Abstract
A CWDM network operating in reflective configuration for multiplexing remote Radio-Frequency (RF) self-referenced fiber-optic intensity sensors is analyzed and experimentally investigated. In the described approach, the use of fiber Bragg gratings as spectral selective mirrors allows to implement delay lines in the electrical domain, achieving more compact sensor-heads and easy-reconfigurable sensing points. Two measurement parameters for the sensing heads are defined and comparatively studied in terms of design parameters, linearity, sensitivity and resolution. The proposed sensor configuration is modeled following the Z-transform formalism, which permits an easy analysis of the system frequency response. Experimental results are presented, showing the characterization of the network performance and considering the properties of sensor self-referencing as well as sensor crosstalk. (C) 2010 Optical Society of America

Abstract
An all fiber Mach-Zehnder interferometer using suspended twin-core fiber is described. Due to the birefringence of the fiber cores, two interferometers are obtained when the fiber is illuminated by a polarized light. Applying curvature or temperature to the sensing head, different sensitivities are observed. In order to discriminate curvature from temperature in the suspended twin-core fiber Mach-Zehnder sensor, the matrix method is used.

Abstract
A low-cost monitoring system for measuring the optical power losses of drop fibres in wavelength division multiplexing (WDM) passive optical networks (PON) is reported. The proposed system is based on radio-frequency intensity modulation and fibre Bragg grating self-referencing measurement techniques using amplitude normalisation. The monitoring unit is built with an optical broadband light source illuminating the PON from the central office for testing purposes, and the signal processing of the measurements is provided by the low-frequency analogue filters and by a lock-in amplifier. The system allows measuring the optical power losses of the PON branches independently, with increased sensitivity in a re-configurable and flexible way. The monitoring technique has been studied and experimentally validated in a coarse WDM-PON prototype, as a first approach to dense WDM-PON applications. The merits of the proposed monitoring system with regards to other WDM-PON monitoring techniques and the scalability of the proposed system to dense WDM-PON architectures are also discussed.

Abstract
In this paper, we demonstrate the interrogation of fiber optic intensity sensors by using the combination of the frequency-modulated continuous wave concept with the spectral selective reflectivity of fiber Bragg gratings. Thus, we multiplex these kinds of sensors with this technique having simultaneously a referenced system. The basis of this dual functionality is described and results are presented for the case of interrogation of two multiplexed intensity sensors. Their evaluation permits to establish the conditions to address a sensor network of this type. Also, it is proposed a strategy to implement this sensing approach without the requirement of using optical fiber delay lines in the sensor heads.

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