Formation and UV absorption of cerium, europium and terbium ions in different valencies in glasses

The techniques for fabrication and the properties of periodic and aperiodic fibre Bragg gratings produced by UV exposure in photosensitive optical fibres are reviwwed with an emphasis on applications.

Uv-written in-fibre Bragg gratings

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

Fibre Bragg Gratings

Several technical revolutions over the last ten years have led to the increasing use of rare earth-doped fiber lasers and amplifiers as a key component of optical communication systems. In this chapter, we review the methods of producing these fibers and the effect of the host composition and the rare earth doping on the quality of the final product. We then review the physics of the dopants and the hosts involved which makes these doped fibers so valuable for optical communications. In the last section, the laser performance itself is summarized; new trends for the future are presented.

Rare Earth-Doped Fiber Lasers and Amplifiers

Two photoinduced Bragg reflectors at 1480 nm are written at both ends of the fibre amplifier. Above threshold, laser oscillation clamps the gain and suppresses low frequency signal or pump induced gain fluctuations.

Gain control in erbium-doped fibre amplifiers by lasing at 1480 nm with photoinduced Bragg gratings written on fibre ends

A new kind of instrumentation based on Optical Fiber Bragg grating sensors is proposed for the main relevant monitoring needs in the electric power industry. The challenging metrological properties of these components are presented and their good resistance to (gamma) -ray irradiations experimentally proved.

Optical fibre Bragg grating sensors for structure monitoring within th nuclear power plants

The performances of fiber gratings can be impaired by coupling to cladding modes, especially for applications in multiplexed systems. This coupling is due to a non-zero weighted overlap integral between the guided mode and the cladding modes. It can generate transmission losses larger than 3 dB over more than 20 nm on the blue side of the resonance wavelength and are commonly observed in high reflectivity gratings (> 50%) (see for example transmission curves of figures 2 and 7 of reference [1]). From a perturbation theory, it comes that, for a tensorial perturbation Δe of the permittivity, the coupling coefficient is proportionnai to the quantity ∬ E g Δ e E c * d S, where Eg is the guided mode field and Ec a cladding mode field. In the case of a circularly symmetrical perturbation (generally assumed in photowritten gratings), the coupling is limited to cladding modes of LP0 symmetry. The above integral can be nulled if Δe is constant over the area where the guided mode field is confined [2]. This is not usely the case of the refractive index difference associated to gratings, since the cladding is far less photorefractive than the germanium-doped core. One way to solve the problem is to obtain the same refractivity in a region of a few core diameters and to ensure a constant UV illumination intensity in the same volume. This implies to modify the dopant concentration profiles of the fiber.

Optical fiber design for strong gratings photoimprinting with radiation mode suppression

A holographic method was used to write refractive-index gratings in ZBLAN fluoroziroconate glasses or fibers doped by a Ce concentration of 5000 or 10,000 parts-in-10(6) weight. Direct pumping of the (2)F(5/2)-5d transitions of Ce(3+) ions near 245 nm resulted in a change in the refractive index. The photoinduced change partly recovered on a time scale of several hours at room temperature. The remaining change in the refractive index looked stable on a time scale of a month. This permanent change reaches 2 x 10(-5) at 1560 nm.

Ultraviolet-induced permanent Bragg gratings in cerium-doped ZBLAN glasses or optical fibers.

1.55 mu m Bragg gratings have been written in cerium-doped fluorozirconate glass singlemode fibres through UV illumination at 246 nm. Photoinduced refractive index changes up to 4*10/sup -4/ have been achieved, leading to grating efficiencies close to 100%. Preliminary results on the thermal behaviour of the gratings and realisation of a tunable laser including such a grating are also reported. The ZBLALi (ZrF/sub 4/-BaF/sub 2/-LaF/sub 3/-AlF/sub 3/-LiF:Ce) glass composition was shown to be the most efficient.

M. Monerie

Papers

Gain control in erbium-doped fibre amplifiers by lasing at 1480 nm with photoinduced Bragg gratings written on fibre ends

Optical fibre Bragg grating sensors for structure monitoring within th nuclear power plants

Optical fiber design for strong gratings photoimprinting with radiation mode suppression

Ultraviolet-induced permanent Bragg gratings in cerium-doped ZBLAN glasses or optical fibers.

Efficiency and thermal behaviour of cerium-doped fluorozirconate glass fibre Bragg gratings