80 research outputs found
Scattering of a cross-polarized linear wave by a soliton at an optical event horizon in a birefringent nanophotonic waveguide
The scattering of a linear wave on an optical event horizon, induced by a
cross polarized soliton, is experimentally and numerically investigated in
integrated structures. The experiments are performed in a dispersion-engineered
birefringent silicon nanophotonic waveguide. In stark contrast with
co-polarized waves, the large difference between the group velocity of the two
cross-polarized waves enables a frequency conversion almost independent on the
soliton wavelength. It is shown that the generated idler is only shifted by 10
nm around 1550 nm over a pump tuning range of 350 nm. Simulations using two
coupled full vectorial nonlinear Schr\"odinger equations fully support the
experimental results
Generation of ultra broadband coherent supercontinuum in tapered and dispersion managed silicon nanophotonic waveguides
Tapered and dispersion managed (DM) silicon nanophotonic waveguides are
investigated for the generation of optimal ultra broadband supercontinuum (SC).
DM waveguides are structures showing a longitudinally dependent group velocity
dispersion that results from the variation of the waveguide width with the
propagation distance. For the generation of optimal SC, a genetic algorithm has
been used to find the best dispersion map. This allows for the generation of
highly coherent supercontinuums that span over 1.14 octaves from 1300 nm to
2860 nm and 1.25 octaves from 1200 nm to 2870 nm at -20 dB level for the
tapered and DM waveguides respectively, for a 2 m, 200 fs and 6.4 pJ input
pulse. The comparison of these two structures with the usually considered
optimal fixed width waveguide shows that the SC is broader and flatter in the
more elaborated DM waveguide, while the high coherence is ensured by the
varying dispersion.Comment: arXiv admin note: substantial text overlap with arXiv:1610.0566
Observation of an optical event horizon in a silicon-on-insulator photonic wire waveguide
We report on the first experimental observation of an optical analogue of an event horizon in integrated nanophotonic waveguides, through the reflection of a continuous wave on an intense pulse. The experiment is performed in a dispersion-engineered silicon-on-insulator waveguide. In this medium, solitons do not suffer from Raman induced self-frequency shift as in silica fibers, a feature that is interesting for potential applications of optical event horizons. As shown by simulations, this also allows the observation of multiple reflections at the same time on fundamental solitons ejected by soliton fission.SCOPUS: ar.jhttp://www.opticsexpress.org/abstract.cfm?URIinfo:eu-repo/semantics/publishe
Physical origin of higher-order soliton fission in nanophotonic semiconductor waveguides
Supercontinuum generation in Kerr media has become a staple of nonlinear
optics. It has been celebrated for advancing the understanding of soliton
propagation as well as its many applications in a broad range of fields.
Coherent spectral broadening of laser light is now commonly performed in
laboratories and used in commercial white light sources. The prospect of
miniaturizing the technology is currently driving experiments in different
integrated platforms such as semiconductor on insulator waveguides. Central to
the spectral broadening is the concept of higher-order soliton fission. While
widely accepted in silica fibers, the dynamics of soliton decay in
semiconductor waveguides is yet poorly understood. In particular, the role of
nonlinear loss and free carriers, absent in silica, remains an open question.
Here, through experiments and simulations, we show that nonlinear loss is the
dominant perturbations in wire waveguides, while free-carrier dispersion is
dominant in photonic crystal waveguides
Water quality assessment by means of HFNI valvometry and high-frequency data modeling
International audienceThe high-frequency measurements of valve activity in bivalves (e.g., valvometry) over a long period of time and in various environmental conditions allow a very accurate study of their behaviors as well as a global analysis of possible perturbations due to the environment. Valvom- etry uses the bivalve's ability to close its shell when exposed to a contaminant or other abnormal environmental conditions as an alarm to indicate possible perturbations in the environment. The modeling of such high-frequency serial valvom- etry data is statistically challenging, and here, a nonparametric approach based on kernel estima- tion is proposed. This method has the advantage of summarizing complex data into a simple den- sity profile obtained from each animal at every 24-h period to ultimately make inference about time effect and external conditions on this profile. The statistical properties of the estimator are pre- sented. Through an application to a sample of 16 oysters living in the Bay of Arcachon (France), we demonstrate that this method can be used to first estimate the normal biological rhythms of permanently immersed oysters and second to de- tect perturbations of these rhythms due to changes in their environment. We anticipate that this ap- proach could have an important contribution to the survey of aquatic systems
In the darkness of the polar night, scallops keep on a steady rhythm
Published version. Source at http://doi.org/10.1038/srep32435.
License CC BY 4.0.Although the prevailing paradigm has held that the polar night is a period of biological quiescence, recent studies have detected noticeable activity levels in marine organisms. In this study, we investigated the circadian rhythm of the scallop Chlamys islandica by continuously recording the animal’s behaviour over 3 years in the Arctic (Svalbard). Our results showed that a circadian rhythm persists throughout the polar night and lasts for at least 4 months. Based on observations across three polar nights, we showed that the robustness and synchronicity of the rhythm depends on the angle of the sun below the horizon. The weakest rhythm occurred at the onset of the polar night during the nautical twilight. Surprisingly, the circadian behaviour began to recover during the darkest part of the polar night. Because active rhythms optimize the fitness of an organism, our study brings out that the scallops C. islandica remain active even during the polar night
Observation of two-photon absorption induced soliton fission
info:eu-repo/semantics/publishe
Monitoring biological rhythms through the dynamic model identification of an oyster population
International audienceThe measurements of valve activity in a population of bivalves under natural environmental conditions (16 oysters in the Bay of Arcachon, France) are used for a physiological model identification. A nonlinear auto-regressive exogenous (NARX) model is designed and tested. The method to design the model has two parts. 1) Structure of the model: The model takes into account the influence of environmental conditions using measurements of the sunlight intensity, the moonlight, tide levels, precipitation and water salinity levels. A possible influence of the internal circadian/circatidal clocks is also analyzed. 2) Least square calculation of the model parameters. Through this study, it is demonstrated that the developed dynamical model of the oyster valve movement can be used for estimating normal physiological rhythms of permanently immersed oysters and can be considered for detecting perturbations of these rhythms due to changes in the water quality, i.e. for ecological monitoring
Supercontinuum generation assisted by dispersive waves trapping in dispersion-managed integrated silicon waveguides
Compact chip-scale comb sources are of significant interest for many
practical applications. Here, we experimentally study the generation of
supercontinuum (SC) in an axially varying integrated waveguide. We show that
the local tuning of the dispersion enables the continuous blue shift of
dispersive waves thanks to their trapping by the strongly compressed pump
pulse. This mechanism provides new insight into supercontinuum generation in a
dispersion varying integrated waveguide. Pumped close to 2.2 m in the
femtosecond regime and at a pulse energy of 4 pJ, the output spectrum
extends from 1.1 m up to 2.76 m and shows good coherence properties.
Octave-spanning SC is also observed at input energy as low as 0.9 pJ. We
show that the supercontinuum is more robust against variations of the input
pulse parameters and is also spectrally flatter in our numerically optimized
waveguide than in fixed-width waveguides. This research demonstrates the
potential of dispersion varying waveguides for coherent SC generation and paves
the way for integrated low power applications, such as chip-scale frequency
comb generation, precision spectroscopy, optical frequency metrology, and
wide-band wavelength division multiplexing in the near-infrared
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