We have efficiently generated colinearly-propagating entangled photon pairs from a nondegenerate type-I and a degenerate type-II quasi-phase matched parametric downconverter based on periodically poled lithium niobate and potassium titanyl phosphate. Entangled photons are essential in many quantum information applications such as quantum communications, implementation of quantum computation algorithms, and cryptographic key distributions. Typically UV-pumped optical parametric downconversion in

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... a thin angle-phase-matched beta barium borate (BBO) crystal produces spatially-separated, entangled photon pairs that are emitted in a cone. The use of BBO is far from optimal in terms of wavelength tunability, generation efficiency, and angular spread. In recent years the material of choice is that of engineerable microstructured nonlinear crystals via periodic poling of ferroelectric materials such as lithium niobate and potassium titanyl phosphate (KTP). Quasi-phase matching using periodically poled lithium niobate (PPLN) or periodically poled KTP (PPKTP) allows a wide range of operating wavelengths, noncritical angle phase matching, and a choice of nonlinear coefficients. A parametric downconverter based on PPLN or PPKTP can yield a significantly