Optical fiber telecommunication systems transmit high-bandwidth optical signals over planetary distances using total internal reflection (TIR). Because the cylindrical silica core possesses a higher refractive index (n₁) than the surrounding outer cladding glass (n₂ < n₁), light rays launched into the core within the numerical aperture acceptance cone strike the core-cladding boundary at angles exceeding the critical angle θ_c = arcsin(n₂/n₁), undergoing lossless 100% internal reflection.