Formation of reconfigurable optical channel waveguides and beam splitters on top of proton-implanted lithium niobate crystals using spatial dark soliton-like structures

We report on the formation of reconfigurable optical channel waveguides (including straight stripes and Y-branches) on top of iron-doped lithium niobate crystals. The sample surface is first implanted by 500 keV protons to form a planar waveguide showing a propagation loss of ~1.6 dB cm−1 after modest post-implantation annealing. Afterwards, the sample surface is illuminated with well-defined stripe patterns (straight channels, beam splitters) of green light using lithographic masks. Due to the photovoltaic effect in lithium niobate resulting in negative index changes in illuminated regions, waveguide layers are formed in the non-illuminated regions perpendicular to the planar waveguide in the same way as it occurs in the dark spatial soliton regime. In this way two-dimensional waveguides are formed in the overlap region on top of the crystal that may be used for reconfigurable optical interconnections and splitters.