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Metamaterials for advanced photonic applications: reconsidering the classical laws of optics

vrijdag, 29 mei, 2009 - 16:00
Campus: Brussels Humanities, Sciences & Engineering campus
Philippe Tassin

In this thesis, the author explores potential applications of metamaterials in photonics.
Such materials are man-made materials with extraordinary properties that are not
available in nature. One of the most fascinating properties that can be achieved with
metamaterials is magnetism at microwave, terahertz and optical frequencies. The author
identifies several photonic components where metamaterials could provide enhanced
efficiency, new functionality, or go beyond traditional limitations of optics related to the
wavelike nature of light.

Photonics—the science and technology of generating, manipulating and detecting light—has had a
significant impact on our society during the last decades. From a fundamental viewpoint, photonics
has allowed for a variety of breakthroughs in physics, such as femtosecond time metrology, laserdriven
particle accelerators, laser fusion, and even the discovery of several elementary particles
that are ultimately measured by the detection of photons. On the other hand, researchers have
also exploited the huge potential of photonics for numerous industrial, medical and consumer
applications, including optical fibre communications for the internet backbone, laser printers, laserbased
processing of metals, LCD display technology, optical data storage on DVDs, etc.

These accomplishments of photonics are based on the ability to control the propagation and other
properties of light to an incredible degree. This precise control of light is possible through the
interaction of photons with a variety of optical materials. Natural materials have, nevertheless, an
important shortcoming: at optical frequencies, we can influence only the electric component of
electromagnetic waves, whereas the magnetic component is out of reach.

In order to control the magnetic component of light, researchers have recently succeeded to create
metamaterials, which are artificial materials that contain small resonant electromagnetic elements.
These electromagnetic elements replace the atoms as the basic units for the interaction with light
and determine as such the electromagnetic properties of the material. The constituents will often
be designed such that the metamaterial has electromagnetic properties that are not observed for
natural materials. The design of suitable electrical and magnetic response allows for the existence
of materials with, for example, negative index of refraction (left-handed materials).

The thesis starts with a brief review of the history of optical metamaterials and of the basic theory
of light propagation in left-handed materials. Plane waves in left-handed materials, negative
refraction, total internal reflection at the interface between a right-handed and a left-handed
medium, and the inverse Doppler effect are reviewed. Subsequently, the author discusses the
propagation of electromagnetic waves in a graded index structure with a gradual transition from
positive to negative index of refraction.

The following chapters each describe a different optical component that makes use of a
metamaterial. Two chapters are devoted to the miniaturisation of photonic components. A design
of an optical waveguide with subwavelength thickness is proposed; this waveguide contains a lefthanded
material in the cladding in order to engineer the phase shifts associated with total internal
reflection of light at the edges of the waveguide. Subsequently, dielectric cavities with
subwavelength dimensions are designed by use of transformation optics, a method that is based on
techniques borrowed from general relativity.

Two more chapters are devoted to the application of left-handed materials in two different
nonlinear optical resonators: a dispersive Kerr resonator and an optical parametric oscillator. It is
shown that the left-handed material can be used for the purpose of diffraction management, i.e., it
is possible to alter the strength and the sign of the diffraction coefficient. Reduced diffraction may
be useful for the downscaling of optical dissipative structures and, hence, for the generation of light
beams with sub-diffraction-limited beam diameter.

Finally, a novel metamaterial is designed to exhibit an electromagnetic response similar to
electromagnetically induced transparency; for this purpose, two coupled quasi-static electric
circuits are designed as a metamaterial constituent. This metamaterial has a narrow transparency
window in its spectral response in which low group velocity and small absorption are observed
simultaneously. It may therefore be useful for slow light applications.