Abstract
This work presents a stud), of displacement sensing based on a fiber eight geometry shape monitored by an optical time domain reflectometer. The displacement sensor is referenced by Fresnel reflection or by a fiber Bragg grating structure located after the sensor. One of the advantages of the fiber Bragg grating as referencing device is its capability to be multiplexed by a number of displacement sensors in series along the optical fiber. This concept is also demonstrated using two Bragg gratings. (c) 2007 Wiley Periodicals, Inc.

Abstract
In this letter, a new configuration for simultaneous strain and temperature discrimination is, presented using two concatenated high-birefringence (Hi-Bi) fiber loop mirrors. The first loop mirror includes a Hi-Bi photonic crystal fiber, while the second one contains a length of internal elliptical cladding fiber. It is shown that by monitoring the wavelength and optical power of one of the peaks of the system spectral transfer function, it is possible to obtain information that permits the simultaneous measurement of strain and temperature.

Abstract
This work presents an optical sensor based on a highly birefringent photonic crystal fiber (Hi-Bi PCF) loop mirror. The length of the sensing head is 380 mm and its corresponding wavelength spacing between two interferometer minima is 8 nm. The optical sensor was characterized in strain and in temperature with an uncoated Hi-Bi PCF and with an acrylate coated Hi-Bi PCF. Different results for strain and temperature sensitivity were obtained. Relatively to the strain measurement, the sensor with the uncoated Hi-Bi PCF presents slightly less sensitivity (1.11 pm/mu epsilon) when compared with coated Hi-Bi PCF (1.21 pm/mu epsilon). For the temperature measurement and with the uncoated Hi-Bi PCF, the optical sensor is insensitive to temperature (0.29 pm/K).

Abstract
Recent advances in devices and applications of high-birefringence fiber loop mirror sensors are addressed. In optical sensing, these devices may be used as strain and temperature sensors, in a separate or in a simultaneous measurement. Other described applications include: refractive index measurement, optical filters for interrogate gratings structures and chemical etching control. The paper analyses and compares different types of high-birefringence fiber loop mirror sensors using conventional and microstructured optical fibers. Some configurations are presented for simultaneous measurement of physical parameters when combined with others optical devices, for example with a long period grating.

Abstract
In this work, a simple sensing head geometry using fibre Bragg gratings for strain and temperature discrimination is presented. The sensing head geometry consists in one fibre with two FBGs bonded with a dummy optical fibre. Due to this new configuration, different strain sensitivities of the two FBGs are obtained (approximate to 65% difference), while temperature sensitivities remain the same. This difference in strain sensitivities is substantially larger than in all previously reported dual grating sensors. The obtained experimental errors were +/- 13.48 mu epsilon and +/- 2.44 degrees C, respectively. It is also demonstrated that this new configuration can be used as a temperature-independent strain sensor.

Abstract
A curvature sensor based on a highly birefringent (Hi-Bi) photonic crystal fiber inserted into a Sagnac interferometer is demonstrated. For this purpose, a novel Hi-Bi photonic crystal fiber was designed and fabricated. Half of the microstructured region of the photonic crystal fiber was composed by large diameter holes, while the other half contained small diameter holes. Because of this geometry, the fiber core was shifted from the center and high birefringence appears in the optical fiber. Curvature was applied for three different fiber directions for a range of 0.6-5 m(-1). Temperature and longitudinal strain was also characterized for constant curvature. The configuration showed insensitivity to these two physical parameters. (C) 2008 Optical Society of America.