Two-Particle Parasitic Effects in Rare-Earth Doped Waveguides

B. Jaskorzynska
1999 Acta Physica Polonica. A  
This paper discusses Er-doped optical waveguides implemented in glass materials. The emphasis is put on physical limitations posed by concentration dependent nonlinear effects and on methods for their characterization. Examples of recently demonstrated, best performance integrated active devices are also given. PACS numbers: 42.65.-k Optical fibers and planar waveguides can be made active, i.e. exhibit amplification, by inserting rare-earth ions in their core. Most of the related research has
more » ... en focused on fibers and planar waveguides doped with erbium (Er) because . they provide gain at the 1.5 µm band, which is of particular interest for telecommunication applications. For pumping Er ions one typically uses laser diodes at 980 nm or 1.48 µm, as it is illustrated in Fig. 1 . Planar active waveguides are considered to be an attractive option for realizing integrated optical devices with gain [1, 2]. A prerequisite for realizing practical active devices is that a sufficiently large gain can be obtained at reasonable pumping powers. While this can easily be achieved in a few meter long active fibers, their planar counterparts tend to suffer from low gain efficiencies. Apart from much higher losses, the main difficulty is that a usable gain must be accumulated over a much shorter (a few centimeters) length. This. typically requires two orders of magnitude higher Era+ concentrations, at which parasitic energy transfer between excited Er-ions reduces the gain [3-10]. The mechanism of the parasitic effect is illustrated in Fig. 2 . The excitation energy (1) is transferred (2) from one excited ion (donor) to the other (acceptor), which typically occurs via electric dipole-dipole interaction. Consequently the donor relaxes (2) to the ground state while the acceptor is upconverted to the 4I9/2 state (2). This is usually followed by two fast, non-radiative relaxation processes (3,4a) down to the metastable level 4 l13/2. However, a small fraction of the ions relaxes to the ground level (4b) emit-. ting photons at 980 nm. As a result only one of the two pump photons absorbed by the Er ions can be used for amplification at 1.5 µm. The energy of the other *
doi:10.12693/aphyspola.95.743 fatcat:dgfm52om4ncthkr4zlr3uuwkeq