The cut-off effect in slightly asymmetric systems prevents the wider practical usage of long-range surface polaritons (LRSP). Due to asymmetry caused by the presence of even a few nanometers wide air gap, the LRSP mode disappears. We propose a solution to this problem by using an effective medium approach. The basic idea is to compensate for the air gap induced asymmetry by introducing an additional layer into the system. That allows us to shift the cut-off to values sufficient for experimental observation of LRSP. Fourier transform infrared spectra of end-fire coupled LRSP in the GaAs/Au/GaAs multilayer system were measured in the (800-3000) cm(-1) range. Various geometric and polarization sensitive effects of the infrared system capable of influencing the LRSP coupling are discussed. A pronounced increase in the p-polarized light transmission at long-wavelengths is explained as an increase in the propagation distance L of LRSP. A fairly good fit between experimental and calculated curves was achieved at long wavelengths. (c) 2005 Elsevier B.V. All rights reserved.