The University of Ghent (UGent) and the nanoelectronics research center IMEC
demonstrated repulsive and attractive nanophotonic forces, depending on the
spatial distribution of the light used. These fundamental research results might
have major consequences for telecommunication and optical signal processing.
Photon impulse is usually considered to be relatively weak. In our macroscopic
world, photons bumping into an object exert an almost negligible force on this
object. Nevertheless, this picture changes dramatically when the object size
is shrunk to nanoscale dimensions. When light is confined to very small cross-sections
and large gradients exist in the spatial field distribution of the light, the
optical gradient force induced per photon increases dramatically.
Using advanced fabrication technologies, including DUV (Deep Ultraviolet) lithography
and critical-point-drying, the researchers created two parallel waveguides on
a silicon-on-insulator chip. The waveguides are freestanding, acting as movable
strings. They have a width of 445nm, a height of 220nm, a length of approximately
25µm and they are separated by a 220nm gap.
By sending laser light through the waveguides the researchers generated optical
forces between them. Depending on the spatial distribution of the light (both
in amplitude and phase) the strings were attracting or repulsing each other.
The repulsive force that had never been demonstrated before makes this experiment
of fundamental scientific importance.
The experiment might eventually have a major impact to achieve very high speed
telecommunication for optical forces provide an interesting option for implementing
all-optical signal processing functions on a chip. All-optical routing is one
of the key challenges in developing faster communication networks (such as the
internet) and the new technique opens up new routes towards solutions for this
The detailed experimental results will be published in the August issue of
the premier scientific journal Nature Nanotechnology, however, they are already
available online (DOI 10.1038/NNANO.2009.186).