We study theoretically the potentiality of dual phononic-photonic (the so-called phoxonic) crystals for liquid sensing
applications. We investigate the existence of well-defined features (peaks or dips) in the transmission spectra of acoustic
and optical waves and estimate their sensitivity to the sound and light velocities of the liquid environment. Two different
sensors are investigated. In the first one, we study the in-plane transmission through a two-dimensional (2D) crystal
made of cylindrical holes in a Si substrate where one row of holes is filled with a liquid. In the second one, the out of
plane propagation is investigated when considering the transmission of the incident wave perpendicular to a periodic
array of holes in a slab. Such ultra compact structure is shown to be a label-free, affinity-based acoustic and optical
nanosensor, useful for biosensing applications in which the amount of analyte can be often limited.
Transmission of acoustic waves through a periodic array of sub-wavelength slits or holes have been studied in several recent works in relation with physical phenomena such as resonant (extraordinary) transmission, broadband sound shielding or acoustic induced transparency (AIT). In this work, we present for the first time the study of analogous phenomena for Lamb waves propagating in a thin plate. We study the transmission through one or two rows of a periodic array constituted by thin bridges separated by rectangular holes. When two rows of such an array are considered, the choice of the distance between both rows allows the realization of a broadband attenuation up to 99% in the transmission. These investigations should have implications for sound isolation, filtering and sensing applications.
In this work, a trilayer graphene is used as a thin non dielectric spacer with a high index of refraction, between Au film
and Au NPs. Encouraged by the sharpness of the localized surface plasmon resonance LSPR induced by this system, we
performed sensitivity measurements to refractive index change in the surrounding medium of the sensor. The presence of
graphene led to both higher sensitivity and sharper full width at half maximum FWHM and thus higher figure of merit
FOM (2.8) compared to the system without graphene (2.1).
We study theoretically the potentiality of phononic and dual phononic-photonic (the so-called phoxonic) crystals for
liquid sensing applications. We investigate the existence of well-defined features (peaks or dips) in the transmission
spectra of acoustic and optical waves and evaluate their sensitivity to the sound velocity or refractive index of the liquid
environment. Several geometries are considered that can be divided into two sets depending on the direction of
propagation of the incident waves with respect to the phononic/photonic crystal, namely in-plane and out-of-plane
propagation configurations. In the first configuration, we study the in-plane transmission through a two-dimensional
(2D) crystal made of cylindrical holes in a Si substrate where one row of holes is filled with a liquid; possibly, the
infiltrated holes may have a different radius than the normal holes. Another geometry we have studied consists of a
periodic array of ridges on top of a thin Si membrane with incident waves parallel to the slab. In the out-of-plane
configuration, we calculate the transmission between two solid substrates connected by a periodic array of pillars as well
as the normally incident transmission upon a phoxonic crystal constituted by a periodic array of holes in a slab.
The concept of photonic and phononic crystal sensors is based on the measurement of changes in the transmission
properties of the devices caused by changes of material properties of one of the materials building the crystal. It has been
demonstrated that in the optical case the key parameter is the refractive index, i.e. speed of light, in the acoustic case it is
sound velocity. Both parameters can be measured with accuracy competitive with other optical and acoustic sensor
principles. A phoxonic crystal sensor combines both concepts in one device, therefore allowing for a dual parallel
determination of two independent material properties. Such a sensor is especially attractive for complex analytes as
common in chemistry and biochemistry. We have designed and modeled a phoxonic crystal consisting of a solid matrix
and holes where the central cavity acts as analyte container. We especially concentrate on the generation of a
characteristic feature within the transmission spectrum like a transmission peak within the phoxonic band gap where the
respective wavelength or frequency of maximum transmission is sensitive to material properties of the analyte. We could
show theoretically that a (geometric) defect is required in photonics whereas in phononics separation of the sensitive
peak is the challenge. The respective wavelength/frequency of maximum transmission moves in accordance to the
resonance conditions. We further analyze the transmission of light and sound through a phoxonic crystal plate at normal incidence.
Sub-micron waveguides and cavities have been shown to produce the confinement of elastic and optical waves in the
same devices in order to benefit from their interaction. It has been shown that square and honeycomb lattices are the
most suitable to produce simultaneous photonic and phononic band gaps on suspended silicon slabs. The introduction of
line defects on such "phoxonic" (or optomechanical) crystals should lead to an enhanced interaction between confined
light and sound. In this work we report on the experimental measurements of light guiding through waveguides created
in these kinds of two-dimensional photonic crystal membranes. The dimensions of the fabricated structures are chosen to
provide a "phoxonic" bandgap with a photonic gap around 1550 nm. For both kinds of lattice, we observe a high-transmission
band when introducing a linear defect, although it is observed for TM polarization in the honeycomb lattice
and for TE in the square. Using the plane-wave expansion and the finite element methods we demonstrate that the guided
modes are below the light line and, therefore, without additional losses beside fabrication imperfections. Our results lead
us to conclude that waveguides implemented in honeycomb and square lattice "phoxonic" crystals are a very suitable
platform to observe an enhanced interaction between propagating photons and phonons.
Periodic media offer impressive opportunities to manipulate the transport of classical waves namely light or sound.
Elastic waves can scatter light through the so-called acousto-optic interaction which is widely used to control
light in telecommunication systems and, additionally, the radiation pressure of light can generate elastic waves.
Concurrent control of both light and sound through simultaneous photonic-phononic, often called phoxonic, bandgap
structures is intended to advance both our understanding as well as our ability to manipulate light with
sound and vise versa. In particular co-localization of light and sound in phoxonic cavities could trigger nonlinear
absorption and emission processes and lead to enhanced acousto-optic effects. In the present communication,
we present our efforts towards the design of different phoxonic crystal architectures such as three-dimensional
metallodielectric structures, two-dimensional patterned silicon slabs and simple one-dimensional multilayers,
and provide optimum parameters for operation at telecom light and GHz sound. These structures can be used
to design phoxonic cavities and study the acousto-optic interaction of localized light and sound, or phoxonic
waveguides for tailored slow light-slow sound transport. We also discuss the acousto-optic interaction in onedimensional
multilayer structures and study the enhanced modulation of light by acoustic waves in a phoxonic
cavity, where a consistent interpretation of the physics of the interaction can be deduced from the time evolution
of the scattered optical field, under the influence of an acoustic wave.
Numerical simulations, based on a FDTD (finite-difference-time-domain) method, of infrared light propagation for
add/drop filtering in two-dimensional (2D) Ag-SiO<sub>2</sub>-Ag resonators are reported to design 2D Y-bent plasmonic
waveguides with possible applications in telecommunication WDM (wavelength demultiplexing). First, we study optical
transmission and reflection of a nanoscale SiO<sub>2</sub> waveguide coupled to a nanocavity of the same insulator located either
inside or on the side of a linear waveguide sandwiched between Ag. According to the inside or outside positioning of the
nanocavity with respect to the waveguide, the transmission spectrum displays peaks or dips, respectively, which occur at
the same central frequency. A fundamental study of the possible cavity modes in the near-infrared frequency band is also
given. These filtering properties are then exploited to propose a nanoscale demultiplexer based on a Y-shaped plasmonic
waveguide for separation of two different wavelengths, in selection or rejection, from an input broadband signal around
1550 nm. We detail coupling of the 2D add/drop Y connector to two cavities inserted on each of its branches.
We study theoretically and experimentally the variation in localized surface plasmon resonance (LSPR) structure
(λ<sub>max</sub>=660 nm) as a function of dielectric coating thickness. The influence of the morphology and interparticle distance
on the LSPR spectra of a glass/Au NSs interface with a constant thickness of diamond (NCD) overcoating was
investigated through the calculation of theoretical transmission spectra. Ajusting the theoretical curve to experimental
LSPR spectra allowed fixing the geometry of the plasmonic interface and permitted to evaluate the change in the
wavelength at maximum absorption (λ<sub>max</sub>) as a function of the thickness of the NCD overlayers. The theoretical data
were compared with experimental ones obtained on glass/AuNSs/ NCD surface.
Using the finite difference time domain method, we investigate theoretically the band structure and phonon transport in a
phononic crystal constituted by a periodical array of cylindrical dots deposited on a thin plate of a homogeneous
material. We show that this structure can display a low frequency gap, as compared to the acoustic wavelengths in the
constituent materials, similarly to the case of locally resonant structures. The opening of this gap is discussed as a
function of the geometrical parameters of the structure, in particular the thickness of the homogeneous plate and the
height of the dots. We show the persistence of this gap for various combinations of the materials constituting the plate
and the dots. Besides, the band structure can exhibit one or more higher gaps whose number increases with the height of
the cylinders. The results are discussed for different shapes of the cylinders such as circular, square or rotated square.
The band structure can also display an isolated branch with a negative slope which can be useful for the purpose of
negative refraction phenomena. We discuss the condition to realize wave guiding through different types of linear
defects inside such a phononic crystal. Finally, we investigate the phonon transport between two substrates connected by
a periodic array of dots. We discuss different features appearing in the transmission spectra such as the Perot-Fabry type
oscillations related to the height and the nature of the dots, the existence of transmission gaps related to the period and
the nature of the substrate, the possibility of a narrow transmission peak close to a zero of transmission.