Abstract
It is reported a LPG dynamic interrogation technique based on the modulation of fibre Bragg gratings located in the readout unit that permits to attenuate the effect of the 1/f noise of the electronics in the resolution of the LPG-based sensing head. The concept is tested to detect variations of the external refractive index and a resolution of 2.0x10 (4) NIR was achieved without system optimization. Additionally, the effect in the sensor resolution when introducing Erbium and Raman optical amplification is experimentally investigated.

Abstract
A hybrid Fabry-Perot/Michelson interferometer sensor using a dual asymmetric core microstructured fiber is demonstrated. The hybrid interferometer presents three waves. Two parallel Fabry-Perot cavities with low finesse are formed between the splice region and the end of a dual-core microstructured fiber. A Michelson configuration is obtained by the two small cores of the microstructured fiber. The spectral response of the hybrid interferometer presents two pattern fringes with different frequencies due to the respective optical path interferometers. The hybrid interferometer was characterized in strain and temperature presenting different sensitivity coefficients for each topology. Due to these characteristics, this novel sensing head is able to measure strain and temperature, simultaneously.

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 the field of aqueous environment studies, long-period fiber gratings are very attractive for the real-time monitoring of physical parameters, such as temperature and salinity. However, due to the fiber jacket removal, these are fragile devices when applied in real conditions, where mechanical loads and contamination with algae and other organic materials must be taken into account. This work describes a refractive index sensing head that has been developed and characterized for in situ measurement of water salinity and resistance to hard conditions.