Tuning the period of square-wave oscillations for delay-coupled optoelectronic systems

We analyze the response of two delay-coupled optoelectronic oscillators.
Each oscillator operates under its own delayed feedback. We show that the
system can display square-wave periodic solutions which can be synchronized
in-phase or out-of-phase depending on the ratio between self- and cross-
delay times. Furthermore, we show that multiple periodic synchronized
solutions can coexist for the same values of the fixed parameters. As a
consequence, it is possible to generate square-wave oscillations with
different periods by just changing the initial conditions.