A cascaded interferometer-microresonator structure for photonic reservoir computing.

Complex dynamics of silicon microring resonators fed by delay elements enable high-speed photonic reservoir computing. Implementing delay elements on a photonic chip can be challenging when the required delay should match the time scales of nonlinear effects in silicon. To increase the computation speed and preclude any need for very long delay lines and silicon's nonlinear effects, we opt for a delay-based photonic reservoir where the nonlinear functionality is provided merely by either of amplitude or phase modulations along with photodetection. Our simulations show that by supplementing its memory with digital memory in the electronic output layer, the time-delay photonic reservoir composed of a Mach-Zehnder interferometer and a microring resonator can perform computations almost one order of magnitude faster than those based on silicon's nonlinearity with its speed only limited by the modulation/detection bandwidth. We also show that such a time-delay reservoir can perform accurately in NARMA-10, Mackey-Glass, and Santa-Fe prediction tasks (normalized mean-squared error, NMSE in the range 0.002-0.05), and enables signal equalization in optical communication systems.