Experimental Study of Dual-Parameter SPR Sensor With Integrated Sensing Channel

Enhancement of SPR effect and sensing characteristics in D-shaped polished grapefruit microstructured optical fiber with silver film

Surface Plasmon Resonance (SPR) based fiber optic curvature sensors have the advantage of being insensitive to temperature and axial strain. However, they have the disadvantage of low sensitivity and small curvature detection range. To improve the performance of SPR curvature sensors, we propose an intensity-modulated microstructured optical fiber (MOF) curvature sensor. In this sensor, two no-core fibers (NCFs) are used as input-output couplers, and MOF with silver film deposited is used as sensing arms. The light in the cladding is used to excite the SPR, and the exciting resonant valley is extremely sensitive to slight bending changes. The performance of this sensor is investigated theoretically and experimentally. Numerical results show that its cladding pattern is more favorable in the excitation of SPR effects. Experimental results show that the cladding mode of MOF is very sensitive to curvature changes, thus giving it a great advantage in bending measurements. Its sensitivity reaches 0.18 dB/m-1, and linearity reaches 0.995 in the curvature range of 0-30 m-1. The sensor has the advantages of high sensitivity, low temperature and axial strain crosstalk, compact structure, and easy fabrication, which make it attractive in the field of bending sensing.

A novel sensitivity-enhanced optical fiber sensor has been presented and demonstrated to measure liquid temperature and refractive index (RI) based on the reflective single-mode–multimode–single-mode fiber structure. The sensing part is packaged in a segment of capillary tube by hot glue. Due to the high coefficient of thermal expansion of hot glue, the increasing temperature bends the fiber in the tube. The measurement is achieved via monitoring the spectral shift of the modal interference between the core and the cladding modes in the ended single-mode fiber, which is well carved to provide a mirror interface. The Fresnel reflection occurred in the interface is utilized to measure liquid RI and temperature. The highest sensitivity of −92.6 pm/°C and −67.9 dB/RIU are achieved, respectively. This structure has many advantages, such as high sensitivity, expectation for simultaneous measurement of liquid temperature and RI, convenient operation, and low cost of fabrication.

A novel magnetic field sensing system based on surface plasma resonance (SPR) optical fiber sensor and filled with magnetic fluid (MF) is proposed and demonstrated for the first time. In the magnetic field SPR optical fiber sensor, SPR is excited by Ag as metallic material and MF is filled into the capillary sealed with epoxy glue, which utilizes the tunable refractive index (RI) of MF, and the transmission spectrum will change with different magnetic field intensities. The magnetic-optic effect of MF and the high RI sensitivity of optical fiber SPR sensor are utilized to enhance the sensitivity of the novel magnetic field sensor significantly. In the experiment, the performances of the magnetic field sensing system are tested by applying different measured magnetic fields. The final results indicated that a sensitivity of 303 pm/Gs is achieved. Compared with other optical fiber magnetic field sensors, the advantages of the proposed sensor in this paper are simple structure, small in size, easy to make, low cost, high sensitivity, and anti-interference.

Herein a gold nanosphere (AuNS)-coated wavelength-mode localized surface plasmon resonance (LSPR) fiber sensor was fabricated by a simple and time-saving electrostatic self-assembly method using poly(allylamine hydrochloride). Based on the localized enhanced coupling effect between AuNSs, the LSPR spectrums of the AuNS monolayer with good dispersity and high density exhibited a favourable capability for refractive index (RI) measurement. Based on the results obtained from the optimization for AuNS distribution, sensing length, and RI range, the best RI sensitivity of the fiber modified by 100 nm AuNS reached up to about 2975 nm/RIU, with the surrounding RI range from 1.3322 to 1.3664. Using an 80 nm AuNS-modified fiber sensor, the RI sensitivity of 3953 nm/RIU was achieved, with the RI range increased from 1.3744 to 1.3911. The effect of sensing length to RI sensitivity was proven to be negligible. Furthermore, the linear relationship between the RI sensitivity and plasma resonance frequency of the bulk metal, which was dependent on the interparticle plasmon coupling effect, was quantified. Additionally, the resonance peak was tuned from 539.18 nm to 820.48 nm by different sizes of AuNSs-coated fiber sensors at a RI of 1.3322, which means the spectrum was extended from VIS to NIR. It has enormous potential in hypersensitive biochemistry detection at VIS and NIR ranges.

PurposeThis paper aims to clarify the relationship between the performance of the metal nanoparticles and the sensitivity of the fiber surface plasma resonance (SPR) sensor. It proposes modeling the sensing effects of a single-mode fiber SPR sensor with a cone angle structure decorated with metal nanoparticles. This study uses the metal nanoparticles to the realize enhanced sensitivity of refractive index sensing.Design/methodology/approachThis paper opted for an exploratory study using a simulation approach of finite-difference time-domain (FDTD). Specifically, the effect of size, the material and the shape of the metal nanoparticle on sensing performance are investigated theoretically.FindingsIn conclusion, it is evident that the localized SPR (LSPR) effect weakens as the diameter of the gold nanosphere increases, the SPR effect enhances and the SPR sensitivity increases first and then decreases. The metal nanoparticle with the different materials and different shapes also have different LSPR and SPR sensitivity and wavelength length dynamic range. The investigation shows that, by changing parameters, the reflection spectra of the fiber SPR sensor exhibit an obvious transition from LSPR to SPR characteristics, and enhanced sensitivity of the refractive index is realized.Originality/valueThis paper fulfills an identified need to study how the sensitivity of the fiber SPR sensor can be enhanced by the metal nanoparticle. After the optimization of parameters, the sensitivity of 5,140 nm/RIU is achieved, which provides a new research direction for sensitivity enhancement of fiber SPR sensor.

We propose and demonstrate a compact all-fiber sensor for simultaneous measurement of temperature and refractive index (RI), which is based on a no-core fiber (NCF) and fiber Bragg grating (FBG). Two segments of NCF used as beam splitter and combiner are embedded on the two ends of an FBG, which constitute a Mach-Zehnder (MZ) interferometer susceptible to the temperature and an ambient RI. With the change of RI and temperature, MZ interference and Bragg reflection result in the variation of transmission spectrum. The experimental results show that the sensitivity of RI is -109.573 nm/RI in the range from 1.333 to 1.398, and the sensitivity of temperature ranging from 10 °C to 70 °C is 0.014 nm/°C, respectively. The feasibility of simultaneous measurement of an external RI and the temperature with this configuration has been demonstrated experimentally.

In this work, a detailed study on volume and surface refractive index (RI) sensitivity of cladding modes for a fiber Bragg grating (FBG) based sensor is presented. Surface RI sensitivity of the cladding mode of FBGs has been illustrated and quantified with the concept of add-layer sensitivity for the first time to the best of our knowledge. A detailed investigation of mode transition of higher-order cladding modes has been revisited and important characteristics of the cladding modes are observed which could open a new designing path of fabrication and innovative way of the use of this family of optical fiber grating-based sensors. The effect of “mode transition” of higher-order cladding modes, higher operating wavelength for respective cladding mode and “mode stretching” effects are combined together to achieve higher volume and surface RI sensitivity of cladding mode of FBG. It has been shown numerically that with proper designing, sub-nanometer (∼0.04 nm) attachment of target analyte could be recognized by cladding mode of FBG which is quite promising for application in optical fiber grating bio-sensors. This critical designing method of FBG based surface refractometer would be very helpful in case of the fabrication of highly sensitive sensors for distinct biochemical applications.

To avoid coating and filling into the fiber holes, facilitate the phase-matching and eliminate cross-sensitivity problems, we propose a surface plasmon resonance sensor based on a fan-shaped microstructured optical fiber (MOF) for the simultaneous sensing of temperature and refractive index (RI). The fan-shaped structure is fabricated by polishing two sides of MOF with an angle of 120°. One side is coated with the gold film and polydimethylsiloxane layer for temperature sensing, and the other side is only coated with the gold film for RI sensing. The two sensing sides can support resonance peaks with two polarized directions at the angle of 120°, which are independent without cross-sensitivity. By monitoring the shifts of the two polarized peaks, our numerical results show that the temperature sensitivity is 2.932 nm/°C in the range of 30 °C to 40 °C, and RI sensitivity is 4235 nm/RIU in the range of 1.38 to 1.39, respectively.

Refractometer based on extinction ratio demodulation using no-core and dispersion-compensating fiber structure

Composite materials offer significant performance advantages due to their lightweight, high-strength, and high stiffness. This led to their adoption in several industrial sectors with particular emphasis on the aerospace industry which has undergone a transformation towards a composite-dominated new standard. In order to respond to the increased demand, it is mandatory to focus on an efficient and well-controlled curing cycle of the resin, which will lead to a significant reduction of cost and an increase in production speed. We investigate, a photonic solution, able of measure key monitoring values that facilitate optimization of the curing process. Simulation and evaluation results on a bragg grating based photonic integrated sensor, developed in 220 nm Silicon-onInsulator platform, are presented. A multi-sensor deployment is considered, enabling monitoring of the temperature and the refractive index of the resin. Serially coupled bragg grating photonic elements will enable concurrent monitoring of both temperature and refractive index. Several bragg configurations have been investigated and experimentally evaluated, specifically regular and phase-shifted ones. Both TE and TM polarization operation sensors that have been designed and fabricated, will be presented. Their sensitivity on resin temperature and refractive index variation will be discussed, resulting in a comparative study outlining the benefits and disadvantages of each solution. Refractive index sensors are realized by employing post-processing etching techniques on Multi-Project-Wafer run fabricated silicon chips, on top of the periodic bragg grating element. The comparative study takes into consideration TE and TM polarization operation, regular and phase-shifted bragg grating configuration elements, while evaluating their sensitivity in temperature and refractive index variations. Temperatures considered are in the range of 27°C to 200°C, while refractive index values lay between 1.5 and 1.6. A Figure-of-Merit is proposed to facilitate the selection of multi-sensor deployment for specific temperature and refractive index ranges.

We report on a novel all-fiber refractometer sensor based on multimode interference (MMI) effects. The operating mechanism is based on the self-imaging phenomena that occur in the multimode fiber (MMF) section, which basically replicates the field at the input of the MMF on the output of the MMF for a specific wavelength. However, the longitudinal position of this image is highly dependent on the MMF diameter (D), since there is D² dependence on the longitudinal position of this image. For the refractive index measurement a section of no-core multimode fiber, whose cladding is air, is surrounded by the liquid sample. The liquid sample now works as the cladding medium and as a result of the Goes-Hanchen shift the effective width (fundamental mode width) of the No-Core fiber is increased. As a result, the maximum coupling resulting from the imaging phenomena occurs at a different wavelength, and this can be used to measure the refractive index of the liquid. Using this scheme we can achieve a resolution on the order of 1x10^-5 for a refractive index range from 1.333 to 1.434. The device was used here to measure refractive index in liquids, but can also be applied for measuring concentration of liquids. These sensors are promising and attractive in chemical and biotechnological applications because of their high sensitivity, immunity to electromagnetic interference, and compact size.

Dual-polarized optical sensing of microstructure fiber with pentagonal-lattice based on surface plasmon resonance in the near-IR spectrum

For fully integrated next-generation plasmonic devices, microstructured optical fibers (MOFs) represent a promising platform technology. This paper describes the use of a dynamic technique to demonstrate the wet chemical deposition of gold and silver nanoparticles (NPs) within MOFs. The plasmonic structures were realized on the internal capillary walls of a three-hole suspended core fiber. Electron micrographs, taken of the inside of the fiber holes, confirm the even distribution of the NP in the MOF over a length of up to 6 m. Accordingly, this procedure is highly productive and makes the resulting MOF-based sensors potentially (very) cost efficient. In proof-of-principle experiments with liquids of different refractive indices, the dependence of the localized surface plasmon resonance (LSPR) on the surroundings was confirmed. Comparing Raman spectra of MOFs with and without NP layers, each one filled with crystal violet, a significant signal enhancement demonstrates the usability of such functionalized MOFs for surface-enhanced Raman spectroscopy (SERS) experiments.

Fiber Bragg grating (FBG) is fabricated in the microfiber by the use of femtosecond laser pulse irradiation. Such a grating can be directly exposed to the surrounding medium without etching or thinning treatment of the fiber, thus possessing high refractive index (RI) sensitivity while maintaining superior reliability. The grating in the microfiber may have a number of propagation modes in its transmission spectrum, depending on the fiber diameter, and the higher order of mode has larger RI sensitivity. The RI sensitivity also depends on the fiber diameter and a smaller diameter corresponds to a large sensitivity. The maximum sensitivity obtained is approximately 231.4 nm per refractive index unit at the refractive index value of approximately 1.44 when the fiber diameter is approximately 2 microm. The FBG fabricated in the microfiber has high potential in various types of optical fiber sensor applications.