Abstract
Optical fiber optrodes are attractive sensing devices due to their ability to perform point measurement in remote locations. Mostly, they are oriented to biochemical sensing, quite often supported by fluorescent and spectroscopic techniques, but with the refractometric approach considered as well when the objective is of high measurement performance, particularly when the focus is on enhancing the measurand resolution. In this work, we address this subject, proposing and analyzing the characteristics of a fiber optic optrode relying on plasmonic interaction. A linearly tapered optical fiber tip is covered by a double overlay: the inner one - a silver thin film and over it a dielectric layer, with this combination allowing to achieve, at a specific wavelength range, surface plasmonic resonance (SPR) interaction sensitive to the refractive index of the surrounding medium. Typically, the interrogation of the SPR sensing structures is performed, considering spectroscopic techniques, but in principle, a far better performance can be obtained, considering the reading of the phase of the light at a specific wavelength located within the spectral plasmonic resonance. This is the approach which is studied here in the context of the proposed optical fiber optrode configuration. The analysis performed shows the combination of a silver inner layer with a dielectric titanium oxide layer with tuned thicknesses enables sensitive phase reading and allows the operation of the fiber optic optrode sensor in the third telecommunication wavelength window.

Abstract
An effective analytical model combining geometrical optics with the transfer-matrix theory for stratified optical media is applied to investigate the sensing properties of tapered optical fiber surface plasmon resonance (SPR) sensors incorporating Ag-Au bimetallic layers, particularly in the context of phase interrogation. The performance of the sensing structures is studied as a function of the tapering parameters and thickness of the metallic layers. It is shown that the Ag-Au bimetallic combination is capable of improving the resolution and tuning working region of SPR fiber-optic sensors and that by tapering the sensing structures enhanced sensitivity can be achieved when phase interrogation is considered.

Abstract
Optical fiber sensors based on the phenomenon of plasmonic resonance can be interrogated applying different methods, the most common one being the spectral approach where the measurand information is derived from the reading of the wavelength resonance dip. In principle, a far better performance can be achieved considering the reading of the phase of the light at a specific wavelength located within the spectral plasmonic resonance. This approach is investigated in this work for surface plasmon based fiber optic sensors with overlays which are combinations of bimetallic layers, permitting not only to tune the wavelength of the plasmon resonance but also the sensitivity associated with the phase interrogation of the sensors. The metals considered for the present analysis are silver, gold, copper, and aluminum.

Abstract
An analytical model based on geometrical optics and multilayer transfer matrix method is applied to the surface plasmonic resonance supported by fibre taper structures in the context of optical sensing applications. Phase interrogation is considered in particular as a methodology to attain enhanced sensitivities, and the performance of the sensing heads as function of the metal clad and taper parameters is analyzed. General topics concerning the actual relevance of plasmonics are also presented, first in a global perspective and then when applied to sensing.

Abstract
In this paper, two techniques for interrogation and multiplexing of fiber loop mirror (FLM) intensity sensors based on optical time domain reflectometer (OTDR) are proposed. These configurations enable series and parallel FLM sensor interrogation. A fiber taper characterized as a displacement sensor was used as the intensity sensor. The OTDR parameters were optimized in order to obtain the best results. The optimized parameters were 100-ns pulse width and 10-dB input signal attenuation which permitted to attain similar to 18 dB dynamic range in the operating wavelength of 1550 nm. The results show a linear behavior for both configurations with similar slope, -15.3 dB/mm, in the normalized displacement range of 0.2 to 0.7 mm. It was also achieved a displacement resolution of 0.027 and 0.093 mm, for the series and parallel configurations, respectively. Sensors multiplexing are demonstrated for both configurations and the systems do not present crosstalk. Based on the experimental results, the best configuration is the parallel one. The proposed approach is a viable alternative for multiplexing and interrogation of remote fiber sensors.

Abstract
An optical fiber sensor based on arrays of silica microspheres is proposed. The microspheres are produced separately using a fusion splicer and then also connected in series by fusion splicing. Three different sensors are presented, differing by the number of microspheres. Due to the geometry of the structures, different behaviors are obtained in strain measurements. Sensors with an odd number of microspheres are more sensitive to strain than the ones with an even number of microspheres. Additionally, the sensing heads are subjected to temperature where a sensitivity of 20.3 pm/degrees C is obtained in a range of 200 degrees C. (C) 2014 Optical Society of America