Fabrication and characterization of porous silicon integrated waveguides

Porous silicon (PS) has been known for quite a long time for its photoluminescence and for its usage as a sensing element. However, only in recent years this material has been proposed as a substrate for integrated optoelectronic devices and, despite the low fabrication costs and the possibility to tailor the refractive index varying the material porosity, its usage is still at the very beginning. In this paper we present the fabrication of integrated waveguides in PS and we describe our efforts to reduce the propagation losses. Different fabrication approaches have been studied: the first one uses selective anodization to obtain layers with different porosity and thus different refractive index. Another one exploits the different oxidation grades of the various porous layers to fabricate dense oxidized porous silicon waveguides. A detailed characterization of the obtained waveguides is reported. In particular, propagation losses as low as 7 dB/cm have been obtained in simple non-optimized multimode planar waveguides at the optical communication wavelength of 1.55 micrometers . This encouraging result paves the way to the next realization of porous silicon-based integrated optical devices for communication and sensing purposes. Finally, the results concerning a completely new approach, based on a laser ablation technique, to define the rib structure of porous silicon channel waveguides is presented.