Laurent Bigot

Photonic crystal fiber design by means of a genetic algorithm

A Genetic Algorithm (GA) is used to design photonic crystal fiber structures with user-defined chromatic dispersion properties. This GA is combined with a full vectorial finite element method in order to determine the effective index of propagation of the modes and then, the chromatic dispersion of structures generated by GA. This method proves to be a powerful tool for solving this inverse problem.

Transient radiation-induced effects on solid core microstructured optical fibers

We report transient radiation-induced effects on solid core microstructured optical fibers (MOFs). The kinetics and levels of radiation-induced attenuation (RIA) in the visible and near-infrared part of the spectrum (600 nm-2000 nm) were characterized. It is found that the two tested MOFs, fabricated by the stack-and-draw technique, present a good radiation tolerance. Both have similar geometry but one has been made with pure-silica tubes and the other one with Fluorine-doped silica tubes. We compared their pulsed X-ray radiation sensitivities to those of different classes of conventional optical fibers with pure-silica-cores or cores doped with Phosphorus or Germanium. The pulsed radiation sensitivity of MOFs seems to be mainly governed by the glass composition whereas their particular structure does not contribute significantly. Similarly for doped silica fibers, the measured spectral dependence of RIA for the MOFs cannot be correctly reproduced with the various absorption bands associated with the Si-related defects identified in the literature. However, our analysis confirms the preponderant role of self-trapped holes with their visible and infrared absorption bands in the transient behaviors of pure-silica of F-doped fibers. The results of this study showed that pure-silica or fluorine-doped MOFs, which offers specific advantages compared to conventional fibers, are promising for use in harsh environments due to their radiation tolerance.

Nanostructuring an erbium local environment inside sol–gel silica glasses: toward efficient erbium optical fiber lasers

To extend the use of erbium- (Er-)/aluminum- (Al-) codoped optical fibers in hostile environments, the reduction of the Al amount has been identified as a serious way to harden them against harsh radiation. In this work, sol–gel monolithic Er3+-doped and Er3+/Al3+-codoped silica glasses were prepared from nanoporous silica xerogels soaked in a solution containing an Er salt together or not with an Al salt. After sintering, these glasses were used as the core material of microstructured optical fibers made by the stack-and-draw method. The influence of Al incorporation on the optical properties of Er3+-doped silica glasses and fibers is investigated. This approach enabled the preparation of silica glasses containing dispersed Er3+ ions with low Al content. The obtained fibers have been tested in an all-fibered cavity laser architecture. The Er3+/Al3+-codoped fiber laser presents a maximum efficiency of 27% at 1530 nm. We show that without Al doping, the laser exhibits lower performances that depend on Er content inside the doped fiber core. The effect of Er pair-induced quenching also has been investigated through nonsaturable absorption experiments, which clearly indicate that the fraction of Er ion pairs is significantly reduced in the Al-codoped fiber.

Using advanced S2 analysis to measure mode coupling in a 2-LP-mode fiber

Mode coupling in a step-index 2-LP-mode fiber has been experimentally studied using advanced S2 analysis. A wire-mesh is used to locally induce micro-bending and it is demonstrated that coupling coefficients can be extracted.

Optical Frequency Domain Reflectometer Distributed Sensing Using Microstructured Pure Silica Optical Fibers Under Radiations

We investigated the capability of micro-structured optical fibers to develop multi-functional, remotely-controlled, Optical Frequency Domain Reflectometry (OFDR) distributed fiber based sensors to monitor temperature in nuclear power plants or high energy physics facilities. As pure-silica-core fibers are amongst the most radiation resistant waveguides, we characterized the response of two fibers with the same microstructure, one possessing a core elaborated with F300 Heraeus rod representing the state-of-the art for such fiber technology and one innovative sample based on pure sol-gel silica. Our measurements reveal that the X-ray radiations do not affect the capacity of the OFDR sensing using these fibers to monitor the temperature up to 1 MGy dose whereas the sensing distance remains affected by RIA phenomena.

Microstructured fibres and applications

In this paper, we explore some new concepts of optical fibre designs exhibiting large active core surrounded by resonant cladding for high power delivery.

Radiation Response of OFDR Distributed Sensors Based on Microstructured Pure Silica Optical Fibers

Temperature sensors based on microstructured pure silica optical fibers are investigated by OFDR and RIA performed during X-ray irradiation up to 50kGy dose. The results evidence that the temperature measures are poorly influenced by irradiation (the error being less than 0.3°C). Such a radiation tolerance is relevant for the use of these Rayleigh based sensors in harsh environments.

Solid-core photonic bandgap fiber laser with hetero-structured cladding and large area Yb-doped Sol-Gel core

A double clad Yb-doped photonic bandgap fiber with Sol-Gel -made core is tested in laser regime. A hetero-structured cladding is used to induce high losses for higher order modes. MFD of 36 μm is observed.

Few Mode Er3+-Doped Fiber with Micro-structured Core for Spatial Division Multiplexing

Er3+-doped fibers amplifying 6 modes over the C-band are analyzed. We show that micro-structuring fiber core permits to tailor the Er3+ distribution, thus making it possible to reach modal and spectral gain equalization.

The inner cladding mode in a photonic crystal fiber for temperature- and refractive index-independent strain sensing applications

Fiber Bragg gratings with strong resonance peaks for both Bragg and cladding modes are made in photonic crystal fiber modified with a germanium doped core. Experimental results for strain, temperature and refractive index sensitivities of fiber Bragg gratings are reported. We show the existence of an inner cladding mode that has the largest coupling from the core mode and that is insensitive to surrounding index changes. The core mode, inner cladding mode and outer cladding modes all have the same temperature sensitivity. By tracking the cladding mode resonances shifts relative to the core mode, a temperature and index insensitive strain sensor can be made.