(color online) Some of the many small metallic and plasmonic lasers that have been proposed. (a) A metal-clad laser that couples its light efficiently to a waveguide.^[34] (b) Simulation of the structure of (a) showing the magnitude of the electric field and that laser light couples well to the waveguide.^[34] (c) A proposal for an extremely small “nanocoin” laser.^[41] (d) Another proposal for a waveguide-coupled nanolaser, but now employing a surface plasmon mode.^[50]