Challenges in fabricating laser fibers with reduced thermo-optic coefficients

Power scaling of fiber lasers and amplifiers is currently limited by nonlinear optical effects, such as transverse mode instability (TMI) and stimulated Brillouin scattering (SBS). Addressing optical nonlinearities through a material approach allows for such challenges to be confronted at their source - the interaction of the light and the material without the need for complex fiber designs. However, effectively mitigating these issues through materials engineering will require much higher dopant concentrations than are now typical for the chemical-vapor-deposition (CVD)-derived silicate glasses from which modern commercial laser fibers are made. As dopant concentrations are increased, new fabrication challenges arise, such as draw- induced, refractive-index changes not related to frozen-in stresses. This paper presents an initial report of these new challenges and offers suggestions to their cause.