TRANSFORMATIONAL OPTICS ’09
Transforming the Field of
Physical Optics
Alexander V. Kildishev and Vladimir M. Shalaev
Recently, a notable e;ort was devot- ed to developing principles, designs
and numerical validation schemes for
cloaking devices in optics. ;e e;ort
was a strong catalyst that helped transform the entire field of physical optics.
;is revolution started with the development of transformation-designed
optical elements by Pendry, Shurig and
Smith. ;ey were the initiators of the
transformation optics movement, which
began with the construction of both
a theory and devices. Although some
theoretical aspects of their approach
were known, it was the publication
of their method confirmed by critical
experiments that made it so important.
Indeed, the potential of using the
invariant transformations of Maxwell’s
equations for solving complex electromagnetic problems became clear after
the early studies of Weyl, Tamm, Dolin, Post and Lax–Nelson followed by
Chew and Weedon, Ward and Pendry,
Milton, and Leonhard and Philbin. But
in contrast to the early works dealing
with simulations, the transformation
optics (TO) approach solves a fundamental problem of designing a continuous material space for arranging a
desired flow of electromagnetic energy.
Naturally, the TO theory is aimed
at improving the inverse design techniques, so that almost any linear optical device could be either designed
or analyzed using the TO principles.
For example, it has been recently
demonstrated that metamaterial
cloaking devices requiring anisotropic permittivity and permeability can
be emulated by TO-designed tapered
waveguides. 1 ;e tapered waveguide
approach leads to low-loss, broadband
performance and therefore to broadband
electromagnetic cloaking in the visible
frequency range on a scale much larger
than the wavelength.
Two devices developed at Purdue. (Left) Broad-band optical cloak experiment with anisotropic permittivity and permeability emulated by a TO-designed tapered waveguide (in
collaboration with BAE and Towson University). (Right) Light beam completely trapped by
a broad-band omnidirectional optical “black hole. The absorbing core-shell structure of
the “black hole” lens is shown; a uniform absorbing core is placed inside the TO-designed
metamaterial shell with a radius-dependent refractive index.
Evidently, TO tactics require a new
breed of artificial optical composites
(optical metamaterials) that feature
extraordinary electromagnetic properties. Metamaterials are, for example,
capable of providing optical mimicry
with invisibility “carpets” that conceal
objects underneath and blend with the
environment. 2 Recently, two nanophotonics teams from Cornell and Berkley
have made bumps look flat under near-infrared light. 3
Following a semi-classical branch
of TO theory, Purdue researchers have
recently developed a novel approach to
broad-band omnidirectional light absorption. 4 ;e proposed system is based
on trapping light with a metamaterial
structure that formed an e;ective “black
hole” that can be used in photovoltaics,
solar energy harvesting and optoelectronics. On top of photonics applications, similar “black holes” and other
specially designed metamaterials proposed by the Berkeley group can serve
as a “table-top universe” for modeling
the motion of massive celestial bodies in
gravitational potentials in a controlled
laboratory environment. 5
Nowadays, the field of TO is no longer centered on cloaking; it is transforming the entire field of physical optics,
substantially expanding the initial
catalytic e;ort.
Alexander Kildishev ( kildishev@purdue.edu) is with
the School of Electrical and Computer Engineering
at Purdue University in West Lafayette, Ind., U.S.A.
Vladimir M. Shalaev is the Robert and Anne Burnett
Professor of Electrical and Computer Engineering
at Purdue.
References
1. I.I. Smolyaninov et al. Phys. Rev. Lett. 102, 213901
(2009).
2. J. Li and J. B. Pendry. Phys. Rev. Lett. 101, 203901
(2008).
3. L.H. Gabrielli et al. Nature Photon. 3, 461 (2009). J.
Valentine et al. Nature Materials 8, 568-571 (2009)
4. E.E. Narimanov and A.V. Kildishev. Appl. Phys. Lett. 95,
041106 (2009).
5. D. A. Genov et al. Nature Phys. 5, 687-92 (2009).
