Infrared Single-Photon Detector based on Silicon Two-Photon Absorption
  We propose a scheme for infrared single-photon detection based on two-photon absorption at room-temperature in Si avalanche photodiodes, where the detected photon's energy is lower than the bandgap and the energy difference is complemented by a pump field. A quantum non-perturbative model is developed for non-degenerate two-photon absorption in direct and indirect semiconductors yielding proper non-divergent rates allowing device efficiency optimization. The proposed monolithic detector is simple, miniature, integrable and does not require phase matching, while not compromising the performance and exhibiting even better efficiency than the competing up-conversion schemes (~1 order of magnitude) for similar optical pump levels. 
Alex Hayat, Pavel Ginzburg and Meir Orenstein