Optically amplifying planar glass waveguides: Laser on a chip

The objective of this work was to devlop optically amplifying planar wavguides, 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 of the films can be controlled by germanium co-doping. The method used for co-doping thins films with erbium and aluminium is described and it is shown that the erbium concentration as well as the relative eribum/aluminium content can be controlled with good precision.

The incorporated erbium ions are excited suing light of 980 nm wavelength and the optical spectrum 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 sluminium co-doping has a beneficial effect on the spectral width as well as on the absolute fluoresence level.

In addition the first measurement of the diffusion coefficient of erbium in silica is presented and it is shown that eribum rich precipitaties 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 carful choice of etching parameters.

This results in low propagation loss for the fabricated waveguides. It is shown that the achivable population inversion depends on the erbium concentration and the relative erbium/aluminium content. 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 change 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.