Abstract
This work presents a fiber-optic Cavity Ring-Down (CRD) configuration using an added-signal for curvature sensing. An Optical Time-Domain Reflectometer (OTDR) was used to send impulses down into the fiber loop cavity, inside of which a long period grating (LPG) was placed to act as sensing device. The added-signal was obtained by the sum of several conventional CRD impulses, thus providing an improvement on the curvature sensitivity when compared to the conventional CRD signal processing. Sensitivity to applied curvature of 15.3 mu s/m(-1) was obtained. This result was found to be 20-fold the one obtained for the conventional CRD signal processing.

Abstract
Cross-bite, as a malocclusion effect, is defined as a transversal changing of the upper dental arch, in relation to the lower arch, and may be classified as skeletal, dental or functional. As a consequence, the expansion of maxilla is an effective clinical treatment used to correct transversal maxillary discrepancy. The maxillary expansion is an ancient method used in orthodontics, for the correction of the maxillary athresia with posterior crossbite, through the opening of the midpalatal suture (disjunction), using orthodontic-orthopaedic devices. Same controversial discussion arises among the clinicians, about the effects of each orthodontic devices as also about the technique to be employed. The objective of this study was to compare the strain field induced by two different orthodontic devices, named disjunctor with and without a connecting bar, in an acrylic model jaw, using fiber Bragg grating sensors to measure the strain patterns. The orthodontic device disjunctor with the bar, in general, transmits higher forces and strain to teeth and maxillae, than with the disjunctor without bar. It was verified that the strain patterns were not symmetric between the left and the right sides as also between the posterior and anterior regions of the maxillae. For the two devices is also found that in addition a displacement in the horizontal plane, particularly in posterior teeth, also occurs a rotation corresponding to a vestibularization of the posterior teeth and their alveolar processes.

Abstract
Fiber probe structures composed of two physical microcavities were created using focused ion beam technology. These structures have a tip-like shape as they were milled in preciously etched tapered fiber tips. The microprobes are then characterized for temperature and refractive index sensing using a signal filtering technique to discriminate signals from distinct microcavities. Using fast Fourier transforms combined with band-pass filters, it is possible to reconstruct the spectra of each cavity independently and thus measure their individual spectral shifts.

Abstract
This letter presents a fiber-optic cavity ring down (CRD) configuration using an added-signal for curvature sensing. An optical time-domain reflectometer was used to send impulses down into the fiber loop cavity, inside of which a long period grating was placed to act as a sensing device. The added-signal was obtained by the sum of several conventional CRD impulses, thus providing an improvement on the curvature sensitivity when compared with the conventional CRD signal processing. A linear response to applied curvature in the range of 2.2-3.6 m(-1) was observed, and a sensitivity of 15.3 mu s/m(-1) was obtained. This result was found to be 20-fold the one obtained for the conventional CRD signal processing. The added-signal increases the optical power but increases as well the ring-down time due to the sum of the several loops that light travels inside the ring. A ring-down time response of 43.3 mu s was attained (versus 23.7 mu s for the conventional CRD signal processing).

Abstract
This work presents a demonstration of the potential of fiber cavity ring-down for remote sensing, by using an OTDR to send impulses down similar to 20 km of optical fiber at the end of which the fiber ring cavity was placed. The OTDR showed almost no losses in the fiber, so other ring-down cavities could be spliced along the same fiber. To study the sensitivity of the cavity ring an intensity sensor based on a taper was placed in the ring and glued to a translation stage. A displacement of the stage imposes a curvature on the taper and an associated loss. The configuration had a sensitivity of (11.8 +/- 0.5) mu s/mm.

Abstract
This work presents a fiber CRD configuration for the measurement of strain. An Optical Time-Domain Reflectometer was used to send impulses down into the fiber loop cavity, inside of which a chirped fiber Bragg grating was placed to act as a strain sensing element. This technique could provide strain results with both conventional CRD-based configuration and the OTDR.