Triply-resonant Continuous Wave Parametric Source with a Microwatt Pump
  We demonstrate a nanophotonic parametric light source with a record high normalized conversion efficiency of $3\times 10^6\, W^{-2}$, owing to resonantly enhanced four wave mixing in coupled high-Q photonic crystal resonators. The rate of spontaneously emitted photons reaches 14 MHz. 
Aude Martin, Gr\'egory Moille, Sylvain Combri\'e, Ga\"elle. Lehoucq,   Thierry Debuisschert, Jin Lian, Sergey Sokolov, Allar...
physics.optics