Highly sensitive and wide-dynamic-range liquid-prism
surface plasmon resonance refractive index sensor based
on the phase and angular interrogations
Guoqiang Lan (兰国强)
1,2
, Shugang Liu (刘书钢)
2
, Xueru Zhang (张学如)
1,
*,
Yuxiao Wang (王玉晓)
1
, and Yinglin Song (宋瑛林)
1,
**
1
Department of Physics, Harbin Institute of Technology, Harbin 150080, China
2
School of Electronic Engineering, Heilong jiang University, Harbin 150080, China
*Corresponding author: xrzhang@hit.edu.cn; **corresponding author: ylsong@hit.edu.cn
Received September 1, 2015; accepted December 11, 2015; posted online February 1, 2016
In this study, a new method utilizing surface plasmon resonance (SPR) sensing technology based on the phase
and angular interrogations for measuring the refractive index of a liquid prism is presented. An orthogonal sam-
ple box that combined the functions of a prism, cell box, and mirror is adopted to simplify the system and provide
the convenience to implement the phase and angular interrogations. The angular interrogation is achieved by the
motorized rotation stage with the new sample box, and the phase interrogation is achieved by the linear polari-
zation interferometry between the s- and p-polarization components. The amplitude reflectivity and the phase
angle, which are the functions of the incident angle, are obtained by the reflection intensity and the interference
intensity of the lights directly. A sensitivity of 7.5 × 10
−7
refractive index unit (RIU)/0.1° and a dynamic range
of 0.5 RIU are obtained experimentally and theoretically.
OCIS codes: 240.6680, 280.4788.
doi: 10.3788/COL201614.022401.
The Kretschmann–Raether configuration is widely used in
surface plasmon resonance (SPR) sensing areas
[1]
. The typ-
ical model of a Kretschmann–Raether SPR configuration
is a prism-metal film sample. The SPR is very sensitive to
the refractive index of the dielectric around the metal film,
and the variations of the refractive index can be indicated
by several SPR interrogations
[2]
. The solid prism is widely
used in the Kretschmann–Raether configuration
[3]
. Inter-
estingly, the liquid can also be used as the “prism” (also
called liquid prism or hollow prism
[4]
); then, the refractive
index of the liquid prism can be detected by the SPR tech-
nology, namely, the liquid prism is the sample for simul-
taneous detections
[5]
.
The SPR sensing methods based on amplitude interrog-
ations, which include angul ar interrogation
[6]
, spectral
interrogation
[7,8]
, and intensity interrogation
[9]
, are the
most popular SPR sensing configurations in the current
literature. In order to obtain a higher sensitivity, the
phase interrogation SPR sensor was introduced in recent
years
[10–14]
, and the sensitivity of the phase interrogation
was improved by 1–3 orders compared with those ampli-
tude interrogations
[15]
. Different from the amplitude inter-
rogations, the phase interrogation cannot obtain the
phase information with respect to the light intensity di-
rectly, and the phase acquirements must depend on
phase-extraction techniques such as interferometry
[13,16–18]
,
polarimetry
[19,20]
, and optical heterodyning
[21,22]
; thus, the
configuration of the phase interrogation is more compli-
cated than that of the amplitude interrogation
[23]
.A
number of pioneering works focused on increasing the sen-
sitivity
[24,25]
, simplifying the structure
[26,27]
, improving the
signal-to-noise ratio (SNR)
[28]
and expanding the dynamic
range
[29]
. However, the main difficulty of current phase
interrogation is that the system cannot obtain high sensi-
tivity, a wide dynamic range, and a compact structure
simultaneously.
We design a new SPR sensing configuration based on
the phase and angular interrogations to achieve a high
sensitivity and a wide dynamic range simultaneously, as
shown in Fig.
1. The liquid sample box is fastened to
the motorized rotation stage, which is placed vertically.
A BK7 glass slide (Agar scientific) covered with Ag film
(50 nm) is adopted as the sensing chip in the liquid sample
box. An He–Ne laser beam with a wavelength of λ ¼
632.8 nm passes through a Glan prism (10000∶1) rotated
45° from the X-axis to obtain a 50% p-polarization com-
ponent and a 50% s-polarization component. The laser
beam is perpendicular to the liquid level after the mirror,
and the light spot on the glass slide is just on the center of
the rotation stage, so it is stationary when the rotation
stage turns a certain angle. The emergent beam reflected
twice in the orthogonal V-shaped box is always parallel to
the incident light, as shown in Fig.
1(a). Considering that
the emergent light shifted parallelly when the rotation
stage turned, a telescopic system is adopted to shrink
the light beam. The light beam is separated into two
beams after a 1∶1 beam splitter. One arm obtained the
intensity of the p-polarization component after a polariz-
ing beam splitter cube to serve as the angular interroga-
tion; meanwhile, the other arm obtained the interference
intensities of the s-and p-polarization components after
another Glan prism (rotated 135° from the X-axis, vertical
to the first Glan prism) to serve as the phase interrogation.
Two power meters and the rotation stage are controlled
COL 14(2), 022401(2016) CHINESE OPTICS LETTERS February 10, 2016
1671-7694/2016/022401(5) 022401-1 © 2016 Chinese Optics Letters