Researchers from the University of Luxembourg and their international research partners have recently reported how a special kind of artificial materials, called epsilon-near-zero metamaterials, might enable an unprecedented control of light properties on a temporal scale which is 1000 billion times smaller than a second. The scientists have published an article in Communications Physics, an open access journal from Nature Springer publishing high-quality research and significant advances in all areas of physics. The publication was the result of joint efforts between researchers at the University of Luxembourg, University of Konstanz (Germany), Università della Calabria (Italy) and the Italian Institute of Technology (Italy).
“We developed an all-optical switching scheme which allows to control one optical signal using another, holding potential to go beyond the limitations of electrical switches via ultrafast manipulation of light,” explains Nicolò Maccaferri, lead scientist of the work and Researcher in the Ultrafast Condensed Matter Physics Group led by Prof. Daniele Brida at the Department of Physics and Materials Science at the University of Luxembourg. “Overcoming the fundamental limits of electronics, such as bandwidth, clock-time/frequency and heating of the device, is one of the main promises of photonics. In this context, many advancements rely on the use of light as information carrier, and this can pave the way towards light-based technologies, which will have a huge impact in terms of reduced energy consumption and performance efficiency. In this framework, all-optical switching has attracted great attention because it can potentially overcome the speed and heat dissipation limitations imposed by electrical switching or passive optical devices” continues Maccaferri.
Figure: Schematic of the modulation of light reflection induced by an ultrafast excitation of a metal-insulator-metal nanocavity. On the left, the off state case: when infrared light impinges on the metamaterial, no light is reflected. On the right, the on state case: if an ultrashort UV light pulse (control) impinges on the metamaterial, then the infrared light (signal) can be reflected by the nanocavity.
In view of practical applications, the key parameters of all-optical switching include modulation depth (defined as the reflection and/or transmission of light contrast between ‘ON’ and ‘OFF’ states) and switching time. In order to achieve this result, the scientists designed and fabricated a sandwich-like system made of two metallic thin layers with in between an insulating material, such as glass, to build a so-called photonic nanocavity (see Figure). This system then allows for sub-3 ps all-optical switching operation time, exhibiting a relative modulation depth of light intensity exceeding 100% at a specific wavelength of the electromagnetic spectrum, and switching bandwidths of few hundred GHz. The flexibility enabled by the use of these metamaterials is particularly valuable when integrating this system with architectures displaying a well-defined and polarization-selective light absorption/emission.
“This approach is very powerful since our system can be designed at will in a broad range of wavelengths (from the ultraviolet to radio frequencies), it relies on a simple fabrication process and it is independent on the polarization of the light. Noticeably, the observed effects cannot be achieved with natural materials. In fact, we need to design special materials, dubbed metamaterials, whose properties go beyond those of materials we can find in nature,” says Maccaferri. “Moreover, we developed a working operation that allows an easy separation of control and signal light via spectral filtering, which is critical in terms of input/output isolation in optical logic applications,” explains Maccaferri. “When combined with other photonic devices, the proposed system can thus be used for ultrafast control of arbitrarily designed electromagnetic fields. We foresee also that the developed approach can be used as platform for the ultrafast manipulation of optical nonlinearities, light emission manipulation and other very promising future and emerging light-driven technologies”, says Maccaferri.
The experiments leading to the published results have been funded by the Luxembourg National Research Fund under the CORE Scheme. The project ‘ULTRON’, led by Maccaferri, has the main scope to obtain a coherent hybridization of optical and magnetic excitations in metamaterials, and disclose a new mechanism to develop future light-driven deterministic (coherently-controlled), ultrafast (sub-ps regime) and ultra-dense (tens of Tb per inch2) data processing nanotechnologies, thus making real the possibility to integrate spintronics with light-based technologies working at even higher speeds than electronics.
“These results were obtained in the framework of our CORE project ‘ULTRON’, and are really important since they represent the foundation to achieve an ultrafast control of light states by using metamaterials. We will then integrate magnetic materials with similar architectures, so that photons can interact coherently with the spin degree of freedom of the electrons, thus achieving the final goal of our project. I am also really grateful to FNR, Prof. Brida and the University to give me all the financial, strategic and infrastructural support to perform high-quality research here in Luxemborug” concludes Maccaferri, who is now planning to move this approach towards lower frequencies of the electromagnetic spectrum, where the spin excitations can be triggered by using this type of architecture, bridging the gap between optical and magnetic technologies.
Original publication: “Ultrafast all-optical switching enabled by epsilon-near-zero-tailored absorption in metal-insulator nanocavities” Joel Kuttruff, Denis Garoli, Jonas Allerbeck, Roman Krahne, Antonio De Luca, Daniele Brida, Vincenzo Caligiuri, and Nicolò Maccaferri Communications Physics 3, 114 (2020).
For additional information about metamaterials, see also the TEDxUniversityofLuxembourg “Metamaterials matter: the smart materials of the future”