Propagation characteristics of surface-plasmon waveguides operating in the mid- and far infrared: Nonperturbative approach

Abstract

The modal propagation characteristics of metal surface-plasmon waveguides (MSPWs) containing n-doped multiple quantum wells with normal and inverted subband occupation are studied theoretically. “Ordinary” (“enhanced”) waveguides modeled by simple three (four) media structures are considered. The appropriate dispersion equations are derived employing the transfer-matrix approach and solved numerically. Analytical solutions are also obtained employing the thin-layer approximation. Special attention is paid to the role of the coupling between the modes guided by passive MSPWs and the intersubband plasmon. The obtained results indicate that modification of the propagation characteristics induced by the above-mentioned coupling plays a very important role. We show that the commonly used perturbed approach based on the concept of the confinement factor has a restricted range of applicability, particularly in the case of the ordinary MSPWs.