The Effect of Absorption Losses on the Optical Behaviour of Macroporous Silicon Photonic Crystal Selective Filters

Abstract

The effect of losses in photonic crystal structures on transmittance and reflectance has been studied by numerical techniques, and compared to fabricated macroporous silicon samples. Material absorption and tolerances of the pores play an essential role in determining performance in optical applications. The relevance of the structure geometry has been investigated through the porosity. The considered photonic crystals in this paper are 3-d macroporous silicon structures fabricated by electrochemical etching with pore profile modulation, and defect inclusion. The examined structures are intended to work with quasi-normal light incidence as selective filters. The effect of losses on the forbidden band and resonance is studied and reported for both transmittance and reflectance. The reflectance peak is less affected by losses, while transmitted light experiences a noticeable reduction even for small absorption factors. This has critical implications for the performance of these structures as transmission filters. Furthermore, it is shown that an optimum can be found for a given absorption coefficient by choosing the appropriate porosity.