Abstract
In this Letter, we present a fiber loop mirror configuration based on a suspended twin-core fiber for sensing applications. Using the suspended twin-core fiber, the fringe pattern is due to the differential optical patch of the light in the two cores associated with a refractive index difference of similar to 10(-3), which indicates an advantage of this approach compared with those based on high-birefringent fibers, namely, the possibility of using a small length of fiber. The sensing configuration was characterized for torsion, temperature, and strain. Using the fast Fourier transform technique, it is possible to obtain measurand-induced amplitude variations of the fringe pattern. The results obtained indicate the viability of a temperature- and strain-independent torsion sensor. (C) 2010 Optical Society of America

Abstract
Fibre optic Bragg gratings (FBGs) written in normal and reduced diameter high birefringence (HiBi) fibres are studied. Chemical etching is used to reduce the diameter of fibres while the optical properties of the FBG spectrum are measured. The results obtained agree qualitatively with the stress enhanced chemical etching. The birefringence of the fibre is determined as a function of the diameter. Optical characterization of the FBG under transverse strain and temperature is also performed. The results obtained show the feasibility of the simultaneous measurement of those parameters with a HiBi FBG sensor.

Abstract
In this letter, a temperature sensor using a fiber loop mirror containing a piece of highly birefringent erbium doped fiber is presented. A Hi-Bi PANDA erbium-doped silica fiber was used and compared with the conventional Hi-Bi PANDA fiber. Different results for strain and temperature sensitivity were obtained. The temperature coefficient sensitivity was -2.22 nm/degrees C and significantly higher when compared with others conventional Hi-Bi fibers. Strain experiments were also performed. (C) 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3152-3154 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23907

Abstract
The use of fiber Bragg grating sensors embedded in hybrid composite laminates for simultaneous measurement of strain and temperature is proposed. The hybrid structure, formed by a pre-impregnated thermoset and thermoplastic composites, contains one single fiber Bragg grating embedded in each material, connected in series with each other. A different response is observed when the smart composite laminate is subjected to strain and to temperature. This is expected due to the distinct properties presented by each material. The rms deviation obtained for a temperature range between 20 and 60 degrees C is +/- 0.97 degrees C and for a strain range from 0 to 1100 mu epsilon is +/- 13.04 mu epsilon.

Abstract
A suspended multicore fiber sensor for simultaneous measurement of curvature and strain is proposed. The spectral response shows evidences of several interferences arising from the seven cores of the fiber. Once the sensing head presents different sensitivities for curvature and strain measurements, these physical parameters can be discriminated by using the matrix method. The rms deviations are +/- 19m(-1) and +/- 12:90 mu epsilon for curvature and strain measurements, respectively. (C) 2011 Optical Society of America

Abstract
Several configurations of ultralong Raman fiber lasers (URFL) based on a distributed mirror combined with Bragg gratings or fiber loop mirrors are studied. Two continuous-wave URFL configurations, with single and cascaded cavities using fiber Bragg gratings as mirrors are explored for a 300 km long fiber. For optical sensing, the cavity length was optimized for 250 km using one of the gratings an intensity sensor. Another URFL configuration based in a fiber loop mirror is also reported. For optical sensing using a 300 km long fiber it is shown that the best choice is a hybrid configuration. The sensitivity of the FBG laser sensor range was from (76 +/- 2) x 10(-6) mu epsilon(-1) (for lower strain) to (9.0 +/- 0.4) x 10 -6 mu epsilon(-1) (for higher strain). (C) 2011 Optical Society of America