Optical Fiber Structure Research Articles

Single-mode—multimode—single-mode and lossy mode resonance-based devices: a comparative study for sensing applications

In this work, a thin-film consisting of 15 bilayers (estimated thickness: 210 nm) of titanium (IV) oxide and poly(sodium 4-styrenesulfonate) is simultaneously deposited onto two optical fiber structures: a single-mode--multimode--single-mode (SMS) device and a lossy mode resonance (LMR)-based device. The performance of both structures, as refractometers and relative humidity sensors, is studied and compared. In both cases, the sensitivity of the LMR-based device (955 nm/RIU and 3.54 nm/RH %, respectively) highly improves the one of the SMS (142 nm/RIU and 0.3 nm/RH %). These facts can be taken into account when developing sensors based on either SMS or LMR technologies.

Bend-insensitive distributed sensing in singlemode-multimode-singlemode optical fiber structure by using Brillouin optical time-domain analysis.

We propose a bend-insensitive distributed Brillouin optical fiber sensing by using a singlemode-multimode-singlemode optical fiber structure for the first time to the best of our knowledge. The sensing fiber is a graded-index multimode fiber (GI-MMF) sandwiched by two standard single-mode fibers (SMFs) with central-alignment splicing at the interface between GI-MMF and SMF to excite the fundamental mode in GI-MMF. The sensing system can resist a minimal bend radius of 1.25mm while maintain the measurement performance, with which the measured coefficients of strain and temperature are 421.6MHz/% and 0.826MHz/°C, respectively. We also demonstrate that the higher-order modes excited in GI-MMF can be easily influenced by bending, so that exciting the fundamental mode is essential for bend-insensitive distributed sensing.

A novel method of damage model recognition for intelligent composite structures based on double-fiber sensors network

Fiber optic smart composite structures technologies have become one of the key technologies in material science. The smart composite structure is used to estimate damage states. But it is difficult to detect the internal damage with little or no indication on the surface of the composite structures. In this paper, we proposed a method for identification of different damage model of composite structures using a double-fiber sensor network. The glass fiber reinforced epoxy resin E-51 honeycomb structure composite which is commonly used in aircraft was chosen to be the base material. The smart structures employed 8-way fibers sensors. Each four-fiber as a layer were orthogonally embedded into different depth of structures. The sensors were connected to a data acquisition system based on ARM. The transmission properties of double-fiber sensors were investigated and then validated by experiments in laboratory. Here three different energy impacts damage experiments were conducted on the double-fiber smart composite structures. The results show the method based on double-fiber sensors network used for the identification of the different damage models is feasible. It has a very important reference value for the future health monitoring technology of the composite structures.

Preparation and photoelectric properties of indium tin oxide depositional optical fiber by centrifugal spinning

The purpose of this paper is to prepare an integrating light propagative, transparent and conductive optical fiber. This optical fiber is made by the coating of a thin layer of indium tin oxide (ITO) nanofibers. ITO nanofibers are fabricated via centrifugal spinning process and wrap around the quartz optical fiber. Field emission scanning electron microscopy, X-ray diffraction analysis, UV–Vis spectrophotometer, Avometer and Luminance colorimeter are used to characterize the morphology, crystal structure and photoelectric properties of ITO-coated optical fiber. Results show that the resistivity of ITO-coated optical fiber is around 0.87 (Ω cm); the average optical transmittance is more than 85 % in the visible range, and the ITO-coated optical fiber has a certain light propagation. This work laid the groundwork for future application in fiber sensors.

Controlling temporal solitary waves in the generalized inhomogeneous coupled nonlinear Schrödinger equations with varying source terms

In this paper, we study the families of solitary-wave solutions to the inhomogeneous coupled nonlinear Schrödinger equations with space- and time-modulated coefficients and source terms. By means of the similarity reduction method and Möbius transformations, many types of novel temporal solitary-wave solutions of this nonlinear dynamical system are analytically found under some constraint conditions, such as the bright-bright, bright-dark, dark-dark, periodic-periodic, W-shaped, and rational wave solutions. In particular, we find that the localized rational-type solutions can exhibit both bright-bright and bright-dark wave profiles by choosing different families of free parameters. Moreover, we analyze the relationships among the group-velocity dispersion profiles, gain or loss distributions, external potentials, and inhomogeneous source profiles, which provide the necessary constraint conditions to control the emerging wave dynamics. Finally, a series of numerical simulations are performed to show the robustness to propagation of some of the analytically obtained solitary-wave solutions. The vast class of exact solutions of inhomogeneous coupled nonlinear Schrödinger equations with source terms might be used in the study of the soliton structures in twin-core optical fibers and two-component Bose-Einstein condensates.

Design and analysis of low bend losses of the air core optical fiber for wavelength selective devices

In this paper, the bending loss, modal field diameter and the modal field distribution of the air core optical fiber are investigated. The effect of optical and geometrical parameters on the bending loss, power confinement and modal field diameter are examined in this special fiber. Detailed design parameters and operation principles of the air core optical fiber are discussed. The structure is based on a unique three layered structure of air core optical fiber, having the central air core, germanium silicate ring core, and silica cladding. It has been demonstrated that air core optical fiber has an excellent mode transformation capability. The air core optical fiber is expected to have a versatile application in local area optical communication networks and tunable wavelength selective devices. The main advantages of air core optical fiber are low bend loss and small mode field diameter, which is a prime focus of this paper.

Sensors Based on Thin-Film Coated Cladding Removed Multimode Optical Fiber and Single-Mode Multimode Single-Mode Fiber: A Comparative Study

Two simple optical fibre structures that do not require the inscription of a grating, a cladding removed multimode optical fibre (CRMOF) and a single-mode multimode single-mode structure (SMS), are compared in terms of their adequateness for sensing once they are coated with thin-films. The thin-film deposited (TiO2/PSS) permits increasing the sensitivity to surrounding medium refractive index. The results obtained can be extrapolated to other fields such as biological or chemical sensing just by replacing the thin-film by a specific material.

On the propagation and sensitivity of optical fiber structure with twisted clad DB interface under slow-wave approximation

The paper deals with the study of slow-wave propagation through an optical fiber having linear, homogeneous and isotropic dielectric core with a newly proposed helical DB interface at the core-clad boundary. The dispersion relation is deduced, and the flux density patterns are studied considering a few low-order hybrid modes under slow-wave approximation. Furthermore, the sensitivity of fiber structure is investigated in terms of variations in the evanescent wave enhancement factor due to the pitch angle of twists and the thickness of clad section. It has been found that the field enhancement factor can be tuned by properly adjusting the pitch, and also, the thickness of clad section as the evanescent waves in this region get greatly affected due to the varying pitch.

Simultaneous strain and temperature measurement by cascading few-mode fiber and single-mode fiber long-period fiber gratings

A hybrid optical fiber structure of two cascading long-period fiber gratings (LPFGs), respectively, inscribed on a segment of few-mode fiber (FMF) and single-mode fiber (SMF), is proposed and experimentally demonstrated. This structure could be used for simultaneous measurement of strain and temperature. The FMF-LPFG exhibits an opposite temperature response and higher strain sensitivity compared to that of the SMF-LPFG, which can improve the measurement resolutions. Experimentally, the strain and temperature sensitivities of the proposed sensor are -2.9 pm/με and -17.6 pm/°C, respectively, for the FMF-LPFG; for the SMF-LPFG, these are -1.47 pm/με and 46.4 pm/°C, respectively. The maximum errors are ±7.98 με and ±0.54°C for strain and temperature, respectively.

Investigation on Closed-loop Fiber Optic Gyroscope Structure and Operation

In this paper, I reviewed comprehensively the structure and operation of closed-loop IFOGs, Feedback Erbium-doped fiber amplifier (EFDA) FOGs, called FE-FOG. The procedure of finding the Sagnac shift for closed-loop IFOG has been studied. The signal processing in the closed-loop IFOG was simulated using PSCAD software. In the closed-loop IFOG, the phase shift was derived through frequent use of Sagnac loop. The output signal is injected in the input again as feedback. The shift phase between clockwise and counterclockwise waves in each complete route, including primary and feedback route, is identified as Sagnac shift phase. According to Sagnac shift phase we could determine angular rotation rate.

Magnetic Field Sensing Based on Magnetic-Fluid-Clad Fiber-Optic Structure With Up-Tapered Joints

A kind of magnetic field sensor based on mode interference effect is proposed. The sensing arm consists of two special up-tapered joints formed on the traditional single-mode fiber by fusion tapering technique. Magnetic fluid is used as the cladding of the structure. The interference valley wavelength or the transmission loss of the sensing structure is sensitive to the external magnetic field, which is utilized for magnetic field sensing. The sensitivity of shift of interference valley wavelength with magnetic field can be up to 325.3 pm/mT in the range of 0-16 mT. The variation of transmission loss at valley wavelength with magnetic field has a sensitivity of -0.2121 dB/mT in the range of 2-30 mT.

Magnetic field sensing based on magnetic-fluid-clad fiber-optic structure with taper-like and lateral-offset fusion splicing.

A kind of magnetic field sensor composed of magnetic fluid surrounding a segment of singlemode fiber is proposed. The taper-like and lateral-offset fusion splicing techniques are employed. The sensing principle is based on cladding mode interference. The interference valley wavelength or transmission loss of the sensing structure is sensitive to the external magnetic field, which is utilized for magnetic field sensing. The linear response regions are obtained in the range of 38-225 Oe and 250-475 Oe. For the valley-wavelength-shift-type sensing, the sensitivities are 14.1 pm/Oe and 26 pm/Oe at low and high field ranges, respectively. For the transmission-loss-variation-type sensing, the sensitivity of -0.024 dB/Oe is achieved for the magnetic field strength ranging from 250 to 475 Oe.

Technology for the Preparation of PDMS Optical Fibers and Some Fiber Structures

We describe a new technology for the fabrication of polydimethylsiloxane (PDMS) optical fibers and PDMS fiber structures, based on fiber drawing from partially cured PDMS. This technology allows the fabrication of PDMS fibers in a wide range of diameters and different lengths. We demonstrate the potential of such prepared PDMS optical fibers on a variety of typical and unconventional fiber structures such as multimode optical fibers, looped and twisted fibers, and optical fiber couplers.

Filtering properties of the tunable microwave photonic filter with stimulated Brillouin scattering

The filtering properties of a continuously tunable single-passband microwave photonic filter based on stimulated Brillouin scattering (SBS) are investigated. The filter utilizes the advantage of combining phase-modulated RF signal and dual-sideband suppressed-carrier pump signal to achieve the SBS-based tunable narrowband filtering. The effects of pump power on the out-of-band rejection (OBR) and 3-dB bandwidth, the optical fiber structure on the resonant sideband, and input RF signal power on the OBR and 3-dB bandwidth are analyzed theoretically and experimentally. The results show that the pump power has the potential of increasing the OBR and tuning 3-dB bandwidth, whereas the RF signal power has nearly no influence on the two parameters.

Temperature insensitive single-mode-multimode-single-mode fiber optic structures with two multimode fibers in series.

We propose and demonstrate a temperature insensitive single-mode-multimode-single-mode fiber optic structure consisting of two in-series multimode fibers of appropriate lengths and of opposite temperature sensitivities. A simple approximate expression to estimate the required length ratio of the multimode fiber sections has also been derived whose prediction is found in good agreement with the experiment. The study should be useful in realizing various fiber optic devices based on multimode interference with zero temperature cross sensitivity.

Spectral width reduction in lossy mode resonance-based sensors by means of tapered optical fibre structures

This contribution pursues the goal of achieving an optical fibre-based platform to detect anti-gliadin antibodies (AGAs), in order to early diagnose celiac disease. To this purpose, the generation of lossy mode resonances (LMRs) in several evanescent field optical structures was studied both theoretically and experimentally. LMRs were obtained by adsorbing a polymeric thin-film onto the optical structures using the layer-by-layer assembly technique. The LMR shape depends on the geometry of the optical structure and its attenuation was controlled just by tuning the length of the device. The best performance was obtained with tapered single-mode optical fibres, which provided more than a 50% reduction in the spectral width of the LMR by using a shorter device. This improvement was successfully applied to detect anti-gliadin antibodies (AGAs) in 5ppm concentration, what can be used to diagnose celiac disease, and shows the potential of this technology to address biosensing applications.

Temperature compensated refractometer based on a cascaded SMS/LPFG fiber structure

A hybrid optical fiber structure for refractive index (RI) measurement with the temperature compensation capability is reported. The structure consists of a CO2 laser-induced long period fiber grating (LPFG) and a section of single mode–multimode–single mode (SMS) fiber structure. The LPFG serves as a refractometer with a temperature compensator using a simple SMS fiber structure. The sensing mechanism of this device has been investigated and experimentally demonstrated. The SMS structure was insensitive towards the change in the ambient RI but was sensitive towards the changes in the ambient temperature whereas the LPFG was sensitive towards both. A sensitivity matrix was built to compensate the temperature-RI crosstalk. The capability of simultaneous measurement of temperature and RI of the sensor was experimentally validated.

Estimation of LiBr-H2O Using Multimode Interference (MMI)

We use multimode interference (MMI) as an alternative optical technique to estimate lithium bromide (LiBr)concentration, of the work pair LiBr-H2O, in absorption heat pumps (AHP). The sensing element is a singlemodemultimode-singlemode (SMS) fiber optic structure. This is fabricated by splicing a precisely dimensioned multimodefiber (MMF) section between two singlemode fibers (SMFs). The operation principle is based on the multimodeinterference (MMI) effect occurring in the MMF section. For that purpose, different concentrations of the mixture wereprepared (from 44.30% to 60.69%) to study their optical response. The input field profile entering the sensing element,which is the naked (no cladding) MMF section of the SMS fiber structure, produced different transmitted intensityresponses for each of these concentrations. Thus the optical characterization of the mixture was used to establish amathematical relation to estimate the LiBr concentration. A linear fit for solutions with concentrations ranging from43.30% to 50.87% and refractive indices between 1.421 and 1.439 is demonstrated.

Study on the bend characteristics of single mode-multimode-single mode optical fiber structure

In this paper, the bend characteristics of the single mode-multimode-single mode (SMS) fiber structure are experimentally investigated. SMS fiber structure is very sensitive to the bend. The central wavelength shifts to shorter wavelength with the increasing of fiber bend angle. The central wavelength shift changes with the changing of multimode fiber(MMF) bend section length. The shorter bend MMF has higher sensitivity to the bend angle.

Fiber structure based on a depressed inner cladding fiber for bend, refractive index and temperature sensing

A fiber-optic structure based on a section of a double-clad fiber with depressed inner cladding is investigated for bend, refractive index and temperature sensing. The structure is formed by splicing a section of SM630 fiber between two standard fibers SMF-28. The operation principle relies on the sensitivity of cladding modes that are induced at a splice of fibers having different refractive index profiles. The mode structure of the double cladding fiber and the mechanism of formation of dips in the transmission spectra are discussed. The transmission spectra of the structure are measured for different curvatures of the inserted fiber section. The shift of dips to long wavelengths with increasing curvature of the fiber is observed and its dependence on the fiber section length and the direction of bending is investigated. The sensitivities of the spectral dips to the external refractive index and temperature are also measured.