  Proposed all optical amplification scenario is based on the properties of
light propagation in two coupled subwavelength metallic slab waveguides where
for particular choice of waveguide parameters two propagating (symmetric) and
non-propagating (antisymmetric) eigenmodes coexist. For such a setup incident
beams realize boundary conditions for forming a stationary state as a
superposition of mentioned eigenmodes. It is shown both analytically and
numerically that amplification rate in this completely linear mechanism
diverges for small signal values.
