Search

High-contrast gratings (HCG) are an excellent candidate for label-free detection of various kinds of biomarkers because they exhibit sharp and sensitive optical resonances. In this work, we experimentally show the performance of pedestal HCG (PHCG), which is significantly enhanced in comparison with that of conventional HCG. PCHGs were found to provide a 11.2% improvement in bulk refractive index sensitivity, from 482 nm/RIU for the conventional design to 536 nm/RIU. The observed resonance was narrower, resulting in a higher Q-factor and figure of merit. By depositing Al2O3, HfO2, and TiO2 of different thicknesses as model analyte layers, surface sensitivity values were estimated to be 10.5% better for PHCG. To evaluate the operation of the sensor in solution, avidin was employed as a model analyte. For avidin detection, the surface of the HCG was first silanized and subsequently functionalized with biotin, which is well known for its ability to bind selectively to avidin. A consistent red shift was observed with the addition of each of the functional layers, and the analysis of the spectral shift for various concentrations of avidin made it possible to calculate the limit of detection (LoD) and limit of quantification (LoQ) for the structures. PHCG showed a LoD of 2.1 ng/mL and LoQ of 85 ng/mL, significantly better than the values 3.2 ng/mL and 213 ng/mL respectively, obtained with the conventional HCG. These results demonstrate that the proposed PHCG have great potential for biosensing applications, particularly for detecting and quantifying low analyte concentrations.

We present a comparative study of optical properties of aluminum nitride (AlN) thin films with different thicknesses. The films with thicknesses ranging from 66 to 303 nm were deposited by reactive sputtering and plasma enhanced atomic layer deposition (PEALD). Permittivity was extracted from an ellipsometry and Fourier-transform infrared (FTIR) spectroscopy reflection measurements. Our particular focus is on the influence of the deposition method and the film thickness on the AlN dielectric function. Here, we show that both PEALD-deposited and sputtered AlN films exhibit a monotonic dependence of negative permittivity on their thickness for vast mid-IR wavelengths including the reststrahlen band around 11.5–15 μm ( ∼ 870 – 667 cm − 1). By structural analysis, it was shown that PEALD-deposited layers contain a lower amount of oxygen and have smoother surfaces than deposited by the sputtering technique. On the other hand, sputtered films have higher densities and crystallinity, which results in the higher background permittivity ( ε ∞). In FTIR spectra of the PEALD-deposited layers, two specific features are observed, which can be explained by a higher concentration of nitrogen due to nitrogen-rich plasma in the ALD process. Such peculiarities of the optical properties of AlN films should be taken into account in potential applications of this material for metamaterials and nanostructured systems.

Optical sensors typically provide compact, fast and precise means of performing quantitative measures for almost any kind of measurand that is usually probed electronically. High-contrast grating (HCG) resonators are known to manifest an extremely sharp and sensitive optical resonance and can constitute a highly suitable sensing platform. In this paper we present two advanced high-contrast grating designs improving the sensing performances of conventional implementations. These configurations, namely pedestal and half-buried HCGs, allow to enhance the shift of the photonic resonance while maintaining the spectral features of the standard configuration. First, the spectral feature of the HCGs was numerically optimized to express the sharpest possible resonance when the structure is immersed in serum. Second, the sensing properties of conventional and advanced HCG implementations were studied by modelling the biological entities to be sensed as a thin dielectric coating layer of increasing thickness. Pedestal HCGs were found to provide a ∼ 12% improvement in sensitivity and a six-fold improvement in resonance quality factor (Q-factor), while buried HCGs resulted in a ∼ 58% improvement in sensitivity at the expense of a slightly broader resonance. Such structures may serve as an improved sensitive biosensing platform for near-infrared spectroscopy.

Photoluminescence including fluorescence plays a great role in a wide variety of applications from biomedical sensing and imaging to optoelectronics. Therefore, the enhancement and control of photoluminescence has immense impact on both fundamental scientific research and aforementioned applications. Among various nanophotonic schemes and nano-structures to enhance the photoluminescence, we focus on a certain type of nanostructures, hyperbolic metamaterials (HMMs). HMMs are highly anisotropic metamaterials, which produce intense localized electric fields. Therefore, HMMs naturally boost photoluminescence from dye molecules, quantum dots, nitrogen-vacancy centers in diamonds, per-ovskites and transition metal dichalcogenides. We provide an overview of various configurations of HMMs, including met-al-dielectric multilayers, trenches, metallic nanowires, and cavity structures fabricated with the use of noble metals, trans-parent conductive oxides, and refractory metals as plasmonic elements. We also discuss lasing action realized with HMMs.

High optical absorptivity or a large absorption cross-section is necessary to fully utilize the irradiation of light for photothermal heating. Recently, titanium nitride (TiN) nanostructures have been demonstrated to be robust optical absorbers in the optical range owing to their nonradiative decay processes enhanced by broad plasmon resonances. Because the photothermally generated heat dissipates to the surroundings, suppressing heat transfer from TiN nanostructures is crucial for maximizing the photothermal temperature increase. In the current work, compared to the planar TiN film, high-aspect-ratio TiN nanostructures with subwavelength periodicities have been demonstrated to enhance the photothermal temperature increase by a 100-fold using nanotube samples. The reason is attributed to the extremely anisotropic effective thermal conductivities. Our work has revealed that high-aspect-ratio TiN nanostructures are effective in improving photothermal heating, and they can be used in various applications, such as solar heating, chemical reactions, and microfluidics.

We theoretically analyze directional surface electromagnetic waves supported at an interface between an isotropic medium and anisotropic metal with effective uniaxial negative permittivity. We identify two types of surface wave solutions, resulting in unique hyperbolic dispersion in the wavevector space. Such anisotropic metal can be realized by alternating dielectric and metallic layers with deep subwavelength thicknesses or metallic nanowires in dielectric host. Such systems serve as a platform for many applications in nanophotonics.

Spin-orbital interaction of light attracts much attention in nanophotonics opening new horizons for modern optical systems and devices. The photonic spin Hall effect or Imbert-Fedorov shift takes a special place among the variety of spin-orbital interaction phenomena. It exhibits as a polarization-dependent transverse light shift usually observed in specular scattering of light at interfaces with anisotropic materials. Nevertheless, the effect of the polarization mixing caused by anisotropy on the Imbert-Fedorov shift is commonly underestimated. In this work, we demonstrate that polarization mixing contribution cannot be ignored for a broad range of optical systems. In particular, we show the dominant influence of the mixing term over the standard one for the polarized optical beam incident at a quarter-wave plate within the paraxial approximation. Moreover, our study reveals a novel contribution with extraordinary polarization dependence not observable within the simplified approach. We believe that these results advance the understanding of photonic spin Hall effect and open new opportunities for spin-dependent optical phenomena.

The mid-infrared (IR) wavelength region is widely utilized for absorption spectroscopy to detect molecules in gas, liquid, and solid phases by taking the advantage of characteristic infrared absorption peaks unique to molecular bonding. MidIR absorption spectroscopy offers a unique label-free detection method with a wide variety of applications from environmental monitoring to medical diagnosis. However, the challenge lies in the huge mismatch of molecular sizes, typically on the order of nanometer as opposed to microns of mid-IR wavelengths, making detection of low concentration of them extremely challenging. Various nanophotonic phenomena enable us to localize mid-IR light at nanoscale to enhance light absorption by molecules and thus sensitivity. We present an overview of nanophotonic phenomena, such as waveguide modes, both propagating and localized plasmon modes, together with micro- and nanostructured platforms that host these phenomena, including dielectric planar waveguides, photonic crystals, plasmonic, and phononic nanostructures.

Generalized Brewster effect is a phenomenon where light of both TE (S-) and TM (P-) polarization transmit through a surface with no reflection for a particular incident angle. Generalized Brewster angle (GBA) in visible and near-infrared (NIR) wavelength region is very useful in many scientific and technical areas of applications. However, it is very rare to find a material having this effect as it demands both dielectric and magnetic response in that wavelength range and usually magnetic response is extremely weak in the optical wavelengths. Here we demonstrate the GBA effect of an anisotropic material composed of highly ordered high aspect ratio aluminium doped zinc oxide (AZO) nanopillar arrays. Along with the experimental demonstration, we also provide a proper numerical analysis to investigate the origin of this effect in the pillar array system which will be useful for many conventional as well as new applications in photonics including protein sensing.

A photonic surface wave, a propagating optical mode localized at the interface of two media, can play a significant role in controlling the flow of light at nanoscale. Among various types of such waves, surface waves with hyperbolic dispersion or simply hyperbolic surface waves supported on anisotropic metal interfaces can be exploited to effectively control the propagation of lightwaves. We used semi-analytical and numerical methods to study the nature of surface waves on several configurations of three-layers metal–dielectric–metal systems including isotropic and anisotropic cases where the metal cladding layers were assumed to have infinite thickness. We used semi-analytical and numerical approaches to study the phenomena. We showed that the propagation of surface wave can be tuned from diverging to converging in the plane of the interface by the combination of metals with different anisotropic properties.

We looked at the typical resolution provided by microspheres in nanoobject imaging. The resolution was studied with two kinds of materials: high-index barium titanate glass and low-index polystyrene. Spheres of different sizes were taken, and thus we also checked if there is any dependence of the resolution capabilities on their dimensions. We concluded that, although we observed an increase in resolution for some of the spheres, practical considerations and lack of consistency in imaging makes this technique too cumbersome for practical applications.

We theoretically inspect, whether a recently proposed metamaterial solid immersion lens (a cluster of closely packed nanospheres) possesses super-resolving properties that could be used for subwavelength optical manipulation. Harnessing the multiple scattering theory for assembly of electric dipoles, we investigate the evanescent-wave and point-source-radiation transmission through the slab of nanospheres to establish the mechanism of super-resolution. Our calculations do not confirm resolution of subwavelength details using the metamaterial solid immersion lens.

In this communication, fabrication of high aspect ratio Al2O3/ZnO/Al2O3 nanotubes is reported and morphological changes at elevated temperatures are investigated. The structures were made by implementing several fabrication methods, such as deep-UV lithography, atomic layer deposition (ALD), and plasma etch methods. During the fabrication, the ALD deposited Al2O3 and ZnO conformally passivated the prepared Si-holes template, resulting in the complex coaxial Al2O3/ZnO/Al2O3 pillars. By utilizing several scanning and transmission electron microscopy techniques, it is experimentally shown that at elevated temperatures, internal voids form in the nanotube due to diffusion of ZnO into surrounding Al2O3 and also ZnAl2O4 spinel structure forms. Finally, the porous tubes have been isolated from the surrounding silicon core using a conventional isotropic selective Si plasma etch process. The presented approach opens the opportunity to build complex optical metamaterial compositions, for example, for a new generation of sensors for gas and biomarker detection.