Roadmap on transformation optics
Artikel i vetenskaplig tidskrift, 2018

Transformation optics asks, using Maxwell's equations, what kind of electromagnetic medium recreates some smooth deformation of space? The guiding principle is Einstein's principle of covariance: that any physical theory must take the same form in any coordinate system. This requirement fixes very precisely the required electromagnetic medium. The impact of this insight cannot be overestimated. Many practitioners were used to thinking that only a few analytic solutions to Maxwell's equations existed, such as the monochromatic plane wave in a homogeneous, isotropic medium. At a stroke, transformation optics increases that landscape from 'few' to 'infinity', and to each of the infinitude of analytic solutions dreamt up by the researcher, there corresponds an electromagnetic medium capable of reproducing that solution precisely. The most striking example is the electromagnetic cloak, thought to be an unreachable dream of science fiction writers, but realised in the laboratory a few months after the papers proposing the possibility were published. But the practical challenges are considerable, requiring meta-media that are at once electrically and magnetically inhomogeneous and anisotropic. How far have we come since the first demonstrations over a decade ago? And what does the future hold? If the wizardry of perfect macroscopic optical invisibility still eludes us in practice, then what compromises still enable us to create interesting, useful, devices? While three-dimensional (3D) cloaking remains a significant technical challenge, much progress has been made in two dimensions. Carpet cloaking, wherein an object is hidden under a surface that appears optically flat, relaxes the constraints of extreme electromagnetic parameters. Surface wave cloaking guides sub-wavelength surface waves, making uneven surfaces appear flat. Two dimensions is also the setting in which conformal and complex coordinate transformations are realisable, and the possibilities in this restricted domain do not appear to have been exhausted yet. Beyond cloaking, the enhanced electromagnetic landscape provided by transformation optics has shown how fully analytic solutions can be found to a number of physical scenarios such as plasmonic systems used in electron energy loss spectroscopy and cathodoluminescence. Are there further fields to be enriched? A new twist to transformation optics was the extension to the spacetime domain. By applying transformations to spacetime, rather than just space, it was shown that events rather than objects could be hidden from view; transformation optics had provided a means of effectively redacting events from history. The hype quickly settled into serious nonlinear optical experiments that demonstrated the soundness of the idea, and it is now possible to consider the practical implications, particularly in optical signal processing, of having an 'interrupt-without-interrupt' facility that the so-called temporal cloak provides. Inevitable issues of dispersion in actual systems have only begun to be addressed. Now that time is included in the programme of transformation optics, it is natural to ask what role ideas from general relativity can play in shaping the future of transformation optics. Indeed, one of the earliest papers on transformation optics was provocatively titled 'General Relativity in Electrical Engineering'. The answer that curvature does not enter directly into transformation optics merely encourages us to speculate on the role of transformation optics in defining laboratory analogues. Quite why Maxwell's theory defines a 'perfect' transformation theory, while other areas of physics such as acoustics are not apparently quite so amenable, is a deep question whose precise, mathematical answer will help inform us of the extent to which similar ideas can be extended to other fields. The contributors to this Roadmap, who are all renowned practitioners or inventors of transformation optics, will give their perspectives into the field's status and future development.


spatial dispersion

spacetime cloaking


transformation optics

spatial cloaking



Martin McCall

Imperial College London

John B. Pendry

Imperial College London

Vincenzo Galdi

Università del Sannio

Yun Lai

Nanjing Univ

S. A. R. Horsley

University of Exeter

Jensen Li

University of Birmingham

Jian Zhu

University of Birmingham

Rhiannon C. Mitchell-Thomas

University of Exeter

Oscar Quevedo-Teruel

Kungliga Tekniska Högskolan (KTH)

Philippe Tassin

Chalmers, Fysik, Kondenserade materiens teori

Vincent Ginis

Vrije Universiteit Brüssel (VUB)

Enrica Martini

Università degli Studi di Siena

Gabriele Minatti

Università degli Studi di Siena

Stefano Maci

Università degli Studi di Siena

Mahsa Ebrahimpouri

Kungliga Tekniska Högskolan (KTH)

Yang Hao

Queen Mary University of London

Paul Kinsler

Lancaster University

Jonathan Gratus

Lancaster University

Daresbury Laboratory

Joseph M. Lukens

Oak Ridge National Laboratory

Andrew M. Weiner

Purdue University

Ulf Leonhardt

Weizmann Institute of Science

Igor I. Smolyaninov

University of Maryland

Vera N. Smolyaninova

Towson University

Robert T. Thompson

Karlsruher Institut für Technologie (KIT)

Martin Wegener

Karlsruher Institut für Technologie (KIT)

Muamer Kadic

Karlsruher Institut für Technologie (KIT)

Steven A. Cummer

Duke University

Journal of Optics

2040-8978 (ISSN) 2040-8986 (eISSN)

Vol. 20 063001


Atom- och molekylfysik och optik

Annan fysik

Matematisk analys