Abstract
A reflective multimode interference based-fiber optic sensor is described, aimed at measuring refractive index variations by means of intensity variation based on the fiber tip-interaction concept. The sensing head is a section of a multimode fiber, spliced to a single-mode fiber at the input end; its characteristics are studied when two multimode fibers, with distinct core diameters (viz. 50 and 105 mu m), are considered. The multimode fiber end face is placed in contact with the liquid sample, so as to provide a refractive index measurement via variation in amplitude of the interference spectral peaks - which is essentially insensitive to temperature changes. Therefore, the proposed configuration permits measurement of refractive index variations free from system temperature cross-sensitivity effects. Resolutions of 2.2 x 10(-4) RIU and 3.8 x 10(-4) RIU, for multimode fiber tips with core diameters of 50 mu m and 105 mu m, respectively, could be achieved.

Abstract
In this work, two all-fiber interferometric configurations based on suspended core fibers (SCF) are investigated. A Fabry-Perot cavity (FPC) made of SCF spliced in-between segments of single-mode and hollow-core fiber is proposed. The interferometric signals are generated by the refractive-index mismatches between the two fibers in the splice region and at the end of the suspended-core fiber. An alternative sensing head configuration formed by the insertion of a length of SCF as a birefringence element in a Sagnac loop interferometer is also demonstrated. In this structure, the interferometric signals are generated by interfering two counter propagating beams with different polarization states which propagate through a length of SCF as a birefringence element. The sensitivity to pressure and temperature was determined for both configurations. The results show that the pressure sensitivities are -4.68 x 10(-5) nm/psi and 0.032 nm/psi for FPC and Sagnac loop interferometers, respectively. The temperature sensitivity of both structures has been obtained and the results have been discussed.

Abstract
Fiber optic sensors have a set of properties that make them very attractive in biomechanics. However, they remain unknown to many who work in the field. Some possible causes are scarce information, few research groups using them in a routine basis, and even fewer companies offering turnkey and affordable solutions. Nevertheless, as optical fibers revolutionize the way of carrying data in telecommunications, a similar trend is detectable in the world of sensing. The present review aims to describe the most relevant contributions of fiber sensing in biomechanics since their introduction, from 1960s to the present, focusing on intensity-based configurations. An effort has been made to identify key researchers, research and development (R&D) groups and main applications. © The Author(s) 2012.

Abstract
A simple nanostrain direct current (DC) measurement system based on a chirped Bragg grating Fabry-Perot (FP) structure is presented. The FP cavity, formed between the chirped fiber Bragg grating (CFBG) and the fiber end face, presents an aperiodic behavior due to the CFBG. A laser located in the fringe pattern slope is used to interrogate the sensing head. The optical power parameter is analyzed when strain is applied, for long and short period fringe pattern wavelengths, and sensitivities of -2.87 µW/µe and -5.48'µW/µe are respectively obtained. This configuration presents a resolution of 70 ne. © The Author(s) 2011.

Abstract
An optical fiber sensor based on a tapered-FBG coated with 150 nm-thick Pd film is proposed for hydrogen pressure detection. The FBG was written in a 50 µm-diameter tapered fiber by DUV femtosecond laser technology. A second FBG was inscribed in the untapered fiber region for temperature compensation. The sensing head was able to detect the variation of hydrogen pressure in the range 0-780 kPa and a maximum sensitivity of 0.15 pm/kPa was achieved. © 2012 OSA.

Abstract
An intensity curvature sensor using a Photonic Crystal Fiber (PCF) with three coupled cores is proposed. The three cores were aligned and there was an air hole between each two consecutive cores. The fiber had a low air filling fraction, which means that the cores remain coupled in the wavelength region studied. Due to this coupling interference is obtained in the fiber output even if just a single core is illuminated. A configuration using transmission interrogation, which used a section fiber with 0.08 m of PCF as the sensing head, and a configuration using reflection interrogation, which used a section fiber with 0.13 m of PCF as the sensing head, were characterized and compared for curvature sensing. When the fiber is bended along the plane of the cores, one of the lateral cores will be stretched and the other compressed. This changes the coupling between the three cores, changing the optical power intensity. The sensibility of the sensing head was strongly dependent on the direction of bending, having its maximum when the bending direction was along the plane of the cores. A maximum curvature sensitivity of 1.8 dB. m was demonstrated between 0 m and 2.8 m.