Four-Wave Mixing in Semiconductor Traveling-wave Amplifiers for Efficient, Broadband, Wavelength Conversion up to 65 nm

Wavelength conversion is recognized as an important function in future fiber networks employing wavelength division multiplexing. The authors have recently demonstrated broad-band wavelength conversion over spans as large as 27 nm. Their approach uses ultra-fast four-wave mixing dynamics associated with intraband relaxation mechanisms in semiconductor traveling-wave amplifiers (TWA's). In the paper the authors present new results showing conversion over wavelength spans as large as 65 nm. This surpasses the previous record by over a factor of two. Of equal importance, they also verify experimentally their previous theoretical prediction that wavelength conversion efficiency varies as the cube of TWA single pass gain. In the course of our previous work, we have shown that the theoretical efficiency, η, of this process can be expressed by the simple relation: η = 3G + 2P + R(Δ⋋) where η is the ratio in dB of the converted signal output power to the signal input power and G is the single pass TWA optical gain. A crucial point is the presence of 3G in this expression - essentially, the wavelength converter uses the available TWA optimal gain three times. We verified this expression using an experimental setup similar to that described in. Tunable, single-frequency, erbium fiber ring lasers were used as pump and signal sources and TWA devices used contained tensile-strained mutli-quantum well active layers described in. Figure 1 shows conversion efficiency data plotted versus single-pass saturated optical gain. The pump power was -5.2 dBm and the signal power was -11.3 dBm. The measured slope of 3.18 confirms the cubic dependence of efficiency on single pass gain

Four-wave mixing wavelength conversion efficiency in semiconductor traveling-wave amplifiers measured to 65 nm of wavelength shift

The efficiency of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers is measured for wavelength shifts up to 65 nm using a tandem amplifier geometry. A quantity we call the relative conversion efficiency function, which determines the strength of the four-wave mixing nonlinearity, was extracted from the data. Using this quantity, gain requirements for lossless four-wave mixing wavelength conversion are calculated and discussed. Signal to background noise ratio is also measured and discussed in this study

Study of interwell carrier transport by terahertz four-wave mixing in an optical amplifier with tensile and compressively strained quantum wells

Interwell carrier transport in a semiconductor optical amplifier having a structure of alternating tensile and compressively strained quantum wells was studied by four-wave mixing at detuning frequencies up to 1 THz. A calculation of transbarrier transport efficiency is also presented to qualitatively explain the measured signal spectra

Efficiency of broadband four-wave mixing wavelength conversion using semiconductor traveling-wave amplifiers

We present a theoretical analysis and experimental measurements of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers. In the theoretical analysis, we obtain an analytical expression for the conversion efficiency. In the experiments, both up and down-conversion efficiencies are measured as a function of wavelength shift for shifts up to 27 nm. The experimental data are well explained by the theoretical calculation. The observed higher conversion efficiency for wavelength down-conversion is believed to be caused by phase interferences that exist between various mechanisms contributing to the four-wave mixing process

Terahertz four-wave mixing spectroscopy for study of ultrafast dynamics in a semiconductor optical amplifier

Ultrafast dynamics in a 1.5-µm tensile-strained quantum-well optical amplifier has been studied by highly nondegenerate four-wave mixing at detuning frequencies up to 1.7 THz. Frequency response data indicate the presence of two ultrafast physical processes with characteristic relaxation lifetimes of 650 fs and <100 fs. The longer time constant is believed to be associated with the dynamic carrier heating effect. This is in agreement with previous time-domain pump-probe measurements using ultrashort optical pulses

Highly nondegenerate four-wave mixing and gain nonlinearity in a strained multiple-quantum-well optical amplifier

Highly nondegenerate four-wave mixing was investigated in a 1.5 µm compressively strained multi-quantum-well semiconductor traveling-wave optical amplifier at detuning frequencies up to 600 GHz. A gain nonlinearity with a characteristic relaxation time of 650 fs was determined from the data, and the nonlinear gain coefficient was estimated to be 4.3×10^–23 m^3. Dynamic carrier heating is believed to be the major source of nonlinear gain in this device at the wavelengths investigated

Four-wave mixing in semiconductor optical amplifiers: physics and applications

Nondegenerate four-wave mixing in semiconductor optical amplifiers was studied both as a spectroscopic tool for probing semiconductor dynamics and as a wavelength conversion technique. Four-wave mixing spectra were measured at detuning frequencies ranging from GHz to THz rates and ultrasfast intraband mechanisms having relaxation time constants of 650 fs and less than 100 fs were revealed in the measurements. Cross-polarization four-wave mixing was also measured to study the inter quantum-well carrier transport process in quantum-well amplifiers. In addition, broadband wavelength conversion using four-wave mixing in semiconductor optical amplifiers was investigated. Results concerning the conversion efficiency over spans up to 65 nm, as well as a demonstration of wavelength conversion with gain are presented. The issue of converted signal-to-background noise in this process is also addressed

Influence of Anthropogenic Subsidies on Movements of Common Ravens

Anthropogenic subsidies can benefit populations of generalist predators such as common ravens (ravens; Corvus corax), which in turn may depress populations of many types of species at lower-trophic levels, including desert tortoises (Gopherus agassizii) or greater sage-grouse (Centrocercus urophasianus). Management of subsidized ravens often has targeted local breeding populations that are presumed to affect species of concern and ignored “urban” populations of ravens. However, little is known about how ravens move, especially in response to the presence of anthropogenic subsidies. Therefore, subsidized ravens from distant populations that are not managed may influence local prey. To better understand this issue, we deployed global positioning system – global system for mobile communications transmitters to track movements of 19 ravens from September to December 2020 relative to 2 land cover types that provide subsidies: developed areas and cultivated crops. On average, ravens moved 41.5 km (±30.5) per day, although daily movement distances ranged from 0.13–206.1 km. Raven movement among cover types during the non-breeding season varied widely, with 100% of individuals each using land cover types that provide subsidy and other types at least once in the season. On 100% of days ravens used areas that did not provide subsidy, on 86.7% of days they used developed areas, and on 20.5% of days they used cultivated crops. Although on some days a raven would stay exclusively in areas that did not provide subsidy, there were no days in which a single raven ever stayed exclusively in developed or cultivated crops. Ravens moved shorter distances on days when they used subsidies more frequently. Further, time spent in developed areas and cultivated crops increased when ravens roosted closer to them, although this effect was greater for developed areas than for cultivated crops. Individual ravens were not associated exclusively with either of the subsidy-providing landscapes we considered, but instead all birds used both subsidized and other landscapes. Our research suggests that management of ravens during the non-breeding season and possibly during the breeding season, intended to reduce risk of predation on desert tortoises, will be most effective if conducted on a broad scale because of distances the birds travel and the lack of separation between putative “urban” and “natural” populations of ravens

Conditional expression of human β-hexosaminidase in the neurons of Sandhoff disease rescues mice from neurodegeneration but not neuroinflammation

This study evaluated whether GM(2) ganglioside storage is necessary for neurodegeneration and neuroinflammation by performing β-hexosaminidase rescue experiments in neurons of HexB(−/−) mice. We developed a novel mouse model, whereby the expression of the human HEXB gene was targeted to neurons of HexB(−/−) mice by the Thy1 promoter. Despite β-hexosaminidase restoration in neurons was sufficient in rescuing HexB(−/−) mice from GM(2) neuronal storage and neurodegeneration, brain inflammation persisted, including the presence of large numbers of reactive microglia/macrophages due to persisting GM(2) presence in this cell type. In conclusion, our results suggest that neuroinflammation is not sufficient to elicit neurodegeneration as long as neuronal function is restored

Neuroleptanalgesia for acute abdominal pain: a systematic review

Background: Acute abdominal pain (AAP) comprises up to 10% of all emergency department (ED) visits. Current pain management practice is moving toward multi-modal analgesia regimens that decrease opioid use. Objective: This project sought to determine whether, in patients with AAP (population), does administration of butyrophenone antipsychotics (intervention) compared to placebo, usual care, or opiates alone (comparisons) improve analgesia or decrease opiate consumption (outcomes)? Methods: A structured search was performed in Cochrane CENTRAL, CINAHL, Database of Abstracts of Reviews of Effects, Directory of Open Access Journals, Embase, IEEE-Xplorer, Latin American and Caribbean Health Sciences Literature, Magiran, PubMed, Scientific Information Database, Scopus, TÜBİTAK ULAKBİM, and Web of Science. Clinical trial registries (ClinicalTrials.gov, World Health Organization International Clinical Trials Registry Platform, and Australian New Zealand Clinical Trials Registry), relevant bibliographies, and conference proceedings were also searched. Searches were not limited by date, language, or publication status. Studies eligible for inclusion were prospective randomized clinical trials enrolling patients (age ≥18 years) with AAP treated in acute care environments (ED, intensive care unit, postoperative). The butyrophenone must have been administered either intravenously or intramuscularly. Comparison groups included placebo, opiate only, corticosteroids, non-steroidal anti-inflammatory drugs, or acetaminophen. Results: We identified 7,217 references. Six studies met inclusion criteria. One study assessed ED patients with AAP associated with gastroparesis, whereas five studies assessed patients with postoperative AAP: abdominal hysterectomy (n=4), sleeve gastrectomy (n=1). Three of four studies found improvements in pain intensity with butyrophenone use. Three of five studies reported no change in postoperative opiate consumption, while two reported a decrease. One ED study reported no change in patient satisfaction, while one postoperative study reported improved satisfaction scores. Both extrapyramidal side effects (n=3) and sedation (n=3) were reported as unchanged. Conclusion: Based on available evidence, we cannot draw a conclusion on the efficacy or benefit of neuroleptanalgesia in the management of patients with AAP. However, preliminary data suggest that it may improve analgesia and decrease opiate consumption