Hetero-core Structure Research Articles

Wide-range pH sensor based on a cascaded MZI up-down tapered hetero-core structure

In this paper, we describe the first demonstration of an optical fiber sensor based on two cascaded architectures of the Mach–Zehnder interferometer (MZI) with an up-down-tapered (UDT) hetero-core fiber structure for simultaneous pH measurement at two different spatial locations. The two fiber structures, namely structures I and II, were fabricated by sandwiching a 45 mm and 60 mm long piece of no-core fiber (NCF) between two single-mode fibers (SMFs), respectively. By inserting a down-taper between two adjacent up-tapers in the NCF section using the over-fusion splicing technique, the UDT hetero-core fiber structure was achieved. The down-taper works as an optical attenuator, while the two up-tapers each function as a fiber splitter/combiner. By cascading the two sensor structures I and II, two distinct interference dips were obtained, resulting in dual sensing points (so-called sensing points I and II). According to experimental results, it was shown that the proposed sensing points I and II are pH-sensitive, and exhibit sensitivities of 1.0428 nm/pH and −1.7857nm/pH for simultaneous measurement for each point as the pH ranged from 8 to 14 and from 1 to 7 pH, respectively. The obtained results show that the proposed dual point pH sensor has the potential to be used for the simultaneous detection of pH parameters in any environment and at various places.

High-sensitivity optical fiber SPR sensor with cascaded biconical fiber and hetero-core structure for simultaneous measurement of seawater salinity and temperature

A novel dual-channel optical fiber surface plasmon resonance (SPR) sensor, which achieves high-sensitivity simultaneous measurement of seawater salinity and temperature, was designed and verified. The hetero-core structure based on no-core fiber (NCF) with 40 nm thick Au film and polydimethylsiloxane (PDMS) overlaying was utilized to excite the SPR effect and serve as the temperature sensing channel. In order to effectively separate from the temperature SPR dip, a silver/gold bimetallic film was deposited on the surface of the biconical fiber with a grinding angle of 14° to construct the salinity channel cascaded with the temperature channel, where the metal thickness was determined as Ag/Au: 30 nm/10 nm. The simulation and experimental results showed that the bimetallic film used in this article can significantly improve the figure of merit (FOM) of the sensor compared with the optical fiber SPR sensor deposited with a single kind of metal film. In addition, further experimental results on salinity and temperature indicated that the proposed sensor had a salinity sensitivity of 0.73 nm/‰ and a temperature sensitivity of −2.43 nm/℃, and demonstrated the advantages of ease of manufacturing, acceptable repeatability, and good stability. Therefore, the proposed dual-channel optical fiber SPR sensor has high research value and application prospects in the field of ocean measurement.

Intensity Loss of ZnO Coated on Fiber Optic

Macrobends are optical fiber structures suitable for detecting motion changes. This structure has been developed using single-mode fibers and a combination of single-mode and multimode fibers called hetero-core. In this study, a new macrobending structure was designed and developed by adding a nano-ZnO element to the fiber optic core based on Revolution 4.0. The addition of nanomaterial elements involves an etching process that uses harmful chemicals or high-cost laser technology. Therefore, hetero-core was applied in this study to replace the etching process. The ZnO-coated fiber optics with 10 (ZnO1), 20 (ZnO2), and 30 (ZnO3) times of dip coating were developed using the dip-coating method and characterized using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. Sensitivity measurement was conducted with glued optical fiber in the form of bending using a tape with a bending dimension of 2.5 cm × 1.5 cm and a wavelength of 1,550 nm. Morphological characterization using SEM proves that nanoparticles are attached to the optical fiber, and the EDX characterization confirms that the nanoparticles are ZnO elements. Optical fiber sensor sensitivity using core sizes 9, 50–9–50, 50–9–50 (ZnO1), 50–9–50 (ZnO2), and 50–9–50 (ZnO3) achieved sensitivity values of 0.91, 1.61, 2.98, 3.34, and 3.51, respectively. This study successfully produced ZnO-coated optical fiber sensors with a hetero-core structure without performing the etching process and successfully increased the sensitivity of the sensors.

Novel Corrugated Long Period Grating Surface Balloon-Shaped Heterocore-Structured Plastic Optical Fibre Sensor for Microalgal Bioethanol Production.

A novel long period grating (LPG) inscribed balloon-shaped heterocore-structured plastic optical fibre (POF) sensor is described and experimentally demonstrated for real-time measurement of the ultra-low concentrations of ethanol in microalgal bioethanol production applications. The heterocore structure is established by coupling a 250 μm core diameter POF between two 1000 μm diameter POFs, thus representing a large core-small core-large core configuration. Before coupling as a heterocore structure, the sensing region or small core fibre (SCF; i.e., 250 μm POF) is modified by polishing, LPG inscription, and macro bending into a balloon shape to enhance the sensitivity of the sensor. The sensor was characterized for ethanol-water solutions in the ethanol concentration ranges of 20 to 80 %v/v, 1 to 10 %v/v, 0.1 to 1 %v/v, and 0.00633 to 0.0633 %v/v demonstrating a maximum sensitivity of 3 × 106 %/RIU, a resolution of 7.9 × 10-6 RIU, and a limit of detection (LOD) of 9.7 × 10-6 RIU. The experimental results are included for the intended application of bioethanol production using microalgae. The characterization was performed in the ultra-low-level ethanol concentration range, i.e., 0.00633 to 0.03165 %v/v, that is present in real culturing and production conditions, e.g., ethanol-producing blue-green microalgae mixtures. The sensor demonstrated a maximum sensitivity of 210,632.8 %T/%v/v (or 5 × 106 %/RIU as referenced from the RI values of ethanol-water solutions), resolution of 2 × 10-4%v/v (or 9.4 × 10-6 RIU), and LOD of 4.9 × 10-4%v/v (or 2.3 × 10-5 RIU). Additionally, the response and recovery times of the sensor were investigated in the case of measurement in the air and the ethanol-microalgae mixtures. The experimentally verified, extremely high sensitivity and resolution and very low LOD corresponding to the initial rate of bioethanol production using microalgae of this sensor design, combined with ease of fabrication, low cost, and wide measurement range, makes it a promising candidate to be incorporated into the bioethanol production industry as a real-time sensing solution as well as in other ethanol sensing and/or RI sensing applications.

Refractive index sensors based on cascaded multimode interference hetero-core optical fibers.

In this work, we demonstrate refractive index (RI) sensors based on the cascade of hetero-core structures using multimode and no-core optical fibers in sequence. The sensor device is engineered to have resonances at different wavelengths using different sensing region lengths. The device fabrication involves simple fiber cleaving and fusion splicing. For the experiments, the two sensor regions are exposed to liquids with different RIs. For the hetero-core fiber insertion length of 45mm, the transmission valley is centered at 1082.5nm with 15.1nm full width at half-maximum (FWHM) for an external medium RI of 1.3370. Additionally, it shifts 4.1nm towards longer wavelengths as the RI of the external medium increases to 1.3840. For the 30mm long hetero-core structure, the valley is centered at 1599.7nm with 23.3nm FWHM for an external medium RI of 1.3370, which shifts 7.4nm as the RI increases to 1.3840. The sensor sensitivities are up to -476d B/r e f r a c t i v e index unit (RIU) and 270nm/RIU. The resolution of the devices is estimated to be 2×10-5 R I U.

Fiber SPR micro displacement sensor based on heterocore structure of graded index multimode fiber

Based on the self-focusing characteristics of graded index multimode fiber, a fiber SPR micro displacement sensor can be constructed, which has two bottleneck problems of difficult to fabricate and the small displacement detection range. In this paper, we proposed and constructed a new heterocore structure of graded multimode fiber-single-mode fiber-graded multimode fiber to realize the micro displacement sensing, which has stable performance and simple fabrication. By increasing the core diameter of modulation graded multimode fiber and displacement fiber, the displacement detection range of probe was increased. The simulating and testing results indicate that the SPR micro displacement sensor based on the graded multimode heterogeneous core structure can well realize the two-parameter sensing of micro displacement, and its average wavelength and light intensity sensitivity can reach 1.23 nm/μm, and 0.00576 a.u./μm respectively, the measurement resolution is 0.813μm. When using step multimode fiber with core diameter of 40μm in place of single-mode fiber as the displacement fiber, the displacement detection range reaches 50μm which is double that of the reported fiber SPR micro displacement sensor. The proposed fiber SPR micro displacement sensor well solved the two bottleneck problems above, which can be used in the field of micro displacement measurement of structural health monitoring.

Liquid Level Sensor With High Sensitivity Based on Hetero Core Structure

In this paper, a novel liquid level sensor with high sensitivity is proposed. The proposed sensor is configured by multimode fiber-No-core fiber-multimode fiber (MMF-NCF-MMF) hetero core structure (MNM-HCS). The sensor is composed of two MMF structures spliced on both ends of NCF, in which NCF is used as a sensing unit, and the MMF at both ends excites higher cladding modes to improve the sensitivity of the sensor to the external environment. Interference occurs when light is transmitted from MMF to NCF. Experimental results show that the compact sensor with a length of 12.2 mm has a high liquid level sensitivity of 1034 pm/mm in the water level (RI <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$ </tex-math></inline-formula> 1.333) range of 0-10 mm. The temperature sensitivity is 20 pm/°C in the range of 35- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$95^{\circ }\text{C}$ </tex-math></inline-formula> . The temperature-liquid level cross sensitivity of the proposed sensor is 0.019 mm/°C. Due to the advantages of high sensitivity, good linearity and stable performance, MNM-HCS has potential application potential application prospects in the field of high sensitivity liquid level measurement.

Fiber cladding SPR bending sensor characterized by two parameters* *Project supported by the National Natural Science Foundation of China (Grant No. 61705025), the Natural Science Foundation of Heilongjiang Province, China (Grant No. F2018027), the Fund from Chongqing Municipal Key Laboratory of Institutions of Higher Education (Grant No. [2017]3), the Program of Chongqing Development and Reform Commission (Grant No. 2017[1007]), the

A fiber cladding surface plasmon resonance (SPR) bending sensor is realized by the cladding of the fiber structure. By employing coating film, the sensing zone is protected and the toughness of the sensor increases. Three different sensing probes are tested, the experiment results indicate that the two parameters (wavelength sensitivity and light intensity sensitivity) sensing performances of the eccentric butt joint structures are superior to that of hetero-core structure, and the SPR bending sensor based on hetero-core structure is stable and uneasy to damage. By employing hetero-core fiber and silver film, a fiber cladding SPR bending sensor with better stabilization and sensing performance is realized. The proposed fabricating method of sensing probe with coating film provides a new approach for fiber SPR-distributed bending sensor.

Beating the shot-noise limit with optical fiber quantum sensors for salinity measurement

An ultra-resolution optical salinity quantum sensor depended on the tapered hetero-core structure coated with a gold film (around 50 nm) is proposed and demonstrated in this paper. Single photons which work as an input source are used for exciting surface plasmon polaritons at the interface between the metal and the seawater. We exploit the statistical analysis method to get the transmission spectroscopy and quantify its estimation error. Experiment results show that the detected estimation errors of the proposed quantum sensor are completely in agreement with the quantum theory. Though various external interference and experimental defects exist, the error bars are beyond the standard quantum limit. The salinity sensitivity of this proposed sensor is about 0.02204/‰. The resolution of this proposed sensor is 0.0016‰, which is one order of magnitude higher than that of traditional optical fiber surface plasmon resonance (SPR) sensors. The resolution and the sensitivity of the quantum sensor can be further enhanced by modifying the metal coating and the structural parameters. This work realizes the combination of optical fiber sensing technology and quantum plasmonic technology, which will pave the way for the development of high-resolution and high-sensitivity sensor.

U-Shaped Polymer Cladding and Hetero-Core Fiber Optic Sensors for Monitoring Scale Formation in Geothermal Brine

In the development of fiber optic sensors for monitoring scale formation in geothermal brine, high sensitivity and easy handling are desirable features. These characteristics have already been successfully enhanced for U-shaped sensors with other applications. In this work, U-shaped fiber optic sensors for scale formation are reported. The sensors were easily fabricated by bending the exposed core of a multimode fiber optic. Two types of fiber optics, i.e., a polymer cladding silica fiber and a hetero-core structure fiber, were used in preparing the U-shaped sensors. The percentage of total internal reflection between water and the fiber core is affected by the high refractive index of the CaCO3 scale formed on the surface. For laboratory measurements, the optical responses of the U-shaped fiber sensors with respect to calcium carbonate formation were investigated in a mixture of calcium chloride dehydrate and sodium hydrogen carbonate using a white-light source and a spectroscopic detector. The U-shaped fiber sensors were responsive to calcium carbonate formation on the sensor surface. Almost no change in the sensitivity was detected when comparing the U-shaped sensors with their straight counterparts. The transmittance changes were independent of the bending radius. Finally, the U-shaped polymer cladding fiber sensor was used to monitor the silica scale formation in geothermal brine at the Takigami geothermal plant.

Localized Surface Plasmon Resonance Based Hetero-Core Optical Fiber Sensor Structure for the Detection of L-Cysteine

In this article, a hetero-core optical fiber sensor structure is developed for the diagnosis of L-Cysteine content in human urine. The hetero-core structure is created by sequentially cascading the single mode-multimode-single mode fibers using thermal fusion splicing. The multimode section of fiber probe is etched out and coated with synthesized gold nanoparticles (AuNPs), polyvinyl alcohol stabilized silver nanoparticles (PVA-AgNPs) and graphene oxide (GO). The AuNPs and PVA-AgNPs are used to initiate the localized surface plasmon resonance (LSPR) phenomenon on the application of exponentially decaying evanescent waves. The layer of GO is used to provide the larger surface area and binding sites for the L-Cysteine (L-Cys) molecules. Based on the combination of NPs, two different configurations of sensor probes are developed. In first one, a layer of AuNPs is deposited over fiber surface and further followed by the coating of GO, and named Probe I. In the second one, a layer of PVA-AgNPs is sandwiched between the fiber surface and GO layer and termed as Probe II. The characterization of synthesized NPs and GO solutions, and developed sensor probes are done by using UV-Vis spectrophotometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). To authenticate the biocompatibility of developed sensor probes, the artificial aqueous samples of L-Cys ranges from 0 μM to 1 mM are tested. To determine the stability of L-Cys, a pH level based study is also carried out to ensure the good stability of analyte in aqueous samples. From the results, it was ascertained that the response of Probe II is better in terms of attained limit of detection and sensitivity that is 126.6 μM and 0.0009 nm/μM, respectively.

Surface-Plasmon-Resonance-Based Optical-Fiber Micro-Displacement Sensor with Temperature Compensation.

Micro-displacement measurements play a crucial role in many industrial applications. Aiming to address the defects of existing optical-fiber displacement sensors, such as low sensitivity and temperature interference, we propose and demonstrate a novel surface plasmon resonance (SPR)-based optical-fiber micro-displacement sensor with temperature compensation. The sensor consists of a displacement-sensing region (DSR) and a temperature-sensing region (TSR). We employed a graded-index multimode fiber (GI-MMF) to fabricate the DSR and a hetero-core structure fiber to fabricate the TSR. For the DSR, we employed a single-mode fiber (SMF) to change the radial position of the incident beam as displacement. The resonance angle in the DSR is highly sensitive to displacement; thus, the resonance wavelength of the DSR shifts. For the TSR, we employed polydimethylsiloxane (PDMS) as a temperature-sensitive medium, whose refractive index is highly sensitive to temperature; thus, the resonance wavelength of the TSR shifts. The displacement and temperature detection ranges are 0–25 μm and 20–60 °C; the displacement and temperature sensitivities of the DSR are 4.24 nm/μm and −0.19 nm/°C, and those of the TSR are 0.46 nm/μm and −2.485 nm/°C, respectively. Finally, by means of a sensing matrix, the temperature compensation was realized.

Enhanced sensitivity of heterocore structure surface plasmon resonance sensors based on local microstructures

A method to improve the refractive index (RI) and temperature sensitivities of optical fiber based on surface plasmon resonance (SPR) sensors is proposed and experimentally demonstrated. It is realized by using a precision femtosecond laser system to manufacture microstructures on a heterocore optical fiber structure (multimode single-mode multimode fiber, MSM). The microstructured MSM structure fiber-optic sensors were coated with 60-nm gold (Au) film to test and verify RI sensing, obtaining an enhancement of the maximum sensitivity range from 2845.18 to 3313.15 nm/RIU. The fabricated sensors were additionally coated with a layer of polydimethylsiloxane, which has a high negative thermos-optic coefficient, to conduct a series of temperature sensing experiments. Experimental results showed that the maximum sensitivity increased from 1.1998 to 1.5646 nm/°C. Compared with nonmicrostructured sensors, the RI and temperature sensitivity of the proposed sensor has increased 16.4% and 30.2%, respectively. The simply fabricated, low-cost, and high-sensitivity SPR sensor has promising applications in many areas, especially in the biochemical field.

Dual-channel surface plasmon resonance refractive index sensor based on modified hetero-core structure fiber

We propose and demonstrate a novel dual-channel SPR refractive index sensor based on hetero-core structure fiber. For the traditional hetero-core structure fiber SPR sensor, the resonance wavelength range is unchangeable. We solve this issue by polishing the traditional hetero-core structure fiber as circular truncated cone shape. By this method, we can adjust the resonance wavelength range flexible by changing fiber polishing angle. With increasing of fiber polishing angle, the resonance wavelength range will red-shift. When fiber polishing angle is 14°, and refractive index range is from 1.333 to 1.385, the resonance wavelength range is from 754 nm to 965 nm, which is away from that of the traditional hetero-core structure fiber SPR sensor (600 nm to 700 nm). Therefore, we realize dual-channel sensing by wavelength division multiplexing technology. The sensitivity of two channels are 1980.77 nm/RIU and 4057.69 nm/RIU respectively. In addition, the resonance wavelength and sensitivity of the sensor have a well consistency no matter which working way we adopt. The proposed dual-channel SPR sensor has important applications for multiple analytes detection.

Refractive Index Measurement in Sucrose Solution and Beverage Using Surface Plasmon Resonance Sensor Based on Hetero-core Structured Fiber Optic

The surface plasmon resonance (SPR) sensor was fabricated by depositing silver thin film on the surface of hetero-core structured fiber optic. The SPR sensor based on hetero-core structured fiber optic was applied to measure refractive index of sucrose solution and fruit juices. The sensor part was immersed in sucrose solution and/or juice and the propagating light spectra were measured. It was shown that the fiber optic SPR sensor showed a good agreement with that measured by conventional refractometer.

Harnessing the fiber fuse for sensing applications.

A simple refractive index sensor based on a small section of fiber damaged by the fiber fuse is proposed and demonstrated with a sensitivity of 350.58 nm/refractive index unit (RIU). For comparison, a hetero-core structure fiber sensor composed of a short no-core fiber (NCF) sandwiched between two pieces of single-mode fibers is demonstrated with a sensitivity of 157.29 nm/RIU. The fiber fuse technique can allow mass production of sensors by incorporating small sections of the damaged fiber of any type into each device. We believe this is the first application of the periodic damage tracks in optical fibers formed by the fiber fuse.

Humidity Sensor Based on Hetero-Core Structured Fiber Optic Covered with Layer-by-Layer Thin Film

Humidity sensors based on hetero-core structured fiber optic has been fabricated. In the hetero-core structured fiber optic, a short piece of singlemode fiber optic is inserted between multi-mode fibers. Layer-by-layer (LBL) technique is applied to prepare humidity sensitive film. The humidity sensitive LBL film, prepared using polyacrylate as polyanion and polyallylamine as polycation, was deposited on the singlemode fiber part of the hetero-core structured fiber optic. According to increasing of deposition cycle, the propagating loss increased because of increasing the refractive index at the sensing part by the formation of the film. After deposition procedure, the sensor part was immersed in calcium chloride solution to dope the deliquescence material in the thin film. The humidity sensors ware characterized as a function of relative humidity (RH). The sensor shows that the propagating light power increased according to increasing of RH. This is because the dry film having a higher refractive index absorbed moisture and swollen, and then the refractive index decreased resulting in the decreasing of the leakage of the propagating light at the singlemode fiber part. In addition, the increasing of calcium chloride concentration caused the enhancement of the sensitivity. This is because calcium chloride is deliquescence material and absorbed water from atmosphere, resulting in the swelling, decreasing of the refractive index at low humidity.

Localized Surface Plasmon Resonance Sensor Based on Hetero-core Structured Fiber Optic

Localized surface plasmon resonance (LSPR) sensor is constructed by immobilizing gold nanoparticles (AuNPs) on the surface of hetero-core structured fiber optic and characterized as a refractive index sensor. According to increasing of dipping time of the aminated sensing part in the AuNPs suspension, the propagating light intensity near 545nm decreased. According to increasing of the sensor length, in addition, the propagating light intensity at 540nm decreased. The sensor showed that the propagating loss at 545nm increased according to increasing of ethanol concentration in water, derived from the refractive index increase of the mixture.

OTDRを用いたヘテロコア型光ファイバセンサ

A new type of fiber sensor using OTDR (Optical Time-Domain Reflectometer) has been developed whose concept is intended for structural damage monitoring through fiber networks spread in wide areas to be monitored. The sensor has a spliced hetero-core structure in which a short-length, different core-size fiber is inserted in a single-mode-fiber network line with low transmission loss for the wavelength of 1.3μm. In this study, two types of sensor are demonstrated which are low-insertion-loss and high-sensitivity ones. The variation of the bending losses has been experimentally measured to be 9x10-2, and 3.6dB/deg for the low-insertion loss and the high-sensitivity types, respectively, as a function of rotation angles with which the hetero-core portion is wound. Qualitative discussions are also made both on how these two sensors show high sensitivities to relatively large-radius-bending of the hetero-core portion and on why their characteristics performances are appeared in different fashions