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
A novel fiber optic curvature sensor based on a core-offset single-mode fiber (SMF) and on a fiber Bragg grating (FBG) is presented. The FBG cladding modes are efficiently excited by the large core misalignment. The curvature of the beam can be obtained by the reflected power of the core mode and the recoupled cladding mode.

Abstract
In this work, a polymeric sensitive layer based on the acid-base equilibrium of phenol and of its derivative p-nitro-phenol is presented for carbon dioxide measurements. Thin films casted on glass slides were tested, using a LED source (lambda c at 410 nm) and an Ocean Optics USB4000 spectrometer, in the 0% to 15.25% CO2 concentrations range, showing a 40% maximum transmittance variation with a 51s response time and a 0.15% resolution. Preliminary results indicate that CO2 also induces refractive index changes in the sensitive layer. Using a fiber based interferometric setup, a CO2 dependent refractive index change of similar to 0.045 RIU was observed, in the 0%-90% CO2 concentration range.

Abstract
An optical fibre sensor for determination of acetic acid is presented. The sensing probe is based on a fibre Bragg grating (FBG) Fabry-Perot cavity, coated with a thin film of sol-gel-PVP (polyvinylpyrrolidone) composite material. The polymeric thin film renders the interferometric output sensitive to the presence of carboxylic acid species. Results show that the wavelength of the interferometric peaks changes with acetic acid concentration, enabling its quantification. Coupling the fibre probe with a serrodyne modulated readout interferometer enables pseudo-heterodyne interrogation and the detection of acetic acid with a sensitivity of 92.6 deg/% L/L and a resolution of 0.2% L/L. The results demonstrate the potential of the proposed scheme to operate as a sensitive chemical sensor platform.