Abstract: Utilizing the process of spontaneous parametric down-conversion in a novel crystal geometry, a source of polarization-entangled photon pairs has been provided that is more than ten times brighter, per unit of pump power, than previous sources, with another factor of 30 to 75 expected to be readily achievable. A high level of entanglement between photons emitted over a relatively large collection angle, and over a 10-nm bandwidth, is a characteristic of the invention. As a demonstration of the source capabilities, a 242-&sgr; violation of Bell's inequalities was attained in fewer than three minutes, and near-perfect photon correlations were achieved when the collection efficiency was reduced. In addition, both the degree of entanglement, and the purity of the state are readily tunable. The polarization entangled photon source can be utilized as a light source for the practice of quantum cryptography.