HARVARD, USA – A Harvard-led research team guided by Federico Capasso at SEAS has discovered a special type of light beam which can propagate over an unprecedented distance without spreading out. While the team calls it a “needle beam”, it’s technically a cosine-Gauss plasmon beam.
A special type of quasi-particles named surface plasmons, confined to metal surfaces, give rise to this beam. Not being hindered by diffraction (lateral spreading of light), the entire beam reaches the intended destination, eliminating the loss of optic signals. Since metallic stripes can easily replace copper interconnects in microprocessors, this will eventually give birth to ultrafast on-chip optical communication.
Experiments have shown that the “needle beam”, a localized surface plasmon wave, can propagate in a straight line of 80 microns in length, without diffraction. It was demonstrated with a metallic grating created with two grooves etched into a gold film. Laser illumination caused the constructive interference of two tilted, plane surface waves, resulting in the “needle beam” visible through an ultrahigh-resolution microscope.
Since it’s already known to travel efficiently at a gold-air interface, the “needle beam” is believed to be the first step towards ultra-powerful optical microprocessors that should lead to faster and less power-hungry mobile processors in the near future.