Unusual eigenmodes of wire-medium endoscopes: impact on transmission properties

Wire-medium endoscopes represent a promising tool of THz sensing/imaging. Bending should not critically harm the endoscope operation and the issue of bending losses is that of key importance for any endoscope. In this paper we show that the frequency-averaged power transmittance of a wire-medium endoscope is weakly sensitive to the bending. However, the frequency dispersion of the power loss/transmittance of the endoscope is strongly oscillating. Frequency maxima of the loss factor result from unusual eigenmodes of an elongated wire medium sample. These modes comprise power vortices and their sensitivity to the sample bending seems to be a critical issue for the future of wire-medium endoscopes.