Search

In this work, a high performance surface plasmon resonance (SPR) fiber sensor based on metallic elliptical nanohole and circular nanodisk binary array has been theoretically designed and investigated. The binary array structure is integrated on the end facet of optical fiber to excite SPR and generate three optical resonance dips in reflection spectra in the near-infrared region. The first resonance dip not only fits the characteristics of narrow linewidth, but also has the advantages of high peak-to-dip signal ratio and sensitivity. When the external environment changes in the refractive index (RI) range of 1.33 ~ 1.40, a high RI sensitivity of 669 nm/RIU, a narrow FWHM of 5.8 nm, and a high FOM value of 115.3 are yielded simultaneously for the first dip. Compared to unitary nanostructure arrays, the composite plasmonic structure of nanodisk and elliptical nanohole array demonstrated here can generate SPR modes with sharper spectral feature which is crucial to high sensitivity and precision detection technology. These features make our proposed plasmonic fiber tip sensor highly promising in terms of high-performance biosensing applications. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel side polished PCF-based SPR sensor with shifted core region employing gold as a plasmonic layer for sensing analytes of refractive index ranging from 1.33 to 1.39. For the ease of plasmonic excitation, we shift the core region towards the edge of the polished cladding. Upon optimizing the sensor structure by varying the geometrical parameters for the sensing range of 1.33–1.39, the proposed PCF sensor structure exhibits a maximum wavelength sensitivity of 24,200 nm/RIU with the resolution of 4.13 × 10−6 RIU. Also, this sensor exhibits a maximum amplitude sensitivity of 432 RIU−1 with a resolution of 2.3 × 10−6 RIU. The proposed sensor exhibits linearity with the R2 value of 0.98791 for the refractive index ranging between 1.33 and 1.39. Furthermore, we carry out perturbation analysis to ensure that the proposed sensor withstands the fabrication tolerance. Therefore, the proposed sensor holds good as a potential contender for sensing in chemical and biological applications. [ABSTRACT FROM AUTHOR]

Kidneys are one of the most important organs in the body. They cleanse the blood and convert waste and excess water into urine. If the kidneys are unable to perform their functions, dialysis is prescribed to assist the patient. Clean and healthy water, as well as accurate evaluation of dissolved substances in water, play a key role in the dialysis process to ensure the patient's safety and well-being. As the dissolved substances change the refractive index of pure water, a refractive index biosensor can be a useful system. In this research, a fiber optic sensor based on surface plasmon resonance with a coating of nanocomposite layers has been studied theoretically. In the numerical simulation, water is used as the sensing medium. The aim of this simulation is to test the sensors that detect impurities in water for dialysis. The simulation is conducted for nanocomposites of nickel-tellurium oxide, platinum-tellurium oxide, and cobalt-tellurium oxide with thicknesses of 50 nm, 70 nm, 90 nm, 110 nm, and 130 nm. The simulation also considers various volume filling factors, including 0.55, 0.65, 0.75, and 0.85. The comparison of the results showed that Ni-TeO2 (with a thickness of 110 nm and a volume filling factor of 0.85) has the highest quality and is considered the winning structure. The graphene layers are tested on the nanocomposites to enhance the quality of the final structure. The results of the simulations show that adding 50 layers of graphene can improve the sensor figure of merit from 80.603 (RIU−1) to 85.522 (RIU−1), while the refractive index of the aqueous media changes from 1.33 to 1.34. [ABSTRACT FROM AUTHOR]

Copyright of Iraqi Journal of Laser is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

In this letter, a novel strain sensor based on four-sided modulated long period fiber grating (FM-LPFG) is introduced and demonstrated. Due to the asymmetric refractive index modulation of the CO2 laser, the cladding radius is reduced and the core deviation effect is strengthened. In addition, by simulating the equivalent strain during tension, the strain sensitive area of FM-LPFG is proposed. The measurement results indicate that the strain sensitivity of FM-LPFG is 127.5 pm/ $\mu \varepsilon $ ($0~\sim ~125~\mu \varepsilon$) and 17.7 pm/ $\mu \varepsilon $ ($125~\sim ~575~\mu \varepsilon$). The proposed FM-LPFG can be realistically applied in precision measurement. [ABSTRACT FROM AUTHOR]

• The holes enclosing core fiber can block the diffusion of dopants from the core to the cladding. • The thermal blocking effect of holes enclosing core fiber is analyzed in simulation and experiment. • Long-period fiber grating devices based on holes enclosing core fiber have a more powerful potential for application in high-temperature and high-pressure environments. We have developed a variety of optical fibers with holes enclosing the core to increase the service life of fiber optic devices under high-temperature and high-pressure environments by blocking the diffusion of dopants in the core with the help of air holes. Simulation results show that the fiber with uniformly distributed holes enclosing the core, the more the hole number, the smaller the core hole distance, and the larger the hole radius, the more significant the blocking effect on thermal diffusion. By comparing the refractive index distribution of three kinds of holes enclosing core fibers and single-mode fibers after prolonged high-temperature heating treatment, the thermal diffusion blocking effect of the holes enclosing core fiber is verified. Long-period fiber gratings fabricated by periodic refractive index modulation of holes enclosing core fibers can realize the measurement of various physical parameters. The thermal diffusion blocking effect of the holes enclosing core fiber enables the long-period fiber grating devices to work for a long time under high-temperature and high-pressure environments, showing the potential for practical applications in various industrial processes. [ABSTRACT FROM AUTHOR]

This paper proposed a fiber sensor based on a Silicon core fiber incorporated with a fused silica grating design. The proposed structure has a high sensitivity in refractive index and temperature variation through theoretical calculation and finite element method simulation. The sensitivities of the refractive index in different polarization directions are 1838.7 and 1949.8 nm/RIU, respectively, within the index range from 1.28 to 1.38 RIU. The temperature range within 15–40 °C has the sensitivity up to 1.6 nm/°C by using ethanol analyte. The proposed fiber sensor can provide a method or a solution for intelligent sensing systems. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This review focuses on the preparation methods and wide applications of optic fiber sensors based on core-offset structure. Firstly, the classification and preparation methods of core-offset structures are introduced. Then, the applications of different types of sensors based on the core-offset structure are investigated, including the measurement of physical parameters such as temperature, strain, refractive index (RI), bending, magnetic field by Mach-Zehnder interferometer (MZI), cascaded sensor, long period fiber grating (LPFG), fiber Bragg grating (FBG), Fabry-Perot interferometer (FPI) and Surface plasmon resonance (SPR). Compared with the traditional fiber sensor, core-offset structure sensor with a non-axisymmetric characteristic has excellent sensing characteristics, especially in the recognition of bending direction and high RI sensitivity. Furthermore, the design scheme, working principle and sensing characteristics of different core-offset sensors are also briefly described. Finally, the existing challenges and development direction of optic fiber sensors based on core-offset structure is discussed and prospected. [ABSTRACT FROM AUTHOR]

An interferometric sensor based on grapefruit photonic crystal fiber (PCF) is proposed and demonstrated for several physical parameter sensing. The PCF is sandwiched between two single-mode fibers (SMFs) through a short multimode fiber (MMF) at its both ends to form a Mach-Zehnder interferometer (MZI) with a total length of less than 2 mm. Combined with femtosecond laser micromachining and selectively filling technique, the micro-channels in the PCF are flexibly used for highly sensitive strain, gas refractive index/pressure, and temperature measurements. Moreover, device can also be used for hydrogen sensing with a high sensitivity of ~3.00 nm/% (vol. %) by coating Pt-loaded WO3 on its lateral surface. Meanwhile, the unique signal demodulation technique based on inverse Fourier transform is adopted to extract out desired information. The proposed device has promising potential in many physical parameter sensing, environmental monitoring, and hydrogen energy measurement owing to its high sensitivity, versatile sensing capability, and compact size. [ABSTRACT FROM AUTHOR]

Featured Application: Probe-like, multi-channel fiber biochemical sensor with ultra-small footprint. Resonant waveguide gratings (RWG) are widely used as on-chip refractometers due to their relatively high sensitivity to ambient refractive index changes, their possibility of parallel high-throughput detection and their easy fabrication. In the last two decades, efforts have been made to integrate RWG sensors onto fiber facets, although practical application is still hindered by the limited resonant peak intensity caused by the low coupling efficiency between the reflected beam and the fiber mode. In this work, we propose a new compact RWG fiber-optic sensor with an additional Fabry-Pérot cavity, which is directly integrated onto the tip of a single-mode fiber. By introducing such a resonant structure, a strongly enhanced peak reflectance and improved figure of merit are achieved, while, at the same time, the grating size can be greatly reduced, thus allowing for spatial multiplexing of many sensors on a tip of a single multi-core fiber. This paves the way for the development of probe-like reflective fiber-tip RWG sensors, which are of great interest for multi-channel biochemical sensing and for real-time medical diagnostics. [ABSTRACT FROM AUTHOR]

• A high sensitivity and low temperature cross-talk magnetic field sensor with small dimension is proposed and investigated. • It is easily fabricated by sandwiching a tiny ferrofluid-filled capillary tube between two SMFs via a short MMF at the capillary tube's both ends. • The magnetic field sensitivity achieves up to 8.966 nm/mT and 4.264 nm/mT for weak longitudinal and vertical magnetic field, respectively, as well as good stability and accuracy. • The temperature cross-talk is very low. A ferrofluid-filled in-fiber Mach-Zehnder interferometer (MZI) is presented and validated for magnetic field sensing. It is constructed by embedding a short capillary tube filled with ferrofluid which is sandwiched between two SMFs through a short MMF at its both ends, and the device is experimentally proved having extreme high refractive index (RI) sensitivity. When the sensor is placed in an external magnetic field, the RI of the ferrofluid changes, causing a shift in the transmission spectrum of the interferometer. Experimental results show that the proposed sensor exhibits a high sensitivity of 8.9657 nm/mT and 4.2642 nm/mT for longitudinal and vertical magnetic field within the range of 0–1.5 mT and 0.8–2.2 mT, respectively. Furthermore, the sensor exhibits excellent low temperature cross-talk in longitudinal and transverse magnetic fields as low as 0.014 mT/°C and 0.030 mT/°C, respectively. The sensor offers advantages such as stable operation, compact size, and robust mechanical structure. [ABSTRACT FROM AUTHOR]

• A concise all-fiber hydrostatic pressure sensor is proposed. • High hydrostatic pressure sensitivity of −0.2358 nm/MPa in the range of 0.1 MPa to 16.1 MPa is obtained. • Ultra-low temperature–pressure cross-sensitivity of 0.04368 MPa/℃ proves our sensor more competitive in harsh environment applications. With the rapid development of physical ocean observation, high-performance pressure sensor integrated with stable mechanical strength, sufficient pressure sensitivity as well as negligible temperature crosstalk is highly desirable but still lack of research. This paper proposes an all-fiber optical sensor based on a Mach-Zehnder interferometer (MZI) for hydrostatic pressure measurement, utilizing a multi-mode fiber (MMF)-single-hole-dual-core fiber (SHDCF)-MMF structure. The MMF sections act as a beam splitter and coupler to enhance the Mach-Zehnder interference. The SHDCF serves as the pressure-sensing section. Under the action of the enclosed air hole in SHDCF, hydraulic variations cause changes in the structural parameters of the fiber, especially the refractive index change caused by the elasto-optical effect, which leads to the shift of the interference dips. The experimental results prove that the SHDCF-based MZI sensor has a higher hydrostatic pressure sensitivity than other hole-less silica fiber-based sensors. The max pressure sensitivity is −0.2358 nm/MPa in the range of 0.1 MPa to 16.1 MPa with good linearity and reliability. Moreover, the low temperature–pressure cross-sensitivity of 0.04368 MPa/℃ also proves our sensor more competitive in harsh environment applications. [ABSTRACT FROM AUTHOR]

• We designed a fiber sensor system comprising fused silica fiber Bragg grating and silicon core fiber-based fiber Bragg grating. • A hybrid fiber Bragg grating sensor system was proposed, employing only two sensing devices to detect three different environmental targets. • Our focus was solely on addressing the connection between two distinct fibers, namely fused silica and silicon core fiber. We discussed the associated loss and spectral distortion issues. In this article, we introduce a multi-parameter fiber sensor system that utilizes a hybrid FBG design. The design combines a fused silica fiber Bragg grating and a fiber Bragg grating based on a silicon core fiber. This combination enables the sensor to detect surrounding temperature, water level, and refractive index. The sensor successfully measured temperature within the range of 10 to 40 °C, water level within the range of 40 to 140 cm, and refractive index within the range of 1.2 to 1.4. These ranges exhibit a high level of linearity within the proposed sensing range. Additionally, we discuss the challenges associated with connecting the fused silica fiber and the silicon core fiber. [ABSTRACT FROM AUTHOR]

A surface plasmon resonance (SPR) sensor based on a photonic crystal fiber (PCF) is proposed for low refractive index (RI) detection. The core of PCF is formed by two-layer air walls and either layer is composed of six identical sector rings with negative curvature. Plasmonic material gold (Au) is coated on the external cladding surface. Finite element method (FEM) is applied to investigate the performance of the SPR sensor. Results show that the sensor is independent of polarization due to the coincident coupling properties of the two polarized modes. Additionally, in low RI ranging from 1.20 to 1.33, the sensor keeps a high spectral sensitivity with an average value of 7738 nm/RIU. When RI varies from 1.32 to 1.33, the resolution reaches to its maximum of 8.3 × 10−6. The proposed sensor shows much significance in low RI detection, which is promising in real-time measurement for medical, water pollution, and humidity. [ABSTRACT FROM AUTHOR]

This paper firstly and experimentally demonstrates an in-fiber axial micro-strain sensing head, combined with a Mach-Zehnder interferometer (MZI) based on the concentric multilayer elliptical-core fiber (CMECF). This MZI with a high extinction ratio (about 15 dB) is successfully achieved with a CMECF-single mode fiber-CMECF (CSC) structure. The MZI sensor theory and the resonance demodulation technology are systematically described in this paper. In this CSC structure, two sections of the CMECF have a role as the mode generator and coupler, respectively. LP01 and LP11even, which have similar excitation coefficients, are two dominated propagating mode groups supported in the CMECF. On account of the distinct dual-mode property, a good stability of this sensor is realized. The detected resonance in the MZI shifts as the axial micro-strain variated due to the strong interaction between higher order modes. High sensitivity of ∼1.78 pm/με is experimentally achieved within the range of 0 με-1250 με, meanwhile, the intensity fluctuation is below 0.38 dB. [ABSTRACT FROM AUTHOR]

In the work, a cholesteric liquid crystal film coated side polished fiber (CLCFC-SPF) is demonstrated to sense the volatile organic compound (VOC) gas. In the CLCFC-SPF, the wavelength selectively coupling from the SPF to the cholesteric liquid crystal film (CLCF) results in the resonant dips in the transmitted spectrum. It is found that the pitch of the CLCF increases with VOC gas concentration, which reduces the refractive index (RI) of CLCF and results in a blue shift of the resonant dips. By tracing the blue shift of the resonant dips, the VOC gas sensing characteristic of the CLCFC-SPF were investigated experimentally. For tetrahydrofuran, acetone and methanol gas, the sensitivities of the CLCFC-SPF are respectively measured as 7.08 nm·L/mmol, 3.46 nm·L/mmol, 0.52 nm·L/mmol. Using the wavelength selectively coupling theory, gaseous-optic coefficient of the CLC can also be obtained and were measured in the experiment as 6.6 × 10 −4 RIU·L/mmol, 2.9 × 10 −4 RIU·L/mmol, 0.6 × 10 −4 RIU·L/mmol, respectively, for tetrahydrofuran, acetone, and methanol gas. Additionally, the experimental results also show that both the sensitivity of CLCFC-SPF and the gaseous-optic coefficient of the CLCF increase with the molar mass of the VOC gas. The work provides a way to incorporate the sensitive liquid crystal onto the fiber for implementation of liquid-crystal-based fiber sensors. [ABSTRACT FROM AUTHOR]

Graphene Oxide (GO) coated silver (Ag) island system based on localized surface plasmon resonance (LSPR) phenomenon have been developed using optical fiber as a sensing probe. The Ag-island is used to excite LSPR field which is responsible for the analyte sensing through a shift in resonance wavelength. The deposition of Ag-islands is confirmed from UV-VIS spectra and Field Emission Scanning Electron Micro-graph (FESEM). The usage of GO helps to protect Ag-island from oxidation along with opening a new window for bio-sensing due to its structural compatibility with the bio-sensing system. We have experientially observed that the GO as a dielectric overlayer on Ag-island shows a refractive index sensitivity of 2217.04 nm/RIU with a resolution of $4.05 \times 10^{-4}$ RIU. [ABSTRACT FROM AUTHOR]

A novel high performance optical fiber refractive index (RI) sensor based on the hybrid transverse magnetic (TM) mode of Tamm plasmon polariton (TPP) and surface plasmon polariton (SPP) is proposed. The structure of the sensor is a multi-mode optical fiber with a one dimensional photonic crystal (1 DPC)/metal multi-films outer coated on its fiber core. A simulation study of the proposed sensor is carried out with the geometrical optical model to investigate the performance of the designed sensor with respect to the center wavelength, bilayer period and the thickness of silver layer. Because the lights transmitted in the fiber sensor have much larger incident angles than those in the prism based sensors, the center wavelength of the 1 DPC should shift to longer wavelength. When the coupling between TM-TPP and SPP is stronger, the sensor exhibits better performance because the electromagnetic field of the TPP-SPP hybrid mode is enhanced more in the analyte. Compared to most conventional fiber surface plasmon resonance sensors, the figure of merit of the proposed sensor is much higher while the sensitivity is comparable. The idea of utilizing TPP-SPP hybrid mode for RI sensing in the solid-core optical fiber structure presented in this paper could contribute to the study of the fiber RI sensor based on TPP. [ABSTRACT FROM AUTHOR]

An optical fiber interference sensor with a fiber end groove structure that was fabricated by a femtosecond laser is presented for temperature and refractive index measurement. In the designed fiber sensor, a groove that was 40 μm deep and 50 μm wide was etched on the fiber end along the core at the SMF-28 fiber. The microstructure was manufactured by the femtosecond laser through a line-by-line scanning method. In an experiment, the sensor head was inserted into NaCl solution. The interferometer wavelength interval was 46 nm, and the stripe contrast was 17 dB. Under different vertical refractive indexes (RIs), the corresponding comb spectrum was obtained. Results showed that the proposed fiber filter exhibited an RI sensitivity of 3282.176 nm per refractive index unit (RIU) and 1317.351 dB/RIU, respectively. In addition, the temperature characteristic was measured. The wavelength variation was not obvious and the power fluctuation curve was linear within 50 °C–100 °C. The sensor spectrum had good repetition at high and low temperatures. The results demonstrated the satisfactory performance of the refraction and temperature sensor. [ABSTRACT FROM AUTHOR]

• The structure of fiber SPR sensor is studied and optimized in this paper, and the tapered fiber SPR sensor is proposed and used to detect mixed oil. The main contributions of this paper can be summarized as follows: • The tapered fiber SPR sensor is designed through tapering processing on the fiber. • Carries out the theoretical analysis and experimental research on the tapered fiber SPR sensor. The experiment results show that the tapered fiber SPR sensor has stable measurement accuracy and linearity in 1.3320–1.4264 RIU. • The tapered fiber SPR sensor proposed in the paper is used to detect mixed oil, to realize rapid and accurate detection of the mixed oil interface in pipeline transportation. • For the mixed oil samples consisting of four oils, petrol 90#, petrol 93#, petrol 97#, diesel oil −10#, complete relevant detection experiments, including single pure oil, mixed samples with different kinds of oil (petrol and diesel), mixed samples with different models of oil (petrol), to prove that the proposed method can detect measured mixed oil with different mixing ratios effectively. To solve the problem that it is difficult to detect the mixed oil during the sequential transportation of product oil, the tapered fiber SPR sensor is designed to detect the mixed oil samples consisting of four kinds of oil, petrol 90#, petrol 93#, petrol 97#, diesel oil −10#. According to the refractive index range of measured oil and the measuring range of tapered fiber SPR sensor, a scheme to reduce the refractive index of measured oil is designed, and the detection experiments for three kinds of oil samples are completed, including the experiment of single pure oil, mixed samples with different kinds of oil (petrol and diesel oil), mixed samples with different models of oil (petrol). The experimental results show that the tapered fiber SPR sensor can effectively identify the measured mixed oil samples, its work is stable and reliable, and the experimental repeatability is also good, which verify the feasibility of the tapered fiber SPR sensor in mixed oil detection and provide a new method for it. [ABSTRACT FROM AUTHOR]

A novel refractive index (RI) sensor based on an asymmetrical Mach–Zehnder interferometer (MZI) with two different step-like tapers is proposed. The step-like taper is fabricated by fusion splicing two half tapers with an appropriate offset. By further applying offset and discharging to the last fabricated step-like taper of MZI, influence of taper parameters on interference spectrum is investigated using only one device. This simple technique provides an on-line method to sweep parameters of step-like tapers and speeds up the optimization process of interference spectrum, meanwhile. In RI sensing experiment, the sensor has a high sensitivity of −185.79 nm/RIU (refractive index unit) in the RI range of 1.3333–1.3673. [ABSTRACT FROM AUTHOR]

A simple high-resolution refractive index (RI) and phase sensor has been demonstrated and the results numerically verified. A free space gap is employed in one arm of a Mach-Zehnder interferometer (MZI) to serve as the sensing mechanism with a physical spacing of 1.4 mm. The propagation constant of transmitted light in the MZI's gap changes due to the small variation in the ambient RI that will further shift the optical phase of the signal. A free space optical delay line is embedded within the MZI's other arm to set the phase reference point and compensate for variations in the optical phase difference. The ambient RI is computed by measuring the phase shift in the transmission spectrum A high-resolution sensing of 0.8 pm/%RH corresponds to phase change of 0.012°/%RH has been achieved in 1520 nm. [ABSTRACT FROM AUTHOR]

• Fabrication methods and mechanisms of the microstructured fiber were summarized. • Applications of the microstructured fibers in different sensing fields were introduced. • State of the art and future directions of the microstructured fiber were discussed. • References covers a wide range of researches on fiber sensor in recent years. Microstructured optical fibers, including not only photonic crystal fibers but also new types of fiber with different configurations on the cross section, are elaborately designed and they usually have special application purposes among which sensing is one of the most common. In this review we first summarize fabrication methods and transmission mechanisms of microstructured fibers. And then application examples using fibers with special and novel microstructures in strain/pressure/bending/twist, temperature, flow rate, electric/magnetic field, humidity, gas, refractive index and chemical/biochemical analyte sensing based on various principles are introduced. Finally, state of the art and developing trends as well as challenges faced by sensing technology based on microstructured optical fibers were discussed. [ABSTRACT FROM AUTHOR]

The interrogation of fiber-Bragg-grating (FBG) sensors using a vertical-cavity surface-emitting laser (VCSEL) is discussed. A long-wavelength (1.54 μm) VCSEL was used as a wavelength-tunable source by variation in the current. Temperature stabilization was performed with a thermoelectric device. Characteristics of temperature and strain sensing were investigated. FBGs with different reflectivities were compared. For temperature sensing, the root-mean-square error in the measurement was reduced to 1/3 that without temperature stabilization. The dependence of the measurement error on the reflectivities of the FBGs was investigated. The measurement error was larger for FBGs with lower reflectivities in both temperature and strain sensing. Improvement on the sensing with low-reflectivity FBGs is discussed. [ABSTRACT FROM AUTHOR]

In this work, the fabrication and experimental investigation of multimode optical fiber with a cladding material replacement is presented. A short piece of fiber’s cladding is etched away and substituted by a polydimethylsiloxane (PDMS) material. This elastomer is characterized by a unique feature of refractive index changes with the increasing particle density. The device principle is based on total internal reflection. If the PDMS is pressed, there is a change of elastomer refractive index and modes confined within the fiber core are partially or totally irradiated. This demonstration paves the way for further development of fiber optic sensors, particularly attractive for weight, load, extension, and pressure parameters monitoring applications. [ABSTRACT FROM AUTHOR]

We report that the main photosensitive mechanism of poly(methyl methacrylate)-based optical fiber Bragg grating (POFBG) under ultraviolet laser micromachining is a complex process of both photodegradation and negative thermo-optic effect. We found experimentally the unique characteristics of Bragg resonance splitting and reunion during the laser micromachining process providing the evidence of photodegradation, while the mean refractive index change of POFBG was measured to be negative confirming further photodegradation of polymer fiber. The thermal-induced refractive index change of POFBG was also observed by recording the Bragg wavelength shift. Furthermore, the dynamic thermal response of the micromachined-POFBG was demonstrated under constant humidity, showing a linear and negative response of around −47.1 pm/°C. [ABSTRACT FROM PUBLISHER]

An optical fiber sensor based on a second-order superstructure fiber Bragg grating (SFBG) is experimentally investigated. In general, a first-order SFBG has been available for many years and has been widely applied in optical fiber communication systems and fiber sensing systems. An SFBG is composed of a fiber Bragg grating (FBG) and a long-period grating (LPG), so it can be regarded as a periodically modulated FBG. In this study, to the best of our knowledge, a second-order SFBG is successfully fabricated for the first time. Moreover, we are the first to experimentally demonstrate that the refractive index sensitivities of a second-order SFBG sensor are larger than those of the first-order SFBG. This configuration and technique can provide simplestructure, low-cost, and high-sensitivity innovative devices for application to refractive index measurement systems. [ABSTRACT FROM AUTHOR]

An in-line fiber sensor for simultaneous measurement of refractive index (RI) and temperature is proposed and demonstrated. The sensor head is composed of an asymmetric Mach–Zehnder interferometer (MZI), which is combining the single mode-multimode-single mode (SMS) fiber structure and a peanut-shape structure. The transmission dips of the sensor will shift as the ambient RI or temperature variation due to the phase changing. The different wavelength transmission dips formed by the cladding modes interfering with the core mode have different sensitivity responses, so the simultaneous measurement of the RI and temperature can be achieved by monitoring the wavelength shifts of the two transmission dips. The experimental results show that the sensing sensitivities of RI and temperature are −86.7434 nm/RIU and 0.0590 nm/°C in the RI range from 1.3105 to 1.3517 and temperature range from 25 °C to 85 °C, respectively. The novel sensor processes easy fabrication, low cost, and high sensitivity, making it offers high potential applications in physical, biological and chemical sensing. [ABSTRACT FROM AUTHOR]

In this paper, a copper (Cu) based fiber surface plasmon resonance (SPR) sensor using two-dimensional (2D) transition metal dichalcogenides (TMDs) is studied theoretically. As the number of layers of TMDs increases, the sensitivity first increases and then decreases, exhibiting a maximum value for each TMDs based fiber SPR sensor. The maximum sensitivities of the fiber SPR sensors with WS 2 , MoS 2 , WSe 2 and MoSe 2 are up to 47.664 µm/RIU, 44.164 µm/RIU, 46.704 µm/RIU and 48.816 µm/RIU, while their resonance wavelengths are 3481.1 nm, 3592.2 nm, 3500.8 nm and 3435.1 nm. In addition, the growth rate of sensitivity in the mid-infrared regime is obviously higher than that in the visible or near-infrared regime. The proposed Cu based fiber SPR sensor with 2D TMDs exhibits ultra-high sensitivity in the mid-infrared regime, and can be used for highly sensitive bio-sensing. • A copper based fiber SPR sensor with 2D TMDs is proposed. • There is an optimal sensitivity by optimizing TMDs layer. • Rapid improvement of sensitivity is exhibited in mid-infrared regime. • Highest sensitivity is 48.816 µm/RIU realized by 151 layers of MoSe 2. • Sensitivity increases with refractive index of sensing medium. [ABSTRACT FROM AUTHOR]

While there is an established literature on the effect of geometric parameters and material properties on the sensitivity of tapered fiber refractive index sensors, the impact of these parameters has been largely overlooked at sensor at diameters comparable to wavelength. Here, we investigate the effect of geometric parameters and materials properties at dimensions comparable to wavelength using full-wave solutions of Maxwell's equations. Our results indicate that to achieve the maximum sensitivity for the tapered fiber sensors, the diameter should be closer to operational wavelength. For diameters less than the operational wavelength, sensitivity reduces instead of further increasing, a phenomenon opposite to what was predicted by ray-tracing based tapered fiber models. Another important finding of this study is the effect of optical loss constant on the sensitivity, a parameter often overlooked in the literature. As the optical loss constant was varied from 0 to 0.04 for each iteration of RI variation range, a linear decrease in sensitivity from 0.12 trans. (A.U)/RIU to 0.05 trans. (A.U)/RIU. [ABSTRACT FROM AUTHOR]

A novel long-tail optical fiber current sensor based on fiber loop ring-down spectroscopy (FLRDS) and magnetic-tunable refractive index properties and magnetic-tunable transmission properties of magnetic fluid is proposed and demonstrated for the first time. In the sensing system, a Fabry-Perot (F-P) cavity filled with magnetic fluid is used as the sensing head, and the sensitivity of current-sensing has been enhanced significantly. Relations between magnetic field and refractive index of magnetic fluid are measured. Refractive index of magnetic fluid increases linearly as the magnetic field increases and according to the F-P interferometer principle, the best gap length of F-P cavity is obtained. In this paper, the FLRDS sensing system has been theoretically modeled, and a new mathematical model developed for optimizing the coupling ratio of couplers has been presented, and the best coupling ratio has been obtained. The new mathematical model could also be used in the similar ring-down systems. Finally, the performances of the current-sensing system are tested by applying different measured currents. The final results indicate that a sensitivity of 14.88 mA/ $\mu $ s is achieved. [ABSTRACT FROM PUBLISHER]

A simple inline Mach Zehnder Interferometer (MZI) with a dumbbell-shaped structure is developed for measuring glucose concentration in distilled water. The MZI is fabricated using an arcing function of a fusion splicer. The sensor consists of two bulges separated by a tapered waist. The MZI generates a good reflected interference spectrum where the dip wavelength is red-shifted with the increase of glucose concentration. This is due to the increase of the surrounding refractive index, which reduces the phase difference between the core and cladding modes. As the glucose concentration increases from 0% to 12%, the dip wavelength increases from 1554.419 to 1554.939 nm in a quadratic manner with the coefficient of determination of 0.9818. It is also found that the sensor has a sensitivity of 0.04 nm/% with a linearity of 96.7%. The limit of detection is 4.5%. This preliminary result shows that the proposed probe can be used as a sensor to detect glucose concentration in distilled water. [ABSTRACT FROM AUTHOR]

ABSTRACT We reported a novel fiber sensor based on two cascaded single mode fiber corners, which has a high sensitivity for refractive index (RI) sensing and a low temperature crosstalk. RI sensing was experimentally demonstrated with an average sensitivity of 235 nm/RI unit in a RI range from 1.333 to 1.418, which is relatively high among the previously reported similar fiber sensors (e.g., it is about 10 times higher than that of the normal two or three-cascaded-taper based Mach-Zehnder interferometer). The proposed RI sensor was fabricated by fiber fusion splicer, where the fiber corner was fabricated by splicing the two overlapping single mode fibers, which ensures that the proposed RI sensor is compact and strong. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2642-2645, 2014 [ABSTRACT FROM AUTHOR]

A novel double-parameter sensor based on a multimode–multimode–multimode (MMM) fiber structure has been proposed and experimentally demonstrated. The principle of operation depends on the effects of a series of interference signal superposition, which include core–core mode interference and core–cladding mode interference. Three dips in the transmitted spectrum of the MMM fiber structure can be observed due to the modal interference effects. The high temperature sensitivities are 0.0771nm/°C, 0.152nm/°C and 0.0582nm/°C at the three dips of 1555.65nm, 1560.48nm and 1550.12 nm respectively from 20°C to 70°C. The refractive index sensitivities are 54.33nm/RIU, 108.23nm/RIU and almost 0nm/RIU from 1.34 to 1.39 at the same three dips. The sensor reveals the advantages of easy fabrication and low cost. [ABSTRACT FROM AUTHOR]

Highlights: [•] We first demonstrate a sensor based on a normal FBG and a core-offset MZI for simultaneous measurement of the refractive index and temperature. [•] The new sensor can measure solutions with high stability. [•] The sensor is simple and easy for fabrication with low-cost. [ABSTRACT FROM AUTHOR]