The focused
ion-beam tool developed at the NIST Center for
Nanoscale Science
and Technology can inject ions into the resonator,
creating tiny
bulges that affect the structure’s resonant properties—akin
to how a bell
maker can change the sound a bell makes by adding material and
changing its
shape. Credit: NIST
(December 23, 2015) Researchers
working at the National Institute of Standards and Technology (NIST) have
developed a novel way to noninvasively measure and map how and where trapped
light vibrates within microscale optical resonators.*
The new technique not only makes for more accurate
measurements but also allows scientists to fine-tune the trapped light’s
frequency by subtly altering the shape of the resonator itself.
Visualizing the vibration patterns will help scientists to
perfect ultrasensitive optical sensors for detecting biomolecules and even
single atoms. The fine-tuning capability will also open the door to creating
optical resonators with identical resonances, a feat now impossible to achieve
during manufacturing, but necessary for applications such as quantum
information processing with single photons.
Microscale optical resonators are like tiny bells that ring
not with sound, but with light. Just like a bell’s tone, the frequency with
which an optical resonator “rings” is determined by its size and shape, so that
it amplifies and sustains some frequencies of light and diminishes others.
The devices are so tiny that the light actually extends
outside their outer surfaces where they form “near-fields.” Where these
vibrating near-fields are strongest, the resonator is hypersensitive to changes
in the environment. Any perturbation of a near field, say by a stray molecule
or atom, will affect the light inside the resonator in a detectable way, much
in the same way that touching a ringing bell will change its tone or volume or
silence the bell altogether.
Mapping these vibration patterns of light in real devices
will help scientists to make them even more sensitive.
At present, the vibrational profiles of these resonators are
measured using sharp, needle-like probes. The problem with using a probe is
that it strongly disturbs the near-fields before it is able to get close enough
to the surface to do high-resolution imaging. High-resolution imaging of the
microresonator requires a probe that is able to reach the surface without
disturbing the near fields.