Photonic circuit in which optical force is harnessed to drive
nanomechanics. (c) H. Tang, Yale University
Science fiction writers have long envisioned sailing a
spacecraft by the optical force of the sun's light. But, the
forces of sunlight are too weak to fill even the oversized sails
that have been tried. Now a team led by researchers at the Yale
School of Engineering and Applied Science has shown that the
force of light indeed can be harnessed to drive machines - when
the process is scaled to nano-proportions.
Their work opens the door to a new class of semiconductor
devices that are operated by the force of light. They envision a
future where this process powers quantum information processing
and sensing devices, as well as telecommunications that run at
ultra-high speed and consume little power.
The research, appearing in the 27 November issue of Nature,
demonstrates a marriage of two emerging fields of research -
nanophotonics and nanomechanics. - which makes possible the
extreme miniaturisation of optics and mechanics on a silicon
The energy of light has been harnessed and used in many ways.
The 'force' of light is different - it is a push or a pull
action that causes something to move.
'While the force of light is far too weak for us to feel in
everyday life, we have found that it can be harnessed and used
at the nanoscale,' said team leader Hong Tang, assistant
professor at Yale. 'Our work demonstrates the advantage of using
nano-objects as 'targets' for the force of light - using devices
that are a billion-billion times smaller than a space sail, and
that match the size of today's typical transistors.'
Until now light has only been used to manoeuvre single tiny
objects with a focused laser beam - a technique called 'optical
tweezers.' Postdoctoral scientist and lead author, Mo Li noted,
'Instead of moving particles with light, now we integrate
everything on a chip and move a semiconductor device.'
'When researchers talk about optical forces, they are generally
referring to the radiation pressure light applies in the
direction of the flow of light,' said Tang. 'The new force we
have investigated actually kicks out to the side of that light
While this new optical force was predicted by several theories,
the proof required state-of-the-art nanophotonics to confine
light with ultra-high intensity within nanoscale photonic wires.
The researchers showed that when the concentrated light was
guided through a nanoscale mechanical device, significant light
force could be generated - enough, in fact, to operate nanoscale
machinery on a silicon chip.
The light force was routed in much the same way electronic wires
are laid out on today's large scale integrated circuits. Because
light intensity is much higher when it is guided at the
nanoscale, they were able to exploit the force. 'We calculate
that the illumination we harness is a million times stronger
than direct sunlight,' adds Wolfram Pernice, a Humboldt
postdoctoral fellow with Tang.
'We create hundreds of devices on a single chip, and all of them
work,' says Tang, who attributes this success to a great optical
I/O device design provided by their collaborators at the
University of Washington.
It took more than 60 years to progress from the first
transistors to the speed and power of today's computers.
Creating devices that run solely on light rather than
electronics will now begin a similar process of development,
according to the authors.
'While this development has brought us a new device concept and
a giant step forward in speed, the next developments will be in
improving the mechanical aspects of the system. But,' says Tang,
'the photon force is with us.'
Tang's team at Yale also included graduate student Chi Xiong.
Collaborators at University of Washington were T. Baehr-Jones
and M. Hochberg. Funding in support of the project came from the
National Science Foundation, the Air Force Office of Scientific
Research and the Alexander von Humboldt post-doctoral fellowship