Transverse magnetic modes in hybrid nanoslot waveguides

Abstract

Light enhancement and confinement in a nanometer-wide low-index material was proposed and demonstrated in a low index slot waveguide (LISW). To further reduce the mode width, a 5-layer metal/high index/low index/high index/metal hybrid nanoslot waveguide (HNSW) was constructed by replacing the outmost layer of LISW with a metal layer in which only TM modes exist. In this work, we analytically solve the guided-wave modes in the HNSW that are divided into six types according to the effective refractive index and the symmetry of the field distribution, and derive their dispersion equations and discuss the cut-off conditions. Two new guided-wave modes appear in HNSW that do not exist in the LISW structure. The abilities of light confinement of zero-order even modes between the HNSW structure and the LISW structure are compared, and the HNSW shows stronger light-confined ability and narrower mode than LISW, which makes it possible to simultaneously increase light-confined ability and reduce mode width in HNSW. For the specific Au/Si/SiO2/Si/Au HNSW, considering the metal loss will not change the basic properties of the zero-order modes at 1550 nm, except that the mode propagation length is reduced to a few microns.