Abstract

The advent of low-loss semiconductor waveguides^1-4 enables us to study loss mechanisms which were previously unobservable. Earlier reports^1,2,3 of GaAs waveguides with propagation loss α < 1 dB/cm emphasized reducing losses due to material absorption and epilayer roughness; guide fabrication must be optimized to further reduce α. We recently demonstrated^4,5 single­mode, low-loss (α = 0.3dB/cm) GaAs guides with the tight confinement necessary for compact waveguide bends; such performance depends critically on rib fabrication (fig. 1), indicating important loss phenomena at rib surfaces. In this paper we explore two phenomena in low-loss GaAs waveguide structures: fabrication-related propagation loss and coherent coupling in circular bends. In both cases, scattering from rib wall roughness plays a significant role.

© 1988 Optical Society of America