Theoretical study on negative permittivity of the
material producing sharp surface plasmon
resonance dips
Dejing Gong (龚德静)
1,2
, Yinquan Yuan (袁银权)
1,
*, Lei Liang (梁 磊)
1,2
,
and Minghong Yang (杨明红)
1,
**
1
National Engineering Laboratory for Fiber Optic Sensing Technology, Wuhan University of Technology,
Wuhan 430070, China
2
School of Information Engineering, Wuhan University of Technology, Wuhan 430070, China
*Corresponding author: ymyyq@whut.edu.cn; **corresponding author: minghong.yang@whut.edu.cn
Received October 30, 2018; accepted January 25, 2019; posted online April 8, 2019
Using theoretical simulations for optical fiber surface plasmon resonance (SPR) sensors and prism-based SPR
sensors coated with negative permittivity material (NPM), we investigated the effect of the permittivity of NPM
on the transmitted spectrum of optical fiber SPR sensors and the reflected spectrum of prism-based SPR sensors
and then obtained optimum permittivity of the NPM, which can excite the sharpest SPR spectrum in the white
light region (400–900 nm).
OCIS codes: 280.4788, 240.6680, 310.6860.
doi: 10.3788/COL201917.042801.
Surface plasmon resonance (SPR) refers to the optical ex-
citation of surface plasmon waves at the interface between
a metal and a dielectric layer
[1,2]
. Till now, the most com-
monly used SPR sensors can mainly be divided into opti-
cal fiber SPR sensors
[3–5]
and prism-based SPR sensors
[6–8]
.
For optical fiber SPR sensors and prism-based SPR sen-
sors, the fiber core or the prism couples the incident light
to the multilayer medium at the sensing probe. As the
wavevector of incident light matches with the wavevector
of the surface plasmon wave, the SPR spectrum shows a
dip at the resonance wavelength or at the resonance angle.
The SPR dip and its resonance wavelength or resonance
angle are sensitive to the change in the refractive index
(RI) of the surrounding medium. By measuring the shift
of the resonance wavelength or resonance angle in the SPR
dip, one can estimate the RI change near the sensor
surface
[1–8]
.
The natural metals that can produce the SPR phenome-
non in the white light region (400–900 nm) are limited to
several metals, such as gold (Au), silver (Ag), copper (Cu),
aluminum (Al), and palladium (Pd)
[9–12]
. Au is often used
because it has very stable optical and chemical properties.
Ag is easily oxidized and has been greatly used after being
protected by a protec tive layer. Cu, a much cheaper metal
than both Au and Ag, can produce a good SPR signal and
a better sensitivity, but it has the drawback of bad chemi-
cal stability in aqueous media. Therefore, Au films with
the thickness of about 50 nm were often used in SPR sen-
sors. But, the SPR spectra given by Au layers have great
resonance dips, the full width at half-maximum (FWHM)
is greater than 50 nm for common optical fiber SPR sen-
sors, and the FWHM is about 2°–3° for typical prism-
based SPR sensors, where such great resonance dips lead
to a low signal-to-noise r atio and low detection accuracy of
traditional SPR sensors. To improve the performance
of SPR sensors, it is very necessary to know one kind of
negative permittivity material (NPM) that can excite
the sharp SPR spectrum in the white light region
(400–900 nm).
Ishimaru et al. clarified the main characteristics of the
SPR sensors based on the NPM and more generally meta-
materials at microwave frequencies
[13]
. Plasmonic sensors
based on metamaterials have been proposed for biosensing
applications in the spectral ranges from visible light to the
terahertz and microwave frequencies
[14–19]
. In this work,
being inspired by the plasmonic sensors based on metama-
terials, we try to introduce an NPM film into the optical
fiber SPR sensor and prism-based SPR sensor by adjust-
ing the permittivity of NPM film. We have investigated
the effects of the permittivity of NPM film on the trans-
mitted spectrum of an optical fiber SPR sensor and the
reflected spectrum of a prism-based SPR sensor and then
proposed the optimum parameters of the NPM film, which
can produce a sharp SPR spectrum.
In the researches for SPR sensors, the most common
method is based on a multilayer configuration consisting
of a prism or fiber core, metal layer, sensing layer, and
sample
[4,20]
. Using the Kretschmann structure and angular
interrogation, the prism-based SPR sensor consists of a
monochromatic light source, a photoelectric detector, a
semi-circular prism, a reaction cell, two symmetrical
actuating arms, and a microcomputer. To calculate the
reflectivity of p-polarized incident light (R
p
), multilayer
models have been used to simulate the SPR sensors.
The first layer is the prism or the fiber core made of fused
silica with the RI of n
1
or n
p
, the secon d layer is the metal
layer with thickness of d
2
, and its permittivity (ε
2
) can be
expressed in a Lorentz–Drude model
[21]
:
COL 17(4), 042801(2019) CHINESE OPTICS LETTERS April 10, 2019
1671-7694/2019/042801(5) 042801-1 © 2019 Chinese Optics Letters