Fully-oxidized AlGaAs heterostructures as broadband passive waveguides for photonic circuit integration

In this paper, we demonstrate propagation losses of less than α = 1.0 cm
^-1
at both λ
₀
= 1.55 and 0.63 μm for an oxidized Al
_0.3
Ga
_0.7
As/Al
_0.85
Ga
_0.15
As waveguide. These loss reductions, and the realization of transparency well above the GaAs band edge, are achieved through both an improved structure (thicker cladding layer, larger Al composition contrast) and a modification to the standard oxidation process (via the controlled addition of O
₂
). The addition of trace amounts of oxygen reduces the oxide surface roughness, increases the index of oxidized Al
_x
Ga
_1-x
As (x < 0.5), and increases oxidation rates (0.3 < x < 0.85). These process enhancements lead to improved mode confinement and reduced absorption and scattering losses.