Oxide-free InP-on-Silicon-on-Insulator Nanopatterned Waveguides: Propagation Losses Assessment Through End-Fire and Internal Probe Measurements

Directly bonded, oxide-free, InP-based epitaxial layer bonding onto nanopatterned silicon-on-insulator structures was performed and result in waveguides with an embedded effective medium. Such a medium ensures flexible form of optical confinement and could also assist heat and electric current transfer optimally to the silicon layer since there is a remarkable absence of oxide, thanks to careful surface preparation processes. The fabricated waveguides, which embed buried 1-D (trenches) or 2-D (holes forming a photonic crystal) nanopatterns have been measured by two techniques. Either the classical end-fire technique, or the “internal light source” technique used for III-V-based photonic crystal waveguides, with a layer that contains several quantum wells. Propagation losses due to scattering in the nanopatterned area are retrieved by both methods and consistently point toward a ~20 cm^-1 loss level. A critical assessment is made of this result. Other local probe techniques allowed by the internal probe methods are reported that could help qualifying thermal transfer at these oxide-free interfaces.