Optical Intensity Research Articles

High-order OAM states unwrapping in multiplexed optical links

To accurately unwrap the high-order orbital angular momentum (OAM) for multiplexed vortex beams is a challenge. In this work, over ±160 order OAM topological charges have been unwrapped in multiplexed optical links. Optical imaging based discrepancy identification enables the multiplexed OAM modes separating in physics, and the intelligent pattern recognition further promotes its unwrapping in numerical domain. Particularly, the combination of annular phase grating and auxiliary beams features compound spiral stripes, which paves the way for optical intensity recognition with low-complexity and high-commonality. Moreover, the spiral direction characterizes the symbol of the OAM states, which dramatically broadens the amount of multiplexed links. Here, optical separating means assisted by intelligent pattern recognition opens up a new route to high-speed and large-capacity optical communication, which may shed new light on 6G application.

Assessment of protein and DNA polymorphisms in corn (Zea mays) under the effect of non-ionizing electromagnetic radiation

Many reports highlight biological responses of crop plants after non-ionizing electromagnetic radiation (EMR) exposure based on the phenotypic and physiological levels. So, this study aimed to estimate genetic alterations in proteins, isozymes, and DNA banding patterns as well as the extent of nuclear DNA damage of economic corn (Zea mays) under the stress of EMR using accurate and reliable bioassays like sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), isozymes (Leucine- aminopeptidase, Esterases, Peroxidase, and Catalases), random amplified polymorphic DNA- polymerase chain reaction (RAPD-PCR), and Comet Assay, respectively. SDS-PAGE analysis showed distinct polymorphisms (96.66%) between EMR exposed and non-exposed corn seedlings depending on the number and type of bands, their intensities as well as molecular weight which ranged from (60.27 to 192.35 kDa), gain, and loss of bands. The four isozymes generated varies isozymatic polymorphisms based on relative front, zymogram number, and optical intensities. RAPD analysis generated 85 amplified DNA products with high polymorphism values ranged from 90.91 to 100% based on primers, band type, DNA sizes which ranged from 153 to 1008-bp, lose, gain, and intensity of DNA bands. Comet Assay scored highest extent of loosed DNA from nuclei (DNA damage) reached the value of (tailed ratio 20%) at EMR exposed corn nuclei for 5 days compared to non-exposed nuclei which reached the value of (tailed ratio 3%). This study concluded that each EMR exposure time had unique interaction with proteins, isozymes, and DNA of corn cells exhibiting wide range of genotoxic stress and subsequently, adversely effect on growth and yield of this sensitive crop plants.

Temperature Dependent Hydrogen Bond Toward High Emission in an Emerging Indium-Based Perovskite.

Low-dimensional organic-inorganic hybrid perovskites (OIHPs) with broadband emission attract immense scientific interest due to their potential application for the next generation of solid-state lighting. However, due to low exciton utilization, organic cations generally adjust structure rather than contribute the band edge to affect optical properties. Based on this, OIHPs are usually allowed to obtain a low photoluminescence quantum yield (PLQY). Herein, a good charge transfer carrier (p-phenylenediamine, PPDA) as organic cation is rationally employed and a novel indium-based perovskite is synthesized. By coupling with H2 O molecules, a strong interaction between organic and inorganic components is realized by hydrogen bonding, which has good transportability and greatly improves the exciton utilization. The regions of hydrogen bonding show high electron mobility, combined with the induced recombination center, improving the progress of charge relaxation. As a result, the regulation of hydrogen bond strength based on the microstructure optimization directly determines the optical emission intensity, realizing nearly 100% PLQY. Further, the polyhydrogen bond structure makes each component a stronger interaction, showing high stability in polar, organic, and acidic solvent, as well as long-term storing, which represents one of the highest overall performances for lighting in OIHPs.

High-speed all-optical digital-to-analog converter based on photonic crystal ring resonators

Abstract In this paper, a 2-bit all-optical digital-to-analog converter, including two ring resonators has been presented. Some nonlinear rods have been placed at the center of the rings which their refractive indices depend on the incoming optical intensity. Concerning the states of two input bits, each ring does the switching operation and guides the optical waves toward the output port. The finite difference time domain method has been used to calculate the electric and magnetic components of optical waves. The maximum absolute error of the digital-to-analog converter is equal to 2.43 %, less than the previous works. Also, the insertion loss varies from −11.13 dB to −8.57 dB for the different states. Besides, the maximum propagation time of the structure is just 1.8 ps suitable for high-speed applications.

Dynamics and feedback sensitivity of vertical-cavity surface-emitting lasers with arbitrary optical feedback intensity

Vertical cavity surface emitting lasers (VCSELs) are the key laser sources in the high-performance computers (HPCs) and data centers (DCs). The explosive growth of data traffic in the HPCs and DCs requires increased bandwidths of VCSELs. In this paper, we deduce the Time-Delay (T-D) model considering the multiple round trips of light in VCSELs with an optical feedback cavity to enhance the modulation bandwidth. The T-D model is suitable for the VCSEL with an arbitrary optical feedback intensity. The influences of the round trip time m of light in the optical feedback cavity on the intensity-modulation responses with strong and weak optical feedback are studied. The feedback coefficients considering the multiple round trips of light in the optical feedback cavity and the dispersions of the distributed Bragg reflector are deduced, and are suitable for the arbitrary optical feedback intensity. The feedback coefficients are influenced by the value of m and the optical feedback intensity, and decrease as the value of m under arbitrary optical feedback intensity increases. The feedback coefficients under strong optical feedback are larger than that under weak optical feedback with the same value of m. The theories are useful for the high-speed VCSELs with optical feedback.

Quiescent Optical Solitons for the Concatenation Model with Nonlinear Chromatic Dispersion

This paper recovers quiescent optical solitons that are self-sustaining, localized wave packets that maintain their shape and amplitude over long distances due to a balance between nonlinearity and dispersion. When a soliton is in a state of quiescence, it means that it is stationary in both space and time. Quiescent optical solitons are typically observed in optical fibers, where nonlinearity and dispersion can lead to the formation of solitons. The concatenation model is considered to understand the behavior of optical pulses propagating through nonlinear media. Here, we consider the familiar nonlinear Schrödinger equation, the Lakshmanan–Porsezian–Daniel equation, and the Sasa–Satsuma equation. The current paper also addresses the model with nonlinear chromatic dispersion, a phenomenon that occurs in optical fibers and other dispersive media, where the chromatic dispersion of the material is modified by nonlinear effects. In the presence of nonlinearities, such as self-phase modulation and cross-phase modulation, the chromatic dispersion coefficient becomes a function of the optical intensity, resulting in nonlinear chromatic dispersion. A full spectrum of stationary optical solitons, along with straddled stationary solitons, are obtained. There are four integration schemes that made this retrieval possible. The numerical simulations are also included for these solitons. The parameter constraints also indicate the existence criteria for these quiescent solitons.

Lasing in a ZnO waveguide: Clear evidence of polaritonic gain obtained by monitoring the continuous exciton screening

The coherent emission of exciton polaritons was proposed as a means of lowering the lasing threshold because it does not require the dissociation of excitons to obtain an electron-hole plasma, as in a classical semiconductor laser based on population inversion. In this work we propose a method to prove clearly the polaritonic nature of lasing by combining experimental measurements with a model accounting for the permittivity change as a function of the carrier density. To do so we use angle resolved photoluminescence to observe the lasing at cryogenic temperature from a polariton mode in a zinc oxide waveguide structure, and to monitor the continuous shift of the polaritonic dispersion towards a photonic dispersion as the optical intensity of the pump is increased (up to 20 times the one at threshold). This shift is reproduced thanks to a model taking into account the reduction of the oscillator strength and the renormalization of the band gap due to the screening of the electrostatic interaction between electrons and holes. Furthermore, the measurement of the carrier lifetime at optical intensities in the order of those at which the polariton lasing occurs enables us to estimate the carrier density, confirming that it is lower than the corresponding Mott density for zinc oxide reported in the literature.

Light-driven photothermal catalytic oxidation of toluene over CuOx-WOx/mTiO2−x-USY: Revealing CuOx-WOx synergy

Light-driven photothermal catalytic oxidation is a promising strategy for sustainable volatile organic compounds (VOCs) elimination. Herein, we report the construction of yCuOx-WOx/mTiO2−x-USY nanocomposite (y = Cu weight percentage and x represents oxygen ratio in metal oxides due to the mixed-valence metal, USY = ultrastable Y zeolite) for the degradation of toluene. Combining both CuOx and WOx metal oxides on the mTiO2/USY induced strong light absorption, improved oxygen mobility, and good catalytic activity. Among the catalysts, the optimized 20CuOx-WOx/mTiO2−x-USY exhibits the highest light-driven catalytic performance of 90.4% toluene conversion and 82.0% CO2 yield at a surface temperature of 235 oC under full light irradiation with an optical intensity of 500 mW/cm2. The existence of a CuOx-WOx synergy amplified the capture of light energy, heat generation, and molecular oxygen activation. Impressively, the catalyst demonstrated satisfactory stability during long-term application. Furthermore, in situ DRIFTS analysis suggested benzoate species as major reaction intermediates.

Output Prediction of Helical Microfiber Temperature Sensors in Cycling Measurement by Deep Learning

The inconsistent response curve of delicate micro/nanofiber (MNF) sensors during cycling measurement is one of the main factors which greatly limit their practical application. In this paper, we proposed a temperature sensor based on the copper rod-supported helical microfiber (HMF). The HMF sensors exhibited different light intensity-temperature response relationships in single-cycle measurements. Two neural networks, the deep belief network (DBN) and the backpropagation neural network (BPNN), were employed respectively to predict the temperature of the HMF sensor in different sensing processes. The input variables of the network were the sensor geometric parameters (the microfiber diameter, wrapped length, coiled turns, and helical angle) and the output optical intensity under different working processes. The root mean square error (RMSE) and Pearson correlation coefficient (R) were used to evaluate the predictive ability of the networks. The DBN with two restricted Boltzmann machines (RBMs) provided the best temperature prediction results (RMSE and R of the heating process are 0.9705 °C and 0.9969, while the values of RMSE and R of the cooling process are 0.786 6 °C and 0.997 7, respectively). The prediction results obtained by the optimal BPNN (five hidden layers, 10 neurons in each layer, RMSE=1.126 6 °C, R=0.995 7) were slightly inferior to those obtained by the DBN. The neural network could accurately and reliably predict the response of the HMF sensor in cycling operation, which provided the possibility for the flexible application of the complex MNF sensor in a wide sensing range.

Partially coherent light propagation through a kinoform lens.

Combining wave optics propagation and geometric ray tracing, the mutual optical intensity (MOI) model is extended to quantitatively simulate the propagation of partially coherent light through a kinoform lens at high speed. The MOI model can provide both a high accuracy and a high efficiency simulation. The intensity and coherence degree distributions at the focal plane are calculated using the MOI model. It is beneficial to improve the focusing capability of the kinoform lens by reducing the coherence or increasing the number of lens steps. In addition, increasing the number of steps is also beneficial to increase the photon flux and reduce the depth of focus.

Dual-Filter Architecture for Blind Feedback Recovery of the Symbol Timing in Bandlimited Optical Intensity Channels

Reliable recovery of transmission parameters is of paramount importance not only for radio frequency receivers, but also for optical wireless communication solutions. This paper discusses a feedback algorithm for recovering the symbol timing in the context of a bandlimited optical intensity link. The link is determined by a PAM scheme and pulse shaping with squared raised cosine or double jump functions. When preambles or pilot sequences are not available to the receiver, non-data-aided (blind) recovery concepts are useful for tracking smaller variations of the timing error affecting the payload data. The current state-of-the-art solution uses a Gardner detector with two samples per symbol, although this introduces a non-negligible amount of inter-symbol interference resulting in an error floor. To avoid this drawback, the authors propose a dual-filter approach which includes an appropriately designed filter operated in parallel to the receiver filter. Despite the additional complexity of the dual-filter architecture, the recovery loop is very simple and requires only one sample per symbol, representing the lowest degree of complexity in this respect. Open-loop characteristic, jitter performance, and acquisition behavior of the suggested recovery loop are investigated.

Attosekundnaya interferometriya pri uchastii diskretnykh sostoyaniy

In the paper we theoretically investigate the features of RABBITT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions) spectroscopy under conditions when transitions through discrete spectrum states play a significant role. Two approaches are applied in the article: the numerical solution of rate equations with continuum discretization and the perturbation theory up to the third order in amplitude. Both approaches use transition matrix elements and photoionization amplitudes obtained by the high-precision R-matrix method. Within the framework of these approaches, photoelectron spectra, the amplitude and phase of RABBITT oscillations were obtained, and the effect of the seed optical field intensity and detuning from a resonance upon excitation of discrete states was studied.

Implementation of input correlation learning with an optoelectronic dendritic unit

The implementation of machine learning concepts using optoelectronic and photonic components is rapidly advancing. Here, we use the recently introduced notion of optical dendritic structures, which aspires to transfer neurobiological principles to photonics computation. In real neurons, plasticity—the modification of the connectivity between neurons due to their activity—plays a fundamental role in learning. In the current work, we investigate theoretically and experimentally an artificial dendritic structure that implements a modified Hebbian learning model, called input correlation (ICO) learning. The presented optical fiber-based dendritic structure employs the summation of the different optical intensities propagating along the optical dendritic branches and uses Gigahertz-bandwidth modulation via semiconductor optical amplifiers to apply the necessary plasticity rules. In its full deployment, this optoelectronic ICO learning analog can be an efficient hardware platform for ultra-fast control.

Experimental investigation of the radially-dependent ignition process in a pulsed capacitively coupled RF discharge: Effects of pressure, voltage and afterglow duration

The effects of the gas pressure, the voltage amplitude and the afterglow duration on the ignition process over 300 mm-diameter in a pulse-modulated capacitively coupled radio-frequency argon discharge are experimentally investigated. A home-made optical probe is used to measure the optical emission intensity (OEI) as a function of time since the beginning of each pulse at various radial positions. A voltage and a current probe are used to measure the voltage and current waveforms at the power feeding point and then the time-dependent power deposition is also obtained. It was found that the radial profile of the OEI exhibits complex evolution when changing these external conditions. At lower pressures, the ignition occurs earlier, and the radial-integral OEI and the power deposition overshoot more slightly during the ignition. By increasing the pressure, these two quantities overshoot more significantly, and the OEI gradually evolves from an edge-peaked radial profile to a center-high radial profile for a given time when the OEI increases rapidly during the ignition. When increasing the voltage amplitude, the ignition tends to occur earlier, featuring a more significant overshoot of the OEI and power deposition at a higher voltage. Compared to that at high voltage, the OEI exhibits a significant center-high radial profile at low voltage amplitude during the ignition. By increasing the afterglow duration, T off, the ignition is delayed and the overshoot becomes more significant, due to a lower initial electron density when each pulse is turned on. During the phase when the growth rate of the OEI versus time is maximum, the OEI exhibits different radial distributions, i.e., it appears a center-high profile at short T off, an edge-peaked profile at intermediate T off, and a center-high profile at relatively long T off.

Experimental Characterization of Photoemission from Plasmonic Nanogroove Arrays

Metal photocathodes are an important source of high-brightness electron beams, ubiquitous in the operation of both large-scale accelerators and table-top microscopes. When the surface of a metal is nanoengineered with patterns on the order of the optical wavelength, it can lead to the excitation and confinement of surface-plasmon-polariton waves that drive nonlinear photoemission. In this work, we aim to evaluate gold plasmonic nanogrooves as a concept for producing bright electron beams for accelerators via nonlinear photoemission. We do this by first comparing their optical properties to numerical calculations from first principles to confirm our ability to fabricate these nanoscale structures. Their nonlinear photoemission yield is found by measuring emitted photocurrent as the intensity of their driving laser is varied. Finally, the mean transverse energy of this electron source is found using the solenoid-scan technique. Our data demonstrate the ability of these cathodes to provide a tenfold enhancement in the efficiency of photoemission over flat metals driven with a linear process. We find that these cathodes are robust and capable of reaching sustained average currents over 100 nA at optical intensities larger than $2\phantom{\rule{0.2em}{0ex}}\mathrm{GW}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ with no degradation of performance. The emittance of the generated beam is found to be highly asymmetric, a fact we can explain with calculations involving the also asymmetric roughness of the patterned surface. These results demonstrate the use of nanoengineered surfaces as enhanced photocathodes, providing a robust air-stable source of high-average-current electron beams hopefully with great potential for industrial and scientific applications.

Detection of multiple anomalous instances in video surveillance systems

Anomalous event recognition has a complicated definition in the complex background due to the sparse occurrence of anomalies. In this paper, we form a framework for classifying multiple anomalies present in video frames that happen in a context such as the sudden moment of people in various directions and anomalous vehicles in the pedestrian park. An attention U-net model on video frames is utilized to create a binary segmented anomalous image that classifies each anomalous object in the video. White pixels indicate the anomaly, and black pixels serve as the background image. For better segmentation, we have assigned a border to every anomalous object in a binary image. Further to distinguish each anomaly a watershed algorithm is utilized that develops multi-level gray image masks for every anomalous class. This forms a multi-class problem, where each anomalous instance is represented by a different gray color level. We use pixel values, Optical Intensity, entropy values, and Gaussian filter with sigma 5, and 7 to form a feature extraction module for training video images along with their multi-instance gray-level masks. Pixel-level localization and identification of unusual items are done using the feature vectors acquired from the feature extraction module and multi-class stack classifier model. The proposed methodology is evaluated on UCSD Ped1, Ped2 and UMN datasets that obtain pixel-level average accuracy results of 81.15%,87.26% and 82.67% respectively.

Consideration of spectroscopic measurements with broadband Fourier domain mode-locked laser with two semiconductor optical amplifiers at ∼1550 nm

In this study, an experimental system was developed using a broadband wavelength-swept laser for fast and broadband spectroscopic measurements at ∼1550 nm. The broadband wavelength-swept laser employed Fourier domain mode-locking (FDML) to realize a high-speed sweep rate of 50.7 kHz. FDML lasers at ∼1550 nm experience a problem of the sweep bandwidth being limited by the amplification wavelength range of the semiconductor optical amplifier (SOA). To realize a sweep bandwidth >100 nm, the proposed broadband FDML laser incorporated SOAs with different amplification wavelength ranges in parallel. Consequently, it expanded the sweep bandwidth to 120 nm at a center wavelength of 1544 nm. The experimental system employed the broadband FDML laser and introduced reference and compensation optics. These optics can compensate for the effects of fluctuations in optical output intensity and wavelength shift in the laser to improve measurement stability. Moreover, the experimental system demonstrated fast transmission spectrum measurements with a wavelength range of 1500 to 1580 nm.

Epoxy-Coated Side-Polished Fiber-Optic Temperature Sensor for Cryogenic Conditions.

We propose coating side-polished optical fiber (SPF) with epoxy polymer to form a fiber-optic sensor for cryogenic temperature measuring applications. The thermo-optic effect of the epoxy polymer coating layer enhances the interaction between the SPF evanescent field and surrounding medium, considerably improving the temperature sensitivity and robustness of the sensor head in a very low-temperature environment. In tests, due to the evanescent field-polymer coating interlinkage, transmitted optical intensity variation of 5 dB and an average sensitivity of -0.024 dB/K were obtained in the 90-298 K range.

Rocket‐Released Neutral Clouds in the Ionosphere: Formation, Evolution, and Detection

AbstractReleasing diffuse artificial clouds into the space environment using a rocket or spacecraft can modify the natural plasma state. This uses space itself as a laboratory for studying plasma phenomena that cannot be reproduced on the ground. The Space Measurement of A Rocket‐released Turbulence (SMART) mission will inject a beam of barium neutral vapor into the ionosphere and perpendicular to the Earth's magnetic field. Barium atoms will be photoionized, forming an ion ring distribution that is unstable to lower hybrid waves. Large amplitude lower hybrid waves nonlinearly scatter to whistler and magnetosonic waves that can propagate out to the magnetosphere. This paper details the theory, modeling, and simulation we used to design this release experiment to optimize the energy in the plasma waves under a variety of constraints. A product of this analysis is quantitative predictions for some in situ and remote measurements. Hydrocode simulations of barium vapourization and acceleration via shaped charge provide the initial state of the neutral beam. We optimize the apogee, orientation, and position of the payload and instruments. Cloud dynamics are simulated with a direct simulation Monte Carlo technique, which includes photoionization with metastable barium states, collisions with the neutral background atmosphere, optical line emission, gravity, and electromagnetic forces. We predict the plasma density measured by the instrument payload and the remotely measured optical intensity. We also examine how the plasma wave growth differs at the measurement location compared to the bulk of the barium cloud.

Enhancing the optical path inside a capillary without sacrificing light intensity: application to a compact and highly sensitive photometer.

In order to increase the optical path and related sensitivity of photometers, multiple axial-reflection of parallel light-beam inside a capillary cavity is one of the most effective ways. However, there is a non-optimum trade-off between optical path and light intensity, e.g., smaller aperture on cavity mirror can increase multiple axial-reflection times (i.e., longer optical path) due to the lower cavity-loss, but it would also reduce coupling efficiency, light intensity, and related signal-to-noise ratio. Herein, an optical beam shaper, which is composed of two optical lenses with an apertured mirror, was proposed to focus the light beam (i.e., increasing coupling efficiency) without deteriorating beam parallelism and related multiple axial-reflection. Thus, by combining the optical beam shaper with a capillary cavity, large optical path enhancement (10-fold of capillary length) and high coupling efficiency (>65%) can be realized simultaneously, where the coupling efficiency was improved 50-fold. An optical beam shaper photometer (with a 7 cm long capillary) was fabricated and applied to detect water in ethanol with a detection limit of 12.5 ppm, which is 800-fold and 32∼80 fold lower than that of the commercial spectrometer (1 cm cuvette) and previous reports, respectively.