Insertion loss reduction between single-mode fibers and diffused channel waveguides.

Methods of reducing the insertion loss between single-mode fibers and graded-index channel waveguides, namely, annealing and backdiffusion, are analyzed theoretically and compared. Mode mismatch and misalignment losses are calculated to determine the best method and the optimal conditions for their use. The main result of this paper is that, in the single-mode regime, there is no apparent advantage in using backdiffusion instead of the simpler annealing process, in contrast with the multimode case. In the coupling loss calculation, a numerical simulation of waveguide formation by potassium-sodium ion exchange in glass is used for illustration.