Study on epsilon crossover wavelength tuning of heavily doped germanium-on-silicon in mid-infrared range

Exploring the resonance absorption of subwavelength-patterned epitaxial-grown group-IV semiconductor composite structures

We experimentally and theoretically demonstrate a mid-infrared perfect absorber with all group-IV epitaxial layered composite structures. The multispectral narrowband strong absorption (>98%) is attributed to the combined effects of the asymmetric Fabry-Perot (FP) interference and the plasmonic resonance in the subwavelength-patterned metal-dielectric-metal (MDM) stack. The spectral position and intensity of the absorption resonance were analyzed by reflection and transmission. While a localized plasmon resonance in the dual-metal region was found to be modulated by both the horizontal (ribbon width) and vertical (spacer layer thickness) profile, the asymmetric FP modes were modulated merely by the vertical geometric parameters. Semi-empirical calculations show strong coupling between modes with a large Rabi-splitting energy reaching 46% of the mean energy of the plasmonic mode under proper horizontal profile. A wavelength-adjustable all-group-IV-semiconductor plasmonic perfect absorber has potential for photonic-electronic integration.

Tunable Berreman mode in highly conductive organic thin films

The unique performances of Epsilon-near-zero (ENZ) materials allow them to play a crucial role in many optoelectronic devices and have spawned a wide range of inventive uses. In this paper, we found that the modified PEDOT:PSS film formed with a kind of so-called "Metastable liquid-liquid Contact (MLLC)" solution treatment method can achieve a wide tuning of ENZ wavelength from 1270 nm to 1550 nm in the near-infrared region. We further analyzed the variation trend of imaginary permittivity for these samples with different ENZ wavelengths. The Berreman mode was successfully excited by a simple structural design to realize a tunable polarization absorber.

Programmable field localization and enhancement effects on a non-structured planar surface with a permittivity gradient

We demonstrate electromagnetic field localization and enhancement effects on the non-structured planar surface of a two-dimensional gradient permittivity material. Surface plasmons are excited by a normally-incident Gaussian illumination beam and are confined to subwavelength rings on the surface of the gradient permittivity material. The performance of the surface is programmable by adjusting the permittivity distribution of the material and polarization of incident light. We show that field localization and enhancement effects can be realized at mid-infrared frequencies by conventional semiconductor materials with designed doping distributions. This demonstration suggests a compact and readily accessible platform for materials characterizations with spatially controlled illumination, providing a convenient approach to explore nanospectroscopy and light-matter interactions of nanomaterials, such as quantum dots, nanowires, and organic molecules.