Emanuele Gemo and Joaquin Faneca present at Photonic West conference

Fourth year students Emanuele Gemo and Joaquin Faneca recently attended Photonic West, the biggest conference in the world of photonics, which was held in San Francisco, Moscone centre. In this conference, Emanuele was presenting his work based on “Sub-wavelength plasmonic enhance phase change memory”. Joaquin Faneca was giving an oral presentation relating to his work on “Reconfigurable integrated circuits based on functional materials” and a poster called “On-chip sub-wavelength Bragg grating design based on GSST”.

Emanuele Gemo presenting
Joaquin Faneca presenting

Emanuele Gemo presenting his recent research at EPCOS

PGR Emanuele Gemo

Fourth year PGR Emanuele Gemo discusses his experience of presenting at this year’s E\PCOS conference.

The E\PCOS (European symposium on Phase-Change and Ovonic Science) started in 2001 as a workshop on the emerging field of phase-change material science and applications. Since then, it has been hold each year in various locations in Europe, and evolved in a conference style collecting contributions from both academic and industry research.

This year I presented my latest research work: the proposal of a novel all-photonic memory architecture, which by use of a bespoke plasmonic nanoantenna is capable to reduce both speed and energy requirements by 1 to 2 orders of magnitude with respect to the conventional configuration:

“A plasmonic route towards the energy scaling of on-chip integrated all-photonic phase-change memories

Emanuele Gemo¹, Santiago García-Cuevas Carrillo¹, Carlota Ruiz De Galarreta¹, Joaquin Faneca¹, Nathan Youngblood², Wolfram H.P. Pernice³, Harish Bhaskaran², C. David Wright¹

1-Department of Engineering, University of Exeter, North Road, Exeter EX4 4QF, UK
2-Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK
3-Institute of Physics, University of Muenster, Heisenbergstrasse 11, 48149 Muenster, Germany

ABSTRACT

Phase-change photonic memory devices, conventionally implemented as a thin layer of phase-change material deposited on the top of an integrated Si or SiN waveguide, have the flexibility to be applied in a widely diverse context, as a pure memory device, a logic gate, an arithmetic processing unit and for biologically inspired computing. In all such applications increasing the speed, and reducing the power consumption, of the phase-switching process is most desirable. In this work, therefore, we investigate, via simulation, a novel integrated photonic device architecture that exploits plasmonic effects to enhance the light-matter interaction. Our device comprises a dimer nanoantenna fabricated on top of a SiN waveguide and with a phase-change material deposited into the gap between the two nanoantenna halves. We observed very considerably increased device speeds and reduced energy requirements, of up to two orders of magnitude, when compared to the conventional structure.”

The conference has been extremely interesting, as it spanned within various field: material science, optical and photonics applications, electronic devices and new applications such as neuromorphic computing. The time spent there has been undeniably valuable, and many presentations provided with lots of new ideas to be explored.
I also had the chance to meet in person with different academics and industry researchers. Among these, I have opened a channel of communication with a representative from Advanced Materials, with the view to further develop a modelling framework I contributed to build in the past.

PGR Emanuele Gemo at ePIXfab Silicon Photonics Summer School

From 1st-5th July 2019, third year PGR Emanuele Gemo attended ePIXfab’s silicon photonics summer school at Scuola Superiore Sant’Anna in Pisa, Italy.

PGR Emanuele Gemo

Emanuele gives an insight into his experience:

The experience in Pisa has been definitely valuable.

From the organization perspective, nothing has been left unplanned or uncared for. The venue was the main hall of the University of S.Anna, Pisa, built on the pre-existing 15th-century monastery, which does not add scientific value but is indeed pleasant. The buffet lunches, the organized visit to the historical city center, and the gala dinner have been spotless, laying the foundation for an efficient network building with researchers and academics from all Europe and beyond.

From the content perspective, the initial focus was on the provision of a needed background on the fundamentals of silicon photonics, to allow the audience to make the most out of the information-packed following lectures. These spanned through a wide range of fields, such as fabrication techniques, plasmonics, non-linear phenomena, conventional and quantum device and applications, with the course program being tailored to follow a natural and logical sequence (i.e. from light sources to passive devices, then to active devices, detectors, integration, and eventually innovative approaches). The visit to the CNIT labs has also been extremely interesting and provided a deeper insight into the hands-on research carried out in Pisa.

Most of the courses were very well delivered. I would have preferred a tighter focus on the fundamentals, but I also acknowledge how the panoramics onto the many fields has been of great value, providing a wider and yet precise picture of the concepts of silicon photonics research and applications.

Integrated phase-change photonics for memory and computing devices

PGR Emanuele Gemo

This video, narrated by our third year PGR Emanuele Gemo, gives a short description of the integrated phase-change photonic memory, a device allowing to store and retrieve non-volatile information on optical chips.

Emanuele’s research project is focused on the theoretical study of this class of devices, and on the proposal of solutions to improve its energy, speed and memory density performances. This device architecture has the potential to be exploited not only for memory applications, but also for in-memory computing: this aim is pursued by the EU2020 funded Fun-COMP research project, led by Prof. C.David Wright, which is a collaboration between seven academic and industrial partners focused to create a light signal based – biologically inspired neuromorphic platform, of which the phase-change photonic memory is an integral part.

The video has been created for the Fun-COMP website, to explain to an extended audience this key building block, with simple terms and yet drawing upon all the essential elements.

Emanuele co-authored “Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics”, a paper which was recently published in prestigious journal Advanced Functional Materials

New Publication: Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics

Congratulations to third year CDT PGR Emanuele Gemo , co-author of a paper, Tunable Volatility of Ge2Sb2Te5 in Integrated Photonics, which was recently published in the prestigious journal Advanced Functional Materials. His co-authors include his supervisors Dr Anna Baldycheva and Prof C David Wright.

This work was led by researchers from the labs of Prof Harish Bhaskaran at Oxford University and Prof Dr Wolfram Pernice at Muenster University. It was carried under the auspices of the EU H2020 project Fun-COMP .

Abstract

The operation of a single class of optical materials in both a volatile and nonvolatile manner is becoming increasingly important in many applications. This is particularly true in the newly emerging field of photonic neuromorphic computing, where it is desirable to have both volatile (short‐term transient) and nonvolatile (long‐term static) memory operation, for instance, to mimic the behavior of biological neurons and synapses. The search for such materials thus far have focused on phase change materials where typically two different types are required for the two different operational regimes.

In this paper, a tunable volatile/nonvolatile response is demonstrated in a photonic phase‐change memory cell based on the commonly employed nonvolatile material Ge2Sb2Te5 (GST). A time‐dependent, multiphysics simulation framework is developed to corroborate the experimental results, allowing us to spatially resolve the recrystallization dynamics within the memory cell. It is then demonstrated that this unique approach to photonic memory enables both data storage with tunable volatility and detection of coincident events between two pulse trains on an integrated chip. Finally, improved efficiency and all‐optical routing with controlled volatility are demonstrated in a ring resonator. These crucial results show that volatility is intrinsically tunable in  normally nonvolatile GST which can be used in both regimes interchangeably.

 

Figure 1
Phase‐change photonic device. a) Illustration of device and measurement scheme. Optical WRITE pulses are used to switch the GST to a partial amorphous state while a counter propagating, variable‐power optical probe is used to control the recrystallization dynamics. b) Optical image of single device with input grating coupler (center), reference waveguide and output coupler (left), and device waveguide and input/output coupler (right). (Scale bar is 50 µm) c) False‐color SEM image of the GST vertical strip overlaying the Si3N4 waveguide. (Scale bar is 1 µm) d) FDTD simulations of the power flow from left to right through the region of GST (outlined by white dashed lines) when GST is in both the amorphous and crystalline states. e) Experimental optical transmission of device with increasing optical probe power. At low probe powers (black line), the device remains in the amorphous state for nonvolatile operation, while increasing the probe power causes recrystallization of the GST. f) Simulated optical transmission and crystallization dynamics of the device during volatile operation.