Short Optical Pulses Research Articles

Modeling of the Dynamics of Extremely Short Optical Pulses in Carbon Nanotubes with Random Impurities Taking into Account Multiphoton Absorption

Modeling of the Dynamics of Extremely Short Optical Pulses in Carbon Nanotubes with Random Impurities Taking into Account Multiphoton Absorption

Ground‐Based Observations of 337 nm and 777 nm Optical Emissions Produced by Lightning

AbstractLightning flashes were observed in Barrancabermeja (Colombia) by two photometers centered at 337 and 777 nm wavelengths, a high‐speed camera, and the Colombia Lightning Mapping Array. Both optical and VHF radio emissions of different lightning processes are investigated. Flash initiations by upward in‐cloud breakdown present a first short optical pulse followed by a period of ∼1 kHz breakdown propagation. The ratio remains at unity or below, associated with the transition to negative horizontal leader propagation. In flash initiations by a fast‐stepped negative downward leader to ground, a dominance of the 337 nm radiance is found. Observations of downward leaders before ground strokes reveal that the luminosity measured by the photometers is dominated most of the time by the light coming from the cloud and not from the visible leader channels. One case of a visible cloud‐to‐ground channel with positive continuing current shows a high similarity in the evolution of the luminosity along the channel, 777 nm radiance, and the energy detected by the Geostationary Lightning Mapper from space. Finally, two types of recoil leaders have been observed: connecting and non‐connecting. Whereas the measured 777 nm peak radiance is similar in both types of recoil leaders, connecting recoil leaders present about seven times higher 337 nm peak radiance. Our observations generally show agreement between the VHF power and optical emissions.

Two-Terminal Perovskite Optoelectronic Synapse for Rapid Trained Neuromorphic Computation with High Accuracy.

Emerging neural morphological vision sensors inspired by biological systems that integrate image perception, memory, and information computing are expected to transform the landscape of machine vision and artificial intelligence. However, stable and reconfigurable light-induced synaptic behavior always relies on independent gateport modulation. Despite its potential, the limitations of uncontrollable defects and ionic characteristics have led to simpler, smaller, and more integration-friendly two-terminal devices being used as sidelines. In this work, the synergy between ion migration barriers and readout voltage is proven to be the key to realizing stable, reconfigurable, and precisely controllable postsynaptic current in two-terminal devices. Following the same mechanism, optical and electrical signal synchronous triggering is proposed to serve as a preprocessing method to achieve a recognition accuracy of 96.5%. Impressively, the gradual ion accumulation during the training process induces photocurrent evolution, serving as a reference for the dynamic learning rate and boosting accuracy to 97.8% in just 10 epochs. The PSC modulation potential under short optical pulse of 20 ns is also revealed. This optoelectronic device with perception, memory, and computation capabilities can promote the development of new devices for future photonic neural morphological circuits and artificial vision.

Extremely short optical pulses in a thin polymer film with carbon nanotubes

Extremely short optical pulses in a thin polymer film with carbon nanotubes

Talbot-Lau devices: a reappraisal

The Talbot effect and the Lau effect have been usefully applied in optical interferometry, and for designing novel X-ray devices, as well as for implementing useful instruments for matter waves. In temporal optics, the above phenomena play a significant role for reconstructing modulated, optical short pulses that travel along a dispersive medium. We note that the Talbot-Lau devices can be spatial frequency tuned if one employs varifocal lenses as a nonmechanical technique. Thus, we identify a pertinent link between the Talbot-Lau sensors and the development of artificial muscle materials, for generating tunable lenses. Our discussion unifies seemly unrelated topics, for providing a global scope on the applications of the Talbot-Lau effect.

Simultaneous temporal and spectral evolution of ultrafast optical pulse propagation using a single bidirectional LSTM network

Numerical simulations of optical pulse evolution are often a cumbersome task, mostly due to the presence of nonlinearities, and standard numerical approaches like splitting methods can be too complex and resource-hungry to compute them. However, under certain conditions, deep learning (DL) techniques can provide accurate alternative approaches to predict such propagation behavior. Here, we show a bidirectional long short-term memory (BiLSTM) network that predicts both temporal and spectral evolution of a short optical pulse going through a 13 m highly nonlinear fiber (HNLF). The BiLSTM performed an RMSE metric of 0.004 and 0.012 for temporal and spectral domains, respectively. A supercontinuum generation was also performed in a 20-cm photonic-crystal fiber, and the BiLSTM returns an RMSE metric of 0.018 and 0.013 for temporal and spectral domains, respectively.

Propagation of extremely short optical pulses in carbon nanotubes with a random tilt

We studied the propagation of electromagnetic waves in a medium with carbon nanotubes. An approximation that the random tilt of the tubes relative to the axis perpendicular to the wave vector of the momentum obeys a normal distribution and is sufficiently small was used. Effective equations for the vector potential of the electromagnetic field are derived. The dependence of the momentum field components on the dispersion of the distribution of the slope of carbon nanotubes was analyzed.

An integrated microwave-to-optics interface for scalable quantum computing.

Microwave-to-optics transduction is emerging as a vital technology for scaling quantum computers and quantum networks. To establish useful entanglement links between qubit processing units, several key conditions must be simultaneously met: the transducer must add less than a single quantum of input-referred noise and operate with high efficiency, as well as large bandwidth and high repetition rate. Here we present a design for an integrated transducer based on a planar superconducting resonator coupled to a silicon photonic cavity through a mechanical oscillator made of lithium niobate on silicon. We experimentally demonstrate its performance with a transduction efficiency of 0.9% with 1 μW of continuous optical power and a spectral bandwidth of 14.8 MHz. With short optical pulses, we measure the added noise that is limited to a few photons, with a repetition rate of up to 100 kHz. Our device directly couples to a 50 Ω transmission line and can be scaled to a large number of transducers on a single chip, laying the foundations for distributed quantum computing.

Effect of a multilevel impurity on the dynamics of 3D extremely short optical pulse in a photonic crystal of carbon nanotubes

"In this paper, we consider the dynamics of three-dimensional extremely short optical pulses in a medium with a spatially variable refractive index (photonic crystal) based on carbon nanotubes. The transitions between impurity levels in carbon nanotubes are taken into account. It has been established that pulses propagate stably with conservation of energy in a limited region of space. The effect of modulation parameters of the refractive index of a photonic crystal on the shape and group velocity of the pulse wave packet is obtained. The rate of one- and two- photon ionization in such medium is estimated."

Fast, Energy‐Efficient InGaAs Synaptic Phototransistors on Flexible Substrate

AbstractPhotodetectors sensing the short‐wave infrared (SWIR) region have great potential due to their significant advantages in a variety of applications because SWIR light possesses both characteristics of visible light and infrared light. Among them, devices using photodetectors to mimic synaptic dynamics and functions have received a great deal of attention due to their capabilities to implement simplified neural systems. However, it is essential to develop synaptic devices that can operate fast with low energy consumption for more efficient implementation of neural systems. Here, a flexible InGaAs synaptic phototransistor with a fast operation speed of under 1 ms and low energy consumption in the atto joule level is developed to femto joule level which is superior to biological synapses (50 ms, 1–100 fJ). By using InGaAs which has high carrier mobility as a channel layer, weak light, and short optical pulse width, fast operation speed in the SWIR region with low energy consumption is obtained. Moreover, the devices demonstrate synaptic behaviors such as “excitatory post synaptic current”, “paired‐pulse facilitation”, “short term plasticity”, “long term plasticity”, and “learning‐experience behavior” as neuro‐synaptic applications. These results provide the possibilities for implementation of complex synaptic functions with fast speed and low power SWIR synaptic phototransistors.

Generating in vivo continuous ultrasound based on sub-terahertz photoacoustic effect

Non-contact ultrasound excitation based on the photoacoustic effect using short optical pulses has been widely used for biomedical and industrial inspections. However, generating and detecting photoacoustic signals in water or aqueous samples requires careful choice of the excitation wavelength. Here, we show that continuous-wave (CW) ultrasound can be directly generated in aqueous samples by irradiating them with the CW sub-terahertz waves modulated at acoustic frequencies, even when the stress confinement condition is not satisfied. The ultrasound generated at resonance can be detected even in the air using a microphone. The sub-terahertz waves exhibit a water absorption coefficient akin to peak near-infrared wavelengths while offering transmittance through diverse materials. Leveraging recent advances in high-frequency electronics, we develop a compact experimental system with the potential for further miniaturization. To demonstrate the potential of the proposed method, we present proof-of-concept applications of bulk modulus measurement of gelatin gels and in vivo anatomical imaging of human hands.

Study on chirped dark, bright solitons conversion and the effect of intermodal dispersion, self-frequency shift, and self-steepening effect on the chirping of bright, dark, and kink solitary waves

This study reveals the dynamics of short optical pulses in nonlinear media. Then, for the survival of different types of solitary waves in the nonlinear medium, the constraint relations to the physical parameters and chirps associated with each of the solitary waves are explicitly shown. We authenticate numerically all those obtained from the analytical method and show the chirping effect is saturative in nature and can be managed by changing coefficients of inter-modal dispersion, stimulated Raman scattering (SRS), and self-steepening effect. We also verify the more operative condition of intermodal dispersion.

Heat accumulation during infrared stimulation impacts the response of ex vivo rat sciatic nerve.

Infrared neural stimulation (INS) is a neuromodulation technique that involves short optical pulses delivered to the neural tissue, resulting in the initiation of action potentials. In this work, we studied the compound neural action potentials (CNAP) generated by INS in five ex vivo sciatic nerves. A 1470 nm laser emitting a sequence of 0.4 ms light pulses with a peak power of 10 W was used. A single 4 mJ stimulus is not capable of eliciting a nerve response. However, repetition of the optical stimuli resulted in the induction of CNAPs. Heat accumulation induced by repetition rates as high as 10 Hz may be involved in the increase in CNAP amplitude. This sensitization effect may help to reduce the pulse energy required to evoke CNAP. In addition, these results highlight the importance of investigating the role of the slow nerve temperature dynamics in INS.

Integrated optical pattern generation on thin-film lithium niobate with electro-optic modulators and phase-change material cells

Reconfigurable photonic integrated circuits enable high-bandwidth signal shaping with the prospect for scalability and compact footprint. Cointegration of electro-optical tunability with nonvolatile attenuation through functional materials allows for implementing photonic devices that operate on both phase and amplitude. Based on this approach, we propose an integrated photonic design for optical pattern generation deploying a continuous-wave laser and a single electrical function generator. We employ the nonvolatile and reconfigurable phase-change material Ge2Sb2Te5 (GST) as a tunable attenuator for an integrated photonic circuit on the lithium-niobate-on-insulator (LNOI) platform. The GST can be switched between its amorphous and crystalline phases, leading to an optical contrast of ≅18dB. Combining this with integrated electro-optical modulators with a 4 GHz bandwidth in LNOI enables the generation of short optical pulses, based on the principles of inverse discrete Fourier transform.

Time-correlated single photon counting for evaluation of cavity dimensions with multibounce photons

Cavity exploration is an important task for optical remote sensing that finds application in many fields, such as the assessment of disaster areas or the evaluation of subsurface cavities in terrestrial and extraterrestrial scenarios. In our work, we use single photon-counting avalanche diode cameras to record temporal signatures in the picosecond time domain and to exploit the impulse response of cavities. When illuminated with a short optical pulse, the photons are reflected several times inside the cavity before exiting it and being detected. In our datasets, we observe several intensity modulations correlated to specific optical paths with different numbers of reflections inside the cavity. We developed an analysis model based on simulation of the radiant transfer that provides a quick rough estimate of the cavity dimensions without costly measurements or computational reconstruction. Specifically, we developed a spherical model and a hemispherical model that can be used to estimate the cavity dimensions (diameter or height). Finally, we present experimental studies of eight different cavities with different dimensions, shapes, and surface materials. Our evaluations show that we can apply our analytical models to signatures of different cavities, which gives us an initial estimate of the cavity sizes before a detailed mapping is carried out.

Quantized topological response in trapped quantum gases

In this letter, we propose a quantized topological response in trapped 1D quantum gases. The experimental protocol for the response requires the application of an instant optical pulse to a half-infinite region in an asymptotically harmonic trap and measuring the density distribution. We show that the corresponding linear response is described by a universal quantized formula in the thermal dynamical limit, which is invariant under local continuous deformations of the trapping potential $V$, atom distribution $f_\Lambda$, the spatial envelope of the optical pulse $\Theta_p$, and the measurement region $\Theta_m$. We test the statement by various numerical analysis, the result of which is consistent with the analytical prediction to high accuracy. We further show that a short but finite optical pulse duration only results in a violation of the quantization near the transition time, which suggests that quantized response could be observed in realistic experiments. We also generalize our results to non-linear quantized topological responses for atoms in higher dimensional harmonic traps.

Low threshold Kerr solitons.

Pumping a nonlinear optical cavity with continuous wave coherent light can result in generation of a stable train of short optical pulses. Pumping the cavity with a non-degenerate resonant coherent dichromatic pump usually does not produce a stable mode-locked regime due to competition of the oscillations at the pump frequencies. We show that generation of stable optical pulses is feasible in a dichromatically pumped cavity characterized with group velocity dispersion optimized in a way that the group velocity value becomes identical for the generated pulses and the beat note of the pump harmonics. The power threshold of the process drops nearly four times in this case and the produced pulses become sub-harmonically locked to the dichromatic pump harmonics. The process is useful for generation of broadband optical frequency combs and optical time crystals.

Temporal Kerr cavity solitons in optical resonators

Cavity Solitons are short optical pulses that propagate indefinitely in driven optical resonators. They are sustained by a double balance which prevents them from spreading or declining. This complex mechanism makes them “dissipative structures”, a general term coined by Ilya Prigogine to describe patterns emerging from noise in nonlinear systems. In the past decade, cavity solitons have attracted a lot of attention both for their fundamental interest and many potential applications. This article aims at introducing the reader to these fascinating objects.

Modeling of the dynamics of extremely short optical pulses in carbon nanotubes with random impurities taking into account multiphoton absorption

In this work, we study the evolution of an extremely short pulse in a dielectric crystal with carbon nanotubes containing an impurity with random parameters (energy level, electron hybridization energy). The dependence of the spatial characteristics of the pulse on the impurity parameters and the number of photons taken into account in the model is analyzed. Keywords: carbon nanotubes, impurities, optical pulse, multiphoton absorption.

Data transmission in a multimode optical fiber using a neural network

In digital data transmission, single mode optical fibers are commonly used since they can carry very short optical pulses without any significant distortions. In contrast, multimode fibers support many propagation modes that travel with different speeds; thus, they cannot maintain the shape of a light pulse. This feature of multiple propagation modes can be a benefit since it makes possible the transmission of data through several channels simultaneously. We demonstrate how multimode fibers can be used to transmit images. Because of the different propagation constants of the modes, the transmitted image is scrambled to apparently random speckle patterns. A simple neural network can be used to model the transmission through the multimode fiber. We show how the neural network can be trained to recognize a set of patterns with high accuracy.