Temperature Dynamics in Silicon Core Fibers during CO2-Laser Processing

Silicon core fibers offer unique possibilities for THz transmission, mid-IR sensing, Raman amplifiers and nonlinear optical devices [1] . Since as-drawn silicon core fibers typically have optical transmission losses in excess of 10dBcm −1 suitable post-processing is required. One method is to anneal the fiber, using CO 2 -laser heating, above the melting point of the silicon core. Under suitable cooling conditions, the core recrystallizes into a single crystal with a subsequent decrease in optical losses. Here, the temperature gradient across the solidification interface is critical to the growth rate and final quality of the crystal [2] . Thermal dynamics during laser scanning has previously been estimated by monitoring the black-body radiation from the silicon core [3] . Here, we present a simple in-situ technique to monitor the temperature dynamics of the fiber during laser scanning and the recrystallization process.