WAVE PROPAGATION THROUGH A WAVEGUIDE SEGMENT WITH RANDOMLY CORRUGATED WALLS: DUAL NATURE OF THE LOCALIZATION

A theory of wave propagation in waveguides incorporating a finite-length segment with randomly corrugated side boundaries is developed. We have shown that the dominant role in the waveguide state formation is played by the so-called gradient scattering mechanism, which is associated with surface asperity sharpness but not with their amplitude. The corrugated portion of the waveguide may be regarded as the modulated potential barrier, whose width is coincident with the length of the corrugated region whereas the height is determined by the corrugation sharpness. There are two possible types of wave localization in such a system. The first one manifests itself through the sharpness-induced mode cut-off which leads to rarefication of the entire (combined) waveguide spectrum, so that at some critical level of the asperity sharpness the waveguide becomes the evanescent-mode one. The other type of localization is a localization of Anderson nature. It is associated with multiple scattering of waves by random fluctuations of the effective potential. We have predicted a jump of the full transmittance of the waveguide at its transition to single-mode regime due to the mode cut-off. This phenomenon is associated with the absence of the inter-mode scattering in the single-mode regime.