Variational design method for dipole-based volumetric artificial media

Significance 

Despite immense progress in the field of optics, to date, the majority of optical devices are designed to perform a single operation on an electromagnetic field, with high efficiency. Although incorporating multiple functionalities in the same physical object is possible, it generally comes at the expense of efficiency and fidelity of the individual functions. If highly efficient multi-functional optical devices could be designed reliably, they may provide the means for major breakthroughs in optical communications, optical and quantum computing, computer vision, imaging, scientific instrument design, and a host of other fields. The emergence in recent years of highly tailorable artificial media, such as metamaterials, has provided the optical design community with the ability to fabricate devices with exquisite control of scattering behavior, with access to unprecedented scattering responses and exquisite control over their spatial distribution. At this time, what is lacking is a general design approach that is able to leverage the vast palette of material optical properties, by producing specifications for highly efficient multi-functional optical devices.

In a recent publication, Roberto Zecca (Ph.D. candidate), Dr. Daniel Marks, and Prof. David Smith from the Center for Metamaterials and Integrated Plasmonics and Department of Electrical and Computer Engineering at Duke University developed a novel optical design method that generates highly efficient multi-functional devices. The method, based on the electromagnetic variational principle, applies to artificial media that can be described as collections of point dipoles, as most metamaterials are. In the paper, the authors demonstrated three devices, two of which multi-functional, that all displayed efficiencies above 95%. Their work is currently published in the research journal Optics Express.

The design method combines the electromagnetic variational principle with adjoint-state techniques and with the discrete-dipole approximation (DDA), a very computationally efficient physical model for metamaterial elements. Instead of directly solving the design problem, which in general is a very challenging task, the method starts from an initial guess at the optical scattering properties of the device and uses successive iterations to improve on the guess, until a satisfactory efficiency is reached. If the desired device is multi-functional, the method takes all functions (input-output wave pairs) into account at the same time, designing a medium that implements all functions concurrently.

In summary, Duke researchers successfully devised an iterative design method for artificial media that can be described as collections of electromagnetic dipoles. Their revolutionary approach was achieved through the combination of the variational formulation of electromagnetism and the discrete-dipole approximation. Altogether, the novel approach showed promise as a candidate for the design of electromagnetic devices able to encode a large number of functions in the same volume.

Variational design method for dipole-based volumetric artificial media - Advances in Engineering
A symphotic three-way hub device that transforms three input beams (at 70, -50, and 20 degrees) into three output beams (at 20, -90, and -40 degrees) with average efficiency greater than 99%. Top left: polarizability of the designed device.

About the author

ROBERTO ZECCA was born in Verona, Italy, in 1988. He received his degrees (B.S. in industrial engineering and M.S. in materials engineering) from the University of Trento, Italy, in 2010 and 2013, respectively. He is now a Ph.D. candidate in electrical and computer engineering at Duke University under the supervision of Dr. David R. Smith. His thesis work concentrates mainly on inverse design techniques for volumetric artificial media and metamaterials.

As a member of the Smith research group, he also researched nonlinear optical processes in nanometric systems, such as lasing in plasmonic nanopatch antennas and the enhancement stimulated Brillouin scattering in waveguides at the nanoscale. He has published 4 research articles and holds 2 patents. His research interests comprise computational electromagnetics and elastomechanics, variational design methods, numerical optimization, holography, and nonlinear optics.

About the author

DANIEL L. MARKS was born in Chicago, Illinois in 1973. He received the B.S. in 1995, M.S. in 1998, and Ph.D. in 2001 from the University of Illinois at Urbana-Champaign. From 2001 to 2008, he was a research scientist at the University of Illinois at Urbana-Champaign Biophotonics Laboratory, and he is current an Associate Research Professor at the Department of Electrical and Computer Engineering at Duke University, which he joined in 2009. He is the author of 85 research articles, 17 patents, and has been an editor of Applied Optics. His research interests include optics, optical design, computational imaging, millimeter-wave and terahertz imaging, metamaterials, and synthetic electromagnetic structures.

About the author

DAVID R. SMITH received the B.S. and Ph.D. degrees in physics from the University of California at San Diego, San Diego, CA, USA, in 1988 and 1994, respectively.

He is currently the James B. Duke Professor of electrical and computer engineering with Duke University and the Director of the Center for Metamaterials and Integrated Plasmonics, Durham, NC, USA. He is an Adjunct Professor with the Physics Department, University of California at San Diego, an Affiliate Faculty Member with the Electrical and Computer Engineering Department, University of Washington, Seattle, WA, USA, and a Visiting Professor of physics with Imperial College, London, U.K.

His research interests include the theory, simulation, and characterization of unique electromagnetic structures, including photonic crystals and metamaterials, as well as applications of such materials.

Reference

Roberto Zecca, Daniel L. Marks, and David R. Smith. Variational design method for dipole-based volumetric artificial media. Volume 27, Number 5 | 2019 | Optics Express 6512.

Go To Optics Express

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