Abstract
An electrical dynamic interrogation technique is reported for long-period grating sensors relying on the modulation of fibre Bragg gratings located in the readout unit that permits us to attenuate the effect of the 1/f noise of the photodetection, amplification and processing electronics on the sensing head resolution. The concept is tested to detect variations of curvature, and a resolution of 9.4 x 10(-3) m is achieved.

Abstract
A 253km ultralong remote displacement sensor system based on a fiber loop mirror interrogated by a commercial optical time-domain reflectometer is proposed and experimentally demonstrated. The use of a fiber loop mirror increases the signal-to-noise ratio, allowing the system to interrogate sensors placed 253km away from the monitoring system without using any optical amplification. The displacement sensor was based on a long period grating spliced inside of the loop mirror, which modifies the mirror reflectivity accordingly to the applied displacement. (C) 2011 Optical Society of America

Abstract
The overall procedure toward the implementation of a compact tunable athermal filter mounted on a piezoelectric actuator and based on a pi-shift chirped fiber Bragg grating is presented. This package ensures an active tunablility over 2 nm with a cross thermal induced Bragg wavelength shift below 100 pm over a temperature range from -20 degrees C to + 80 degrees C. The proposed filter makes use of the overall response of a p-shift chirped fiber Bragg grating and a bulk broadband microfilter that enables a sharp optical transmission spectrum response having a FWHM below 20 pm within a 2 nm region and 20 dB rejection band to be obtained. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3656751]

Abstract
We present a compact in-line fiber interferometric sensor fabricated in a boron doped two-mode highly birefringent microstructured fiber using a CO2 laser. The intermodal interference arises at the fiber output due to coupling between the fundamental and the first order modes occurring at two fiber tapers distant by a few millimeters. The visibility of intermodal interference fringes is modulated by a polarimetric differential signal and varies in response to measurand changes. The proposed interferometer was tested for measurements of the strain and temperature, respectively, in the range of 20-700 degrees C and 0-17 mstrain. The sensitivity coefficients corresponding to fringe displacement and contrast variations are equal respectively for strain -2.51 nm/mstrain and -0.02561/mstrain and for temperature 16.7 pm/degrees C and 5.74 x 10(-5) 1/degrees C. This allows for simultaneous measurements of the two parameters by interrogation of the visibility and the displacement of interference fringes. (C) 2011 Optical Society of America

Abstract
This paper presents an overview of optical fiber sensors based on multimode interference with a focus on refractometric applications. A specific configuration is presented to measure the refractive index of the surrounding liquid based on the Fresnel reflection in the fiber tip, combined with a simple interrogation technique that uses two fiber Bragg gratings as discrete optical sources, with the measurand information encoded in the relative intensity variation of the reflected signals. A resolution of 1.75 x 10(-3) RIU is achieved. (C) 2011 Optical Society of America

Abstract
Fiber Bragg Gratings are structures with remarkable characteristics that have induced new qualitative developments in the broad field of optical fiber technology, most notably in optical communications and in optical sensing. When these devices are applied for sensing, the underlying concept is the modulation of the grating Bragg wavelength by the measured and, therefore, a central issue is the sensitive and accurate conversion of the resonant wavelength into a proportional electrical signal with the adequate format for further processing. This topic is broadly known as Fiber Bragg Grating interrogation and is the subject of the present chapter. It is organized in two parts: in the first one, the techniques developed by the scientific community looking for this functionality are reviewed, with emphasis on the identification of general conceptual classes where they fit; in the second part, illustrative and state-of-the-art commercial Fiber Bragg Grating interrogation systems are described.