Measurement of the Diffusion Coefficient of Dopant in Fiber Using Interferometry

We report the measurement of the reflection spectrum of a Fabry-Perot interferometer during the diffusion of dopants in optical fiber caused by high-temperature heating, thus indirectly and accurately obtaining the diffusion coefficient of the dopants. The diffusion coefficient of the dopant is measured through the wavelength shift of the interferometer spectrum when diffusion of the dopant from the core to the cladding results in a decrease in the refractive index of the core. The diffusion coefficient of germanium-doped single-mode fiber before and after hydrogen loading was measured. The results show that hydrogen in the fiber significantly enhances the diffusion rate of the germanium dopant. The measured germanium-doped diffusion coefficients are in good agreement with the results of previous studies. Our proposed method of dopant diffusion coefficient measurement is simpler and more convenient. Accurate characterization of dopant diffusion coefficients in optical fibers helps to accurately understand the dopant diffusion process and is particularly important for the fabrication of various optical fiber-integrated optical devices using thermal diffusion techniques.