  We present a simple but highly efficient source of polarization-entangled
photons based on spontaneous parametric down-conversion (SPDC) in bulk
periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405
nm laser diode. Utilizing one of the highest available nonlinear coefficients
in a non-degenerate, collinear type-0 phase-matching configuration, we generate
polarization entanglement via the crossed-crystal scheme and detect 0.64
million photon pair events/s/mW, while maintaining an overlap fidelity with the
ideal Bell state of 0.98 at a pump power of 0.025 mW.
