Abstract: Optical fibers in long line communication links fail often in tensile strength. Analysis of tensile properties reveals a variation in tensile strength with fiber length, pointing to uncommon structural defects randomly occurring along the fiber length. Failures occur from crack propagation at these defects. The defects can be revealed according to the invention by nondestructive monitoring during production via off-plane light scattering. A narrow light beam incident across the fiber diameter is refracted in a pattern characteristic of the fiber geometry. Variations in that pattern are produced by structural variations in the fiber or by surface contamination. The nature of the pattern change can indicate the type of defect.

Abstract: A cylindrical strand with a thermoplastic outer shell (e.g., plastic insulated wire) is bonded along its length to a similar or different cylindrical strand by laser heating. The strands are brought into contact with one another at a contact point. A laser beam of selected power and wavelength is directed at the contact point in a direction approximately parallel to the axis of the strands as the strands are carried past this point. Absorption of the light by the plastic causes melting sufficient to produce bonding. The depth of penetration of the thermal energy into the plastic is controlled by selection of the wavelength of the laser radiation relative to the absorption spectrum of the thermoplastic material. The laser power level is adjusted to control the total energy input in accordance with the strand feed rate.