Spatial distribution effects and laser efficiency in Er/Yb-doped fibers

Abstract

It is well known that the efficiency of silica based Er/Yb fiber lasers and amplifiers can be greatly enhanced by a high level of phosphorus co-doping. The interaction of phosphorus with the rare earths and with the further co-dopant aluminium during the preparation process leads to peculiar effects concerning chemistry of dopant incorporation, diffusion behaviour and microscopic glass structure. Until now however, it has been disregarded that these interactions give rise to strong radial and even axial concentration profiles in preform and fiber (for the codopants phosphorus and aluminium, but also for the rare earth components erbium and ytterbium) with remarkable consequences for the laser efficiency. Here, we have studied the incorporation mechanism and the diffusion behaviour (diffusion coefficients in dependence on temperature and concentrations) by X-ray microprobe analysis concerning the dopant interaction effects. Moreover, we have investigated both fluorescence intensities and lifetimes, radially and axially resolved in the fiber preforms. The results were correlated with the properties of double clad fiber lasers made from these preforms. First attempts have been undertaken to interpret and control the incorporation mechanism on the basis of model calculations regarding phosphorus diffusion and chemistry.

Measuring the spatial distribution of rare-earth dopants in high-power optical fibers

“…Unlike wavelength dispersive X-ray analysis [14][15][16] , which provides a spatially resolved map of each constituent doping element, the present technique does not directly measure the local concentration of rare-earth but instead is based on the optical intensity of the spontaneous emission (SE) of the rare-earth doped glass. By directly measuring the SE, the technique described here reveals the relative gain (assuming uniform optical pumping).…”

“…Furthermore, spectroscopic changes are known to occur during the draw process, as is reorganization of the dopant concentration due to dopant diffusion, especially in co-doped glasses hosting rare-earths 14,15 . Finally, some complex fiber designs can only be assembled on the draw tower and therefore there is no preform available for analysis prior to draw.…”

“…While spatially resolved spectroscopy can be performed in an optical fiber preform 14 , it is much harder in a drawn fiber due to the much smaller dimensions of the sample. Furthermore, spectroscopic changes are known to occur during the draw process, as is reorganization of the dopant concentration due to dopant diffusion, especially in co-doped glasses hosting rare-earths 14,15 .…”

Effect of Er⁺³ Concentration on the Small Signal Gain Coefficient and the Gain in the Erbium Doped Fiber Amplifier

“…For example, Chernyak and Qian (2002) established modeling highconcentration L-band EDF A at high optical powers based on inversion function. Johannes (2004) reported spatial distribution effects and laser efficiency in Er/Yb-doped fibers. Wei et al (2004) utilized a genetic algorithm to optimize multistage erbium-doped fiber amplifier systems with complex structures.…”