arXiv subjects

Uday K. Chettiar

Publications and source records attributed to Uday K. Chettiar.

11 recordsLinked to original sources

arXiv2009

Frequency-domain simulations of a negative-index material with embedded gain

We solve the equations governing light propagation in a negative-index material with embedded nonlinearly saturable gain material using a frequency-domain model. We show that available gain materials can lead to complete loss compensation only if they are located in the regions where the field enhancement is maximal. We study the increased enhancement of the fields in the gain composite as well as in the metal inclusions and show analytically that the effective gain is determined by the average near-field enhancement.

physics.optics↗

arXiv2009

Tunable magnetic response of metamaterials

We demonstrate a thermally tunable optical metamaterial with negative permeability working in the visible range. By covering coupled metallic nanostrips with aligned nematic liquid crystals (NLCs), the magnetic response wavelength of the metamaterial is effectively tuned through control of the ambient temperature, changing the refractive index of LC via phase transitions. By increasing the ambient temperature from 20 degree to 50 degree, the magnetic response wavelength shifts from 650nm to 632nm. Numerical simulations confirm our tests and match the experimental observations well.

physics.optics↗

arXiv2009

Yellow-light Negative-index Metamaterials

A well-established, silver fishnet design has been further miniaturized to function as a negative-index material at the shortest wavelength to date. By studying the transmittance, reflectance, and corresponding numerical simulations of the sample, we report in this paper a negative refractive index of -0.25 at the yellow-light wavelength of 580 nm.

physics.optics↗

arXiv2008

Optical Metamagnetism and Negative Index Metamaterials

A new class of artificially structured materials called metamaterials makes it possible to achieve electromagnetic properties that do not exist in nature. In this paper we review the recent progress made in the area of optical metamaterials. It was predicted that nanostructured metamaterials could provide us with artificial magnetic response and negative refractive index at optical frequencies. To date, optical metamagnetics have been already fabricated to demonstrate artificial magnetic response in the infrared and across the entire visible spectrum, while metamaterials showing negative refractive index, also called negative index materials (NIM), have been demonstrated in the infrared and at the border with the visible spectral range. Here we report the results of a sample that displays NIM behavior for red light at a wavelength of 710 nm. This is the shortest wavelength so far at which NIM behavior has been observed for light (excluding a device built on surface plasmon polaritons). We also discuss the fabrication challenges and the impact of fabrication limitations, specifically surface roughness of the fabricated structures on the optical properties of the metamaterials.

physics.optics↗

arXiv2007

Non-Magnetic Cloak without Reflection

In an electromagnetic cloak based on a transformation approach, reduced sets of material properties are generally favored due to their easier implementation in reality, although a seemingly inevitable drawback of undesired reflection exists in such cloaks. Here we suggest using high-order transformations to create smooth moduli at the outer boundary of the cloak, therefore completely eliminating the detrimental scattering within the limit of geometric optics. We apply this scheme to a non-magnetic cylindrical cloak and demonstrate that the scattered field is reduced substantially in a cloak with optimal quadratic transformation as compared to its linear counterpart.

physics.optics↗

arXiv2007

Optical Magnetism: from Red to Blue

A family of coupled nano-strips with varying dimensions is fabricated to obtain optical magnetic responses across the whole visible spectrum, from red to blue. The proposed approach provides one with a universal building block and a general recipe for producing controllable optical magnetism for various practical implementations.

physics.optics↗

arXiv2006

Dual-Band Negative Index Metamaterial: Double-Negative at 813 nm and Single-Negative at 772 nm

This work is concerned with the experimental demonstration of a dual-band negative index metamaterial. The sample is double-negative (showing both a negative effective permeability and a negative effective permittivity) for wavelengths between 799 and 818 nm of linearly polarized light with a real part of refractive index of about -1.0 at 813 nm; the ratio -Re(n)/Im(n) is close to 1.3 at that wavelength. For an orthogonal polarization, the same sample also exhibits a negative refractive index in the visible (at 772 nm). The spectroscopic measurements of the material are in good agreement with the results obtained from a finite element electromagnetic solver for the actual geometry of the fabricated sample at both polarizations.

physics.optics↗

arXiv2006

A negative permeability material at red light

Experimental demonstration of a negative permeability due to near-field coupling of periodic thin silver strips is presented. Two samples with different strip thicknesses are fabricated; optical measurements of the samples confirm our initial design projections by showing the real part of permeability to be about -1 for the sample with thinner strips and -0.8 for the sample with thicker strips at wavelengths of 770 nm and 720 nm.

physics.optics↗

arXiv2006

Optical Cloaking with Non-Magnetic Metamaterials

Artificially structured metamaterials have enabled unprecedented flexibility in manipulating electromagnetic waves and producing new functionalities, including the cloak of invisibility based on coordinate transformation. Here we present the design of a non-magnetic cloak operating at optical frequencies. The principle and structure of the proposed cylindrical cloak are analyzed, and the general recipe for the implementation of such a device is provided. The cloaking performance is verified using full-wave finite-element simulations.

physics.optics↗

arXiv2006

Comment on "Negative Refractive Index in Artificial Metamaterials" [A. N. Grigorenko, Opt. Lett., 31, 2483 (2006)]

A key optical parameter characterizing the existence of negative refraction in a thin layer of a composite material is the effective refractive index of an equivalent, homogenized layer with the same physical thickness as the initial inhomogeneous composite. Measuring the complex transmission and reflection coefficients is one of the most rigorous ways to obtain this parameter. We dispute Grigorenko's statement (Optics Letters 31, 2483 (2006)) that measuring only the reflection intensity spectrum is sufficient for determining the effective refractive index. We discuss fundamental drawbacks of Grigorenko's technique of using a best-fit approximation with an a priori prescribed dispersive behavior for a given metamaterial and an 'effective optical thickness' that is smaller than the actual thickness of the sample. Our simulations do not confirm the Grigorenko paper conclusions regarding the negative refractive index and the negative permeability of the nanopillar sample in the visible spectral range.

physics.optics↗

arXiv2006

Negative index metamaterial combining magnetic resonators with metal films

We present simulation results of a design for negative index materials that uses magnetic resonators to provide negative permeability and metal film for negative permittivity. We also discuss the possibility of using semicontinuous metal films to achieve better manufacturability and enhanced impedance matching.

physics.optics↗