Photonics and Nanostructures-Fundamentals and Applications最新文献

Manipulating surface plasmon polariton waves for the development of micro-nano devices has been widely studied in recent years. Two-dimensional artificial photonic crystals have bandstructure characteristics like semiconductors. However, the requirement for light to be incident along the structural periodic direction poses a challenge in coupling light into the photonic crystal, thereby impeding its integrations and applications. In this work, we proposed coupling vertically incident left-circularly polarized light into a photonic crystal waveguide using a chiral plasmonic lens. Linearly-polarized light can also generate surface plasmon polariton waves and couple them into photonic crystal waveguides, but the intensity is lower. In contrast, right-circularly polarized light propagates in the opposite direction and exhibits minimal propagation into the photonic crystal waveguide. The results indicate that the proposed structure can operate broadband within the wavelength range of 620–670 nm. This method provides a simple and easily integrated coupling method for photonic crystal devices.

This work proposes an inverse design tool for porous silicon photonic structures. This tool is based on 2D-convolutional mixture density neural networks given that this type of architecture allows to tackle the nonuniqueness problem present in the optical response of photonic crystals. Moreover, a preprocessing reshaping method was implemented to use 2D-convolution neural networks due to their powerful ability in pattern recognition. A data set of porous silicon photonic spectra was generated. The photonic structures consist of 12 assembled layers of different thicknesses and porosities, generating incommensurate one-dimensional photonic crystals. The model was tested with four test data sets. First, a periodic validation was carried out, showing that incommensurate structures can generate well-defined photonic bandgaps. The second test set found that incommensurate photonic structures can resemble the optical response of a modulated photonic crystal and retrieve defective modes within the bandgap. The third test data set consisted of ideal distributed Bragg reflectors. It was found that the neural network could not predict accurate design due to the notorious differences in the optical properties of the two structures. Last, the neural network was tested with the experimental spectrum of a porous silicon photonic crystal, and it was shown that the predictions made were inaccurate because the simulations did not consider critical experimental aspects.

This article examines the role of field strength, frequency, and many-body scattering during the ultrafast optoelectronic response in a direct-gap semiconductor nanowire using numerical simulation. Following resonant laser excitation, an AC or bias DC field perturbs the 1D e-h plasma as it relaxes by carrier-phonon and Coulomb scattering. For bias DC fields, the laser-excited carrier distributions evolve to a static non-equilibrium from which a stable DC mobility is calculated. Carrier-phonon collisions contain the e-h carriers near energy minima for fields of 0.5 kV/cm or less, while the Coulomb collisions redistribute some electrons across the Brillouin zone where they drift into other band structure energy minima and are there contained by phonon scattering. This behavior results in carrier mobilities with a field-strength dependence specific to a 1D solid. For AC probe fields, the analyze the resulting frequency-dependent conductivity for frequencies between the plasmon frequency and interband resonance. In all cases, we compare results to standard-conductivity models by calculating distribution-averaged collision rates and times, and show how, unlike in the bulk, these quantities for the nanowire are strongly dependent on both field magnitude and frequency.

In this work, a single nanoparticle sensor based on a slot-bridge-slot photonic crystal nanobeam cavity is presented. To investigate the sensor feasibility of a single particle detection, the shift of the resonance wavelength of the cavity mode is calculated by employing perturbation theory and the simulation results of the mode profile. A mode volume of $2.61\times {10}^{-3}{\left(\lambda /n\right)}^3$is realized, which is reduced by a factor of $150$ times in comparison with nanobeam cavity. We demonstrate the detection of streptavidin molecules with radius ∼ 2.65 nm with a large resonant wavelength shift (25.4 pm). This represents the largest wavelength shift ever reported in single nanoparticle sensors. Owing to the ultracompact footprint and high sensitivity demonstrated here, the proposed structure holds great potential for lab-on-a-chip biosensing applications.

Cellulose acetate is a safe, sustainable, and cost-effective material that is capable of forming nanostructures through facial processing methods such as surface imprinting. Forming optically active structures using cellulose acetate can advance green photonic device design. In this work, we create a hybrid material consisting of nanoscale plasmon active metal–semiconductor Schottky junctions. Demonstrating that such a hybrid material possesses improved performance when applied to Raman-based sensing. Boosting surface-enhanced Raman detection sensitivity through electromagnetic and chemical enhancement mechanisms from the metal-semiconductor junction, in addition to photonic resonances created via the imprinted nanoscale metamaterial array surface features. This work expands the use of cellulose-based materials for sensing-based applications.

Metasurfaces can extend the optical properties of conventional materials by structuring surfaces at a subwavelength scale. These artificial subwavelength surfaces mimic the physics of conventional materials and can, in principle, be designed to provide novel optical material properties. Metal-insulator-metal (MIM) antenna metasurfaces are among the most widely used as ideal absorbers and emitters. In this work, we present MIM metasurfaces in the mid-infrared that comply in the electric and magnetic forms of Babinet’s, Lorentz’s, and Kirchhoff’s principles. To verify the validity of Babinet's, Lorentz's, and Kirchhoff's MIM metasurfaces, we computed their reflection and absorption spectra as well as electric and magnetic field maps. We found that even in the presence of graphene on top of the electric and magnetic MIM metasurfaces, these principles still hold qualitatively. However, the excitation of gap surface plasmon polaritons (SPPs) and graphene SPPs fails to comply quantitatively. Additionally, we fabricated the MIM metasurfaces and used imaging Fourier transform infrared spectroscopy in the mid infrared spectrum to validate them. Finally, we explore the potentials and limits of the use of graphene as tunability material, with a tunability bandwidth up to 0.6 µm. Our findings can be applied to the development of electric and magnetic frequency selectivity metasurfaces, polarizers, coherent thermal sources, and detectors.

In this study, a grating with a Gaussian distribution was used to increase the absorption of light by amorphous silicon thin film solar cells. A grating is an effective structure for trapping light inside the active layer of a cell, so a two-dimensional Gaussian grating with a rectangular structure was placed on the front surface of the cell. The results obtained by using the finite element method showed that the Gaussian grating significantly enhanced the absorption of light in the visible and near-infrared ranges by a cell with a thickness of 0.5 μm compared with a cell without gratings and a cell with normal gratings. The maximum average light absorption by the cell with a Gaussian grating was 84.8%, which was 90% higher compared with the reference cell. In addition, the short-circuit current density and efficiency were determined as 34.2 and 17.6 mA/cm², respectively, which were 72% and 72.5% higher, respectively, compared with the reference cell. The proposed structure could be used in a cell to convert more light into electricity.

Optical excited photoconductive antennas are a central technology for the Terahertz (THz) domain, crucial for both emitting and detecting THz radiation. This work proposes and experimentally realises a new approach in digitated photoconductive antennas (d-PCAs) based on a single digitated high resistivity metal contact with integrated resistances as voltage dividers. This permits a uniform applied electric field over a large surface area and a single step device processing procedure, simplifying the device realisation. This concept is further combined with digitated plasmonic nano-antennas that permits to enhance the light-matter interaction. Through femtosecond optical excitation of such structures, THz pulses can be generated efficiently through this device. Further, for the plasmonic d-PCA, the detected THz electric field of the device shows the effect of polarisation of the incident IR beam, highlighting the role of the nanostructured digitated contacts. This work is supported by electromagnetic simulations showing the optical and THz response of this new type of photoconductive antenna with integrated resistances.

Thermoelectrically-coupled nanoantennas (TECNAs)—nanoantennas that use the Seebeck effect to detect radiation—are a promising modality for spectrally resolved detection in the infrared. By tailoring the geometry of a nanoantenna coupled to a micro-cavity, their responsivity and spectral selectivity can be carefully designed. However, to date no measurements have directly established the spectral response of these detectors over a large frequency span in the infrared regime, particularly from 2 μm to 20 μm. In this work, we provide a comprehensive analysis of the spectral selectivity of TECNAs operating within the mid- and long-wave infrared (MWIR and LWIR) regions. We engineer arrays of detectors at 5.5 μm, 10.6 μm, and 14 μm, and we verify their selectivity using polarization-dependent Fourier-transform infrared spectroscopy (FTIR). We also show that the response can be tailored using a combination of antenna and cavity design. Our results not only underscore the potential of TECNAs in advancing sensing applications within the MWIR and LWIR domains, but also offer a promising direction for enhancing other detector modalities.

This study investigates the enhancement and nanofocusing of a radially polarized electric field by a conical plasmonic structure (CPS). The CPS is a dielectric cone with nanometer metal cladding on a dielectric substrate. Concentric circular slanted grooves are etched on the surface of the dielectric substrate. These grooves converge the incident field on the structure. Angled periodic gratings are engraved on the CPS metal surface near the tip, creating a plasmonic momentum and contributing to the field enhancement above the apex. The symmetry of the incident radially polarized light and the structure significantly boosts nanofocusing and field enhancement. The optimal width of the nanofocusing and the electric field enhancement factor obtained are approximately 9 nm and 30000, respectively. Because of its impressive effects, this scheme is a valuable tool for plasmonic, optics, and laser applications.