In integrated optics many functions (eg. splitting of signals) will result in a reduction of the output signal level of the component. One of the roles of active waveguides is to compensate for this loss. Amplification in the 1530-1560 nm wavelength range can be achieved by doping the waveguides with Er3+-ions, then optically pumping these ions into the metastable 4I13/2 state using an external laser source. A weak signal sent through the waveguide will then cause stimulated emission (to the ground state, 4I15/2) from these excited ions, resulting in amplification. The challenge is to incorporate the Er3+-ions into the host material (here a silica matrix) without having them clustering together, as this undesirable effect reduces the population of the metastable state and hence the amplification. In 1996 extensive studies of co-doping the Er-doped silica matrix with La and/or Al in order to reduce the degrading effects of Er-clustering have been performed. The lanthanum acts by mixing with the erbium and thus keeping these ions apart in the clusters, whereas the aluminum increases the solubility of Er in silica. Adequate levels of La to sufficiently separate the Er-ions in the clusters were not obtained in the studies, however the aluminum co-doping proved to be particular effective. This was verified by Transmission-Electron-Microscopy studies and in an optical characterisation set-up especially made for determination of clustering degrees in waveguides. A vital key to the success of active waveguides is the ability to combine sections of amplifying waveguides with passive waveguides (in which other functionality are performed) on the same chip. Development work on this aspect has been initiated in 1996. This, together with work initiated with NMRC, Ireland aiming at hybridising 980 nm laser diodes (the external laser source) are important steps towards highly complex and compact photonic devices.
|Period||01/01/96 → 31/12/99|