to have a constant value or increase with respect to the radius r ₁ .

In more detail, Δ1 including the specific refractive index differences Δ1a and Δ1b of the first core region 11 has a flat refractive index profile structure when n _1a = n _1b , and when n _1a > n _1b . The center of the shortest part has a tapered refractive index profile structure, and the specific refractive index difference Δ1 satisfies the following Equations 2 and 3 with respect to the radius r ₁ .

(In Equation 2, r satisfies a relation of -r ₁ <r <0.)

(In equation 3, r satisfies the relation 0 <r <r _1. )

According to the conditions of Equations 2 and 3, the optical fiber 100 has an effective refractive index increase in the first core region 11, and the refractive index increases due to a specific refractive index difference Δ1 having a tapered refractive index profile structure in the center of the shortest portion. Can be relatively suppressed to concentrate the optical power in the center. That is, even if the specific refractive index difference Δ1 is increased, the increase in the blocking wavelength caused by the increase in the specific refractive index difference Δ1 can be suppressed, and the dispersion slope can be reduced and the effective cross-sectional area can be reduced.

In addition, the refractive index profile structure of the first core region 11 shifts the position of the zero dispersion wavelength band to the short wavelength side of 1400 nm or less, thereby optimizing the dispersion of the optical fiber 100. That is, by optimizing the dispersion to ensure sufficient dispersion in the wavelength band of 1460nm, it is possible to suppress FWM (Four-Wave Mixing, FWM) due to the increase in the specific refractive index difference Δ1.

Accordingly, even if the specific refractive index difference Δ1 is increased, the effective cross-sectional area is reduced without signal distortion caused by the FWM, thereby maximizing Raman amplification efficiency in the S-band having a region of 1460 to 1530 nm.

The optical fiber 100 satisfying Equations 1 to 3 was used in the WDM optical transmission system to measure dispersion, dispersion slope, zero dispersion wavelength, mode diameter, effective cross-sectional area, and Raman gain efficiency. The measurement results are described below with reference to Tables 1 and 2. In this case, Table 1 is the radius of the core area (r ₁ To r refractive index difference (Δ1 to Δ3) according to r ₃ ), and the radius r ₁ of Table ₁ To r ₃ The error rate for is within ± 0.6 μm, and the error rate for the specific refractive index difference Δ1 to Δ3 is ± 0.03%. In addition, Table 2 is a measured value according to Table 1, the mode diameter and effective cross-sectional area of Table 2 are measured values in the wavelength band which is 1550 nm, and Raman gain efficiency is the efficiency in the pump wavelength which is 1420 nm. In addition, the constituent regions of the optical fiber according to Comparative Examples of Tables 1 and 2 and the refractive index profile diagrams according to the constituent regions are as shown in FIGS. 1 and 2.

Classification Core area First core region Second core region Third core region r ₁ (μm) Δ1 (%) r ₂ (μm) Δ2 (%) r ₃ (μm) Δ3 (%) Example 3.38 0.47 6.77 -0.07 9.59 0.21 Comparative example 3.42 0.41 6.35 -0.05 9.71 0.12

Classification Dispersion (ps / nm / km) Dispersion Slope (ps / nm ² / km) Zero Dispersion Wavelength (nm ^-1 ) Mode diameter (μm) Effective cross section (㎛ ² ) Raman gain efficiency (W ^-1 km ^-1 ) 1460 nm 1530nm 1565 nm 1625nm Example 4.4 7.4 8.7 10.9 0.040 1364.6 8.25 53.1 0.82 Comparative example 2.9 7.4 9.4 12.7 0.055 1402 9.5 67.5 0.57

As can be seen through Table 1 and Table 2, the dispersion slope of the optical fiber according to the comparative example is 0.055 ps / nm ² / km it can be seen that the larger value than the embodiment. Here, when the dispersion slope becomes large, dispersion in the wavelength band of 1625 nm becomes large, and dispersion compensation is necessary. On the other hand, the dispersion slope of the embodiment is 0.040 ps / nm ² / km is less than 0.055 ps / nm ² / km of the comparative example can be optical transmission without guaranteeing dispersion in the long wavelength band.

In addition, the effective cross-sectional area of the embodiment is 53.1㎛ ² is smaller than 67.5㎛ ² of the comparative example Raman gain efficiency is maximized to 0.82W ^-1 km ^{- 1} , according to the following equations 4 and 5 according to Table 1 and Table 2 The Raman gain efficiency of an optical fiber is as follows.

(Equation 4, G is the Raman gain, g _r is the Raman gain factor, P ₀ is the pump power applied to the optical fiber, L _eff is the effective length according to Raman amplification, K is the polarization coefficient, α _s Is the light loss factor and A _eff is the effective cross-sectional area.)

(Equation 5, C _r is Raman gain efficiency.)

According to Equations 4 and 5, the Raman gain (G) is inversely proportional to the effective cross-sectional area (A _eff ) and the Raman gain efficiency (C _r ) is proportional to the Raman gain (G). Raman gain efficiency of the a _eff) (C _r) is 0.57W ^-1 km ^{- 1} to the embodiment of the Raman gain efficiency (C _r) of less than 0.82W ^-1 km ^-1. On the other hand, when increasing the specific refractive index difference Δ1 to increase the Raman gain efficiency (C _r ) of the comparative example to reduce the effective cross-sectional area (A _eff ), Raman gain efficiency (C _r ) increases, but signal distortion due to FWM increases. As a result, the bit error ratio (BER) increases, which adversely affects optical transmission.

On the other hand, the embodiment increases the Raman gain efficiency (C _r ) 0.80 W ⁻¹ km ⁻¹ without increasing the specific refractive index difference Δ1 to reduce the dispersion slope and reduce the effective cross-sectional area A _eff . We can maximize more than this.

In an embodiment of the invention, the Raman amplification process directs the Raman pump energy with high power in the direction of the transmission source. The pump light source then couples with the vibration mode of the transmission fiber and amplifies the signal when the pump wavelength is shorter than the signal wavelength. At this time, the Raman amplification is a signal amplification in the optical fiber itself, it is possible to optical amplification in the wavelength band of 1100 ~ 1700nm that EDFA (Erbium Doped Fiber Amplifier) does not amplify.

Referring back to FIGS. 3 and 4 and Equations 1 to 5, when the specific refractive index difference Δ1 of the first core region 11 is Δ1a = Δ1b, the specific refractive index difference Δ1 is a refractive index profile structure having the shortest flat portion, When the specific refractive index difference Δ1 gradually increases from Δ1a> Δ1b, the specific refractive index difference Δ1 increases to a refractive index profile structure in which the center of the shortest portion is tapered, so that the zero dispersion of the optical fiber 100 moves to a short wavelength band. Effective cross-sectional area is reduced, Raman gain efficiency in the 1420 nm pump wavelength band is increased, dispersion slope in the 1550 nm wavelength band is reduced, and bending loss in the 1625 nm wavelength band is reduced. Here, as Δ2 of the second core region 12 of the optical fiber 100 decreases, the characteristic of the optical fiber 100 is further improved.

In this case, when the specific refractive index difference Δ1a = Δ1b of the first core region 11, the zero-dispersion wavelength band of the optical fiber 100 is 1399 nm, the effective cross-sectional area is 65 ㎛ ² , Raman gain efficiency is 0.6W ^-1 km ^{- 1,} and the dispersion slope is 0.053 ps / nm ² / km, the bending loss is 5.29 dB / km.

On the other hand, the characteristic values according to the zero dispersion, the effective cross-sectional area, the Raman gain efficiency, the dispersion slope and the bending loss of the optical fiber 100 according to the present invention are further improved under the condition of Δ1a> Δ1b compared to the condition of Δ1a = Δ1b.

That is, when Δ1a is gradually increased compared to Δ1b and Δ2 is gradually decreasing, the zero dispersion wavelength band of the optical fiber 100 is 1360 to 1390 nm, the effective cross-sectional area is 55 to 60 μm ² , and the Raman gain efficiency is 0.6 to 0.8W ^-1 km ^{- 1,} and the dispersion slope is 0.04 to 0.05 ps / nm ² / km, the bend loss is one satisfying the range of 0.03 to 0.3 dB / km in the range is not limited to this.

The optical fiber 100 satisfying the above Equations 1 to 5 can not only maximize the Raman gain efficiency in the S-band without signal distortion, but also S-, which has a dispersion of 1460 nm to 1625 nm according to the dispersion slope, Meets G.655.B and G.656, the standards of the International Telecommunication Union, Telecommunication standardization sector (ITU-T) in the C- and L-bands, and L- and U- in the wavelength band of 1625 nm to 1675 nm when cabling. The bending loss occurring in the band is suppressed, which will be described with reference to Tables 3 and 4 below.

At this time, the embodiment of Table 3 is the radius of the core area (r ₁ To r ₃ ) shows the amount of change in the specific refractive index difference Δ1 to Δ3. Further, the radius r ₁ of the core region according to the embodiment To r ₃ ) each has r ₁ of 3.38 ± 0.6 μm, r ₂ of 6.77 ± 0.6 μm and r ₃ of 9.59 ± 0.6 μm.

Meanwhile, the constituent regions of the optical fiber according to the comparative example and the refractive index profile diagrams according to the constituent regions are shown in FIGS. 1 and 2, and the radius r ₁ to the core region according to the comparative example r ₃ ) each has r ₁ of 3.42 ± 0.6 μm, r ₂ of 6.35 ± 0.6 μm and r ₃ of 9.71 ± 0.6 μm. In addition, the Raman gain efficiency of Table 4 is a measured value in the pump wavelength band of 1420 nm, a dispersion slope is a measured value in the wavelength band of 1550 nm, and a bending loss is a measured value in the wavelength band of 1625 nm.

Classification Specific refractive index difference Δ (%) of core region Specific refractive index difference Δ1 (%) of the first core region Specific refractive index difference Δ2 (%) of the second core region Specific refractive index difference Δ3 (%) of the third core region Δ1a (%) Δ1b (%) Example 1 0.474 0.474 -0.075 0.233 Example 2 0.543 0.474 -0.075 0.233 Example 3 0.543 0.474 -0.096 0.233 Example 4 0.577 0.474 -0.075 0.233 Example 5 0.543 0.474 -0.096 0.233 Example 6 0.577 0.474 -0.165 0.233 Comparative example 0.41 -0.05 0.12

Classification Dispersion (ps / nm / km) Dispersion Slope (ps / nm ² / km) Zero Dispersion Wavelength (nm) Bending loss (dB / km) Effective cross section (㎛ ² ) Raman gain efficiency (W ^-1 km ^-1 ) 1460 nm 1530nm 1565 nm 1625nm Example 1 2.6 6.2 7.9 11.0 0.053 1399.0 5.29 65.0 0.60 Example 2 3.3 6.8 8.5 11.3 0.048 1387.5 0.14 59.8 0.68 Example 3 3.4 6.8 8.4 11.0 0.046 1384.2 0.24 58.5 0.70 Example 4 3.7 7.2 8.8 11.5 0.047 1381.6 0.03 57.6 0.73 Example 5 3.4 6.8 8.4 11.0 0.046 1378.6 0.25 56.4 0.78 Example 6 4.4 7.4 8.7 10.9 0.040 1364.6 0.30 53.1 0.82 Comparative example 2.9 7.4 9.4 12.7 0.055 1402.0 5.30 67.5 0.57

As can be seen through Table 3 and Table 4, the first core region 11 according to the embodiment of the present invention has a refractive index n _1a And n _{1a for} n _1b The relation ≥ n _1b is satisfied, and accordingly, the refractive index difference Δ1 is increased to decrease the dispersion slope in the wavelength band of 1550 nm, the effective area is reduced, and the Raman gain efficiency in the pump light source in the wavelength band of 1420 nm It can be seen that the increase.

In this case, it can be seen that the specific refractive index difference Δ1 increases as the difference between Δ1a and Δ1b increases. That is, it can be seen that the specific refractive index difference Δ1 is increased when the center of the shortest part is a tapered refractive index profile structure than when the shortest part is a flat refractive index profile structure, and the optical power can be concentrated in the center.

In addition, when comparing the embodiment of the present invention with the comparative example, it is seen that the first core region 11 is increased by having a tapered refractive index profile structure in which the center of the shortest portion is increased, and the second core region 12 is reduced. Can be. In this case, the reduction of the second core region 12 suppresses the increase in the blocking wavelength according to the refractive index profile structure, and concentrates the optical power by Raman amplification at the center of the shortest portion.

At this time, the position of the zero-dispersion wavelength band of the embodiment is moved to the short wavelength side of 1400nm or less, it can be seen that the dispersion of the optical fiber is optimized. Here, it can be seen that the embodiment of the present invention can secure sufficient dispersion in the wavelength band of 1460 nm by optimizing the dispersion, and can suppress FWM due to the increase in the specific refractive index difference Δ1.

In addition, it can be seen that the optical fiber 100 having the structures of the first to third core regions 11 to 13 reduces the bending loss in the wavelength band of 1625 nm as the specific refractive index difference Δ1 increases.

In addition, the optical fiber 100 has a dispersion of 6.2 to 8.8 nm / ps / km in the C-band, satisfying the range of 1.0 to 10.0 ps / nm / km, which is the standard of ITU-T G.655.B. Dispersion ranges from 2.6 to 11.5 nm / ps / km in wavelength bands including S-, C- and L-bands, satisfying ITU-T G.656 standard 2-14 nm / ps / km do. In particular, as the specific refractive index difference Δ1a increases and the specific refractive index difference Δ2 decreases, dispersion is 3.3 to 4.4 nm / ps / km in the S-band, and zero dispersion does not exist, so it is suitable for the condition of high speed transmission. Can be.

On the other hand, it can be seen that the comparative example has a relatively high Raman gain efficiency, a large bending loss, and does not comply with G.656, which is a standard of ITU-T, because of the large dispersion slope and the effective cross-sectional area.

As described above, the optical fiber according to the present invention employs a core region that satisfies Equations 1 to 5 to maximize the Raman amplification efficiency in the S-band, while suppressing an increase in the cutoff wavelength, It reduces the bending loss in the U-band and satisfies the ITU-T standards G.655.B and G.656.

Although the present invention has been described above by means of limited embodiments and drawings, the present invention is not limited thereto and will be described below by the person skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of the claims.

As described above, the present invention improves the structure of the optical fiber, it is possible to maximize the Raman amplification efficiency in the S-band without increasing the signal distortion and the cut-off wavelength, the bending loss in the L-band and U-band is suppressed It satisfies G.655.B and G.656 standards of ITU-T, and can provide optical fibers optimized for WDM optical transmission system.

In addition, it is possible to easily lower the position of the zero-dispersion wavelength band for maximizing Raman amplification efficiency, it is possible to ensure sufficient dispersion in the wavelength band of 1460nm, it is possible to suppress the nonlinear phenomenon.

In addition, 0.6 to 0.8W ^-1 km at 1420nm of pump ^wavelengths it is possible to secure the Raman gain efficiency in the range of ^1.

In addition, it is easy to reduce the dispersion slope and to reduce the effective cross-sectional area.

Claims (26)

A single mode optical fiber comprising a core region and a clad region surrounding the core region, and suitable for a wavelength division multiplexing (WDM) optical transmission system, The core region is, (A) a first core region located in the optical center axis, the radius from the optical center axis being r ₁ , and the specific refractive index difference being Δ1 including Δ1a and Δ1b; (B) a second core region surrounding the first core region and having a radius from the optical central axis of r ₂ and a specific refractive index difference of Δ2; And (C) a third core region surrounding the second core region and having a radius from the optical central axis of r ₃ and a specific refractive index difference of Δ3; Each of the radiuses of the first to third core regions satisfies a relationship of r ₁ <r ₂ <r ₃ , and each of the specific refractive index differences has a relationship of Δ1a≥Δ1b> Δ2, Δ2 <Δ3 and Δ1a≥Δ1b> Δ3. Satisfies each of the non-refractive index difference satisfies the following equations 1 to 3, The radius r ₁ of the first core region is 3.38 ± 0.6 μm, Δ1a is at least 0.474 ± 0.03%, Δ1b is 0.474 ± 0.03%; The radius r ₂ of the second core region is 6.77 ± 0.6 μm and Δ2 is no greater than −0.075 ± 0.03%; The radius r ₃ of the third core region is 9.59 ± 0.6 μm, and Δ3 is 0.233 ± 0.03%. Equation 1

Equation 2

Equation 3

(Where n _1a and n _1b in Equation 1 are the refractive indices of the first core region, and n ₂ and n ₃ are the refractive indices of the second and third core regions. In addition, r in Equation 2 is -r ₁ < satisfies r <0 the relational expression, and r of equation (3) satisfies 0 <r <r ₁ of equations.) The method of claim 1, The wavelength band of the optical fiber for use in the wavelength division multiplex optical transmission system, characterized in that satisfying the range of 1460 ~ 1675nm. The method of claim 2, [Delta] 1 of the first core region has a refractive index profile structure having the shortest portion or a refractive index profile structure where the center of the shortest portion forms a tapered tip. The method of claim 3, As the Δ1 increases and the Δ2 decreases, the effective cross-sectional area of the optical fiber decreases, the Raman gain efficiency in the 1420 nm pump wavelength band is increased, the dispersion slope in the 1550 nm wavelength band is decreased, and in the 1625 nm wavelength band. An optical fiber for a wavelength division multiple optical transmission system, characterized in that bending loss is reduced. The method of claim 4, wherein The effective cross-sectional area is 60㎛ ² or less optical fiber for wavelength division multiplex optical transmission system. The method of claim 4, wherein The Raman gain efficiency of the optical fiber for wavelength division multiplex optical transmission system, characterized in that more than 0.6W ^-1 km ^-1 . The method of claim 4, wherein The dispersion slope is an optical fiber for wavelength division multiplex optical transmission system, characterized in that less than 0.05 ps / nm ² / km. The method of claim 4, wherein The bending loss is optical fiber for wavelength division multiplex optical transmission system, characterized in that less than 0.3 dB / km. The method of claim 4, wherein An optical fiber for a wavelength division multiple optical transmission system, wherein the zero-dispersion wavelength band of the optical fiber is shifted to 1390 nm or less. The method of claim 4, wherein The optical fiber for wavelength division multiplex optical transmission system, characterized in that the dispersion in the 1460 to 1530nm wavelength band of the optical fiber is 3 ps / nm / km or more. The method of claim 2, When the specific refractive index difference Δ1 including Δ1a and Δ1b of the first core region is Δ1a = Δ1b, the specific refractive index difference Δ1 has a refractive index profile structure having a flattened shortest portion. delete delete delete delete delete delete delete delete delete delete delete The method of claim 1, Dispersion in the wavelength band of 1460 to 1625nm of the optical fiber is a wavelength division multiple optical transmission system, characterized in that to satisfy the range of 2 to 14 nm / ps / km. The method of claim 1, Dispersion in the wavelength band of 1530 to 1565nm of the optical fiber is a wavelength division multiple optical transmission system, characterized in that to satisfy the range of 0.1 to 10 nm / ps / km. An optical transmission line comprising the optical fiber of claim 1. A wavelength division multiple optical transmission system comprising the optical transmission line of claim 25.

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