We address the behavior of mid-infrared localized plasmon resonances in elongated germanium antennas integrated on silicon substrates. Calculations based on Mie theory and on the experimentally retrieved dielectric constant allow us to study the tunability and the figures of merit of plasmon resonances in heavily-doped germanium and to preliminarily compare them with those of the most established plasmonic material, gold.
The use of heavily doped semiconductors to achieve plasma frequencies in the mid-IR has been recently proposed as a promising way to obtain high-quality and tunable plasmonic materials. We introduce a plasmonic platform based on epitaxial n-type Ge grown on standard Si wafers by means of low-energy plasma-enhanced chemical vapor deposition. Due to the large carrier concentration achieved with P dopants and to the compatibility with the existing CMOS technology, SiGe plasmonics hold promises for mid-IR applications in optoelectronics, IR detection, sensing, and light harvesting. As a representative example, we show simulations of mid-IR plasmonic waveguides based on the experimentally retrieved dielectric constants of the grown materials.
We present a compact real-time multispectral camera operating in the mid-infrared wavelength range. Multispectral images of a scene with two differently spectrally signed objects and of a burning solid propellant will be shown. Ability of real-time acquisition will thus be demonstrated and spectra of objects will be retrieved thanks to inversion algorithm applied on multispectral images.
We study experimentally and theoretically band-pass filters based on guided-mode resonances in free-standing metal-dielectric structures with subwavelength gratings. A variety of filters are obtained: polarizing filters with lD gratings, and unpolarized or selective polarization filters with 2D gratings, which are shown to behave as crossed-lD structures. In either case, a high transmission (up to ≈ 79 %) is demonstrated, which represents an eight-fold enhancement compared to the geometrical transmission of the grating. We also show that the angular
sensitivity strongly depends on the rotation axis of the sample. This behavior is explained with a detailed description of the guided-mode transmission mechanism.
We present the experimental study of a new design of band-pass filter based on guided-mode resonances in a
free-standing metal-dielectric structure with subwavelength gratings. Component consists of a subwavelength
gold grating with narrow slits deposited on a silicon nitride membrane. High optical transmission is measured
with up to 78% transmission at resonance. Experimental angularly resolved spectra are presented: they reveal
the role of the diffracted orders and of the waveguide eigenmode in the resonance. Spectra have a typical profile of
Fano resonances: we show that this profile is due to interferences between a direct transmission channel through
the 0th order, and an indirect transmission channel which results from the excitation by the ±1 diffracted orders
of a waveguide eigenmode.
We will present a brief overview of the interest in subwavelength gratings for spectral filtering in the mid-infrared wavelength range. Guided-mode, plasmonic and dipolar resonances will be considered. We will particularly focus on components fabricated in our laboratories, achieving band-pass or cut-band filtering. Optical characterization will be shown, revealing resonances with high quality factors. Multispectral camera has been realized by integrating our components into a cooled infrared focal plane array.