Toward a new generation of photonic devices based on the integration of metal oxides in silicon technology

[ES] La búsqueda de nuevas soluciones e ideas innovadoras en el campo de la fotónica de silicio mediante la integración de nuevos materiales con prestaciones únicas es un tema de alta actualidad entre la comunidad científica en fotónica y con un impacto potencial muy alto. Dentro de esta temática, esta tesis pretende contribuir hacia una nueva generación de dispositivos fotónicos basados en la integración de óxidos metálicos en tecnología de silicio. Los óxidos metálicos elegidos pertenecen a la familia de óxidos conductores transparentes (TCO), concretamente el óxido de indio y estaño (ITO) y el óxido de cadmio (CdO), y materiales de cambio de fase (PCM) como el dióxido de vanadio (VO2). Dichos materiales se caracterizan especialmente por una variación drástica de sus propiedades optoelectrónicas, tales como la resistividad o el índice de refracción, frente a un estímulo externo ya sea en forma de temperatura, aplicación de un campo eléctrico o excitación óptica. De esta forma, nuestro objetivo es diseñar, fabricar y demostrar experimentalmente nuevas soluciones y dispositivos clave tales como dispositivos no volátiles, desfasadores y dispositivos con no linealidad óptica. Tales dispositivos podrían encontrar potencial utilidad en diversas aplicaciones que comprenden las comunicaciones ópticas, redes neuronales, LiDAR, computación, cuántica, entre otros. Las prestaciones clave en las que se pretende dar un salto disruptivo son el tamaño y capacidad para una alta densidad de integración, el consumo de potencia, y el ancho de banda.[CA] La recerca de noves solucions i idees innovadores al camp de la fotònica de silici mitjançant la integració de nous materials amb prestacions úniques és un tema d'alta actualitat entre la comunitat científica en fotònica i amb un impacte potencial molt alt. D'aquesta temàtica, aquesta tesi pretén contribuir cap a una nova generació de dispositius fotònics basats en la integració d'òxids metàl·lics en tecnologia de silici. Els òxids metàl·lics elegits pertanyen a la família d'òxids conductors transparents (TCO), concretament l'òxid d'indi i estany (ITO) i l'òxid de cadmi (CdO), i materials de canvi de fase (PCM) com el diòxid de vanadi (VO2). Aquests materials es caracteritzen especialment per una variació dràstica de les propietats optoelectròniques, com ara la resistivitat o l'índex de refracció, davant d'un estímul extern ja siga en forma de temperatura, aplicació d'un camp elèctric o excitació òptica. D'aquesta manera, el nostre objectiu és dissenyar, fabricar i demostrar experimentalment noves solucions i dispositius clau com ara dispositius no volàtils, desfasadors i dispositius amb no-linealitat òptica. Aquests dispositius podrien trobar potencial utilitat en diverses aplicacions que comprenen les comunicacions òptiques, xarxes neuronals, LiDAR, computació, quàntica, entre d'altres. Les prestacions clau en què es pretén fer un salt disruptiu són la grandària i la capacitat per a una alta densitat d'integració, el consum de potència i l'amplada de banda.[EN] The search for new solutions and innovative ideas in the field of silicon photonics through the integration of new materials featuring unique optoelectronic properties is a hot topic among the photonics scientific community with a very high potential impact. Within this topic, this thesis aims to contribute to a new generation of photonic devices based on the integration of metal oxides in silicon technology. The chosen metal oxides belong to the family of transparent conducting oxides (TCOs), namely indium tin oxide (ITO) and cadmium oxide (CdO), and phase change materials (PCMs) such as vanadium dioxide (VO2). These materials are characterized by a drastic variation of their optoelectronic properties, such as resistivity or refractive index, in response to an external stimulus either in the form of temperature, application of an electric field, or optical excitation. Therefore, our objective is to design, fabricate and experimentally demonstrate new solutions and key devices such as non-volatile devices, phase shifters, and devices with optical nonlinearity. Such devices could find potential utility in several applications, including optical communications, neural networks, LiDAR, computing, and quantum. The key features in which we aim to take a leapfrog are footprint and capacity for high integration density, power consumption, and bandwidth.This work is supported in part by grants ACIF/2018/172 funded by Generaliltat Valenciana, and FPU17/04224 funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”.Parra Gómez, J. (2022). Toward a new generation of photonic devices based on the integration of metal oxides in silicon technology [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/19088

Non-volatile silicon photonic devices enabled by phase change material

We review our recent research progress on silicon-Ge 2 Sb 2 Te 5 hybrid photonic devices. The optical transmission can be varied by 20 dB using micron-length GST. The inherent "self-holding" feature of GST make it attractive for low-power applications

Design of Ultra-Compact Optical Memristive Switches with GST as the Active Material

In the following study, we propose optical memristive switches consisting of a silicon waveguide integrated with phase-change material Ge2Sb2Te5 (GST). Thanks to its high refractive index contrast between the crystalline and amorphous states, a miniature-size GST material can offer a high switching extinction ratio. We optimize the device design by using finite-difference-time-domain (FDTD) simulations. A device with a length of 4.7 μm including silicon waveguide tapers exhibits a high extinction ratio of 33.1 dB and a low insertion loss of 0.48 dB around the 1550 nm wavelength. The operation bandwidth of the device is around 60 nm

Ultracompact Si-GST Hybrid Waveguides for Nonvolatile Light Wave Manipulation

Phase change materials (PCMs) combined with silicon photonics are emerging as a promising platform to realize miniature photonic devices. We study the basic optical properties of a sub-wavelength-dimension silicon ridge waveguide with a 20-nm-thick Ge2Sb2Te5 (GST) top-clad layer. Numerical simulations show that the effective index of the Si-GST hybrid waveguide varies significantly when the GST changes from the amorphous to the crystalline states. This change can be utilized to make micron-size photonic devices. To experimentally verify the effectiveness of the Si-GST hybrid waveguide on light wave manipulation, we fabricated a series of unbalanced Mach-Zehnder interferometers with one arm connected with a section of Si-GST hybrid waveguide in different lengths. The transmission spectra are measured and the complex effective indices are extracted for GST at crystalline, amorphous and intermediate phases. The experimental results overall agree well with the simulation ones. The nonvolatile property of GST makes it attractive to reduce the static power consumption. This research represents a significant step towards the realization of ultra-compact Si-GST hybrid devices that will play a key role in high-density photonic integrated circuits, opening the door to many potential applications, including optical switch, memory and logic operation

Impact of GST thickness on GST-loaded silicon waveguides for optimal optical switching

[EN] Phase-change integrated photonics has emerged as a new platform for developing photonic integrated circuits by integrating phase-change materials like GeSbTe (GST) onto the silicon photonics platform. The thickness of the GST patch that is usually placed on top of the waveguide is crucial for ensuring high optical performance. In this work, we investigate the impact of the GST thickness in terms of optical performance through numerical simulation and experiment. We show that higher-order modes can be excited in a GST-loaded silicon waveguide with relatively thin GST thicknesses (<100 nm), resulting in a dramatic reduction in the extinction ratio. Our results would be useful for designing high-performance GST/Si-based photonic devices such as non-volatile memories that could find utility in many emerging applications.This work is supported by grants PID2019-111460GB-I00, ICTS-2017-28-UPV-9F, and FPU17/04224 funded by MCIN/AEI/ 10.13039/501100011033, by "ERDF A way of making Europe" and "ESF Investing in your future". Funding from Generalitat Valenciana (PROMETEO/2019/123). Funding for open access charge: Universitat Politecnica de Valencia. The authors would like to thank Helen Urgelles for her help with the experimental measurements.Parra Gómez, J.; Navarro-Arenas, J.; Kovylina-Zabyako, M.; Sanchis Kilders, P. (2022). Impact of GST thickness on GST-loaded silicon waveguides for optimal optical switching. Scientific Reports. 12(1):1-9. https://doi.org/10.1038/s41598-022-13848-01912

Spatio-spectral control of coherent nanophotonics

Fast modulation of optical signals that carry multidimensional information in the form of wavelength, phase or polarization has fueled an explosion of interest in integrated photonics. This interest however masks a significant challenge which is that independent modulation of multi-wavelength carrier signals in a single waveguide is not trivial. Such challenge is attributed to the longitudinal direction of guided-mode propagation, limiting the spatial separation and modulation of electric-field. Here, we overcome this using a single photonic element that utilizes active coherent (near) perfect absorption. We make use of standing wave patterns to exploit the spatial-degrees-of-freedom of in-plane modes and individually address elements according to their mode number. By combining the concept of coherent absorption in spatio-spectral domain with active phase-change nanoantennas, we engineer and test an integrated, reconfigurable and multi-spectral modulator operating within a single element. Our approach demonstrates for the first time, a non-volatile, wavelength-addressable element, providing a pathway for exploring the tunable capabilities in both spatial and spectral domains of coherent nanophotonics

Hybrid photonic integrated circuits for neuromorphic computing [Invited]

The burgeoning of artificial intelligence has brought great convenience to people’s lives as large-scale computational models have emerged. Artificial intelligence-related applications, such as autonomous driving, medical diagnosis, and speech recognition, have experienced remarkable progress in recent years; however, such systems require vast amounts of data for accurate inference and reliable performance, presenting challenges in both speed and power consumption. Neuromorphic computing based on photonic integrated circuits (PICs) is currently a subject of interest to achieve high-speed, energy-efficient, and low-latency data processing to alleviate some of these challenges. Herein, we present an overview of the current photonic platforms available, the materials which have the potential to be integrated with PICs to achieve further performance, and recent progress in hybrid devices for neuromorphic computing