There are provided a multi-core optical fiber including four step-index type cores with a standard cladding diameter and having excellent mass productivity, quality, and yield while meeting desired specifications, and a design method thereof. A multi-core optical fiber according to the present disclosure includes: four cores arranged in a square lattice shape along a longitudinal direction, each of the four cores having a step-index type refractive index distribution with a radius a; and a cladding region having a lower refractive index than that of each core and a diameter of 1251 m and provided on an outer peripheral portion of each core, where an absolute value of a relative refractive index difference between each core and the cladding region is . The four cores are arranged so that a relationship between a minimum distance (OCT) from the center of each core to an outer periphery of the cladding region, a minimum value of spacing between the cores, and the MFD at a wavelength of 1310 nm satisfies Formula C1, and the radius a of each core and the relative refractive index difference between the core and the cladding region are set.

[00001]$\left[\mathrm{Formula}C1\right]$$\begin{array}{cc}\mathrm{OCT}3.73\mathrm{MFD}+3.43-5.28\mathrm{MFD}+83.54& \left(\mathrm{C1}\right)\end{array}$

The present invention relates to an optical fiber 100 having a core (102) which is up doped and a cladding (104) surrounding the core (102). Particularly, the cladding (104) has a first cladding (104a) defined by a first relative refractive index difference (1). Moreover, the first cladding (104a) is a continuous region adjacent to the core (102) such that a relative refractive index profile of the first cladding (104a) is an alpha profile. Further, the optical fiber (100) has mode field diameter in the range of 8.2 micrometer (m) to 9.0 m at a wavelength of 1310 nanometer (nm), and a cut-off wavelength less than or equal to 1260 nm.

The optical fibers disclosed have single mode and few mode optical transmission for VCSEL-based optical fiber transmission systems. The optical fibers have a cable cutoff wavelength .sub.C of equal to or below 1260 nm thereby defining single mode operation at a wavelength in a first wavelength range greater than 1260 nm and few-mode operation at a wavelength in a second wavelength range from 970 nm and 1070 nm. The mode-field diameter is in the range from 9.3 microns to 10.9 microns at 1550 nm. The optical fibers have an overfilled bandwidth OFL BW of 1 GHz.Math.km to 3 GHz.Math.km at the at least one wavelength in the second wavelength range. VCSEL based optical transmission systems and methods are disclosed that utilize both single core and multicore versions of the optical fiber.

An MCF of the present embodiment has eight or more cores. A diameter of a common cladding is not more than 126 m. Optical characteristics of each core are as follows: a TL at a predetermined wavelength of 1310 nm is not more than 0.4 dB/km; an MFD at the predetermined wavelength is from 8.0 m to 10.1 m; a BL in a BR of not less than 5 mm or in the BR of not less than 3 mm and, less than 5 mm is not more than 0.25 dB/turn at the predetermined wavelength; 0 is from 1300 nm to 1324 nm; cc is not more than 1260 nm; an XT or XTs at the predetermined wavelength is not more than 0.001/km.

An MCF of the present embodiment has eight or more cores. A diameter of a common cladding is not more than 126 m. Optical characteristics of each core are as follows: a TL at a predetermined wavelength of 1310 nm is not more than 0.4 dB/km; an MFD at the predetermined wavelength is from 8.0 m to 10.1 m; a BL in a BR of not less than 5 mm or in the BR of not less than 3 mm and, less than 5 mm is not more than 0.25 dB/turn at the predetermined wavelength; 0 is from 1300 nm to 1324 nm; cc is not more than 1260 nm; an XT or XTs at the predetermined wavelength is not more than 0.001/km.

An optical fiber having both low macrobend loss and low microbend loss. The fiber has a central core region, a first (inner) cladding region surrounding the central core region and having an outer radius r.sub.2>16 microns and relative refractive index .sub.2, and a second (outer) cladding region surrounding the first cladding region having relative refractive index, .sub.3, wherein .sub.1>.sub.3>.sub.2. The difference between .sub.3 and .sub.2 is greater than 0.12 percent. The fiber exhibits a 22 m cable cutoff less than or equal to 1260 nm, and r.sub.1/r.sub.2 is greater or equal to 0.24 and bend loss at 1550 nm for a 15 mm diameter mandrel of less than 0.5 dB/turn.

An optical fiber including a core and a cladding including an inner cladding layer and an outer cladding layer is provided. The refractive index of the core 1, the refractive index of the inner cladding layer 2, and the refractive index of the outer cladding layer 3 have a relationship denoted by the following expressions: 1max>2min and 1max>3, and 0.01%<|2min3|<0.03%. An outer circumference radius r1 of the core, an outer circumferential radius r2 of the inner cladding layer, and an outer circumferential radius r3 of the outer cladding layer have a relationship denoted by the following expressions: r1<r2<r3, and 0.2r1/r20.5. A cable cut-off wavelength cc 1260 nm or less. A mode field diameter at a wavelength of 1310 nm is 8.6 m or more and 9.5 m or less.

An optical fiber including a core and a cladding including an inner cladding layer and an outer cladding layer is provided. The refractive index of the core 1, the refractive index of the inner cladding layer 2, and the refractive index of the outer cladding layer 3 have a relationship denoted by the following expressions: 1max>2min and 1max>3, and 0.01%<|2min3|<0.03%. An outer circumference radius r1 of the core, an outer circumferential radius r2 of the inner cladding layer, and an outer circumferential radius r3 of the outer cladding layer have a relationship denoted by the following expressions: r1<r2<r3, and 0.2r1/r20.5. A cable cut-off wavelength cc 1260 nm or less. A mode field diameter at a wavelength of 1310 nm is 8.6 m or more and 9.5 m or less.

The present invention relates to an optical fiber (100, 101, 103, 105, 107) having a core region (102) and a cladding region (104). In particular, the cladding region (104) has exactly one down-doped region (210, 310) and an undoped region (212, 312). The down doped region (210, 310) is a continuous region adjacent to core region (102) such that radial position of minimum relative refractive index (214, 314) of the optical fiber (100, 101, 103, 105, 107) is within 3 micrometers (m) from interface between the down doped region (210, 310) and the undoped region (212, 312). Further, the mode field diameter of the optical fiber (100, 101, 103, 105, 107) is in range of 8.8 m to 9.6 m at a wavelength 1310 nanometres (nm), and cable cut-off of the optical fiber (100, 101, 103, 105, 107) is less than or equal to 1260 nm.

An optical fiber having both low macrobend loss and low microbend loss. The fiber has a central core region, a first (inner) cladding region surrounding the central core region and having an outer radius r.sub.2>16 microns and relative refractive index .sub.2, and a second (outer) cladding region surrounding the first cladding region having relative refractive index, 4.sub.3, wherein .sub.1>.sub.3>.sub.2 . The difference between .sub.3 and .sub.2 is greater than 0.12 percent. The fiber exhibits a 22m cable cutoff less than or equal to 1260 nm, and r.sub.1/r.sub.2 is greater or equal to 0.24 and bend loss at 1550 nm for a 15 mm diameter mandrel of less than 0.5 dB/turn.