Spectral phase conjugation via extended phase matching
  It is shown that the copropagating three-wave-mixing parametric process, with appropriate type-II extended phase matching and pumped with a short second-harmonic pulse, can perform spectral phase conjugation and parametric amplification, which shows a threshold behavior analogous to backward wave oscillation. The process is also analyzed in the Heisenberg picture, which predicts a spontaneous parametric down conversion rate in agreement with the experimental result reported by Kuzucu et al. [Phys. Rev. Lett. 94, 083601 (2005)]. Applications in optical communications, signal processing, and quantum information processing can be envisaged. 
Mankei Tsang