Optical rotation in a Bi4Ge3O12 : RE surface modified by He-ion beam implantation

Planar optical waveguides have been formed by He-ion beam implantation at 7 7 K on Bi4Ge3O12 crystals doped with different rare earth ions of Nd, Er, T m, and Eu. The energy and the dose of the He-ion beam are 2 MeV and 5x10(16 ) ions/cm(2) respectively. The loss of the waveguides has been measured and improved with increasing annealing temperature up to 450 degrees C. The io n beam modified the surface of the bulk material in such way that within th e region of the waveguide, the structure becomes anisotropic. This was obse rved after 450 degrees C annealing. The evidence suggests this is due to a phase change of the BGO, which has been modified from the cubic structure i nto an anisotropic guide layer, resulting in a net optical rotary power aro und 4.1 degrees/mm for 632.8 nm wavelength. (C) 1999 Elsevier Science B.V. All rights reserved.