Our lab is dedicated to utilizing nanostructures for fundamental studies in optics
and for optoelectronics applications.
Observation of slowlight
in a metamaterials waveguide at microwave frequencies
We report an experimental observation of slowlight in the GHz microwave regime
utilizing the mechanism of the degeneracy of forward and backward waves in a planar
waveguide consisting of a dielectric core cladded by singlenegative metamaterial.


Storing light in active
optical waveguides with singlenegative materials
We show that a nonresonant planar waveguide consisting of conventional dielectric
cladded with singlenegative materials supports degenerate propagating modes for
which the group velocity and total energy ﬂow can be zero if the media are lossless.
Absorptive losses will destroy the zerogroup velocity condition for real frequency/complex
wave vector modes.


Superresolution imaging
using a threedimensional metamaterials nanolens
Superresolution imaging beyond Abbe’s diffraction limit can be achieved by utilizing
an optical medium or “metamaterial” that can either amplify or transport the decaying
nearﬁeld evanescent waves that carry subwavelength features of objects. Here, we
present an experimental demonstration of superresolution imaging by a lowloss
threedimensional metamaterial nanolens consisting of aligned gold nanowires embedded
in a porous alumina matrix.


Slow light, opencavity
formation, and large longitudinal electric ﬁeld on a slab waveguide made of indeﬁnite
permittivity metamaterials
The optical properties of slab waveguides made of indeﬁnite permittivity (ε) materials
(IEMs) are considered. In this medium, the real part of the transverse permittivity
is negative while that of the longitudinal permittivity is positive. At any given
frequency, the IEM waveguide supports an inﬁnite number of transverse magnetic (TM)
eigenmodes. For a slab waveguide with a ﬁxed thickness, at most only one TM mode
is forward wave.


NanoOptical Microlens
with UltraShort Focal Length using Negative Refraction
We have experimentally realized an ultrashort focal length planoconcave microlens
in an InP/InGaAsP semiconductor twodimensional photonic crystal with negative index
of refraction n = 0.7. At wavelength 1.5 microns, the lens exhibits ultrashort
focal lengths of 12 microns (~ 8x wanelength) and numerical aperture close to unity.


Nanoengineering of a NegativeIndex
BinaryStaircase Lens for the Optics Regime
We show that a binarystaircase optical element can be engineered to exhibit an
effective negative index of refraction, thereby expanding the range of optical properties
theoretically available for future optoelectronic devices. The mechanism for achieving
a negativeindex lens is based on exploiting the periodicity of the surface corrugation.


Nanowire waveguide made
from extremely anisotropic metamaterials
Exact solutions are obtained for all the modes of wave propagation along an anisotropic
cylindrical waveguide. Closedform expressions for the energy flow on the waveguide
are also derived. For extremely anisotropic waveguide where the transverse permittivity
is negative while the longitudinal permittivity is positive, only transverse magnetic
(TM) and hybrid modes will propagate on the waveguide.


Superlens Imaging Theory
for Anisotropic Nanostructured Metamaterials with Broadband Allangle Negative Refraction
We show that a metamaterial consisting of aligned metallic nanowires in a dielectric
matrix has strongly anisotropic optical properties. For long wavelngths, the longitudinal
SPR, the material exhibits positive transverse permittivity and negative longitudinal
permittivity, relative to the nanowires axis, enabling the achievement of broadband
allangle negative refraction and superlens imaging.


A New Mechanism for
Negative Refraction and Focusing using Selective Diffraction from Surface Corrugation
Refraction at a smooth interface is accompanied by momentum transfer normal to the
interface. We show that corrugating an initially smooth, totally reflecting, nonmetallic
interface provides a momentum kick parallel to the surface, which can be used to
refract light negatively or positively.


Alternative Approach to
AllAngleNegativeRefraction in TwoDimensional Photonic Crystals
We show that with an appropriate surface modification, a slab of photonic crystal
can be made to allow wave transmission within the photonic band gap. Furthermore,
negative refraction and allangle negative refraction _AANR_ can be achieved by
this surface modification in frequency windows that were not realized before in
twodimensional photonic crystals _C.


Negative Refraction and PlanoConcave
Lens Focusing in OneDimensional Photonic Crystals
Negative refraction is demonstrated in onedimensional _1D_ dielectric photonic
crystals _PCs_ at microwave frequencies. Focusing by planoconcave lens made of
1D PCs due to negative refraction is also demonstrated.


Slow Microwaves in Lefthanded
Materials
Remarkably slow propagation of microwaves in two different classes of lefthanded
materials LHM's is reported from microwavepulse and continuouswave transmission
measurements.


Flat Lens Without
Optical Axis: Theory of Imaging
We derive a general theory for imaging by a flat lens without optical axis. We show
that the condition for imaging requires a material having elliptic dispersion relations
with negative group refraction.


Focusing by PlanoConcave
Lens Using Negative Refraction
We demonstrate focusing of a plane microwave by a planoconcave lens fabricated from
a photonic crystal having a negative refractive index and lefthanded electromagnetic
properties.


Left Handed Metamaterials
Artificial materials with negative refractive index are called left handed materials
becaue of the unusual electromagnetic wave propagation in them. In these material
the wave travel backwards while the energy propagates along the incident direction,
contrary to the naturally available materials.


Negative Refraction in Photonic Crystal
Prisms
An intriguing property of the lefthanded material is negative refraction. The optical
properties of materials that are transparent to electromagnetic (EM) waves can be
characterized by an index of refraction. Given the direction of the incident beam
at the interface of vacuum and the material, the direction of the outgoing beam
can be determined using Snell's formula.


Imaging by Flat Lens
Negative refarcation can be exploted to make novel lenses having flat surfaces.
All conventional lenses have curved surfaces due to positive index of refraction.
However, negative index of refraction allows a flat slab of a material to behave
as a lens and focus electromagnetic waves as well as produce a real 3D image. We
have demonstrated this unique feature of imaging by a flat lens, using the phenomenon
of allangle negative refraction in a photonic crystalline material.


Fabrication of Lefthanded Materials
We explore design and fabrication techniques that allow photonic cristals and metamaterials
to possess left handed behavior.

