Abstract: The invention provides a monomode optical fiber and a monomode preform (2) having a mother preform (22) housed in an outer sleeve tube (20). It is characterized in that it also includes an intermediate tube (21) between the mother preform (22) and the outer tube (20), the intermediate tube (21) possessing viscosity at fiber-drawing temperature which is less than the viscosity(ies) at fiber-drawing temperature of the mother preform (22) and of the outer tube (20). The invention also provides a method of manufacturing a monomode optical fiber. The fiber has a core that is better centered and less deformed than in the prior art. An application of the invention lies in making an optical amplifier.

Abstract: The invention provides a monomode preform (2) comprising a mother preform (22) housed in an outer sleeve tube (20). It is characterized in that it also includes an intermediate tube (21) between the mother preform (22) and said outer tube (20), the intermediate tube (21) possessing viscosity at fiber-drawing temperature which is less than the viscosity(ies) at fiber-drawing temperature of said mother preform (22) and of said outer tube (20). The invention also provides a method of manufacturing a monomode optical fiber. The fiber has a core that is better centered and less deformed than in the prior art. An application of the invention lies in making an optical amplifier.

Abstract: A method of fabricating a fluoride glass optical fiber preform which has a fluoride glass core surrounded by a fluoride glass optical cladding includes the following steps: introducing the cladding glass in the molten state into a bottom part of a mold having a cylindrical inside cross-section, introducing the core glass in the molten state into a top part of the mold above the cladding glass, and inwardly solidifying the core glass and the cladding glass from the interface between the glasses and the mold. The kinetics of solidification of the core glass are such that complete solidification of the cladding glass occurs before complete solidification of the core glass.