  Semiconductor nanowires (NWs) are promising for realizing various on-chip
nonlinear optical devices, due to their nanoscale lateral confinement and
strong light-matter interaction. However, high-intensity pulsed pump lasers are
typically needed to exploit their optical nonlinearity because light couples
poorly with nanometric-size wires. Here, we demonstrate microwatts
continuous-wave light pumped second harmonic generation (SHG) in AlGaAs NWs by
integrating them with silicon planar photonic crystal cavities. Light-NW
coupling is enhanced effectively by the extremely localized cavity mode at the
subwavelength scale. Strong SHG is obtained even with a continuous-wave laser
excitation with a pump power down to ~3 uW, and the cavity-enhancement factor
is estimated around 150. Additionally, in the integrated device, the NW's SHG
is more than two-order of magnitude stronger than third harmonic generations in
the silicon slab, though the NW only couple s with less than 1% of the cavity
mode. This significantly reduced power-requirement of NW's nonlinear frequency
conversion would promote NW-based building blocks for nonlinear optics,
specially in chip-integrated coherent light sources, entangled photon-pairs and
signal processing devices.
