Mode selective fibre coupling using long-range surface-plasmons

A number of in-line single-mode fibre devices, including polarizers and fibre sensors, have been reported using long-range surface plasmons (LRSPs). In these devices, a side-polished fibre half-coupler block is coated with a thin metal layer supporting a LRSP mode that phase-matches to the fibre mode. This produces a resonance condition at which light is coupled from the fibre mode to the LRSP. In this paper, we explore the use of this resonance condition (which under certain conditions has high finesse) for mode-selective coupling into a dual-mode fibre; envisaged applications include to modal division multiplexing