Effects of the equivalent coupling layer on ultra-long-range surface-plasmon-polariton waves

The mechanism and design of p- and s- polarized ultra-long-range surface-plasmon-polariton (SPP) propagation in the configuration {prism/ equivalent coupling layer (ECL)/ silver film (20 nm)/ equivalent substrate (ES)} are investigated using a normalized admittance diagram (NAD). The excitation of ultra-long-range SPP waves is characterized as a huge open loop of the NAD of the metal film at a designated angle of incidence. We propose three kinds of ECLs to complete the multilayer ultra-long-range SPP design: the normalized admittance of the ECL is (i) real (ii) infinite (iii) imaginary. The ultra-long propagation lengths in the three designs are compared at a wavelength of 632.8 nm for p- and s-polarization states.