Abstract
In this work, we demonstrate the possibility of fabricating short-length long-period gratings and rocking filters in highly birefringent Photonic Crystal Fiber using a CO2 laser. In our experiments both kinds of gratings were made in the same Boron doped highly birefringent PCF using similar exposure parameters. We also present the sensing capabilities of both fabricated gratings to temperature, strain and hydrostatic pressure by interrogation of the wavelength shifts at different resonances. Crown Copyright

Abstract
A review of refractive index measurement based on different types of optical fiber sensor configurations and techniques is presented. It addresses the main developments in the area, with particular focus on results obtained at INESC Porto, Portugal. The optical fiber sensing structures studied include those based on Bragg and long period gratings, on micro-interferometers, on plasmonic effects in fibers and on multimode interference in a large spectrum of standard and microstructured optical fibers.

Abstract
A sensing head based on a hollow-core photonic crystal fiber for in-reflection measurement of micro-displacements is presented. The sensing structure takes advantage of the multimodal behavior of a short segment of hollow-core photonic crystal fiber in-reflection, being spliced to a single mode fiber at its other end. A modal interferometer is obtained when the sensing head is close to a mirror, through which displacement is measured.

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.