  The results of spectroscopic studies of the diffraction anomalies (the
so-called resonant Wood anomalies) in spatially-periodic hybrid structures
based on halcogenide (GST225)-coated opal films of various thickness are
presented. A theoretical analysis of spectral-angular dependencies of the Wood
anomalies has been made by means of a phenomenological approach using the
concept of the effective refractive index of waveguiding surface layer.
