Abstract

When used with conventional communication optical fibers, with a typical core diameter of 8µm, conventional channel waveguides geometries need to present similar thicknesses for good mode overlaps between the two. This has been a difficult goal to achieve with semiconductor waveguides due to their high index of refraction. The waveguides were typically much thinner than the fiber core and, consequently, input efficiencies were quite low. This problem was addressed some time ago with the demonstration of the antiresonant reflecting waveguide (ARROW) geometry⁽¹⁾. Although these are intrinsically leaky waveguides quite acceptable losses were feasible in silicon⁽²⁾ and GaAs⁽³⁾ geometries. On the other hand when dealing with nonlinear interactions in semiconductor waveguides, it was realised quickly that in other to maintain acceptable overall efficiencies the waveguide thickness had to be kept unreasonably small ⁽⁴⁾. This obviously led to input coupling difficulties. In our previous work, presented two years ago at this topical meeting ⁽⁵⁾, we demonstrated a new multilayer AIGaAs waveguide geometry with surface harmonic emission efficiencies well above what was possible in uniform films. This led to the development of several devices ^(6,7) such as correlators, spectrometers and intracavity diode laser second harmonic generators⁽⁸⁾. However, little attention has been given to the problem of fiber input coupling to the nonlinear waveguide. We present the first results, to our knowledge, of multi-layer core ARROW waveguides and their use in nonlinear harmonic generation. There has been little mention of the ARROW geometry in a nonlinear context, with the recent exception of inter-guide coupling⁽⁹⁾, since they tend to be thick guiding structures.

© 1992 Optical Society of America