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Two prototypes of microstructured capillaries (MSCs) were designed, manufactured, and used to carry out different experiments. MSC-1 consisted of six holes of ≈28 μm id whereas MSC-2 consisted of 85 holes of ≈7.7 μm id. A fundamental study on the hydrodynamic injection through a commercial CE equipment was conducted. Experimental times to flush specific volumes were approximately three times larger than the theoretical values. Then, the detection of starch was carried out by using the MSCs and conventional capillaries, and the electropherograms were compared on the basis of analytical parameters employed in CE. An improvement in peak asymmetry was obtained for the MSC-1 compared to the conventional capillaries. S/N was one order of magnitude increased with the MSC, improving ten times the sensitivity. Considering this advantage, the separation and detection of nitrostarch was performed as a first application of the MSC-1. Minimal sample amounts of nitrostarch (1.7 μg) were detected. Results present a real interest in forensics since this substance had not been previously detected through CE, leading to new investigations in the design of new capillaries capable of enhancing CE performance., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This paper provides an up-to-date overview on the use of microstructured optical fibers (MOFs) in chemical sensing during the last ten years, more specifically, applications in liquid media including the use of solid-core photonic crystal fibers, hollow-core PCFs and other MOFs and related microstructures. To this aim, a classification of different types of fiber-based chemical sensors is first made, followed by a description of the most important MOFs and their operation principles in chemical sensing. Then, studies on the use of MOFs in fluorescence, Raman and SERS detection among other detection principles are discussed. Finally, literature including the implementation of these microstructures in homemade and commercial analytical equipment is summarized. This review intends not only to give a current perspective on the use of MOFs and microstructures in chemical sensing, but also to make an approach between the fields of optical fiber and analytical chemistry, in order to understand the basic principles of operation in this promising frontier of knowledge. [ABSTRACT FROM AUTHOR]

Nowadays there is an increasing demand for the cost-effective monitoring of potential threats to the integrity of high-voltage networks and electric power infrastructures. Optical fiber sensors are a particularly interesting solution for applications in these environments, due to their low cost and positive intrinsic features, including small size and weight, dielectric properties, and invulnerability to electromagnetic interference (EMI). However, due precisely to their intrinsic EMI-immune nature, the development of a distributed optical fiber sensing solution for the detection of partial discharges and external electrical fields is in principle very challenging. Here, we propose a method to exploit the third-order and second-order nonlinear effects in silica fibers, as a means to achieve highly sensitive distributed measurements of external electrical fields in real time. By monitoring the electric-field-induced variations in the refractive index using a highly sensitive Rayleigh-based CP-φOTDR scheme, we demonstrate the distributed detection of Kerr and Pockels electro-optic effects, and how those can assign a new sensing dimension to optical fibers, transducing external electric fields into visible minute disturbances in the guided light. The proposed sensing configuration, electro-optical time domain reflectometry, is validated both theoretically and experimentally, showing experimental second-order and third-order nonlinear coefficients, respectively, of χ(2) ~ 0.27 × 10−12 m/V and χ(3) ~ 2.5 × 10−22 m2/V2 for silica fibers. [ABSTRACT FROM AUTHOR]

We demonstrate a method to achieve an extremely wide and flexible external control of the group velocity of signals as they propagate along an optical fiber. This control is achieved by means of the gain and loss mechanisms of stimulated Brillouin scattering in the fiber itself. Our experiments show that group velocities below 71 000 km/s on one hand, well exceeding the speed of light in vacuum on the other hand and even negative group velocities can readily be obtained with a simple benchtop experimental setup. We believe that the fact that slow and fast light can be achieved in a standard single-mode fiber, in normal environmental conditions and using off-the-shelf instrumentation, is very promising for a future use in real applications. [ABSTRACT FROM AUTHOR]

Distributed optical fiber sensors (DOFS) have been postulated as a suitable technique for long-range monitoring of sinkhole-related subsidence, and possibly for the anticipation of catastrophic collapse (early-warning systems). The strain data published in previous works refer to artificial experiments considering real and virtual cover collapse sinkholes characterized by rapid subsidence and sharp lateral deformation gradients. The influence of the subsidence mechanism (sagging, collapse, suffosion) on the capability of DOFS to satisfactorily detect active subsidence is discussed. Sagging sinkholes with poorly-defined lateral edges, low lateral deformation gradients and slow subsidence are identified as the most challenging scenario. The performance of BOTDA optical fiber for monitoring such type of sagging sinkholes is evaluated in the active Alcalá sinkhole, which affects a flood-control dike creating a high-risk and -uncertainty scenario. This sinkhole shows active subsidence in sections tens of meters long with maximum subsidence rates ranging between 5 and 35 mm/yr. The comparison of vertical displacement data measured by high-precision leveling and the strain recorded by two types of fiber optic cables shows good spatial and temporal correlation. The subsidence sections are captured in the strain profiles by: (1) troughs of negative strain (contraction) in the area affected by subsidence, with the maximum strain associated with the point of most rapid settlement; and (2) lateral ridges of positive values (extension) in the marginal zones. A subsidence acceleration phase associated with a flood is also captured by substantial increments in the strain values. In this challenging scenario, despite the reasonably good spatial and temporal correlation between the displacement and strain data, the unambiguous identification of the active subsidence area with the fiber optic data alone might be difficult. Better results could be obtained improving the monitoring system (e.g., tighter cable-ground coupling) and testing other types of sinkholes with more localized deformation zones and higher subsidence rates. • Slow moving sagging sinkhole monitored by BOTDA optical fiber. • Spatial and temporal correlation with subsidence measured by high-precision leveling. • Impact of the subsidence mechanism of the performance of optical fiber sensors. • Potential applicability of optical fiber sensors to early warning. [ABSTRACT FROM AUTHOR]