Native-oxide-defined low-loss AlGaAs-GaAs planar waveguide bends

Abstract

Data are presented on planar waveguide S-bends fabricated from AlxGa1−xAs-GaAs p-n quantum well heterostructure (QWH) laser material by a wet native oxidation process. The oxide’s low refractive index (n∼1.55) is used to define ∼3.5-μm-wide single mode guides exhibiting low excess losses for raised-cosine S-bends with 100 μm offsets. The waveguide’s routing properties are determined by the lateral effective index profile which is controlled by the native oxide thickness. Guides with two different oxidation depths are investigated. For the deepest oxidation, excess bend losses of 3 dB are measured for transition distances of ∼180 μm and ≲120 μm for transverse electric (TE) and transverse magnetic (TM) polarizations, respectively. Theoretical loss calculations for the guides show good agreement with measured data. Guides with a shallow oxidation exhibit 3 dB transition lengths of ∼260 μm and ∼220 μm for the TE and TM polarizations.