J. P. Goure

Linear and nonlinear optical fibre devices

The authors give the fundamental concepts of all-fibre devices and the basic technology that has been developed to realise those concepts. In addition, they present a review of the state of the art in the design and performance of linear and nonlinear optical all-fibre devices with particular emphasis on recent progress in such devices in he field of lightwave technology including optical fibre communications, optical fibre sensing and optical signal processing.

Optical fibre refractive index sensor using surface plasmon resonance and a TiO2 coating obtained by sol-gel process

A simple fiber sensor for continuous monitoring of refractive index variations of liquid mixtures is described. The principle of this senor, based on the excitation of a surface plasmon at ta metal/dielectric interface, has been described in previous articles. In this paper it is shown that this set-up, which used monochromatic incident light, can work as a refractive index variation sensor either in a range between 1.36 and 1.40 when using a single silver layer or in a range shifted down to 1.33 when coating silver by a thin TiO2 adaptive layer obtained by sol-gel process.

Efficient ball lens coupling between a single-mode optical fiber and a silica microguide at 1.3 μm

An efficient coupling between a single-mode optical fiber and a silica guide by a ball lens is demonstrated. We investigate this coupling scheme by a theoretical analysis and by the experiment. The contribution of all the loss factors is evaluated. The tolerances of the fiber positionment are studied and then, this coupling solution is compared to the current butt-coupling.

Measurements of Mode Propagation Time in Multimode Fibers using a Real Time Interferometric Amplitude Correlator

The method we propose consists in a modified version of the one presented above, because the amplitude correlator is different and has the avantage of directly displaying in real time the correlation function. This amplitude correlator has already been used for autocorrelation measurement with short laser pulses and is modified here to achieve cross-correlation with cw wide bandwidth laser light.

Measurement of mode times of flight in multimode fibers by an interferometric method using polychromatic light: theoretical approach and experimental results

The propagation of several modes in an optical fiber is not easy to study. The experiment that we propose permits us to measure the difference in time propagation between two successive modes of a multimode fiber. The same laser beam is coupled into the fiber to be tested and into the reference single-mode fiber. The correlation of output electric fields of the modes propagated by each fiber is realized by an interferometric system.

Détermination de défauts de circularité de la section d’une fibre optique non gainée

Study of the light scattered from an unclad optical fiber illuminated by a laser beam perpendicular to its axis gives a valuation of little defects of the fiber cross section. The shifts of some bright fringes that occur when the fiber is rotated are observed. Comparison between experimental measurements and ray interference computations shows that the cross section of the fiber under test is neither circular nor elliptical, but can be described with good approximation by a limited Fourier series, the coefficients of which are estimated.

Diamètre intrinsèque d'une fibre non gainée de forme quelconque: définition et détermination numérique.

In this paper, the intrinsic diameter of the noncircular cross section of an unclad optical fiber is defined and determines the fiber dimension. Its value can be determined by studying the forwardscattering pattern from the fiber illuminated by a laser beam perpendicular to its axis. A knowledge of the shape of the fiber is not necessary. The suggested method is nondestructive. Moreover, it provides an estimate of the deformation of the fiber cross section.

Optimisation de l'efficacité de couplage entre un guide d'onde confiné et une fibre optique monomode par l'intermédiaire d'une lentille boule

RésuméĽefficacité de couplage théorique entre un guide ďonde confiné et une fibre optique monomode par ľintermédiaire ďune lentille boule est optimisée en faisant varier les différents paramètres du système optique : positions relatives des éléments, indice de réfraction et diamètre de la lentille. Les calculs sont effectués numériquement grâce à un logiciel spécifique en approximant les distributions des champs à coupler par des profils gaussiens. Les pertes dues aux erreurs de positionnement des éléments guidants par rapport à leur position idéale sont ensuite évaluées. Tous ces résultats sont confrontés aux résultats obtenus dans le cas ďun couplage direct (sans lentille intermédiaire).AbstractTheoretical coupling efficiency between a channel waveguide and a single-mode optical fibre using a ball lens is optimized by varying the parameters of the optical system such as the relative position of the components, the refractive index and the size of the lens. A specific software has been used for the optimization. Numerical calculations have been done under the Gaussian approximation of the fields distributions. The losses due to waveguides misalignments with respect to their ideal position have been evaluated. All these theoretical results are compared with those obtained from buttcoupling.

Intensity Fluctuations Observed At A Pigtailed Source End-Face In Optical System

Interferences between the different propagation modes in an optical fiber called the modal noise, is already a well-known problem. Intensity fluctuations severely affect the perforMance in optical communication systems ; on the other hand, they can be used for sensors design. Pigtailed sources are often used in order to characterize optical fibers as well as in some optical devices. These fluctuations are caused by the instability of the source and by the presence of the pigtail. More particularly, we studied the fluctuations of the available energy and its repartition on the end-face of a graded index pigtail for different types of sources (coherent or incoherent), for various light wavelengths and constraints. We used a near field method and the convolution of the end pigtail image by an area of the same size. When the fiber has random vibrations in incoherent light, experimental values can be compared to the calculated values for the coupled energy and signal to noise ratio (S/B). In incoherent light, when fiber is motionless and in coherent light, an experimental study has been carried out for several wavelengths with the same set-up. In this paper, we give the results concerning the signal to noise ratio S/B according to the strain. We also estimate the speckle mean diameter with experimental values for several wavelengths. We characterized the modal noise influence in measurements for particular optical applications. The results of our experiments show the limits of the use of such sources in optical devices.

Light Power Fluctuations at the Output End of a Fiber in Partial Coupling with a Detector in Coherent Light

The power emitted from the end-face of a multimode graded index fiber illuminated by a coherent light source shows fluctuations caused by the different propagating modes and by the source. The perfect knowledge of these phenomena is important in optical communications and in light power measurements. Indeed, the modal noise brings unaccuracy for the result. These phenomena have been studied by several authors, the signal to noise ratio and the probability density function (P.D.F.) have been evaluated [1-7]. The coupling misalignment [8-9] and the influence of external strains such as vibrations have been studied.