Formation of planar waveguides in bismuth germanate by⁴He⁺ion implantation

Planar optical waveguides have been formed in crystalline bismuth germanate (BGO) Bi 4 Ge 3 O 12 , by He + ion implantation. The refractive index profiles have been determined using a dark-mode technique at 0.6328 and 0.488 mu m. In the region of the electronic and nuclear stopping power of the ion beam in BGO there is an index enhancement, which forms an optical 'well'. This is stable up to approximately 200 degrees C, but then there is a gradual recovery of index up to 400 degrees C. Between 425 and 450 degrees C, for heavily implanted samples (>or=4*10 16 ions/cm 2 ), the well rapidly disappears, and is replaced by a sharp 'barrier' of reduced index. For lower dose implants (<4*10 16 ion/cm 2 ) at 450 degrees C many of the modes disappear without being replaced by a sharp barrier.