Band-Gap Engineering in two-dimensional periodic photonic crystals

A theoretical investigation is made of the dispersion characteristics of plasmons in a two-dimensional periodic system of semiconductor (dielectric) cylinders embedded in a dielectric (semiconductor) background. We consider both square and hexagonal arrangements and calculate extensive band structures for plasmons using a plane-wave method within the framework of a local theory. It is found that such a system of semiconductor-dielectric composite can give rise to huge full band gaps (with a gap to midgap ratio $\approx 2$) within which plasmon propagation is forbidden. The most interesting aspect of this investigation is the huge lowest gap occurring below a threshold frequency and extending up to zero. The maximum magnitude of this gap is defined by the plasmon frequency of the inclusions or the background as the case may be. In general we find that greater the dielectric (and plasmon frequency) mismatch, the larger this lowest band-gap. Whether or not some higher energy gaps appear, the lowest gap is always seen to exist over the whole range of filling fraction in both geometries. Just like photonic and phononic band-gap crystals, semiconducting band-gap crystals should have important consequences for designing useful semiconductor devices in solid state plasmas.Comment: 16 pages, 5 figure

Self-organized synchronization of mechanically coupled resonators based on optomechanics gain-loss balance

We investigate collective nonlinear dynamics in a blue-detuned optomechanical cavity that is mechanically coupled to an undriven mechanical resonator. By controlling the strength of the driving field, we engineer a mechanical gain that balances the losses of the undriven resonator. This gain-loss balance corresponds to the threshold where both coupled mechanical resonators enter simultaneously into self-sustained limit cycle oscillations regime. Rich sets of collective dynamics such as in-phase and out-of-phase synchronizations therefore emerge, depending on the mechanical coupling rate, the optically induced mechanical gain and spring effect, and the frequency mismatch between the resonators. Moreover, we introduce the quadratic coupling that induces enhancement of the in-phase synchronization. This work shows how phonon transport can remotely induce synchronization in coupled mechanical resonator array and opens up new avenues for metrology, communication, phonon-processing, and novel memories concepts.Comment: Comments are welcome

Parametrically enhancing sensor sensitivity at an exceptional point

We propose a scheme to enhance the sensitivity of Non-Hermitian optomechanical mass-sensors. The benchmark system consists of two coupled optomechanical systems where the mechanical resonators are mechanically coupled. The optical cavities are driven either by a blue or red detuned laser to produce gain and loss, respectively. Moreover, the mechanical resonators are parametrically driven through the modulation of their spring constant. For a specific strength of the optical driving field and without parametric driving, the system features an Exceptional Point (EP). Any perturbation to the mechanical frequency (dissipation) induces a splitting (shifting) of the EP, which scales as the square root of the perturbation strength, resulting in a sensitivity-factor enhancement compared with conventional optomechanical sensors. The sensitivity enhancement induced by the shifting scenario is weak as compared to the one based on the splitting phenomenon. By switching on parametric driving, the sensitivity of both sensing schemes is greatly improved, yielding to a better performance of the sensor. We have also confirmed these results through an analysis of the output spectra and the transmissions of the optical cavities. In addition to enhancing EP sensitivity, our scheme also reveals nonlinear effects on sensing under splitting and shifting scenarii. This work sheds light on new mechanisms of enhancing the sensitivity of Non-Hermitian mass sensors, paving a way to improve sensors performance for better nanoparticles or pollutants detection, and for water treatment.Comment: 12 pages, 5 figures. Comments are welcom

Optomechanic Coupling in Ag Polymer Nanocomposite Films

[Image: see text] Particle vibrational spectroscopy has emerged as a new tool for the measurement of elasticity, glass transition, and interactions at a nanoscale. For colloid-based materials, however, the weakly localized particle resonances in a fluid or solid medium renders their detection difficult. The strong amplification of the inelastic light scattering near surface plasmon resonance of metallic nanoparticles (NPs) allowed not only the detection of single NP eigenvibrations but also the interparticle interaction effects on the acoustic vibrations of NPs mediated by strong optomechanical coupling. The “rattling” and quadrupolar modes of Ag/polymer and polymer-grafted Ag NPs with different diameters in their assemblies are probed by Brillouin light spectroscopy (BLS). We present thorough theoretical 3D calculations for anisotropic Ag elasticity to quantify the frequency and intensity of the “rattling” mode and hence its BLS activity for different interparticle separations and matrix rigidity. Theoretically, a liquidlike environment, e.g., poly(isobutylene) (PIB) does not support rattling vibration of Ag dimers but unexpectedly hardening of the extremely confined graft melt renders both activation of the former and a frequency blue shift of the fundamental quadrupolar mode in the grafted nanoparticle Ag@PIB film