Proceedings Article | 9 June 2014
KEYWORDS: Glasses, Refractive index, Silica, Fiber lasers, Scattering, Thermal optics, Raman scattering, Optical fibers, Photoelasticity, Acoustics
Fiber lasers are susceptible to a number of nonlinear and parasitic effects that can significantly inhibit performance. From a system perspective, requirements of a fiber laser may cover average or peak power, amplitude stability, and spectral content of the source. Nonlinear and parasitic phenomena, including Brillouin scattering, Raman scattering, mode stability, self-phase modulation, four-wave mixing in multi-wavelength lasers, etc. can each influence one or all of these performance characteristics. Conventionally, these system-limiting undesirables have been addressed with complex waveguide designs. However, each of these light-medium interactions can be described by material coefficients that lead to estimates of ‘threshold’ values where these phenomena become significant. For example, this may be the Brillouin gain coefficient for Brillouin scattering, the nonlinear refractive index, n2, for self-phase modulation, or the thermo-optic coefficient, dn/dT, for mode stability. Furthermore, these coefficients tend to be strong functions of the material, and surprisingly wide ranges of values exist between known material systems. For example, both the Pockels’ photoelastic constant, p12, and thermo-optic coefficient may be either positive or negative for a material. It follows logically that mixtures of materials with coefficients of opposing signs would then give rise to compositions where these coefficients may be zero. Example of such effect negation may include the barium aluminosilicate system for p12 and the phosphosilicate or titanosilicate system for dn/dT. Compositional tailoring of the optical fiber is therefore suggested as an alternative means to suppressing these parasitics, and methods to do so will be discussed at the conference.
