We propose a simple model to elucidate the dispersion behavior of spiraling modes on silver nanowire by finding correspondence parameters and building a simple equivalent relationship with the planar insulator-metal-insulator geometry. The characteristics approximated for the proposed structure are compared with the results from an exact solution obtained by solving Maxwell's equation in cylindrical coordinates. The effective refractive index for our proposed equivalent model is in good agreement with that for the exact solution in the 400-2000 nm wavelength range. In particular, when the radius of the silver nanowire is 100 nm, the calculated index shows typical improvements; the average percentage error for the real part of the effective refractive index is reduced to only 5% for the $0^{th}$ order mode (11.9% in previous results) and 1.5% for the $1^{st}$ order mode (24.8% in previous results) in the 400-800 nm wavelength range. This equivalent model approach is expected to provide further insight into understanding the important behavior of nanowire waveguides.

Keywords: Silver nanowire, Planar insulator-metal-insulator geometry,

OCIS codes: 240.6680; 250.5403; 230.7370