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R&D: Fast and Reliable Storage Using 5bit Nonvolatile Photonic Memory Cell

Work represents step in development of photonic memories and potential for novel integrated photonic applications.

Optica (OSA) has published an article written by Xuan Li, Nathan Youngblood, Department of Materials, University of Oxford, Oxford, UK, Carlos Ríos, Department of Materials, University of Oxford, Oxford, UK, and Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA, Zengguang Cheng, Department of Materials, University of Oxford, Oxford, UK, C. David Wright, Department of Engineering, University of Exeter, Exeter, UK, Wolfram HP Pernice, Department of Physics, University of Münster, Münster, Germany, and Harish Bhaskaran, Department of Materials, University of Oxford, Oxford, UK.

Fig. 1. Concept of the dual-pulse programming technique. (a) From left to right, optical image of our device with a GST photonic memory cell, magnified image of GST on top of the waveguide, and schematic cross section of the completed device. (b) Schematic of the optical pulse shapes used to amorphize and crystallize the integrated phase-change photonic memory cell. A rectangular programming pulse with increasing peak powers (red pillars) amorphizes an increasing fraction of GST while a fixed ERASE pulse returns the material back to a fully crystalline state. Simulated transmission and crystalline fraction as a function of the programming pulse energy. The optical transmission through the waveguide (and the corresponding absorption in the GST) increases (decreases) as the crystalline fraction decreases. (d) Simulated temperature distribution in the GST memory cell after a 20ns programming pulse. Area surpassing the melting temperature of GST (890K [31]) is marked by the dark red region and is inversely related to the crystalline fraction plotted in (c).

OSA 5bit, nonvolatile photonic memory cell

Abstract: Optically storing and addressing data on photonic chips is of particular interest as such capability would eliminate optoelectronic conversion losses in data centers. It would also enable on-chip non-von Neumann photonic computing by allowing multinary data storage with high fidelity. Here, we demonstrate such an optically addressed, multilevel memory capable of storing up to 34 nonvolatile reliable and repeatable levels (over 5 bits) using the phase change material Ge2Sb2Te5 integrated on a photonic waveguide. Crucially, we demonstrate for the first time, to the best of our knowledge, a technique that allows us to program the device with a single pulse regardless of the previous state of the material, providing an order of magnitude improvement over previous demonstrations in terms of both time and energy consumption. We also investigate the influence of write-and-erase pulse parameters on the single-pulse recrystallization, amorphization, and readout error in our multilevel memory, thus tailoring pulse properties for optimum performance. Our work represents a significant step in the development of photonic memories and their potential for novel integrated photonic applications.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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