Modeling of the Creation of an Internal Cladding in Sapphire Optical Fiber Using the⁶ Li(n,α)³H Reaction

The focus of this study is to model the creation of an internal waveguide in sapphire optical fiber. The model investigates ion implantation using the ⁶Li(n,α)³H reaction as a method for creating an internal waveguide in sapphire optical fiber. The method involves irradiating a sapphire fiber that is surrounded by an annulus of Li-6 enriched lithium carbonate (Li₂CO₃) powder, in a nuclear reactor. The ⁶Li(n,α)³H reaction creates high-energy tritons and alpha particles that irradiate the fiber simultaneously to a depth of 24 μm, along the entire periphery of the sapphire fiber. The triton and alpha particle irradiation slightly reduces the index of refraction in the fiber's periphery, thus creating a refractive cladding within the fiber. Refractive index profiles are predicted by tracking tritons and alpha particles, using the Monte-Carlo radiation transport code MCNP. Measured transmitted light intensity profiles are compared with predicted light intensity profiles, by modeling the transport of 1550 nm light through modified sapphire fiber using FIMMWAVE software.