Low-Loss FEP-Clad Silica Fibers

Easy-to-fabricate, low-loss optical fibers are described that consist of a pure fused silica core surrounded with a loosely fitting, extruded, FEP cladding tube. Because of their large numerical aperture (NA), these fibers are particularly well suited for the transmission of the incoherent light emitted by light-emitting diodes. Whereas the losses approached those of the core material for small angle excitation (i.e., 7.6 dB/km at 0.8 microm for a Suprasil 2 fiber of 230-m length), they increased to 14 dB/km for a steady-state NA of 0.3. The measured pulse dispersion of up to 30 nsec agrees well with the expected 24 nsec for a stepindex fiber with an NA of 0.3.