RESUMEN
GeSn alloys are promising materials for CMOS-compatible mid-infrared lasers manufacturing. Indeed, Sn alloying and tensile strain can transform them into direct bandgap semiconductors. This growing laser technology however suffers from a number of limitations, such as poor optical confinement, lack of strain, thermal, and defects management, all of which are poorly discussed in the literature. Herein, a specific GeSn-on-insulator (GeSnOI) stack using stressor layers as dielectric optical claddings is demonstrated to be suitable for a monolithically integration of planar Group-IV semiconductor lasers on a versatile photonic platform for the near- and mid-infrared spectral range. Microdisk-shape resonators on mesa structures were fabricated from GeSnOI, after bonding a Ge0.9Sn0.1 alloy layer grown on a Ge strain-relaxed-buffer, itself on a Si(001) substrate. The GeSnOI microdisk mesas exhibited significantly improved optical gain as compared to that of conventional suspended microdisk resonators formed from the as-grown layer. We further show enhanced vertical out-coupling of the disk whispering gallery mode in-plane radiation, with up to 30% vertical out-coupling efficiency. As a result, the GeSnOI approach can be a valuable asset in the development of silicon-based mid-infrared photonics that combine integrated sources in a photonic platform with complex lightwave engineering.
RESUMEN
A thermal antenna is an electromagnetic source that emits in its surrounding a spatially coherent field in the infrared frequency range. Usually, its emission pattern changes with the wavelength so that the heat flux it radiates is weakly directive. Here, we show that a class of hyperbolic materials of type II possess a Brewster angle, which is weakly dependent on the wavelength, so that they can radiate like a true thermal antenna with a highly directional and p-polarized heat flux. The realization of these sources could open a new avenue in the field of thermal management in far-field regime.
RESUMEN
Impulsive interband excitation with femtosecond near-infrared pulses establishes a plasma response in intrinsic germanium structures fabricated on a silicon substrate. This direct approach activates the plasmonic resonance of the Ge structures and enables their use as optical antennas up to the mid-infrared spectral range. The optical switching lasts for hundreds of picoseconds until charge recombination redshifts the plasma frequency. The full behavior of the structures is modeled by the electrodynamic response established by an electron-hole plasma in a regular array of antennas.
RESUMEN
Symmetric metal-dielectric guided-mode resonators (GMR) can operate as infrared band-pass filters, thanks to high-transmission resonant peaks and good rejection ratio. Starting from matrix formalism, we show that the behavior of the system can be described by a two-mode model. This model reduces to a scalar formula and the GMR is described as the combination of two independent Fabry-Perot resonators. The formalism has then been applied to the case of asymmetric GMR, in order to restore the properties of the symmetric system. This result allows designing GMR-on-substrate as efficient as free-standing systems, the same high transmission maximum value and high quality factor being conserved.
RESUMEN
Midinfrared plasmonic sensing allows the direct targeting of unique vibrational fingerprints of molecules. While gold has been used almost exclusively so far, recent research has focused on semiconductors with the potential to revolutionize plasmonic devices. We fabricate antennas out of heavily doped Ge films epitaxially grown on Si wafers and demonstrate up to 2 orders of magnitude signal enhancement for the molecules located in the antenna hot spots compared to those located on a bare silicon substrate. Our results set a new path toward integration of plasmonic sensors with the ubiquitous CMOS platform.
RESUMEN
Optical Helmholtz resonators (OHRs) have been adapted from acoustics designs for light absorbing structures, exhibiting extreme light confinement. Here, extraordinary transmission of light is theoretically demonstrated through symmetric OHRs, comprising a cavity with two λ/500 narrow slits on either side. This device has appealing features to act as a spectral bandpass filter in the context of multispectral imaging, in particular its high angular tolerance because of the localized nature of the resonance. Besides, the cavity can be modeled as an inductor and the two slits can be modeled as capacitors, the whole design acting as a LC circuit thus preventing any harmonic features.
RESUMEN
We theoretically study metal-dielectric structures made of bi-atomic metallic gratings coupled to a guided-mode dielectric resonator. The bi-atomic pattern grating allows tailoring of the Fourier spectrum of the inverse grating permittivity in order to adapt the frequency gap and obtain a flat dispersion band over a wide angular range. A significant enhancement (two-fold) of the angular tolerance as compared to a simply periodic structure is obtained.
RESUMEN
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 1D gratings, and unpolarized or selective filters with 2D gratings, which are shown to behave as two crossed-1D 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.
RESUMEN
We present the experimental study of a free-standing metallic guided-mode resonant structure, for bandpass filtering applications in the mid-IR wavelength range. Structure 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. Angularly resolved spectra are presented revealing Fano-type resonance.