Side-polished Multimode Fiber Research Articles

Directional bending sensor based on Mach-Zehnder interferometer formed by side-polished multimode fiber

This work proposes a fiber bending sensor based on the Mach-Zehnder interferometer (MZI) constructed using a side-polished multimode fiber (MMF) with bending direction recognition. The sensor is fabricated by directly fusing a section of side-polished MMF sandwiched between two no-core fibers (NCFs) to an input and output single-mode fibers (SMFs). As the applied curvature varies from 0 m−1 to 1.64 m−1, the transmission spectra of the sensor exhibit distinct and linear wavelength shift in opposite directions. The maximum sensitivity observed in 0° and 180° bending is 3.252 nm/m−1 and −1.146 nm/m−1, respectively. The maximum temperature sensitivity is 0.0621 nm/°C and this effect can be compensated by using the sensitivity matrix. The advantages of the proposed sensor include its ability to accurately quantify the direction and magnitude of bending, temperature crosstalk elimination, and cost-effectiveness. These features make the sensor highly desirable for a wide range of practical directional bending applications, such as medical wearable devices for human joint range of motion monitoring.

Sensitive and reproducible on-chip SERS detection by side-polished fiber probes integrated with microfluidic chips

The combination of surface-enhanced Raman scattering (SERS) and microfluidic technology offers a promising solution to improve the reproducibility and reliability of SERS detection. Optical fiber SERS probes, as an important class of SERS substrates, provide a large SERS interaction area and flexible integration with microfluidic chips. In this article, a side-polished multimode fiber (SPMF) SERS probe is prepared by depositing Au nanorods on a planar polished fiber surface and integrating it into a microfluidic channel to form a glass-based microfluidic-SERS chip. The impact of SPMF residual thickness on SERS performance is thoroughly investigated, and the optimized residual thickness of 62 μm is determined by considering the evanescent wave intensity, transmission loss, and experimental feasibility. The optimized microfluidic-SERS chip shows low detection limits (as low as 10-8 M for MG) and good spectral reproducibility (RSD less than 10%) due to the large SERS interaction area provided by the SPMF SERS probe and the stable liquid flow in the microfluidic channel. The chip is furtherly used to detect pesticide and antibiotic residues in tap water, with the detection limits of 10-9 M for thiram and 10-6 M for levofloxacin. This work provides an effective way to realize highly sensitive and reproducible SERS detection, and may find important applications in environmental science, food safety, and biomedicine.

Side-Polished Single-Mode-Multimode-Single-Mode Fiber Structure for the Vector Magnetic Field Sensing

A vector magnetometer, composed of a side-polished single-mode-multimode-single-mode fiber structure coated with ferrofluids, is proposed and investigated. The side-polishing of the multimode fiber can expose the evanescent field to the surrounding ferrofluids, whose refractive index in the vicinity of the polished surface can be tuned by both the intensity and direction of the applied magnetic field, thus in turn realizing the magnetic vector sensing. The sensing principles are illustrated in details, and the sensing performances, especially the dependence on the residual thickness (RT) of the side-polished multimode fiber, are well investigated experimentally. It is found that the decrease of the RT can significantly improve the sensitivity to both the magnetic field intensity and the direction, and the highest intensity and direction sensitivities of −0.053 nm/Oe and −5.68 nm/degree have been achieved respectively, when the RT reduces to 50.5 μm. The proposed vector magnetometer, featuring the advantages of simple structure, low cost, and ease of fabrication, can find the potential applications in the fields such as industry, military, and environment.

Long-Range Surface Plasmon Resonance Sensor Based on Side-Polished Fiber for Biosensing Applications

A long-range surface plasmon resonance (LRSPR) sensor with enhanced performance has been theoretically calculated and experimentally investigated for biosensing applications. The LRSPR-based sensor is fabricated by employing a side-polished multimode fiber as a waveguide and MgF2 as a buffer layer beneath a thin silver film for supporting LRSPR excitation. Theoretical optimization based on transfer matrix method and the corresponding validation experiments were carried out in detail. The theoretical and experimental results consistently indicate that the sensing performance parameters of the LRSPR-based sensor are improved with varying degrees in comparison to conventional SPR (CSPR) sensors. It was experimentally achieved that the maximal figure of merit of the LRSPR-based sensor exceeds that of the CSPR sensor by a factor of 1.14. At last the bovine serum albumin (BSA) concentration detection was performed to further confirm the sensitivity enhancement of the optimized sensor in biosensing. This SPR sensor design and development is expected to exert a positive influence on real-time and label-free.

A High-Temperature Humidity Sensor Based on a Singlemode-Side Polished Multimode-Singlemode Fiber Structure

A relative humidity (RH) sensor based on a simple singlemode-side polished multimode-singlemode (SSPMS) fiber hybrid structure is investigated, which is capable of working over a relatively high-temperature range, at which many RH sensors based on moisture sensitive material coatings cannot operate. The beam propagation method is used to analyze the light transmission characteristics within the side polished multimode fiber (SPMMF) structure. Experimental results show that the SPMMF surface roughness has a significant influence on the sensor's humidity sensing performance, as a result of the adsorption and desorption of water molecules along the side polished surface. A higher surface roughness results in an increased RH sensitivity. It is concluded that the SSPMS fiber structure based RH sensor can achieve around 0.069 dB/%RH within the humidity range of 30%RH–90%RH for a temperature range of 70 °C to 90 °C. In addition, the temperature cross-sensitivity has been investigated experimentally. The developed fiber optic sensor in this investigation provides a simple and effective approach for RH measurement in a variety of production applications.

Design and optimization of surface plasmon resonance sensor based on multimode fiber

We optimized the design of surface plasmon resonance sensor based on side polished multimode fiber using the method of finite element. The effects of the residual fiber thickness, gold layer thickness and the guiding modes on the depth, the full width at half maximum of the resonance dips were investigated numerically. The sensitivity to the variation in refractive index of analyte and the figure of merit are evaluated for design optimization. The results show that the fiber propagation modes have negligible influence on the resonant wavelength but have effect on the resonance strength. The optimal design was achieved at the residual fiber thickness of 75 μm and the gold film thickness of 50 nm. The optimized sensor has an average sensitivity of 4989 nm/RIU in the refractive index range from 1.33 to 1.40.

An Enhanced Optical Multimode Fiber Sensor Based on Surface Plasmon Resonance With Cascaded Structure

A cascaded side-polished multimode fiber sensor based on surface plasmon resonance (SPR) is proposed. The sensing area is a multimode optical fiber in which half of the core has been polished away and a 40-nm gold thin film is deposited on to the polished surface. The cascaded structure is demonstrated in the small difference variation of the refractive index between the two solutions, deionized (DI) water and phosphate buffered saline (PBS). The transmitted intensity of SPR fiber sensor in dynamic measurement between single SPR fiber structure and the cascaded structure achieved to increase the variation from 73% to 58% for DI water and 70.5% to 53% for PBS, and enhance the difference between DI water and PBS from 2.5% to 5% is obtained in the experiment. The stability and the double variation to enhance the high sensitivity of the intensity measurement is achieved to be 2 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> refractive-index units.

The enhancement method of optical fiber biosensor based on surface plasmon resonance with cold plasma modification

Abstract Cold plasma modification on optical fiber biosensor based on surface plasmon resonance (SPR) is proposed to enhance the SPR effect on biosensing. A side-polished multimode fiber sensor based on surface plasmon resonance as the transducing element with a halogen light source is carried out for the measurement of the BSA for the sensitivity analysis. The comparison with detection surface was fabricated by binding chemically to self-assembly monolayer (SAM) of 11-mercaptoundecanoic acid (MUA) and cold plasma modification method on gold (Au) surface of optical fiber, and then was activated by EDC/NHS for BSA. The pretreatment of cold plasma modification using isopropanol (IPA) to deposited carboxyl group on side-polished surface of optical fiber biosensor, and there are easily to combine biomolecule by EDC/NHS modification. The results of the comparison between traditional surface modification and cold plasma modification with the measurement for 5 ng BSA is observed on OSA and shifted obviously in wavelength. The side-polished fiber sensor based on surface plasmon resonance can provide the SPR response on spectrum, and the IPA plasma treatment can increase the sensitivity of the SPR dip shifted with 10–40 nm under the 10 min treatment time of the surface modification.

Side-polished multimode fiber biosensor based on surface plasmon resonance with halogen light

A side-polished multimode fiber sensor based on surface plasmon resonance (SPR) as the transducing element with a halogen light source is proposed. The SPR fiber sensor is side polished until half the core is closed and coated with a 37 nm gold thin film by dc sputtering. The SPR curve on the optical spectrum is described by an optical spectrum analyzer and can sense a range of widths in wavelengths of SPR effects. The measurement system using the halogen light source is constructed for several real-time detections that are carried out for the measurement of the index liquid detections for the sensitivity analysis. The sensing fiber is demonstrated with a series of refractive index (RI) liquids and set for several experiments, including the stability, repeatability, and resolution calibration. The results for the halogen light source with the resolution of the measurement based on wavelength interrogation were 3 x 10(-6) refractive index units (RIUs). The SPR dip shifted in wavelength is used as a measure of the RI change at a surface, and this RI change varies directly with the number of biomolecules at the surface. The SPR dip shift in wavelength, which was hybridized at 0.1 microM of the target DNA to the probe DNA, was 8.66 nm. The all-fiber multimode SPR sensor, which has the advantages of being low cost, being disposable, having high stability and linearity, being free of labeling, and having potential for real-time detection, permit the sensor and system to be used in biochemical sensing and environmental monitoring.

Cross-point analysis for a multimode fiber sensor based on surface plasmon resonance

A novel analysis based on surface plasmon resonance (SPR) with a side-polished multimode fiber and a white-light (halogen light) source is presented. The sensing system is a multimode optical fiber in which half of the core has been polished away and a 40 nm gold layer is deposited on to the polished surface by dc sputter. The SPR dip in the optical spectrum is investigated with an optical spectrum analyzer (OSA). In our SPR fiber sensor, the use of liquids with different refractive indices leads to a shift in the spectral dip in the SPR curve. The cross point (CP) of the two SPR spectra obtained from the refractive-index liquid and the deionized water measurements was observed with the OSA. The CP is shifted sensitively in wavelength from 630 to 1300 nm relative to a change in the refractive index of the liquid from 1.34 to 1.46. High sensitivities of 1.9 x 10(-6) refractive-index units (RIUs) in the range of the refractive index of the liquid from 1.40 to 1.44 of 5.7 x 10(-7) RIUs above the value of 1.44 are proposed and demonstrated in our novel SPR analysis.