DISPERSION SHIFTED OPTICAL FIBER

Abstract

A dispersion shifted optical fiber where a radius r.sub.0 of a first center segment is 0.5 μm to 2.8 μm, and a relative refractive index difference Δ.sub.0 is 0.4% or more and 0.9% or less. A radius r.sub.1 of a first segment is 1.8 μm or more and 4.5 μm or less. A radius r.sub.2 of a second segment is 4.0 μm or more and 8.0 μm or less, and a relative refractive index difference Δ.sub.2 is 0.00% or more and 0.07% or less. A radius r.sub.3 of a third segment is 4.5 μm or more and 8.5 μm or less, and a relative refractive index difference Δ.sub.3 is 0.285% or more and 0.5% or less. A radius r.sub.4 of a fourth segment is 8.0 μm or more and 16.0 μm or less, and a relative refractive index difference Δ.sub.4 is 0.005% or more and 0.04% or less.

Claims

1. A dispersion shifted optical fiber comprising: a core, the core further comprising: a first segment including a center axis of the core, a second segment that surrounds an outer circumferential surface of the first segment with no gap, a third segment that surrounds an outer circumferential surface of the second segment with no gap, and a fourth segment that surrounds an outer circumferential surface of the third segment with no gap, wherein the first segment further comprises a first center segment having the center axis, a radius r.sub.0 of the first center segment is 0.5 μm or more and 2.8 μm or less, a radius r.sub.1 of the first segment is 1.8 μm or more and 4.5 μm or less, a radius r.sub.2 of the second segment is 4.0 μm or more and 8.0 μm or less, a radius r.sub.3 of the third segment is 4.5 μm or more and 8.5 μm or less, a radius r.sub.4 of the fourth segment is 8.0 μm or more and 16.0 μm or less, and a relation r.sub.0≦r.sub.1<r.sub.2<r.sub.3<r.sub.4 is held, a relative refractive index difference Δ.sub.0 of the first center segment to a cladding surrounding the core is 0.4% or more and 0.9% or less, a relative refractive index difference Δ.sub.2 of the second segment to the cladding is 0.00% or more and 0.07% or less, a relative refractive index difference Δ.sub.3 of the third segment to the cladding is 0.285% or more and 0.5% or less, a relative refractive index difference Δ.sub.4 of the fourth segment to the cladding is 0.005% or more and 0.04% or less, and in the first segment, a relative refractive index difference to the cladding is reduced from an outer circumference of the first center segment to an inner circumference of the second segment, and wherein the dispersion shifted optical fiber has a dispersion value of a light beam at a wavelength in a range of 1,530 to 1,625 nm is 2.0 ps/nm/km or more and 13.5 ps/nm/km or less, a dispersion slope of a light beam at a wavelength of 1,550 nm is 0.092 ps/nm.sup.2/km or less, a cable cutoff wavelength is a wavelength of 1,450 nm or less, an effective area of a light beam at a wavelength of 1,550 nm is 65 μm.sup.2 or more and 90 μm.sup.2 or less, and a mode field diameter of a light beam at a wavelength of 1,550 nm is 9.2 μm or more and 10.5 μm or less.

2. The dispersion shifted optical fiber according to claim 1, wherein the radius r.sub.0 of the first center segment is 1.8 μm or more and 2.8 μm or less, the radius r.sub.1 of the first segment is 1.8 μm or more and 2.8 μm or less, the radius r.sub.0 of the first center segment is matched with the radius r.sub.1 of the first segment, the radius r.sub.2 of the second segment is 5.0 μm or more and 6.6 μm or less, and the radius r.sub.3 of the third segment is 6.1 μm or more and 8.5 μm or less, and the relative refractive index difference Δ.sub.0 of the first center segment to the cladding is 0.4% or more and 0.8% or less, and the relative refractive index difference Δ.sub.2 of the second segment to the cladding is 0.00% or more and 0.06% or less.

3. The dispersion shifted optical fiber according to claim 2, wherein the radius r.sub.0 of the first center segment is 2.0 μm or more and 2.6 μm or less, the radius r.sub.2 of the second segment is 5.0 μm or more and 6.0 μm or less, the radius r.sub.3 of the third segment is 6.1 μm or more and 7.5 μm or less, and the radius r.sub.4 of fourth segment is 11.0 μm or more and 15.0 μm or less, and the relative refractive index difference Δ.sub.0 of the first center segment to the cladding is 0.47% or more and 0.67% or less, the relative refractive index difference Δ.sub.2 of the second segment to the cladding is 0.02% or more and 0.06% or less, the relative refractive index difference Δ.sub.3 of the third segment to the cladding is 0.285% or more and 0.35% or less, and the relative refractive index difference Δ.sub.4 of the fourth segment to the cladding is 0.010% or more and 0.025% or less.

4. The dispersion shifted optical fiber according to claim 1, wherein the radius r.sub.0 of the first center segment is smaller than the radius r.sub.1 of the first segment, the radius r.sub.0 of the first center segment is 0.5 μm or more and 1.3 μm or less, the radius r.sub.1 of the first segment is 2.0 μm or more and 4.5 μm or less, the radius r.sub.2 of the second segment is 5.0 μm or more and 8.0 μm or less, the radius r.sub.3 of the third segment is 6.0 μm or more and 8.5 μm or less, and the radius r.sub.4 of the fourth segment is 9.0 μm or more and 16 μm or less, and the relative refractive index difference Δ.sub.0 of the first center segment to the cladding is 0.5% or more and 0.9% or less.

5. The dispersion shifted optical fiber according to claim 4, wherein the radius r.sub.0 of the first center segment is 0.5 μm or more and 1.0 μm or less, the radius r.sub.1 of the first segment is 3.0 μm or more and 4.5 μm or less, the radius r.sub.2 of the second segment is 5.2 μm or more and 6.5 μm or less, the radius r.sub.3 of the third segment is 6.5 μm or more and 8.0 μm or less, and the radius r.sub.4 of the fourth segment is 10.0 μm or more and 13.5 μm or less, and the relative refractive index difference Δ.sub.0 of the cladding surrounding the core of the first center segment is 0.6% or more and 0.8% or less, the relative refractive index difference Δ.sub.2 of the second segment to the cladding is 0.020% or more and 0.065% or less, the relative refractive index difference Δ.sub.3 of the third segment to the cladding is 0.285% or more and 0.4% or less, and the relative refractive index difference Δ.sub.4 of the fourth segment to the cladding is 0.01% or more and 0.03% or less.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG. 1 is a diagram of a structure in a cross section perpendicular to the longitudinal direction of a dispersion shifted optical fiber according to one or more embodiments of the present invention.

[0023] FIG. 2 is a diagram of a relative refractive index profile of the dispersion shifted optical fiber in FIG. 1 to a cladding.

[0024] FIG. 3 is a diagram of a dispersion shifted optical fiber according to one or more embodiments of the present invention.

[0025] FIG. 4 is a diagram of a relative refractive index profile of the dispersion shifted optical fiber in FIG. 3 to a cladding.

DETAILED DESCRIPTION

[0026] In the following, one or more embodiments of a dispersion shifted optical fiber will be described in detail with reference to the drawings.

[0027] FIG. 1 is a diagram of a structure in a cross section perpendicular to the longitudinal direction of a dispersion shifted optical fiber.

[0028] In a dispersion shifted optical fiber DSF1, a dispersion value of a light beam at a wavelength in a range of 1,530 to 1,625 nm is 2.0 ps/nm/km or more and 13.5 ps/nm/km or less, a dispersion slope of a light beam at a wavelength of 1,550 nm is 0.092 ps/nm.sup.2/km or less, a cable cutoff wavelength is a wavelength of 1,450 nm or less, an effective area of a light beam at a wavelength of 1,550 nm is 65 μm.sup.2 or more and 90 μm.sup.2 or less, and a mode field diameter of a light beam at a wavelength of 1,550 nm is 9.2 μm or more and 10.5 μm or less. In other words, the dispersion shifted optical fiber DSF1 is a dispersion shifted optical fiber that transmits light in the C band and the L band.

[0029] As illustrated in FIG. 1, the dispersion shifted optical fiber DSF1 includes a core 1 and a cladding 2 that surrounds the outer circumferential surface of the core 1 with no gap.

[0030] The core 1 includes a first segment 11, a second segment 12 that surrounds the outer circumferential surface of the first segment 11 with no gap, a third segment 13 that surrounds the outer circumferential surface of the second segment 12 with no gap, and a fourth segment 14 that surrounds the outer circumferential surface of the third segment 13 with no gap. As depicted by a broken line in FIG. 1, the first segment 11 includes a first center segment 10 including the center axis of the core 1. Thus, the dispersion shifted optical fiber DSF1 has four segments.

[0031] A radius r.sub.0 of the first center segment 10 is 0.5 μm or more and 2.8 μm or less. A radius r.sub.1 of the first segment 11 is 1.8 μm or more and 4.5 μm or less. A radius r.sub.2 of the second segment 12 is 4.0 μm or more and 8.0 μm or less. A radius r.sub.3 of the third segment 13 is 4.5 μm or more and 8.5 μm or less. A radius r.sub.4 of the fourth segment 14 is 8.0 μm or more and 16.0 μm or less. Note that, the radius of each segment means the radius of the outer circumferential surface of each segment.

[0032] Among the radius r.sub.0 of the first center segment 10, the radius r.sub.1 of the first segment 11, the radius r.sub.2 of the second segment 12, the radius r.sub.3 of the third segment 13, and the radius r.sub.4 of the fourth segment 14, a relation below is held.

r.sub.0<r.sub.1<r.sub.2<r.sub.3<r.sub.4

[0033] FIG. 2 is a diagram of the profile of the relative refractive index difference to the cladding 2 in the radial direction of the dispersion shifted optical fiber DSF1 in FIG. 1. However, FIG. 2 shows the refractive index profile only on one side of the radial direction from the center axis of the dispersion shifted optical fiber DSF1. A relative refractive index difference Δ.sub.0 of the first center segment 10 to the cladding 2 is 0.4% or more and 0.9% or less. A relative refractive index difference Δ.sub.2 of the second segment 12 to the cladding 2 is 0.00% or more and 0.07% or less. Thus, the relative refractive index difference Δ.sub.2 of the second segment 12 to the cladding 2 is smaller than the relative refractive index difference Δ.sub.0 of the first center segment 10 to the cladding 2. In the first segment 11, the relative refractive index difference to the cladding 2 is reduced from the outer circumference of the first center segment 10 to the inner circumference of the second segment 12. A relative refractive index difference Δ.sub.3 of the third segment 13l to the cladding 2 is 0.285% or more and 0.5% or less. A relative refractive index difference Δ.sub.4 of the fourth segment 14 to the cladding 2 is 0.005% or more and 0.04% or less.

[0034] Materials configuring the core 1 and the cladding 2 of the dispersion shifted optical fiber DSF1 are materials below. For example, the cladding 2 is formed of pure silica. The first segment 11 and the third segment 13 of the core 1 are formed of silica doped with a dopant that increases the refractive index. The second segment 12 and the fourth segment 14 are formed of silica appropriately doped with a dopant that increases the refractive index or a dopant that decreases the refractive index. A representative dopant that acts to increase the refractive index can be germanium (Ge). Germanium is doped as GeO.sub.2. A representative dopant that acts to decrease the refractive index can be fluorine (F). Note that, dopants added to the segments of the core 1 are at least one kind or two kinds selected from germanium, aluminum (Al), phosphorus (P), and fluorine. Types and loadings of dopants are appropriately selected so that the relative refractive index differences to the cladding 2 are in the ranges described above.

[0035] The segments of the core 1 have the radii and the relative refractive index differences to the cladding 2 described above. Hence, the dispersion shifted optical fiber DSF1 has the dispersion value, the dispersion slope, the cable cutoff wavelength, the effective area, and the mode field diameter as described above.

[0036] As described above, the segments of the core 1 have the radii and the relative refractive index differences to the cladding 2 described above. Hence, the dispersion shifted optical fiber DSF1 can reduce a change in a bending loss of light propagating through the core 1, even in the case in which the ratio between the diameter (the core diameter) of the core 1 and the diameter (the cladding diameter) of the cladding 2 is changed.

[0037] Note that, as described above, the dispersion shifted optical fiber DSF1 has a relation r.sub.0<r.sub.1. In the first segment 11, the relative refractive index difference to the cladding 2 is reduced from the outer circumference of the first center segment 10 to the inner circumference of the second segment 12. Hence, in r.sub.0<r.sub.1, the shape of the refractive index profile of the first segment 11 is generally in a trapezoid.

[0038] Thus, in the case in which the shape of the refractive index profile of the first segment 11 is generally in a trapezoid, the segments may have the radii and the relative refractive index differences to the cladding 2 in ranges below.

[0039] In other words, the radius r.sub.0 of the first center segment 10 is 0.5 μm or more and 1.3 μm or less, the radius r.sub.1 of the first segment 11 is 2.0 μm or more and 4.5 μm or less, the radius r.sub.2 of the second segment 12 is 5.0 μm or more and 8.0 μm or less, the radius r.sub.3 of the third segment 13 is 6.0 μm or more and 8.5 μm or less, and the radius r.sub.4 of the fourth segment 14 is 9.0 μm or more and 16.0 μm or less. However, as described above, the relation r.sub.1<r.sub.2<r.sub.3<r.sub.4 is held.

[0040] The relative refractive index difference Δ.sub.0 of the first center segment 10 to the cladding 2 is 0.5% or more and 0.9% or less, the relative refractive index difference Δ.sub.2 of the second segment 12 to the cladding 2 is 0.00% or more and 0.07% or less, the relative refractive index difference Δ.sub.3 of the third segment 13 to the cladding 2 is 0.285% or more and 0.5% or less, and the relative refractive index difference Δ.sub.4 of the fourth segment 14 to the cladding 2 is 0.005% or more and 0.04% or less.

[0041] In the case in which the first segment 11 has a refractive index profile generally in a trapezoid shape, the segments of the core 1 have the radii and the relative refractive index differences to the cladding 2 described above. Hence, the difference in viscosity can be gradually changed in the portion from the outer circumference of the first center segment 10 to the second segment 12 in the first segment 11. Consequently, a large residual stress can be decreased, and an increase in transmission losses can be reduced.

[0042] Thus, in the case in which the shape of the refractive index profile of the first segment 11 is generally in a trapezoid, the segments may have the radii and the relative refractive index differences to the cladding 2 in ranges below.

[0043] In other words, the radius r.sub.0 of the first center segment 10 is 0.5 μm or more and 1.0 μm or less, the radius r.sub.1 of the first segment 11 is 3.0 μm or more and 4.5 μm or less, the radius r.sub.2 of the second segment 12 is 5.2 μm or more and 6.5 μm or less, the radius r.sub.3 of the third segment 13 is 6.5 μm or more and 8.0 μm or less, and the radius r.sub.4 of the fourth segment 14 is 10.0 μm or more and 13.5 μm or less. However, as described above, the relation r.sub.1<r.sub.2<r.sub.3<r.sub.4 is held.

[0044] The relative refractive index difference Δ.sub.0 of the first center segment 10 to the cladding 2 is 0.6% or more and 0.8% or less, the relative refractive index difference Δ.sub.2 of the second segment 12 to the cladding 2 is 0.02% or more and 0.065% or less, the relative refractive index difference Δ.sub.3 of the third segment 13 to the cladding 2 is 0.285% or more and 0.4% or less, and the relative refractive index difference Δ.sub.4 of the fourth segment 14 to the cladding 2 is 0.01% or more and 0.03% or less.

[0045] The segments of the core 1 have the radii and the relative refractive index differences to the cladding 2 described above. Thus, a change in a bending loss of light propagating through the core 1 can be further reduced, even in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 is changed.

[0046] Next, referring to FIGS. 3 and 4, a dispersion shifted optical fiber according to one or more embodiments the present invention will be described in detail. Note that, components the same as or equivalent to the components of the dispersion shifted optical fiber DSF1 are designated the same reference numerals and signs unless otherwise specified, and the overlapping description is omitted.

[0047] FIG. 3 is a diagram of a structure in a cross section perpendicular to the longitudinal direction of the dispersion shifted optical fiber.

[0048] Also, in a dispersion shifted optical fiber DSF2, a dispersion value of a light beam at a wavelength in a range of 1,530 to 1,625 nm is 2.0 ps/nm/km or more and 13.5 ps/nm/km or less, a dispersion slope of a light beam at a wavelength of 1,550 nm is 0.092 ps/nm.sup.2/km or less, a cable cutoff wavelength is a wavelength of 1,450 nm or less, an effective area of a light beam at a wavelength of 1,550 nm is 65 μm.sup.2 or more and 90 μm.sup.2 or less, and a mode field diameter of a light beam at a wavelength of 1,550 nm is 9.2 μm or more and 10.5 μm or less. In other words, similarly to the dispersion shifted optical fiber DSF1, the dispersion shifted optical fiber DSF2 is a dispersion shifted optical fiber that transmits light in the C band and the L band.

[0049] The dispersion shifted optical fiber DSF2 has four segments. However, the dispersion shifted optical fiber DSF2 is different from the dispersion shifted optical fiber DSF1 in a relation r.sub.0=r.sub.1.

[0050] In the dispersion shifted optical fiber, a radius r.sub.0 of a first center segment 10 is equal to a radius r.sub.1 of a first segment 11. The radii are 1.8 μm or more and 2.8 μm or less.

[0051] FIG. 4 is a diagram of the relative refractive index profile of the dispersion shifted optical fiber DSF2 in FIG. 3 in a manner similar to FIG. 2. Similarly, the relative refractive index difference to a cladding 2 is reduced from the outer circumference of the first center segment 10 to the inner circumference of a second segment 12 in the first segment 11. However, as illustrated in FIG. 4, in order to hold the relation r.sub.0=r.sub.1, the outer circumference of the first center segment 10 is matched with the inner circumference of the second segment 12 (the outer circumference of the first segment 11). As illustrated in FIG. 4, the shape of the refractive index profile of the first segment 11 is generally a step-index shape.

[0052] Thus, in the case in which the shape of the refractive index profile of the first segment 11 is generally in a step-index shape, the segments may have the radii and the relative refractive index differences to the cladding 2 in ranges below.

[0053] In other words, the radius r.sub.0 of the first center segment 10 (the radius r.sub.1 of the first segment 11) is 1.8 μm or more and 2.8 μm or less, a radius r.sub.2 of the second segment 12 is 5.0 μm or more and 6.6 μm or less, a radius r.sub.3 of a third segment 13 is 6.1 μm or more and 8.5 μm or less, and a radius r.sub.4 of a fourth segment 14 is 8.0 μm or more and 16.0 μm or less. However, as described above, a relation r.sub.0 (r.sub.1)<r.sub.2<r.sub.3<r.sub.4 is held.

[0054] A relative refractive index difference Δ.sub.0 of the first center segment 10 to the cladding 2 (a relative refractive index difference Δ.sub.1 of the first segment 11 to the cladding 2) is 0.4% or more and 0.8% or less, a relative refractive index difference Δ.sub.2 of the second segment 12 to the cladding 2 is 0.00% or more and 0.06% or less, a relative refractive index difference Δ.sub.3 of the third segment 13 to the cladding 2 is 0.285% or more and 0.5% or less, and a relative refractive index difference Δ.sub.4 of the fourth segment 14 to the cladding 2 is 0.005% or more and 0.04% or less.

[0055] In the case in which the first segment has a refractive index profile generally in a trapezoid shape, the segments of the core 1 have the radii and the relative refractive index differences to the cladding 2 described above. Hence, the dispersion shifted optical fiber is more easily manufactured than in the case in which the refractive index is changed in the first segment 11.

[0056] Thus, in the case in which the shape of the refractive index profile of the first segment 11 is generally in a step-index shape, the segments may have the radii and the relative refractive index differences to the cladding 2 in ranges below.

[0057] In other words, the radius r.sub.0 of the first center segment 10 (the radius r.sub.1 of the first segment 11) is 2.0 μm or more and 2.6 μm or less, the radius r.sub.2 of the second segment 12 is 5.0 μm or more and 6.0 μm or less, the radius r.sub.3 of the third segment 13 is 6.1 μm or more and 7.5 μm or less, and the radius r.sub.4 of the fourth segment 14 is 11.0 μm or more and 15.0 μm or less. However, as described above, the relation r.sub.1 (r.sub.1)<r.sub.2<r.sub.3<r.sub.4 is held.

[0058] The relative refractive index difference Δ.sub.0 of the first center segment 10 to the cladding 2 (the relative refractive index difference Δ.sub.1 of the first segment 11 to the cladding 2) is 0.47% or more and 0.67% or less, the relative refractive index difference Δ.sub.2 of the second segment 12 to the cladding 2 is 0.02% or more and 0.06% or less, the relative refractive index difference Δ.sub.3 of the third segment 13 to the cladding 2 is 0.285% or more and 0.35% or less, and the relative refractive index difference Δ.sub.4 of the fourth segment 14 to the cladding 2 is 0.010% or more and 0.025% or less.

[0059] The segments of the core 1 have the radii and the relative refractive index differences to the cladding 2 described above. Thus, a change in a bending loss of light propagating through the core 1 can be further reduced, even in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 is changed.

[0060] As described above, one or more embodiments of the present invention are described and are taken as examples. However, the present invention is not limited to these embodiments.

[0061] For example, in one or more embodiments, the relative refractive index to the cladding 2 is decreased from the outer circumferential surface of the first center segment 10 to the inner circumference of the second segment 12 in the first segment 11. However, the relative refractive index to the cladding 2 only has to be decreased from the outer circumferential surface of the first center segment 10 to the inner circumference of the second segment 12 in the first segment 11. The relative refractive index to the cladding 2 may be decreased in a step-index shape.

EXAMPLES

[0062] In the following, the content according to one or more embodiments of the present invention will be described more in detail using examples and comparative examples. However, the present invention is not limited to these examples and comparative examples.

Example 1

[0063] Simulation was conducted using the dispersion shifted optical fiber DSF1 illustrated in FIGS. 1 and 2 as a model. The radius r.sub.0 of the first center segment 10 of the first segment 11, the radius r.sub.1 of the first segment 11, the radius r.sub.2 of the second segment 12, the radius r.sub.3 of the third segment 13, and the radius r.sub.4 of the fourth segment 14 were set as shown in Table 1. The relative refractive index difference Δ.sub.0 of the first center segment 10 to the cladding 2, the relative refractive index difference Δ.sub.2 of the second segment 12 to the cladding 2, the relative refractive index difference Δ.sub.3 of the third segment 13 to the cladding 2, and the relative refractive index difference Δ.sub.4 of the fourth segment 14 to the cladding 2 were set as shown in Table 1. The dispersion shifted optical fiber DSF1 was configured in which the relative refractive index difference to the cladding 2 was decreased in a slope from the outer circumferential surface of the first center segment 10 to the inner circumference of the second segment 12 in the first segment 11.

[0064] In the dispersion shifted optical fiber DSF1 having the radii of the segments and the relative refractive index differences of the segments to the cladding 2 as described above, the cutoff wavelength (λc) of the dispersion shifted optical fiber DSF1, the effective area (Aeff) in the case in which a light beam at a wavelength of 1,550 nm propagates, the mode field diameter (MFD) in the case in which a light beam at a wavelength of 1,550 nm propagates, the dispersion value (Disp) of a light beam at a wavelength of 1,550 nm, the dispersion slope (Slope) of a light beam at a wavelength of 1,550 nm, the bending loss (Bloss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF1 bent at a diameter of 20 mm, and the loss (Loss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF1 linearly constructed were as shown in Table 2.

[0065] The variability rate of the bending loss (Bloss VR) in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 fluctuates by 1% was as shown in Table 2.

Examples 2 to 11

[0066] Other than the radius (r.sub.0, r.sub.1, r.sub.2, r.sub.3, and r.sub.4) of the segments and the relative refractive index differences (Δ.sub.0, Δ.sub.2, Δ.sub.3, and Δ.sub.4) of the segments to the cladding 2 were set as shown in Table 1, simulation of the dispersion shifted optical fiber DSF1 was conducted similarly to example 1.

[0067] The cutoff wavelength (Xc) of the dispersion shifted optical fiber DSF1 in this case, the effective area (Aeff) in the case in which a light beam at a wavelength of 1,550 nm propagates, the mode field diameter (MFD) in the case in which a light beam at a wavelength of 1,550 nm propagates, the dispersion value (Disp) of a light beam at a wavelength of 1,550 nm, the dispersion slope (Slope) of a light beam at a wavelength of 1,550 nm, the bending loss (Bloss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF1 bent at a diameter of 20 mm, and the loss (Loss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF1 linearly constructed were as shown in Table 2.

[0068] The variability rate of the bending loss (Bloss VR) in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 fluctuates by 1% was as shown in Table 2.

Example 12

[0069] Simulation was conducted using the dispersion shifted optical fiber DSF2 illustrated in FIGS. 3 and 4 as a model. Thus, the radius r.sub.0 of the first center segment 10 is equal to the radius r.sub.1 of the first segment 11. The radius r.sub.0 of the first center segment 10 of the first segment 11 (the radius r.sub.1 of the first segment 11), the radius r.sub.2 of the second segment 12, the radius r.sub.3 of the third segment 13, and the radius r.sub.4 of the fourth segment 14 were set as shown in Table 1. The relative refractive index difference Δ.sub.0 of the first center segment 10l to the cladding 2, the relative refractive index difference Δ.sub.2 of the second segment 12 to the cladding 2, the relative refractive index difference Δ.sub.3 of the third segment 13 to the cladding 2, and the relative refractive index difference Δ.sub.4 of the fourth segment 14 to the cladding 2 were set as shown in Table 1.

[0070] Thus, in the dispersion shifted optical fiber DSF2 having the radii of the segments and the relative refractive index differences of the segments to the cladding 2 as described above, the cutoff wavelength (λc) of the dispersion shifted optical fiber DSF2, the effective area (Aeff) in the case in which a light beam at a wavelength of 1,550 nm propagates, the mode field diameter (MFD) in the case in which a light beam at a wavelength of 1,550 nm propagates, the dispersion value (Disp) of a light beam at a wavelength of 1,550 nm, the dispersion slope (Slope) of a light beam at a wavelength of 1,550 nm, the bending loss (Bloss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF2 bent at a diameter of 20 mm, and the loss (Loss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF2 linearly constructed were as shown in Table 2.

[0071] The variability rate of the bending loss (Bloss VR) in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 fluctuates by 1% was as shown in Table 2.

Examples 13 to 18

[0072] Other than the radius (r.sub.0 (r.sub.1), r.sub.2, r.sub.3, r.sub.4) of the segments and the relative refractive index differences (Δ.sub.0 (Δ.sub.1), Δ.sub.2, Δ.sub.3, and Δ.sub.4) of the segments to the cladding 2 were set as shown in Table 1, simulation of the dispersion shifted optical fiber DSF2 was conducted similarly to example 4.

[0073] The cutoff wavelength (λc) of the dispersion shifted optical fiber DSF2 in this case, the effective area (Aeff) in the case in which a light beam at a wavelength of 1,550 nm propagates, the mode field diameter (MFD) in the case in which a light beam at a wavelength of 1,550 nm propagates, the dispersion value (Disp) of a light beam at a wavelength of 1,550 nm, the dispersion slope (Slope) of a light beam at a wavelength of 1,550 nm, the bending loss (Bloss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF2 bent at a diameter of 20 mm, and the loss (Loss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF2 linearly constructed were as shown in Table 2.

[0074] The variability rate of the bending loss (Bloss VR) in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 fluctuates by 1% was as shown in Table 2.

Comparative Example 1

[0075] Other than a dispersion shifted optical fiber having three segments was formed, from which the fourth segment 14 of the dispersion shifted optical fiber DSF1 shown in FIGS. 1 and 2 was removed, and the radius (r.sub.0, r.sub.1, r.sub.2, and r.sub.3) of segments and the relative refractive index differences (Δ.sub.0, Δ.sub.2, and Δ.sub.3) of the segments to a cladding 2 were set as shown in Table 1, simulation of the dispersion shifted optical fiber was conducted similarly to example 1.

[0076] The cutoff wavelength (λc) of the dispersion shifted optical fiber in this case, the effective area (Aeff) in the case in which a light beam at a wavelength of 1,550 nm propagates, the mode field diameter (MFD) in the case in which a light beam at a wavelength of 1,550 nm propagates, the dispersion value (Disp) of a light beam at a wavelength of 1,550 nm, the dispersion slope (Slope) of a light beam at a wavelength of 1,550 nm, the bending loss (Bloss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber bent at a diameter of 20 mm, and the loss (Loss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber linearly constructed were as shown in Table 2.

[0077] The variability rate of the bending loss (Bloss VR) in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 fluctuates by 1% was as shown in Table 2.

Comparative Example 2

[0078] Other than a dispersion shifted optical fiber having three segments was formed, from which the fourth segment 14 of the dispersion shifted optical fiber DSF2 illustrated in FIGS. 3 and 4 was removed, and the radius (r.sub.0, r.sub.1, r.sub.2, and r.sub.3) of segments and the relative refractive index differences (Δ.sub.0, Δ.sub.2, and Δ.sub.3) of the segments to a cladding were set as shown in Table 1, simulation of the dispersion shifted optical fiber was conducted similarly to example 4.

[0079] The cutoff wavelength (λc) of the dispersion shifted optical fiber in this case, the effective area (Aeff) in the case in which a light beam at a wavelength of 1,550 nm propagates, the mode field diameter (MFD) in the case in which a light beam at a wavelength of 1,550 nm propagates, the dispersion value (Disp) of a light beam at a wavelength of 1,550 nm, the dispersion slope (Slope) of a light beam at a wavelength of 1,550 nm, the bending loss (Bloss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber bent at a diameter of 20 mm, and the loss (Loss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber linearly constructed were as shown in Table 2.

[0080] The variability rate of the bending loss (Bloss VR) in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 fluctuates by 1% was as shown in Table 2.

Comparative Example 3

[0081] Other than the radius (r.sub.0, r.sub.1, r.sub.2, r.sub.3, and r.sub.4) of the segments and the relative refractive index differences (Δ.sub.0, Δ.sub.2, Δ.sub.3, and Δ.sub.4) of the segments to the cladding 2 were set as shown in Table 1, simulation of the dispersion shifted optical fiber DSF1 was conducted similarly to example 1.

[0082] The cutoff wavelength (λc) of the dispersion shifted optical fiber DSF1 in this case, the effective area (Aeff) in the case in which a light beam at a wavelength of 1,550 nm propagates, the mode field diameter (MFD) in the case in which a light beam at a wavelength of 1,550 nm propagates, the dispersion value (Disp) of a light beam at a wavelength of 1,550 nm, the dispersion slope (Slope) of a light beam at a wavelength of 1,550 nm, the bending loss (Bloss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF1 bent at a diameter of 20 mm, and the loss (Loss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF1 linearly constructed were as shown in Table 2.

[0083] The variability rate of the bending loss (Bloss VR) in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 fluctuates by 1% was as shown in Table 2.

Comparative Examples 4 to 6

[0084] Other than the radius (r.sub.0 (r.sub.1), r.sub.2, r.sub.3, r.sub.4) of the segments and the relative refractive index differences (Δ.sub.0 (Δ.sub.1), Δ.sub.2, Δ.sub.3, and Δ.sub.4) of the segments to the cladding 2 were set as shown in Table 1, simulation of the dispersion shifted optical fiber DSF2 was conducted similarly to example 4.

[0085] The cutoff wavelength (λc) of the dispersion shifted optical fiber DSF2 in this case, the effective area (Aeff) in the case in which a light beam at a wavelength of 1,550 nm propagates, the mode field diameter (MFD) in the case in which a light beam at a wavelength of 1,550 nm propagates, the dispersion value (Disp) of a light beam at a wavelength of 1,550 nm, the dispersion slope (Slope) of a light beam at a wavelength of 1,550 nm, the bending loss (Bloss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF2 bent at a diameter of 20 mm, and the loss (Loss) of a light beam at a wavelength of 1,550 nm propagating through the dispersion shifted optical fiber DSF2 linearly constructed were as shown in Table 2.

[0086] The variability rate of the bending loss (Bloss VR) in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 fluctuates by 1% was as shown in Table 2.

[0087] Tables 1 and 2 are shown below. Note that, Table 1 describes the shape of the refractive index profile of the first segment 11.

TABLE-US-00001 TABLE 1 Core shape r0 r1 r2 r3 r4 Δ1 Δ2 Δ3 Δ4 Unit um um um um um % % % % Example 1 Trapezoid 0.8 3.7 6.5 8.1 13.9 0.62 0.01 0.30 0.04 Example 2 Trapezoid 1.1 2.9 6.2 7.3 12.3 0.77 0.07 0.42 0.02 Example 3 Trapezoid 0.5 1.8 4.0 4.5 8.0 0.90 0.07 0.50 0.04 Example 4 Trapezoid 2.8 4.5 8.0 8.5 16.0 0.40 0.00 0.285 0.03 Example 5 Trapezoid 2.8 3.0 5.7 6.7 11.5 0.40 0.00 0.285 0.005 Example 6 Trapezoid 0.6 2.0 4.1 4.7 8.2 0.90 0.07 0.50 0.04 Example 7 Trapezoid 1.0 4.5 6.5 8.0 13.5 0.60 0.02 0.285 0.01 Example 8 Trapezoid 0.5 3.0 5.2 6.5 10.0 0.80 0.065 0.40 0.03 Example 9 Trapezoid 0.6 3.0 5.5 6.5 10.5 0.74 0.03 0.33 0.03 Example 10 Trapezoid 0.7 3.1 6.1 7.2 12.1 0.72 0.06 0.32 0.02 Example 11 Trapezoid 0.8 3.1 6.2 7.2 12.3 0.70 0.05 0.40 0.01 Example 12 Step — 2.7 6.1 7.6 11.5 0.57 0.01 0.31 0.02 Example 13 Step — 2.6 6.4 8.4 12.6 0.50 0.06 0.29 0.01 Example 14 Step — 1.8 5.0 6.1 16.0 0.65 0.05 0.50 0.005 Example 15 Step — 2.6 6.0 7.5 15.0 0.47 0.02 0.285 0.01 Example 16 Step — 2.0 5.0 6.1 11.0 0.67 0.06 0.35 0.025 Exannple 17 Step — 2.3 5.7 6.9 12.0 0.55 0.03 0.32 0.01 Example 18 Step — 2.3 5.5 7.0 12.1 0.60 0.04 0.35 0.02 Comparative Trapezoid 0.7 3.5 6.1 7.6 — 0.67 0.02 0.33 — example 1 Comparative Step — 2.5 6.0 7.5 — 0.54 0.02 0.31 — example 2 Comparative Trapezoid 0.7 3.4 6.1 7.8 12.5 0.65 0.01 0.23 −0.04 example 3 Comparative Step — 2.2 4.8 7.1 11.0 0.60 0.02 0.23 −0.03 example 4 Comparative Step — 2.7 5.1 7.4 11.5 0.50 −0.03 0.25 −0.08 example 5 Comparative Step — 1.9 3.9 5.9 9.5 0.69 0.04 0.25 0.05 example 6

TABLE-US-00002 TABLE 2 λc Aeff MFD Disp Slope Bloss Loss BlossVR um um{circumflex over ( )}2 um ps/nm/km ps.sup.2/nm/km dB/m dB/km % Example 1 1.44 71.5 9.7 4.2 0.078 12.0 0.197 5.6 Example 2 1.32 73.2 9.7 4.4 0.091 11.2 0.194 5.2 Example 3 1.02 85.0 10.4 7.1 0.092 38.0 0.203 7.5 Example 4 1.23 74.2 9.9 13.0 0.058 7.2 0.198 8.3 Example 5 1.00 79.0 10.1 9.8 0.066 29.0 0.197 8.2 Example 6 1.10 71.9 9.7 4.2 0.091 12.4 0.201 6.8 Example 7 1.44 62.0 9.2 8.8 0.070 5.0 0.2 3.5 Example 8 1.45 87.8 10.4 5.1 0.092 15.0 0.199 3.9 Example 9 1.34 69.8 9.6 4.3 0.091 7.3 0.196 3.7 Example 10 1.36 72.7 9.7 4.0 0.090 9.3 0.196 2.8 Example 11 1.36 72.2 9.6 4.4 0.088 9.0 0.195 3.1 Example 12 1.38 68.7 9.5 4.7 0.860 11.0 0.206 5.1 Example 13 1.45 78.0 9.9 5.0 0.087 17.2 0.203 4 Example 14 1.43 88.8 10.3 7.0 0.092 15.0 0.204 7 Example 15 1.35 85.1 10.5 7.5 0.085 20.0 0.2 3.3 Example 16 1.32 64.4 9.2 3.5 0.092 5.0 0.201 3.9 Example 17 1.28 74.8 9.7 4.3 0.087 17.0 0.201 2.6 Example 18 1.21 71.9 9.6 4.3 0.088 15.8 0.199 3.8 Comparative example 1 1.37 71.8 9.6 4.1 0.086 8.9 0.197 16.2 Comparative example 2 1.37 71.5 9.5 4.3 0.084 8.3 0.199 15.9 Comparative example 3 1.29 66.0 9.3 2.8 0.081 13.1 0.199 17.4 Comparative example 4 1.27 68.8 9.4 4.3 0.091 7.0 0.207 21 Comparative example 5 1.40 73.0 9.6 4.2 0.085 11.3 0.203 17.9 Comparative example 6 1.38 7.1 9.5 3.9 0.098 5.0 0.201 22.6

[0088] Table 2 shows that according to the dispersion shifted optical fibers of examples 1 to 18, a change in a bending loss is reduced, even in the case in which the ratio between the core diameter and the cladding diameter is changed. Consequently, it is revealed that according to the dispersion shifted optical fiber according to one or more embodiments of the present invention, a bending loss of propagating light can be reduced, even in the case in which the diameter of the cladding glass body of the optical fiber preform fluctuates due to manufacture.

[0089] Specifically, in examples 1 to 11 in which the shape of the refractive index profile of the first segment 11 is in a trapezoid shape, the dispersion shifted optical fibers of examples 7 to 11 achieved an excellent result in which the variability rate (Blass VR) of a bending loss in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 fluctuates by 1% can be reduced to less than 4%. In examples 12 to 18 in which the shape of the refractive index profile of the first segment is a step-index shape, the dispersion shifted optical fibers of the examples 15 to 16 achieved an excellent result in which the variability rate (Bloss VR) of a bending loss in the case in which the ratio between the diameter of the core 1 and the diameter of the cladding 2 fluctuates by 1% can be reduced to less than 4%.

[0090] As described above, even in the case in which the ratio between the core diameter and the cladding diameter fluctuates, a change in a bending loss of propagating light can be reduced, and the dispersion shifted optical fiber can be used in the field of optical communications.

[0091] While the disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present disclosure. Accordingly, the scope should be limited only by the attached claims

REFERENCE SIGNS LIST

[0092] DSF1, DSF2 . . . dispersion shifted optical fiber [0093] 1 . . . core [0094] 2 . . . cladding [0095] 10 . . . first center segment [0096] 11 . . . first segment [0097] 12 . . . second segment [0098] 13 . . . third segment [0099] 14 . . . fourth segment