Strong Off-Resonant Enhancement of Spontaneous Emission in   Metal-Dielectric-Metal Plasmon Waveguide Structures
  We theoretically investigate the spontaneous emission process of an optical, dipolar emitter in metal-dielectric-metal slab and slot waveguide structures. We find that both structures exhibit strong off-resonant emission enhancements due to the tight confinement of modes between two metallic plates. The large enhancement of surface plasmon-polariton excitation enables dipole emission to be preferentially coupled into plasmon waveguide modes. These structures find applications in creating nanoscale local light sources or in generating guided single plasmons in integrated optical circuits. 
Y.C. Jun, R.D. Kekapture, J.S. White, and M.L. Brongersma