Deep time-delay reservoir computing based on a single photonic nonlinear node

A novel, to the best of our knowledge, dual-layer deep time-delay reservoir computing (TDRC) is demonstrated based on a single semiconductor ring laser (SRL) using directional mode multiplexing. A single SRL with co-directional optical feedback inherently supports the clockwise (CW) and counter-clockwise (CCW) dynamics with weak interferences between opposite directions. Making use of this property, the CW and CCW reservoirs can be simultaneously achieved based on only one single laser using directional mode multiplexing. To form a deep configuration, the two reservoirs are connected by feeding the CW emission into the CCW direction through counter-directional optical feedback. The computing performances are first evaluated by task-independent indicators, and then further evidenced by popular benchmark tasks. Based on similar hardware resources with a single-layer configuration, the proposed dual-layer deep configuration not only expands the parameter ranges, but also enhances the computing accuracies. This work provides a novel solution to reduce the system complexity of multi-layer deep TDRCs and improve the efficiency of hardware usage.