Spatiotemporal complexity of chaos in a phase-conjugate feedback laser system

Abstract

An 852 nm semiconductor laser is experimentally subjected to phase-conjugate time-delayed feedback achieved through four-wave mixing in a photorefractive (BaTiO 3 ) crystal. Permutation entropy (PE) is used to uncover distinctive temporal signatures corresponding to the sub-harmonics of the round-trip time and the relaxation oscillations. Complex spatiotemporal outputs with high PE mostly upwards of ∼0.85 and chaos bandwidth (BW) up to ∼31 GHz are observed over feedback strengths up to 7%. Low feedback region counterintuitively exhibits spatiotemporal reorganization and the variation in the chaos BW is restricted within a small range of 1.66 GHz; marking the transition between the dynamics driven by the relaxation oscillations and the external cavity round-trip time. The immunity of the chaos BW and the complexity against such spatiotemporal reorganization shows promise as an excellent candidate for secure communication application.

Optimized properties of chaos from a laser diode

“…The latter is characterised by the self-pulsating dynamics regularly oscillating close to a multiple of the frequency of the external cavity [7,8]. Previously, we have also experimentally demonstrated that the PCF-generated chaos significantly enhances the chaos bandwidth when compared to the case of conventional optical feedback (COF) [9] and can exhibit highly spatiotemporally-complex outputs [10].…”

“…1 and is similar to the one in Refs. [7,10,19]. We use a commercial Fabry-Pérot laser diode emitting at 852 nm, model JDS-Uniphase SDL-5420.…”

“…Last, the permutation entropy quantifies the entropy and measures the predictability at operating condition under consideration [18]. Previous studies on the PCF systems were limited to the evolution of chaos bandwidth [9,19] or the permutation entropy [10] versus the feedback strength.…”

Robust Synchronization of Class Chaotic Systems Using Novel Time‐Varying Gain Disturbance Observer‐Based Sliding Mode Control

“…where the sliding mode surface s i is defined in (7). ε i , σ i , and c i are the positive constants.…”

“…In the past decades, with the development of theoretical analysis methods of chaos, many chaos systems such as the Lorenz system [1], Rossler system [2], and Chen system [3] have been wildly studied. ese theoretical advancements of chaotic systems have been influentially applicated in many fields, such as power electrical systems [4,5], robotics [6], lasers [7], and secure communications [8]. Among these applications, to achieve the desired chaotic characteristic, the high-precision synchronization problem is the key problem that must be solved.…”