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Quantum-Dot Optical Switch
Only 140 photons switch energy in a solid-state device
An optical switch developed at the Joint Quantum Institute (JQI)
spurs the prospective integration of photonics and electronics. The
JQI switch can steer a beam of light from one direction to another in
only 120 ps using only about 90 attojoules of input power. At the
wavelength used, in the near infrared (921 nm), this amounts to
about 140 photons.
In the PFC-supported experiment, an all-optical switch has been
created using a quantum dot placed inside a resonant cavity, within a
photonic crystal. When light travels down the nearby waveguide
some of it makes its way into the cavity, where it interacts with the
quantum dot.
It is this interaction which transforms the waveguide’s
transmission properties. Previous optical switches have been able to
work only by using bulky nonlinear-crystals and high input power.
The switch, by contrast, achieves high-nonlinear interactions using a
single quantum dot and very low power input. Switching required
only 90 aJ of power, some five times less than the best previous
reported all-optical switch, albeit at a temperature of around 40 K.
JQI researcher Ranojoy Bose says he expects an improvement
(reduction) in the number of photons needed to switch the resonant
cavity on and off. In the meantime, the switch represents a great
start toward creating a usable ultrafast, low-energy on-chip signal
router. The paper shows that switching can be achieved physically by
using only 6 photons of energy, which is completely unprecedented.
This is the achievement of fundamental physical milestones—sub100-aJ switching and switching near the single photon level.
Figure: Setup of a waveguide made from a photonic crystal. A
quantum dot (QD) is placed inside a tiny zone (cavity) clear of holes.
Light is sent into and out of the waveguide via endcaps (the semicircular structure at both ends, indicated by green arrows). If
properly timed, a pump (control) laser pulse will allow an
accompanying probe pulse to exit out the side. If the probe and pump
beams are not aligned, the probe beam will exit out the far end of the
waveguide. (Figure from Ranojoy Bose.)
“Low photon number optical switching with a single
quantum dot coupled to a photonic crystal cavity,”
Deepak Sridharan, Ranojoy Bose, Hyochul Kim, Glenn S.
Solomon, and Edo Waks, Physical Review Letters, in press.