Optik
124 (2013) 4725–
4728
Contents
lists
available
at
ScienceDirect
Optik
jou
rn
al
homepage:
www.elsevier.de/ijleo
Optical
characteristics
of
subwavelength
metallic
grating
coupled
porous
film
surface
plasmon
resonance
sensor
with
high
sensitivity
Gaige
Zheng
∗
,
Yunyun
Chen,
Linhua
Xu,
Min
Lai
School
of
Physics
&
Optoelectronic
Engineering,
Nanjing
University
of
Information
Science
&
Technology,
Nanjing
210044,
Jiangsu,
PR
China
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
8
September
2012
Accepted
23
January
2013
Keywords:
Surface
plasmons
Subwavelength
metallic
grating
Surface
plasmon
resonance
sensor
Rigorous
coupled
wave
analysis
a
b
s
t
r
a
c
t
A
high
performance
sub-wavelength
metallic
grating
coupled
surface
plasmon
resonance
(SWMGCSPR)
sensor
with
metal
and
porous
composite
layer
is
proposed.
Rigorous
coupled-wave
analysis
(RCWA)
is
conducted
to
prove
the
design
feasibility,
characterize
the
sensor’s
performance
and
determine
geo-
metric
parameters
of
the
structure,
which
is
also
employed
to
compute
the
electromagnetic
(EM)
field
distributions
at
the
resonant
wavelengths.
Parameters
of
sensing
platform
are
optimized
to
achieve
the
best
performance
of
the
SPR
sensor.
Obtained
results
reveal
that
the
proposed
structure
can
excite
SPR
with
negative
diffraction
order
of
SWMG.
Both
wavelength
and
angular
sensitivities
are
greatly
enhanced
because
surface
plasmon
wave
(SPW)
exhibits
a
large
penetration
depth
which
will
enlarge
the
distance
of
interactions
between
SP
and
analytes.
The
detection
sensitivities
and
quality
parameters
are
estimated
to
be
700
nm/RIU
and
509
◦
/RIU
with
full
width
at
half
maximum
(FWHM)
less
than
2.5
nm
using
the
same
optimized
structure.
© 2013 Elsevier GmbH. All rights reserved.
1.
Introduction
Surface
plasmons
(SPs)
are
defined
as
propagating
electron
density
waves
at
the
interface
between
dielectric
and
metal
[1].
Surface
plasmon
resonance
(SPR)
happens
when
the
wave
vec-
tor
of
the
evanescent
wave
matches
the
wave
vector
of
the
SPs.
SPR
is
regarded
as
one
of
the
most
powerful
and
widely
used
method
applied
in
current
biosensor
with
its
capability
in
sensi-
tively
biomolecular
detection
[2].
The
features
of
no-labeling,
real
time
and
highly
sensitivity
enables
SPR
sensors
a
remarkable
future
in
the
application
of
biological
detecting,
clinical
diagnostics,
food
analysis
and
so
on.
SPR
sensors
are
conventionally
based
on
detec-
ting
changes
of
refractive
indices
around
the
metallic
films
or
in
the
vicinity
of
the
continuous
metallic
films
employing
both
angular
and
wavelength
interrogation
methods
[3–6].
To
remove
stringent
coupling
angle
requirements
in
the
con-
ventional
Kretschmann
based
SPR
sensors
and
enable
capability
of
miniaturization,
many
researches
on
improving
the
sensitivity
of
grating-based
system
have
been
reported
[7–9].
However,
most
of
the
grating-based
methods
are
improving
the
sensitivity
through
making
the
dips
of
positive
diffraction
orders
better,
which
cannot
exceed
the
sensitivity
of
the
prism-based
systems
[10].
In
this
study,
we
propose
a
sub-wavelength
metallic
grating
cou-
pled
surface
plasmon
resonance
(SWMGCSPR)
sensors
that
does
∗
Corresponding
author.
E-mail
address:
eriot@126.com
(G.
Zheng).
not
employ
the
Kretschmann
configuration
and
is
based
on
direct
coupling
of
normally
incident
radiation
into
metallic
nano-gratings
which
would
be
easily
implemented
into
a
portable
system
with
high
sensitivity.
The
use
of
SWMG
can
enhance
the
refractive
index
sensitivity
of
SPR
sensors
by
large
resonance
wavelength
or
angle
shifts
with
the
surrounding
materials
and
sharp
reflection
reso-
nance
peaks.
The
aim
of
this
paper
is
to
improve
the
sensitivity
of
the
SWMGCSPR
sensors
by
utilizing
negative
diffraction
orders.
The
influence
of
structural
factors
of
SWMG
on
the
sensitivity
of
SWMGCSPR
sensor
is
investigated
with
rigorous
coupled
wave-
guide
analysis
(RCWA)
method.
Numerical
simulation
indicates
that
SWMGCSPR
sensors
can
improve
the
sensitivity
considerably
by
using
-1
diffraction
order
of
the
metallic
grating
to
excite
SP.
2.
Numerical
model
and
simulations
RCWA
algorithm
allows
a
full
vectorial
solution
of
the
Maxwell’s
equations
in
the
Fourier
domain
[11–14].
In
this
algorithm,
the
electric
and
magnetic
fields
in
the
incident,
grating,
and
transmit-
ted
media
are
expanded
as
a
summation
of
multiple
diffraction
orders.
Due
to
the
periodicity
of
the
grating
structure,
the
dielec-
tric
function
(or
relative
electric
permittivity)
of
the
grating
region
can
be
expressed
as
a
Fourier
expansion.
By
matching
the
bound-
ary
conditions
(i.e.,
continuity
of
tangential
components
of
electric
and
magnetic
fields)
at
boundaries
of
the
incident,
grating,
and
transmitted
media,
closed
linear
equations
can
be
obtained.
This
way
of
solving
the
Maxwell’s
equations
allows
the
calculation
of
the
reflectance
R,
the
transmittance
T,
and
thus
of
the
absorption
0030-4026/$
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matter ©
2013 Elsevier GmbH. All rights reserved.
http://dx.doi.org/10.1016/j.ijleo.2013.01.087