Abstract
The implementation of refractometric based fiber optic sensors for environmental monitoring is discussed. Several sensing head configurations and interrogation schemes are presented and compared in the framework of different biochemical sensing applications. Results are presented demonstrating the suitability of this technology to monitor a diversity of chemical and biological parameters of environmental significance.

Abstract
In this work it is presented a system to control a self-referencing fiber optic intensity displacement sensor using virtual instrumentation. To ensure higher flexibility and dynamic optimization, the use of an optical fiber delay line or an electrical delay line is avoided by implementing a delay line in the virtual domain, preserving the self-referencing and sensitivity characteristics of the proposed optical intensity sensing structure.

Abstract
A digital control system to interrogate optical fiber interferometric sensors is presented. The system was implemented using a DAQ board and LabView Software, it is based on white light interferometry, and can use four different synthetic heterodyne and pseudo-heterodyne signal detection schemes. The system was tested and compared with standard hardware instrumentation using a fiber optic Mach-Zehnder interferometer to readout strain sensitive Fabry-Perot sensors in a differential configuration. It is shown that the virtual instrumentation has a good performance being a viable alternative for use in compact portable sensing systems.

Abstract
An optical fibre sensor for simultaneous measurement of refractive index and temperature is presented. The refractive index measurement is based on the visibility variations of a Fabry- Perot interferometer with interfering waves generated in a low reflectivity Bragg grating inscribed on a Panda fibre and in the fibre tip (Fresnel reflection) in contact with the liquid. The temperature measurement is based on the wavelength shift of the FBG peaks. Results obtained show the feasibility of simultaneous measurement of refractive index and temperature and also the possibility of adjusting fringe visibility via polarization control.

Abstract
An indicator free optical fiber sensor for determination of carbon dioxide is presented. The sensing layer is based on the acid-basic equilibrium of phenol and of its derivative p-nitro-phenol that, in the presence of CO2, are prone to protonation introducing refractive index changes. The new sensitive layer is characterized and tested in different refractometric fiber optic sensor configurations. Using a fiber based interferometric setup, a CO 2 dependent refractive index change of ~0.05 RIU is observed, in the 10%-90% CO2 concentration range, demonstrating the membrane viability. Preliminary results are presented for an all-fiber LPG-based carbon dioxide sensor.

Abstract
The analysis of the quality of food oils is of paramount importance because the degradation of oils can lead to formation of harmful substances to the human organism With the increase of the degradation of oils an increase of its refractive index occurs The objective of this work is to develop and to characterize optical fiber refractometers sensitive to variations of refractive index of food oil samples The optical fiber refractometers thanks to the intrinsic characteristics make them suitable for monitoring the quality of frying oils They possess the advantages to require small volumes of sample for analysis do not contaminate the sample and supply the response in real time In this work a long period grating (LPG) as refractometer is used because of their sensitivity to refractive index of the external media degraded and not degraded frying oil samples The oil samples had been characterized by the analysis of total polar components The refractive index of oil is above 1 47 this region the LPG does not show enough sensitivity a nanolayer of an organic material was coated onto the fiber Using the Langmuir-Blodgett technique the response of LPG is modified according to the refractive index and thickness of the film (he deposition of the film modifies the rates effective modes of cladding thus improving the response of the changes in the refractive index of the external media higher than that the refractive index of the cladding (n = 1 457)