Optical stripe waveguides in lithium niobate formed by helium ion implantation.

The implantation of helium ions into lithium niobate produces a reduction in its refractive indices, due to radiation damage produced close to the end of the ion trajectories. This reduction can be utilised to form the boundaries of optical waveguides, which form the basis of any integrated optical circuit. Stripe waveguide fabrication using ion implantation has been demonstrated for the first time in this work. Firstly a buried damage layer was formed to define the depth of the waveguide, followed by additional implants around a gold mask to form the waveguide sidewalls. The gold mask was used to protect the guiding region during the latter implantation process. The waveguides were evaluated using the end-fire coupling technique to excite individual modes. Propagation loss and modal dimensions were determined experimentally for the fundamental mode of each guide, and it was shown that these properties are sensitive to both the ion energy of the wall implants, and the number of wall implants. Each of these two variables affects the propagation loss in the opposite sense to the other, and therefore the lowest propagation loss becomes dependant on the trade off between these two effects. The lowest loss of the waveguides presented in this thesis was found to be ~1 dB/cm, and it is expected that this figure may be further reduced by the optimisation suggested in the conclusions of this work. Additional results are presented which consider the electrooptic and photorefractive properties of ion implanted LiNbO3. Previous work of others suggested that the electrooptic effect would be considerably reduced in the implanted material, but the results were much more encouraging, showing a reduction of only ~20% in the r13 electrooptic coefficient. Furthermore, one of the most serious drawbacks of Ti:indiffused waveguides is the undesirable reduction of the output intensity due to the photorefractive effect, which has been shown not to affect the waveguides presented in this thesis