TIME: 3:30 PM

LOCATION: GMCS 314

SPEAKER: Filippo Capolino, UC, Irvine, Electrical Engineering and Computer Science

ABSTRACT: There are two classes of exceptional point degeneracies (EPDs): one related to coupled resonators and the other to coupled-mode waveguides. EPDs are observed among the eigenstates of such systems, i.e., in the eigenfrequencies for the first class and in the guided eigenmodes in the second class, where at least two eigenstates are fully degenerate. We explore EPDs in systems with saturable (hence, nonlinear) gain and their possible applications in sensing [1] and high-power radiators (e.g., lasers) [2]. EPDs are degenerate solutions in the parameter space of a system’s governing equations.  In this talk we focus on nonlinear systems with saturable gain.  A theory describing EPDs in such systems is presented, focusing on the saturated steady state that leads to stable oscillations.

In the first systems’ class, the oscillation frequency is extremely sensitive to perturbations, leading to “bad” oscillators that are however useful for sensing when high sensitivity is required. A system of two coupled nonlinear oscillators is found to have either a cube-root or square root sensitivity to perturbations [3].

In the second class, the wavenumber of the exceptionally degenerate guided modes is sensitive to perturbations, however the oscillation frequency is very stable, leading to possible large arrays of radiating oscillators whose radiated power is increasing with the size of the array, without losing the synchronization [2]. 

We provide theoretical explanations and experimental demonstrations to prove these new fundamental concepts in each class and discuss applications in sensing and radiation. 

References

[1] A. Nikzamir and F. Capolino. “Highly sensitive coupled oscillator based on an exceptional point of degeneracy and nonlinearity”. Phys. Rev. Appl., (18): 054059, 2022.

[2] A. Nikzamir, A. Herrero-Parareda, N. Furman, B. Bradshaw, M. Saavedra-Melo, F.  Capolino. “Array oscillator in coupled waveguides with nonlinear gain and radiation resistances saturating at exceptional point”. arXiv:2501.14978, 2025.

[3] B. Bradshaw, A. Hakimi and F. Capolino. “Steady-state exceptional point degeneracy and sensitivity of nonlinear saturable coupled oscillators”. arXiv:2601.13638, 2026.

BIO: Filippo Capolino received the Ph.D. degree in electrical engineering from the University of Florence, Italy, in 1997. He is currently a Professor with the Department of Electrical Engineering and Computer Science at the University of California, Irvine, CA, USA. Previously he has been an Assistant Professor at the Department of Information Engineering at the University of Siena, Italy from 2002 to 2008. From 1997 to 1999, he was a Fulbright Scholar and Postdoctoral Fellow with the Department of Aerospace and Mechanical Engineering, Boston University, MA, USA. From 2000 to 2001, part of 2005 and in 2006, he was a Research Assistant Visiting Professor with the Department of Electrical and Computer Engineering, University of Houston, TX, USA. He has been a short-term Visiting Professor at the Fresnel Institute, Marseille, France (2003) and at the Centre de Recherche Paul Pascal, Bordeaux, France (2010). In 2022 he has been the recipient of the Cathedra of Excellence from the University of Carlos III, Madrid, Spain.

His research interests include applied electromagnetics, sensors in both microwave and optical ranges, photonics, metamaterials and their applications, traveling wave tubes, antennas, propagation, wireless systems, chip-integrated systems, etc. He is an IEEE Fellow, an Optica Fellow, and he is the editor of the two volume “Metamaterials Handbook”, and he has published 230 journal articles in IEEE, Optica, Physics journals, etc.

HOST: Jose Castillo