Abstract
We report the first electrooptic depolarization (TE guided wave to TM substrate modes) modulator on Y-cut LiNb03 proton-exchanged channel waveguides operating at 632.8 nm. The depolarization scattering associated with PE planar waveguides has also been consistently observed in PE channel waveguides. The phase matching condition of this scattering is NeffiCos(0) = No, where Neff is the effective index of the guided mode, 0 the coherent depolarization scattering angle, and No the ordinary index of the guiding layer. All the mode indices small than No can satisfy this equation. Since the proton exchange process only increases the extraordinary index of the guiding layer the TM scattered wave will automatically goes to the substrate. In this paper we use the combination of thermal annealing and external electric field to induce the coherent depolarization scattering. Tunability of the waveguide ordinary and extraordinary indices through thermal annealing provides an alternative way to reduce the drive voltage. 13.5 dB extinction ratio is achieved with 10 volt applied voltage on a modulator with 4 μm channel width and 3 mm electrode length. The measured capacitance is 4.2 pF which gives a theoretical modulation bandwidth of 1.5 GHz.