Abstract

Abstract
An evaluation of two optical fiber sensing heads for measuring transversal load is presented. Their construction introduces power loss without the need of a pair of deformer plates and is based on crossing two fibers in braid-type (braid twisted), and of an optical fiber stretched out which is wrapped up by another one in spiral form (spiral twisted), respectively. For a higher sensitivity, the braid twisted configuration is preferable. Nevertheless, in both sensing heads, the sensitivity can be enhanced by decreasing the enrollment period and/or by choosing the appropriate encapsulation of the sensing head. Relative to resolution and hysteresis, the spiral twisted sensing head presented the best result. However, further work on the plasticity of the coatings is needed to decrease hysteresis. These configurations can be embedded in composite materials and used in many applications. (c) 2005 American Institute of Physics.

Abstract
We report an alternative technique to interrogate a long-period fiber grating (LPG) when the grating sensitivity is based on the peak amplitude changes of the resonant wavelength. To read the amplitude changes, a conventional optical domain reflectometer was used. Bend measurements were performed to apply such method and to determine the grating sensitivity for this physical parameter. Reflective measurements, temperature insensitive, and the possibility of multiplexing LPG sensors are some advantages offered by this technique. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Abstract
A high birefringent D-type fiber loop mirror used as refractometer is reported. The D-type fiber section was etched by hydrofluoric acid (HF) being sensitive to the surrounding-medium refractive index allowing the measurement of different refractive indices in liquids. The refractometer was also tested in temperature, and simultaneous measurement of refractive index and temperature was demonstrated. © 2008 IEEE.

Abstract
In recent years the need to monitor different parameters has led to the development of several architectures able to make real time, un-attended measurements. Particularly in regard to environmental issues, it is very important that the equipment and measuring systems be small and light to avoid maximum interference of the ecosystems Studied. In this context, optical fibre sensors have become extremely attractive for use in natural environments to monitor different parameters of biological interest, due to their intrinsic small weight and size and low reactivity to chemical and biological parameters. In this paper we present an innovative and technologically advanced system for the simultaneous measurement of temperature and salinity based on optical fibre Bragg grating sensors and on an optical sensing cable especially designed for large-scale and distributed or quasi-distributed measurements. A prototype of this optical cable was installed in the Mira Channel at Ria de Aveiro, Portugal. Temperature variation during three weeks from 4 to 23 June 2002 is investigated and presented here.

Abstract
A refractometric sensor based on a phase-shifted long-period fiber grating written by electric-arc discharges is presented. Transmission and reflective configurations for refractive index measurements are studied. It is observed that the reflective topology permits better performance compared with the transmission one, which is the approach normally utilized in the context of long-period fiber sensing. The resolution achieved in the measurement of refractive index enables the application of this sensing head structure in demanding situations, such as the measurement of the level of salinity of water. (c) 2006 Optical Society of America.