Optical transmission spectra of 2D photonic macroporous silicon structures are
investigated. The absolute bandgap for high values of the out-of-plane component kz is
situated between the second and third photonic bands. Essential reduction in the
transmittance of electromagnetic radiation and the step formation are observed for
wavelengths less than the optical period of structures due to directed and decay optical
modes formed by macroporous silicon as a short waveguide. The absorption in the
macroporous silicon structure is determined by a maximum of the longitudinal
component of electromagnetic waves, its interaction with 2D surface oscillations, and the
appearance of polaritonic resonances.