Multimode silica optical fiber with a reflecting cover from a fluorinated thermoplastic polymer

The optical properties of a silica–polymer optical fiber with a light-guide core with a diameter of 430 $\mu$m and a reflecting shell with a thickness of 70 $\mu$m from a thermoplastic copolymer of tetrafluoroethylene with ethylene of Tefzel brand have been experimentally studied. The polymer coating is applied to a silica fiber directly in the fiber draw apparatus by the die method from a thermoplastic melt. The optical losses of the drawn fiber and the numerical aperture and its dependence on the fiber length are measured. It is established that a light propagating through the fiber is noticeably scattered by the reflecting shell, which is associated with the crystallinity of the polymer. The distribution of the scattered radiation intensity along the fiber axis and the indicatrix of radiation scattering by the shell are measured. The relative contributions of scattering and absorption of light in the shell to the total optical losses of the fiber are estimated. The possible use of optical fibers of this structure in laser medicine is considered.