A consideration of fabrication-induced imperfections in photonic crystals for optical frequencies

We analyze fabrication-induced imperfections and disorder in our photonic crystals (PC) fabricated by micro-system technologies. Based on a correspondence between holograms and photonic crystals, we introduce technological figures of merit valid for arbitrary PC structures. We use these figures of merit to analyze a practical example of a 1D PC structure. For this purpose, we designed our PCs for the middle-wavelength infrared range using the transfer matrix technique and fabricated them in silicon/silica using RF sputtering. We used scanning electron microscopy to determine the cross-sectional geometrical parameters of PCs and to find their deviations from the designed values. Fourier infrared spectroscopy was used to measure spectral transmittance of the samples. The observed imperfections result in spectral transmission curves deviating from the designed characteristics, and reduce overall transmission by scattering. The presented analysis enables the prediction of attainable quality of PCs. The approach is applicable to 1D, 2D or 3D photonic crystals.