Optical Fiber Structure Research Articles

A displacement sensor based on balloon-like optical fiber structure

A modal interferometric fiber-optic displacement sensor based on the balloon-like structure is investigated experimentally. When the bending radius of the balloon-like structure is reduced to 3.0 mm, the displacement sensitivity could reach up to 71.49 nm/mm. Moreover, the evolution process of the transmission spectra in a wide dynamic displacement range exceeding 22 mm is analyzed, which can provide guiding significance for sensor designing. The proposed displacement sensor is extremely low-cost, robust, and compact.

Spin-orbit coupling suppressed high-capacity dual-step-index ring-core OAM fiber.

We design and fabricate a dual-step-index ring-core fiber (RCF) for orbital angular momentum (OAM) mode transmission. It has been proven that the proposed novel, to the best of our knowledge, dual-step-index ring-core structure can suppress the spin-orbit coupling and cut off the radial higher-order modes when the mode number becomes very large. In experiments, we demonstrate that the fabricated fiber can support OAM8,1 with the interferometric method, where four higher-order mode groups are weakly-coupled. We also measure the loss of each mode according to the cut-back method and the loss can achieve <0.3 dB/km for the OAM modes with an order from |l| = 1 to |l| = 5. The exploration of this novel optical fiber structure may provide ideas and knowledge for the improvement of the optical fiber communication capacity.

A fiber-optic formic acid gas sensor based on molybdenum disulfide nanosheets and chitosan works at room temperature

In this paper, two optical fiber gas sensors were successfully developed, and the detection of formic acid gas was realized at room temperature. The limit of detection for the chitosan material modified probe for formic acid can reach 1 ppm. The combination of molybdenum disulfide (MoS2) nanosheets and chitosan effectively improves sensor response and recovery time. The gas-sensitivity characteristics of the two sensors have been studied, compared and discussed respectively, and the good selectivity and repeatability have been verified by experiments. By combining the gas-sensitive material with the optical fiber structure, this paper verifies and broadens the method for enhancing the sensitivity of the formic acid gas sensor and the realization of concentration detection at room temperature. Because it breaks through the limitation of high-temperature catalytic conditions, the probe is expected to be used for formic acid gas detection, and can be extended to the room temperature detection of other gases under harsh environmental conditions such as strong electromagnetic interference.

Low-cost wearable device based D-shaped single mode fiber curvature sensor for vital signs monitoring

A low-cost wearable pulse and respiratory monitoring system based on D-shaped single mode fiber (SMF) curvature sensor is proposed and investigated. The curvature sensing performance of D-shaped SMFs with different transmission loss are tested and analyzed, and the sensitivity up to − 7.208%/m−1. The D-shaped optical fiber structure is encapsulated by polydimethylsiloxane (PDMS) and implanted in a wrist strap, which realizes good wearability and comfort in the process of human pulse monitoring. The system adopts laser source module and signal acquisition module for integrated and miniaturized design, and real time signal acquisition using Field-Programmable Gate Array (FPGA). The real-time monitoring of pulse signal intensity and frequency before and after exercise was realized. The results show that pulse intensity increased after exercise, with a 10%− 30% increase in pulse frequency, which is consistent with the results in medical theory. In addition, the D-shaped SMF encapsulated by PDMS also was implanted into the belt, which also successfully applied to the monitoring of respiratory signals under quiet and walking conditions.

MoS2-spaced bimetal composite structure as SERS-SPR sensor for glucose detection

To obtain more information and reduce false alarms during molecular identification, the Molybdenum disulfide (MoS2) spaced gold (Au)-silver (Ag) bimetal composite structure for surface-enhanced Raman scattering (SERS)-surface plasmon resonance (SPR) sensor is proposed. The sensor combines the advantages of D-shape plastic optical fiber (D-POF), MoS2-spaced Au and Ag bimetallic composite structure, showing excellent sensitivity. Compared with the Ag/Au bimetallic D-POF experiment (the sensitivity is 2163.57 nm/RIU), the sensitivity of proposed sensor was improved effectively and calculated as 2473.37 nm/RIU in a range of alcohol solution. To evaluate the SERS activity of the proposed sensor, Rhodamine 6 G (R6G) molecules has been successfully detected by Au/MoS2/Ag D-POF sensor with low limited of detection (LOD) of 10−9 M. Meanwhile, the proposed sensor successfully detected glucose with a concentration of 0.625~20% by observing the change of resonance wavelength and the characteristic peak of SERS signal. The highly sensitive spectral signals, richer and more comprehensive information can be obtained to reduce false positives in identification of biomolecules.

Improving the sensitivity of new passive optical fiber ring sensor based on meta-dielectric materials

In this paper a new passive optical fiber sensor depends on surface plasmon resonance (SPR) decorate by fabricating a configuration on metal-dielectric materials. A single-mode fiber is applied to harness the transmission light. In this work, FDTD method is introduced to control the injected refractive index on ring and fiber; hence, this leads to the shifting of the fiber SPR resonance wavelength. The advantageous of this mechanism is optical fiber sensor has a high sensitivity with the maximum of up to 1700 nm/RIU, wide detection range of 1–1.4 RIU (refractive index unit), and a nanometer resolution with a minimum of 4 nm. In addition, moreover we consider several performance parameters like sensitivity and FOM, interestingly it is shown applying silicon optical fiber improve the sensitivity. Comparing with the reported numerical and measurements based on an optical fiber structure, the experimental results based on fiber ring resonator demonstrate good ability and agreement, therefore the proposed structure pave the path new operation of optical fiber sensors.

Temperature sensing characteristics based on coreless- few mode-coreless optical fiber structure

提出了一种基于无芯-少模-无芯光纤结构的温度传感器，对传感器进行了理论分析和实验研究。该传感器将无芯光纤(coreless fiber, CLF)与少模光纤(few-mode fiber, FMF)同轴熔接，构建无芯-少模-无芯的光纤结构，结构两端熔接单模（single mode fiber, SMF）光纤作为输入输出光纤，第1段无芯光纤与单模光纤的模式失配起到激发高阶模的作用，少模光纤中的LP01与LP11两种模式沿少模光纤纤芯传输，在第2段无芯光纤的作用下LP01与LP11两种模式重新耦合回单模光纤，LP01与LP11两种模式发生干涉，形成干涉光谱。当外界温度变化时，两种模式的光程差发生变化，干涉光谱的干涉波谷发生漂移，选取2个不同的干涉波谷作为特征波长，进行实验分析。实验结果表明：波长在1 550 nm和1 534 nm附近的干涉谷均发生红移，相应的温度灵敏度分别为68 pm/℃和44.5 pm/℃。该传感结构制作简单、灵敏度高，有很好的应用前景。

A Label-Free Biosensor Based on E-SMS Optical Fiber Structure for Anti BSA Detection

A Label-Free Biosensor Based on E-SMS Optical Fiber Structure for Anti BSA Detection

Simultaneous Measurement of Seawater Salinity and Temperature With Composite Fiber-Optic Interferometer

A seawater salinity and temperature simultaneous measurement sensor is proposed and demonstrated in this article, which consists of a Fabry-Perot interferometer (FPI) and Mach-Zehnder interferometer (MZI) composite fiber-optic structure. The femtosecond laser micromachining technique is used to modify the single-mode fiber (SMF) and inscribe three consecutively connected waveguides, in which the modified areas are corroded by hydrofluoric (HF) acid to form in-fiber channels. One internal channel forms a FPI and is selectively filled with the low refractive index UV adhesive to measure temperature. The other channel is combined with the waveguide structure to constitute a MZI, which has a wavelength shift response to salinity and temperature variations. In theoretical modeling, the sensing performances of the composite interference structure are analyzed separately. The experimental results show that the salinity and temperature sensitivities are −2.323 nm/‰ and 2.176 nm/°C, respectively. Besides, the repeatability, stability, and measurement error are tested, which shows that the sensor has good sensing performance and has the potential for seawater parameter measurements.

Polymer-coated polishing seven-core Mach-Zehnder interferometer for temperature sensitivity enhancement

A novel high sensitivity temperature sensor based on side-polished Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The configuration of sensor is a section of side-polished seven-core optical fiber (SCF) structure sandwiched between two waist-enlarged tapers. In the proposed sensing structure, the temperature sensitivity can be improved theoretically by coating polymer on its polished part because of the different thermal expansion effects between polymer and fiber. The experimental results show that the temperature sensitivity of the polymer-coated sensor is 4.58 times as that of the sensor without polymer coating, and the maximum sensitivity is 336.67 pm/°C in the range of 30 °C to 65 °C. The improving time is not obviously changed before coating polymer, but affected by the polishing depth of SCF in the coated structure. The results show that the temperature sensitivity of sensor can be effectively improved, and it is easy to manufacture and operate.

In-Plane Strain Measurement in Composite Structures with Fiber Bragg Grating Written in Side-Hole Elliptical Core Optical Fiber.

In this paper, the application of a fiber Bragg grating written in a highly birefringent side-hole elliptical core optical fiber for two-axial strain measurement is presented. Hybrid optical fiber structures achieved by combining large side-holes and elliptical core result in a very high birefringence of 1 × 10−3 and thus high initial Bragg peak spectral separation of 1.16 nm, as well as a very high transverse force sensitivity, of up to 650 pm/(N/mm) or even −1150 pm/(N/mm), depending on the fiber orientation with respect to the applied force. Due to the ~22 %m/m GeO2 concentration in the core the fiber being highly photosensitive, which significantly simplifies FBG fabrication by UV illumination without the need for prior hydrogen loading, which worsens thermal stability. Finally, the developed FBGs written in the highly birefringent side-hole elliptical core optical fiber were embedded in the square composite plates and applied for strain measurements. Tests of two-directional four-point bending have shown usability of such FBG for two-axial in-plane strain measurement with a single FBG in iso-thermal conditions.

Taper-in-taper fiber structure-based LSPR sensor for alanine aminotransferase detection

Alanine aminotransferase (ALT), a critical component of human blood, is inextricably associated with liver injury. The current study develops a novel biosensor based on the localized surface plasmon resonance (LSPR) principle for the detection of ALT analytes at concentrations ranging from 0 to 1000 Units per liter (U/L). According to the authors' knowledge, this is the first time an optical fiber structure with a taper-in-taper structure has been developed for biosensing applications. It is fabricated using the three-electrode semi-vacuum taper technique and is characterized using a combiner manufacturing system. Gold nanoparticles (AuNPs), molybdenum disulfide nanoparticles (MoS2-NPs), and cerium oxide nanoparticles (CeO2-NPs) are immobilized on the sensing region to improve the sensing performance. Prior to application, these nanoparticles are characterized using a high-resolution transmission electron microscope (HR-TEM) and a UV-Visible spectrophotometer. AuNPs promote the LSPR phenomenon, whereas MoS2-NPs/CeO2-NPs contribute to the sensor probe's biocompatibility and stability. Following that, the probe surface was functionalized with glutamate oxidase (GluOx) to improve selectivity. The probe demonstrated an excellent linear relationship with the subsequent assay's ALT concentration. Additionally, the probe's performance characteristics such as reusability, reproducibility, stability, and selectivity are evaluated in order to determine its clinical utility in diagnosing liver injury.

Phototherapy in the Treatment of Diabetic Foot — A Preliminary Study

Abstract The first part of the publication presents a substantively insightful literature study on the essence and effects of light waves on wound healing in living organisms, including the use of phototherapy in the treatment of the diabetic foot. A knitted textile dressing was designed and manufactured for phototherapy of patients with diabetes suffering from diabetic foot syndrome (DFS). The proposed solution is intended for the treatment of dermal tissues within the patient's foot affected because of diabetic disease at an early stage. Thus, the use of a knitted dressing with incorporated fiber optic structures and powered by a semiconductor laser emitting a 405 nm light wave from its entire surface would prevent further anomalies of the patient's tissues and help to avoid surgical intervention.

Optical Bend Sensor Based on Eccentrically Micro-Structured Multimode Polymer Optical Fibers

We report on a novel bend sensor with high flexibility and elasticity based on Bragg grating structures in polymer optical fibers to detect bending for the measurement of movement. The concept is very simple and relies on the inscription of eccentrical Bragg gratings into multimode graded-index polymer optical fibers via contact exposure with a krypton fluoride excimer laser in the ultraviolet region and an optimized phase mask. Depending on the fiber deformation, the lattice constant of the inscribed Bragg grating is strained or compressed due to its position relative to the fiber core. This in turn results in a specific shift of the Bragg wavelength of up to $1.3\text{ nm}$ to the red or blue wavelength region, respectively, which is sufficiently large to be reliably detected. Therefore, as proof of principle, deformation along one axis can be observed with a single Bragg grating with a maximum sensitivity of up to $65\text{ pm/m}^{-1}$ . Moreover, multiple Bragg gratings inscribed into the same polymer optical fiber at different positions around the fiber axis allow to determine the shape deformation of the fiber relative to a reference frame with similar accuracy. Consequently, this technology could form the basis for new applications in the areas of medical diagnostics, robotics or augmented reality, which are lacking affordable sensor systems to date.

A highly stretchable optical strain sensor monitoring dynamically large strain for deformation-controllable soft actuator

In this paper, we report a highly stretchable optical strain sensor that can be compatible with artificial muscle and wearable human-assistive devices. The optical strain sensor is fabricated by embedding a polymeric optical fiber thermoformed for bi-tortuous structure in silicone elastomer. The strain sensor can detect uniaxial strain using amplitude of output light intensity that increases as curvature of the curved regions becomes enlarged with uniaxial strain. Due to the benefits from curvilinear design of the optical fiber and sensor structure with the elastomeric matrix securing geometric recovery from being elongated, the strain sensor is capable of reliable detection of arbitrary tensile strain in a wide range from 0% to 120%. It possesses fast, reversible, and durable strain-sensing performance with a small hysteresis even under continuative cyclic loadings of large strain. As integrated into a soft rolled-actuator based on acrylic elastomer, we finally demonstrate the strain-sensor performance is enough to monitor dynamic deformation response of the soft actuator.

Influence of Two-Frequency Radiation Intensity Fluctuations on the Output Signal of a Vortex Optical Fiber Forming OAM Address in Polyharmonic Sensor Technology

A schematic diagram of a RoF radio-optic system with vortex signals is presented, in which the radio frequency is determined by the difference between the wavelengths of two lasers. It is assumed that the generation of a vortex signal can be performed through a vortex fiber-optic periodic structure, which can be obtained using a technology similar to the manufacture of long-period fiber Bragg gratings. The parameters of the grating are modeled assuming that the fundamental light-guide mode (LP01) is applied to the specified vortex element, and the higher-order mode (LP11) is reflected. It was found that the distortion of the vortex signal can be reduced by introducing apodization and chirping of this periodic structure. The following optimal parameters have been estimated: the apodization and chirp multiplier functions, at which the distortions of the amplitude and phase of the vortex signal, as well as the appearance of an unwanted angle distortion, will be minimal. It is shown that such gratings can be exploited in addressed sensors systems using the orbital angular momentum (OAM) of a lightwave as a unique sensor address.

An Ultra-High Sensitivity Optical Fiber Refractive Index Sensor Based on Plasmonic Mach-Zehnder Interferometer

An ultra-high sensitivity refractive index sensor is proposed and designed by integrating plasmonic Mach-Zehnder interferometer and the optical fiber structure together. The configuration, the numerical simulations and the performance of the proposed structure have been analyzed and discussed by the finite element method. At the working wavelength of 1.55 μm, the designed sensor is optimized to obtain the sensing sensitivity 20141.7 nm/RIU. Furthermore, it is found that with the increase of the working wavelength, the sensitivity will also increase, thus the proposed sensor has the potential to work in the near-infrared band. This sensor not only shows a high sensitivity to refractive index detection, but also is highly applicable in the detection of liquid concentration, gas concentration or temperature.

High sensitivity and ultra compact fiber-optic microtip SPR thermometer coated with Ag/PDMS bilayer film

In this paper, we report an ultra-compact reflective SPR microtip temperature probe, which can achieve 2-D spatial resolution of several microns. The pencil-shaped all-fiber microtip proposed by us is a SO2 cone-cylinder with a length of 40 μm and a gradient diameter of 2 μm-10 μm, which can be used to develop multi-type tiny functionalized sensors. Due to the strong evanescent field of the ultra-fine microtip, the surface plasmon resonance (SPR) can be effectively stimulated by depositing nano-silver (Ag) film on its surface. Owing to the high refractive index (RI) sensitivity of SPR effect and the high thermo-optic coefficient (TOC) of polydimethylsiloxane (PDMS), the temperature sensitivity of microtip SPR probe coated with PDMS micron-film can reach to 1.985 nm/°C. Teflon 1600 nano-film on the surface of the SPR thermometer can effectively enhance the non-stickiness, moisture-proof and wear resistance. The test results show that the probe is hardly disturbed by humidity. This new sensing platform can be demonstrated by assembling high-performance sensing materials and ultra-compact fiber-optic structures.

Fiber optic hybrid structure based on an air bubble and thin taper for measurement of refractive index, temperature, and transverse load

A hybrid-structured optical fiber sensor for measurement of refractive index (RI), temperature, and transverse load is proposed and experimentally demonstrated, which is made by fusing a section of single-mode fiber (SMF) between an air bubble and a thin taper. The air bubble acts as a Fabry-Perot interferometer (FPI) and at the same time serves as excitation for Mach-Zehnder interferometer (MZI). The transverse load can be measured by demodulating the reflection spectrum of the FPI. The RI and temperature can be measured by demodulating the transmission spectrum of the MZI. The experimental results show that the transverse load sensitivity of FPI is 1.596 nm/N. The RI and temperature sensitivities are -103.2 nm/RIU and 103.2 pm/°C, respectively. Due to its ease of manufacture, low cost, and high sensitivity, the hybrid-structured optical fiber sensor is practical for sensing applications.

The impact of polarization‐maintaining and multimode fibre lengths on strain and temperature sensitivities of single‐mode–multimode–polarization‐maintaining–multimode–single‐mode‐based fibre optic sensors

A fibre loop mirror sensor is proposed and demonstrated for strain and temperature measurements in experiment. In these schemes, fibre loop mirrors are constructed with single-mode-multimode-polarization-maintaining-multimode-single-mode optical fibre (SMPMS) structures. The strain and temperature characteristics of the sensor, depending on the lengths of multimode fibre (MMF) and polarization-maintaining fibre (PMF), are studied in the experiment. The results indicate that PMF and MMF lengths have less impact on strain sensitivity but a remarkable impact on temperature sensitivity, which is consistent with the theoretical analysis. The best strain and temperature sensitivities of an SMPMS structure sensor can reach up to 39.0 pm/με and 2.366 nm/°C, respectively. The sensors have the merits of easy fabrication, cost-efficiency and high temperature sensitivity and are quite suitable for fields requiring high-precision measurement.