Design and Characterization of SiN-based integrated optical components for Wavelength Division Multiplexing

To follow the trend of the data traffic and to limit the size of the hyperscale data centers, communication solutions offering small footprint, low cost and low power consumption are needed. Optical interconnects used in data centers are mostly short reach (approximately 100 m) basedon GaAs-based 850 nm vertical-cavity surface emitting lasers (VCSELs) and OM4 multimode fibers (MMF). However, with 1 km-long optical links, the use of VCSEL-MMF at 850 nm becomes challenging at high data rates (Tb/s) due to large modal dispersion and high propagation loss. Therefore, other cost-effective methods are needed to compensate these limits. Single mode GaAs-based VCSELs have been demonstrated at 1060 nm of wavelength, where the chromatic dispersion is lower, for optical links ranging between 300 m and 10 km. This solution could be a better alternative than InP-based distributed feedback laser sources at 1310 nm in terms of cost and energy dissipation. As the modulation bandwidth of GaAs-based single mode VCSELs is limited to around 30 GHz, reaching the capacity target then requires a wavelength division multiplexing scheme with parallel single-core fibers (SCFs) or even multi-core fibers (MCFs).In this thesis we discuss different types of demultiplexers at 1060 nm of wavelength. The proposed designed demultiplexers are arrayed waveguide gratings (AWGs) and cascaded Mach-Zehnder interferometers (MZIs). These two technologies are compared in terms of transmission,bandwidth, crosstalk, and footprint with the number of output channels. Grating couplers at 1060 and 850 nm for on-chip coupling are also studied. The goal is to couple the light coming from a single mode fiber or a VCSEL with the lowest possible loss and back reflection

Stable isotopes of captive Cetaceans (Killer Whales and Bottlenose dolphins)

There is currently a great deal of interest in using stable-isotope methods to investigate diet, trophic level and migration movement in wild cetaceans. Fundamental to the interpretation of these methods is the need to understand how diet isotopic values are reflected in consumer tissues. In this study, we investigated patterns of isotopic discrimination between diet and blood constituents of two species of cetaceans (killer whale, Orcinus orca and 19 bottlenose dolphin, Tursiops truncutus) fed with controlled diets during 350 days. Diet discrimination factors ( ) for plasma were estimated to 13C =2.3‰ and 1520 N =1.8‰ respectively for both species and to 13C =2.7‰ and 1521 N =0.5‰ for red blood cells (RBC). Delipidation had no significant effect on carbon and nitrogen isotopic values of blood constituents, confirming that cetacean blood no serving as reservoirs of lipids. In contrast, carbon isotopic values are higher in delipidated samples of blubber, liver and muscle of orca tissues. The mean half life for plasma was 32.9 days for killer whales and 27.2 days for bottlenose dolphin and for RBC was greater than 175 days. The potential for conflict between fisheries and cetaceans has heightened the need for trophic information about this taxa within those ecosystems. These results provide the first published stable isotope turnover rates and discrimination factors for cetaceans, which are essential if conclusions are to be drawn on issues concerning trophic structures, carbon sources and diet reconstruction

Trophic diversity of idoteids (Crustacea, Isopoda) inhabiting the Posidonia oceanica litter

The coexistence of three idoteid species in Posidonia oceanica litter raises the question of trophic diversity and their role in the litter degradation process. Hence, diet composition of Idotea balthica, Idotea hectica and Cleantis prismatica was studied using a combination of gut contents and stable isotopes analysis. Gut content observations indicate that P. oceanica dead leaves are an important part of the ingested food for the three species, although their tissues are constituted of only a small to medium fraction of P. oceanica carbon. Our results also underlined the potential role of these species in the degradation of P. oceanica litter by mechanically fragmenting the litter and by assimilating a small to medium fraction of carbon. Moreover, we showed that there were considerable inter- and intra-specific differences in diet composition. Diet differed between juveniles and adults for I. balthica. Crustaceans are an important food source for adults of I. balthica, while I. hectica indicated a major contribution of algal material. C. prismatica showed an intermediate diet. This trophic diversity is probably one of the factors allowing these species to coexist in the same biotope

Multilayer integration in silicon nitride: decoupling linear and nonlinear functionalities for ultralow loss photonic integrated systems

Silicon nitride is an excellent material platform for its extremely low loss in a large wavelength range, which makes it ideal for the linear processing of optical signals on a chip. Moreover, the Kerr nonlinearity and the lack of two-photon absorption in the near infrared enable efficient nonlinear optics, e.g., frequency comb generation. However, linear and nonlinear operations require distinct engineering of the waveguide core geometry, resulting in a tradeoff between optical loss and single-mode behavior, which hinders the development of high-performance, ultralow-loss linear processing blocks on a single layer. Here, we demonstrate a dual-layer photonic integration approach with two silicon-nitride platforms exhibiting ultralow optical losses, i.e., a few dB/m, and individually optimized to perform either nonlinear or linear processing tasks. We demonstrate the functionality of this approach by integrating a power-efficient microcomb with an arrayed waveguide grating demultiplexer to filter a few frequency comb lines in the same monolithically integrated chip. This approach can significantly improve the integration of linear and nonlinear optical elements on a chip and opens the way to the development of fully integrated processing of Kerr nonlinear sources

Effects of fish predation on Posidonia oceanica amphipod assemblages

Amphipod assemblages that inhabit Posidonia oceanica seagrass meadows are potentially relevant trophic resources for ichthyofauna. However, the effects of fish predation on amphipod assemblages in this system have received little attention. To address this gap in knowledge, experimental manipulations of predation intensity (exclusion and inclusion cages) were conducted at two sites in a Mediterranean marine protected area, where different levels of fish predation were expected to occur. We found that in the absence of predatory fishes (exclusion cages), total amphipod density and biomass were higher than in uncaged areas and partially controlled cages. At the species level, Caprella acanthifera and Iphimedia minuta responded to caging with increased abundance, while in most cases different species did not exhibit differences in density or biomass between treatments. The presence of one enclosed labrid fish predator (inclusion cages) resulted in a lower density and biomass of Aora spinicornis and a lower biomass of Phtisica marina, although total amphipod density and biomass were unchanged. In the inclusion cages, a size-frequency analysis revealed that predators mainly targeted large A. spinicornis and Apherusa chiereghinii individuals. Our results suggest that predation by fish may be an important factor in controlling amphipod abundances and biomasses in P. oceanica meadows. Overall, amphipod community composition was not affected by exclusion or inclusion of fish predators. However, some significant effects at the species level point to more complex interactions between some amphipods and fish

Isotope analysis reveals foraging area dichotomy for Atlantic leatherback turtles

Background: The leatherback turtle (Dermachelys corlacea) has undergone a dramatic decline over the last 25 years, and this is believed to be primarily the results of mortality associated with fisheries bycatch followed by egg and nesting female harvest, Atlantic leatherback turtles undertake long migrations across ocean basins from subtropical and tropical nesting beaches to productive frontal areas; Migration between two nesting seasons can last 2 or 3 years, a time period termed the remigration interval (RI). Recent satellite transmitter data revealed that Atlantic leatherbacks follow two major dispersion patterns after nesting season, through the North Gulf Stream area or more eastward across the North Equatorial Current. However, information on the whole RI is lacking, precluding the accurate identification of feeding areas where conservation measures may need to be applied. Methodology/Principal Findings: Using stable isotopes as dietary tracers we determined the characteristics of feeding grounds of leatherback females nesting in French Guíana. During migration, 3-year RI females diffred from 2-year RI females in their isotope values, implying differences in their choice of feeding habitats (offshore vs. more coastal) and foraging latitude (North Atlantic vs. West African coasts, respectively). Egg-yolk and blood isotope values are correlated in nesting females, indicating that egg analysis is a useful tool for assessing isotope values in these turtles, including adults when not available. Conclusions/Significance: Our results complement previous data on turtle movements during the first year following the nesting season, integrating the diet consumed during the year before nesting. We suggest that the French Guiana leatherback population segregates into two distinct isotopic groupings, and highlight the urgent need to determine the feeding habitats of the turtle in the Atlantic in order to protect this species from incidental take by commercial fisheries. Our results also emphasize the use of eggs, a less-invasive sampling material than blood, to assess isotopic data and feeding habits for adult female leatherbacks

Phenology of marine turtle nesting revealed by statistical model of the nesting season

BACKGROUND: Marine turtles deposit their eggs on tropical or subtropical beaches during discrete nesting seasons that span several months. The number and distribution of nests laid during a nesting season provide vital information on various aspects of marine turtle ecology and conservation. RESULTS: In the case of leatherback sea turtles nesting in French Guiana, we developed a mathematical model to explore the phenology of their nesting season, derived from an incomplete nest count dataset. We detected 3 primary components in the nest distribution of leatherbacks: an overall shape that corresponds to the arrival and departure of leatherback females in the Guianas region, a sinusoidal pattern with a period of approximately 10 days that is related to physiological constraints of nesting female leatherbacks, and a sinusoidal pattern with a period of approximately 15 days that likely reflects the influence of spring high tides on nesting female turtles. CONCLUSION: The model proposed here offers a variety of uses for both marine turtles and also other taxa when individuals are observed in a particular location for only part of the year

The effects of fire on ant trophic assemblage and sex allocation

Fire plays a key role in ecosystem dynamics worldwide, altering energy flows and species community structure and composition. However, the functional mechanisms underlying these effects are not well understood. Many ground-dwelling animal species can shelter themselves from exposure to heat and therefore rarely suffer direct mortality. However, fire-induced alterations to the environment may change a species' relative trophic level within a food web and its mode of foraging. We assessed how fire could affect ant resource utilization at different scales in a Mediterranean forest. First, we conducted isotopic analyses on entire ant species assemblages and their potential food resources, which included plants and other arthropods, in burned and unburned plots 1 year postfire. Second, we measured the production of males and females by nests of a fire-resilient species, Aphaenogaster gibbosa, and analyzed the differences in isotopic values among workers, males, and females to test whether fire constrained resource allocation. We found that, in spite of major modifications in biotic and abiotic conditions, fire had little impact on the relative trophic position of ant species. The studied assemblage was composed of species with a wide array of diets. They ranged from being mostly herbivorous to completely omnivorous, and a given species' trophic level was the same in burned and unburned plots. In A. gibbosa nests, sexuals had greater δ15N values than workers in both burned and unburned plots, which suggests that the former had a more protein-rich diet than the latter. Fire also appeared to have a major effect on A. gibbosa sex allocation: The proportion of nests that produced male brood was greater on burned zones, as was the mean number of males produced per nest with the same reproductive investment. Our results show that generalist ants with relatively broad diets maintained a constant trophic position, even following a major disturbance like fire. However, the dramatically reduced production of females on burned zones compared to unburned zones 1 year postfire may result in considerably reduced recruitment of new colonies in the mid to long term, which could yield genetic bottlenecks and founder effects. Our study paves the way for future functional analyses of fire-induced modifications in ant populations and communities.This work was funded by MICINN (project CONSOLIDER-MONTES CSD2008-00040), MICINN and FEDER (projects CGL2009-12472 to RB and CGL2009-09690 to XC), the Consejo Superior de Investigaciones Cientıficas (JAE postdoctoral contract to SC), and the National Science Foundation (International Research Fellowship to J.M.C P-D)

Intrapopulation Variability Shaping Isotope Discrimination and Turnover: Experimental Evidence in Arctic Foxes

Tissue-specific stable isotope signatures can provide insights into the trophic ecology of consumers and their roles in food webs. Two parameters are central for making valid inferences based on stable isotopes, isotopic discrimination (difference in isotopic ratio between consumer and its diet) and turnover time (renewal process of molecules in a given tissue usually measured when half of the tissue composition has changed). We investigated simultaneously the effects of age, sex, and diet types on the variation of discrimination and half-life in nitrogen and carbon stable isotopes (δ15N and δ13C, respectively) in five tissues (blood cells, plasma, muscle, liver, nail, and hair) of a top predator, the arctic fox Vulpes lagopus. We fed 40 farmed foxes (equal numbers of adults and yearlings of both sexes) with diet capturing the range of resources used by their wild counterparts. We found that, for a single species, six tissues, and three diet types, the range of discrimination values can be almost as large as what is known at the scale of the whole mammalian or avian class. Discrimination varied depending on sex, age, tissue, and diet types, ranging from 0.3‰ to 5.3‰ (mean = 2.6‰) for δ15N and from 0.2‰ to 2.9‰ (mean = 0.9‰) for δ13C. We also found an impact of population structure on δ15N half-life in blood cells. Varying across individuals, δ15N half-life in plasma (6 to 10 days) was also shorter than for δ13C (14 to 22 days), though δ15N and δ13C half-lives are usually considered as equal. Overall, our multi-factorial experiment revealed that at least six levels of isotopic variations could co-occur in the same population. Our experimental analysis provides a framework for quantifying multiple sources of variation in isotopic discrimination and half-life that needs to be taken into account when designing and analysing ecological field studies

Sexual and parent-offspring dietary segregation in a colonial raptor as revealed by stable isotopes

Diet composition and foraging behaviour may show considerable variation among population groups (such as sex- and age-classes), with potentially important consequences for population dynamics. Thus, failure to account for within-species differences in trophic ecology can bias our understanding of different aspects of population ecology and limit the implementation of effective management and conservation strategies. Although countless studies have investigated the diet of birds, comparatively few have tried to describe intraspecific sources of dietary variation. Here, we used stable isotope analysis (SIA) to investigate sex- and age-related dietary segregation in the lesser kestrel (Falco naumanni) breeding in South Iberia and to discuss potential mechanisms involved in such segregation. Females had a narrower isotopic niche width and significantly more depleted δ1339 C signatures than males during the courtship period, likely due to a higher consumption of energetically rich mole crickets. Our results suggest that sex-specific differences in the diet of lesser kestrels do not result from intra-specific competition and are unlikely to be explained by sexual size dimorphism alone. Instead, the main driving force of observed sexual segregation appears to be the different energetic requirements of males and females before laying, when females need a higher allocation of resources to egg production. δ1545 N isotopic signatures differed significantly between adults and chicks and niche overlap between these age classes was low. Stable isotopic mixing models (SIAR) showed that, compared to adults, the diet of chicks was less diverse and mainly dominated by grasshoppers. Different resource allocation between chicks and adults might also result from different energy requirements, as rapidly growing chicks require 50 more energy than adults, ultimately leading to a parent-offspring dietary segregation. Finally, overall agreement between pellet analysis and SIA methods highlight the potential of SIA for assessing intra-specific variation in dietary regimes which is often unfeasible through conventional approaches of diet assessment