Mode-matched Fano resonances for all-optical switching applications

We introduce the concept of mode-matched Fano resonances in one-dimensional, subwavelength, diffraction gratings. These resonances are characterized by an extremely high quality (Q)-factor and lend themselves well for applications to ultra-low power, all-optical switching devices at telecommunication wavelengths. We provide examples of diffraction gratings made of a chalcogenide glass (As₂S₃) where, thanks to the mode-matched Fano resonances, all-optical switching is obtained at local field intensities well below the photo-darkening threshold of the material.     

基于激发态吸收的C60分子全光开关特性研究

用５３２．０ｎｍ的脉冲Ｎｄ：ＹＡＧ激光作为泵浦光，７４７．０ｎｍ的连续半导体激光作为探测光，在Ｃ₆₀甲苯溶液中，利用Ｃ₆₀分子的三重态－三重态非线性吸收效应，获得Ｃ₆₀分子的全光开关和全光调制特性，并用速率方程进行了动力学数值模拟，得到与实验相一致的结果。 关键词：     

Plasmonic all-optical bistable device based on nematic liquid crystal

Low-power all-optical bistable liquid crystal (LC) devices are reported in which surface plasmons propagate along a metallic grating. The threshold switching illumination was 1.4 mW/mm² in the device with the twisted-nematic LC cell. This is a lower value than for all-optical bistable devices reported previously. This low-power bistability device can be used in two-dimensional optical memories or spatial light modulators.     

A study of threshold switching of NbO2 using atom probe tomography and transmission electron microscopy

Threshold switching is a phenomenon where the resistivity of an insulating material changes and the insulator exhibits metallic behavior. This could be explained by phase transformation in oxide materials; however, this behavior is also seen in amorphous insulators. In this study, through an ex-situ experiment using transmission electron microscopy (TEM), we proved that threshold switching of amorphous NbO₂ accompanies local crystallization. The change in I–V characteristics after electroforming was examined by evaluating the concentration profile. Atom probe tomography (APT) combined with in-situ TEM probing technique was performed to understand the threshold switching in amorphous NbO₂. The local crystallization in amorphous NbO₂ was validated by the observed difference in time-of-flight (ToF) between amorphous and crystalline NbO₂. We concluded that the slower ToF of amorphous NbO₂ (a-NbO₂) compared with crystalline NbO₂ (c-NbO₂) is due to the resistivity difference and trap-assisted recombination.     

Study on all-optical switching characteristics of ethyl orange-doped polymer film

The all-optical switching polymer thin films with azobenzene dye ethyl orange as the guest material and polyvinyl alcohol (PVA) as the host material were prepared by adulteration and spin-coating methods. The all-optical switching characteristics of the samples were measured at different intensities and modulation frequencies of the pump beam (532 nm, CW); the influence of doping concentration on the all-optical switching effect of the films was studied. It is shown that, under room temperature conditions and with a low pump power of 6 mW, the all-optical switch has a response time of about 2 ms and a modulation depth of 45%, and the maximal modulation depth reaches 90%. In addition, it is found that samples with higher doping concentration show a stronger all-optical switching effect but a larger background signal, and good switching performance is obtained by choosing the doping concentrations from 0.8% to 2% of the sample.     

Intrinsic resistive switching and memory effects in silicon oxide

Resistive switching behaviors are described in silicon oxide (SiO _x ) systems employing vertical E/SiO _x /E (E denotes the electrode) structures. The switching is largely independent of the electrode material and attributed to the intrinsic properties of SiO _x . Based on the recent experimental observation (Yao et al. in Nano Lett. 10:4105, 2010) of a silicon filament embedded in the SiO _x matrix, we further discuss the switching mechanism in light of the measured electrical phenomena. The set voltages are largely SiO _x -thickness independent, consistent with the mechanistic picture of point switching in the silicon filament. The multi-state switching and shifts in the set voltages with respect to the reset voltages are consistent with an electrochemical redox process (Si ↔ SiO _y ) at the switching site.     

Third-order nonlinear optical properties in [(C4H9)4N]2[Cu(C3S5)2]-doped PMMA thin film using Z-scan technique in picosecond pulse

An organometallic complex, [(C₄H₉)₄N]₂[Cu(C₃S₅)₂], abbreviated as BuCu, was synthesized. Then the BuCu-doped polymethylmethacrylate (PMMA) thin film with a doping concentration 1% by weight (1 wt.%) was fabricated using a spin-coating method and its third-order nonlinear optical properties were characterized using the Z-scan technique with 20 ps pulse duration at 532 and 1064 nm, respectively. The Z-scan curves have revealed that the material exhibits a self-defocusing effect at both wavelengths. Saturable absorption at 532 nm and two-photon absorption at 1064 nm were also found, respectively. Additionally, the calculated results of the material in film were compared with that of acetone solution, which indicated that the values in film were larger than that of acetone solution for about two orders in magnitude. The origins were analyzed of the difference between the two wavelengths. Our results suggest that considerable nonlinear optical properties were confirmed in BuCu-doped PMMA film. The material can easily be doped into PMMA film and forms a waveguide mode. So this material should be considered to be manufactured into devices and applied in all-optical switching, laser locking-mode, optical limiting fields etc.     

Au/MXene based ultrafast all-optical switching

All-optical switches have arisen great attention due to their ultrafast speed as compared with electric switches. However, the excellent optical properties and strong interaction of two-dimensional (2D) material MXene show great potentials in next-generation all-optical switching. As a solution, we propose all-optical switching used Au/MXene with switching full width at half maximum (FWHM) operating at 290 fs. Compared with pure MXene, the Au/MXene behaves outstanding performances due to local surface plasmon resonance (LSPR), including broadband differential transmission, strong near-infrared on/off ratio enhancement. Remarkably, this study enhances understanding of Au/MXene based ultrafast all-optical switching red-shifted about 34 nm in comparison to MXene, validating all optical properties of Au/MXene opening the way to the implementation of optical interconnection and optical switching.     

High-contrast all-optical switching with Pt:ethynyl complex

We have theoretically analyzed all-optical switching in Pt:ethynyl complex based on nonlinear excited-state absorption. A detailed analysis for Pt:ethynyl complex has been presented based on rate equation approach. It is shown that a pulsed pump laser beam at 355 nm switches the transmission of a cw probe laser beam at 633 nm through a Pt:ethynyl sample. The effect of various parameters, such as pump pulse width, peak pumping intensity, normalized parameter , transition times of S₁→S₀ and S₁→T₁ states and lifetime of triplet state, on switching characteristics has been analyzed in detail. It has been shown that the probe beam can be completely switched off (i.e. 100% modulation) by a pulsed pump laser beam at 50 kW/cm². These results have been used to design all-optical NOT and the universal NOR and NAND logic gates with multiple pump laser pulses.     

Wavelength-conversion type picosecond optical switching using a waveguide QPM-SHG/DFG device

We report picosecond all-optical switching in optical communication band using a LiNbO₃ waveguide quasi-phase matched second-harmonic generation/difference-frequency generation device. Analysis based on the beam propagation method showed that 1 ps switching with 3.1% efficiency is feasible with 10 W peak control pulse power. Switching efficiency of ?22 dB was demonstrated using control pulses of 10 ps width and 2 W peak power.     

Dynamic holograms recording in fullerene-containing solid-state matrices: Porous glass slides and PMMA films

Fullerene-containing solid-state matrices were studied theoretically and experimentally as the active material for all-optical switching devices. Dynamics hologram recording and spectral analysis were used to study temporal stability and efficiency of nonlinear response of the media. Porous glass and polymethylmethacrylate hosts were utilized as C₆₀-containing matrices. Experiments were carried out using nano- and picosecond laser radiation with wavelength 532 nm.     

All-optical control of the time delay in a one-dimensional photonic bandgap formed by double-quantum-wells

In this work, we show the feasibility of all-optical control of time delay in a Bragg grating with an active defect that consists in an asymmetric double quantum-well GaAs/Al_xGa_1−xAs. The double quantum-well is modeled as a Λ-V-type four level system. The refractive index of the defect can be modified by a control field due to the tunneling-induced quantum interference. It is shown that index changes as large as 0.4 can be obtained via cross-phase modulation. This allows for the development of a propagating mode at the selected wavelength. The existence of the mode permits the slow-down of light pulses, thus the system may act as a delay line with a group index as high as 100 operating at bandwidths of tens of GHz. We demonstrate that this defective photonic bandgap structure could enable ultrafast and ultrasensitive nonlinear all-optical switching at moderate powers of the control field.     

Nonlinear All-Optical Switching Device by Using the Spatial Soliton Collision

We propose a new nonlinear all-optical switching device by using the spatial solitons collision. This is 1 × N switching device controlled by two control beams. The numerical results show that this device could really function as a 1 × N all-optical switching device. This device is a potential key component in the application of optical signal processing and optical computing systems.     

Investigation of all-optical analog-to-digital quantization using a chalcogenide waveguide: A step towards on-chip analog-to-digital conversion

We have investigated all-optical analog-to-digital quantization by broadening the pulse spectrum in a chalcogenide (As₂S₃) waveguide and subsequently slicing the measured spectrum using an array of filters. Pulse spectral broadening was measured for 8 different power levels in a 6 cm long As₂S₃ waveguide and used to analyze an 8-level all-optical quantization scheme employing filters with full-width at half-maximum (FWHM) bandwidth of 2 nm. A supercontinuum spectrum with −15 dB spectral width up to 324 nm was observed experimentally at large powers. This large spectral broadening, combined with filtering using a 128 channel arrayed waveguide grating (AWG) with 2 nm filter spacing, has the potential for all-optical quantization with 7-bit resolution. In order to encode the quantized signal we propose an encoder scheme which can be implemented using optical Exclusive-OR gates. Demonstrating all-optical quantization using a planar waveguide is an important step towards realizing all-optical A/D conversion on a chip.     

Electrical properties of micrometric metallic dots obtained by porous polymeric membranes

We report on the fabrication of micrometric regular metallic arrays obtained by using, as a template, a polymeric membrane with regular pores. The membranes were prepared by embedding hydrophobized silica colloids into a polymer layer and subsequently removing them. We have investigated the electronic transport properties of the metallic arrays as a function of the applied electric field and temperature. Simple current voltage (IV) characteristics present a strong switching behavior with I_ON/I_OFF ratios up to 10⁴. Different temperature dependences of the resistance in the different ranges of the applied electric field have been observed. Finally, the performances of a field effect device (FET), with the conducting channel and insulating layer consisting of a Gold dot array and a STO substrate, respectively, have been investigated. The channel resistivity has been modified at least of two orders of magnitude and a mobility of about 2 cm²/V*s has been extracted by the analysis of the FET transfer curve.     

Effect of AlN layer on the resistive switching properties of TiO2 based ReRAM memory devices

The present study reports the resistive switching behaviour in Titanium Dioxide (TiO₂) material, with possible implementations in non volatile memory device. The Cu/TiO₂/Pt memory device exhibit uniform and stable bipolar resistive switching behaviour. The current-voltage (I-V) analysis shows two discrete resistance states, the High Resistance State (HRS) and the Low Resistance State (LRS). The effect of an additional AlN layer in the resistive memory cell is also investigated. The Cu/TiO₂/AlN/Pt device shows a multilevel (tri-state) resistive switching. Multilevel switching is facilitated by ionic and metallic filament formation, and the nature of the formed filaments is confirmed by performing a resistance vs. temperature measurement. The bilayer device shows improved reliability over the single layer device. The formation of high thermal conductive interfacial oxy-nitride (AlON) layer is the main reasons for the enhancement of resistive switching properties in Cu/TiO₂/AlN/Pt cell. The performance of device was measured in terms of endurance and retention, which exhibits good endurance over 10⁵ cycles and long retention time of 10⁵ s at 125 °C. The above result suggests the feasibility of Cu/TiO₂/AlN/Pt devices for multilevel non volatile ReRAM application.     

Resistive switching of silicon-rich-oxide featuring high compatibility with CMOS technology for 3D stackable and embedded applications

This paper discusses the resistive switching devices based on highly compatible silicon-rich-oxide, including silicon monoxide (SiO) and SiO _x N _y material, which can be fabricated by low temperature process, and thus fully compatible with the back-end CMOS technology. The demonstrated SiO based RRAM suitable for 3D stackable applications shows repeatable unipolar resistive switching behavior with excellent on/off resistance ratio and good retention performance, but a little bit high switching voltage. The presented silicon-rich silicon-oxynitride RRAM device can effectively reduce the switching voltages (∼1 V) and shows good retention capability under 180°C baking as well as fast speed, giving great potentials for 3D stackable and embedded applications. The switching mechanisms in the studied devices are discussed. The method of switching voltage reduction through nitrogen doping, as a kind of defect engineering, can provide some guidelines for RRAM design.     

Resistive switching behaviors of Cu/TaOx/TiN device with combined oxygen vacancy/copper conductive filaments

Forming-free and self-compliant bipolar resistive switching is observed in Cu/TaO_x/TiN conductive bridge random access memory. Generally, Pt has been investigated as an inert electrode. However, Pt is not desirable material in current semiconductor industry for mass production. In this study, all electrodes are adapted to complementary metal-oxide-semiconductor compatible materials. The self-compliant resistive switching is achieved via usage of TiN bottom electrode. Also, dissolved Cu ions in TaO_x lead to forming-free resistive switching behavior. The resistive switching mechanism is formation and rupture of combined oxygen vacancy/metallic copper conductive filament. We propose that Cu/TaO_x/TiN is a promising candidate for a conductive bridge random access memory structure.     

H2 storage efficiency and sorption kinetics in composite materials

We have prepared two different kinds of composite materials for hydrogen storage and studied their H₂ storage capacity and desorption kinetics. The first composite material consists of magnesium-containing transition metal nanoclusters distributed in the Mg matrix (Mg:TM): this composite material shows better H₂ desorption performances than pure Mg. This improvement is attributed to the role of the MgH₂-TM nanocluster interface as preferential site for hexagonal Mg (h-Mg) nucleation and to the rapid formation of interconnected h-Mg domains where H diffusion during desorption occurs. The second composite material consists of LaNi₅ particles (size<30 μm) distributed in a polymeric matrix. The H₂ storage capacity is negligible at low metal content (50 wt%) when the metal particles are completely embedded in the polymeric matrix. The H₂ storage capacity is comparable to that of the pure LaNi₅ powders at high metal content (80 wt%) when a percolative distribution is assumed by the LaNi₅ particles: this evidence points out the role of metal-metal interfaces and of interconnected metallic networks for H transport.     

Picosecond nonlinearity of GeO2–Bi2O3–PbO–TiO2 glasses at 532 and 1,064 nm

The third-order optical properties of GeO₂–Bi₂O₃–PbO–TiO₂ glasses at 532 nm and 1,064 nm were studied to evaluate their potential for optical limiting and all-optical switching. The Z-scan technique was used to determine the nonlinear (NL) refractive index, n ₂, and the NL absorption coefficient, α ₂, of samples with different amounts of the constituent oxides. Values of n ₂ ≈ + 0.7 × 10^?14 cm²/W at 1,064 nm and ≈+1.5 × 10^?14 cm²/W at 532 nm were measured. The NL absorption coefficient, α ₂, was smaller than the minimum that our apparatus can measure (α ₂ < 0.01 cm/GW) in the near-infrared (1,064 nm); in the visible region (532 nm), we obtained α ₂ ≈ 4.4 cm/GW. The set of NL parameters measured indicates the potential usefulness of the GeO₂–Bi₂O₃–PbO–TiO₂ glasses for all-optical switching at 1,064 nm and for optical limiting at 532 nm.