Square-wave oscillations with different duty cycles

A fundamental property of nonlinear dynamical systems controlled by a delayed feedback is their tendency to exhibit 2τ -periodic square-wave oscillations of equal plateau lengths (τ is the delay) [1]. The question was recently raised whether an optical system could exhibit stable square-wave oscillations with different plateau lengths [2]. We have experimentally found these regimes using a single optoelectronic oscillator (OEO) with a bandpass feedback [3]. See Fig. 1. The period is close to τ (and not 2τ). The response of the OEO is accurately described by the following delay differential equations (time s = t/τ ) [4]