Tailoring of the Local Environment of Active Ions in Rare-Earth- and Transition-Metal-Doped Optical Fibres, and Potential Applications

Abstract

During the last two decades, the development of optical fibre-based sophisticated devices have benefited from the development of very performant optical fibre components. In particular, rare-earth (RE)-doped optical fibres have allowed the extremely fast development of fibre amplifiers for optical telecommunications (Desurvire, 1994, 2002), lasers (Digonnet, 2001) and temperature sensors (Grattan & Sun, 2000). The most frequently used RE ions are Nd3+, Yb3+, Er3+ and Tm3+ for their optical transitions in the near infrared (NIR) around 1, 1.5 and 2 μm. A great variety of RE-doped fibres design have been proposed for specific applications: depending of the RE concentration and nature of the fibre glass, various schemes (in terms of electronic transition within the RE populations) have been implemented. For example, Er3+-doped fibre amplifiers (EDFA) for long haul telecommunications use the very efficient 1.55 μm optical transition, whereas high concentrations of Yb3+ and Er3+ codoped in the same fibre allowed efficient non-radiative energy transfers from the ‘sensitizer’ (Yb3+) to the ‘acceptor’ (Er3+) in order to increase the power yield of the system, applied in power amplifiers and lasers. All the developed applications of amplifying optical fibres are the result of time consuming and careful optimization of the material properties, particularly in terms of dopant incorporation in the glass matrix, transparency and quantum efficiency. RE-doped fibres are made of a choice of glasses: silica is the most widely used, sometimes as the result of some compromises. Alternative glasses, including low maximum phonon energy (MPE) ones, are also used because they provide better quantum efficiency or emission bandwidth to some optical transitions of particular RE ions. The icon example is the Tm3+-doped fibre amplifier (TDFA) for telecommunications in the S-band (1.48-1.53 μm) (Komukai et al., 1995), for which low MPE glasses have been developed: oxides (Minelly & Ellison, 2002; Lin et al., 2007), fluorides (Durteste et al., 1991), chalcogenides (Hewak et al., 1993), etc. Although some of these glasses have a better transparency than silica in the infrared spectral region (above 2.3 μm), for applications in the NIR these glasses have some drawbacks not acceptable at a commercial point of view: high