The name of the invention: the dispersion shifted optical fiber Technical field [0001] 　The present invention relates to a dispersion-shifted optical fiber, it is suitable for the case of suppressing the variation in the bending loss of light propagating through the core. Background technique [0002] 　In optical communication transmission network, it has been used single mode optical fiber. WDM (WDM transmission) has been widely accepted as an optical communication using the single-mode optical fiber. WDM is not wave wavelength of optical communications, a method of transmitting a plurality of optical signals using a plurality of wavelengths, an optical transmission method suitable for large-capacity high-speed communication. [0003] 　In wavelength multiplexing transmission, there is the dispersion shifted optical fiber is used to suppress the wavelength dispersion, non-zero dispersion shifted optical fiber not to the dispersion to zero while suppressing the dispersion by the wavelength of inter alia the light (Non-Zero Dispersion Shifted Fiber: NZDSF) sometimes is used. [0004] 　The following Patent Document 1 discloses a dispersion-shifted optical fiber. Dispersion shifted optical fiber according to Patent Document 1, the core has three segments. [0005] Patent Document 1: Japanese Patent No. 4393708 Summary of the Invention [0006] 　However, in the dispersion shifted optical fiber according to Patent Document 1, a so-called bending loss loss light propagating in bending the dispersion shifted optical fiber, varies when the ratio of the cladding diameter and the core diameter changes easy it was found. Common optical fiber preform includes a core made of a core glass rods shaped as a core, the inner peripheral side cladding glass body serving as a portion of the inner circumferential side of the coated cladding an outer circumferential surface of the core glass body It produced using coating rods. Then, using a jacket method or OVD method (Outside Outside Vapor Deposition method), covering the outer peripheral surface of the core coated rods (on the outer peripheral surface of the inner peripheral side cladding glass body) at the outer peripheral side cladding glass body that becomes the outer peripheral side of the clad . Generally, since the outer peripheral side cladding glass body it is often produced inexpensively, the outer diameter of the outer peripheral side cladding glass body easily varied. Thus the fact that the outer diameter of the outer peripheral side cladding glass body fluctuates, leading to the outer diameter of the optical fiber preform is changed. On the other hand, the cladding diameter of the optical fiber to be manufactured by drawing the optical fiber preform is a constant and so on for example, 125 [mu] m. Therefore, the outer diameter of the optical fiber preform is changed, the ratio between the cladding diameter and the core diameter is changed. Thus by producing definitive errors that the ratio between the core diameter and the cladding diameter as described above is changed, there is a concern that variation in the light bending losses propagating the dispersion shifted optical fiber to be produced increases. Optical fibers not only be laid in a straight line, it may be laid in bent state. Therefore, it is not preferable that the bending loss of light propagating as described above varies. [0007] 　Accordingly, the present invention, even when the ratio between the core diameter and the cladding diameter is changed, and an object thereof is to provide a dispersion shifted optical fiber which can suppress the bending loss varies. [0008] 　To solve the above problems, the present invention is the dispersion value in the light of a wavelength above 1530 nm 1625 nm is not more than 2.0 ps / nm / miles above 13.5ps / nm / km, dispersion slope in the optical wavelength of 1550nm There 0.092 ps / nm 2 is at / km or less, the cable cutoff wavelength is less 1450 nm, the effective core area in the light of the wavelength of 1550nm is 65 .mu.m 2 or 90 [mu] m 2 or less, the mode of light having a wavelength of 1550nm field diameter is characterized in following a dispersion-shifted optical fiber is less than 10.5μm than 9.2 .mu.m. [0009] 　The core comprises a first segment including the center axis of the core, a second segment surrounding without gaps an outer peripheral surface of the first segment, a third segment surrounding without gaps an outer peripheral surface of said second segment, said third the outer peripheral surface of the segment and a fourth segment which surrounds with no gap, the first segment includes a first central segment containing the central axis. [0010] 　Further, the radius r of the first central segment 0 is the 0.5μm or 2.8μm or less, the radius r of the first segment 1 is less than 4.5μm or 1.8 .mu.m, the radius r of the second segment 2 is less than 8.0μm or 4.0 .mu.m, the radius r of the third segment 3 is a 4.5μm or 8.5μm or less, the radius r of the fourth segment 4 below 16.0μm or 8.0μm is a, and, r 0 ≦ r 1