Credit: © 2008 ACS

Surface plasmons — spatially localized electromagnetic fields that exist at metal–dielectric interfaces — are being investigated for the fabrication of next-generation telecommunications devices, as well as in fields such as biosensing. In particular, surface plasmons show potential for producing light emitters — known as surface plasmon polariton lasers — operating at industrially important wavelengths (∼1,500 nm). However, potential optical applications of surface plasmons are elusive because these electromagnetic waves do not travel very far in metals. As a result, there is intense interest in the development of metal–dielectric structures in which surface plasmons propagate over long distances. Now, Xiang Zhang and colleagues1 at the University of California, Berkeley, report the first direct observation of stimulated emission of surface plasmon polaritons (SPP) at a telecom wavelength (1,532 nm) from gold strips — 20-nm-thick and 8-µm-wide — embedded in erbium-doped phosphate glass.

Stimulated emission was induced by irradiating the edge of the erbium-bonded chip with signal SPP (1,532 nm) and pump SPP (1,480 nm) laser light, which travelled along the metal strip sandwiched in the erbium glass. The pump SPP excites active erbium ions in the glass to higher energy states, which then decay by spontaneous emission of light with the use of the signal SPP.

As well as SPP amplifiers and SPP lasers, the authors expect that the system could be useful in the development of integrated devices that couple electronic and photonic data transmissions.