Combining a passive spatial photonic reservoir computer with a semiconductor laser increases its nonlinear computational capacity

Photonic reservoir computing has been used to efficiently solve difficult and time-consuming problems. The physical implementations of such reservoirs offer low power consumption and fast processing speed due to their photonic nature. In this paper, we investigate the computational capacity of a passive spatially distributed reservoir computing system. It consists of a network of waveguides connected via optical splitters and combiners. A limitation of its reservoir is that it is fully linear and that the nonlinearity - which is often required for solving computing tasks - is only introduced in the output layer. To address this issue, we investigate the incorporation of an additional active nonlinear component into the system. Our approach involves the integration of a single semiconductor laser in an external optical delay line within the architecture. Based on numerical simulations, we show that the architecture with this semiconductor laser has a nonlinear computational capacity that is significantly increased as compared to the original passive architecture, which can be beneficial to solving difficult computational tasks.