Spotlight on Plasmon Lasers

A plasmonics-based design approach is enabling coherent light sources to be built at the nanometer scale. Lasers are the workhorse of the information age, sending massive amounts of light packets through vast networks of optic fibers. Demands for ever-increasing speed and functionalities call for scaling down of photonic devices, similar to the trend in electronics. However, photonic devices face the fundamental challenge of the diffraction limit of light—a limitation that prevents squeezing light into spaces smaller than half of its wavelength. This barrier limits traditional optical components to sizes that are hundreds of times larger than that of their electronic counterparts. Surface plasmons are collective electronic oscillations on a metal-dielectric interface with a much smaller wavelength than the excitation or emitted photons, and have emerged as a promising solution to overcome such a barrier (1). In 2003, the surface plasmon laser or “spaser” was theoretically proposed. The idea was to tightly confine light in the form of localized plasmons into deep subwavelength dimensions overlapping with a gain medium to achieve stimulated emission and light amplification or lasing, creating a coherent light source at the nanometer scale (2). That proposal is now being realized with several plasmonics-based design approaches being used to fabricate nanometer-scale coherent light sources.