Evidence of 3D Topological-Domain Dynamics in KTN:Li Polarization-Supercrystal Formation

We experimentally and theoretically investigate thermal domain evolution in near-transition KTN:Li. Results allow us to establish how polarization supercrystals form, a hidden 3D topological phase composed of hypervortex defects. These are the result of six converging polarization vortices, each associated to one orientation of the 3D broken inversion symmetry. We also identify rescaling soliton lattices and domain patterns that replicate on different scales. Findings shed light on volume domain self-organization into closed-flux patterns and open up new scenarios for topologically protected noise-resistant ferroelectric memory bits.

Anomalous Optical Properties of KTN:Li Ferroelectric Supercrystals

We report a spectroscopic investigation of potassium-lithium-tantalate-niobate (KTN:Li) across its room-temperature ferroelectric phase transition, when the sample manifests a supercrystal phase. Reflection and transmission results indicate an unexpected temperature-dependent enhancement of average index of refraction from 450 nm to 1100 nm, with no appreciable accompanying increase in absorption. Second-harmonic generation and phase-contrast imaging indicate that the enhancement is correlated to ferroelectric domains and highly localized at the supercrystal lattice sites. Implementing a two-component effective medium model, the response of each lattice site is found to be compatible with giant broadband refraction.

Intense Wave Formation from Multiple Soliton Fusion and the Role of Extra Dimensions

We experimentally and numerically explore the role of dimensionality in multiple (three or more) soliton fusion supported by nonreciprocal energy exchange. Three-soliton fusion into an intense wave is found when an extra dimension, with no broken inversion symmetry, is involved. The phenomenon is observed for 2+1D spatial waves in photorefractive crystals, where solitons are supported by a spatially local saturated Kerr-like self-focusing and fusion is driven by the leading nonlocal correction, the spatial analog of the nonlinear Raman effect.

Enhancing DNT Detection by a Bacterial Bioreporter: Directed Evolution of the Transcriptional Activator YhaJ

Detection of buried landmines is a dangerous and complicated task that consumes large financial resources and poses significant risks to the personnel involved. A potential alternative to conventional detection methodologies is the use of microbial bioreporters, capable of emitting an optical signal upon exposure to explosives, thus revealing to a remote detector the location of buried explosive devices. We have previously reported the design, construction, and optimization of an Escherichia coli-based bioreporter for the detection of 2,4,6-trinitrotoluene (TNT) and its accompanying impurity 2,4-dinitrotoluene (DNT). Here we describe the further enhancement of this bioreporter by the directed evolution of YhaJ, the transcriptional activator of the yqjF gene promoter, the sensing element of the bioreporter's molecular circuit. This process resulted in a 37-fold reduction of the detection threshold, as well as significant enhancements to signal intensity and response time, rendering this sensor strain more suitable for detecting the minute concentrations of DNT in the soil above buried landmines. The capability of this enhanced bioreporter to detect DNT buried in sand is demonstrated.

Evidence of Chaotic Dynamics in Three-Soliton Collisions

We observe chaotic optical wave dynamics characterized by erratic energy transfer and soliton annihilation and creation in the aftermath of a three-soliton collision in a photorefractive crystal. Irregular dynamics are found to be mediated by the nonlinear Raman effect, a coherent interaction that leads to nonreciprocal soliton energy exchange. Results extend the analogy between solitons and particles to the emergence of chaos in three-body physics and provide new insight into the origin of the irregular dynamics that accompany extreme and rogue waves.

Electro-optic active Q-switched Tm:YLF laser based on polarization modulation

An electro-optic active Q-switched Tm:YLF laser (1880 nm) employing a novel, to the best of our knowledge, switching scheme is presented. The switching is done by a potassium lithium tantalate niobate (KLTN) crystal operated slightly above the ferroelectric phase transition, cut in a trapezoidal shape for reducing acousto-optic oscillations. The novel switching scheme exploits the emission cross section difference between the π and σ polarizations in the Tm:YLF and overcomes the residual oscillation effects even at high repetition rates. The laser exhibited stable operation yielding pulses of 0.81 mJ and pulse duration of 30 ns at 5 kHz, and pulses of 1.25 mJ and pulse duration of 19 ns at 500 Hz.

An autonomous bioluminescent bacterial biosensor module for outdoor sensor networks, and its application for the detection of buried explosives

We describe a miniaturized field-deployable biosensor module, designed to function as an element in a sensor network for standoff monitoring and mapping of environmental hazards. The module harbors live bacterial sensor cells, genetically engineered to emit a bioluminescent signal in the presence of preselected target materials, which act as its core sensing elements. The module, which detects and processes the biological signal, composes a digital record that describes its findings, and can be transmitted to a remote receiver. The module is an autonomous self-contained unit that can function either as a standalone sensor, or as a node in a sensor network. The biosensor module can potentially be used for detecting any target material to which the sensor cells were engineered to respond. The module described herein was constructed to detect the presence of buried landmines underneath its footprint. The demonstrated detection sensitivity was 0.25 mg 2,4-dinitrotoluene per Kg soil.

Direct Observation of Fractal-Dimensional Percolation in the 3D Cluster Dynamics of a Ferroelectric Supercrystal

We perform percolation analysis of crossed-polarizer transmission images in a biased nanodisordered bulk KTN:Li perovskite. Two distinct percolative transitions are identified at two electric field thresholds. The low-field transition involves a directional fractal chain of dimension D=1.65, while the high-field transition has a dimension D>2. Direct cluster imaging in the volume is achieved using high-resolution orthographic 3D projections based on giant refraction. Percolation is attributed to a full-3D domain reorientation that mediates the transition from a ferroelectric supercrystal state to a disordered domain mosaic.

Detection of buried explosives with immobilized bacterial bioreporters

The unchecked dispersal of antipersonnel landmines since the late 19th century has resulted in large areas contaminated with these explosive devices, creating a substantial worldwide humanitarian safety risk. The main obstacle to safe and effective landmine removal is the identification of their exact location, an activity that currently requires entry of personnel into the minefields; to date, there is no commercialized technology for an efficient stand-off detection of buried landmines. In this article, we describe the optimization of a microbial sensor strain, genetically engineered for the remote detection of 2,4,6-trinitrotoloune (TNT)-based mines. This bioreporter, designed to bioluminescence in response to minute concentrations of either TNT or 2,4-dinitotoluene (DNT), was immobilized in hydrogel beads and optimized for dispersion over the minefield. Following modifications of the hydrogel matrix in which the sensor bacteria are encapsulated, as well as their genetic reporting elements, these sensor bacteria sensitively detected buried 2,4-dinitrotoluene in laboratory experiments. Encapsulated in 1.5 mm 2% alginate beads containing 1% polyacrylic acid, they also detected the location of a real metallic antipersonnel landmine under field conditions. To the best of our knowledge, this is the first report demonstrating the detection of a buried landmine with a luminescent microbial bioreporter.

Genome-wide gene-deletion screening identifies mutations that significantly enhance explosives vapor detection by a microbial sensor

Genetically engineered microbial biosensors, capable of detecting traces of explosives residues above buried military ordnance and emitting an optical signal in response, may potentially serve for the standoff detection of buried landmines. A promising candidate for such an application is a previously reported Escherichia coli-based reporter strain that employs the yqjF gene promoter as its sensing element; however, for this sensor to be able to detect actual landmines reliably, it was necessary for its detection sensitivity and signal intensity to be enhanced. In this study, a high-throughput approach was employed to screen the effects of individual gene deletions on yqjF activation by 2,4-dinitrotoluene (DNT). Several genes were identified, the deletion of which elicited a significant enhancement of yqjF induction by DNT. The most promising of these mutations were introduced into the sensor strain, individually or in pairs, yielding a considerable increase in signal intensity and a lowering of the detection threshold. A strain harboring two of the identified mutations, ygdD and eutE, appears to be the most sensitive microbial biosensor currently described for the detection of traces of landmine explosives.

Soliton Maxwell demons and long-tailed statistics in fluctuating optical fields

We demonstrate experimentally in biased photorefractive crystals that collisions between random-amplitude optical spatial solitons produce long-tailed statistics from input Gaussian fluctuations. The effect is mediated by Raman nonlocal corrections to Kerr self-focusing that turn soliton-soliton interaction into a Maxwell demon for the output wave amplitude.

Topological control of extreme waves

From optics to hydrodynamics, shock and rogue waves are widespread. Although they appear as distinct phenomena, transitions between extreme waves are allowed. However, these have never been experimentally observed because control strategies are still missing. We introduce the new concept of topological control based on the one-to-one correspondence between the number of wave packet oscillating phases and the genus of toroidal surfaces associated with the nonlinear Schrödinger equation solutions through Riemann theta functions. We demonstrate the concept experimentally by reporting observations of supervised transitions between waves with different genera. Considering the box problem in a focusing photorefractive medium, we tailor the time-dependent nonlinearity and dispersion to explore each region in the state diagram of the nonlinear wave propagation. Our result is the first realization of topological control of nonlinear waves. This new technique casts light on shock and rogue waves generation and can be extended to other nonlinear phenomena.

Observation of replica symmetry breaking in disordered nonlinear wave propagation

A landmark of statistical mechanics, spin-glass theory describes critical phenomena in disordered systems that range from condensed matter to biophysics and social dynamics. The most fascinating concept is the breaking of replica symmetry: identical copies of the randomly interacting system that manifest completely different dynamics. Replica symmetry breaking has been predicted in nonlinear wave propagation, including Bose-Einstein condensates and optics, but it has never been observed. Here, we report the experimental evidence of replica symmetry breaking in optical wave propagation, a phenomenon that emerges from the interplay of disorder and nonlinearity. When mode interaction dominates light dynamics in a disordered optical waveguide, different experimental realizations are found to have an anomalous overlap intensity distribution that signals a transition to an optical glassy phase. The findings demonstrate that nonlinear propagation can manifest features typical of spin-glasses and provide a novel platform for testing so-far unexplored fundamental physical theories for complex systems.

Observation of polarization-maintaining light propagation in depoled compositionally disordered ferroelectrics

We investigate the evolution of the state of polarization of light propagating through bulk depoled composite ferroelectrics below the Curie temperature. In contrast to standard depoled ferroelectrics, where random birefringence causes depolarization and scattering, light is observed to suffer varying degrees of depolarization and remains fully polarized when linearly polarized along the crystal principal axes. The effect is found to be supported by the formation of polarized speckles organized into a spatial lattice and occurs as the ferroelectric settles into a spontaneous super-crystal, a three-dimensional coherent mosaic of ferroelectric clusters. The polarization lattices gradually disappear as the ferroelectric state reduces to a disordered distribution of polar nanoregions above the critical point.

Fast electroholographic wavelength selective switching implemented in a slab waveguide

We present wavelength selective switching with a rise time of 25 ns implemented in a slab waveguide constructed in a KLTN:Cu crystal. The waveguide was fabricated by implantations of alpha particles at 2.1 MeV which produced a 0.5 μm thick cladding layer with reduced refractive index at 4.5 μm underneath the crystal surface. This demonstrates the feasibility of implementing electroholography in waveguides maintaining the performance obtained in bulk crystals, providing in potential the basis for constructing integrated photonic circuits which incorporate interconnected electroholographic wavelength selective switches and electrical wavelength tuning devices for employing wavelength addressing routing schemes in computer networks, in particular for relieving the bandwidth bottlenecks in data center networks.

Liquid-solid directional composites and anisotropic dipolar phases of polar nanoregions in disordered perovskites

Using temperature-resolved dielectric spectroscopy in the range of 75-320 K we have inspected the solid-like and liquid-like arrangements of nanometric dipoles (polar nanoregions) embedded in sodium-enriched potassium-tantalate-niobate (KNTN), a chemically-substituted complex perovskite crystal hosting inherent substitutional disorder. The study of order versus direction is carried out using Fröhlich entropy measurements and indicates the presence of four long-range symmetry phases, two of which are found to display profoundly anisotropic features. Exotic phases are found for which the dipoles at one fixed temperature manifest a liquid reorientational response along one crystal axis and a solid-like behavior along another axis. The macroscopic anisotropy observed in the sequence of different phases is found to match a microscopic order-disorder sequence typical of nominally pure perovskites. Moreover, experimental demonstration of the onset of a frozen state above transitions is provided.

Miniaturized photogenerated electro-optic axicon lens Gaussian-to-Bessel beam conversion

We experimentally demonstrate an electro-optic Gaussian-to-Bessel beam-converter miniaturized down to a 30×30  μm pixel in a potassium-lithium-tantalate-niobate (KLTN) paraelectric crystal. The converter is based on the electro-optic activation of a photoinduced and reconfigurable volume axicon lens achieved using a prewritten photorefractive funnel space-charge distribution. The transmitted light beam has a tunable depth of field that can be more than twice that of a conventional beam with the added feature of being self-healing.

Turbulent Transitions in Optical Wave Propagation

We report the direct observation of the onset of turbulence in propagating one-dimensional optical waves. The transition occurs as the disordered hosting material passes from being linear to one with extreme nonlinearity. As the response grows, increased wave interaction causes a modulational unstable quasihomogeneous flow to be superseded by a chaotic and spatially incoherent one. Statistical analysis of high-resolution wave behavior in the turbulent regime unveils the emergence of concomitant rogue waves. The transition, observed in a photorefractive ferroelectric crystal, introduces a new and rich experimental setting for the study of optical wave turbulence and information transport in conditions dominated by large fluctuations and extreme nonlinearity.

Intrinsic Negative Mass from Nonlinearity

We propose and provide experimental evidence of a mechanism able to support negative intrinsic effective mass. The idea is to use a shape-sensitive nonlinearity to change the sign of the mass in the leading linear propagation equation. Intrinsic negative-mass dynamics is reported for light beams in a ferroelectric crystal substrate, where the diffusive photorefractive nonlinearity leads to a negative-mass Schrödinger equation. The signature of inverted dynamics is the observation of beams repelled from strongly guiding integrated waveguides irrespective of wavelength and intensity and suggests shape-sensitive nonlinearity as a basic mechanism leading to intrinsic negative mass.

Standoff detection of explosives and buried landmines using fluorescent bacterial sensor cells

A standoff detection scheme for buried landmines and concealed explosive charges is presented. The detection procedure consists of the following: Live bacterial sensor strains, genetically engineered to produce a dose-dependent amount of green fluorescent protein (GFP) in the presence of explosives' vapors, are encapsulated and spread on the suspected area. The fluorescence produced by the bacteria in response to traces of the explosive material in their microenvironment is remotely detected by a phase-locked optoelectronic sampling system. This scheme enables fast direct access to a large minefield area, while obviating the need to endanger personnel and equipment. Moreover, the employment of phase locking detection efficiently isolates the bacterial sensors' fluorescent output from the background optical signals. This facilitates the application of bacterial sensors in an outdoor environment, where control of background illumination is not possible. Using this system, we demonstrate standoff detection of 2,4-DNT both in aqueous solution and when buried in soil, by sensor bacteria either in liquid culture or agar-immobilized, respectively, at a distance of 50 m in a realistic optically noisy environment.

Spatial Rogue Waves in Photorefractive Ferroelectrics

Rogue waves are observed as light propagates in the extreme nonlinear regime that occurs when a photorefractive ferroelectric crystal is undergoing a structural phase transition. The transmitted spatial light distribution contains bright localized spots of anomalously large intensity that follow a signature long-tail statistics that disappears as the nonlinearity is weakened. The isolated wave events form as out-of-equilibrium response and disorder enhance the Kerr-saturated nonlinearity at the critical point. Self-similarity associable to the individual observed filaments and numerical simulations of the generalized nonlinear Schrödinger equation suggests that dynamics of soliton fusions and scale invariance can microscopically play an important role in the observed rogue intensities and statistics.

Continuous Solitons in a Lattice Nonlinearity

We study theoretically and experimentally the propagation of optical solitons in a lattice nonlinearity, a periodic pattern that both affects and is strongly affected by the wave. Observations are carried out using spatial photorefractive solitons in a volume microstructured crystal with a built-in oscillating low-frequency dielectric constant. The pattern causes an oscillating electro-optic response that induces a periodic optical nonlinearity. On-axis results in potassium-lithium-tantalate-niobate indicate the appearance of effective continuous saturated-Kerr solitons, where all spatial traces of the lattice vanish, independently of the ratio between beam width and lattice constant. Decoupling the lattice nonlinearity allows the detection of discrete delocalized and localized light distributions, demonstrating that the continuous solitons form out of the combined compensation of diffraction and of the underlying periodic volume pattern.

Volume integrated phase modulator based on funnel waveguides for reconfigurable miniaturized optical circuits

We demonstrate the integration of a miniaturized 30(x)  μm×30(y)  μm×2.7(z)  mm electro-optic phase modulator operating in the near-IR (λ=980  nm) based on the electro-activation of a funnel waveguide inside a paraelectric sample of photorefractive potassium lithium tantalate niobate. The modulator forms a basic tassel in the realization of miniaturized reconfigurable optical circuits embedded in a single solid-state three-dimensional chip.

Electro-optical modulation with immunity to optical damage by bipolar operation in potassium lithium tantalate niobate

A method for suppressing the formation of optical damage in quadratic electrooptic devices operated at short wavelengths is presented. Formation of optical damage is attributed to the generation of a trapped space charge induced by photoionization of impurity ions by the propagating beam. It is shown that in potassium lithium tantalate niobate where the electrooptic effect is quadratic, operating the electrooptic device by a bipolar driving voltage prevents the space charge from accumulating, which inhibits the formation of the optical damage. A 6 hours continuous operation of electrooptic modulator for a 30 W/cm(2) at λ = 445 nm input beam is demonstrated.

Anti-diffracting beams through the diffusive optical nonlinearity

Anti-diffraction is a theoretically predicted nonlinear optical phenomenon that occurs when a light beam spontaneously focalizes independently of its intensity. We observe anti-diffracting beams supported by the peak-intensity-independent diffusive nonlinearity that are able to shrink below their diffraction-limited size in photorefractive lithium-enriched potassium-tantalate-niobate (KTN:Li).

Observation of electro-activated localized structures in broad area VCSELs

We demonstrate experimentally the electro-activation of a localized optical structure in a coherently driven broad-area vertical-cavity surface-emitting laser (VCSEL) operated below threshold. Control is achieved by electro-optically steering a writing beam through a pre-programmable switch based on a photorefractive funnel waveguide.

Circular polarization induced by the three-dimensional chiral structure of human sweat ducts

The upper part of the human eccrine sweat ducts, embedded within the epidermis layer, have a well-defined helical structure. It was recently suggested that, as electromagnetic entities, the sweat ducts interact with sub-mm waves [Y. Feldman et al., Phys. Rev. Lett. 100, 128102 (2008)]. Although correlation between changes in the reflectance spectrum in this frequency range and physiological activities has been shown, a direct link between the electromagnetic reflection and the helical structure itself has remained to be established. The fact that the sweat ducts manifest natural homochirality is henceforth used to produce this link. We report the detection of circular polarization asymmetry in the electromagnetic reflection from the human skin at sub-THz frequencies in vivo. We compare the results to numerical simulations and to measurements of a fabricated metamaterial. We argue that the observed circular dichroism can be interpreted uniquely as the signature of the helical structure itself. By twisting reflected electromagnetic waves, the human skin exhibits properties which are usually discussed only in the framework of metamaterial science.

Photorefractive light needles in glassy nanodisordered KNTN

We study the formation of 2D self-trapped beams in nanodisordered potassium-sodium-tantalate-niobate (KNTN) cooled below the dynamic glass transition. Supercooling is shown to accelerate the photorefractive response and enhance steady-state anisotropy. Effects in the excited state are attributed to the anomalous slim-loop polarization curve typical of relaxors dominated by non-interacting polar-nano-regions.

Aging solitons in photorefractive dipolar glasses

We study experimentally the aging of optical spatial solitons in a dipolar glass hosted by a nanodisordered sample of photorefractive potassium-sodium-tantalate-niobate (KNTN). As the system ages, the waves erratically explore varying strengths of the nonlinear response, causing them to break up and scatter. We show that this process can still lead to solitons, but in a generalized form for which the changing response is compensated by changing the normalized wave size and intensity so as to maintain fixed the optical waveform.

Full C-band tunable laser based on electroholography

A tunable laser that spans the entire C band is presented. The laser consists of an Er-doped fiber amplifier gain medium, a fiber ring resonator, and an electroholography-based tuning mechanism. The electrohologram used is in the g44 configuration where the Bragg condition can be electrically tuned for a specific wavelength. Two laser architectures are presented, one in which the diffracting beam and one in which the direct beam of the electrohologram is used as the laser output. Switching time between wavelengths is limited by the gain medium relaxation time, since the electrohologram switching time is less than 1 ns.

A sub wavelength localization scheme in optical imaging using conical diffraction

In this paper we present a scheme for the acquisition of high temporal resolution images of single particles with enhanced lateral localization accuracy. The scheme, which is implementable as a part of the illumination system of a standard confocal microscope, is based on the generation of a vector beam that is manipulated by polarimetry techniques to create a set of illumination PSFs with different spatial profiles. The combination of data collected in different illumination states enables the extraction of spatial information obscured by diffraction in the standard imaging system. An implementation of the scheme based on the utilization of the unique phenomenon of conical diffraction is presented, and the basic strategy it provides for enhanced localization in the diffraction limited region is demonstrated.

Programming scale-free optics in disordered ferroelectrics

Using the history dependence of a dipolar glass hosted in a compositionally disordered lithium-enriched potassium tantalate niobate (KTN:Li) crystal, we demonstrate scale-free optical propagation at tunable temperatures. The operating equilibration temperature is determined by previous crystal spiralling in the temperature/cooling-rate phase space.

Diffraction cancellation over multiple wavelengths in photorefractive dipolar glasses

We report the simultaneous diffraction cancellation for beams of different wavelengths in out-of-equilibrium dipolar glass. The effect is supported by the photorefractive diffusive nonlinearity and scale-free optics, and can find application in imaging and microscopy.

Electro-activation and electro-morphing of photorefractive funnel waveguides

We demonstrate the electro-activation of funnel waveguides through the quadratic electro-optic effect in paraelectric potassiumlithium- tantalate-niobate. This allows us to achieve electro-optic intensity modulation in a single optical beam, a 1x2 switch, and finally the electrically controlled morphing of a single waveguide into a 1x2 and a 1x4 divider.

The electromagnetic response of human skin in the millimetre and submillimetre wave range

Recent studies of the minute morphology of the skin by optical coherence tomography revealed that the sweat ducts in human skin are helically shaped tubes, filled with a conductive aqueous solution. This, together with the fact that the dielectric permittivity of the dermis is higher than that of the epidermis, brings forward the supposition that as electromagnetic entities, the sweat ducts could be regarded as low Q helical antennas. The implications of this statement were further investigated by electromagnetic simulation and experiment of the in vivo reflectivity of the skin of subjects under varying physiological conditions (Feldman et al 2008 Phys. Rev. Lett. 100 128102). The simulation and experimental results are in a good agreement and both demonstrate that sweat ducts in the skin could indeed behave as low Q antennas. Thus, the skin spectral response in the sub-Terahertz region is governed by the level of activity of the perspiration system and shows the minimum of reflectivity at some frequencies in the frequency band of 75-110 GHz. It is also correlated to physiological stress as manifested by the pulse rate and the systolic blood pressure. As such, it has the potential to become the underlying principle for remote sensing of the physiological parameters and the mental state of the examined subject.

A tunable channel waveguide array fabricated by the implantations of He+ ions in an electrooptical KLTN substrate

An electrooptical channel waveguide array was constructed in potassium lithium tantalate niobate substrate by the implantation of He(+) ions at high energies. The array was fabricated by two successive implantation sessions at 1.6 MeV and 1.2 MeV through a comb-like stopping mask that limited the implanted ions to penetrate the substrate in 1 microm wide stripes periodically distributed at 3.5 microm intervals. This generated a grating of amorphized stripes with reduced refractive index. This was followed by a uniform implantation of He(+) ions at 1.8 MeV which created a bottom cladding layer below the array. Wave propagation in the array was studied by focusing a light beam at 636 nm into the central channel, and observing the wavefront it created at the output plane of the array. It was found that applying an electric field across the array strongly affects the coupling between adjacent channels and governs the width of the wavefront at the output plane.

Fast electroholographic switching

Electroholographic switching with a rise time of 13 ns is henceforth presented. The switching was demonstrated in a potassium lithium tantalate crystal doped with copper and titanium with Tc=10 degrees C. The crystal was operated at 17 degrees C. The switching operation was done in the g11/g12 configuration, in which the Bragg condition remains fulfilled at all levels of the applied field. As electroholography is a wavelength-selective switching method, this opens the way for implementing optical packet switching and fast wavelength addressing schemes in optical fiber networks that apply wavelength division multiplexing.

Photorefractive solitons of arbitrary and controllable linear polarization determined by the local bias field

We discuss and experimentally demonstrate a scheme to achieve photorefractive solitons of arbitrary linear polarization using the quadratic electro-optic effect and describe the observation of the self-trapping of a set of linear polarized beams in different positions of a paraelectric photorefractive crystal of potassium-lithium-tantalate-niobate (KLTN) biased by the inhomogeneous field produced by two miniaturized top electrodes. The polarization of the single solitons of the set is determined by the local electrostatic configuration and the underlying tunable anisotropy, which is detected through zero-field electro-activation.

Human skin as arrays of helical antennas in the millimeter and submillimeter wave range

Recent studies of the minute morphology of the skin by optical coherence tomography showed that the sweat ducts in human skin are helically shaped tubes, filled with a conductive aqueous solution. A computer simulation study of these structures in millimeter and submillimeter wave bands show that the human skin functions as an array of low-Q helical antennas. Experimental evidence is presented that the spectral response in the sub-Terahertz region is governed by the level of activity of the perspiration system. It is also correlated to physiological stress as manifested by the pulse rate and the systolic blood pressure.

Design methodology of refractive index engineering by implantation of high-energy particles in electro-optic materials

Slab waveguides were constructed in K(1-x)Li(x)Ta(1-y)Nb(y)O(3) crystals by the implantation of (12)C(+4) ions at 30 MeV and (16)O(+5) ions at 30 and 40 MeV. The waveguides were characterized by a prism coupler setup. A refractive index drop of 10.9% was observed in a layer formed by the implantation of (16)O(+5) ions at 30 MeV. The carbon-implanted waveguides were found to be thermally stable after annealing at 450 degrees C. A semiempirical formula for predicting the change in the refractive index given the parameters of the implantation process was developed. It is argued that the combination of the basic implantation process with the semiempirical formula can be developed to become a generic method for constructing complex electro-optic circuits with a wave-guided architecture.

Electroholographic tunable volume grating in the g44 configuration

The g(44) grating is an electroholographic transmission grating in which the applied field is perpendicular to both the grating vector and the wave vector of the incident beam. It is argued that in this configuration the incident beam traverses through a periodically rotating index ellipsoid. It is shown that in the g(44) configuration the Bragg condition is fulfilled for a specific value of the applied field and for a diffracting beam polarization that is perpendicular to that of the incident beam. Consequently, the g(44) grating can be used as an electrically controlled filter. Tunability of 7 nm is demonstrated in a 2mm thick grating.

Soliton-based Y-branch in photorefractive crystals induced through dispersion-shifted optical fiber

We experimentally demonstrate for what is believed to be the first time that a dispersion-shifted fiber can be used to electro-optically induce a soliton Y-branch structure in a photorefractive centrosymmetric paraelectric crystal (potassium lithium tantalate niobate). The application of a nonstationary external bias field enables us to stabilize the spatially partially coherent behavior of the optical beam at the fiber output. Furthermore, we show the switching capabilities of this soliton-based device in the optical communication field guiding a probe beam at a nonphotorefractive wavelength (1557 nm).

Emergence of linear wave segments and predictable traits in saturated nonlinear media

We find the key behind the existence traits of asymptotic saturated nonlinear optical solitons in the emergence of linear wave segments. These traits, produced by the progressive relegation of nonlinear dynamics to wave tails, allow a direct and versatile analytical prediction of self-trapping existence conditions and simple soliton scaling laws, which we confirm experimentally in saturated-Kerr self-trapping observed in photorefractives. This approach provides the means to correctly evaluate beam tails in the saturated regime, which is instrumental in the prediction of soliton interaction forces.

Electro-optic beam manipulation through photorefractive needles

We demonstrate electro-optic spatial two-dimensional mode switching in a bulk sample of potassium lithium tantalate niobate. Spatial confinement, mode coupling, and electro-optic functionality are mediated by two photorefractive needle solitons of opposite electroholographic charges embedded together in their anisotropic lobular structure.

Anisotropic charge displacement supporting isolated photorefractive optical needles

Strong asymmetry in the charge distribution supporting a single noninteracting spatial needle soliton in a paraelectric photorefractive is directly observed by means of electroholographic readout. Whereas in trapping conditions a quasi-circular wave is supported, the underlying double-dipolar structure can be made to support two distinct propagation modes.

Stable oscillating nonlinear beams in square-wave-biased photorefractives

We demonstrate experimentally that, in a paraelectric, nonstationary boundary conditions can dynamically halt the intrinsic instability of quasi-steady-state photorefractive self-trapping, driving beam evolution into a stable oscillating two-soliton-state configuration.

Soliton electro-optic effects in paraelectrics

The combination of charge separation induced by the formation of a single photorefractive screening soliton and an applied external bias field in a paraelectric is shown to lead to a family of useful electro-optic guiding patterns and properties.

Collisions and inhomogeneous forces between solitons of different dimensionality

We exploit nonlinear propagation in photorefractive crystals to observe the phenomenology associated with the collision and interaction of solitons of different tranverse dimensions: a self-trapped stripe and a round soliton. Along with evidence of particlelike behavior, our results indicate the emergence of a new phenomenology related to the hybrid-dimensional system.