Giant optical gain in a rare-earth-ion-doped waveguide amplifier

For optical amplification, typically rare-earth-ion (RE) doped fiber amplifiers (RDFA) or semiconductor optical amplifiers (SOAs) are selected. Despite the weak transition cross-sections of RE ions and their low doping level in silica fibers, resulting in very low gain per unit length, the extremely long interaction lengths realized in fibers can lead to significant overall gain. SOAs can deliver similarly high overall gain over much shorter distances, which makes them suitable for providing on-chip gain. Very high material gain in the nanometer-wide recombination region of a III-V semiconductor, but small overlap with the usually µm-sized signal beam results in a modal gain of several hundred dB/cm. In contrast, the gain per unit length in RE-doped integrated waveguides has hardly exceeded a few dB/cm. Here we demonstrate an ultra-high modal gain of 950 dB/cm in a RE-doped waveguide amplifier, comparable to the modal gain reported for SOAs. The potassium double tungstates KGd(WO4)2, KY(WO4)2, and KLu(WO4)2 are excellent host materials for RE-doped lasers, partly thanks to the high transition cross-sections of RE ions in these hosts. In 2006, the first planar KY(WO4)2:Yb3+ waveguide laser was demonstrated. Co-doping the layer with Gd3+ and Lu3+ ions offers the possibility for lattice matching with the undoped KY(WO4)2 substrate and a significantly enhanced refractive index contrast, hence improved mode confinement. Microstructuring by Ar+ beam etching resulted in channel waveguides, in which lasing with 418 mW output power at 1023 nm and 71% slope efficiency vs. launched pump power was demonstrated. Replacing Y3+ in the layer completely by Gd3+ and Yb3+ ions results in highly doped channel waveguides with a refractive-index contrast of >2 x 10-2. These novel dielectric micro-structures combine a high dopant concentration, large transition cross-sections, and strong light confinement, all features that are crucial for achieving high optical gain, in a single device. When pumping such a KGd0.447Lu0.078Yb0.475(WO4)2 channel waveguide with a 932-nm Ti:Sapphire laser via a microscope objective, high inversion of the Yb3+ system is obtained. Signal light at the zero-phonon line at 980.6 nm, which is the wavelength of highest absorption and emission cross-section, exhibits a small-signal modal gain of 950 dB/cm, exceeding the gain per unit length previously reported in RE-doped materials by two orders of magnitude, thus paving the way for applications of on-chip integrated RE-doped amplifiers

Theoretical study of loss compensation in long-range dielectric loaded surface plasmon polariton waveguides

In this paper, a theoretical study of loss compensation in long-range dielectric loaded surface plasmon waveguides (LR-DLSPPs) is presented. Although extendable to other gain materials, rare-earth doped double tungstates are used as gain material in this work. Two different structures are studied and the effect of the different waveguide geometrical parameters on the material gain required to fully compensate the propagation losses are reported. The simulations were performed at 1.55 micrometer wavelength. A material gain as low as 12.5 dB/cm was determined as sufficient to obtain complete loss compensation in one of the proposed waveguide structures supporting sub-micron lateral mode dimension

Draining Sustainable Profit Fase 1: deskstudie naar mogelijkheden voor benutting van drainwater voor het kweken van algen voor oesterteelt

Drainwater dat vrij komt in de glastuinbouw bevat zouten en voedingsstoffen die bij lozing een belasting op de watersystemen geven, hetgeen lozingsheffingen met zich meebrengt en waardoor tevens waardevolle nutriënten verloren gaan. De uitdaging van het reduceren van de milieubelasting ligt in het hergebruiken van de nutriënten, waardoor een kostenpost kan worden omgezet in een renderende reststroom. Het (beperkte) zoutgehalte (3 ppt of in geconcentreerde vorm 12 ppt) van het drainwater maakt het water mogelijk geschikt voor de kweek van brakwater (en adaptieve mariene) algensoorten. Hierdoor worden waardevolle nutriënten onttrokken en wordt de anorganische belasting van het drainwater lager. Het gekweekte algenproduct kan geschikt zijn voor een aanvullende teelt van een aquacultuurproduct zoals schelpdieren, deze kunnen aan elkaar gekoppeld worden. Aangezien dergelijke mogelijkheden nieuw zijn, bestaan er nog een aantal onbekende factoren, zoals het selecteren van geschikte soorten algen voor kweek, de voedingswaarde van de oester en voedselveiligheidsrisico’s. Deze parameters worden aan de hand van een desk studie gekoppeld aan laboratorium experimenten onderzocht

Fork naar Farm. deelrapport: experimentele kweek van yellowtail kingfish (Seriola lalandi) en de implementatie hiervan

In Nederland is sprake van een toenemende vraag naar duurzaam en lokaal geproduceerde vis. Het doel van het Fork naar Farm project was het begeleiden van de productie van een nieuwe vissoort binnen de Nederlandse viskweeksector en Afrikaanse meerval volgens een certificeringsschema waarin duurzaamheid een rol speelt. Binnen het kader van het Fork naar Farm project behandelt dit rapport het onderzoek naar de opkweek van de yellowtail kingfish (Seriola lalandi) in recirculatiesystemen en de implementatie hiervan in de praktijk. Er zijn verschillende groepen jonge yellowtail kingfish met een gewicht van ongeveer 0,5 gram aangekocht vanuit Australië en in Nederland opgekweekt in recirculatiesystemen. Er is in de faciliteiten van IMARES Wageningen UR onderzoek verricht naar diverse houderijomstandigheden: temperatuur, pH en saliniteit van het water en het voer

Predictive frequency-based sequence estimator for control of grid-tied converters under highly distorted conditions

This paper proposes a novel frequency-based predictive sequence extractor that allows to isolate the harmonic components of both voltages and currents needed for the control of grid-tied converters. The proposed method is based on a modification of the Sliding Goertzel Transformation (SGT) that allows to include a predictive behavior with a prediction horizon equal to the processing window needed for the algorithm. The technique performance is compared with the well-established DSOGI alternative, allowing for a higher bandwidth in the estimation as well as improved immunity to changes in the magnitude, frequency and phase of the tracked signals. Additionally, the impact of the proposed method on the closed-loop performance of the current controlled converter is proposed as a metric, thus enabling other researches to have a clear view about the expected real impact of the different existing methods

A randomized controlled trial comparing nerve block and mandibular infiltration techniques in posterior mandible implant surgeries

To compare global surgical pain under nerve block and mandibular infiltration anesthesia techniques, and to evaluate pain during drilling and the distance to the mandibular canal in posterior mandible implant surgeries. A prospective, randomized, controlled, double-blind, clinical trial was conducted to compare nerve block (Group A) to mandibular infiltration (Group B) techniques for dental implant placement. Global surgical pain (VAS = visual analogue scale), pain during drilling or implant placement (MPQ = McGill pain questionnaire) and distance to the mandibular canal (Image J) were statically analyzed. Age, gender, anxiety levels, tooth to be replaced, implant size, adjacent teeth and duration of surgery were also analyzed. 172 patients were included and 283 dental implants were analyzed. VAS values were significantly higher in Group B (p<0.05). In Group A, 99% of the surgeries were performed painlessly during drilling and implant placement, but in Group B, 11.6% of implant placements (17 implants) felt pain during these surgical steps. Mean distance to mandibular canal (3.8 mm, range: 0.0 to 7.0) in those 17 implants placed under mandibular infiltration was clinically and statistically similar to the mean distance (3.0 mm, range: 0.0 to 9.0) of 130 implants placed painless (p=0.10). Pain during drilling under mandibular infiltration was significantly associated with the duration of surgery (p<0.05) and to both adjacent teeth being present (p<0.05). Although both techniques are safe and effective for placing implants in the posterior mandible, nerve block provides a more profound analgesia than mandibular infiltration. When placing implants under mandibular infiltration, as getting closer to the canal does not increase the feeling of pain, it is not recommended to use the presence of pain as a preventive resource to avoid inferior alveolar nerve injuries