The present disclosure provides optical fibers that exhibit low macrobend loss at 1550 nm at bend diameters greater than 40 mm. The relative refractive index profile of the fibers includes a trench cladding region having a trench volume configured to minimize macrobend loss at large bend diameters. The thickness and/or depth of the trench cladding region are controlled to reduce trench volume to a degree consistent with reducing macrobend loss at bend diameters greater than 40 mm. The optical fiber includes an outer cladding region that surrounds and is directly adjacent to the trench cladding region and an optional offset cladding region between the trench cladding region and the core region. In some embodiments, the core region is a segmented core region that includes inner and outer core regions. The low macrobend loss available from the optical fibers makes them particularly suitable for applications in submarine telecommunications systems.

A single mode optical fiber is provided that includes a core region having an outer radius r.sub.1 and a maximum relative refractive index Δ1.sub.max. The single mode optical fiber has a bend loss at 1550 nm for a 15 mm diameter mandrel of less than about 0.75 dB/turn, has a bend loss at 1550 nm for a 20 mm diameter mandrel of less than about 0.2 dB/turn, and a bend loss at 1550 nm for a 30 mm diameter mandrel of less than 0.002 dB/turn. Additionally, the single mode optical fiber has a mode field diameter of 9.0 microns or greater at 1310 nm wavelength and a cable cutoff of less than or equal to about 1260 nm.

Optical systems that employ concentric multi core fibers (MCFs) are discussed. Some of the systems discussed are based on the use of a concentric MCF that has a single mode core, capable of carrying a broadband data signal, and a multimode core, which carries optical signals that do not require as high a bandwidth as the broadband data signal. In one embodiment, the multimode core carries system management data. In another embodiment, the multimode core carries a high power optical signal that provides remote power. In another embodiment, the multimode core carries a pump signal for a downstream fiber amplifier. In yet another embodiment, the multimode core carries an optical signal, for example visible light, that can be used to verify connectivity.

An optical fiber line of one embodiment comprises an HNLF, an SMF, and an MFD transition portion. The MFD transition portion includes end portions of both the HNLF and the SMF facing with a fusion point thereof, and is a section in which an MFD changes such that a difference between a maximum value and a minimum value is 0.3 μm or more for a 100 μm-length. A splicing loss of the HNLF and the SMF at 1,550 nm is one-fifth or less than an ideal butting loss at stationary portions thereof. A total length of the MFD transition portion is 10 mm or less. In a region between one end surface of the HNLF at the fusion point and the other end surface separated from the one end surface by 50 μm or more and 300 μm or less, the MFD increases monotonically from the other end surface to the one end surface.

An optical fiber line of one embodiment comprises an HNLF, an SMF, and an MFD transition portion. The MFD transition portion includes end portions of both the HNLF and the SMF facing with a fusion point thereof, and is a section in which an MFD changes such that a difference between a maximum value and a minimum value is 0.3 μm or more for a 100 μm-length. A splicing loss of the HNLF and the SMF at 1,550 nm is one-fifth or less than an ideal butting loss at stationary portions thereof. A total length of the MFD transition portion is 10 mm or less. In a region between one end surface of the HNLF at the fusion point and the other end surface separated from the one end surface by 50 μm or more and 300 μm or less, the MFD increases monotonically from the other end surface to the one end surface.

An optical fiber according to an embodiment has a structure capable of reducing an increase in transmission loss. The optical fiber includes a glass part extending in a direction of a central axis, and the glass part is comprised of silica-based glass, includes a core and a cladding, and has residual stress approximately uniform throughout a cross section of the glass part orthogonal to the central axis, the core having the central axis and being doped with chlorine with a mass fraction of 1% or more, the cladding surrounding the core and having a refractive index lower than a maximum refractive index of the core.

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.

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 assembly may comprise an input fiber to provide a beam, a process fiber comprising a ring-shaped outer core surrounded by a cladding, and a first beam shifter arranged to receive the beam from the input fiber and to shift the beam spatially to illuminate the ring-shaped outer core of the process fiber. The optical assembly may further comprise a second beam shifter arranged to receive the beam from the first beam shifter and to add skew to the beam that is launched into the ring-shaped outer core of the process fiber.

An optical assembly may comprise an input fiber to provide a beam, a process fiber comprising a ring-shaped outer core surrounded by a cladding, and a first beam shifter arranged to receive the beam from the input fiber and to shift the beam spatially to illuminate the ring-shaped outer core of the process fiber. The optical assembly may further comprise a second beam shifter arranged to receive the beam from the first beam shifter and to add skew to the beam that is launched into the ring-shaped outer core of the process fiber.