Collinear source of polarization-entangled photon pairs at nondegenerate wavelengths

We report on a simple but highly efficient source of polarization-entangled photon pairs at nondegenerate wavelengths. The fully collinear configuration of the source enables very high coupling efficiency into a single optical mode and allows the use of long nonlinear crystals. With optimized dispersion compensation, it is possible to use a free-running laser diode as pump source and to reach an entanglement fidelity of 99.4% at rates as high as 27 000 pairs/s/mW of pump power. (C) 2008 American Institute of Physics.