The emergence, bifurcations, and dynamics of line-defects in a period-2 oscillatory medium

The instability of a period-1 spiral wave resulting a period-2 spiral wave with a line-defect is investigated for the first time in a laboratory system. At the very onset the transition proceeds by an emergence of spiraling line-defect, ``breathing'' intermittently but retaining the symmetry of a period-1 spiral wave. With a further change in a control parameter, the line-defect undergoes a meandering transition producing a compound tip trajectory, following a dynamic shape transition. The observed phenomena have strong analogy to the phase synchronization transition of a system of two coupled nonlinear oscillators and the meandering transition of a period-1 spiral wave. In the regime far away from the primary period-doubling bifurcation, line-defects can also arise in a form of a simply connected loop ("bubble") independent of spiral core. The dynamic processes of bubble formation and decay will be discussed as well.