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We report here a study on extrinsic propagation losses in silicon slot photonic crystal waveguides. This specific geometry of hollow slow light waveguides offers an exceptional platform for the integration of active materials on silicon because of the strong light/matter overlap and the flexibility in dispersion engineering at moderate group indices that it allows. However, the exploitation of slow modes simultaneously increases the propagation losses as it has been already demonstrated in non-slotted waveguides. We present in this work an experimental study of the influence of the e-beam and etching fabrication steps of photonic structures on the level of propagation losses in both the fast and slow wave propagation regimes and for the first time in slotted configuration. We have studied the influences from the e-beam lithography exposure method and dose control for periodic pattern writing, and measured the level of propagation losses as a function of the group index of the excited Bloch modes. The collected results have revealed a strong influence of the stages of fabrication of the structures and opened the way to a possible technological optimization of the propagation losses of slotted slow light waveguides. Among the points to be remarked, we have observed that the lithographic writing of the slot in a truncated way could lead to a reduction of propagation losses in the light propagation regime with a group index greater than 15. Our qualitative interpretation of these results is that by imposing certain constraints on the scanning of the electron beam, we induce a modification of the auto-correlation function which characterizes the fabrication roughness of the edges of the slot of the waveguides. Additional approaches will be presented, opening the optimization of slotted waveguide for diverse applications.
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