Abstract
Birefringence monitoring of a Hi-Bi fibre under chemical etching is conducted. The Hi-Bi fibre (a bow-tie type) was inserted in a fibre loop mirror and the optical spectral response was measured while chemical etching of the Hi-Bi fibre was taking place. The birefringence of the bow-tie fibre has decreased due to the etching and the wavelength spacing of the fringe minima of the fibre loop mirror has increased.

Abstract
We report on the analysis and experimental validation of the strain sensitivity dependences of a fiber Bragg grating written in standard optical fiber when combined with fused tapers. By controlling the difference between the cross sections of the fused taper and the Bragg grating, the strain sensitivity of the Bragg wavelength can be changed by acting on the gauge length. The strain sensing characteristics of an interferometric structure formed by fabricating a fused taper in the middle of a fiber Bragg grating are also reported. (C) 2007 Optical Society of America.

Abstract
We present a new configuration based on a fiber ring laser sensor with four-wave mixing effect generation for simultaneous measurement of strain and temperature. The fiber ring laser sensor, corresponding to the signal wavelength, is based on an erbium-doped fiber amplifier, a highly nonlinear bismuth-based optical fiber, and a Bragg grating filter. Four-wave mixing is generated when an external pump laser is combined with a ring laser sensor. Two new peaks appear and are named the converted and satellite wavelengths. With efficiency conversion, which corresponds to the optical power ratio between the converted signal and ring laser input signal, and a Bragg wavelength it is possible to discriminate strain and temperature. Maximum errors of +/- 1.8 degrees C and +/- 12 mu epsilon are reported over 100 degrees C and 1000 mu epsilon measurement ranges, respectively. (c) 2007 Society of PhotoOptical Instrumentation Engineers.

Abstract
In this work, a Brillouin fibre laser sensor for strain and temperature discrimination is presented. The fibre laser sensor consists of a Fabry-Perot cavity with 20 m of optical fibre between two Bragg gratings. For the strain measurement, the 20 m were split in half and in 10 m a pre-tension was applied originating two Brillouin peaks. For the temperature measurement all of the sensing head was heated. The resolutions achieved were +/- 1 mu epsilon and +/- 1 degrees C for strain and temperature measurements, respectively.

Abstract
An optical fibre intensity sensor referenced by stimulated Brillouin scattering is presented. The optical sensor uses Fresnel reflection signal at the sensor fibre end and employs an adequate relationship between Brillouin and Rayleigh scattering and Fresnel reflection to have a referenced optical fibre intensity sensor addressed in reflection.

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.