Theoretical analysis of tapering fused silica optical fibers using a carbon dioxide laser

Tapering of fused silica optical fiber using a carbon dioxide (CO2) laser as the heating source is analyzed taking into account a Gaussian profile for the laser power distribution. The differential thermal equation is solved numerically using an implicit Crank-Nicolson finite difference method. The interaction of the CO2 laser electromagnetic (EM) radiation with the optical fiber is treated using Mie theory following the approach of plane-wave light scattering from thin rods. The fiber surface temperature is studied as a function of fiber diameter and laser power. The effect of different EM polarizations (parallel and perpendicular to the fiber axis) on the fiber temperature is also investigated. The final taper diameter values predicted by the present model are compared with experimentally acquired data. The analysis shows that to achieve final taper diameters of the order of 20 mm laser powers in excess of 25 W are required.