In this paper, we theoretically design and numerically verify a broadband plasmonic absorber that works continuously in ultraviolet to near-infrared region. Different from the traditional metal-insulator-metal (MIM) three-layer structure, our perfect absorber is based on insulator-metal-insulator-metal (IMIM) four-layer structure. This perfect absorber has 280 nm ultra-thin thickness, and the combination of refractory metal titanium nitride and high-melting-point insulator silica gives our absorber strong thermal stability. The novel titanium nitride ring-square array layer combines the absorption of different wavelength bands so that the absorber can achieve a continuous absorption of more than 90% from wavelength 200 to 1200 nm. Finite-difference time-domain (FDTD) calculated average absorption rate reaches 94.85%, which 99.40% maximum absorption at wavelength 270 nm and 90.30% minimum absorption at 390 nm. In addition, polarization independence under normal incidence and large incident angle insensitivity under oblique incidence, making our perfect absorber more advantageous in applications such as solar energy collection, photothermal conversion, and invisibility cloak.
We propose and demonstrate an open-cavity fiber extrinsic Fabry-Perot (FP) interferometer (EFPI), fabricated by using 800 nm femtosecond (fs) laser micromachining, for refractive index (RI) measurement. The sensor probe consists of two single-mode fiber (SMF) and a notched hollow-core fiber (HCF) fused together to form an all-silica structure of SMFHCF-SMF. The open micro-cavity is formed by removing part of the HCF in the center of its surface by fs laser micromachining technology, allowing liquid or gaseous sample to flow in. Such a sensor can provide an extremely highprecision RI measurement of 10-6 RIU (refractive index unit) and the sensitivity can reach up to 4×105 nm/RIU within the range between 1.355 and 1.374.
We proposed a compact and cost-effective red–green dual-color fiber optic surface plasmon resonance (SPR) sensor based on the smartphone. Inherent color selectivity of phone cameras was utilized for real-time monitoring of red and green color channels simultaneously, which can reduce the chance of false detection and improve the sensitivity. Because there are no external prisms, complex optical lenses, or diffraction grating, simple optical configuration is realized. It has a linear response in a refractive index range of 1.326 to 1.351 (R2 = 0.991) with a resolution of 2.3 × 10 − 4 RIU. We apply it for immunoglobulin G (IgG) concentration measurement. Experimental results demonstrate that a linear SPR response was achieved for IgG concentrations varying from 0.02 to 0.30 mg / ml with good repeatability. It may find promising applications in the fields of public health and environment monitoring owing to its simple optics design and applicability in real-time, label-free biodetection.
In this paper, we present a tilted fiber Bragg gratings (TFBG) based surface Plasmon resonance (SPR) label-free sensors with boronic acid derivative (ABA-PBA) as receptor molecule to detect glycoprotein with high sensitivity and selectivity. Tilted fiber Bragg gratings (TFBG) as a near infrared wavelengths detecting element can be able to excite a number of cladding modes whose properties can be detected accurately by measuring the variation of transmitted spectra. A 10° TFBG coated by 50nm gold film was manufactured to stimulate surface plasmon resonance on the surface of the sensor. The sensor was loaded with boronic acid derivative as the recognition molecule which has been widely used in various areas for the recognition matrix of diol-containing biomolecules. The proposed TFBG-SPR sensors exhibit good selectivity and repeatability with the protein concentration sensitivity up to 2.867dB/ (mg/ml) and the limit of detection was 2*10-5g/ml.
This paper has developed a novel single-mode core-offset fiber optic sensor based on the principle of Michelson
interferometer, which can be used for refractive index measurement in sugar solution while making temperature
compensation to eliminate or weaken temperature sensitivity. Experimental results show that when the temperature range
is from 18.1°C to 84.3°C there will be an increasing relationship between characteristic wavelength and temperature.
When the sensor's sensing range is from 1.331 to 1.335, there will be a better decrease gradually relationship between
characteristic wavelength and refractive index (0.0416nm/0.01R.I.U) after temperature compensation. This sensor has a
simple-structure and high-sensitivity.
Comparing to core-modes of optical fibers, some cladding-modes are more sensitive to the surroundings which are very
valuable to sensing application; recently, a novel type of FBG sensor with core-offset structure attracts more and more
interests. Normally, the forward core-mode is not only reflected and coupled to the backward core mode by the Fiber
Bragg Grating in the step-type photosensitive single mode fiber, but also coupled to the backward cladding-modes and
the radiation modes, eventually they will leak or be absorbed by the high refraction index coating layer. These backward
cladding-modes can also be used for sensing analysis. In this paper, we propose and develop a core-offset structure to
obtain the backward core-mode and backward cladding-modes by using the wavelength shift of the backward core-mode
and the power of the backward cladding-modes in Fiber Bragg Grating sensor, and the power of the backward
cladding-modes are independent from temperature variation. We develop a mode coupling sensor model between the
forward core-mode and the backward cladding-modes, and demonstrate two coupling methods in the core-offset
structure experimentally. The sensor is fabricated and demonstrated for refractive index monitoring. Some specific works
are under investigation now, more analysis and fabrication will be done to improve this cladding-mode based sensor
design for applicable sensing technology.
Non-equilibrium interferometric Fiber Bragg Grating (FBG) sensor is suitable for the accurate measurements of
high-frequency dynamic stress, vibration, etc because of its high sensitivity and high frequency response compared to
other types of FBG sensors. In this paper, a Phase Generation Carrier (PGC) demodulation technique of non-equilibrium
interferometric FBG sensor that based on ARCTAN algorithm by using an arctangent algorithm with a simple method,
has been investigated ,which can avoid the high-frequency noise increases, the error accumulation, the integrator signal
jump of the integrator and other inherent weaknesses in the system. ARCTAN has a better response characteristic of the
mutant signals, especially for low-frequency large-signal that can be demodulated with a greater range. The experimental
result demonstrate that implementing measured resolution can up to 10nε/√Hz@500Hz in vibration strain, a signal sampling rate to 100 KHz and a frequency response range up to 1 KHz. This method can improve the performance of the system greatly which has potential significance for practical sensor application.
Surface Plasmon Resonance (SPR) has been widely investigated for chemical and biological sensing applications.
Especially, fiber optic SPR sensors have recently drawn considerable attention because of their fundamentally simpler
structure, lower cost, and suitability for remote-sensing applications. This paper will present a research work for a novel
multichannel SPR sensing technology. Based on the Kretschmann's SPR theory, we theoretically investigate the surface
parameters effects to SPR wavelength changes. Emphasis will be placed on a theoretical design and numerical
simulation of a multichannel fiber optic SPR sensing scheme based on a geometrical tapered fiber optic sensor probe that
coated with nanoparticles imprinted polymer on the SPR sensing region. The parameter effects of SPR sensing area that
include metal thickness, sensing area length and dielectric overcoat layer. SPR spectra that change with incidence angle
and wavelength are investigated by using numerical calculations and simulations. While nanoparticles imprinted polymer
for enhancement of sensitivity can serve as an enhanced transduction mechanism for recognition and sensing of target
analytes in accordance with different requirements, the scheme of a multichannel fiber optic SPR sensor can be further
adapted to the design and development of multi-channel optical fibers SPR sensor probes by combining SPR with other
technology as a comprehensive sensor design.
As an important member of optical fiber sensor, fiber optic Extrinsic Fabry-Perot Interferometric (EFPI) sensor has
prospects for a wide range of industrial applications due to its small size, compact configuration, good reliability and
flexibility. In a white light based fiber optic EFPI sensor system, which has the advantages of large dynamic range and
high resolution, spectral analysis equipment is the most important part which takes the major cost of the system.
Therefore, multiplexing spectral analysis equipment to measure multiple sensors simultaneously is an effective and
necessary way that can save the cost of the whole sensor system. In this paper, a scheme based on the frequency division
multiplexing of EFPI optical fiber sensors is proposed. Two EFPI sensors with different gap lengths are parallely
connected through the optical fiber coupler. The overlapped interference spectrum of the two EFPI sensors is measured
by using an optical spectrum analyzer, which is separated into two individual interference spectrums with a Finite
Impuse Response (FIR) band-pass filter. Their envelope components are extracted with Hilbert transform, and then the
interference spectrums are normalized by the envelope components. The respective gap lengths of the two EFPI sensors
are achieved with the cross correlation calculation. Using this frequency division spectral analysis method, a two-channel
multiplexing EFPI sensor system is implemented in the laboratory. The deployment of this frequency division
multiplexing technology can greatly reduce the cost of the whole system which has extensive potential applications for
distributed fiber optic EFPI sensor system.
The low-coherence broadband white light source presents the problem of aging, damage. Such light source with problem
used in the white light Interferometric instrument will cause incorrect data. Especially when the damage of the light
source is not obvious, the wrong result will not be found easily. In this paper with the theoretical analysis and computer
numerical simulation, some kinds of exceptional spectral distributions and some kinds of exceptional interferometer
fringes are given. The same conclusions are achieved in the experiment. The erroneous judgment of zero-order fringe
due to the damage of the light source will be avoided.
KEYWORDS: Interferometry, Fiber optics sensors, Digital signal processing, Algorithm development, Signal processing, Sensors, Field programmable gate arrays, Homodyne detection, Linear filtering, Lead
One important advantage of interferometric optical fiber sensor is high sensitivity. The development of the
interferometric optical fiber sensor is partly restricted with the demodulating technique. Because of advantages such as
high sensitivity, high dynamic range, and good linearity, PGC (Phase Generated Carrier) demodulating scheme is widely
applied for interferometric optical fiber sensor now. In this paper, an arctangent approach of the PGC demodulating
scheme is introduced. CORDIC (Coordinate Rotation Digital Computer) algorithm is used to realize the arctangent
function. CORDIC algorithm is a method for computing elementary functions using minimal hardware such as shifts,
adds/subs and compares. CORDIC algorithm works by rotating the coordinate system through constant angles until the
angle is reduces to zero. The angle offsets are selected such that the operations on X and Y are only shifts and adds. This
method will lead in less complexity and higher accuracy. Since digital signal processing technology has achieved great
development, especially the appearances of high speed processors such as FPGA and DSP, PGC demodulating scheme
based on CORDIC algorithm is implemented conveniently. The experiments are carried out to verify the PGC demodulating scheme based on CORDIC algorithm.
In this paper, a multiplexed optical fiber extrinsic Fabry-Perot interferometric (EFPI) sensor system with optical switch is implemented. To obtain the absolute length of the EFPI air gap, a cross-correlation signal processing method is introduced. The multiplexing of the sensors is basically based on a 1×N optical switch directly connected to a N-element EFPI sensor array. The EFPI sensors are interrogated one after the other with the same spectrometer by activating the corresponding channel of the optical switch. A multiplexed sensor system prototype with two EFPI sensors is demonstrated to verify the performance of the multiplexing method.
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