In this paper an angle transducer based on Fiber Bragg Grating (FBG) is presented. Two gratings are glued to a metallic
platen, one in each side. It is insensitive to temperature changes, given that the temperature shifts affect equally to both
FBG. When the platen is uniformly bent an uniform strain appears in both sides of the platen. It depends on the bend
angle and the platen length and thickness. The transducer has been designed to be used in the auscultation of tunnels
during their construction process and during their live time. The transducer design and its characterization are presented.
An optical fibre transducer able to work in high temperatures environments is experimentally demonstrated in the
laboratory. It is based on a permanent Long period gratings (PLPG) written using a thermo-mechanical technique. The
fabrication technique, the experimental works, their results and the conclusions are presented and discussed in this paper.
Gas detection and gas sensing based on hollow core photonic bandgap fiber (HC-PBF) is a very promising technique due
to the long interaction light-gas lengths that are achievable. However, long path-lengths also imply higher gas filling
times of the hollow fiber and higher response times of the detection systems what can constitute a serious practical
inconvenience. In this paper, the high sensitivity is maintained but the sensor response time is reduced by using multiple-coupling
fiber gaps. The results and conclusions extracted from a systematic experimental study (comparing the spectra
and filling time of different HC-PBF lengths and different number of coupling gaps) are presented and discussed.
Finally, the maximum number of gaps allowed in the system is modelled.
An erbium doped fiber ring laser (EDFRL) that incorporates four non-adiabatic concatenated single-mode fiber tapers
(acting as tunable filter in the laser cavity) is presented. These concatenated fiber tapers integrates a filter with a
narrower band-pass and a higher modulation depth than a single taper. The tuning of this filter was implemented
applying a controlled perturbation in the fiber taper. The proposed laser architecture was successfully demonstrated in
the laboratory in which a tuning range of 20.8nm (1544.5nm-1565.3nm) were measured.
In recent years, hollow-core photonic bandgap fibers (HC-PBFs) have been demonstrated to be a promising technology
for gas sensing. In particular, the long interaction path lengths available with these fibers are especially advantageous for
the detection of weakly absorbing gases such as methane. In the near-infrared region, methane has the strongest
absorption band, 2ν3, at 1670 nm. However, HC-PBFs were not available until recently in this wavelength range and gas
sensing devices based on HC-PBFs were previously made in the weaker band of 1300 nm. In this paper, we report the
demonstration of a methane sensor based on a 1670-nm-band HC-PBF. A strong spectral feature, the R(6) manifold
(near 1645 nm), was selected for sensing purposes as it shows a good signal-to-noise ratio. This absorption line is
comprised of six energy transitions, strongly overlapped at our experimental conditions. For that reason, we applied a
multiline algorithm that used information from the six transitions to fit the manifold. The goodness of the fitting was
assessed measuring the concentration of different methane samples. With this method, a minimum detectivity of 10
ppmv for the system configuration was estimated.
The effective index, fundamental mode width, numerical aperture are some important parameters of a fibre. The
behaviour of these parameters for a Modified Total Internal Reflection (MTIR) Photonic Crystal Fibre (PCF) is studied
when strain is applied. We chose a range of normalized frequency (&Lgr;/&lgr;) and a range of d/&Lgr; and we analyzed the
behaviour for different values of strain. The sensibilities of the studied parameter are obtained in the chosen range.
Finally, the region of maximum influence of the strain is observed.
Distributed fiber sensing based on Brillouin gain scattering (BGS) principle is a useful way to develop devices capable to
measure temperature and/or strain in optical fibers. In these distributed sensors, spatial resolution is a topic of special
interest in the distributed fiber sensing field. The influence of the probe-pulse shape in the interaction between the pulsed
light and the continuous wave laser in a pump-probe system. This study has the purpose of improving the spatial
resolution of the measurement without losing stability in the BGS is presented. Also it is showed how the backscattering
Brillouin gain is affected by inducing variations on the final value of the BGS intensity. Theoretical analysis of the probe
pulse in the Brillouin shift and intensity values using triangular, sinusoidal and saw tooth shapes around the phonon
lifetime (~10ns) are presented; and also considerations and conclusions are explained.
An arbitrary FBG spectrum can be obtained as the addition of the contribution of some concatenated subFBGs written
without phase jump using the same phase mask. An adaptive filter is used in order to obtain, from the desired spectrum,
the parameters of the different subFBGs reproducing the required response.