Development of a continuously operating pulsed detonation engine (PDE) without a high energy ignition system or a deflagration-to- detonation transition (DDT) device will increase engine efficiency, reduce cost, improve performance, and reduce weight. This report is a study of configurations that allow a consistent and predictable transition of a detonation from one detonation tube to second tube. The intent was, via visualization of detonation propagation through a cross-over tube, to develop a cross-over passage leading to minimization of energy losses and effective and repeatable tube-to-tube initiation. Detonation tube cross-over width, cross-over geometry and fuels were varied to determine their effect on tube-to-tube detonation initiation. The cross-over detonations studied decoupled into and out of the cross-over tube due to propagation as subcritical spherical detonations. It was shown that the mechanism of shock reflection could be used to transition the spherical detonation back to a planar detonation.