Electro-optical Methods Research Articles

Universal switching of plasmonic signals using optical resonator modes

We propose and investigate, both experimentally and theoretically, a novel mechanism for switching and modulating plasmonic signals based on a Fano interference process, which arises from the coupling between a narrow-band optical Fabry–Pérot cavity and a surface plasmon polariton (SPP) source. The SPP wave emitted from the cavity is actively modulated in the vicinity of the cavity resonances by altering the cavity Q-factor and/or resonant frequencies. We experimentally demonstrate dynamic SPP modulation both by mechanical control of the cavity length and all-optically by harnessing the ultrafast nonlinearity of the Au mirrors that form the cavity. An electro-optical modulation scheme is also proposed and numerically illustrated. Dynamic operation of the switch via mechanical means yields a modulation in the SPP coupling efficiency of ~80%, while the all-optical control provides an ultrafast modulation with an efficiency of 30% at a rate of ~0.6 THz. The experimental observations are supported by both analytical and numerical calculations of the mechanical, all-optical and electro-optical modulation methods.

Manifestation of side-chain interactions in solution properties of “loose” PI-graft-PMMA molecular brushes

ABSTRACTThe molecular properties of polymer brushes composed of polyimide with polymerization degree 50 and loosely grafted poly(methyl methacrylate) chains of variable length (PI-graft-PMMA) were studied by viscometry, dynamic light scattering, and equilibrium electro-optical Kerr effect methods in a diluted solution. It was established that the intrinsic viscosity and hydrodynamic dimension of PI-graft-PMMA copolymers increase when the electro-optical Kerr constant decreases with the elongation of PMMA side chains in the range of 40–110 monomer units. The observed difference in the solution properties of the copolymers was explained by their side-chain interactions in spite of a large distance between the neighboring grafting points typical of “loose brushes.” A strong effect of the chain rigidity and dipole structure on solution properties of the studied samples was demonstrated. The Kuhn segment lengths for PI-graft-PMMA copolymers were estimated to vary in the range 3.8–12.1 nm.

Effect of chain length and fluorination on the dielectric and electro-optic properties of three partially fluorinated biphenylyl benzoate rigid core based ferroelectric liquid crystals

ABSTRACTThree partially fluorinated ferroelectric liquid crystals (4F4R, 4F5R and 7F3R) with biphenylyl benzoate rigid core have been investigated by frequency-dependent dielectric spectroscopy and electro-optic methods. Molecular structures of the compounds differ only by the length of the carbon chain and the number of oligomethylene spacers. 4F4R and 4F5R exhibit ferroelectric SmC* phase over a considerable temperature range and directly melts into isotropic phase, 4F4R also shows a ferroelectric type subphase. Only Goldstone mode (GM) relaxation is observed in these compounds, but no soft mode (SM). 7F3R exhibits both the SmC* and SmA* phases, has higher stability of SmC*. Both the GM and SM relaxations are observed in this case, signifying that SM relaxation is possible only when SmC* is formed on cooling from SmA*. Increase of dielectric strength and critical frequency with temperature, in all cases, has been explained in the light of generalised Landau model. Spontaneous polarisation is found to decrease with increasing flexibility, and optical tilt depends more on fluorination than on chain length.

Electro-optic modulation methods in range-gated active imaging.

A time-resolved imaging method based on electro-optic modulation is proposed in this paper. To implement range resolution, two kinds of polarization-modulated methods are designed, and high spatial and range resolution can be achieved by the active imaging system. In the system, with polarization beam splitting the incident light is split into two parts, one of which is modulated with cos(2) function and the other is modulated with sin(2) function. Afterward, a depth map can be obtained from two simultaneously received images by dual electron multiplying charge-coupled devices. Furthermore, an intensity image can also be obtained from the two images. Comparisons of the two polarization-modulated methods indicate that range accuracy will be promoted when the polarized light is modulated before beam splitting.

Towards Quantitative Optical Cross Sections in Entomological Laser Radar - Potential of Temporal and Spherical Parameterizations for Identifying Atmospheric Fauna.

In recent years, the field of remote sensing of birds and insects in the atmosphere (the aerial fauna) has advanced considerably, and modern electro-optic methods now allow the assessment of the abundance and fluxes of pests and beneficials on a landscape scale. These techniques have the potential to significantly increase our understanding of, and ability to quantify and manage, the ecological environment. This paper presents a concept whereby laser radar observations of atmospheric fauna can be parameterized and table values for absolute cross sections can be catalogued to allow for the study of focal species such as disease vectors and pests. Wing-beat oscillations are parameterized with a discrete set of harmonics and the spherical scatter function is parameterized by a reduced set of symmetrical spherical harmonics. A first order spherical model for insect scatter is presented and supported experimentally, showing angular dependence of wing beat harmonic content. The presented method promises to give insights into the flight heading directions of species in the atmosphere and has the potential to shed light onto the km-range spread of pests and disease vectors.

Biphenyl Based Non-symmetrical Bent-Core Mesogens Containing a Chiral Moiety and an Olefinic End Group

New nonsymmetrical bent-core compounds consisting of a biphenyl-3,4′-diol central unit, a chiral terminal chain and an olefinic end group at the other terminus have been synthesized and characterized to study the influence of a chiral moiety, the length of terminal alkenyl chain, and the number of aromatic rings in the rod-like wings which are substituted at the 3- and 4-position of central biphenyl core on mesophase properties of bent-core mesogens. The liquid crystalline properties of the compounds were investigated by differential scanning calorimetry, optical polarizing microscopy, and electro-optic methods. Depending on the length of the olefinic chain and the number of aromatic rings in the rod-like wings, the bent-core compounds with a chiral moiety show B1 type mesophase, polar smectic C phase (SmCP) or nonmesomorphic behavior.

Electro-optical properties of nanodispersions based on ferroelectric thiobenzoates

The influence of differential nanoparticles on the properties of ferroelectric liquid crystal based on chiral thiobenzoates series was investigated by optical and electro-optical methods. MHOBS4/ZnO, MHOBS4/Ag and MHOBS10/SWCN nanocomponents were prepared. A small addition of nanoparticles leads to changes in electro-optical properties. This is due probably to the various mutual arrangements of nanoparticles and liquid crystal molecules.

Partial Discharges Registration in Transformer Oil at the ‘Point-Plane’ Electrode System

The results of the experimental studies of partial discharges in GK transformer oil with electrode system “point-plane” that provide sharp inhomogeneous electric field are presented. It was found out that two types of partial discharge pulses which differ in form and time duration appeared at the negative point polarity of the needle. The study of different types of pulses was conducted by electric and electro-optical methods of partial discharge registration.

New antiferroelectric compound studied by complementary methods

New antiferroelectric compound has been studied by electrooptic methods. The electrooptic parameters such as spontaneous polarization, tilt angle and switching time were measured. Using texture observation and differential scanning calorimetric methods, the phase sequences at cooling and heating have been obtained.

Thermal and Optical Properties of Some Hydrogen-Bonded Liquid Crystal Mixtures

Phase transition properties of the mixtures of hydrogen-bonded nematic liquid crystals (HBLC) 4-hexylbenzoic acid (6BA), 4-(octyloxy)benzoic acid (8OBA), and 4-(decyloxy)benzoic acid (10OBA) have been investigated by means of differential scanning calorimetry (DSC) and polarize optic microscope (POM). The DSC and POM results clearly indicate the existence of smectic and nematic phase transitions in binary mixtures. The phase transition temperature values of 6BA/10OBA mixtures have clearly increased with increasing heating rate. The activation energies were calculated for the phase transitions of 6BA/10OBA liquid crystal (LC) mixture. The optical transmittance of these mixed hydrogen-bonded nematic liquid crystals was investigated in terms of temperature variations through electrooptic methods. The electrooptic experiments indicate that, while low in the nematic phase, the optical transmittance is very high at the nematic-isotropic phase transition. The transmitted light intensity values of 6BA/8OBA mixture are somewhat higher than those of other binary mixtures, 6BA/10OBA and 8OBA/10OBA, a result associated with the different alkyloxy chain lengths.

Stable colloids at the isoelectric point: Dipolar vs. electrostatic interactions

HypothesisThe strange stability of some colloid systems at the isoelectric point may be explained by interparticle electrostatic interactions (attractive and repulsive) of different electric charge patches on the particles’ surface, related to differences of their surface structure and possibly to adsorption of charged species on them. The coincidence of the minimum colloid stability with the electro-optically observed minimum of the particle electric polarizability (EP) is not in favor of attractive interparticle dipolar interactions playing a major role for the stability as stated before [1]. ExperimentsAqueous dispersions of rod-like palygorskite particles+surfactant cetyl pyridinium chloride (CPC) were studied at different CPC concentrations by optic, electro-optic and microelectrophoretic methods. Thus the CPC concentration dependences of the stability, EP and ζ-potential were established. FindingsLowest colloid stability at considerable ζ-potentials (about −30mV) well below the isoelectric point was found in Ref. [1]. The CPC concentrations, at which the lowest stability was observed experimentally, corresponded well to that of a minimum value of the EP. The new hypothesis and interpretation for the major importance of electrostatic interactions are in good accord with the present day knowledge in Colloid Science for deviations from the Derjaguin–Landau–Verway–Overbeek (DLVO) theory of colloid stability.

RETRACTED: Electro Optic Conversion Methods in Intra-Body Communication

Retracted paper: Galvanic coupling method has been observed to be the best method for data transmission in intra-body communication, which is proposed by Zimmerman in 1995. With the increasing transmission requirements and the development of optical fiber communication, a high speed data transmission system is required and it is possible to design an apparatus to realize the electro optic conversion. In this paper, the characteristics of the intra-body communication system are introduced. Principles and structures of the electro-optic modulation methods for intra-body communication are reviewed. Internal and external modulation methods are introduced and discussed. A system of the electro-optic and acousto-optic modulation are recommended for the intra-body communication system and discussed.

Crystallization of amorphous boron by the calorimetric method

The kinetics of formation of crystal boron was studied by X-ray structure and differential-thermal analyses. The enthalpy of transition of amorphous boron to crystal boron with formation of an intermediate non-equilibrium phase was determined by the calorimetric method. Studies were carried out by using the differential scanning calorimeter SETARAM. Amorphous boron received by diboron cracking was used as the starting material. The test sample is cha- racterized by stability even at a high temperature. When heated, amorphous boron first transforms to crystal boron of α-modification, and during a further heating, there occur several phase transitions, which means the transition of α-rhombohedric crystal boron to the β' and β'' metastable states. Studies of various modifications were carried out by radiographic and electro-optic methods. The high sensitiveness of the calorimeter made it possible to control temperature in the oven, make records and detect even the smallest thermal effects.

Development of polar order and tilt in lamellar liquid crystalline phases of a bent-core mesogen

A new bent-core mesogen combining a 4-cyanoresorcinol unit with two terephthalate based rod-like wings and terminated by two long alkyl chains, was synthesized and investigated by DSC, XRD, optical, electrooptical and dielectric methods. A series of liquid crystalline phases in the unique sequence SmA-SmA(P)-SmCPR-(M1/SmCPα)-SmCsPA-SmCPA-SmCaPA, mainly distinguished by the degree and mode of correlation of tilt and polar order, was observed. The development of polar order is associated with the emergence of a small tilt (<10°). With decreasing temperature the tilt changes from random (SmA) via synclinic to anticlinic, while the coherence length of the polar domains grows. This small tilt gives rise to an only weak layer coupling which is in competition with the polar coupling and this leads to new modes of self assembly in lamellar phases of bent-core mesogens, among them the SmCPR and the SmCPα phases. The SmCPR phase is an only slightly tilted biaxial smectic phase with randomized polar order and the SmCPα phase is a slightly tilted and antiferroelectric switching, but uniaxial smectic phase. For this phase a regular change of the in-plane polarization vector between the layers by an angle between >0° and <90° is proposed.

Terahertz electro-optical detection: optical phase or energy measurements

Models of different available single-photodetector electro-optic sampling schemes are considered from the unified theoretical position. It is taken into account that under electro-optic terahertz wave detection, not only do the polarization states of the femtosecond optical pulse components change but the modules of their amplitudes are also varied. As a result, information concerning the terahertz wave can be obtained not only using the conventional ellipsometry readout scheme (probe-phase sampling) but also by simple measuring of the induced power of the optical pulses (probe-energy sampling). Spectral sensitivities of both of these electro-optic sampling methods are calculated for the cases of nonlinear-optical crystals with zinc-blende symmetry (like ZnTe) and the crystals with one active component of the second-order optical susceptibility tensor (like PPLN). It is found that the ratio between spectral sensitivities of the pure probe-phase and pure probe-energy schemes is proportional to the ratio between the optical and terahertz wave frequencies in all types of the crystals. It is shown that the signal in the near-zero optical transmission point scheme, which is the best for terahertz imaging, has a mixed character. While the contribution of the probe-phase sensitivity appears to be due to spatially nonuniform residual birefringence of the nonlinear zinc-blende crystal, the probe-energy part of the sensitivity has a uniform distribution and can be increased by the angle misalignment of the optical polarization element.

RETRACTED: Electro Optic Methods in Intra-Body Communication System

Retracted paper: Intra-body communication is proposed by Zimmerman in 1995 and the galvanic coupling has been observed to be the best method for data transmission. With the increasing transmission requirements and the development of optical fiber communication, a high speed system is possible to be designed based on the Electro optic methods. In this paper, the characteristics of the intra-body communication system are introduced. Principles and structures of optic modulation for intra-body communication are reviewed. Internal and external modulation methods are introduced and discussed. A system of the electro optic modulation is recommended and discussed.

Optical Switching and Spatial Routing by a Delay-Controlled Optical Emitter

Semiconductor Laser or Light Emitting Diodes, (LEDs) as active elements of optical switches or spatial routingdevices are widely used in integrated optical circuitry. Electro-optic, magneto-optic, mechanical or other methods areapplied for that purpose. The present paper deals with a novel effect, which appears in the light field of a. c. drivenluminescence emitters in Fabry-Perot structure under electrical excitation depending on time (a.c.), characterizedbecause the light band emitted on the side face of the device moves up and down due to the finite diffusion velocity ofthe injected excess minority carriers. The combination of such emitter with a portioned detector element, allows spatialrouting between these two detector segments. Particular emphasis is laid on a theoretical treatment of lightpropagation inside the emitter bulk which finally allows the construction of the light field intensity on the side face ofthe Fabry-Perot body, necessary to prove the proposed effect.

Measurement of the liquid crystal pretilt angle in cells with homogeneous and inhomogeneous liquid crystal director configuration

Optical and electro-optical methods of liquid crystal (LC) director pretilt angle measurement are described for LC cells with homogeneous and inhomogeneous LC director distribution. The LC pretilt on both LC substrates can have the same or opposite direction. The phase retardation difference of both extraordinary and ordinary polarized rays passing through an LC cell with homogeneous and inhomogeneous LC director distribution has been calculated versus the LC pretilt angle θ(0) on the cell's substrates in the range 0≤θ(0)≤90°. The experimental procedure for phase retardation difference determination by measurement of the LC cell transmission between crossed polarizers for cells with LC tilted alignment is described. The method developed can also be used in optical compensator design.

Size dependence of harvested BaTiO3 nanoparticles on the electro-optic and dielectric properties of ferroelectric liquid crystal nanocolloids

The influence of the size of harvested barium titanate nanoparticles on the properties of ferroelectric liquid crystal (FLC) nanocolloids was investigated by electro-optical and dielectric methods. The spontaneous polarization and the switching time are decreased for the liquid crystalline nanocolloids compared to nondoped FLC mixtures of different dipole strengths; this dependence is stronger for small size particles (9 nm) and weaker for larger size particles (26 nm) by the same concentration in weight. The decrease of the Goldstone mode (GM) relaxation frequency and the decrease of the dielectric GM absorption strength of the nanocomposites compared to the nondoped FLC mixture go stepwise with the increase of the nanoparticles diameter. Results have been interpreted via strong interaction between the FLC dipoles and the dipoles of the highly polar barium titanate nanoparticles.

Investigations on photo and electrically switchable asymmetric bent-core liquid crystals

New series of bent-core liquid crystals (8a–8d) synthesized and their photo and electrical switching properties were investigated. The homologous series of liquid crystals was constructed with five-ring system using structurally non-symmetrical rod-like mesogens connected with 1, 3-phenylene unit. The synthesized precursor and bent-core liquid crystals were characterized by FT-IR, 1H-NMR, and 13C-NMR spectroscopy. The mesophase characterization of the asymmetric bent-core liquid crystals was carried out using polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction studies. The significance of tail length (alkyl chain) and nature of mesogen was explored; shorter alkyl chains bent-core compounds exhibited non-switchable rectangular columnar B1 phase. Whereas longer alkyl chain induces switchable lamellar B2 phase, which was further confirmed by electro-optical methods. This lamellar B2 phase exhibits antiferroelectric–anticlinic organization (SmCAPA) of the molecules in the layers. The photo-switching properties of bent-core azo molecules were investigated using UV–Vis spectroscopy, the trans to cis photoisomerization was observed at 30 s, whereas reverse processes take place in 40 s in chloroform.