An optical fiber includes: a core portion made of glass; and a cladding portion made of glass, having a refractive index lower than the refractive index of the core portion, and positioned on an outer periphery of the core portion. Further, the cladding portion has an outer diameter smaller than 100 μm, and the core portion has a relative refractive-index difference of 0.32% to 0.40% with respect to the cladding portion.

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 125±1 μm 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 Δ. 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 A 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 Δ between the core and the cladding region are set.

[Formula C1]

OCT≥3.73MFD+3.43

A≤−5.28MFD+83.54  (C1)

This MCF ensures sufficient manufacturing tolerance, is excellent in mass productivity, and is also capable of suppressing degradation of splice loss. The MCF includes four cores and a common cladding. Each core has adjacent relationships with two cores of remaining cores, an adjacent core interval Λ is from Λ.sub.nominal−0.9 μm to Λ.sub.nominal+0.9 μm, a common cladding diameter is from 124 μm to 126 μm, an MFD, λ.sub.cc and d.sub.coat at a wavelength of 1310 nm satisfy a predetermined relationship, the MFD is from a MFD-reference-value−0.4 μm to the MFD-reference-value+0.4 μm with the MFD-reference-value of from 8.6 μm to 9.2 μm, a zero-dispersion wavelength is from a wavelength-reference-value−12 nm to the wavelength-reference-value+12 nm with the wavelength-reference-value of from 1312 nm to 1340 nm, a dispersion slope at a zero-dispersion wavelength is 0.092 ps/(nm.sup.2.Math.km) or less, λ.sub.cc is 1260 nm or less, and a predetermined structural condition and an optical condition are satisfied.

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 λ.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.km to 3 GHz.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.

A multi-core optical fiber includes: four cores arranged in a 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 125±1 μm 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 Δ. The four cores are arranged so that a relationship between a minimum distance from the center of each core to an outer periphery of the cladding region, a minimum value Λ of spacing between the cores, and the MFD satisfies a formula, and the radius a of each core and the relative refractive index difference Δ between the core and the cladding region are set.

An optical fiber includes: a core portion made of glass; a cladding portion that is located on an outer periphery of the core portion and that is made of glass having a lower refractive index than a refractive index of the core portion; and a coating portion that covers an outer periphery of the cladding portion. Further, an average value of a relative refractive-index difference of a center core of the core portion is 0.1 to 0.5%, a fiber diameter including the coating portion is equal to or smaller than 220 μm, an effective cutoff wavelength is longer than 1260 nm and smaller than 1530 nm, and a mode field diameter of light at 1550 nm is equal to or larger than 9 μm.

The present disclosure provides an optical fibre (100). The optical fibre (100) includes a glass core (102), a trench region (106) and a cladding (108). The trench region (106) has a trench curve parameter α.sub.trench in range of 5 to 8. The optical fibre (100) has a mode field diameter in range of 8.7 micrometers to 9.7 micrometers at wavelength of 1310 nanometer.

An optical fiber includes: a core portion made of glass; and a cladding portion made of glass, having a refractive index lower than the refractive index of the core portion, and positioned on an outer periphery of the core portion. Further, the cladding portion has an outer diameter smaller than 100 μm, and the core portion has a relative refractive-index difference of 0.32% to 0.40% with respect to the cladding portion.

The present invention relates to an optical fiber (100) comprising a core region (102) having radius R1 and a cladding region (104) having a radius R3. In particular, the core region (102) is defined along a central longitudinal axis (110) and the cladding region (104) is defined along the central longitudinal axis (110) of the optical fiber (100). Moreover, the optical fiber (100) has a Mode Field Diameter in a range of 8.5+/−0.3 microns at a wavelength of 1310 nanometers, a micro-bending loss of less than equal to 0.5 dB/Km at a wavelength of 1550 nanometers, macro-bending loss of less than 1 dB/Km at a wavelength 1550 nanometers. Further, the optical fiber (100) has a diameter of less than 210 microns.

An optical waveguide component is configured to have a dual structure in which a core region of the first optical waveguide is contained within the core region of the second optical waveguide in a cross-section perpendicular to the length direction of the optical waveguide. The refractive index of a first material of the core of the first optical waveguide is greater than a refractive index of a second material of the core of a second optical waveguide. The refractive index of a second material constituting the core of a second optical waveguide is greater than a refractive index of a third material constituting cladding of the second optical waveguide. The center height of the core of the first optical waveguide and the center height of the core of the second optical waveguide are aligned, which solves connectivity problems caused by worsened butt coupling efficiency, and incomplete adiabatic coupling in an SSC structure of prior art.