Mutually coupled random lasers in complex photonic networks

Coupled optical resonators show a rich dynamical behaviour that can be exploited in different applications, e.g. chaos based communication and sensing, information processing and mimicking of neural networks [1] . Random lasers (RLs) are light sources in which optical feedback is provided by scattering elements, resulting in multi-mode emission with narrow resonances randomly distributed in frequency [2] . Our group has previously demonstrated that RLs can be implemented by placing the active medium between two scattering surfaces [3] . Here, we apply this fabrication approach to the realization of in-plane networks in which the nodes are made of disordered scattering media, acting as coupling elements between different resonators [4] . The active medium employed is a dye doped polymer film and the single RL consists of a stripe shaped pumped area, placed between two scattering elements. Each scattering element, obtained by pulsed laser ablation of the polymer film, consists of random surface defects at the polymer/air interface able to provide feedback for lasing. We first consider a network formed by two RLs which share one scattering node. In Fig. 1(a) , RL1 (RL2) consists of the pumped stripe labelled 1 (2) and the two scattering nodes A and B (B and C). Independent spectral signatures are detected at node B, when one laser at a time is turned on, see Fig. 1(b) . In Fig. 1(c) , we compare the compound cavity emission, when both lasers are turned on (RL1&RL2), with the sum of the emissions of each laser turned on, one at a time (RL1+RL2). A rearrangement of lasing peaks is observed with respect to the sum of spectral profiles that would result only from the scattering of each independent laser from node B.