  Miniaturization of devices has been a primary objective in microelectronics
and photonics for decades, aiming at denser integration, enhanced
functionalities and drastic reduction of power consumption. Headway in
nanophotonics is currently linked to the progress in concepts and technologies
necessary for applications in information and communication, brain inspired
computing, medicine and sensing and quantum information. Amongst all
nanostructures, semiconductor photonic crystals (PhCs) occupy a prominent
position as they enable the fabrication of quasi ultimate optical cavities. Low
threshold laser diodes or Raman lasers , low power consuming optical memories ,
efficient single photon sources or single photon quantum gates are impressive
examples of their capabilities. We report the demonstration of about 20 micron
long PhC semiconductor optical parametric oscillator (OPO) at telecom
wavelength exploiting nearly diffraction limited optical modes. The pump power
threshold is measured below 0.2 mW. Parametric oscillation was reached through
the drastic enhancement of Kerr optical Four Wave Mixing by thermally tuning
the high Q modes of a nanocavity into a triply resonant configuration.
Miniaturization of this paradigmatic source of coherent light paves the way for
quantum optical circuits, dense integration of highly efficient nonlinear
sources of squeezed light or entangled photons pairs.
