Optical Characterization of High-Order 1-D Silicon Photonic Crystals

In this paper, we present numerical and experimental results on the spectral reflectivity of hybrid, high-order (up to 22nd) 1-D silicon photonic crystals (PCs) in the near-infrared region (wavelength range 1– $1.7\ \mu $m). Mechanically robust, vertical 1-D PCs with high aspect ratio and spatial period of $8\ \mu $m were fabricated by electrochemical micromachining of silicon, and tested in reflection with an improved optical setup, incorporating standard telecommunication single-mode optical fibers and a lensed fiber pigtail. A detailed theoretical, numerical analysis was performed to assess the effects of both non-idealities of the structures under test and constraints of the optical setup, on the spectral reflectivity. Experimental data were found in very good agreement with theoretical calculations, performed by using the characteristic matrix method, keeping into account an in-plane porosity variation for 1-D PCs, due to surface roughness of silicon walls, and the limited resolution bandwidth of the spectrum analyzer. Best optical performances, measured on the fabricated 1-D PC mirrors, consist of optical losses less than 0.8 dB in a bandgap around $1.5\ \mu $m and a $-$35 dB reflectivity minimum at a bandgap edge.