Srinivasan Iyer

Impact of apexes on the resonance shift in double hole nanocavities

The transmission of light through metallic films with periodic double nanoholes is studied using vectorial three-dimensional finite element method. Special emphasis is given on understanding different transmission resonances arising in gold and silver films with periodic sub-wavelength holes of different shapes. The spectral shift of the hole-shape resonance resulting from a variation of the hole refractive index is analyzed for a double nanohole geometry in the transmission mode using numerical simulations. Specifically, the role of field enhancement at the apexes of the double nanohole in the sensing of medium within the hole cavity is pointed out and discussed. The presence of sharp apexes within the double nanoholes significantly improves the resonance sensitivity as compared to rectangular holes of comparable area. Impact of possible manufacturing errors on the overall sensitivity is also characterized. Robustness and a relatively simple fabrication procedure make these kinds of refractive index sensors practically attractive.

Transmission resonances in periodic U-shaped metallic nanostructures

The spectral response of crescent-like metallic nanostructures, a sub-class of U-shaped split-ring resonators, on a glass substrate at normal incidence is studied numerically. Also, the interpretation of transmission resonances arising from periodic conventional standard split-ring resonators with rectangular edges (SSRR) at normal incidence is revisited. In particular, we focus on one specific transmission resonance which is present for nano-crescents (NC) but absent in the case of SSRRs used for metamaterials. It is proposed that for a U-shaped metallic structure of arbitrary geometry, coupling of plasmonic eigen modes at all the surfaces of the three-dimensional structure is essential to be considered. The manner in which the coupling takes place between plasmonic modes at all the surfaces of the three-dimensional structure is what completely characterizes transmission resonances, and it is unique for each given resonance.

Effective tunability and realistic estimates of group index in plasmonic metamaterials exhibiting electromagnetically induced transparency

We study the phenomenon of the electromagnetically induced transparency in planar and stacked plasmonic metamaterials (MMs) using the finite integration time domain and finite element methods. For such structures, the dependence of the tunability of the inherent structural resonances on geometry design is clarified. We also analyze the performance of recently demonstrated MM designs in terms of the achievable group refractive index and losses, which are of great interest for slowing light applications.

3D fabrication of waveguide and grating coupler in SU-8 by optimized gray scale electron beam lithography

Gray scale electron beam lithography is optimized for simple and accurate prototyping of 3D waveguides and grating output couplers in SU-8. Gratings with complex profiles and free of lag effect can be realized with this technique.

Gray scale E-beam lithography to fabricate 3D microsized waveguide and grating coupler in SU-8

Gray scale electron beam lithography is applied to prototype 3D waveguides and grating output couplers in SU-8 with simple and accurate method. The lag effect in reactive ion etching of Silicon-on-insulator gratings is avoided here.

Linear birefringence in split-ring resonators.

We study polarization-dependent transmission of light through arrays of single-slit split-ring resonator (SSRR) based systems at normal incidence using finite integration time domain (FITD) and finite element methods (FEM). It is found that a conventional planar array of SSRRs acts as an effective optical wave plate at certain polarizations of incident light. The effect is attributed to the intrinsic linear birefringence of individual SSRRs. A comparison is made with other split-ring resonator-based systems exhibiting wave-plate-like properties due to inter-SSRR coupling.

Refractive index sensor performance based on enhanced transmission of light through perforated metallic films

The transmission of light through a thin Au film with periodic subwavelength double nanoholes at normal incidence is analyzed numerically and compared to other conventional hole shapes. The performance of such perforated metallic films as a potential refractive index sensor is discussed.

Physical reason behind far-field transmission resonances from U-shaped metallic structures

The far-field transmission spectrum of crescent-like metallic nanostructures on a glass substrate at normal incidence is studied numerically. The interpretation of transmission resonances arising from a periodic subwavelength U-shaped metal nanostructure in terms of plasmonic eigen modes is revisited.

Impact of dielectric permittivity of a substrate on the THz scattering enhanced due to near-field effect

Enhanced scattering of the THz radiation caused by the interaction of near field component with plasmons in a substrate material results in sub-wavelength resolution within THz range. Variation of dielectric permittivity of organic materials placed on a metal substrate can improve contrast of the image obtained with such a technique.

Pulsed THz Radiation in near-Field Domain: Enhanced Scattering and Exceeding Diffraction Limitations

SNOM technique used in THz range demonstrates enhanced scattering in far-field region and increased resolution of the scanned image. We develop a rigorous numerical model which can properly describe both these phenomena.