Transistors based on semiconductor materials are widely used electronic components with many remarkable properties. For example, they have a non-reciprocal electrical response, which means they can isolate two parts of a circuit such that one of the parts (the input section) can influence the other part (the input section). output), but not the other. way around. Additionally, transistors can amplify voltage signals and thus provide power to a system. Interactions without energy conservation are generally called “non-Hermitian”.
Researchers from the Instituto de Telecomunicações of the University of Coimbra and the University of Lisbon have recently introduced a new class of bulk materials that draws inspiration from the non-reciprocal and non-Hermitian responses of conventional semiconductor-based transistors. drivers. They presented these massive three-dimensional (3D) transistor-like metamaterials in a paper published in Physical examination letters.
Mário Silveirinha, one of the researchers who conducted the study, told Phys.org: “The ideas developed in our article were mainly driven by the question: would it be possible to somehow imitate another the answer of standard transistors in a bulk metamaterial?We were intrigued to know if it would be possible to have a bulk material that, when properly biased, could manipulate electromagnetic waves in the same way as a transistor manipulates a voltage signal.”
A key goal of the recent study by Silveirinha and colleagues was to identify a new way to achieve non-reciprocal and/or non-Hermitian responses, which can be controlled by a static electric field in a photonic system. Systems controllable using electric fields have significant advantages over more conventional solutions, such as those based on bulky magnetic circuits, because they are ubiquitous, can achieve better performance, and are easier to downsize.
“In our paper, we theoretically show that nonlinear materials with broken inversion symmetry can have rather exotic non-Hermitian responses in non-equilibrium situations when biased by an electric field,” Silveirinha said. “Specifically, we predicted that the interaction of a static electric field bias with material nonlinearities can result in an overall non-reciprocal and non-Hermitian response, somewhat analogous to the response of a semiconductor MOSFET, but in a massive 3D material.”
The new massive 3D metamaterials identified by the researchers could exhibit very exotic physics. For example, due to their non-Hermitian response, different field modes do not carry power independently and interference between two waves can give rise to what is called a “power beat”. the bulk material can behave either as a gaining material (i.e. acquiring energy) or as a losing material (i.e. dissipating energy), depending on the polarization of the field.
“We introduced the idea of mimicking the operation of transistors, which are point-like (i.e., zero-dimensional) devices in a 3D bulk metamaterial,” Silveirinha said. “We believe that our work may have important practical applications, due to the superiority of electrically biased systems in terms of performance, integrability and miniaturization.”
In the future, the massive transistor-inspired 3D metamaterials introduced by this team of researchers could be used to create electromagnetic isolators, two-port devices that transmit energy in a single direction. These isolators could be a feasible alternative to Faraday isolators, devices that transmit light in one specific direction and block light in the opposite direction, which are commonly used to protect a laser source from destabilizing feedback or damage from radiation. retro-reflected light.
“Electromagnetic isolators are very important for the development of all-optical circuits, because typical communication systems are designed in a modular way (that is, with modules that are supposed to perform specific tasks or process signals in a certain way). specific),” explained Silveirinha. “Ideally, the response of a given module should be independent of the other modules to which it is connected. For this, it is essential to isolate the different modules, allowing only “one-way” responses (that is i.e. non-reciprocal) interactions.”
In addition to allowing non-reciprocal interactions in devices, the newly identified metamaterials exhibit a non-Hermitian response, meaning they can amplify electromagnetic signals. In the future, they could therefore also be used to create terahertz lasers and terahertz amplifiers.
“There are many exciting avenues to explore next, as the non-Hermitian, non-reciprocal response we identified can lead to different innovations and devices,” Silveirinha said. “For example, it may enable the realization of a new class of oscillators, distributed amplifiers, optical isolators and circulators, and other devices for nanophotonics applications.
As part of their current research efforts, Silveirinha and his colleagues are exploring various possible practical implementations of their 3D bulk metamaterials. The most obvious of these might be to use them to create systems containing arrays of transistors.
“Our preliminary analyzes show that when used to create transistor arrays, metamaterials can indeed provide the desired answers,” Silveirinha added. “We are currently working on the experimental demonstration of a 1D version of such systems. We also believe that related answers can be achieved using natural materials in non-equilibrium situations (e.g. with injection current) , and we are exploring that and other opportunities.”
A system for the non-reciprocal transmission of microwave acoustic waves
Sylvain Lannebère et al, Non-reciprocal and non-Hermitian hardware response inspired by semiconductor transistors, Physical examination letters (2022). DOI: 10.1103/PhysRevLett.128.013902
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