Bismuth germanate (Bi4Ge3O12) BGO is an interesting material for a wide range of optical sensing applications. The high electro-optic coefficient makes BGO suitable for high voltage and field sensing applications with high accuracy . Further, single crystals are used as scintillator in combination with photo multiplier tubes or avalanche photodiodes. Arrays of these scintillator devices are used for positron emission tomography (PET), a common medical imaging system. However, the size of crystals arrays limits the resolution and makes the system expensive. To fully enhance the potential of this material in integrated optical circuits the fabrication of buried waveguides by ion implantation has been discussed . The highly flexible technique of optical waveguide writing by tightly focused femtosecond laser pulses is a promising alternative; however, the inscription of positive index changes in crystals is difficult due to the crystal lattice.