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 77 K on Bi4Ge3O12 crystals doped with different rare earth ions of Nd, Er, Tm, 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 ion beam modified the surface of the bulk material in such way that within the region of the waveguide, the structure becomes anisotropic. This was observed 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 into an anisotropic guide layer, resulting in a net optical rotary power around 4.1 degrees/mm for 632.8 nm wavelength. (C) 1999 Elsevier Science B.V. All rights reserved.