Rios, Stegmaier et al., Integratable all-photonic nonvolatile multi-level memory Integratable all-photonic nonvolatile multi-level memoryWe show that individual memory elements can be addressed using a wavelength multiplexing scheme. Our multi-level, multi-bit devices provide a pathway towards eliminating the von-Neumann bottleneck and portend a new paradigm in all-photonic memory and non-conventional computing.* These authors contributed equally.-2-The advent of photonic technologies, in particular in the area of optical signaling, coupled with advances made in nanofabrication capabilities has created a growing need for practical allphotonic memories 3,[7][8][9][10] . Such memories are essential to supercharge computational performance in serial computers by speeding up the von-Neumann bottleneck, i.e. the information traffic jam between the processor and the memory. This bottleneck limits the speed of almost all processors today; it has already led to the introduction of multicore processor architectures and drives the search for viable on-chip optical interconnects. However, shuttling information optically from the processor to electronic memories is presently not efficient because electrical signals have to be converted to optical ones and vice-versa. Instead, information transfer and storage exclusively by optical means is highly desirable because of the inherently large bandwidth 1,3 , low residual cross-talk and high speed of optical information transfer. On a chip this has been challenging to achieve because practical photonic memories would need to retain information for long periods of time and require full-integration with the ancillary electronic circuitry, thus requiring compatibility with semiconductor processing 11.Ideal candidates for all-optical memories are phase-change materials (PCMs), already the subject of intense research and development over the last decade, but in the context of electronic memories [12][13][14] . A striking and functional feature of these materials is the high contrast between the crystalline and amorphous phase of both their electrical and optical properties 15,16 . In particular, chalcogenide-based PCMs have the ability to switch between these two states in response to appropriate heat stimuli (crystallization) or melt-quenching processes down to nanoscale cell sizes, which enables dense packaging and low-power memory switching. In our devices, data is stored in a nanoscale GST cell placed directly on top of a nanophotonic waveguide. Both writing into the memory cell and read-out of the stored information is carried out via evanescent coupling to the phase-change material and is thus not subject to the diffraction limit; because this is done directly within the waveguide using nanosecond optical pulses, our approach provides a promising route towards fast all-optical data storage in photonic circuits.The geometry of our memory cell and the operating principle is shown schematically in Fig. 1a. We store information in the GST (yellow region) by employing evanescent coup...
Machines that simultaneously process and store multistate data at one and the same location can provide a new class of fast, powerful and efficient general-purpose computers. We demonstrate the central element of an all-optical calculator, a photonic abacus, which provides multistate compute-and-store operation by integrating functional phase-change materials with nanophotonic chips. With picosecond optical pulses we perform the fundamental arithmetic operations of addition, subtraction, multiplication, and division, including a carryover into multiple cells. This basic processing unit is embedded into a scalable phase-change photonic network and addressed optically through a two-pulse random access scheme. Our framework provides first steps towards light-based non-von Neumann arithmetic.
Integrated chip‐level photonics has the potential to revolutionize future computer systems by eliminating the “von‐Neumann information bottleneck” and the power losses resulting from the use of electrical interconnects. Yet, the need for optical‐to‐electrical conversion has so far hindered the implementation of chip‐level all‐optical routing schemes, which remain operational without continuous power consumption. Here, a crucial component to successful implementation of such all‐photonic networks is demonstrated – an effective, practicable all‐optical nonvolatile switch. Current integrated all‐optical switches require constant bias power to operate, and lose their state when it is removed. By contrast, our switch is entirely nonvolatile, with the direction of light flow altered by switching the phase state of an embedded phase‐change cell using 1 ps optical pulses. High on/off switching contrast devices are achieved that are fully integrated and compatible with existing photonic circuits. It is shown that individual switching events occur with transition times below 200 ps and thus hold promise for ultrafast light routing on chip. The approach offers a reliable and simple route toward hybrid reconfigurable photonic devices without the need for electrical contacting.
Phase change materials (PCMs) are highly attractive for nonvolatile electrical and all-optical memory applications because of unique features such as ultrafast and reversible phase transitions, long-term endurance, and high scalability to nanoscale dimensions. Understanding their transient characteristics upon phase transition in both the electrical and the optical domains is essential for using PCMs in future multifunctional optoelectronic circuits. Here, we use a PCM nanowire embedded into a nanophotonic circuit to study switching dynamics in mixed-mode operation. Evanescent coupling between light traveling along waveguides and a phase-change nanowire enables reversible phase transition between amorphous and crystalline states. We perform time-resolved measurements of the transient change in both the optical transmission and resistance of the nanowire and show reversible switching operations in both the optical and the electrical domains. Our results pave the way toward on-chip multifunctional optoelectronic integrated devices, waveguide integrated memories, and hybrid processing applications.
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