A multicore optical fiber comprises a common cladding and a plurality of core portions disposed in the common cladding. Each of the core portions includes a central axis, a core region extending from the central axis to a radius r.sub.1, the core region comprising a relative refractive index Δ.sub.1, an inner cladding region extending from the radius r.sub.1 to a radius r.sub.2, the inner cladding region comprising a relative refractive index Δ.sub.2, and a depressed cladding extending from the radius r.sub.2 to a radius r.sub.3, the depressed cladding region comprising a relative refractive index Δ.sub.3 and a minimum relative refractive index Δ.sub.3 min. The relative refractive indexes may satisfy Δ.sub.1>Δ.sub.2>Δ.sub.3 min. The mode field diameter of each core portion may greater than or equal to 8.2 μm and less than or equal to 9.5 μm.

A multicore fiber includes: n pieces of first core regions in a circular shape with a radius r1 that are arranged about points P11 to P1n, and that has a first core portion and a first cladding portion; a second core region in a circular shape with a radius R1 that is arranged about the point a1, and that has a second core portion and a second cladding portion; and a cladding region that is formed on an outer circumferences of the first core region and the second core region. Further, abutting surfaces that are flat surfaces abutting on each other are formed in portions on the outer circumferences of the first core region and the second core region.

The present invention relates to an optical fiber with improved bend performance and manufacturing method thereof. The optical fiber (100) comprises a core region (108) defined by a core refractive index profile (200) and a cladding region (106) surrounding the core region defined by a cladding refractive index profile (400). Particularly, the core region has a first core (102) defined by a first core refractive index (RI) profile (202) and a first core RI max (Δpeak) and a second core (104) defined by a second core RI profile (204) and a second core RI max (Δcore). Moreover, the cladding region further comprises a first cladding (106) and a third cladding (110) composed of pure silica and a second cladding (108) composed of a down-doped silica, where the down-dopant is fluorine.

According to embodiments of the present invention, a fiber preform or an optical fiber is provided. The fiber preform or the optical fiber includes a core region having a plurality of cores, wherein two cores of the plurality of cores are bridged by an air gap, and a cladding arrangement including a first cladding region having a plurality of structures surrounding the core region, and a second cladding region in between the core region and the first cladding region, the second cladding region having a plurality of tubes, wherein at least one split is defined in the second cladding region. According to further embodiments of the present invention, a method for forming the fiber preform, a method for forming the optical fiber, an optical coupler having the optical fiber, an optical combiner having the optical fiber, and an optical apparatus having the optical fiber are also provided.

A manufacturing method includes forming one or more first holes in a cladding rod, inserting a first glass rod into each of the one or more first holes, heating the cladding rod together with the inserted first glass rod to integrate the first glass rod and the cladding rod and to form an intermediate preform, forming one or more second holes in the intermediate preform, inserting a second glass rod into each of the one or more second holes, and heating the intermediate preform together with the inserted second glass rod to integrate the second glass rod and the intermediate preform.

A multi-core optical fiber preform includes: a rod-shaped main cladding body having one or more main inner holes; main core rods inserted into the one or more main inner holes; and a tip continuously-installed portion disposed at one end of the rod-shaped main cladding body and including a glass rod having no core rod or having one core rod.

An optical fiber preform production method includes: inserting at least one glass rod into at least one through-hole that penetrates a cladding glass body that is a cladding of an optical fiber; integrating a dummy rod by either integrating a solid dummy silica rod with a first end of the cladding glass body by heating the first end to close a first opening of the through-hole that opens in the first end, or forming a base end seal that closes the first opening in the first end and integrating the solid dummy silica rod with the base end; and closing a second opening of the through-hole that opens in a second end of the cladding glass body by heating and deforming the second end.

Provided is an optical fiber manufacturing method that uses a low-cost large optical fiber preform having high precision. The optical fiber manufacturing method includes at least a positioning step of positioning core rods in a hollow carbon pipe that contains carbon as a main component, a soot preform preparation step of filling a gap between the carbon pipe and the core rods with silica powder that contains SiO.sub.2 as a main component, thereby producing a soot preform, a consolidating step of introducing the soot preform into a furnace and consolidating the silica powder, thereby producing a transparent intermediate preform from the soot preform, an extraction step of extracting the transparent intermediate preform from the carbon pipe, and a drawing step of drawing the transparent intermediate preform, thereby manufacturing an optical fiber.

A manufacturing method includes forming one or more first holes in a cladding rod, inserting a first glass rod into each of the one or more first holes, heating the cladding rod together with the inserted first glass rod to integrate the first glass rod and the cladding rod and to form an intermediate preform, forming one or more second holes in the intermediate preform, inserting a second glass rod into each of the one or more second holes, and heating the intermediate preform together with the inserted second glass rod to integrate the second glass rod and the intermediate preform.

A method for producing a preform for producing a multi-core fiber. The method includes removing a first part-tube segment having a first part-tube segment cross-sectional area from a center of a receiving tube having a receiving tube internal diameter so that the receiving tube has a first core rod receiving cut-out, axially introducing a central filling rod having a filling rod external diameter into the receiving tube so that the receiving tube contains the central filling rod, inserting a first core rod having a first core rod cross-sectional area into the core rod receiving cut-out so that the receiving tube contains the core rod, axially introducing the receiving tube containing the first core rod and the central filling rod into a jacketing tube so as to obtain a jacketing tube containing the receiving tube, and fusing the jacketing tube containing the receiving tube to form the preform.