Remote-Point Photonic Sensors (Rphos): Concepts-Materials-Devices

Photonic sensors receive an increasing global attention focusing on critical applications such as the protection of the environment, the health and safety of the citizens. In this work we are concerned with sensing of gaseous environments and focus on a novel class of nanocomposite sensor materials, which are capable to react to external stimulant-agents. These interactions amend their optical properties, fact which provides the means for optical detection. An unpowered sensor device is thus formed, which is interrogated optically and remotely to provide quantitative detection of the “agent”. “Sensing-by-light” thus unfolds the emerging conceptsof “Remote-point Photonic Sensors (RPHOS)”,we review and revisit in this work. The method offers unique means for spatially localized, real-time, multivariable sensing. This “point-in-space” detection may be contrasted to opticalpath- integrating LIDAR operations. Synergy with diffractive and holographic approaches enhance detectability and offer further innovative modes of operation. The low cost of this unpowered sensor-head, the flexibility of fabrication, the capacity for parallel / multiplexed/ data transmission and the immunity to electromagnetic interference, makes this technology ideal for use in harsh and adverse environments of industrial and security applications.

Hybrid photosensitive structures based on nematic liquid crystals and lithium niobate substrates

Liquid crystal cells based on lithium niobate substrates have recently been proposed as good candidates for optofluidic devices and for light-induced controlled generation of defects in liquid crystal films. The peculiarity of these structures lies in the possibility of using the bulk photovoltaic effect of lithium niobate to obtain an optically induced dc field able to affect the molecular liquid crystal director. Reversible fragmentation and self-assembling of liquid crystal droplets driven by the lithium niobate pyroelectric properties have also been reported. We review the basic results obtained so far with the aim of making the point and seeing what else can be done in the framework of the realization of hybrid structures combining lithium niobate with the electro-optical and nonlinear optical properties of liquid crystals.

Photovoltaic light valving induced in a vertically aligned nematic liquid crystal on a x-cut Fe:LiNbO3substrate

Photovoltaic fields induced in x-cut Fe-doped lithium niobate (Fe:LiNbO3)were used to achieve optically induced defect formation and light valving in a vertically aligned nematic liquid crystal. Initially, the optical axis of the LC was vertically aligned (along the surface-normal of the planar, photovoltaic substrates) throughout the whole sample. Samples were exposed with a focused continuous wave laser beam and investigated via microscopic imaging in-between crossed polarizers. The optical axis of the planar, x-cut Fe:LiNbO3 substrates was in the substrate plane and oriented parallel to one of the polarizers, which resulted in an initially dark state. Optically induced surface fields (with high in-plane components) generated within the substrates led to director reorientations and defect formation. Accordingly, the samples were locally switched into a transmissive state. The area affected by exposure was larger (300 μm) than the FWHM of the Gaussian exposure beam (14 μm). Switching from dark to bright states (light valving) could be achieved in the investigated samples much more eficiently than in previously investigated samples with z-cut Fe:LiNbO3-substrates. Realignments of the LC director were induced at lower optical power density (140 mW/cm2) than would be required to excite the intrinsically present nonlinear optical responses in a nematic LC such as the light induced Fredericks transition.

Reconfigurable and Permanent Wetting Patterns on Polymer Surfaces Obtained Using Plasma Oxidation and Laser Ablation

Smart surfaces with preferably reconfigurable wetting properties can lead to key applications in labon- a-chip analytical and preparative systems. In this paper, we present our recent results obtained using polymer surfaces whose wetting properties are modified in a permanent manner using laser ablation and in a reconfigurable manner using plasma oxidation. Polydimethylsiloxane (PDMS) diluted in solvent is used as the polymeric material coated over microscope glass slides in our studies. In the first part, the tracks of ~ 70 μm width are defined over the surface by surface oxidation using cold plasma exposure through a microfluidic channel. In the second part, femtosecond laser micromachining is used for selective removal of polymer coating and uncovering the hydrophilic glass substrate. We experimentally demonstrate guiding of water in the form of filaments and droplets over the obtained hydrophilic tracks of ~ 110 μm. We also discuss preliminary experiments to coat light sensitive azobenzene over a glass substrate with the help of a silane in order to achieve reversible isomerization upon periodic exposure to UV/vis radiation. Furthermore, we elaborate advantages, challenges and the significant role of such patterned surfaces in future applications.

Photo-Induced Holographic Recording in an Optically Active Cholesteric Liquid Crystal Layer

A few microns thick layer of an optically active cholesteric liquid crystal is realized by using a photoisomerizable nematic component and a chiral dopant. It is shown that such a photosensitive optically active medium can be used as a holographic material for optical information and dynamic grating recording. The photo-induced gratings are written by exploiting the light-induced photoisomerization phase transition from an optically active chiral liquid crystal to an isotropic liquid, which results in the rotation of the light polarization plane from 90 to 0 degrees and corresponding to maximum, respectively, zero transmittance. The results highlight applications in the field of optical storage by the recording of static gratings, as well as in the feld of nonlinear beam-coupling via the holographic writing of dynamic gratings

Random laser in a fiber: combined effects of guiding and scattering lead to a reduction of the emission threshold

Random fiber lasers incorporate scattering particles with optical gain in a fiber geometry and offer potential for sensing and biophotonics applications. In this work, the combined effects of waveguiding and scattering in random fiber lasers were investigated. A dye solution with nanoparticles was inffltrated into the hollow core of the microstructured optical fibers and the fibers were side pumped by a frequency-doubled Nd:YAG laser. The resulting emission threshold was reduced in comparison with the bulk solution.We used a Matlab model to gain a better understanding of the competing feedback mechanisms involved.

Augmented reality using holographic display

Augmented reality (AR) provided extra information to the user by applying virtual image onto the real environment. There are many methods achieving AR. Holographic display is one of the potential ways due to its perfect 3D demonstration. Holographic display can provide the virtual 3D object with depth information. It can be realized an AR device with real 3D scene by combing holographic display. However, it is difficult to realize a compact holographic display with wide viewing angle and enough resolution. It limits holographic display to apply to AR. In this paper, we will discuss the requirements of holographic display based on the development of LCD, including resolution (ppi), viewing angle, image quality and backlight. We wish this article can provide preliminary direction for the LCD industry to develop AR technology using holographic display.

THz plasmonic resonances in hybrid reduced-graphene-oxide and graphene patterns for sensing applications

In this contribution, we effectively combine important developments of nowadays technology: graphene based THz plasmonics, reduced-graphene-oxide (rGO) based sensors, and capability of patterning graphene materials at micro and nano scale. Surface waves in graphene were observed for the first time only few years ago, confirming the ability of this exceptional material to support plasmons at relatively low frequencies - a few THz - due to its intrinsically huge selfinductance. On the other hand, graphene oxide, and its reduced forms, has emerged as a very interesting material for several applications, including gas sensors and biosensors. In this work, the possibility of a _ne and controlled patterning of the above materials is considered as a useful degree of freedom to govern plasmon resonances and consequent electromagnetic absorption. In particular, the excitation of THz plasmons in arrays of nanoribbons, made of graphene and rGO, has been deeply investigated, in order to quantify the sensitivity to surface changes of conductivity, due to possible external perturbations. Fullwave analysis of hybrid metal-graphene-rGO is also presented and discussed. The effects of substrate thickness and of higher diffraction modes are rigorously taken into account, as a possible mean to enhance the sensing capability of the proposed device.

Analytical Calculation for Capacitances of Electrode Patterns in Touch Panels

In this paper, an accurate 3-dimensional (3-D) analytical solution is proposed to calculate the projective capacitances of touch panels. In this study, both simple and complex patterns were investigated for the calculation. We propose a partition strategy to divide a pattern into many rectangular or triangular sub-patterns. Each sub-pattern can be further cut into 2-D slices. The capacitance of a 2-D slice was then solved by our closed-form formulae. The total capacitance of a pattern was obtained by integrating up all the partial capacitances of the slices. In this study, the precision of our analytical method was examined by comparing the simulation results obtained from Q3D

Monolayer Graphene Can Emit SHG Waves

The usually-held notion that monolayer graphene, a centrosymmetric system, does not allow even-harmonic generation when illuminated at normal incidence is challenged by the discovery of a peculiar effect we term the dynamical centrosymmetry breaking mechanism. This effect results in a global pulse-induced oscillation of the Dirac cones which in turn produces second harmonic waves. We prove that this result can only be found by using the full Dirac equation and show that the widely used semiconductor Bloch equations fail to reproduce this and some other important physics of graphene. These results clear the way for further investigation concerning nonlinear light-matter interactions in a wide range of two-dimensional materials admitting either a gapped or ungapped Dirac-like spectrum.