Nanooptics and Nanophotonics

Our lab is dedicated to utilizing nanostructures for fundamental studies in optics and for optoelectronics applications.

Observation of slow-light in a metamaterials waveguide at microwave frequencies

We report an experimental observation of slow-light 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 single-negative metamaterial.

Storing light in active optical waveguides with single-negative materials

We show that a nonresonant planar waveguide consisting of conventional dielectric cladded with single-negative 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 zero-group velocity condition for real frequency/complex wave vector modes.

Super-resolution imaging using a three-dimensional metamaterials nanolens

Super-resolution imaging beyond Abbe’s diffraction limit can be achieved by utilizing an optical medium or “metamaterial” that can either amplify or transport the decaying near-field evanescent waves that carry subwavelength features of objects. Here, we present an experimental demonstration of super-resolution imaging by a low-loss three-dimensional metamaterial nanolens consisting of aligned gold nanowires embedded in a porous alumina matrix.

Slow light, open-cavity 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.

Nano-Optical Microlens with Ultra-Short Focal Length using Negative Refraction

We have experimentally realized an ultrashort focal length planoconcave microlens in an InP/InGaAsP semiconductor two-dimensional 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 Negative-Index Binary-Staircase Lens for the Optics Regime

We show that a binary-staircase 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 negative-index 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. Closed-form 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 All-angle 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 all-angle 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, non-metallic interface provides a momentum kick parallel to the surface, which can be used to refract light negatively or positively.

Alternative Approach to All-Angle-Negative-Refraction in Two-Dimensional 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 all-angle negative refraction _AANR_ can be achieved by this surface modification in frequency windows that were not realized before in two-dimensional photonic crystals _C.

Negative Refraction and Plano-Concave Lens Focusing in One-Dimensional Photonic Crystals

Negative refraction is demonstrated in one-dimensional _1D_ dielectric photonic crystals _PCs_ at microwave frequencies. Focusing by plano-concave 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 left-handed materials LHM's is reported from microwave-pulse and continuous-wave 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 Plano-Concave 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 left-handed 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 left-handed 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 3-D image. We have demonstrated this unique feature of imaging by a flat lens, using the phenomenon of all-angle 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.