  Broadband correlated photon pairs (biphotons) are valuable in quantum
metrology, but current generation methods either involve complex nonlinear
structures or lack sufficient bandwidth and brightness. In this work, we
theoretically describe and experimentally demonstrate a novel technique for
generation of a bright collinear biphoton field with a broad spectrum, achieved
by using a tightly focused pump in a bulk nonlinear crystal. As the most
straightforward application of the source, we employ Michelson
interferometer-based quantum optical coherence tomography (QOCT). Utilizing the
source enables the demonstration of record resolution and dispersion
cancellation for this QOCT scheme.
