  Optical quantum information processing needs ultra-bright sources of
entangled photons, especially from synchronizable femtosecond lasers and
low-cost cw-diode lasers. Decoherence due to timing information and spatial
mode-dependent phase has traditionally limited the brightness of such sources.
We report on a variety of methods to optimize type-I polarization-entangled
sources - the combined use of different compensation techniques to engineer
high-fidelity pulsed and cw-diode laser-pumped sources, as well as the first
production of polarization-entanglement directly from the highly nonlinear
biaxial crystal BiB3O6 (BiBO). Using spatial compensation, we show more than a
400-fold improvement in the phase flatness, which otherwise limits efficient
collection of entangled photons from BiBO, and report the highest fidelity to
date (99%) of any ultrafast polarization-entanglement source. Our numerical
code, available on our website, can design optimal compensation crystals and
simulate entanglement from a variety of type-I phasematched nonlinear crystals.

Quantum Physics