Signal Processing - March 2016 - 14

wavelength is calculated as the ultimate
as the sensing material for an optical
signal. "Due to the independence of each
Fabry-Perot cavity (a small light-trappeak wavelength, the random noise of
ping device, approximately a millionth
the average wavelength has been subof an inch wide, built out of small, halfstantially suppressed," Han says. "We
silvered mirror), which forms the basis
use curve fitting to find the peak waveof the sensing scheme," Han says.
lengths precisely,
The researchers
With several sensor
then we make an
also created a novel
average to all the fitsignal processing
prototypes already
ted wavelengths," he
method that averagsuccessfully tested,
notes, adding that the
es multiple wavethe researchers are
approach provides a
length peaks to help
now working toward
relatively simple, yet
lower noise interferdeveloping a fieldvery effective signal
ence, which can
deployable version
processing method
introduce artificial
for sensor noise
temperature fluctuadesigned to operate in
reduction. "For each
tions that adversely
extreme conditions.
peak wavelength, we
affect sensor preciused a Gaussian function to fit a set of
sion. "Compared to other fiber-optic
discrete data of the spectrum to get the
thermometers that are mostly based on
value more precisely," Han says. In their
silica material, silicon not only proexperiments, the researchers were able to
vides us with higher sensitivity and
achieve an ultimate temperature resolufaster response, but also a very high
tion of less than 1 × 10-3 °C. "This highrefractive index that endows the reflection spectrum from the Fabry-Perot
resolution surveillance on temperature
cavity with many more wavelength
variation is a huge necessity for oceanpeaks," Han says.
ography," Han says.
Since each of the peak wavelengths
With several sensor prototypes
can be used to monitor temperature
already successfully tested, the researchchange, and because they all have almost
ers are now working toward developing
the same sensitivity, the average
a field-deployable version designed to

am
be er
no ilev
Na ant
C

nanooptics and pLasmonics Laboratory of mipt.

Pump Signal

Probe Signal

e
aveguid
tonic W

ho
Nanop

figure 2. In the chemical and biological sensor developed by researchers at the Nanooptics and
Plasmonics Laboratory of MIPT, a nanobeam cantilever is suspended above a photonic waveguide.
A pump optical signal excited at a light wavelength and sinusoidally modulated at a frequency actuates the cantilever. Simultaneously, the power of the continuous wave probe signal excited at a light
wavelength and propagating along the same waveguide is controlled by the vibrating nanobeam,
providing the capability to gauge the amplitude of mechanical oscillations. By doing a scan of the
modulation frequency, it is possible to measure the decrease in the resonant frequency of the cantilever and determine the mass of adsorbed molecules.

IEEE Signal Processing Magazine

March 2016

operate in extreme conditions. "We are
still working on improving the package
and designing the graphical user interface for more convenient operation and
smarter data processing," Han says.
Han is also looking forward to developing versions of the sensors for other
environmental measurement applications. "We have demonstrated that this
sensor can also be explored for use as a
fast response anemometer and temperature-compensated pressure sensor by
using a laser to get the silicon optical
cavity heated," he remarks.

Sensitive sniffer
Chemical sensors used to detect hazardous gases and environmental pollutants
are the focus of a growing number of
research projects. At the Nanooptics and
Plasmonics Laboratory of the Moscow
Institute of Physics and Technology
(MIPT), Dmitry Fedyanin and his doctoral student, Yury Stebunov, have created a
small, highly sensitive nanomechanical
sensor designed to analyze the chemical
composition of various natural, manmade, and biological substances.
"The ultimate goal in chemical and
biological sensing is detection and measurement of very low molecule concentration in air, blood, and other
environments," says Fedyanin, the project
leader and a senior fellow at MIPT. "In
order to achieve this goal, the sensor
should be able to resolve a single molecule, which is bound to the sensor surface," Fedyanin explains.
The new sensor contains no electronic circuits, yet can be produced
through a standardcomplementary
metal-oxide semiconductor process
technology. The device consists of two
parts: a photonic nanowave guide to
control the optical signal, and a cantilever (a rigid structure anchored at only
one end) hanging over the waveguide
(Figure 2). The cantilever, which measures 5 nm long, 1 nm wide, and 90
nm thick, is connected tightly to a chip.
Two optical signals travel through
the waveguide during oscillations: a
pump optical signal and a probe optical
signal. Vibrations of the nanobeam cantilever are excited by the pump signal.
"The pump signal propagates along the

Table of Contents for the Digital Edition of Signal Processing - March 2016