Propagation properties of tapered graded-index waveguides

摘要

Propagation of light in multimode parabolic-index linear tapers is studied using a geometrical optics approach. Considering a two-dimensional model, ray trajectories are derived analytically for tapers with small angles. Both bound and leaky rays are examined. It is shown that ray trajectories are described by modulated sinusoidal functions with decreasing amplitude and period as light propagates in the direction of decreasing thickness of the taper core, thus gradual concentration of power from the larger area to the smaller one. Radiation loss of tapers when used to connect two multimode optical waveguides with different core areas, and coupling efficiencies when they are used to couple power from collimated-beam and Lambertian light sources to waveguides are determined. Numerical results for ray trajectories illustrating the gradual concentration of light power, radiation loss, coupling efficiency, and improvement in coupling efficiency for collimated-beam illumination and Lambertian sources are presented for an example case.