A subwavelength near-infrared negative index material

Abstract

A single layer of a subwavelength negative index material ͑NIM͒ operating at a wavelength of 1 m is demonstrated. The geometrical parameters of the nanostructure are determined by characterizing its optical transmission spectrum. We show through photonic band calculations that these parameters give rise to a negative index in a corresponding bulk NIM. The fabrication inaccuracies in the dielectric spacer thickness that are likely to be introduced in a prism composed of multiple layers of this structure are shown through full-wave simulations to be within a range that preserves its negative refractive behavior.

Interferometric characterization of a sub-wavelength near-infrared negative index metamaterial

“…4a). This is due to the single cell resonance [12] that is responsible for the negative index band and the weak inter-layer interaction, which is necessary for inferring the bulk optical properties from single layer measurements [11]. There is, however, a substantial shift between the TM phase advances from scattering simulations in Fig.…”

“…Furthermore, a single layer of unit cells was also theoretically shown through the S-parameter method to possess a negative effective index [11]. Structural characterization and optical transmission measurements of a fabricated single-layer structure [12] indicate that its physical dimensions are consistent with the design of the NIM structure. In this work, we present experimental evidence for negative phase advance through this sample using a polarization interferometer.…”

“…A schematic of the near-infrared NIM unit cell [12], extending infinitely along the direction ẑ , is shown in Fig. 1.…”

“…However, transmission of the TE polarization [15] is sufficient for conducting polarization interferometry experiments described below. The NIM used for the interferometric measurement was fabricated using a combination of optical and electron beam lithography in 100µm x 100µm sample blocks on a glass substrate [12]. The dimensions of the NIM obtained by fitting the transmission spectra [12] give an Au strip and central layer thickness of t = 22nm, strip width W = 105nm, and thicknesses h t = 15nm and h b = 9nm for the top and bottom dielectric spacer layers, respectively.…”

“…The NIM used for the interferometric measurement was fabricated using a combination of optical and electron beam lithography in 100µm x 100µm sample blocks on a glass substrate [12]. The dimensions of the NIM obtained by fitting the transmission spectra [12] give an Au strip and central layer thickness of t = 22nm, strip width W = 105nm, and thicknesses h t = 15nm and h b = 9nm for the top and bottom dielectric spacer layers, respectively. The refractive indices used for theoretical fitting are 1.45 for the glass substrate, and 1.56 for the dielectric layers, as obtained from ellipsometry.…”