2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/226659We experimentally control the spectral structure of photon pairs created via spontaneous four-wave mixing in microstructured fibers. By fabricating fibers with designed dispersion, one can manipulate the photons' wavelengths, joint spectrum, and, thus, entanglement. As an example, we produce photon-pairs with no spectral correlations, allowing direct heralding of single photons in pure-state wave packets without filtering. We achieve an experimental purity of $85.9\pm1.6%$, while theoretical analysis and preliminary tests suggest 94.5% purity is possible with a much longer fiber.Quantum Physicstext