: In this work, we report the experimental results and theoretical analysis of strong localization of resonance transmission modes generated by hybrid periodic/quasiperiodic heterostructures (HHs) based on porous silicon. The HHs are formed by stacking a quasiperiodic Fibonacci (FN) substructure between two distributed Bragg reflectors (DBRs). FN substructure defines the number of strong localized modes that can be tunable at any given wavelength and be unfolded when a partial periodicity condition is imposed. These structures show interesting properties for biomaterials research, biosensor applications and basic studies of adsorption of organic molecules. We also demonstrate the sensitivity of HHs to material infiltration.

: Theoretical demonstration and experimental evidence of photon Bloch oscillations and Wannier-Stark ladders (WSLs) in dual-periodical (DP) multilayers, based on porous silicon, are presented. An introduction of the linear gradient in refractive indices in DP structure, which is composed by stacking two different periodic substructures N times, resulted in the appearance of WSLs. Theoretical time-resolved reflection spectrum shows the photon Bloch oscillations with a period of 130 fs. Depending on the values of the structural parameters, one can observe the WSLs in the near infrared or visible region which may allow the generation of terahertz radiation with a potential applications in several fields like imaging.

The propagation of longitudinal acoustic waves in multilayer structures based on porous silicon and the experimental measurement of acoustic transmission for the structures in the gigahertz range are reported and studied theoretically. The considered structures exhibit band gaps in the transmission spectrum and these are localized modes inside the band gap, coming from defect layers introduced in periodic systems. The frequency at which the acoustic resonances appear can be tuned by changing the porosity and/or thickness of the defect layer.

Using analytical results for viscous dissipation in phononic crystals, we calculate the decay coefficient of a sound wave propagating at low frequencies through a two-dimensional phononic crystal with a viscous fluid background. It is demonstrated that the effective acoustic viscosity of the phononic crystal may exceed by two to four orders of magnitude the natural hydrodynamic viscosity of the background fluid. Moreover, the decay coefficient exhibits dependence on the direction of propagation; that is, a homogenized phononic crystal behaves like an anisotropic viscous fluid. Strong dependence on the filling fraction of solid scatterers offers the possibility of tuning the dissipative decay length of sound, which is an important characteristic of any acoustic device. This article is part of the theme issue ‘Wave generation and transmission in multi-scale complex media and structured metamaterials (part 2)’.

This paper briefly presents some relevant aspects of an innovative educational resource that allows real experimentation through Internet in the area of electronics. The developed platform, named eLab3D, is based in a 3D environment in which the user can conduct all the operations that he/she would carried out in a hands-on laboratory. The authors intend to demonstrate the basic operation of the platform to perform electronics experiments.

We present an experimental study of the resonance modes in dual-periodical multilayer structures based on porous silicon. These multilayered structures are composed by stacking $N$ times two substructures $A$, and $B$, i.e., ${(A_n{B}_m)}^N$. The $A_n$ and $B_m$ are in turn composed of two different period units, $a$ and $b$, respectively, where subscripts $n$ and $m$ are the period number in the $a$ and $b$ substructures. Both substructures $a$ and $b$ consist of a pair of alternating layers with high and low refractive indices $n_1$ and $n_2$, respectively. The thickness parameters of the dielectric layers in $a$ and $b$ are all different. We observe several resonance transmission peaks due to the periodical repetition of the $A_n{B}_m$ structure. The number of resonance peaks, their full width at half-maximum (FWHM), etc., can be controlled by selecting the structural parameters of the system. The experimental data are in good agreement with those calculated using the transfer matrix method. These optical superlattices are very promising, since they can be designed so that the reflectance response presents a determined number of resonance modes in the most important window for optical communications, making them good candidates for direct applications.