Fabrication and characteristics of three-dimensionally buried porous silicon optical waveguides

A fabrication technology of three-dimensionally buried porous silicon (PS) optical waveguide with an extremely high refractive index contrast is prese nted, including its fundamental properties. The origins of attenuation loss es are investigated by experimental and theoretical analyses in terms of mi croscopic observations, edge emission measurements, polarization mode deter mination of guided wave, and evaluation of bending loss. The results of the se studies indicate that attenuation losses in PS waveguides are due to sel f-absorption by residual silicon, structural and optical inhomogeneities in the core region, and roughness at interfaces between the core and the clad ding layers. Some possible ways for reducing these attenuation losses are d iscussed. It is also demonstrated that a buried bent PS waveguide with an e xtremely small curvature of 250 mu m can be fabricated by simple planar pro cessing, and that a visible optical wave propagates along it owing to a sig nificantly high refractive index contrast between the core and the cladding layers. (C) 1999 American Institute of Physics. [S0021-8979(99)01321-3].