High reflectivity Bragg gratings fabricated by 248nm excimer laser holographic ablation in thin Ta₂O₅ films overlaid on glass waveguides

Relief Bragg grating reflectors inscribed on channel waveguides may be used in optical communications as add-drop wavelength multiplexers, gain-flattening filters, distributed feedback laser mirrors, or in sensing technology as high sensitivity devices for precise monitoring of chemical or biomedical processes. We present strong Bragg grating reflectors in Ta2O5 thin oxide films overlaid on potassium ion exchanged channel waveguides in BK-7 glass, inscribed using 248nm excimer laser holographic ablation. The grating pattern was created employing two-beam interference using a modified Mach-Zehnder interferometric cavity and the output of a narrow-lined injection cavity 248nm excimer laser. The experimental data presented are divided into two sections: the first section refers to the study of the grating ablation process of thin Ta2O5 films with respect to the exposure conditions; and the second focuses in the implementation of those relief grating in functional waveguide devices

Near-infrared Fourier transform room-temperature photoluminescence of erbium complexes

A modified Fourier transform (FT) Raman bench spectrometer designed for the detection of weak light emission in the 800–1700 nm wavelength region has been used to demonstrate the advantages of FT spectroscopy for measuring near-infrared photoluminescence spectra of lanthanide complexes with a good resolution and very good sensitivity. This apparatus has been tested with an ultraviolet laser source (325 nm) on three standard erbium complexes. The 4I13/24I15/2 emission of tris-(acetylacetonato) (1,10 phenanthroline) erbium [Er(acac)3(phen)], tris-(4,4,4,-trifluoro-1-(2 thenoyl)-1,3-butenedione) (1,10 phenanthroline) erbium [Er(TTFA)3(phen)] and tris(8-hydroxyquinolinato) erbium [Erq3] has thus been recorded in solution and in the solid state and compared with literature. ©2003 American Institute of Physics

A Hybrid Beam Steering Free-Space and Fiber Based Optical Data Center Network

Wireless data center networks (DCNs) are promising solutions to mitigate the cabling complexity in traditional wired DCNs and potentially reduce the end-to-end latency with faster propagation speed in free space. Yet, physical architectures in wireless DCNs must be carefully designed regarding wireless link blockage, obstacle bypassing, path loss, interference and spatial efficiency in a dense deployment. This paper presents the physical layer design of a hybrid FSO/in-fiber DCN while guaranteeing an all-optical, single hop, non-oversubscribed and full-bisection bandwidth network. We propose two layouts and analyze their scalability: (1) A static network utilizing only tunable sources which can scale up to 43 racks, 15,609 nodes and 15,609 channels; and (2) a re-configurable network with both tunable sources and piezoelectric actuator (PZT) based beam-steering which can scale up to 8 racks, 2,904 nodes and 185,856 channels at millisecond PZT switching time. Based on a traffic generation framework and a dynamic wavelength-timeslot scheduling algorithm, the system-level network performance is simulated for a 363-node subnet, reaching >99% throughput and 1.23 μ s average scheduler latency at 90% load

Space-Division Multiplexing in Data Center Networks: On Multi-Core Fiber Solutions and Crosstalk-Suppressed Resource Allocation

The rapid growth of traffic inside data centers caused by the increasing adoption of cloud services necessitates a scalable and cost-efficient networking infrastructure. Space-division multiplexing (SDM) is considered as a promising solution to overcome the optical network capacity crunch and support cost-effective network capacity scaling. Multi-core fiber (MCF) is regarded as the most feasible and efficient way to realize SDM networks, and its deployment inside data centers seems very likely as the issue of inter-core crosstalk (XT) is not severe over short link spans (<1  km ) compared to that in long-haul transmission. However, XT can still have a considerable effect in MCF over short distances, which can limit the transmission reach and in turn the data center’s size. XT can be further reduced by bi-directional transmission of optical signals in adjacent MCF cores. This paper evaluates the benefits of MCF-based SDM solutions in terms of maximizing the capacity and spatial efficiency of data center networks. To this end, we present an analytical model for XT in bi-directional normal step-index and trench-assisted MCFs and propose corresponding XT-aware core prioritization schemes. We further develop XT-aware spectrum resource allocation strategies aimed at relieving the complexity of online XT computation. These strategies divide the available spectrum into disjoint bands and incrementally add them to the pool of accessible resources based on the network conditions. Several combinations of core mapping and spectrum resource allocation algorithms are investigated for eight types of homogeneous MCFs comprising 7–61 cores, three different multiplexing schemes, and three data center network topologies with two traffic scenarios. Extensive simulation results show that combining bi-directional transmission in dense core fibers with tailored resource allocation schemes significantly increases the network capacity. Moreover, a multiplexing scheme that combines SDM and WDM can achieve up to 33 times higher link spatial efficiency and up to 300 times greater capacity compared to a WDM solution

Breakfast glycaemic index and exercise: combined effects on adolescents' cognition

The aim of the present study was to examine the combined effects of breakfast glycaemic index (GI) and a mid-morning bout of exercise on adolescents’ cognitive function. Participants were randomly allocated to a high or low GI breakfast group in a mixed research design, where each participant completed two experimental trials (exercise and resting). Forty-two adolescents (12.4±0.5 years old), undertook a bout of exercise (ten repeats of level one of the multi-stage fitness test; exercise trial) or continued to rest (resting trial) following consumption of either a high or low GI breakfast. A battery of cognitive function tests (visual search test, Stroop test and Sternberg paradigm) was completed 30 min before and 45 min following the exercise. Average heart rate during exercise was 170±15 beats.min-1. On the complex level of the Stroop test, response times improved across the morning following the low GI breakfast on both the exercise and resting trials, though the improvement was greatest on the exercise trial. However, response times only improved on the resting trial following the high GI breakfast (p = 0.012). On the 5 letter level of the Sternberg paradigm, response times improved across the morning following the low GI breakfast (regardless of exercise) and only on the exercise trial following the high GI breakfast (p = 0.019). The findings of the present study suggest that the combined effects of breakfast GI and exercise in adolescents depend upon the component of cognitive function examined. A low GI breakfast and mid-morning bout of exercise were individually beneficial for response times on the Sternberg paradigm, whereas they conferred additional benefits for response times on the Stroop test

Dispersion measurements of chirped fibre gratings

A wavelength scanning interferometric technique has been used to provide phase dispersion and time delay measurements of photorefractive fibre gratings with sub-picosecond time-delay and 3µm wavelength resolutions for the first time. Chirped fibre grating filters for dispersion compensation in long fibre telecommunications links have been fully characterised

Time delay characterization of a tunable chirped fibre grating for dispersion compensation

The development of chirped fibre grating filters for dispersion compensation in long fibre telecommunications links requires full and accurate amplitude and time delay characterisation of these devices. We have recently demonstrated a wavelength scanning interferometric technique with sub-picosecond time-delay and 3µm wavelength resolutions to provide such measurements. The system is based on an all-fibre Michelson interferometer. The reference arm of the interferometer is phase-modulated to generate an electric signal at the photodetector which carries the optical phase and amplitude information of the reflective fibre device under test, which is included in the signal arm. The amplitude response of the interferometer is directly proportional to the field reflection coefficient whilst the time delay is given by the derivative of the relative phase with respect to wavelength. A high wavelength resolution tunable laser source (HP8168A/C) is used in conjunction with a fully automated set-up to provide sub-picosecond resolution

Microtubule-associated STOP protein deletion triggers restricted changes in dopaminergic neurotransmission.: Accumbic DA system in STOP KO mice

International audienceThe microtubule-associated stable tubule only polypeptide (STOP) protein plays a key-role in neuron architecture and synaptic plasticity. Recent studies suggest that schizophrenia is associated with alterations in the synaptic connectivity. Mice invalidated for the STOP gene display phenotype reminiscent of some schizophrenic-like symptoms, such as behavioral disturbances, dopamine (DA) hyper-reactivity, and possible hypoglutamatergia, partly improved by antipsychotic treatment. In the present work, we examined potential alterations in some DAergic key proteins and behaviors in STOP knockout mice. Whereas the densities of the DA transporter, the vesicular monoamine transporter and the D(1) receptor were not modified, the densities of the D(2) and D(3) receptors were decreased in some DAergic regions in mutant versus wild-type mice. Endogenous DA levels were selectively decreased in DAergic terminals areas, although the in vivo DA synthesis was diminished both in cell bodies and terminal areas. The DA uptake was decreased in accumbic synaptosomes, but not significantly altered in striatal synaptosomes. Finally, STOP knockout mice were hypersensitive to acute and subchronic locomotor effects of cocaine, although the drug equally inhibited DA uptake in mutant and wild-type mice. Altogether, these data showed that deletion of the ubiquitous STOP protein elicited restricted alterations in DAergic neurotransmission, preferentially in the meso-limbic pathway

Tunable dispersion compensating grating in a 10Gbit/s 100-220km step index fibre link

Chirped fibre gratings are of particular interest for compensating the dispersion (~17ps/nm.km @ 1.55µm) of installed step index (SI) fibre links since they are compact, low-loss, polarisation-insensitive and offer high negative-dispersion. In this paper we present a detailed investigation of the bandwidth-dispersion trade-off for a fixed (40mm) length tunable linearly-chirped fibre grating. In addition we demonstrate that such a grating can precisely compensate the dispersion in a 10Gbit/s transmission experiment for SI fibre lengths in the range 103-216km