Excitable multivibrators: Switching dynamics between astable and monostable modes via opto-electronic threshold modulation

Excitation phenomena in nonlinear circuits are realized using light-sensitive multivibrators that alternate between quiescent and oscillatory modes under external illumination. Circuit dynamics are governed by the continuous-time evolution of an analog internal state (capacitor voltage). Simultaneously, the output switches discretely between high and low levels, forming a hybrid system with mixed continuous-discrete behavior. Crucially, the switching threshold is not fixed but modulated by both the output state and the incident light, enabling tunable excitability. A class of such circuits was designed and theoretically analyzed, and their spike-like transient responses were quantitatively verified experimentally. The proposed configuration offers a compact platform for realizing spatially extended excitable media with discrete outputs that continuously evolve.