Abstract
A torsion active sensor based on a figure-of-eight configuration is presented. The interferometric fiber loop mirror, composed by a section of photonic crystal fiber, also acts as a sensing element. When torsion is applied over a range of 180 degrees, a sensitivity of 7.13 pm/degree is achieved. Besides, this configuration can also be used to measure optical power variations and it presents low sensitivity to temperature.

Abstract
In this work, we present a method to predict the behaviour of a remote optical fiber sensor system based on a long period grating, Raman amplification and electrical interrogation were investigated. The interrogation unit is composed by two fiber Bragg gratings modulated by two piezoelectrics transductors. Optical fiber sensor systems are typically limited to operate at distances of only few kilometers due to the attenuation effects and noise that adversely affects the performance of the sensor interrogation process. We present experimental and simulation results obtained in the context of analysis of remote optical fiber sensors. The simulation models use numerical methods to compute the Raman interaction between the pumps and the sensor signals and allow speeding up the analyses regarding the setup to be experimentally implemented to measure environmental temperature. The results obtained show that under Raman amplification the power ratio between the two central wavelengths of the FBGs has a linear relation with the change of the LPG resonance induced by temperature variation.

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
A figure-of-eight based fibre laser cavity is proposed for the measurement of torsion. In one of the loops a section of photonic crystal fibre is inserted, acting both as an optical filter and the sensing head. The laser emission depends on the optical filter polarization and length. A single lasing band is achieved with a full width at half maximum of similar to 1.72 nm. The proposed sensor presents sensitivity to torsion of 7.13 pm/degree over a range of 180 degrees. This configuration can also be used to measure optical power variations. Besides, due to the properties of the optical filter this sensor presents low sensitivity to temperature.

Abstract
Many optical systems based on Surface Plasmon Resonance (SPR) have been developed for work as refractometers, chemical sensors or even for measure the thickness of metal and dielectric thin films. These kinds of systems are usually large, expensive and cannot be used for remote sensing. Optical fiber sensors based on SPR has been widely studied for the last 20 years with several configurations mostly using multimode optical fibers with large cores and plastic claddings. Sensors based on SPR present very high sensitivity to refractive index variations when compared to the traditional refractive index sensors. Here we propose a SPR sensor based in a single mode fiber. The fiber end is chemically etched by emersion in a 48% hydrofluoric acid solution, resulting a single mode fiber with the cladding removed in a small section. A resonance dip around 1580 nm was attained in good agreement with the simulation scenario that takes into account the real characteristics of the fiber.

Abstract
A sensing configuration based on an intensity optical fibre sensor for temperature measurement is reported. Two sensing heads, with identical geometrical configuration, connected in series are implemented. Each sensing head is placed between two fibre Bragg gratings (FBGs), being able to provide a self-referenced measurement, and thus eliminate errors that may arise from undesired intensity fluctuations in the configuration. The first FBG, placed before the aluminium tube, acts as the reference FBG, while the second FBG, placed after the aluminium tube, acts as the signal FBG. It is observed that the amplitude of the signal FBG decays when temperature increases, due to the increase of the ferrules' gap and as result of the material thermal expansion. The temperature response has a behaviour that corresponds to a polynomial fit of third order. The crosstalk between the two sensing heads in series is analysed. The temperature sensitivities obtained in the intervals regions of [36, 48.5] degrees C and [64, 85] degrees C are 2.67 x 10(-3) degrees C-1 and 1.74 x 10(-4) degrees C-1, respectively. Ten sensing heads with this configuration can be multiplexed in series network topology.