Sapphire and Ti:sapphire buried waveguide structures

Due to its excellent thermal, mechanical, and optical properties, sapphire is one of the most suitable material for integrated optical devices. Although this hard crystalline material is particularly difficult to process, fabrication of Ti3+-doped sapphire surface channel waveguides by surface structuring [1,2] of planar waveguides or ion in-diffusion [3] has been demonstrated. Generally, device performance can be considerably improved by burying the guiding structure into the bulk of the sample. Advantages of buried waveguides derive not only from surface scattering losses being avoided, but also from a reduction in mode asymmetry compared to surface waveguides, thus providing higher efficiency for mode coupling to optical fibers. We reported the fabrication of complex waveguiding structures such as buried and stacked planar as well as buried single and parallel channel waveguides in sapphire by high-energy proton implantation [4]. Compared to the significant damage created in sapphire by He+ implantation, which resulted in poor waveguiding quality, protons create less damage in the guiding region, thus assuring better waveguiding quality. Moreover, deeper damage profiles are obtained with protons, for the same incident energy, thus providing larger design flexibility. Pure c-cut, optically polished sapphire substrates of dimensions 8 mm x 8 mm x 1 mm were irradiated by use of a Van de Graaf accelerator with incident ion energies of 0.4-1.5 MeV and doses of 1015-1016 ions/cm2. Good control of the implantation parameters enables writing of precisely localized optical barriers with well-defined decrease of refractive index, resulting in excellent confinement of the propagating light in each structure, with significantly reduced vertical mode asymmetry in the case of buried waveguides. Different mode shapes can be obtained by adjusting the implantation parameters, which demonstrates the versatility of the fabrication method. Fundamental-mode, buried channel waveguides with propagation losses