Abstract
A fiber optic sensor for simultaneous measurement of refractive index and temperature is presented. The sensing probe is achieved by introducing multimode interference inside a high birefringence fiber loop mirror resulting in a configuration capable of refractive index and temperature discrimination. The multimode interference peak is sensitive to the surrounding refractive index (90 nm/RIU) and slightly responsive to the temperature (0.005 nm/degrees C). On the other hand, the birrefringent fiber loop mirror is highly sensitive to temperature (2.39 nm/degrees C) and has no response to refractive index. Therefore, a temperature independent refractive index measurement can be made with a resolution of +/- 2.5x10(-5).

Abstract
In this work a novel optical-fiber sensor for carbon dioxide measurement is presented. A polymeric sensitive layer based on the acid-base equilibrium of phenol and of its derivative 4-nitro-phenol is used for carbon dioxide determination. The sensitive material presents changes in color and in its refractive index. Colorimetric and refractometric measurements were performed. The results show the sensor is more sensitive for lower concentrations and a saturation effect occurs for higher levels. For the colorimetric response, a resolution of +/- 0.15% was estimated and a response time of 30s was measured. For the refractometric measurements, a resolution of +/- 0.50% could be estimated and a response time of 12s was measured. Reversibility and reproducibility were also demonstrated.

Abstract

Abstract

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.