Thin-core Fiber Modal Interferometer Research Articles

Switchable Fiber Ring Laser Sensor for Air Pressure Based on Mach–Zehnder Interferometer

This work shows a study of pressure gas sensing using an optical fiber interferometer inside a gas cell; here, a thin-core fiber modal interferometer (TCFMI) is fabricated using two distinct types of fiber, a single-mode fiber (SMF model 1060XP) and thin-core fiber (TCF model 460 HP). This interferometric structure is set into a ring fiber laser with an ytterbium-doped fiber (YDF) pumped with a 980 nm laser diode. The TCFMI interference spectrum shows wavelength shifting and amplitude variations as the chamber pressure is altered in the range of 5 to 40 PSI; these changes control the ring fiber laser cavity response linearly and lead to good stability in its wavelength operation in a range of 30 nm. The proposed interferometer operates as a wavelength-selective filter in the fiber ring laser cavity. The single laser emission shows a side mode suppression ratio of 34.17 dB. The fiber ring laser is a reliable alternative for air pressure sensing applications.

Highly Sensitive Fiber Ring Laser Sensor for Curvature Using a Modal Interferometer

A curvature sensing Ytterbium-doped fiber ring, using a Thin Core Fiber Modal Interferometer (TCFMI) was experimentally demonstrated in this work. The TCFMI was implemented by fusion splicing a segment of a thin-core fiber, with a small core diameter, between two single-mode fiber sections. The proposed TCFMI functioned as a wavelength-selective filter in the fiber ring laser cavity. It was optimized to achieve a Side Mode Suppression Ratio (SMSR) of 35 dB; the laser emission produced a sensor resolution of 0.37 nm. The experimental results also showed a high curvature sensitivity close to −38.26 nm/ $\text{m}^{{-1}}$ from 0 $\text{m}^{{-1}}$ to 0.399 $\text{m}^{{-1}}$ curvature range. Here, the laser sensor exhibited a bandwidth of 16 nm in the 1072 nm to 1056 nm wavelength range. The fiber ring laser is a low-cost alternative for curvature sensing applications.

Sensitivity-Enhanced Strain Sensor Based on Thin-Core Fiber Modal Interferometer Interacted With Tilted Fiber Bragg Grating

A sensitivity-enhanced strain sensor constructed by a 7-mm-long thin-core fiber (TCF) splicing with a 10-mm-long tilted fiber Bragg grating (TFBG) was proposed. The modal interferometer formed by the TCF will interact with the spectrum of the TFBG to form an overlapped spectrum, which will extremely increase the axial strain sensitivity of the TFBG. Experimental results showed that the wavelength shifts of the resonant dip in the overlapped spectra for the applied axial strain have a high sensitivity of 0.67 pm/ $\mu \varepsilon $ . Meanwhile, the proposed sensor has the temperature self-compensation function for the variation of the external temperature simply by measuring the relative wavelength shifts of the Bragg mode of the TFBG.

Ultrahigh sensitivity with different taper geometries of thin-core fiber modal interferometer for refractive index sensing

A highly sensitive refractive index sensor based on a fiber in-line Mach–Zehnder interferometer sensor based on single-mode–tapered thin-core–single-mode fiber is proposed. We developed a theoretical model using wide-angle beam propagation method in cylindrical coordinates to simulate light propagation performance of such fiber devices. Tapered structures using different taper geometries (linear, exponential, and parabolic taper) with waist diameters as low as 30 μm are presented. The proposed sensor has an ultrahigh sensitivity of 996.4 nm/refractive index unit in glycerin solution with different concentrations in water using the linear taper geometry. The designed structure presents the merits of high sensitivity, which is 6 times higher than that of the thin-core fiber modal interferometer and makes it an excellent candidate for biochemical sensing applications.

Reversible and Fast Responsive Optical Fiber Relative Humidity Sensor Based on Polyelectrolyte Self-Assembly Multilayer Film

A high-performance fiber-optic relative humidity (RH) sensor was prepared by layer-by-layer self-assembly of polycation, poly (4-vinylpyridinium chloride), and polyanion, sodium alginate, on the surface of a thin-core fiber modal interferometer. The process of layer-by-layer self-assembly was monitored by UV-vis spectroscopy and surface profilometer. The morphology of the fabricated multilayer film was characterized by atomic force microscopy and field emission scanning electron microscopy. A fast, reversible, and linear response to RH with a high resolution of 0.1 nm/1% RH has been experimentally demonstrated by the proposed fiber-optic sensor.

Long-period fiber grating cascaded to thin-core fiber for simultaneous measurement of liquid refractive-index and temperature

PurposeThe purpose of this paper is to demonstrate a simple fiber sensor for simultaneous measurement of liquid refractive-index (RI) and temperature.Design/methodology/approachThe sensor structure is formed by a long period fiber grating cascaded with a section of thin-core fiber. The long period fiber grating is fabricated on single mode fiber, followed by a section of 20-mm length thin-core fiber which is a modal interferometer.FindingsCladding mode interference between long period fiber grating and thin-core fiber modal interferometer is weak in the experimental investigation. Both of these two cladding mode type fiber devices are sensitive to surrounding RI and temperature. So the RI and temperature can be measured simultaneously by monitoring the spectral characteristics of the compound sensor. The sensitivity is calibrated and sensor matrix is provided in the experiment.Originality/valueThis proposed fiber sensor is simple, tough, cost-effective and suitable for discriminate the liquid RI and temperature with high sensitivity.

Trace hydrogen sulfide gas sensor based on tungsten sulfide membrane-coated thin-core fiber modal interferometer

A novel fiber-optic hydrogen sulfide sensor based on a thin-core Mach-Zehnder fiber modal interferometer (TMZFI) is demonstrated and fabricated. This in-line interferometer is composed of a short section of thin-core fiber sandwiched between two standard single mode fibers, and the fast response to hydrogen sulfide is achieved via the construction of tungsten sulfide film on the outside surface of the TMZFI using the dip-coating and calcination technique. The fabricated sensing nanofilm is characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) spectrometer, Fourier transform infrared (FTIR) and spectroscopic analysis technology, etc. Experimental results showed that the WS2 sensing film has a hexagonal structure with a compact and porous morphology. The XPS and FTIR indicate that the existence of two elements (W and S) is demonstrated. With the increasing concentration of hydrogen sulfide, the interference spectra appear blue shift. In addition, a high sensitivity of 18.37 pm/ppm and a good linear relationship are obtained within a measurement range from 0 to 80ppm. In addition, there is an excellent selectivity for H2S, which has also been proved by the surface adsorption energy results of tungsten sulfide with four gases (H2S, N2, O2 and CO2) by using the density functional theory calculations. This interferometer has the advantages of simple structure, high sensitivity and easy manufacture, and could be used in the safety monitoring field of hydrogen sulfide gas.

An in-line Mach-Zehnder Interferometer Using Thin-core Fiber for Ammonia Gas Sensing With High Sensitivity

Ammonia is an important indicator among environmental monitoring parameters. In this work, thin-core fiber Mach-Zehnder interferometer deposited with poly (acrylic acid) (PAA), poly (allyamine hydrochloride) (PAH) and single-walled carbon nanotubes (SWCNTs-COOH) sensing film for the detection of ammonia gas has been presented. The thin-core fiber modal interferometer was made by fusion splicing a small section of thin-core fiber (TCF) between two standard single mode fibers (SMF). A beam propagation method (BPM) is employed for the design of proposed interferometer and numerical simulation. Based on the simulation results, interferometer with a length of 2 cm of thin-core fiber is fabricated and experimentally studied. (PAH/PAA)2 + [PAH/(PAA + SWCNTs-COOH)]8 film is deposited on the outer surface of thin-core fiber via layer-by-layer (LbL) self-assembly technique. The gas sensor coated with (PAH/PAA)2 + [PAH/(PAA + SWCNTs-COOH)]8 film towards NH3 gas exposure at concentrations range from 1 to 960 ppm are analyzed and the sensing capability is demonstrated by optical spectrum analyzer (OSA). Experimental results show that the characteristic wavelength shift has an approximately linear relationship in the range 1–20 ppm, which is in accordance with the numerical simulation. Thus, this paper reveals the potential application of this sensor in monitoring low concentration NH3 gas.

Simultaneous measurement of magnetic field and temperature based on an etched TCFMI cascaded with an FBG

In this paper, a dual-parameter measurement scheme based on an etched thin core fiber modal interferometer (TCMI) cascaded with a fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous measurement of magnetic field and temperature. The magnetic field and temperature responses of the packaged TCFMI were first investigated, which showed that the magnetic field sensitivity could be highly enhanced by decreasing of the TCF diameter and the temperature-cross sensitivities were up to 3–7Oe/°C at 1550nm. Then, the theoretical analysis and experimental demonstration of the proposed dual-parameter sensing scheme were conducted. Experimental results show that, the reflection of the FBG has a magnetic field intensity and temperature sensitivities of −0.017dB/Oe and 0.133dB/°C, respectively, while the Bragg wavelength of the FBG is insensitive to magnetic field and has a temperature sensitivity of 13.23pm/°C. Thus by using the sensing matrix method, the intensity of the magnetic field and the temperature variance can be measured, which enables magnetic field sensing under strict temperature environments. In the on–off time response test, the fabricated sensor exhibited high repeatability and short response time of ∼19.4s. Meanwhile the reflective sensing probe type is more compact and practical for applications in hard-to-reach conditions.

Trace dissolved ammonia sensor based on porous polyelectrolyte membrane-coated thin-core fiber modal interferometer

A fiber-optic ammonia sensor based on a thin-core fiber modal interferometer (TCFMI) is fabricated and evaluated. The fast response to ammonia is achieved via the construction of poly(acrylic acid) (PAA) and poly(allyamine hydrochloride) (PAH) nanoporous films on the side surface of the TCFMI using the layer-by-layer (LbL) assembly technique. The fabricated sensing nanocoating is characterized by FT-IR spectrometer, UV–vis absorption spectroscopy, surface profiler, and scanning electron microscopy (SEM). Porous structure is beneficial to the diffusion of ammonia molecules through the multilayers. The TCFMI with a 10-cycle PAH/PAA nanoporous film sensor presented an excellent reproducibility with a fast response time to ammonia. The optimal detection range of this sensor is around 1–260ppm with a low limit of detection (LOD).

Simultaneous measurement of displacement and temperature based on thin-core fiber modal interferometer

An optical-fiber sensor based on a thin core fiber (TCF) has been proposed and experimentally demonstrated for simultaneous measurement of displacement and temperature. This in-line sensor consists of a segment of TCF between two segments of single-mode fibers (SMFs), and the interference between the core mode and the cladding mode of the TCF occurs. The transmission spectral responses to displacement as well as environmental temperature have been investigated. Experimental results show that the displacement sensitivities of –0.01028nm/μm and −0.01535nm/μm for a displacement range of 0–650μm have been achieved, and the corresponding temperature sensitivities reach about 0.00942nm/°C and 0.00493nm/°C within a large temperature range of 20–90°C, respectively. The proposed sensor exhibits such advantages as simple structure, compact size, ease of fabrication, high sensitivity, etc. Therefore, it has potential applications in accurate multi-parameter measurements.

Liquid seal for temperature sensing with fiber-optic refractometers.

Liquid sealing is an effective method to convert a fiber-optic refractometer into a simple and highly sensitive temperature sensor. A refractometer based on the thin-core fiber modal interferometer is sealed in a capillary tube filled with Cargille oil. Due to the thermo-optic effect of the sealing liquid, the high refractive-index sensitivity refractometer is subsequently sensitive to the ambient temperature. It is found that the liquid-sealed sensor produces a highest sensitivity of −2.30 nm/°C, which is over 250 times higher than its intrinsic sensitivity before sealing and significantly higher than that of a grating-based fiber sensors. The sensing mechanisms, including the incidental temperature-induced strain effect, are analyzed in detail both theoretically and experimentally. The liquid sealing technique is easy and low cost, and makes the sensor robust and insensitive to the surrounding refractive index. It can be applied to other fiber-optic refractometers for temperature sensing.

Ultrasensitive Temperature Sensor Based on Refractive Index Liquid-Sealed Thin-Core Fiber Modal Interferometers

An ultrasensitive temperature sensor based on a thin-core fiber modal interferometer (TCFMI) is proposed and demonstrated in this paper. After its middle is etched to a thin residual diameter, the TCFMI is sealed in a capillary tube filled with refractive index (RI) liquid. The thermo-optic effect of RI liquid turns the TCFMI into an ultrasensitive temperature sensor with sensitivity up to -22.23 nm/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C at 3.2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. The sensitivity is over 1000-fold that of the bare TCFMI in air. This proposed temperature sensor is also simple, cost-effective, and suitable for a variety of applications.

Label-free, disposable fiber-optic biosensors for DNA hybridization detection

A novel and highly sensitive fiber-optic DNA sensor based on a thin-core fiber modal interferometer (TCFMI) is demonstrated by using a layer-by-layer (LbL) self-assembly technology. Poly(ethylenimine) (PEI), poly(acrylic acid) (PAA) and single-stranded DNA (ssDNA) were used for the preparation of a polyelectrolyte multilayer film for DNA detection. The film thickness was measured through a surface profilometer. The surface morphologies of (PEI/PAA)4, (PEI/PAA)4.5 and (PEI/PAA)4(PEI/DNA)1 multilayer films were characterized by atomic force microscopy. The fabricated DNA sensors were tested with different types of target ssDNA solutions with a concentration of 1 μM. The results show that the sensitivity of the TCFMI-based ssDNA sensor is 0.27 nm/matched-base at the concentration of 1 μM and can even distinguish the number of matched bases of ssDNA chains.

Biocompatible Fiber-Optic pH Sensor Based on Optical Fiber Modal Interferometer Self-Assembled With Sodium Alginate/Polyethylenimine Coating

We report a new biocompatible fiber-optic pH sensor based on optical fiber modal interferometer. Two biocompatible polyelectrolytes, i.e., sodium alginate (SA) and polyethylenimine (PEI), are alternatively deposited on the side surface of the thin-core fiber modal interferometer (TCFMI) via a layer-by-layer (LbL) electrostatic self-assembly (ESA) technique for pH sensing applications. With a measurement of water contact angles, it is revealed that the hydrophilicity of such a coating depends on the pH values. The refractive index (RI) of the coating is modulated through swelling/deswelling behavior when the pH of the solution is changed. The induced RI change is precisely determined by the TCFMI through a measurement of the destructive-interference wavelength. The thickness and morphology of the self-assembled sensing coating are characterized by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The sensor exhibits a liner, fast, reversible and monotonic response in a large pH range with resolution of 0.0093 pH unit which makes the sensor very promising for biomedical and clinical pH measurement applications.

Hydrostatic pressure sensor based on a gold-coated thin-core fiber modal interferometer and ripple shift measurement

We propose a hydrostatic pressure sensor based on a gold-coated thin-core fiber modal interferometer (TCFMI). A thin-core fiber is spliced to a single mode fiber forming a single-end fiber modal interferometer (FMI) due to the core mismatch and the fiber end reflection. Relative reflection spectra of TCFMIs based on thin-core fibers with different lengths are investigated. The TCFMI is gold-coated to enhance the optical reflectivity, which also results in the ripple of the relative reflection spectra of TCFMI. A high hydrostatic pressure sensor test system is proposed and the performance of the pressure sensor has been experimentally investigated. A pure-ripple-shift measurement method is used to achieve the demodulation of the sensor. The proposed pressure sensor has a sensing range up to 40MPa and a sensitivity of 44.8pm/MPa.

基于薄芯光纤模态干涉技术的曲率光纤传感器

A new fiber-optic bending curvature sensor based on thin-core fiber modal interferometer is presented.In order to eliminate the environment effect on curvature measurement,one standard single-mode fiber with a segment of thin-core fiber is used for sensing,while the other without is used for reference.The insertion of thin-core optical fiber and single mode fiber core mode mismatch,resulting in high-order cladding modes are excited and interfere with the core mode to form an in-fiber modal interferometer.When a curvature applied to the thin-core fiber,the mode indices and the fiber length will change,and thus the transmission peaks will shift.Both ends of the fiber are connected to the translation stage.When adjusting the translation stage distance,the curvature of thin-core optical fiber is changed,leading to the transmission dip move to shorter wavelength.According to this distance,the bending curvature of the sensor can be measured.Experimental results show that this device has low loss,low cost and high sensitivity.

基于薄芯光纤模态干涉技术的曲率光纤传感器

基于薄芯光纤模态干涉技术的曲率光纤传感器

Highly sensitive and selective fiber-optic modal interferometric sensor for detecting trace mercury ion in aqueous solution

A novel type of fiber-optic mercury ion (Hg2+) sensor was prepared by coating poly (N-ethyl-4-vinylpyridinium chloride) (P4VP·HCl) and poly (sodium-p-styrenesulfonate) (PSS) ultrathin film on the surface of a thin-core fiber modal interferometer (TCFMI) with layer-by-layer (LbL) electrostatic self-assembly method. The fabricated TCFMI Hg2+ sensor exhibits a high selectivity to Hg2+ and its detection limit and response time are 10−9 M and 30 s, respectively. The LbL electrostatic self-assembly process is monitored with a quartz crystal microbalance (QCM) and UV–vis spectroscopy for film growth. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) were used to characterize the morphology of the ultrathin film. Both demonstrated nanoporous film, which is helpful in shortening the response time of the TCFMI Hg2+ sensor.

Fiber-optic metal ion sensor based on thin-core fiber modal interferometer with nanocoating self-assembled via hydrogen bonding

A new fiber-optic metal ion sensor based on a thin-core fiber modal interferometer (TCFMI) is presented. Poly(4-vinylpyridine) (P4VP) and poly(acrylic acid) (PAA) are layer-by-layer deposited on the side surface of the TCFMI via hydrogen bonding for the detection of metal ion in aqueous solutions. Ultraviolet–visible (UV–vis) absorption spectroscopy is employed to monitor the self-assembly process, and the thickness and morphology of the nanocoating are characterized by scanning electron microscopy (SEM). When the sensor is immersed into the aqueous solutions containing metal ions, the refractive index (RI) of the nanocoating is changed because of the association of metal ions with the nanocoating, which was verified by energy dispersive X-ray (EDX). Based on the RI sensing capability of TCFMI, one can detect the concentration of metal ions through the measurement of the dip wavelength of the sensor's transmission spectrum. The experiment results exhibit that the sensor is reusable and with a fast response in a wide metal ion concentration range (10 nM–0.1 M). The limit of detection (LOD) of the sensor is around 9.6 nM experimentally.