Precise measurement of semiconductor laser chirp using effect of propagation in dispersive fiber and application to simulation of transmission through fiber gratings

Measurements of small-signal intensity modulation from direct-modulated distributed feedback (DFB) semiconductor lasers after propagation in dispersive fiber have previously been used to extract intrinsic laser chirp parameters such as linewidth enhancement factor and crossover frequency. Here, we demonstrate that the simple rate equations do not satisfactorily account for the frequency response of real DFB lasers and describe some experimental techniques that conveniently determiner the precise laser chirp. Implications for simulation of high-speed lightwave systems are also considered

Effect of many weak side modes on relative intensity noise of distributed feedback semiconductor lasers

An increase of the relative intensity noise of nearly single-mode distributed feedback lasers with respect to that predicted by single-mode theory after propagation in dispersive fiber at frequencies up to 5 Ghz has been measured. A simplified multimode theory is presented which explains the increase in noise

Frequency control using a complex effective reflectivity in laterally coupled semiconductor laser arrays

Frequency selectivity of a novel type of multielement, multisection laterally coupled semiconductor laser array is studied using the round-trip method. It is found that such a structure should lead to a strong frequency selectivity owing to a periodic dependency of the threshold gain on the frequency. A gain-guided two-coupled-cavity device was fabricated. The experimental results show excellent agreement with the theoretical prediction

Monolithic electro-optic modulator array

A PIN GaAlAs diode structure is provided with parameters for index guiding of light in a single mode. The index of refraction of the central layer I (which in practice may be lightly doped .pi. or .nu.) is greater than the p- and n-layers to create a slab waveguide in the transverse direction. Stripe contacts define separate waveguide channels that are separated electrically and optically by implanting protons or etching grooves between the stripe contacts in the upper layer. Separate reverse biasing voltages may be applied to the stripe contacts for modulation of the light in proportions to the voltage, either with absorption modulation, if the light wavelength is within about 500.ANG. of the bandgap of the .pi.-material, or phase-delay modulation, if the wavelength is separated from the bandgap of the .pi.-material by at least 900.ANG.

Kelvin wave hydraulic control induced by interactions between vortices and topography

The interaction of a dipolar vortex with topography is examined using a combination of analytical solutions and idealized numerical models. It is shown that an anticyclonic vortex may generate along-topography flow with sufficient speeds to excite hydraulic control with respect to local Kelvin waves. A critical condition for Kelvin wave hydraulic control is found for the simplest case of a 1.5-layer shallow water model. It is proposed that in the continuously stratified case this mechanism may allow an interaction between low mode vortices and higher mode Kelvin waves, thereby generating rapidly converging isopycnals and hydraulic jumps. Thus, Kelvin wave hydraulic control may contribute to the flux of energy from mesoscale to smaller, unbalanced, scales of motion in the ocean

Quaternary Ammonia Compounds in Disinfectant Products: Evaluating the Potential for Promoting Antibiotic Resistance and Disrupting Wastewater Treatment Plant Performance

Quaternary ammonium compounds (QACs) are a class of compounds that were widely used as disinfectants during the COVID-19 pandemic and continue to be used as disinfecting agents. After consumer usage, QAC concentrations are diluted in wastewater as they enter wastewater treatment plants. At sub-inhibitory concentrations, QACs may have unintended repercussions, including increased antibiotic resistance and inhibition of process performance in wastewater treatment plants. This review first summarizes how QACs inhibit bacteria and then highlights the mechanisms by which QACs can promote antibiotic resistance in general. Reported environmental concentrations of QACs are compared to concentrations that are suspected to impact antibiotic resistance, and the role QACs may have on antibiotic resistance proliferation in wastewater treatment is addressed. Finally, the specific impacts that QACs can have on biological wastewater processes (activated sludge and anaerobic digestion) are reviewed. We highlight key research gaps along with recommendations for future research. Of particular interest, research is needed to elucidate the relationship between the chemical structure of QACs and impacts on antibiotic resistance as well as process performance in wastewater treatment plants. Finally, the ability to mitigate (reverse) these impacts if QACs are removed needs to be determined

A Search for Exozodiacal Clouds with Kepler

Planets embedded within dust disks may drive the formation of large scale clumpy dust structures by trapping dust into resonant orbits. Detection and subsequent modeling of the dust structures would help constrain the mass and orbit of the planet and the disk architecture, give clues to the history of the planetary system, and provide a statistical estimate of disk asymmetry for future exoEarth-imaging missions. Here we present the first search for these resonant structures in the inner regions of planetary systems by analyzing the light curves of hot Jupiter planetary candidates identified by the Kepler mission. We detect only one candidate disk structure associated with KOI 838.01 at the 3-sigma confidence level, but subsequent radial velocity measurements reveal that KOI 838.01 is a grazing eclipsing binary and the candidate disk structure is a false positive. Using our null result, we place an upper limit on the frequency of dense exozodi structures created by hot Jupiters. We find that at the 90% confidence level, less than 21% of Kepler hot Jupiters create resonant dust clumps that lead and trail the planet by ~90 degrees with optical depths >~5*10^-6, which corresponds to the resonant structure expected for a lone hot Jupiter perturbing a dynamically cold dust disk 50 times as dense as the zodiacal cloud.Comment: 22 pages, 6 figures, Accepted for publication in Ap

ESTABLISHING TRAINING PARAMETERS FOR A DEEP NEURAL NETWORK TO ASSESS 2D, FRONTAL PLANE KINEMATICS

The purpose of this study was to establish the optimal training parameters to assess frontal plane, 2D kinematics using DeepLabCut. DeepLabCut is an open-source platform that allows the user to train neural networks for customized feature detection in 2D videos. Deep neural networks were trained using frontal plane videos from 41 participants who completed single- and double-leg drop landings. Networks were trained with an increasing number of training iterations (25-250k) and training frames (200-800). Our results indicate that a minimum of 175k training iterations and 400 training frames were adequate for stable network performance (training/test errors= 2.8/3.7 pixels)