Photonics and Nanostructures-Fundamentals and Applications最新文献

The design of plasmonic metasurfaces is often based on solving the Maxwell electromagnetic equations, which can be a time-consuming and expensive process considering many geometrical parameters that can limit design flexibility. To speed up the design flow, a model based on the classical transmission line theory is presented. The proposed equivalent circuit model can predict the plasmon resonance wavelength based on various geometrical parameters including dielectric thickness and disk diameter. In addition, unlike other reported circuit models, the developed model considers the nanostructure array pitch size, which is crucial in metasurface design. Comparison between the results obtained from circuit model and full wavelength simulation showed that the circuit parameters accurately determine the response of the structure. Finally, as a metasurface design demonstration, we utilized our model to simulate aluminum-based gap-plasmon nanodisk arrays for optimizing their optical response to maximize structural color saturation.

In this work, we present wavelength splitting characteristics of whispering gallery modes in a system where two disks with different refractive indices are coupled together. This study utilizes finite difference time domain based simulations. The spectral changes caused by the presence of nanoparticles are analyzed, taking factors such as the number of nanoparticles, their size and distance from the surface of the disks into account. The investigation also encompasses the interaction of a thin nanolayer. Our findings demonstrate that the wavelength splitting is highly influenced by the specific disk where the nanoparticle or nanolayer is located. This distinct property sets it apart from conventional coupled disks with identical features. A perturbation theory of coupled structures has also been applied to gain insights into the simulation results.

We have experimentally demonstrated an ultra-high sensitivity gold-based fiber refractive index (RI) sensor whose main structure is composed of multimode fiber (MMF) and photonic crystal fiber (PCF). The gold film is deposited on V-shaped PCF by magnetron sputtering, and sensing experiments are performed based on the principle of surface plasmon resonance (SPR). Numerical simulation results indicate that the cladding mode of the V-shaped PCF is more capable of stimulating the SPR effect than the core mode. The experimental results show that the RI measurement range of the sensor is 1.333–1.421, with a maximum sensitivity of 10015 nm/RIU. In addition to RI sensing, sensing probes can be coated with polydimethylsiloxane (PDMS) on a gold film for temperature sensing. For temperature detection, the range is from 10 to 100 °C and the maximum sensitivity is 3.5 nm/℃. Besides high sensitivity in RI measurement, the proposed sensor also has good sensing performance in temperature sensing. With the advantages of high sensitivity, good stability, and easy preparation, this sensor has become an important reference in the field of high-performance sensing.

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.