Carlos Ríos

On‐Chip Photonic Memory Elements Employing Phase‐Change Materials

Phase-change materials integrated into nanophotonic circuits provide a flexible way to realize tunable optical components. Relying on the enormous refractive-index contrast between the amorphous and crystalline states, such materials are promising candidates for on-chip photonic memories. Nonvolatile memory operation employing arrays of microring resonators is demonstrated as a route toward all-photonic chipscale information processing.

On-chip photonic synapse

An on-chip photonic device mimics the function of synaptic connections between neurons. The search for new “neuromorphic computing” architectures that mimic the brain’s approach to simultaneous processing and storage of information is intense. Because, in real brains, neuronal synapses outnumber neurons by many orders of magnitude, the realization of hardware devices mimicking the functionality of a synapse is a first and essential step in such a search. We report the development of such a hardware synapse, implemented entirely in the optical domain via a photonic integrated-circuit approach. Using purely optical means brings the benefits of ultrafast operation speed, virtually unlimited bandwidth, and no electrical interconnect power losses. Our synapse uses phase-change materials combined with integrated silicon nitride waveguides. Crucially, we can randomly set the synaptic weight simply by varying the number of optical pulses sent down the waveguide, delivering an incredibly simple yet powerful approach that heralds systems with a continuously variable synaptic plasticity resembling the true analog nature of biological synapses.

All-optical signal processing using phase-change nanophotonics

Photonic data storage would dramatically improve performance in existing computing architectures by avoiding time and energy consuming electro-optical conversion. To date, photonic memories have been predominantly volatile and lose their content if the input power is switched off. We exploit hybrid photonic-phase-change materials for realizing non-volatile, all-photonic memories and computing structures. By using optical near-field coupling we realize bit storage of up to ten levels in a single device that readily switches between intermediate states. We show that individual phase-change elements can be addressed through two-pulse encoding in waveguide arrays. Such multi-level, multi-bit devices provide a pathway towards eliminating the von Neumann bottleneck and point towards a new paradigm in all-photonic memory and non-conventional computing.

On-chip phase-change photonic memory and computing

The use of photonics in computing is a hot topic of interest, driven by the need for ever-increasing speed along with reduced power consumption. In existing computing architectures, photonic data storage would dramatically improve the performance by reducing latencies associated with electrical memories. At the same time, the rise of ‘big data’ and ‘deep learning’ is driving the quest for non-von Neumann and brain-inspired computing paradigms. To succeed in both aspects, we have demonstrated non-volatile multi-level photonic memory avoiding the von Neumann bottleneck in the existing computing paradigm and a photonic synapse resembling the biological synapses for brain-inspired computing using phase-change materials (Ge2Sb2Te5).