Patent ID: 7162161

Claim:
An optical communication system comprising: an optical communications route comprising system fiber or a laser pigtail fiber having a given mode field radius at an operating wavelength of the system, an optical route component for performing a function within the optical system, said optical route component forming part of the optical communications route and being connected to the system fiber or a laser pigtail fiber, and enclosed in a sealed container, the optical route component providing an optical output which passes along the system fiber or the laser pigtail fiber from the container, the output of the optical route component passing through a mode field transformer and thence along the system fiber or the laser pigtail fiber, the mode transformer including a section of optical fiber disposed at a location downstream of said container and serving to increase locally the mode field radius at said wavelength, the optical system being operated with an optical power density in the system fiber or the laser pigtail fiber above a level at which optical power induced damage can propagate in the system fiber or the laser pigtail fiber, the mode transformer reducing the optical power density for said given power level such that within the mode transformer the power density is reduced below the threshold level, so that in the event that optical power induced damage occurs in the system fiber or the laser pigtail fiber downstream of said mode transformer is prevented from propagating into the optical route component.