Resonant optical strain sensors, obtained by closing in loop coupled pi-shifted Bragg gratings (pi-FBGs), are reported. Despite of a conventional pi-FBG, showing a transmission Lorentzian resonance ...in the reflection band, the coupled pi-shifted Bragg grating structure is characterised by a spectral response formed by a split doublet of the primary transmission Lorentzian mode of pi-FBG. By closing in loop this structure, the coupled pi-shifted Bragg grating ring resonators show better performance than pi-shifted Bragg grating ring resonators in terms of strain sensitivity (i.e. 2.86 pm/ mu epsilon ) is demonstrated. Thus, the coupled pi-FBGRR is suitable for enhanced sensitivity strain sensing applications.
Resonant optical strain sensors, obtained by closing in loop coupled π-shifted Bragg gratings (π-FBGs), are reported. Despite of a conventional π-FBG, showing a transmission Lorentzian resonance in ...the reflection band, the coupled π-shifted Bragg grating structure is characterised by a spectral response formed by a split doublet of the primary transmission Lorentzian mode of π-FBG. By closing in loop this structure, the coupled π-shifted Bragg grating ring resonators show better performance than π-shifted Bragg grating ring resonators in terms of strain sensitivity (i.e. 2.86 pm/με) is demonstrated. Thus, the coupled π-FBGRR is suitable for enhanced sensitivity strain sensing applications.
Studies have reported evidence that consumption of carotenoids provides many health benefits. Therefore, assuring the maintenance of their nutritional/nutraceutical properties after food processing ...is gaining increasing interest. Products such as breakfast cereals and ready-to-eat snacks are commonly consumed foods that potentially could serve as ideal vehicles of bioactive compounds, such as carotenoids. Some of these foods are produced by extrusion. The impact of the extrusion process on bioactive compounds is harsh and may require control of the processing conditions to alleviate the negative effects of the process on the product’s nutritional quality. Extrusion process parameters, such as temperature, screw speed, shear rate, and the feed moisture content, can affect the retention of carotenoids in the final product. The influence of those parameters on products is discussed in this review, taking into account aspects of carotenoid stability and the conservation of its nutritional properties. Further, some strategies to increase carotenoid retention during extrusion processes are discussed.
We report the theoretical description and the experimental demonstration of an optical resonator formed by inserting a Fiber Bragg Grating (FBG) in a closed fiber loop. The spectral characteristics ...of such a resonator strongly depend on the reflectivity of the FBG. In the wavelength region where the FBG reflectivity R is negligible, the system behaves like a conventional ring resonator. On the other hand, when R is not vanishing, a split-mode structure can be observed, associated to the degeneracy removal of two counterpropagating resonant modes. The magnitude of the mode splitting can be used to sense small variations of the FBG physical parameters, such as length, temperature or group index. An example of strain sensing with this setup is reported, showing that the mode splitting is sensitive to a mechanical strain applied to the FBG, while it is almost insensitive to a strain applied to any other point of the resonator. This peculiar feature allows to perform cavity-enhanced, local strain measurements with a reduced sensitivity to environmental perturbations, which represents an important improvement in the framework of the fiber-optic sensors.
In this paper, we report, for the first time, on the effects of two counterpropagating laser beams in a passive ring resonator to be used as a key element of an integrated optical angular velocity ...sensor, in order to optimize the design of the whole sensor. The ring resonator is modeled and the analytical expressions of the power transfer function for both drop- and through-port configurations are derived. At both drop and through ports, the two counterpropagating beams provide an increase of the amplitude of the transfer function, while at the through port, we observed also a mode suppression due to a physical effect similar to the Vernier effect. A parametric analysis has been carried out to optimize the sensor design. A minimum angular velocity as low as a few degrees per hour has been achieved, which is suitable for aerospace applications.
The capability of optical resonators to extend the effective radiation-matter interaction length originates from a multipass effect, hence is intrinsically limited by the resonator's quality factor. ...Here, we show that this constraint can be overcome by combining the concepts of resonant interaction and coherent perfect absorption (CPA). We demonstrate and investigate super-resonant coherent absorption in a coupled Fabry-Perot (FP)/ring cavity structure. At the FP resonant wavelengths, the described phenomenon gives rise to split modes with a nearly-transparent peak and a peak whose transmission is exceptionally sensitive to the intracavity loss. For small losses, the effective interaction pathlength of these modes is proportional respectively to the ratio and the product of the individual finesse coefficients of the two resonators. The results presented extend the conventional definition of resonant absorption and point to a way of circumventing the technological limitations of ultrahigh-quality resonators in spectroscopy and optical sensing schemes.
A glutamic acid to lysine (E40K) residue substitution in superoxide dismutase 1 (SOD1) is associated with canine degenerative myelopathy: the only naturally occurring large animal model of ...amyotrophic lateral sclerosis (ALS). The E40 residue is highly conserved across mammals, except the horse, which naturally carries the (dog mutant) K40 residue. Here we hypothesized that in vitro expression of mutant dog SOD1 would recapitulate features of human ALS (ie, SOD1 protein aggregation, reduced cell viability, perturbations in mitochondrial morphology and membrane potential, reduced ATP production, and increased superoxide ion levels); further, we hypothesized that an equivalent equine SOD1 variant would share similar perturbations in vitro, thereby explain horses’ susceptibility to certain neurodegenerative diseases. As in human ALS, expression of mutant dog SOD1 was associated with statistically significant increased aggregate formation, raised superoxide levels (ROS), and altered mitochondrial morphology (increased branching (form factor)), when compared to wild‐type dog SOD1‐expressing cells. Similar deficits were not detected in cells expressing the equivalent horse SOD1 variant. Our data helps explain the ALS‐associated cellular phenotype of dogs expressing the mutant SOD1 protein and reveals that species‐specific sequence conservation does not necessarily predict pathogenicity. The work improves understanding of the etiopathogenesis of canine degenerative myelopathy.
Speed manipulation of optical pulses is a very attractive research challenge enabling next-generation high-capacity all-optical communication networks. Pulses can be effectively slowed by using ...different integrated optical structures such as coupled-resonator waveguiding structures or photonic crystal cavities. Fast light generation by means of integrated photonic devices is currently a quite unexplored research field in spite of its crucial importance for all-optical pulse processing. In this paper, we report on the first theoretical demonstration of fast light generation in an ultra-compact double vertical stacked ring resonator coupled to a bus waveguide. Periodic coupling between the two rings leads to splitting and recombining of symmetric and anti-symmetric resonant modes. Re-established degenerate modes can form when a symmetric and an anti-symmetric mode having different resonance order exhibit the same resonance wavelength. Under degenerate mode conditions, wide wavelength ranges where the group velocity is negative or larger than the speed of light in vacuum are generated. The paper proves how this physical effect can be exploited to design fast light resonant devices. Moreover, conditions are also derived to obtain slow light operation regime.
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