Abstract
Using surface resonance (SPR) as a sensitivity enhancer, this work describes the development of a transmissive multimode optical fiber sensor with a gold (Au) thin film that measures glucose concentration. The fiber's cladding was initially removed, and an Au layer was then sputtered onto its surface to simultaneously excite SPR and reflect light, making the SPR sensor extremely sensitive to changes in the environment's refractive index. A range of glucose concentrations, from 0.0001 to 0.5000 g/ml, were tested on the sensor. A maximum sensitivity of 161.302 nm/(g/mL) was attained for the lowest glucose concentration, while the highest concentration yielded a sensitivity of 312.000 nm/(g/mL). The proposed sensor's compact size, high sensitivity, good stability and practicality make it a promising candidate for a range of applications, including detecting diabetes.

Abstract
A paracetamol concentration-sensing scheme based on a linear cavity fiber laser configuration is demonstrated experimentally. The laser cavity has a fiber sensor at one end, that allows refractive index measurements. The refractometer consists of a cleaved fiber tip combined with an FBG functioning as a reflecting mirror. The combination of a fiber loop mirror at the other end allows to reflect all the light from the FBG and refractometer, forming a linear cavity. By measuring the intensity variation of the Fresnel reflection at the fiber-to-liquid interface, the measured concentration is linear and have a concentration sensitivity of [( - 8.74 & PLUSMN; 0.34) x 10-5 ] & mu;W/(g/kg), over a range of 52.61 to 219.25 g/kg, and with a resolution of 2.77 g/kg. The results obtained present high stability and prove the potential of the fiber laser system to performed realtime measurements of concentration, in a non-invasive way.

Abstract
A spatial optical filter based on splice misalignment between optical fibers with different diameters is proposed for gas refractometry. The sensing head is formed by a 2 mm long optical fiber with 50 mu m diameter that is spliced with a strong misalignment between two single-mode fibers (SMF28) and interrogated in transmission. The misalignment causes a Fabry-Perot behavior along the reduced-size fiber and depending on the lead-out SMF28 position, it is possible to obtain different spectral responses, namely, bandpass or band-rejection filters. It is shown that the spatial filter device is highly sensitive to refractive index changes on a nitrogen environment by means of the gas pressure variation. A maximum sensitivity of -1390 nm/RIU for the bandpass filter was achieved. Both devices have shown similar temperature responses with an average sensitivity of 25.7 pm/degrees C. (C) 2012 Optical Society of America

Abstract
Suspended core fiber tapers with different cross sections (from 70 mu m to 120 mu m diameter) were produced by filament heating. Before obtaining the taper, the spectral behavior of the suspended core fiber presents multimode interference. When the taper is made an intermodal interference is observed. This effect is clearly visible for high taper reduction. The spectral response of the microtaper inside the suspended core fiber is similar to a beat of two interferometers. The microtaper was subjected to strain, and an increase of sensitivity with the reduction of the transverse area was observed. When the taper was immersed in liquids with different refractive indices or subjected to temperature variations, no spectral change occurred.

Abstract
A spatial optical filter based on splice misalignment between optical fibers with different cladding dimensions is proposed for gas refractometry. The sensing head is formed by a 2 mm-long optical fiber with 50 mu m diameter spliced with a strong misalignment between two single mode fibers (SMF28) and interrogated in transmission. This fiber structure causes a Fabry-Perot-behavior along the reduced-size fiber giving at its output end a well defined spatial filtering selectivity. Depending on the misalignment position of the lead-out SMF28, it is possible to obtain two different spectral responses, namely, bandpass or band-rejection filters. It is shown that this filter device is highly sensitive to refractive index changes on a nitrogen (N-2) environment by means of the gas pressure variation. A maximum sensitivity of -1390 nm/RIU for the bandpass filter was achieved.

Abstract
Tapering single mode-multimode-single mode structures to enhance sensitivity is proposed and experimentally demonstrated. 50 mm-long coreless MMF sections are spliced between SMFs and tapered. They are characterized in strain and an increase in strain sensitivity is obtained with taper diameter reduction. Sensitivities as high as -23.69 pm/mu epsilon for the 15 mu m taper are attained. A combination of an untapered and tapered SMS is proposed as a sensing system for the simultaneous measurement of strain and temperature.