Nonlinear Transmission Properties Research Articles

Study of resistive properties and neural response of ZrO2/TiO2 heterojunction nanowire array (NWA) RRAM

Nowadays, the researcher has an eye on enhancing the performance of resistive random-access memory (RRAM) and exploring new demands and applications, particularly in the field of artificial intelligence and neural computing. It is crucially important for accurately replicating the observed plasticity within synapses to achieve superior RRAM performance in low-dimensional nanomaterials. In this work, we focus on addressing certainly unsatisfactory electrical properties of RRAM based on titanium oxide nanowire array (TiO2 NWA), for example, short retention time (∼103 s). Theoretically and experimentally, a novel and solution-based RRAM structure, namely ZrO2/TiO2(NWA), has been conducted. With the help of the ZrO2 insertion layer, the RRAM device shows impressive resistive switching characteristics, including 200 current–voltage(I-V) sweeps without degradation, increased cycling endurance (>105 cycles), and a long retention time (∼9 × 104 s). These findings hold significant implications for digital computing systems. Moreover, the successful implementation of the proposed device enables the emulation of fundamental synaptic biological features such as non-linear transmission properties, learning experiences behavior, short-term potentiation (STP) and long-term potentiation (LTP). This research provides evidence of the immense potential of the Ag/ZrO2/TiO2(NWA)/FTO RRAM device in bipolar non-volatile memory (NVM) and biomimetic neuromorphic systems.

Femtosecond nonlinear losses in multimode optical fibers

Multimode optical fibers are attracting a growing interest for their capability to transport high-power laser beams, coupled with novel nonlinear optics-based applications. However, optical fiber breakdown occurs when beam intensities exceed a certain critical value. Optical breakdown associated with irreversible modifications of the refractive index, triggered by multiphoton absorption, has been largely exploited for fiber material micro-structuration. Here we show that, for light beam intensities slightly below the breakdown threshold, nonlinear absorption strongly affects the dynamics of a propagating beam as well. We experimentally analyze this subthreshold regime and highlight the key role played by spatial self-imaging in graded-index fibers for enhancing nonlinear optical losses. We characterize the nonlinear power transmission properties of multimode fibers for femtosecond pulses propagating in the near-infrared spectral range. We show that an effective N-photon absorption analytical model is able to describe the experimental data well.

Low-Power and Tunable-Performance Biomemristor Based on Silk Fibroin.

Biomemristors have attracted significant attention because of their potential applications in logic operations, nonvolatile memory, and synaptic emulators, thus leading to the urgent need to improve memristive performance. In this work, a silk fibroin (SF)-based memristor, integrated with both low power and low operating current simultaneously, has been reported. Doping the SF with Ag and an ethanol-based post-treatment promote microcrystal formation in the bulk of the SF. This induces carrier transport along fixed, short paths and results in a low set voltage, low operating current, and high memristive stability. Such performances can greatly reduce power consumption and heat generation, beneficial for the accuracy and durability of memristor devices. The memristive mechanism of SF-based memristors with different Ag contents is the space-charge-limited conduction (SCLC) mechanism. In addition, the nonlinear transmission property of SF-based memristors suggests useful applications in bioelectronics.

Nonlinear optical behavior and optical power limiting characteristics of peripheral symmetrical and non-symmetrical zinc phthalocyanines with nanosecond pulsed excitation

In this study, the optical nonlinear absorption and optical limiting performances of symmetrical and non-symmetrical zinc phthalocyanines in tetrahydrofuran (THF) solution were conducted by the open aperture z-scanning technique. A new non-symmetrically substituted metallophthalocyanine, namely 2(3)-[(4-nitrophenyl)ethynyl]-{9(10),16(17),23(24)-tris-(3,5-bis(trifluoromethyl)phenoxy)-phthalocyaninato}zinc(II) (1b), was synthesized and then characterized by applying different spectroscopic methods, such as FT-IR, 1H NMR and MALDI-TOF spectroscopy. According to the literature, {2(3),9(10),16(17),23(24)-tetrakis-(3,5-bis(trifluoromethyl)phenoxy)-phthalocyaninato}zin(II) (1a), {2,3,9,10,16,17,23,24-octakis-(3,5-bis(trifluoromethyl)phenoxy)-phthalocyaninato}zinc(II) (2a) and 2(3)-[(4-nitrophenyl)ethynyl]-{9,10,16,17,23,24-hexakis-(3,5-bis(trifluoromethyl)phenoxy)-phthalocyaninato}zinc(II) (2b) were prepared. The effect of the symmetry and substituent’s number on the nonlinear behavior was determined. A Nd:YAG laser, nanosecond pulsed at 532 nm, was used as the excitation source. The measurements of the input-output power and the nonlinear transmission properties were carried out for different excitation power values and different concentrations of the phthalocyanines in the THF solution. The nonlinear absorption coefficient of βand the imaginary part of the third order nonlinear susceptibility of the medium (X3) were found to be strongly dependent on the concentration. All the zinc phthalocyanine complexes showed good optical limiting performances, attributed to a reverse saturable absorption (RSA) process. The results indicate that the zinc phythcyanine complexes are promising candidates for optical limiting materials.

Nonlinear transmission properties of chloroindium phthalocyanines for picosecond pulse trains

We studied the optical dynamics and propagating properties of two chloroindium phthalocyanines with α- and β-alkoxyl substituents interacting with picosecond pulse trains. The pulse train contains 35 picosecond subpulses with 12 ns spacing, and the width of each subpulse is 100 ps. We applied a five-level model to simulate the interaction by solving two-dimensional paraxial field equation coupled with rate equations. Photophysical parameters of molecules are extracted from the experiment and we employed Crank–Nicholson numerical method to get accurate and credible results. The sequential (singlet-singlet) × (triplet-triplet) two-photon absorption is the vital optical limiting channel for long pulse trains. Our work indicates that chloroindium phthalocyanine with β-alkoxyl substituent shows better optical limiting behaviors for picosecond pulse trains, which is opposite with the result for one single nanosecond laser.

Dye concentration dependence of spectral triplet in one-dimensional photonic crystal with cyanine dye J-aggregate in strong coupling regime

We report on the dye concentration dependence of nonlinear transmission properties of one-dimensional photonic crystal microcavities containing cyanine dye J-aggregates. Using femtosecond nonlinear transmission spectroscopy, we observed a transition from a polariton doublet state to a spectral triplet state over the whole tested concentration range, even at room temperature. In these samples, changes in the dye concentration affected the Rabi splitting energy in the linear transmission measurements; however, we found that changes in the concentration did not greatly affect the triplet formation.

Self-Assembly of Silver and Gold Nanoparticles in a Metal-Free Phthalocyanine Liquid Crystalline Matrix: Structural, Thermal, Electrical and Nonlinear Optical Characterization

The properties of self-assembled supramolecular structures change remarkably upon the dispersion of a minute amount of metal nanoparticles in them. Here we present, for the first time, investigations of the effect of dispersing alkyl thiol functionalized group-XI metal nanoparticles (silver and gold) in a phthalocyanine-based discotic liquid crystal on their structural, electrical, thermal and nonlinear optical transmission properties, and supramolecular order. Results indicate uniform dispersion of about 0.5-3 % metal nanoparticles in the columnar matrix which results in an increase of the electrical conductivity of the system by two to four orders of magnitude, without disrupting the mesophase. We also show that dispersing metal nanoparticles in these nanocomposites enhances their nonlinear optical absorption, when measured under excitation by nanosecond laser pulses at 532 nm. These results indicate that the present self-assembling supramolecular soft nanocomposites are potential candidates for applications in optoelectronic devices such as thin film transistors, photovoltaic solar cells, and optical limiters.

Implementation of Linear Sensory Signaling via Multiple Coordinated Mechanisms at Central Vestibular Nerve Synapses

Signal transfer in neural circuits is dynamically modified by the recent history of neuronal activity. Short-term plasticity endows synapses with nonlinear transmission properties, yet synapses in sensory and motor circuits are capable of signaling linearly over a wide range of presynaptic firing rates. How do such synapses achieve rate-invariant transmission despite history-dependent nonlinearities? Here, ultrastructural, biophysical, and computational analyses demonstrate that concerted molecular, anatomical, and physiological refinements are required for central vestibular nerve synapses to linearly transmit rate-coded sensory signals. Vestibular synapses operate in a physiological regime of steady-state depression imposed by tonic firing. Rate-invariant transmission relies on brief presynaptic action potentials that delimit calcium influx, large pools of rapidly mobilized vesicles, multiple low-probability release sites, robust postsynaptic receptor sensitivity, and efficient transmitter clearance. Broadband linear synaptic filtering of head motion signals is thus achieved by coordinately tuned synaptic machinery that maintains physiological operation within inherent cell biological limitations.

Research on the controllable nonlinear laser transmission properties of MoS2 nano-micron film

Ultrashort femtosecond pulse laser (pulse duration 2 nano-micron films (thickness 150–200 nm) are prepared by spin-coating method. Optical limiting test results show that for the ultrashort pulse laser, this film shows increasing transparency at low light intensity, while it shows decreasing transparency at a higher light intensity (optical limiting). It is capable of changing the optical limiting threshold by changing the incident wavelength which can be used for transparency enhancement and protection against damage of concentrator solar cells. Using this method to have a commercial GaAs solar cells coated found the conversion efficiency reduction 50%.

Pulse width shaping of passively mode-locked soliton fiber laser via polarization control in carbon nanotube saturable absorber

We report the continuous control of the pulse width of a passively mode-locked fiber laser via polarization state adjustment in a single-walled carbon nanotube saturable absorber (SWCNT-SA). The SWCNT, coated on the side-polished fiber, was fabricated with optimized conditions and used for stable mode-locking of the fiber laser without Q-switching instabilities for any polarization state of the laser intra-cavity. The 3-dB spectral bandwidth of the mode-locked pulses can be continuously tuned from 1.8 nm to 8.5 nm with the polarization control for a given laser cavity length and applied pump power. A pulse duration varying from 470 fs to 1.6 ps was also observed with a change in the spectral bandwidth. The linear and the nonlinear transmission properties of the SA were analyzed, and found to exhibit different modulation depths depending on the input polarization state in the SA. The largest modulation depth of the SA was observed at the polarization state of the transverse electric mode that delivers shortest pulses at the laser output.

Ultrafast transition between polariton doublet and alternating current Stark triplet in organic one-dimensional photonic crystal microcavity

This work investigates nonlinear transmission properties of cavity polaritons in a one-dimensional photonic crystal microcavity containing pseudoisocyanine J-aggregates. It was observed that an unexpected transmission peak appeared between the two peaks of cavity polaritons, when the incident light intensity was high. The decay time of this third peak, determined by the pump-probe transient transmission spectroscopy, was less than 1 ps. We observed ultrafast transition between the cavity polariton doublet and AC Stark triplet in an organic system.

Nonlinear transmission properties of hydrogenated amorphous silicon core fibers towards the mid-infrared regime

The nonlinear transmission properties of hydrogenated amorphous silicon (a-Si:H) core fibers are characterized from the near-infrared up to the edge of the mid-infrared regime. The results show that this material exhibits linear losses on the order of a few dB/cm, or less, over the entire wavelength range, decreasing down to a value of 0.29 dB/cm at 2.7μm, and negligible nonlinear losses beyond the two-photon absorption (TPA) edge ~ 1.7μm. By measuring the dispersion of the nonlinear Kerr and TPA parameters we have found that the nonlinear figure of merit (FOM(NL)) increases dramatically over this region, with FOM(NL) > 20 around 2μm and above. This characterization demonstrates the potential for a-Si:H fibers and waveguides to find use in nonlinear applications extending beyond telecoms and into the mid-infrared regime.

Blue-phase liquid crystal cored optical fiber array with photonic bandgaps and nonlinear transmission properties

Blue-phase liquid crystal (BPLC) is introduced into the pores of capillary arrays to fabricate fiber arrays. Owing to the photonic-crystals like properties of BPLC, these fiber arrays exhibit temperature dependent photonic bandgaps in the visible spectrum. With the cores maintained in isotropic as well as the Blue phases, the fiber arrays allow high quality image transmission when inserted in the focal plane of a 1x telescope. Nonlinear transmission and optical limiting action on a cw white-light continuum laser is also observed and is attributed to laser induced self-defocusing and propagation modes changing effects caused by some finite absorption of the broadband laser at the short wavelength regime. These nonlinear and other known electro-optical properties of BPLC, in conjunction with their fabrication ease make these fiber arrays highly promising for imaging, electro-optical or all-optical modulation, switching and passive optical limiting applications.

Asymmetric Positive-Negative Index Nonlinear Waveguide Couplers

Nonlinear optical couplers have attracted significant attention largely due to the many advantages they offer for optical communications and signal processing. Combined with the unique properties of an emerging new class of materials, metamaterials, nonlinear directional couplers open fundamentally new opportunities for the development of ultracompact signal processing functionalities for on-chip applications. In this paper, we explore theoretically nonlinear transmission properties of asymmetric nonlinear couplers with one channel made of positive index material and the other channel made of negative index material while only one of the channels is nonlinear. We demonstrate that such asymmetric couplers can be bi- and multistable, and we optimize the design with respect to the bistability threshold.

Simple way for achieving passive all-optical switching of continuous waves lasers using pure nematic liquid crystal

We have examined pure nematic liquid crystal (LC), 4'-pentyl-4-biphenylcarbonitrile (5-CB), with a 90° twisted alignment within a cell made of two cross-polarized absorptive plastic polarizers, and investigated the nonlinear transmission properties using cw (532 nm) lasers. We observed optically self-activated polarization switching with a factor of three lower switching power than a dye-doped LC cell with similar linear transmittance using glass substrates. We also studied the dynamics of the switching processes and observed millisecond switching time. These studies have demonstrated a simpler but more efficient way for fabricating broadband, low switching power, millisecond time scale switching, and optical limiting devices.

Nonlinear optical characterization of new thiophene‐based conjugated polymers for photonic switching applications

AbstractThis research article describes a technique to synthesize new donor−acceptor‐type conjugated polymers carrying 1,3,4‐oxadiazolyl‐naphthalene and 3,4‐(ethylenedioxy/diphenyl)‐thiophene moieties (P1 and P2) starting from 2,2′‐sulfanediyldiacetic acid and diethyl ethanedioate through multistep reactions. The newly synthesized intermediates and the final polymers have been characterized by different spectroscopic techniques followed by elemental analysis. Their optical and electrochemical properties have been investigated by UV–visible, fluorescence spectroscopy, and cyclic voltammetric studies, respectively. Furthermore, the nonlinear optical transmission properties of these polymers have been investigated by the open aperture z‐scan technique. The new polymers P1 and P2 have well‐defined structures, good thermal stability, and band gaps of 1.98 and 1.88 eV, respectively. They emit bluish‐green fluorescence both in solution and in film state. Interestingly, these polymers show saturable absorption behavior. The results of nonlinear optical studies reveal that they are potential candidates for photonic switching device applications. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 30: 312–321, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20227

Hybrid ion acceleration with ultrathin composite foils irradiated by high intensity circularly-polarized laser light

A complete analytical description of ion acceleration in the laser radiation-pressure regime is presented. The combined effects of hot electron and light-pressure phenomena are used to qualitatively and quantitatively describe most recent experimental results in this regime. An essential part of the developed model is exhibited in the calculation of nonlinear laser light reflection and transmission properties, as well as in the spectral characterization of the laser light after interaction. The validity of the analytical model is supported by recent experimental results and by particle-in-cell simulations.

Nonlinear transmission properties of hydrogenated amorphous silicon core optical fibers

The nonlinear properties of a low loss hydrogenated amorphous silicon core fiber have been characterized for transmission of high power pulses at 1540 nm. Numerical modelling of the pulse propagation in the amorphous core material was used to establish the two-photon absorption, free-carrier absorption and the nonlinear refractive index, which were found to be larger than the values typical for crystalline silicon. Calculation of a nonlinear figure of merit demonstrates the potential for these hydrogenated amorphous silicon core fibers to be used in nonlinear silicon photonics applications.

Tetrabrominated Lead Naphthalocyanine for Optical Power Limiting

The complex 2,(3)-tetrabromo-3,(2)-tetra[(3,5-di-tert-butyl)phenyloxy]-naphthalocyaninato lead [Br(4)(tBu(2)C(6)H(3)O)(4)NcPb, 1] has been prepared and its optical limiting properties for ns light pulses have been measured. Complex 1 behaves as a reverse saturable absorber within the spectral range 440-720 nm with a limiting threshold of 0.1 J cm(-2) at 532 nm. The lifetime of the absorbing triplet excited state has been evaluated as 3.8 x 10(-7) s and the quantum yield of triplet formation has been measured as 0.07 in toluene. The nonlinear optical transmission properties of complex 1 have also been determined in Plexiglas [naphthalocyanine content: 5.0 x 10(-4) M (0.1% by weight)]. A reversible nonlinear absorption was again observed for a fluence above 0.4 J cm(-2), but through different excited-state dynamics. This may be rationalized in terms of aggregation of the molecule in the polymer matrix.

Coupled mode analysis of nonlinear defects in photonic crystals

We present a general analysis of the coupling of nonlinear photonic crystal cavities using coupled-mode theory. The nonlinear transmission properties of two coupled nonlinear cavities have been investigated. We validate the analysis by comparing the theoretical result with rigorous numerical simulations based on finite-difference time-domain techniques. A device consisting of two nonidentical photonic crystal cavities is proposed, by which we demonstrate that this theory can be employed for designing high-contrast all-optical switches or diodes.