Second-harmonic generation enabled by longitudinal electric-field components in photonic wire waveguides

We investigate second-harmonic generation in III-V semiconductor wire waveguides aligned with a crystal-lographic axis. In this direction, because of the single nonzero tensor element coming from the zinc-blende symmetry of III-V semiconductors, only frequency conversion by mixing with the longitudinal components of the optical fields is allowed. We experimentally study the impact of the propagation direction on the conversion efficiency and confirm the role played by the longitudinal components through the excitation of an antisymmetric second-harmonic higher-order mode