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Title:Determination of the Thermo-Optic Coefficient of Germanium-Doped Fibers
Author(s):Fabbro Barroso, Riccardo Enrique
Contributor(s):Dragic, Peter
Subject(s):Brillouin scattering
modal index
thermo-optic coefficient
germanium-doped fibers
Abstract:Light transmission through optical fiber depends on the fiber's refractive index profile, which in standard single mode transmission fibers is typically a simple step index given by the core and cladding. If the refractive index of the fiber undergoes a change due to pressure variations in the glass while light is being transmitted through it, an effect known as Brillouin scattering occurs. Brillouin scattering is a strong parasitic effect that limits the power that can be transmitted in coherent systems. The thermo-optic effect has a strong impact on Brillouin scattering and thus by analyzing this effect it is possible to obtain the thermo-optic coefficient of a fiber's glass core. The thermo-optic coefficient is an important characteristic of optical glasses because it relates the change in a material's refractive index to the temperature that the material experiences. Germanium-doped fibers were chosen due to the element's range of very useful characteristics for light transmission. The measurement procedure is as follows. A length of germanium-doped fiber is incorporated into a ring fiber laser system with known characteristic and is then submerged in a crucible of water and exposed to temperatures ranging from room temperature to slightly below boiling. The change in laser free spectral range of a particular harmonic is measured every 5 degrees Fahrenheit, enabling the determination of the derivative of free spectral range versus temperature, which in turn enables the determination of several other characteristics of the fiber, namely its thermo-optical coefficient.
Issue Date:2015-12
Date Available in IDEALS:2016-02-22

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