A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models

Densification involved in the UV-based photosensitivity of silica glasses and optical fibers

Fiber Bragg grating coupled light sources can acheive tunable single-frequency (single axial and lateral spatial mode) operation by correcting for a quadratic phase variation in the lateral dimension using an aperture stop. The output of a quasi-monochromatic light source such as a Fabry-Perot laser diode is astigmatic. As a consequence of the astigmatism, coupling geometries that accommodate the transverse numerical aperture of the laser are defocused in the lateral dimension, even for apsherical optics. The mismatch produces the quadratic phase variation in the feedback along the lateral axis at the facet of the laser that excites lateral modes of higher order than the TM00. Because the instability entails excitation of higher order lateral submodes, single frequency operation also is accomplished by using fiber Bragg gratings whose bandwidth is narrower than the submode spacing. This technique is particularly pertinent to the use of lensed fiber gratings in lieu of discrete coupling optics. Stable device operation requires overall phase match between the fed-back signal and the laser output. The fiber Bragg grating acts as a phase-preserving mirror when the Bragg condition is met precisely. The phase-match condition is maintained throughout the fiber tuning range by matching the Fabry-Perot axial mode wavelength to the passband center wavelength of the Bragg grating.

Fiber grating coupled light source capable of tunable, single frequency operation

A novel method and apparatus for varying the index of refraction of a material using an interference pattern is disclosed. The method and apparatus incorporate an ultra short duration pulse laser source. Electromagnetic radiation provided from the laser propagates to a diffractive element positioned in close proximity to the target material. The diffracted electromagnetic radiation forms an interference pattern, the peaks of which are sufficiently intense to cause a change in index of refraction.

Bragg grating and method of producing a Bragg grating using an ultrafast laser

Regeneration, regenerated gratings and composite glass properties: the implications for high temperature micro and nano milling and optical sensing

The advent of optical fibres based on air holes running along their entirety opens up new directions in addressing various properties relevant to sensing, including the temperature/strain challenge of optical fibre sensors. This paper looks at the measurement challenges associated with temperature and strain, examines the potentially unique functionality structured fibre designs with and without gratings open up, and briefly describes some current research directions within conventional fibre and grating technologies.

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Properties of Specialist Fibres and Bragg Gratings for Optical Fiber Sensors

UV-induced excess losses have been measured at various pulse energy
densities and exposure times in germanosilicate optical fiber preform cores.
The corresponding refractive-index changes have been determined through a
Kramers–Kronig analysis. Because of the nonlinear behavior of the excess
losses as a function of both exposure time and fluence per pulse, one should
be careful when comparing the refractive-index modulation deduced from such
measurements with that obtained from Bragg grating reflectivity. Indeed
nonlinear effects such as saturation imply that it is necessary to take into
account the local character of the change in absorption to calculate the
evolution of the refractive-index modulation accurately as a function of the
exposure time. Implications of these results are discussed.

Analysis of color-center-related contribution to Bragg grating formation in Ge:SiO 2 fiber based on a local Kramers -Kronig transformation of excess loss spectra.

An optical fiber for producing energy-dissipative and wavelength—selective filters is presented. The fiber includes a core and a cladding that are photosensitive to radiation and have a periodic perturbation of the refractive index. The periodic perturbation defines at least one Bragg grating with lines tilted with respect to the axis of the fiber. The refractive index difference between the core and the cladding is less than 3×10−3.

Optical fiber suitable for producing doped-fiber amplifier gain equalizing filters

Experiments have shown that it is possible to realize laser cavities photowritten within rare-earth-doped silicate fibers. Experimental results on a particular application, namely, the detection of gas traces by identification of one of the gas's absorption lines, are presented. Experiments on an absorption line of atmospheric water have been carried out to illustrate this purpose. Two lasers have been designed with particular characteristics (spectral linewidths, slope efficiencies, thresholds). Preliminary experimental results on the detection of an absorption line of atmospheric water have been obtained with fiber lasers and optoacoustic detection.

Design of a photowritten cavity neodymium-doped fiber laser tunable around an absorption molecular line.

La presente invention concerne une fibre optique, caracterisee par le fait qu'elle comprend un coeur (10) et une gaine (20) photosensible a un rayonnement, presentant une perturbation periodique de l'indice de refraction du coeur (10) et de la gaine photosensible (20), definissant au moins un reseau de Bragg selon des traits inclines par rapport a l'axe (O-O) de la fibre, dans laquelle la difference d'indice de refraction entre le coeur (10) et la gaine (20) est inferieur a 3. 10-3 .

Fibre optique concue pour realiser des filtres egalisateur de gain d'amplificateur a fibre dopee

La presente invention concerne un dispositif formant laser a fibre de puissance emettant un rayonnement monomode transverse controle, caracterise par le fait qu'il comprend : une source de pompe (40), un troncon (10) de fibre optique amplificatrice gainee, deux reflecteurs (20, 25) disposes sur les extremites de ce troncon (10), et un filtre (30) coupe bande apte a emettre un rayonnement laser centre vers 980 nm dans ledit troncon.

Jean Francois Bayon

Papers

Analysis of color-center-related contribution to Bragg grating formation in Ge:SiO 2 fiber based on a local Kramers -Kronig transformation of excess loss spectra.

Optical fiber suitable for producing doped-fiber amplifier gain equalizing filters

Design of a photowritten cavity neodymium-doped fiber laser tunable around an absorption molecular line.

Fibre optique concue pour realiser des filtres egalisateur de gain d'amplificateur a fibre dopee

Laser a fibre de puissance emettant un rayonnement monomode transverse centre vers 980 nm