Fibre Bragg grating location and spatial period determination in DBR lasers by side-scatter detection of pump radiation

A simple technique for locating the position of Bragg grating reflectors in erbium-doped fibre lasers is proposed. The technique consists of the side detection of the pump radiation scattered from the grating. It is also possible to obtain the spatial period of the grating by measuring the diffraction angle, which closely depends on this parameter. This technique can also be applied to passive fibre Bragg gratings.     

Curved elastic beam with opposed fiber-Bragg gratings for measurement of large displacements with temperature compensation

In this paper, a temperature-compensated configuration for extending the working range of fiber-Bragg grating (FBG) strain sensors has been proposed. This technique consists of the application of two FBGs to the opposite surfaces of a straight elastic beam which was bent in a horizontal direction. The difference of the two FBGs' wavelengths depends on the beam curvature, while the mean value is taken in order to compensate for the temperature effects. The sensor proposed is less fragile than the bare fiber and seems particularly suited as large displacement sensor, and for structures in which it is impossible to affix the bare fiber, such as breaks or separate elements.     

Biconically-tapered optical fiber probes for the measurement of esophageal pressure

A miniaturized optical fiber probe for measuring esophageal pressure, that makes use of biconically-tapered fibers, has been built and characterized. The functioning of this probe is based on the decrease in transmitted power in the fiber, when it is bent in its biconical part under the action of pressure. We made and tested several probes, using different fibers (monomode and few-modes) and different tapering values. Our best result was achieved with a probe which utilizes a biconical monomode fiber that has a waist diameter of 36 μm. The resolution obtained was 2 mm Hg in the range between 5 and 55 mm Hg.     

Influence of a central depression on the dispersion characteristics of a graded-index profile

Ray-tracing techniques and modal relations are utilised for evaluating the dispersion characteristics of multimode fibres with a quasiparabolic profile having a central depression. The results show that the dispersion increases with the dimensions of the depression; however, such an increase may be negligible if the dimensions of the depression approach those corresponding to realistic preforms produced by the c.v.d. technique.     

Ray-tracing technique for evaluating the dispersion characteristics of graded-index cylindrical fibres

A method which uses ray-tracing techniques and modal relations is sketched for the determination of the dispersion characteristics of cylindrical fibres with radial graded-index distribution. Examples of the results obtained are described, which show how it is possible, applying this procedure, to fully analyse propagation in optical fibres with any refractive-index distribution.     

Reproducibility of splicer-based long-period fiber gratings for gain equalization

We fabricated long-period fiber gratings(LPFGs) using electric arc discharges. We observed that the fiber becomes slightly tapered due to longitudinal tension during the arc:this effect depends on the arc current and time length. We experimentally investigated how these characteristics can influence grating's performances,especially in view of employing the LPFG as gain equalizer for an erbium-doped optical amplifier. As expected,we found that the spectral response of the grating depends on the period Λ,the intensity of the perturbation,the grating length and the type of mode-coupling induced. Since this last parameter cannot be estimated directly from the transmission spectra,we propose a method to determine the mode-coupling occurring in the device and to assess the index modulation induced by the electric arcs. This method combines both experimental and simulated data,and can be used to characterize LPFGs made-up by any method.