Nonlinear optical response of low loss silicon germanium waveguides in the mid-infrared.

We have investigated the nonlinear optical response of low loss Si(0.6)Ge(0.4) / Si waveguides in the mid-infrared wavelength range from 3.25- 4.75µm using picosecond optical pulses. We observed and measured the three and four-photon absorption coefficients as well as the Kerr nonlinear refractive index. The dynamics of the spectral broadening suggests that, in addition to multiphoton absorption, the corresponding higher order nonlinear refractive phenomena also needs to be included when high optical pulse intensities are used at mid-infrared wavelengths in this material.

Mid-infrared nonlinear optical response of Si-Ge waveguides with ultra-short optical pulses.

We characterize the nonlinear optical response of low loss Si(0.6)Ge(0.4) / Si waveguides in the mid-infrared between 3.3 µm and 4 µm using femtosecond optical pulses. We estimate the three and four-photon absorption coefficients as well as the Kerr nonlinear refractive index from the experimental measurements. The effect of multiphoton absorption on the optical nonlinear Kerr response is evaluated and the nonlinear figure of merit estimated providing some guidelines for designing nonlinear optical devices in the mid-IR. Finally, we compare the impact of free-carrier absorption at mid-infrared wavelengths versus near-infrared wavelengths for these ultra-short pulses.

Reconfigurable photonic crystal waveguides created by selective liquid infiltration.

We experimentally demonstrate reconfigurable photonic crystal waveguides created directly by infiltrating high refractive index (n≈2.01) liquids into selected air holes of a two-dimensional hexagonal periodic lattice in silicon. The resulting effective index contrast is large enough that a single row of infiltrated holes enables light propagation at near-infrared wavelengths. We include a detailed comparison between modeling and experimental results of single line defect waveguides and show how our infiltration procedure is reversible and repeatable. We achieve infiltration accuracy down to the single air hole level and demonstrate control on the volume of liquid infused into the holes by simply changing the infiltration velocity. This method is promising for achieving a wide range of targeted optical functionalities on a "blank" photonic crystal membrane that can be reconfigured on demand.

Amorphous silicon nanowires combining high nonlinearity, FOM and optical stability.

We demonstrate optically stable amorphous silicon nanowires with both high nonlinear figure of merit (FOM) of ~5 and high nonlinearity Re(γ) = 1200W(-1)m(-1). We observe no degradation in these parameters over the entire course of our experiments including systematic study under operation at 2 W coupled peak power (i.e. ~2GW/cm(2)) over timescales of at least an hour.

Slow-light dispersion engineering of photonic crystal waveguides using selective microfluidic infiltration.

We experimentally demonstrate dispersion engineering of slow light photonic crystal (PhC) waveguides using selective infiltration of the first two rows of air holes with high index ionic liquids. The infiltrated PhC waveguide exhibits a dispersion window of 3 nm with a nearly constant group velocity of ~c/80 that depends on the liquid physical properties. We investigate how the effective refractive index changes in time due to the dynamics of the liquids in the holes. This demonstration highlights the versatility, flexibility, and tunability offered by optofluidics in PhC circuits.

Four-wave mixing in slow light engineered silicon photonic crystal waveguides.

We experimentally investigate four-wave mixing (FWM) in short (80 µm) dispersion-engineered slow light silicon photonic crystal waveguides. The pump, probe and idler signals all lie in a 14 nm wide low dispersion region with a near-constant group velocity of c/30. We measure an instantaneous conversion efficiency of up to -9dB between the idler and the continuous-wave probe, with 1W peak pump power and 6 nm pump-probe detuning. This conversion efficiency is found to be considerably higher (>10 × ) than that of a Si nanowire with a group velocity ten times larger. In addition, we estimate the FWM bandwidth to be at least that of the flat band slow light window. These results, supported by numerical simulations, emphasize the importance of engineering the dispersion of PhC waveguides to exploit the slow light enhancement of FWM efficiency, even for short device lengths.

Liquid crystal dynamics in a photonic crystal cavity created by selective microfluidic infiltration.

A microfluidic double heterostructure cavity is created in a silicon planar photonic crystal waveguide by selective infiltration of a liquid crystal. The spectral evolution of the cavity resonances probed by evanescent coupling reveals that the liquid crystal evaporates, even at room temperature, despite its relatively low vapor pressure of 5 × 10(-3) Pa. We explore the infiltration and evaporation dynamics of the liquid crystal within the cavity using a Fabry-Perot model that accounts for the joint effects of liquid volume reduction and cavity length variation due to liquid evaporation. While discussing how the pattern of the infiltrated liquid can be optimized to restrict evaporation, we find that the experimental behavior is consistent with basic microfluidic relations considering the small volumes of liquids and large surface areas present in our structure.

Optical signal processing on a silicon chip at 640Gb/s using slow-light.

We demonstrate optical performance monitoring of in-band optical signal to noise ratio (OSNR) and residual dispersion, at bit rates of 40Gb/s, 160Gb/s and 640Gb/s, using slow-light enhanced optical third harmonic generation (THG) in a compact (80microm) dispersion engineered 2D silicon photonic crystal waveguide. We show that there is no intrinsic degradation in the enhancement of the signal processing at 640Gb/s relative to that at 40Gb/s, and that this device should operate well above 1Tb/s. This work represents a record 16-fold increase in processing speed for a silicon device, and opens the door for slow light to play a key role in ultra-high bandwidth telecommunications systems.

Dispersion engineering of slow light photonic crystal waveguides using microfluidic infiltration.

We present a technique based on the selective liquid infiltration of photonic crystal (PhC) waveguides to produce very small dispersion slow light over a substantial bandwidth. We numerically demonstrate that this approach allows one to control the group velocity (from c/20 to c/110) from a single PhC waveguide design, simply by choosing the index of the liquid to infiltrate. In addition, we show that this method is tolerant to deviations in the PhC parameters such as the hole size, which relaxes the constraint on the PhC fabrication accuracy as compared to previous structural-based methods for slow light dispersion engineering.

A proposal for enhancing four-wave mixing in slow light engineered photonic crystal waveguides and its application to optical regeneration.

In this paper, we investigate both analytically and numerically four-wave mixing (FWM) in short (80 microm) dispersion engineered slow light photonic crystal waveguides. We demonstrate that both a larger FWM conversion efficiency and an increased FWM bandwidth (approximately 10 nm) can be achieved in these waveguides as compared to dispersive PhC waveguides. This improvement is achieved through the net slow light enhancement of the FWM efficiency (almost 30dB as compared to a fast nanowire of similar length), even in the presence of slow light increased linear and nonlinear losses, and the suitable dispersion profile of these waveguides. We show how such improved FWM operation can be advantageously exploited for designing a compact 2R and 3R regenerator with the appropriate nonlinear power transfer function.

Description of the outbreak of bluetongue in Corsica in 2003, and lessons for surveillance.

Since 1999, several serotypes of bluetongue virus (btv) have been isolated in the western part of the Mediterranean basin, and since 2000, Corsica has been exposed to three different serotypes: BTV serotype 2 in 2000, BTV serotype 4 (BTV-4) in 2003 and BTV serotype 16 in 2004. In 2000 there were no surveillance systems for bluetongue, but in 2003, active surveillance of the circulation of BTV and its vector Culicoides species, aided by a raised level of awareness in farmers and veterinarians, made it possible to study the introduction of BTV-4. The monitoring and analysis of the seroconversions of sentinel herds of goats, clinical signs and meteorological variables showed that the serotype had been present in the island since May that year, but clinical signs were first observed only in October. Moreover, the weather conditions and wind patterns were suitable for the transport of Culicoides species from Sardinia in May. These observations suggest that btv had been transported on air currents from a southern infected area, and that it could have spread without causing clinical signs of disease for a few months.

Schmallenberg virus in Culicoides Latreille (Diptera: Ceratopogonidae) populations in France during 2011-2012 outbreak.

Following the emergence of the Schmallenberg virus (SBV) in 2011 in Germany and its rapid spread in Europe, Culicoides (Diptera: Ceratopogonidae) collected through the French surveillance network were analysed in order to record the presence of virus genome into species diversity collected, to assess the minimum infectious rates (MIR) and the virus circulation dynamics in Culicoides populations. Two vector activity periods were selected (2011, August to October, 53 sites and 2012, June to October, 35 sites) corresponding to 704 night collections. A total of 29,285 individual midges covering at least 50 species were tested either in pools of maximum 50 females or individually (for Culicoides obsoletus/Culicoides scoticus) using real-time RT-PCR. Nine species were found SBV positive (C. obsoletus, C. scoticus, Culicoides chiopterus, Culicoides dewulfi, Culicoides imicola, Culicoides pulicaris, Culicoides newsteadi, Culicoides lupicaris and Culicoides nubeculosus) with overall MIR ranging from 0.2% to 4.2%. While the Culicoides nubeculosus laboratory strain is generally considered to have only low vector competence for viruses, interestingly, field-caught C. nubeculosus specimens were found positive twice for SBV. The first SBV-positive pool was recorded in August 2011 in north-eastern France, dating the virus circulation in France 5 months earlier than the first recorded congenital malformations and 2 months earlier than the former recorded date based on retrospective serological data. The MIR were maximum in October 2011, and in July 2012 according to dates of virus arrival in the studied areas. Moreover, our study also showed that virus circulation could be locally intense with infection rate (IR) reaching up to 16% for C. obsoletus/C. scoticus in July 2012 in one site of western France. This retrospective study demonstrates the importance of large-scale analysis to describe the spatio-temporal dynamics of virus circulation.

Peste des petits ruminants (PPR) outbreak in Tajikistan.

The occurrence of outbreaks of peste des petits ruminants (PPR) in three districts of Tajikistan is described. The causal strain (PPR Tajikistan) was characterized and the sequence of its N gene was compared with that of 43 other strains isolated since 1968 in Africa, the Middle East and Asia. The study demonstrated (1) the value of the N gene as a target in comparing isolates obtained over an extended period of evolution, and (2) that clustering was related to the geographical origin of strains.

[Bluetongue, an emerging disease in Northern Europe]. / La fièvre catarrhale ovine (bluetongue) : quand une maladie du sud s'invite au nord.

Bluetongue is a non contagious viral disease of sheep transmitted by bites of haematophagous midges. The disease is caused by an orbivirus belonging to the Reoviridae family. The genome is segmented in 10 double-strand RNA encapsidated in a non-enveloped spherical particle with a icosaedral symetry. Twenty distinct serotypes have been identified so far, each of them inducing limited cross-protection against the others. Sheep are usually the only ones showing clinical signs like pyrexia, congestion of mucosa and cyanosis of the tongue. However, cattle, goat and wild ruminants can be asymptomatically infected. Formerly restricted to the area between the 30/40th south and 40/50th north parallels, the infection has progressively extended to the south of Europe and was more recently introduced in the north. The reason for this extension might be twice: the northward spreading of the tropical vector Culicoides imicola and the adaptation of the virus to a yet unknown endemic biting midge. Control of the disease is based on the use of live-attenuated or inactivated vaccines specific of the serotype. In free area, emergency measures can also consist in the rapid detection and elimination of the outbreaks.

Analytic properties of photonic crystal superprism parameters.

We study the analytic properties of the photonic crystal superprism resolution parameters p , q , and r introduced previously by Baba and Matsumoto [Appl. Phys. Lett. 81, 2325 (2002)], which characterize the potential dispersive power of a superprism. We find closed form expressions for these quantities that greatly simplify their accurate evaluation and reveal significant insights about their behavior. The expressions imply general properties of the parameters which are true for all bands and all photonic crystals. In particular, we demonstrate that all photonic crystals exhibit infinite resolution as measured by the parameter r along particular contours in any photonic band.

Stimulation of corticosteroid biosynthesis by angiotensin I [des-asp1]angiotensin I, angiotensin II and [des-asp1]-angiotensin II in bovine adrenal fasciculata cells.

The effect of angiotensin I (AI), angiotensin II (AII), [des-asp1]AI, [des-asp1]AII and [des-asp1-arg2]AII on corticosteroid production in isolated fasciculata cells from bovine adrenals has been studied. AII and [des-asp1]AII in concentrations ranging from 10(-9)M to 10(-6)M had a potent stimulatory effect on steroid biosynthesis. The dose-response curves for both peptides were identical. AI was about 3 times less potent than AII and [des-asp1]AII. The effect of AI was not due to its conversion to AII. [Des-asp1]AI was as active as AI. No significant conversion to [des-asp1]AII was observed. [Des-asp1-arg2]AII had only a minimal effect on steroidogenesis. The structural analog [sar1,-ala8]AII inhibited all angiotensins specifically and competitively. The affinity of the cellular binding site was higher for AII and [des-asp1]AII than for [sar1,ala8]ALL, but lower for AI and [des-asp1]AI than for the inhibitor. Combination of submaximal doses of AI and AII resulted in an additive effect on steroid production. By contrast, combination of maximal doses of both peptides had the same effect as AII alone. These data demonstrate a potent steroidogenic activity for AII as well as AI, [des-asp1]AI and [des-asp1]AII in bovine adrenal fasciculata cells. A common receptor site for all four peptides is suggested.

Goat immune response to capripox vaccine expressing the hemagglutinin protein of peste des petits ruminants.

Sheep-pox and capripox are contagious diseases of domestic small ruminants for which the causal agent is a poxvirus classified into the Capripoxvirus genus. Viruses of this group have a host range specific to sheep, goats, cattle, and possibly buffalo. Thus, they are clearly indicated as vectors for the development of recombinant vaccines for peste des petits ruminants (PPR). Here we report the immune response of goats inoculated with a recombinant capripox-PPR hemagglutinin.

[Syncytia formation in cultures and analysis of the protein composition of various strains of caprine arthritis encephalitis virus (CAEV)]. / Formation de syncytia en culture et analyse de la composition protéique de plusieurs souches de virus de l'arthrite et de l'encéphalite de la chèvre (CAEV).

The syncytia forming activity of 9 caprine arthritis encephalitis virus (CAEV) strains isolated from lesions or normal goat tissue was evaluated in vitro. No discrepancies were seen between the structural proteins of the 9 strains by gel electrophoresis. Goat synovial membrane cells were the most susceptible to the 9 CAEV strains. Goat monocytes in culture were susceptible to all the strains tested. At 39 degrees C, all the strains produced more syncitial lesions. In nasal turbinate cells, 2 strains did not form syncytia; one strain induced lysis of all the goat cells used.

Copper deficiency in ruminants in the Rift Valley of East Africa.

Enzootic ataxia of newborn domestic ruminants and particularly of small ruminants is a widespread disease often observed in East Africa. It is characterised by very low blood copper levels and sometimes by histological lesions characteristic of a severe copper deficiency. This disease observed and described by various authors in Kenya, Ethiopia and Djibouti seems to be closely associated with the pedogeological area of the Rift Valley. Climatic conditions and geo-morphological characteristics of this area, particularly the molybdenum and sulphur excess in this volcanic region, seem to account for the marked clinical signs of this mineral deficiency.