  The AlGaAs material platform has been intensively used to develop nonlinear
photonic devices on-a-chip, thanks to its superior nonlinear optical
properties. We propose a new AlGaAs waveguide geometry, called half-core
etched, which represents a compromise between two previously studied
geometries, namely the nanowire and strip-loaded waveguides, combining their
best qualities. We performed tunable four-wave mixing (FWM) experiments in all
three of these geometries in the telecommunications C-band (wavelengths around
1550 nm), with a pulsed pump beam and a continuous-wave (CW) signal beam. The
maximum FWM peak efficiencies achieved in the nanowire, strip-loaded and
half-core geometries were about -5 dB, -8 dB and -9 dB, respectively. These
values are among the highest reported in AlGaAs waveguides. The signal-to-idler
conversion ranges were also remarkable: 161 nm for the strip-loaded and
half-core waveguides and 152 nm for the nanowire. Based on our findings, we
conclude that the half-core geometry is an alternative approach to the nanowire
geometry, which has been earlier deemed the most efficient geometry, to perform
wavelength conversion in the spectral region above the half-bandgap. Moreover,
we show that the half-core geometry exhibits fewer issues associated with
multiphoton absorption than the nanowire geometry.
