A PHOTONIC TRANSISTOR

A PHOTONIC TRANSISTOR, which uses one laser to control the
amplification of signals in another laser beam, has been developed
by researchers at the National Institute of Advanced Industrial
Science and Technology in Tsukuba, Japan (Junji Tominaga, 81-
298-61-2924, j-tominagaaist.go.jp). The development represents
the latest attempt to streamline optical systems (see also Updates
340 and 413). In contemporary optical devices, signals encoded in
light must be converted to electrical signals to be manipulated and
subsequently converted back to light for transmission. The scheme
leads to complex hybrids of optical and electrical components,
with high speed optical data transmission interrupted by sluggish
electronics. The novel optical transistor involves two lasers, one
red and one blue, focused at the same spot on a thin film composed
of metal and plastic layers. The lasers form energy-storing
plasmons, local groups of collectively moving electrons, on the
surface of the film. One of the lasers, usually the red one, also
generates a light-scattering particle of silver in a layer of silver
oxide that comprises a portion of the film. The silver particle
couples energy from the plasmons into the other laser beam,
enhancing a signal in the blue beam by up to sixty times. The
power of the red beam determines the size of the scattering silver
particle and, therefore, regulates the magnitude of the energy
coupled from the plasmons and the resulting amplification. If the
new device can be sufficiently perfected, photonic transistors may
become building blocks in all-optical circuits analogous to, but
much faster than, modern electrical circuitry. (J. Tominaga et al,
Applied Physics Letters, 23 April 2001.)