Japanese research heralds optical transistors

17 Jun 2002

Local plasmon interactions enable one laser to amplify the signal from another.

In the latest step towards all-optical systems, Japanese scientists have developed a transistor that uses only two lasers and a thin film to create signal amplification in one of the lasers (see Applied Physics Letters 78 (17) 2417).

Junji Tominaga and colleagues at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, together with researchers H Fuji at Sharp and T Kikukawa at TDK demonstrated a photonic transistor by focusing two laser beams, one red and one blue, in one small spot on a high-speed rotating optical disk. The disk was coated with a thin film comprising metal and plastic layers. They found that the laser irradiation resulted in plasmons (entities in which metallic electrons group together to present a collective excitation) on the surface of the film. The plasmons interacted with a light-scattering particle of silver, which was created in the silver oxide part of the film by the red laser.

This interaction caused the local plasmon energy to couple into the blue laser beam, resulting in a large signal amplification - up to 60 times - whose magnitude could be controlled by the power of the red laser. The scientists believe that their system has the potential to realise photonic transistors containing only thin-film components.