Collinear source of polarization-entangled photon pairs at non-degenerate wavelengths

We report on a simple but highly efficient source of polarization-entangled photon pairs at non-degenerate 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 27000 pairs/s per mW of pump power. This greatly enhances the practicality of the source for applications in quantum communication and metrology.