Gain Stability Research Articles

Wavelength-tunable high-repetition-rate pulse generation in a SOA-based fiber laser with gain instability

Abstract Introducing negative optical feedback into a semiconductor optical amplifier-based laser presents a straightforward and effective approach for generating high-repetition-rate pulses through the mechanism of self-sustaining cross-gain modulation. In this work, we demonstrate, for the first time, the tunability of high-frequency pulse generation over a wide wavelength range by adjusting the central transmission wavelength of a tunable filter. Our laser system achieved a full tuning range from 1480 nm to 1556 nm (76 nm) while maintaining pulsed lasing. Remarkably, the laser exhibited a maximum pulse contrast exceeding 85% over a tuning range of 43 nm, from 1505.7 nm to 1548.7 nm. At any wavelength within this range, stable, self-starting pulse generation was consistently achieved, with a pulse repetition rate of 1.3 GHz.

Research on underwater acoustic detection technology based on optical waveguide resonator cavity

PurposeIn acoustic detection technology, optical microcavities offer higher detection bandwidth and sensitivity than traditional acoustic sensors. However, research on acoustic detection technologies involving optical microcavities has not yet been reported. Therefore, this paper aims to design and construct an underwater acoustic detection system based on optical microcavities and study its acoustic detection technology to improve its performance.Design/methodology/approachBased on the principles of optical microcavity acoustic sensors, a signal-detection circuit was designed to form a detection system in conjunction with a laser, an optical waveguide resonator and an oscilloscope. This circuit consists of two modules: a photodetection module and a filter amplification module.FindingsThe photodetection module features a baseline noise of −106.499 dBm and can detect device spectral line depths of up to 2410 mV. The gain stability of the filter amplification module was 58 dB ± 1 dB with a noise gain of −107.626 dBm. This design allows the acoustic detection system to detect signals with high sensitivity within the 10 Hz−1.2 MHz frequency band, achieving a maximum sensitivity of −126 dB re 1 V/µPa at 800 Hz and a minimum detectable pressure (MDP) of 0.37 mPa/Hz1/2, corresponding to a noise equivalent pressure (NEP) of 51.36 dB re 1 V/µPa.Originality/valueThis study designs and constructs a broadband underwater acoustic detection system specifically for optical waveguide resonators based on the sensing principles of silicon dioxide optical waveguide resonators. Experiments demonstrated that the signal detection module improves the sensitivity of underwater acoustic detection based on optical waveguides.

Weak signal ultrafast interrogation of a micro-nano FBG probe sensor based on the hybrid amplified dispersion Fourier-transform method.

To elucidate the thermal transport mechanisms at interfaces in micro- and nanoscale electronic devices, real-time monitoring of temperature variations at the microscopic and nanoscopic levels is crucial. Micro-nano fiber Bragg grating (FBG) sensors have been demonstrated as effective in-situ optical temperature probes for measuring local temperatures. Time-stretch dispersion Fourier transform (TS-DFT) that enables fast, continuous, single-shot measurements in optical sensing has been integrated with a micro-nano FBG probe (FBGP) for local temperature sensing. However, its temperature sensitivity and interrogation resolution are limited by the detection sensitivity. In this paper, we propose a hybrid amplified dispersion Fourier transform (ADFT) method to achieve ultrafast interrogation of FBGP's weak signal. Thanks to the combined effect of TS-DFT and hybrid optical amplification, the reflection signal of the FBGP is amplified, and the wavelength shift of the FBGP sensor is converted to a temporal spacing change between two dispersed pulses through dispersion-induced wavelength-to-time mapping. The proposed method uses a homemade dissipative soliton mode-locked laser as the light source. The hybrid optical amplification technique comprises a L-band erbium-doped fiber amplifier and a distributed Raman amplifier. Their noise figure and net gain for the FBGP are 4.81 dB and 15.93 dB, respectively. In addition, the temperature calibration experiments show that a sampling rate of 51.43 MHz and the maximum temperature measurement error of 1.98°C are achieved within the temperature range of 20.3°C to 97°C. The stability of the net gain provided by the hybrid ADFT system is demonstrated by the coefficient of variation, which ranges from 2.22% to 2.95% in the peak voltage signal of the FBGP. This approach applies to scenarios requiring the handling of weak optical signals, particularly in temperature measurement at the micro-nano scale.

A wideband dual-circularly polarized traveling wave dielectric resonator antenna array

ABSTRACT In order to meet the demand of high capacity and high speed transmission of satellite communication system, a wideband dual-circularly polarized dielectric resonator antenna (DRA) array is proposed based on the traveling wave principle. Four DRA elements with slot-coupling excitation are sequentially placed on the ground, and the feeding network is designed to realize the two orthogonal circular polarization radiation waves. A notched copper loop (NCL) around the antenna array is adopted to improve the radiation performance. Depending on the operation of the two ports, the NCL generates the induced currents which rotates clockwise/counterclockwise, increasing the axial ratio bandwidth. In order to further improve the gain stability, the copper sheets are embedded on the top surface of each radiation element, and the copper cylinders perturb the internal field distribution of the DRA to introduce higher-order modes. The measurement results show that the left-hand circular polarization and the right-hand circular polarization operating bandwidths are 11.8% (14.97–16.85 GHz) and 12% (14.91–16.82 GHz). The antenna gain achieves 9.0 dBic. This DRA array can be applied for the vehicle mounted RF terminals in satellite communication.

Simulation studies of charging-up effect for single GEMs

Many experiments revealed a charging-up effect inside the Gas Electron Multipliers (GEMs) holes, resulting in variation of GEM effective gain. Charge accumulation on the insulator surface inside the GEM hole (charge process) is involved in the present simulation models. With only the charge process in the simulation, a longer and larger gain stability of GEM was observed while comparing the charging-up curves to references, even distinct in the relatively high conductivity of GEM insulator. This observation indicates that charge transportation within the GEM insulator (discharge process) is non-negligible; the charging-up stability depends on the dynamic balance of the charge and discharge process. Therefore, a discharge model is induced and expressed by a piecewise function based on the presence of a simulation framework. Charging-up curves are compared for single GEMs with two different structures under different gain values and input flux; the trend from simulation with the discharge process is consistent with those from references. Although the deviation of simulated charging-up curves is observed at the region started to be stable, indicating improvements in the discharge formulation, it can still predict the trend of stability and values of GEM effective gain. This study improves the present simulation model of the charging-up effect for single GEMs and provides a reference for other charging-up models.

Gain stability of Hamamatsu R5912-MOD photomultipliers at low temperature

The Photon Detection System (PDS) is a crucial component of the ICARUS detector in the Short Baseline Neutrino (SBN) Program at Fermi National Accelerator Laboratory (FNAL). It consists of 360 PhotoMultiplier Tubes (PMTs) 8” Hamamatsu R5912-MOD and, since June 2020, it has been operating at the liquid Argon cryogenic temperature. During these years, the PMTs have shown gain losses as an aging effect. Using a climatic chamber at the INFN Sezione di Catania, we confirmed a stable gain for a single PMT 8” Hamamatsu R5912-MOD when operated at room temperature, and a persistent gain loss at temperatures around -70 °C, although this temperature is rather higher than that of the liquid Argon.

Three-Port Reflectionless Down-Converter for Wideband and Multichannel Receiver With Flat Gain, Enhanced EVM, and High Stability

Three-Port Reflectionless Down-Converter for Wideband and Multichannel Receiver With Flat Gain, Enhanced EVM, and High Stability

Effective bandwidth improvement of Travelling-Wave waveguide array antennas using double Parallel-Slot radiating elements

The effective bandwidth of a travelling-wave slotted waveguide array antenna is improved by using a proposed broadband single radiating element based on a pair of longitudinal slots CNC-machined in the broad wall of the waveguide. The TE10 mode excites two resonances generated by each slot, providing an effective bandwidth improvement. As a proof of concept, an array antenna formed by 16 double longitudinal parallel-slot elements is designed. A prototype has been manufactured in printed technology in order to experimentally validate the antenna performance. Measurements show high stability of efficiency, maximum gain and radiation patterns in a broadband higher than 20% in the K-band.

Phosphine Oxide-Nd3+ Coordination Chains with Cumulated Output Enable Efficient LED-Pumping Optical Amplification.

Near-infrared luminescent rare-earth organic complexes have attracted intensive attention in the field of optical waveguide amplification. However, their optical gains were commonly less than 4 dB/cm due to limited doping concentrations. Herein, two one-dimensional (1D) Nd3+ coordination chains, namely, [Nd(TTA)3(DBTDPO)]n (Nd1) and [Nd(TTA)3(DPEPO)]n (Nd2), bridged by phosphine oxide ligands were developed for the neodymium-doped waveguide amplifier. Despite its P-P distance being similar to DBTDPO, the different P═O orientation of DPEPO renders markedly shorter intra- and interchain Nd-Nd distances for Nd2 in comparison to Nd1. Furthermore, the weaker intermolecular interactions alleviate the quenching effect for Nd2. Therefore, Nd2 can provide more locally concentrated and radiative Nd3+ ions, leading to a larger Nd3+-characteristic 1.06 μm emission intensity and duration than Nd1. Based on embedded and evanescent-field waveguide structures, Nd2 achieves state-of-the-art gain maxima of 5.7 and 4.9 dB/cm as well as outstanding gain stability. These results indicate that controllable coordination assembly of lanthanide ions in multidimension provides a flexible approach to combine local high-density outputs and effective suppression of quenching.

A MeerKAT Polarization Survey of Southern Calibration Sources

We report on full-Stokes L-band observations of 98 MeerKAT calibration sources. Linear polarization is detected in 71 objects above a fractional level of 0.2%. We identify ten sources with strong fractional linear polarization and low Faraday rotation measure that could be suitable for wide-band absolute polarization calibration. We detect significant circular polarization from 24% of the sample down to a detection level of 0.07%. Circularly polarized emission is seen only for flat spectrum sources α > −0.5. We compare our polarized intensities and Faraday synthesis results to data from the NVSS at 1400 MHz and the ATCA SPASS survey at 2300 MHz. NVSS data exist for 54 of our sources and SPASS data for 20 sources. The percent polarization and rotation measures from both surveys agree well with our results. The residual instrumental linear polarization for these observations is measured at 0.16%, and the residual instrumental circular polarization is measured at 0.05%. These levels may reflect either instabilities in the relative bandpass between the two polarization channels with either time or antenna orientation, or atmospheric/ionospheric variations with pointing direction. Tracking of the hourly gain solutions on J0408-6545 after transfer of the primary gain solutions suggests a deterioration of the gain stability by a factor of several starting about 2 hr after sunrise. This suggests that observing during the nighttime could dramatically improve the precision of polarization calibration.

Enhanced radiation use efficiency and grain filling rate as the main drivers of grain yield genetic gains in the CIMMYT elite spring wheat yield trial

Common wheat (Triticum aestivum L.) is a major staple food crop, providing a fifth of food calories and proteins to the world’s human population. Despite the impressive growth in global wheat production in recent decades, further increases in grain yield are required to meet future demands. Here we estimated genetic gain and genotype stability for grain yield (GY) and determined the trait associations that contributed uniquely or in combination to increased GY, through a retrospective analysis of top-performing genotypes selected from the elite spring wheat yield trial (ESWYT) evaluated internationally during a 14-year period (2003 to 2016). Fifty-six ESWYT genotypes and four checks were sown under optimally irrigated conditions in three phenotyping trials during three consecutive growing seasons (2018–2019 to 2020–2021) at Norman E. Borlaug Research Station, Ciudad Obregon, Mexico. The mean GY rose from 6.75 (24th ESWYT) to 7.87 t ha−1 (37th ESWYT), representing a cumulative increase of 1.12 t ha−1. The annual genetic gain for GY was estimated at 0.96% (65 kg ha−1 year−1) accompanied by a positive trend in genotype stability over time. The GY progress was mainly associated with increases in biomass (BM), grain filling rate (GFR), total radiation use efficiency (RUE_total), grain weight per spike (GWS), and reduction in days to heading (DTH), which together explained 95.5% of the GY variation. Regression lines over the years showed significant increases of 0.015 kg m−2 year−1 (p < 0.01), 0.074 g m−2 year−1 (p < 0.05), and 0.017 g MJ−1 year−1 (p < 0.001) for BM, GFR, and RUE_total, respectively. Grain weight per spike exhibited a positive but no significant trend (0.014 g year−1, p = 0.07), whereas a negative tendency for DTH was observed (− 0.43 days year−1, p < 0.001). Analysis of the top ten highest-yielding genotypes revealed differential GY-associated trait contributions, demonstrating that improved GY can be attained through different mechanisms and indicating that no single trait criterion is adopted by CIMMYT breeders for developing new superior lines. We conclude that CIMMYT’s Bread Wheat Breeding Program has continued to deliver adapted and more productive wheat genotypes to National partners worldwide, mainly driven by enhancing RUE_total and GFR and that future yield increases could be achieved by intercrossing genetically diverse top performer genotypes.

Tunable gain clamping L-band erbium-doped fiber amplifier based on FBG and BBM

An improved structure for the L-band Erbium-doped fiber amplifier (EDFA) with gain clamping is suggested to address gain instability resulting from variations in the number of optical channels and the compromised gain clamping performance due to misalignment in the center wavelength of the grating. Here, a linear resonant cavity is formed by a broad-band mirror (BBM) and fiber Bragg grating (FBG), and a variable optical attenuator (VOA) is used for cavity loss adjustment. Experimental results show that the L-band EDFA solves the problem that the center wavelength of the narrowband grating pairs needs to be consistent. The 20 dB gain bandwidth is 42 nm(1582 ∼ 1623 nm). For signal at 1605 nm, the gain can be tuned from 28.8 to 34.8 dB, and a 40 dB (−50 to −10 dBm) gain clamped dynamic range is obtained at the gain of 28.8 dB, with stability of ± 0.25 dB, for which noise figure (NF) is less than 5.3 dB.

Polarization evolution in Brillouin scattering with a partially polarized pump

Polarization sensitivity has been a major issue in Brillouin scattering-based optical fiber sensing systems. Randomization of the polarization state of the pump is one of the ways to circumvent the problem. However, there could exist a residual degree of polarization (DOP) for the pump after polarization randomization, and hence, a model to characterize the polarization evolution in Brillouin scattering with a partially polarized pump is essential for the performance evaluation. In this work, a comprehensive theoretical model to characterize the beam variation with the partially polarized pump wave and Stokes wave is proposed, which is based on a set of stochastic differential equations (SDEs). The polarized part of the pump wave and the Stokes wave, as well as the total powers of the waves, are incorporated in the coupled SDE simultaneously, which enables the comprehensive simulation of the polarization evolution in the fiber. It is revealed in the study that the DOPs of the pump wave and the Stokes wave affect the gain stability and should be reduced simultaneously by polarization scrambling to ensure a fixed Brillouin gain without fluctuations.

The effect of kangaroo mother care in improvement of weight gain and vital signs stability in preterm and critically ill neonates.

The effect of kangaroo mother care in improvement of weight gain and vital signs stability in preterm and critically ill neonates.

Hop (Humulus lupulus L.) extract reverts glycaemic imbalance and cognitive impairment in an animal model of obesity.

The rates of overweight and obesity around the world have increased in past years. The body's adipose tissue stimulates the antioxidant and oxidation imbalance capacity at the cellular level. This scenario favors an inflammatory low-grade systemic condition starting with insulin resistance, which in turn may involve diabetes mellitus type 2 and cognitive decline afterward. Neurological diseases have been correlated to senile age diseases over time. This scenario calls for a change in the incidence of obesity in the younger generation. An unhealthy dietary consumption together with sedentary habits might lead to poor gut absorption of nutrients. Several plants and foods have bioactive compounds that can reduce or inhibit radical scavengers, reactive oxygen species, and metal ion complexes that threaten the cerebral defense system. The bitter acids from hops (Humulus lupulus L.) have been demonstrated to have promising effects on lipid and carbohydrate metabolism improvement, reducing inflammatory responses through alpha acids, beta acids, and analogs action. Therefore, the current study aimed to investigate the bioactivity of hop bitter acids in obese and lean mice. For that, a dry hop extract (DHE) was obtained by applying carbon dioxide as the fluid of supercritical extraction. Afterward, seventy-eight male mice of the C57BL/6J strain were weighed and randomly distributed into six groups of 13 animals each according to the diet offered: (NO) normolipidic diet, (NO1) normolipidic diet containing 0.35% alpha acids, (NO2) normolipidic diet containing 3.5% alpha acids, (HP) hyperlipidic diet, (HP1) hyperlipidic diet containing 0.35% alpha acids, and (HP2) hyperlipidic diet containing 3.5% alpha acids. After applying the glycemic tolerance and insulin tolerance tests, a better stabilization of glycemia levels and weight gain among those animals fed with DHE (NO2 and HP2) were observed in comparison to the obese control group (HP) (p < 0.05). There was also an amelioration of antioxidant capacity observed by checking the enzymatic profile by SOD and an apparent mitigation of brain degeneration by checking GSK3β and p-IRS1 proteins expression (p < 0.05). The y-maze cognitive test applied to highlight possible obesity-harmful animal brains did not indicate a statistical difference between the groups. Although the weekly dietary intake between the obese HP2 group (33.32 ± 4.11, p < 0.05) and control HP (42.3 ± 5.88, p < 0.05) was different. The bioactive compounds present in DHE have demonstrated relevant effects on glycemic control, insulin signaling, and the consequent modulatory action of the obesity-related markers with the brain's inflammatory progression.

Performance Comparison of MIMO Gain/Phase Analysis Methods for Sub-Synchronous Instability

Recently, there has been great interest in the development of stability criteria for grid-connected power converters and generators using frequency-domain impedance models. We consider two recently introduced stability analysis methods and compare their small-signal stability performance for a DFIG wind farm connected to a series-compensated grid. The first method, known as the Low-Complexity Global Nyquist Condition, uses Gershgorin disks derived from the loop gain matrix to provide a stability criterion. The second method, introduced by the authors, uses a combined matrix gain and phase stability analysis. The two methods are compared by using them to predict the onset of instability in a series-compensated wind farm under a tripped line. The results reveal that the gain/phase based approach achieves less conservatism than the Nyquist-based method.

Weight Loss, Stability, and Low Weight Gain during Pregnancy among Individuals with Obesity: Associations with Adverse Perinatal Outcomes: An Observational Study.

The safety of weight loss and low weight gain during pregnancy remains unclear. To determine how different patterns of gestational weight gain (GWG), including weight loss, stability, and low GWG relate to perinatal outcomes by prepregnancy obesity class. The study population included 29,408 singleton livebirths among pregnant people with obesity from Kaiser Permanente Northern California (2008-2013). Clinically measured GWG was grouped into meaningful categories (Adequate: reference, met 2009 National Academy of Medicine [NAM] Guidelines [5-9.1 kg], Excessive [>9.1 kg], Low [1-4.9 kg], Stable [±1 kg], Weight Loss [>1 kg]) or GWG Z-score quintiles. Modified Poisson regression was used to estimate risk of adverse outcomes, stratified by obesity class. Electronic health record data were used to define outcomes, including cesarean delivery, preterm birth, admission to the neonatal intensive care unit, small- and large-for-gestational age infants. Prevalence of weight stability and weight loss was 3.8 and 3.4%, respectively. Compared with those who gained within NAM, increased risk of small-for-gestational age was observed among those with weight loss among obesity class I (Risk Ratio (RR): 1.57, 95% confidence interval [CI]: 1.12, 2.19), obesity class II (RR: 2.18, 95% CI: 1.52, 3.13), and obesity class III (RR: 1.72, 95% CI: 1.21, 2.45). Weight loss was associated with a decreased risk of cesarean delivery among obesity class III, compared with NAM. Weight loss during pregnancy is associated with increased risk of small-for-gestational age among all obesity classes, but not other adverse perinatal outcomes and may reduce risk of cesarean delivery. Low weight gain and weight stability are not associated with risk of adverse outcomes among those with class III obesity. GWG guidelines may need to vary by obesity class. · Weight loss during pregnancy is associated with increased risk of small-for-gestational age among all obesity classes; but weight loss was not associated with other adverse perinatal outcomes.. · Among class III, low weight gain and weight stability are not associated with adverse perinatal outcomes.. · GWG guidelines may need to vary by obesity class..

The influence of diet on gut microbiome and body mass dynamics in a capital-breeding migratory bird.

Gut-associated microbial communities are known to play a vital role in the health and fitness of their hosts. Though studies investigating the factors associated with among-individual variation in microbiome structure in wild animal species are increasing, knowledge of this variation at the individual level is scarce, despite the clear link between microbiome and nutritional status uncovered in humans and model organisms. Here, we combine detailed observational data on life history and foraging preference with 16S rRNA profiling of the faecal microbiome to investigate the relationship between diet, microbiome stability and rates of body mass gain in a migratory capital-breeding bird, the light-bellied Brent goose (Branta bernicla hrota). Our findings suggest that generalist feeders have microbiomes that are intermediate in diversity and composition between two foraging specialisms, and also show higher within-individual plasticity. We also suggest a link between foraging phenotype and the rates of mass gain during the spring staging of a capital breeder. This study offers rare insight into individual-level temporal dynamics of the gut microbiome of a wild host. Further work is needed to uncover the functional link between individual dietary choices, gut microbiome structure and stability, and the implications this has for the reproductive success of this capital breeder.

Analytical results for a spin–orbit coupled atom held in a non-Hermitian double well under synchronous combined modulations

We propose a simple method of synchronous combined modulations to generate the exact analytic solutions for a spin–orbit (SO) coupled ultracold atom held in a non-Hermitian double-well potential. Based on the obtained analytical solutions, we mainly study the parity-time () symmetry of this system and the system stability for both balanced and unbalanced gain–loss between two wells. Under balanced gain and loss, the effect of the proportional constants between synchronous combined modulations and the SO-coupling strength on the -symmetry breaking is revealed analytically. Surprisingly, we find when the Zeeman field is present, the stable spin-flipping tunneling between two wells cannot occur in the non-Hermitian SO-coupled ultracold atomic system, but the stable spin-conserving tunneling can be performed. Under unbalanced gain and loss, the unique set of parameter conditions that can cause the system to stabilize is found. The results may provide a possibility for the exact control of -symmetry breaking and quantum spin dynamics in a non-Hermitian SO-coupled system.

Gain enhancement of perovskite nanosheets by a patterned waveguide: excitation and temperature dependence of gain saturation

Optical gain enhancement of two-dimensional CsPbBr3 nanosheets was studied when the amplified spontaneous emission is guided by a patterned structure of polyurethane-acrylate. Given the uncertainties and pitfalls in retrieving a gain coefficient from the variable stripe length method, a gain contour g(hslash omega ,x) was obtained in the plane of spectrum energy (ℏω) and stripe length (x), whereby an average gain was obtained, and gain saturation was analysed. Excitation and temperature dependence of the gain contour show that the waveguide enhances both gain and thermal stability due to the increased optical confinement and heat dissipation, and the gain origins were attributed to the two-dimensional excitons and the localized states.