Directionally induced quasi-phase matching in homogeneous AlGaAs waveguides

We report on the experimental observation of quasi-phase
matching in a homogeneous waveguide. By fabricating a
monolithic snake-shaped suspended AlGaAs nanowire on
a (001) GaAs wafer, we demonstrate the unraveled version
of a χ 2 whispering-gallery-mode microdisk, obtaining
second-harmonic generation in the optical telecom wavelength
range. With a radius of curvature of 50 μm and four
spatial oscillations along the (110) average direction, a splitting
of the second-harmonic spectrum occurs around the
phase-matching wavelength of the corresponding straight
waveguide. This splitting, which increases as the radius of
curvature decreases, provides a useful degree of freedom for
the design of small-footprint nonlinear photonic devices
on-chip.