1 Department of Photonics Engineering, Technical University of Denmark2 DTU Danchip, Technical University of Denmark3 Department of Micro- and Nanotechnology, Technical University of Denmark
The objective of this work was to develop optically amplifying planar waveguides, using erbium-doped germano-silicate glass films deposited by PECVD (Plasma Enhanced Chemical Vapour Deposition). The waveguides should exhibit enough gain to be useful as optical amplifiers in integrated planar lightwave circuits, as well as provide the gain medium for integrated planar waveguide lasers. The work and the obtained results are presented in this thesis: The manufacturing of silica thin films is described and it is shown that the refractive index o fthe films can be controlled by germanium co-doping. the method used for co-doping thin films with erbium and aluminium is described and it is shown that the erbium concentration as well as the relative erbium/aluminium content can be controlled with good precision. The incorporated erbium ions are excited using light of 980 nm wavelength and the optical sepctrum of the induced fluorescence is analysed. It is shown that the spectral distribution as well as the absolute level of the fluorescence is influenced by post-processing annealing temperature, and that aluminium co-doping has a beneficial effect on the spectral width as well as on the absolute fluorescence level. In addition the first measurement of the diffusion coefficient of erbim in silica is presented and it is shown that erbium rich precipitates are formed in areas of high erbium concentration. The manufacturing of planar waveguide structures using RIE (Reactive Ion Etching) is described and it is shown that sidewall roughness resulting from micro masking by non-volatile reaction products can be minimised through a careful choice of etching parameters. This results in low propagation loss for the fabricated waveguides. It is shown that the achievable population inversion depends on the eribum concentration and the relative erbium/aluminium contenct. Waveguides with a gain factor of 0.3 dB/cm are presented and used to fabricate a loss less lightwave circuit consisting of an amplifier-and a splitter section. It is shown that the refractive index of the fabricated amplifying waveguides can be changed with UV-light and that permanent Bragg-gratings can be induced. Planar waveguide lasers with integrated Bragg-gratings are manufactured and characterised. It is shown that linewidths below 125 kHz and output powers around 0.5 mW can be obtained, and that the manufactured lasers are resistant to mechanical as well as thermal influence. A simple method for producing an array of planar waveguide lasers is presented and it is shown that the difference in output wavelength of the individual lasers can be controlled with great accuracy.