Cyril Lupi

Experimental synthesis of fiber Bragg gratings using optical low coherence reflectometry

We apply a combination of optical low coherence reflectometry and a layer-peeling method to the synthesis of a fiber grating. The index modulation amplitude we obtain is compared with a Krug measurement result and the dc refractive index is derived from the phase measurement.

Determination of strain distribution and temperature gradient profiles from phase measurements of embedded fibre Bragg gratings

In this paper, a powerful method for measuring non-uniform strain is reviewed and extended to the measurement of temperature gradients inside an epoxy part. The sensor is an embedded fibre Bragg grating and the method is based on the measurements of the grating phase obtained by combining optical low coherence interferometry and an inverse scattering algorithm. This method has a great potential and for the first time experimental results obtained for both strain distribution and temperature gradient are presented. By applying a tensile test, strain distribution measurements are first compared with finite element simulations to validate previous published results. Second, original temperature gradient measurements in a solid body are shown. The results are in good accordance with reference measurements achieved with thermocouples incorporated into the body.

Local characterization of fiber-Bragg gratings through combined use of low-coherence interferometry and a layer-peeling algorithm

The technique presented here allows us to obtain an accurate determination of the refractive index modulation amplitude, the mean effective index, and the chirp of fiber-Bragg gratings. A layer-peeling algorithm is used to extract this information from low-coherence interferometry measurements. Finally, we present a systematic study over 10 uniform and chirped gratings to proof the reliability and accuracy of this technique.

Optical characterization of PZT thin films for waveguide applications

In order to develop an electro-optic waveguide, Pb(Zr, Ti)O3 ceramic ferroelectric thin films were elaborated by a modified sol-gel process on glass substrate. In the aim to study the optical properties of the PZT films, an accurate refractive index and thickness measurement apparatus was set up, which is called M-lines device. An evaluation of experimental uncertainty and calculation of the precision of the refractive index and thickness were developed on PZT layers. Two different processes of PZT elaboration were made and studied with this apparatus. The reproducibility of one fabrication process was tested and results are presented in this paper.

Optical properties of PZT thin films deposited on a ZnO buffer layer

The optical properties of lead zirconate titanate (PZT) thin films deposited on ZnO were studied by m-lines spectroscopy. In order to retrieve the refractive index and the thickness of both layers from the m-lines spectra, we develop a numerical algorithm for the case of a two-layer system and show its robustness in the presence of noise. The sensitivity of the algorithm of the two-layer model allows us to relate the observed changes in the PZT refractive index to the PZT structural change due to the ZnO interface of the PZT/ZnO optical waveguide.

Architecture of optical fiber sensor for the simultaneous measurement of axial and radial strains

The aim of this paper is to investigate the ability to measure simultaneously the axial and radial strain with a single optical fiber sensor. The discussion begins with the analytical study of a cylinder subjected to pure tensile strain and thermal load. We emphasize the necessity of measuring the radial strain in order to determine the axial strain of an embedded sensor with accuracy. Then, we describe a few sensors able to measure axial and radial strains and study their efficiency. The conclusion is that the best structure is made of the juxtaposition of a short and a long period grating.

Accurate low-coherence interferometric relative group delay and reflectance measurements: characterization of a free-space optics multiplexer/demultiplexer

In this paper, we present more results obtained on fibre Bragg gratings submitted to Round Robin tests and compare them with those obtained at NIST. We confirm that the reflectance and the relative group delay can be accurately measured with optical low-coherence interferometry. Then, complete characterization of the reflectance and group delay of a free-space optics multiplexer/demultiplexer is performed. We show the similarity of the response of the different channels.

A method to retrieve optical and geometrical characteristics of three layer waveguides from m-lines measurements

We consider three layer optical waveguides and present a method to measure simultaneously the refractive index and the thickness of each layer with m-lines spectroscopy. We establish the three layer waveguide modal dispersion equations and describe a numerical method to solve these equations. The accuracy of the method is evaluated by numerical simulations with noisy data and experimentally demonstrated using a PZT thin film placed between two ZnO layers.

Accelerated aging and life tests of optical fibers

The reliability of the network optical fibers is a critical issue for telecommunications. New investigations methods have been developed within a cooperative program supported by France Telecom. They include low coherence interferometry and optical near field microscopy in association with classical analysis tools such as Scanning Electron Microscopy and Shear Force Microscopy. One aim of the study is the localization and the characterization of the defects from which failure originates. The aging effect has been investigated in silica fibers immersed in desionized water at 65 °C and 85 °C for different times : from 3 to 12 months

Local and Spectral Characterization of Optical Fibers and Fiber Bragg Gratings with Low Coherence Interferometry

Abstract In this article, we describe local and spectral characterization of fibers and integrated optical components using low coherence interferometry. Chromatic dispersion and group birefringence measurements of erbium-doped fibers or photonic crystal fibers are presented, as well as local characterization of fiber Bragg gratings which allows the determination of strain and profile temperature gradient inside a material.