Input Pulse Width Research Articles

Self-Powered Dye-Sensitized Solar-Cell-Based Synaptic Devices for Multi-Scale Time-Series Data Processing in Physical Reservoir Computing.

Physical reservoir computing (PRC) using synaptic devices has attracted attention as a promising edge artificial intelligence device. To handle time-series data on various time scales, it is necessary to fabricate devices with the desired time scale. In this study, we fabricated a dye-sensitized solar-cell-based synaptic device with controllable time constants by changing the light intensity. This device showed synaptic features, such as paired-pulse facilitation and paired-pulse depression, in response to light intensity. Moreover, we found that the high computational performance of the time-series data processing task was achieved by changing the light intensity, even when the input pulse width was varied. In addition, the fabricated device can be used for motion recognition tasks. This study paves the way for realizing multiple time-scale PRC.

Optimization of efficiency of short-pulsed fast flow CO2 laser amplifier with dual-band and multispectral lines

In this paper, we optimize the amplification efficiency of a nanosecond pulse CO2 laser in a fast flow amplifier using dual-band and multispectral lines techniques. Utilizing a six-temperature model and a random rotational relaxation model, we simulate the time-domain amplification process of dual-band and multispectral lines short-pulse seeds in a fast flow CO2 laser amplifier, analyzing the effects of input pulse fluence, pulse width, and spectral line composition on amplification efficiency. Compared to single-line 10P(20) amplification, the extraction efficiency of 10.6-µm and 9.6-µm dual-band two-line 15-ns pulses is improved by approximately 70%, surpassing that of 10.6-µm single-band four-line amplification. This study is of great significance for the efficient amplification of short-pulse CO2 lasers and the generation of extreme ultraviolet light from laser produced plasma.

Enhancement of Q-Switched Erbium-Doped Fibre Laser Performance using Graphene Oxide-Calcium Oxide Thin Film Saturable Absorbers

This paper presents an experiment utilizing calcium oxide (CaO) from the cuttlefish bone combined with graphene oxide (GO) to create a graphene oxide-calcium oxide (GO-CaO) based saturable absorber (SA) for Q-switched erbium-doped fibre lasers. The experiment aims to investigate the impact of calcium oxide when added to graphene oxide to form the SA thin film. The laser performance of both types of SA was compared, considering their input pump power, repetition rate, pulse width, and output power. The results indicated that the graphene oxide – calcium oxide SA thin film provided the best output power and the lowest threshold input pump power at 10.76 µW and 53.12 mW, respectively. In the characterization, UV-Vis spectroscopy was utilized to determine the number of discrete wavelengths in UV or visible light that the materials absorbed or transmitted. The UV-Vis results indicated that the graphene oxide thin film exhibited an absorbance value of 0.049 AU and a transmittance value of 89.25 % at a wavelength of 1565 nm. In comparison, the GO-CaO SA thin film displayed an absorbance value of 0.037 AU and a transmittance value of 91.89 % at the same wavelength. Raman spectroscopy was also conducted to provide details about the chemical structure and crystallinity of the thin film samples. The results showed high-intensity peaks for the GO thin film at wavenumbers of 1353.74 cm-1 and 1609.85 cm-1, and for GO – CaO thin film at wavenumbers of 1358.56 cm-1 and 1612.18 cm-1. Additionally, SEM was utilized to study the morphology of the thin film samples. Based on the characterization and laser performance results, it was concluded that the addition of calcium oxide to graphene oxide enhances the properties of the SA thin film, leading to improved laser performance due to its higher thermal conductivity.

Method to determine the optimal impedance profile of nonuniform transmission lines used for pulsed power accelerators

Nonuniform transmission lines (NTLs) are widely used in pulsed power accelerators because they provide an efficient way to achieve impedance matching and pulse shaping. Since designing and constructing these accelerators typically demands substantial effort, finding the optimal impedance profile to maximize the power transmission efficiencies of the NTLs is important. In this paper, a convenient numerical method to determine the optimal impedance profile is proposed. First, the output of the NTL with arbitrary parameters is theoretically analyzed under arbitrary input conditions. It was found that only four factors affect the power transmission efficiency: the ratio of output impedance to input impedance, the ratio of input pulse width to the NTL’s one-way transit time, the normalized impedance profile, and the normalized input pulse. Based on these findings, a method designed to minimize the reflected component within the working frequency range is proposed. Using this method, an impedance profile demonstrating superior power transmission efficiency compared to the traditional exponential profile is identified. This work can provide a rapid and effective method to determine the impedance profile of the NTL, undoubtedly benefiting the design process of pulsed power accelerators. Published by the American Physical Society 2024

Investigation of Multimode Self-Similar Pulse Compression in Tapered Photonic Crystal Fibers

In this paper, we theoretically investigate the multimode self-similar pulse compression (MM-SSPC) in tapered photonic crystal fibers. To expand the self-similar theory beyond single-mode scenarios, we have discovered through analytical analysis that the width of the input pulse has a significant impact on perturbing the MM-SSPC process. We proceed to solve the multimode generalized nonlinear Schrödinger equation using numerical methods for various input pulse widths, which leads to the observation of three distinct types of multimode pulse compression. MM-SSPC only takes place when the input pulse width is comparatively longer. Our numerical results are consistent with the predictions of analytical calculations. Our results demonstrate that by using input pulses of 2.5 ps in duration, three modes can be compressed in a self-similar manner to 200 fs, which corresponds to a compression factor of 12.5. Finally, We establish the minimum input pulse width required to enable the MM-SSPC to function for the three specific modes of interest. Our findings provide an effective guidance to design pulse compressor for the generation of pedestal-free, high-energy femtosecond pulses.

Pulsed Eddy Current Sensor for Cascade Electrical Conductivity and Thickness Estimation in Nonferrous Metal Plates

This paper presents a pulsed eddy current (PEC) sensor design for cascade electrical conductivity and thickness estimation in non-ferrous metal plates. With a single excitation coil design, the combined change in magnetic flux density caused by the excitation coil and the induced eddy current (EC) in the test plate is detected by a compact anisotropic magneto-resistive (AMR) sensor. The effects of the varying input pulse width are discussed with both numerical simulations in commercial finite element analysis (FEA) software and experimental results, and the time-domain characteristics of the responses are analyzed in relation to the properties of the test plates. It is revealed that the electrical conductivity can be gauged based on the peak value of the short pulse response, and with a known electrical conductivity value, plate thickness can be subsequently derived with the rise time of the long pulse response. A cascade estimation process is therefore proposed to calculate the parameters sequentially by adopting hybrid input signals with both short and long input pulses. Verified by the FEA results, this cascade estimation process was then experimentally validated with a prototype of the PEC sensor.

Pulse width dependent operations of a Ag2S island network reservoir

The rapid growth in demand for edge artificial intelligence increases importance of physical reservoirs that work at low computational cost with low power consumption. A Ag2S island network also works as a physical reservoir, in which various physicochemical phenomena contribute to a reservoir operation. In this study, we investigated its frequency dependence and found that diffusion of Ag+ cations in a Ag2S island, which has a relaxation time of about 100 μs, plays a major role when performance is improved. Modified National Institute of Standards and Technology (MNIST) classification task using an input pulse width of 100 μs resulted in the accuracy of 91%. Iterative operations up to 10 million cycles revealed a small enough standard deviation of output, suggesting a potential for practical use of a Ag2S island network as a reservoir.

Phase-change material-assisted all-optical temporal differentiator.

This paper proposes a novel microring resonator (MRR)-based all-optical tuning temporal differentiator (DIFF). Specifically, the DIFF uses nonvolatile phase-change material Ge2Sb2Te5 (GST) to achieve low energy consumption and high-speed optical control of the state of the MRR, avoiding the traditional electro-optic (EO) and thermo-optic (TO) tuning designs. By changing the crystallinity of GST to changing the coupling regimes of the MRR, a broad range for the differentiation order α, i.e., 0.47-1.64 can be realized. The intensity response and phase response of the GST-assisted MRR, and normalized intensity in the output of the temporal DIFFs for Gaussian optical pulses have been obtained by simulation. Furthermore, input pulse width and detuning influence on the differentiation order and output deviation are discussed. Finally, our structure can effectively reduce the chip area and power consumption compared with the traditional EO and TO tuning designs.

All-optical pulse shaper based on the cascaded axis-aligned SFS fiber structure filter

We proposed a cascaded axis-aligned single mode-four mode-single mode (SFS) fiber structure filter as an all-optical pulse shaper. It’s shown that pulse shapers with different intensity profiles output can be achieved by adjusting the parameters of the cascaded SFS fiber structures. We designed and obtained flat-top, triangular and parabolic pulse shapers using cascaded axis-aligned SFS fiber structure filters at different input pulse widths, followed by characterizations. The proposed design provides a simple and competitive way to implement optical arbitrary waveform generators.

Influence of modulator injection width on comprehensive two-dimensional gas chromatography peak dimensions.

This study examines how the height and width of peaks exiting the secondary column of a comprehensive two-dimensional gas chromatography (GC × GC) separation are affected by the width of the pulse introduced to the secondary column. A flow-modulated GC × GC apparatus was assembled that allowed input pulse widths to be controlled precisely over a range of 10 to 70ms. GC × GC chromatograms were obtained using secondary columns containing a polyethylene glycol stationary phase with internal diameters of 0.25 and 0.32mm. The area, height, and width of peaks emerging from the secondary column were found to be accurately modeled by the convolution of a rectangular function with a Gaussian distribution. The rectangular function represents the input pulse, and the Gaussian distribution represents the broadening that occurs in the secondary column. The minimum peak width that could be produced by the secondary column was determined for a wide range of compounds. Injection pulse widths that matched a compound's minimum peak width produced peaks that were 25% wider than the minimum width and had heights that were 76% of the maximum possible peak height. Increasing the injection width significantly above the minimum width yielded substantially broader peaks with only a modest increase (< 25%) in peak height.

Generation of Parabolic pulse by nonlinear pulse reshaping inside a Silicon on Insulator (SOI) Waveguide

In recent times, silicon photonics attracts a lot of attraction of researchers. It is the technology that converts many functions of the circuit on the thumb-size chip. Nowadays, various types of technology platforms are being used to design photonic integrated circuits using various materials such as high index glass, semiconductors, polymers, and silicon. In our work, we have used silicon to design rectangular silicon on Insulator (SOI) buried waveguide. This type of waveguide has shown great potential in the field of pulse reshaping. We have used the effective index method for the calculation of group velocity dispersion and nonlinearity. Though the two-photon absorption and free-carrier generation contribute significantly to loss parameters, the highly nonlinear buried waveguide is found to be capable of reshaping super-Gaussian pulse input into a parabolic shape. Moreover, the values of input chirp, pulse width, and peak power are further optimized for the generation of a high-quality parabolic pulse at shorter lengths. The length required for pulse reshaping is much less when compared to optical fibers. Thus, our design waveguide has potential in the domain of pulse generation, signal processing, and many more.

Numerical Study of Parabolic Pulse Generation in Backward-Pumped Erbium-Doped Fiber Amplifiers

In this paper, the actual shape of the gain spectrum and the whole dispersion curve of the Er-doped fiber are employed in the vectorial coupled nonlinear Schrödinger equation to model the parabolic pulse (similariton) generation in the backward-pumped Er-doped fiber amplifier. The input of the amplifier is Gaussian pulses of a high repetition rate. The numerical model is developed to account for the combination of input and amplified spontaneous emission powers to consider the average of all prior iterations in the present interaction to reach a converged solution rather than oscillating between two solutions. The excess kurtosis factor identifies the parabolic pulse among other pulse shapes. The effect of the input pulse width, peak power, and polarization and the impact of the input pump power and the fiber length on the similariton generation are studied.

Generation of stable temporal doublet by a single-mode silicon core optical fiber

A highly nonlinear single mode anomalous dispersion silicon-core fiber is designed and optimized at the operating wavelength of 2.2 µm for the purpose of generating stable temporal pulse doublets. To designate the output pulse pair as a perfect Gaussian doublet, two new parameters, dissimilarity factor () and co-similarity index (μ cs) are introduced. Different input pulse parameters such as power, pulse width and chirp are optimized to obtain Gaussian temporal doublets at the shortest optimum length (∼few cm) which is sufficiently smaller in comparison to silica fibers reported earlier. The output pulse pairs remain as a doublet for quite a good stability length. In view of serving practical purposes, the possibilities of fluctuations of input power and pulse width are included to investigate the changes in stability length and effective repetition rate (ERR). The change in ERR along the fiber length produces a remarkable change in free carrier concentration in core, which has also been taken into account for the first time as per our knowledge to obtain the temporal pulse doublet in the so designed Si-core fiber.

Two-Photon Absorption Effect on Pseudorandom Bit Sequence for High-Speed Operation

Study of two-photon absorption (TPA) has been carried out for all-optical logic operation based on quantum-dot semiconductor optical amplifier (QD-SOA). XOR gate, AND gate and pseudo-random bit sequence (PRBS) were all modeled with the TPA effect on the existing rate equation. Inclusion of TPA induced pumping has increased the output Q-factor (quality). The output result demonstrates that the quality of the output is dependent on the input pulse width and the operation speed. The PRBS system modeled with TPA shows that it can operate at 250 Gb/s and 320 Gb/s and increase in pulse width decrease the Q-factor.

Scaling of self-compression of near-IR femtosecond pulses in hollow-core fibers down to the single-cycle limit

We numerically investigate the scaling of self-compression processes with experimental parameters for near-infrared ultrashort pulses (30 fs) in gas-filled hollow-core fiber (HCF). These simulations over a wide-range of input pulse energies as well as filling gas pressures reveal a remarkable scaling of the self-compression process and dynamics. As a function of soliton order N, we identify the relation between the propagation distance after which self-compression in the HCF begins and the subsequent propagation length up to which the pulse remains maximally compressed; both these length scales decrease with an increase in N, the soliton order. Although previous investigations revealed pulse compression scaling laws which provide a good approximation for input pulse-widths ∼100 fs down to the limit where soliton fission begins to dominate the dynamics, these are not sufficiently accurate to describe the entire scaling dynamics. Instead, we identify a more generalized set of scaling laws by taking both third-order dispersion and the saturation of the compression factor due to soliton fission into account. These conclusions about scaling are robust: our simulations were carried out over a wide range of realistic input pulse energies and gas pressures as implemented in laboratories taking into account higher-order dispersive properties of the gaseous propagating medium. Therefore, given that these numerical investigations consider conditions typically applied in practice in laboratories, this work provides elegant design principles and guideposts relevant to realizing systems capable of achieving self-compression at substantially high pulse energies down to the few-cycle limit; they are of paramount importance in generating single as well as trains of attosecond pulses and acceleration strategies for electrons and ions in intense laser pulses.

A Time-Domain z−1 Circuit with Digital Calibration

This paper presents a novel circuit of a z−1 operation which is suitable, as a basic building block, for time-domain topologies and signal processing. The proposed circuit employs a time register circuit which is based on the capacitor discharging method. The large variation of the capacitor discharging slope over technology process and chip temperature variations which affect the z−1 accuracy is improved using a novel digital calibration loop. The circuit is designed using a 28 nm Samsung FD-SOI process under 1 V supply voltage with 5 MHz sampling frequency. Simulation results validate the theoretical analysis presenting a variation of capacitor voltage discharging slope less than 5% over worst-case process corners for temperature between 0 °C and 100 °C while consuming only 30 μA. Also, the worst-case accuracy of z−1 operation is better than 33 ps for input pulse widths between 5 ns and 45 ns presenting huge improvement compared with the uncalibrated operator.

Ultraslow light propagation in photorefractive SBN:75

Slowing down of light pulses to ∼1.9 mm/s has been obtained theoretically in SBN:75 via degenerate two-wave mixing (TWM) configuration. The optical delay has been tuned by varying the input pulse width & beam crossing angle. At the optimum beam crossing angle (2θ ∼ 10◦), very high TWM gain ∼107 has been achieved. Maximum fractional delay (FD) of 1.04 and 0.20 is obtained for 150 ms pulse in case of SBN:75 and SBN:60 respectively. Further, the optical delay, group velocity, FWHM, pulse broadening and amplification in case of SBN:75 is compared with SBN:60. SBN:75 showed minimal pulse broadening, large amplification (∼105), five times more FD and two degrees of higher optical delay than that of SBN:60.

Conditions for walk-off soliton generation in a multimode fiber

It has been recently demonstrated that multimode solitons are unstable objects which evolve, in the range of hundreds of nonlinearity lengths, into stable single-mode solitons carried by the fundamental mode. We show experimentally and by numerical simulations that femtosecond multimode solitons composed by non-degenerate modes have unique properties: when propagating in graded-index fibers, their pulsewidth and energy do not depend on the input pulsewidth, but only on input coupling conditions and linear dispersive properties of the fiber, hence on their wavelength. Because of these properties, spatiotemporal solitons composed by non-degenerate modes with pulsewidths longer than a few hundreds of femtoseconds cannot be generated in graded-index fibers.

Fast and Accurate SER Estimation for Large Combinational Blocks in Early Stages of the Design

Soft Error Rate (SER) estimation is an important challenge for integrated circuits because of the increased vulnerability brought by technology scaling. This paper presents a methodology to estimate in early stages of the design the susceptibility of combinational circuits to particle strikes. In the core of the framework lies MASkIt , a novel approach that combines signal probabilities with technology characterization to swiftly compute the logical, electrical, and timing masking effects of the circuit under study taking into account all input combinations and pulse widths at once. Signal probabilities are estimated applying a new hybrid approach that integrates heuristics along with selective simulation of reconvergent subnetworks. The experimental results validate our proposed technique, showing a speedup of two orders of magnitude in comparison with traditional fault injection estimation with an average estimation error of 5 percent. Finally, we analyze the vulnerability of the Decoder, Scheduler, ALU, and FPU of an out-of-order, superscalar processor design.

Slow light in rod type 2D photonic crystal waveguide comprising of cavity: Optimization and analysis

Structure comprising of 2D photonic crystal waveguide and cavity (PhCWC) is designed in this paper and propagation of slow light through it is investigated for its potential application as optical delay device. Rod type 2D photonic crystal structure has been considered here. Two-dimensional finite difference time domain (2DFDTD) method has been used in the present investigations. The proposed PhCWC structure is optimized in two steps. In the first step, Q factor is optimized by varying the number of rods of the cavity. In the second step, number of rods are kept fixed (as optimized for Q in the first step), and the delay is maximized by varying radius of the cavity rods. The resultant structure thus obtained is further investigated for (i) dispersion and group velocity, (ii) variation of optical delay with input pulse width, (iii) variation of optical delay with wavelength and (iv) variation of optical transmission with wavelength.The present paper proposes optical delay in the one cavity structure that could be manipulated by manipulating the number of cavity rods in the waveguide and radius of the central rod of the cavity. Further, the structure can be designed to operate at a desired wavelength.