Alain Chandonnet

High-power Q-switched erbium fiber laser using an all-fiber intensity modulator

The authors report on the demonstration of a Q-switched erbium-doped fiber laser using a novel all-fiber intensity modulator acting as an efficient intracavity switching element. Switching speed and holdoff losses are compatible with the Q-switching dynamics of rare-earth-doped fiber lasers. The modulator is completely integrated in a spliceless erbium-doped fiber cavity. Pulses of less than 15 ns full width at half maximum (FWHM) and peak power close to 400 W were obtained for a launched pumping power of 100 mW at 980 nm. This compact source could find many uses in applications such as nonlinear optics, laser ranging and remote sensing, eyesafe free-space communication, time-gated fiber sensor systems, and long-distance optical time-domain reflectometry.

Photoinduced absorption in thulium-doped ZBLAN fibers.

We report on the observation of photoinduced absorption in four different thulium-doped ZBLAN fibers exposed to 1.12-μm light. The darkening rate is shown to follow a fourth-power dependence on the pumping intensity and a strong dependence on the Tm3+ concentration. The photoinduced absorption is observed mainly in the UV–visible part of the spectrum but extends slightly beyond 1 μm in the near-infrared.

Photobleaching of thulium-doped ZBLAN fibers with visible light.

Photobleaching of darkened thulium-doped ZBLAN fibers is observed after short exposure to visible light. The bleaching process is characterized by a stretched-exponential function of time with an exponent beta independent of both the bleaching intensity and the thulium concentration. The bleaching rate 1/ is also shown to scale linearly with the bleaching intensity and to have a 1/3 -power dependence on the thulium concentration. Incomplete and slow recovery of the color centers is observed in previously bleached fibers, suggesting the presence of at least two types of defect.

Thulium-doped ZBLAN fiber laser

The thulium-doped ZBLAN fiber laser is emitting visible radiation through an upconversion process which allows for the generation of hundreds of milliwatts of output power at 480 nm. The main features of this laser are presented and analyzed on the basis of an equation rate analysis. Cross- relaxation processes are shown to play an important role in the dynamical evolution of the population levels. The problem of the onset of a photo-induced absorption in the fluoride-glass matrix is also addressed in connection with its detrimental effects on laser operation. Practical solutions to this problem are explored.

Ultraviolet-induced color centers and annealing in thulium-doped fluorozirconate optical fibers

We have investigated the dynamics of color center formation (darkening) in a 1000 ppm thulium-doped ZBLAN (ZrF 4 -BaF 2 .-LaF 3 -AlF 3 -NaF) optical fiber by ultraviolet (285, 300, 351, 364 nm) and infrared (1112 nm) exposures. We observe that color centers are simultaneously created and photobleached by the UV light and that upon exposure to 1112 nm the color centers are thermally activated. We make the hypothesis that the mechanism responsible for the formation of color centers is a charge transfer to trap sites following the ionization of the glass matrix by an excitation from the 5d level of the thulium ion by ∼55 000 cm -1 . Also, thermal annealing of the color centers is investigated with the use of a standard stretched-exponential model. The annealing results are consistent with the assumption of a distribution of energies of color center states.

Stable blue emission from a 2500 ppm thulium-doped ZBLAN fiber laser

Summary form only given. A great interest in blue thulium-doped ZBLAN fiber lasers has developed in recent years due to their potential for hundreds of milliwatts of output power and simple configuration compared to frequency-doubled solid-state lasers. However, blue fiber lasers have been reported to suffer from a degradation of their performance over minutes or hours of operation. This degradation has been associated with the formation of color centers in the fiber core leading to an increase in the background losses of the fiber. In this paper, we demonstrate a stable 70-mW blue thulium-doped ZBLAN fiber and report on two different methods to restore the full transparency of darkened fibers.

SYNAPSE: an access network WDM test bench

SYNAPSE is a consortium of private companies and research centers associated in a pre-competitive effort to foster the development of new components, systems and applications likely to be needed in future transparent optical networks. It plans to deploy a high data rate DWDM-based test bench linking the Quebec, Rimouski and Montreal metropolitan areas to allow in situ validation of new components, sub-systems, network topologies and applications requiring large bandwidth. The scope and goals of this 5-year initiative, as well as technical aspects and distinctive features of the projected test bench, will be briefly reviewed in this article.

Lasing characteristics of a thulium-doped ZBLAN fiber laser at 481 nm

The main features of a thulium-doped ZBLAN fiber laser are presented and compared to the results of a numerical analysis. Particularly, the problem of the photoinduced absorption arising from the formation of color-centers is addressed with special attention to its detrimental effects on laser operation. Practical solutions to this problem are also explored.

All-fiber intensity modulator for Q switching

We present an efficient all-fiber intensity modulator designed for repetitive Q-switching of rare-earth doped fiber lasers. This device shows many advantages over standard bulk modulation technique like immunity to mechanical vibrations and lower excess losses. The principle of operation is simple and relies on the evanescent field coupling of the fiber mode to an overlay medium plate which is rapidly moved away from the surface of a standard polished coupler using a fast piezoelectric translator. A spliceless Q-switched erbium fiber laser incorporating this modulator was also tested.