Increase Of Effective Refractive Index Research Articles

Detailed balance analysis of plasmonic metamaterial perovskite solar cells.

Whether dispersal of plasmonic nanoparticles (NPs) within a perovskite active layer can increase the efficiency of solar cells is a long-standing question. It is well known that inclusion of metallic NPs in an active layer can boost the surrounding near-field intensity around them owing to the dipolar localized surface plasmon resonance (LSPR, also called antenna effect), which can increase light absorption by solar cells. However, the use of plasmonic NPs in perovskite solar cells has been barely reported, and it is not known whether inserting plasmonic NPs into a perovskite active layer produces any performance advantage compared with a pure perovskite counterpart. We explore the fundamental and practical limits of "plasmonic metamaterial" perovskite solar cells by applying effective medium theory and a detailed balance analysis. Our results indicate that an increase in effective refractive index of perovskite through dispersed plasmonic NPs can in principle enhance the performance of solar cells.

Performance analysis of a liquid-filled glass prism-coupled metal-clad planar waveguide sensor

The performance of a metal-clad planar waveguide-based sensor coupled with a liquid-filled prism is studied and is compared with a similar waveguide sensor coupled with a solid prism. The characteristic equations of these waveguides are obtained by matching field components at various boundaries, and the reflectivity of these waveguides is obtained using transfer matrix method. The obtained dispersion characteristic shows that the transverse electric field components are loosely bound in liquid-filled prism-coupled waveguide-based sensor. Unlike to solid prism-coupled waveguide sensor, the performance of liquid-filled prism-coupled waveguide sensor increases with increase of effective refractive index. Hence, the proposed liquid-filled prism-coupled waveguide-based sensor shows better performance at high effective refractive index.

Enhanced-gain printed slot antenna using an electric metasurface superstrate

In this article, a method to enhance the radiation characteristics of a slot antenna by using an electric metasurface as a high refractive index superstrate has been presented. The gain enhancement mechanism described here uses the phenomena of enhanced space field by increasing the effective aperture of the antenna, resulting from increase in effective refractive index of the metasurface. As a fundamental constituent of the superstrate, a unit cell of the metasurface composed of symmetrically placed triple pairs of split-ring resonators is introduced. The unit cell of such metasurface has been configured to realize a high refractive index by using the principle of nearest-neighbor coupling. An equivalent circuit model is developed to understand the influence of coupling on the effective refractive index of the metasurface. The presence of the metasurface as a superstrate enhances the broadside gain of the slot by 8.71 dB and the efficiency by 20.35 %. The total height of the proposed configuration is 0.237 λ 0 where λ 0 is the free space wavelength at the resonance frequency of the slot antenna.

Highly efficient tunable optical filter based on liquid crystal micro-ring resonator with large free spectral range

A highly efficient tunable optical filter of liquid crystal (LC) optical micro-ring resonator (MRR) was proposed. The 4-μm-radius ring consists of a silicon-on-insulator (SOI) asymmetric bent slot waveguide with a LC cladding. The geometry of the slot waveguide resulted in the strong electro-optic effect of the LC, and therefore induced an increase in effective refractive index by 0.0720 for the quasi-TE mode light in the slot-waveguide. The ultra-wide tuning range (56.0 nm) and large free spectral range (FSR) (~28.0 nm) of the optical filters enabled wavelength reconfigurable multiplexing devices with a drive voltage of only 5 V. The influences of parameters, such as the slot width, total width of Si rails and slot shift on the device’s performance, were analyzed and the optimal design was given. Moreover, the influence of fabrication tolerances and the loss of device were both investigated. Compared with state-of-the-art tunable MRRs, the proposed electrically tunable micro-ring resonator owns the excellent features of wider tuning ranges, larger FSRs and ultralow voltages.

Surface layer reflective index changes of Au nanoparticle functionalized porous silicon microcavity for DNA detection

A technique is demonstrated to detect DNA hybridization based on surface layer of Au/porous silicon microcavity (Au/PSM) substrate for very small amount of biomolecules. Simulations show that the increase of effective refractive index for the first layer of PSM will cause a blue shift for its reflectance spectrum, and the blue shift becomes less with the increase of refractive index for one more layers. In experiments, such a blue shift of reflectance spectrum of PSM comes from the increase of refractive index by DNA hybridization on the surface. The detection limit of Au/PSM biosensor is 15.15 nM for 19-base pair DNA, which is comparable to that of reported biosensors based on porous silicon (PS). Therefore such an Au/PSM could be very useful to develop simple, rapid and sensitive optical biosensors when the amount of target is very small.

Surface enhanced Raman scattering and localized surface plasmon resonance of nanoscale ultrathin films prepared by atomic layer deposition

An approach was proposed to characterize nanoscale ultrathin films using surface enhanced Raman scattering (SERS). Raman spectroscopy of the TiO2 film as thin as ∼2 nm, which was prepared by atomic layer deposition, was obtained by depositing a nanostructured Au layer on the film surface. Red-shift in the extinction spectrum of the nanostructured Au layer was observed with increasing TiO2 film thickness, ascribed to the increase in effective refractive index of the substrate slab and coupled plasmon resonance. This SERS technique can be applied to investigate a variety of solid-state ultrathin films in nanosclae materials and devices in future studies.

Combining micro- and nano-texture to fabricate an antireflective layer

We combined photonic crystal (PC) and nanoporous structures in silicon (Si) to decrease the reflectance of the Si surface. Due to gradual increase of effective refractive index in this structure, reflection is reduced drastically over a broad spectral range. A two-dimensional Si PC was fabricated by interference lithography, then a nanoporous structure was made on the PC by using metal-assisted chemical etching. The obtained reflectance is about 3% across a spectral range of 400 to 2000 nm. This indicates an improvement of reflectance up to 90% compared to bare Si.

Effects of medium composition on optical properties and microstructures of non-close-packed colloidal crystalline arrays

The effects of medium composition on the optical properties and microstructures of non-close-packed silica colloidal crystalline arrays have been demonstrated. Water–alcohol mixtures were used as dispersion media for these arrays. Optical properties and microstructures were examined using angle-resolved reflection spectra measurements. The Bragg diffraction peaks of the colloidal crystalline arrays shifted with changing of concentration or hydrocarbon number of alcohol. With an increase in concentration or hydrocarbon number of alcohol, the effective refractive index of the dispersion increased and the interplanar spacing of the colloidal crystalline array decreased. The increase in effective refractive index was caused by an increase in the refractive index of the mixed medium with the change in solvent. The decrease in interplanar spacing of the array was caused by decreased electrostatic repulsions between the silica spheres with decreasing dielectric constant. The current work suggests new possibilities for the control of optical properties and microstructures of colloidal crystalline arrays.