A multicore optical fiber includes two or more cores, a common interior cladding surrounding the two or more cores, and a common exterior cladding surrounding the common interior cladding. The common exterior cladding has a lower relative refractive index than the common interior cladding and reduces tunneling losses from the cores. The reduced tunneling loss allows placement of cores closer to the edge of the fiber, thus providing multicore optical fibers having higher core count for a given fiber diameter. Separation between cores is controlled to minimize crosstalk.

A multicore optical fiber includes two or more cores, a common interior cladding surrounding the two or more cores, and a common exterior cladding surrounding the common interior cladding. The common exterior cladding has a lower relative refractive index than the common interior cladding and reduces tunneling losses from the cores. The reduced tunneling loss allows placement of cores closer to the edge of the fiber, thus providing multicore optical fibers having higher core count for a given fiber diameter. Separation between cores is controlled to minimize crosstalk.

An optical fiber (10) capable of minimizing strength deterioration includes a core (11) and a clad (12) arranged around the core (11) such that part of the core (11) is exposed. A rough surface portion is provided at least at part of an outer surface of the exposed portion (11a) of the core (11) exposed through the clad (12). The arithmetic surface roughness Ra of the rough surface portion is equal to or greater than 0.2 μm. The average length Rsm of a rough curve element of the rough surface portion is equal to or greater than 17 μm.

One embodiment of the present disclosure relates to an SFG (slanted fiber grating) that can easily realize a high-performance gain equalizer. The SFG includes an optical fiber comprised of silica-based glass and including a core, a first cladding containing a photosensitive material, and a second cladding. A specific section between two different points arranged along a fiber axis in the optical fiber is configured with a first region, a pair of second regions, and a third region. The first region includes a slanted Bragg grating provided in a region as the first cladding. The pair of second regions are arranged to sandwich the first region. The third region is disposed to sandwich both the first region and the pair of second regions. An MFD at a wavelength of 1.55 μm in the third region is smaller than an MFD at a wavelength of 1.55 μm in the first region.

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.

A multicore optical fiber includes two or more cores, a common interior cladding surrounding the two or more cores, and a common exterior cladding surrounding the common interior cladding. The common exterior cladding has a lower relative refractive index than the common interior cladding and reduces tunneling losses from the cores. The reduced tunneling loss allows placement of cores closer to the edge of the fiber, thus providing multicore optical fibers having higher core count for a given fiber diameter. Separation between cores is controlled to minimize crosstalk.

A gain fiber assembly for use in optical fiber amplification systems such as fiber amplifiers and fiber lasers utilizes an active or “bare” fiber that has a single glass cladding with an outer diameter of less is less than 80 μm and preferably less than 60 μm or even 40 μm. A passive double-clad input fiber is stripped of the outer cladding and tapered to match the outer diameter of the bare fiber. A glass-fluid or glass-vacuum interface along the taper provides guidance of the pump into and along the cladding of the bare fiber and a NA>1 for a vacuum or gasses and an NA>0.8 for liquids. This allows for much shorter fiber lengths to reach max signal power and higher pump conversion efficiencies.

An optical fiber includes a core with radius r1, a first clad layer with outermost radius r2 adjacent to the core at radial position r1 and covering the outer periphery of the core, a second clad layer with outermost radius r3 adjacent to the first clad layer at radial position r2 and covering the outer periphery of the first clad layer, and a third clad layer adjacent to the second clad layer at radial position r3 and covering the outer periphery of the second clad layer. The refractive index of the first clad layer decreases continuously from the inside to the outside, reaching a maximum value at radial position r1 and a minimum value at radial position r2. The refractive index of the second clad layer increases continuously from the inside to the outside, reaching a minimum value at radial position r2 and a maximum value at radial position r3.

A multi-core fiber includes: plural cores made of silica-based glass; and a cladding enclosing the plural cores and made of silica-based glass, the cladding having a refractive index lower than a maximum refractive index of the plural cores. Further, the multi-core fiber has a mode field diameter of 5.0 μm or larger at a wavelength of 1100 nm, the multi-core fiber provides single-mode propagation at the wavelength of 1100 nm, the multi-core fiber has a bending loss of 1 dB/turn or less at the wavelength of 1100 nm when the multi-core fiber is bent at a radius of 2 mm, and the multi-core fiber has a crosstalk between cores of −30 dB/km or less.

Optical fibers having a large effective area and a low cutoff wavelength are disclosed. Three main embodiments of the optical fiber allow for single-mode operation at wavelengths greater than 980 nm, and have a large effective area with low bend losses and low dispersion at 1310 nm. The large effective area optical fiber is expected to be particularly useful for data center applications due to its ability to efficiently optically couple with VCSELs and photonic integrated devices. Integrated systems and optical communication systems that employ the optical fibers are also disclosed.