Fiber Segments Research Articles

Discriminative measurement for temperature and humidity using hollow-core Fabry-Perot interferometer

In this work, an in-fiber Fabry-Perot interferometer (FPI) is proposed and experimentally demonstrated for ambient relative humidity (RH) and temperature measurements. The FPI is manufactured from short segments of hollow-core fiber (HCF) and photonic crystal fiber (PCF). The air-cavity in the HCF segment enables a strong light-air interaction whereas the air holes of the PCF serve as vents which enable the exchange of air between the air-cavity and the surrounding medium. Our findings show that the dip intensity is solely sensitive to the change in RH with a linear sensitivity of 0.06273 dB/%RH in the range of 35–71%RH whereas the dip wavelength is solely sensitive to the ambient temperature with a linear sensitivity of 10.64 pm/°C in the range of 25–70 °C. The cross-sensitivity between the two measurands can be disregarded, therefore no sophisticated equation is required for the discriminative measurement of humidity and temperature.

Experimental and numerical investigation on hollow core photonic crystal fiber based bending sensor.

Recent progress in designing optimized microstructured optical fiber spreads an application scenario of optical fiber sensing. Here, we investigate the bending measurement based on a specially designed hollow core photonic crystal fiber (HC-PCF). Numerical simulation indicates that the bending sensitivity is mainly determined by the diameter of the hollow core and also depends on the coupled modes. Experimentally, a direction-independent bending sensor is fabricated by sandwiching a segment of specially designed HC-PCF into two segments of single mode fibers. The bending sensitivity of our device is improved 10 times by increasing the diameter of the hollow core. Bending measurement is validated at two orthogonal planes. The maximum sensitivity up to 2.8nm/deg is obtained at 14° bending angle. Additionally, a low thermal sensitivity of 2.5pm/°C is observed from 18°C to 1000°C. The sensor is robust, easy to fabricate and cost effective, which is promising in the field of small-angle bending measurement under a large temperature range.

Practical reflective birefringent fiber interferometer sensor.

This paper proposes a simple and practical reflective birefringent fiber interferometer sensor that consists of a polarization beam splitter, a polarization-maintaining transmission fiber, and a sensor unit comprising two segments of birefringent fibers and a thin-film reflector. This sensor could be used for dual parameter sensing. Experiments with different temperatures and lateral loads applied to the sensor unit demonstrated temperature and load sensitivity of ∼0.0010 nm/°C and 0.298nm/N, respectively. Further study showed that temperature-insensitive lateral load measurement can be achieved by using equal length of birefringent fibers and performing differential wavelength measurement. The sensor is robust against environmental disturbance on the transmission fiber, making it potentially attractive for practical field applications.

Brillouin optical time-domain analysis enhanced by forward stimulated Brillouin scattering: proof-of-concept demonstration

A distributed Brillouin optical time-domain analysis (BOTDA) sensor enhanced by forward stimulated Brillouin scattering (FSBS) based distributed Brillouin amplification (DBA) was proposed and presented. Due to co-propagating of pump and Stokes lights, the Stokes pulse is effectively amplified in front segment of fiber, resulting in flatter gain distribution. As a proof-of-concept, FSBS-DBA based BOTDA sensing with distance of ∼74.2 km, Brillouin frequency shift standard deviation of less than ∼2 MHz and spatial resolution of ∼10 m was demonstrated. This method is compatible and complementary with backward SBS-based DBA, and features better pumping efficiency than Raman amplification.

Enhanced Distributed Fiber Optic Vibration Sensing and Simultaneous Temperature Gradient Sensing Using Traditional C-OTDR and Structured Fiber with Scattering Dots.

We present results demonstrating several beneficial effects on distributed fiber optic vibration sensing (DVS) functionality and performance resulting from utilizing standard single mode optical fiber (SMF) with femtosecond laser-inscribed equally-spaced simple scattering dots. This modification is particularly useful when using traditional single-wavelength amplitude-based coherent optical time domain reflectometry (C-OTDR) as sensing method. Local sensitivity is increased in quasi-distributed interferometric sensing zones which are formed by the fiber segments between subsequent pairs of the scattering dots. The otherwise nonlinear transfer function is overwritten with that of an ordinary two-beam interferometer. This linearizes the phase response to monotonous temperature variations. Furthermore, sensitivity fading is mitigated and the demodulation of low-frequency signals is enabled. The modification also allows for the quantitative determination of local temperature gradients directly from the C-OTDR intensity traces. The dots’ reflectivities and thus the induced attenuation can be tuned via the inscription process parameters. Our approach is a simple, robust and cost-effective way to gain these sensing improvements without the need for more sophisticated interrogator technology or more complex fiber structuring, e.g., based on ultra-weak FBG arrays. Our claims are substantiated by experimental evidence.

Fiber-Optic Interferometric Sensor Based on the Self-Interference Pulse Interrogation Approach for Acoustic Emission Sensing in the Graphite/Epoxy Composite

Fiber-optic acoustic emission sensors are highly attractive for non-destructive testing applications in composites due to their small size, galvanic isolation, and immunity to electromagnetic interference (EMI). The significant part of such sensors is based on the Fabry-Perot interferometers (FPIs) because of their small size, high sensitivity, and their ease of embedding into a composite structure. However, linear demodulation techniques of their signals suffer from the limited dynamic range and require an additional operating point control. In this paper, we propose the novel self-interference interrogation approach for the fiber-optic FPI-based acoustic emission sensor, which allows the FPI to be interrogated as a two-beamlike interferometer with current-induced frequency modulation of the light source. Then, with using of a PGC-ATAN demodulation algorithm or similar, phase signals can be measured independently of the interferometer operating point with the extended dynamic range. The sensor is based on the fiber-optic FPI that consists of the optical fiber segment bounded by two TiO2 mirrors: the semitransparent one (20%-25% reflecting and -1.6-dB loss) in the fiber and the external one (99.9% reflecting) at the fiber tip. The mirrors are spaced 7 mm apart. Two FPI sensors were fabricated and experimentally investigated. One sensor was mounted on the surface of the graphite/epoxy composite plate, and another one was embedded into its structure. The experimental investigation results of two considered interferometric acoustic emission sensors in comparison with the reference piezoelectric transducer GT301 are presented. Obtained results confirmed the efficiency of the proposed interrogation approach in terms of FPI usage as a two-beamlike interferometer for acoustic emission signals detection and might be used for the implementation in existing and new FPI-based acoustic emission sensing systems.

Spatial analysis of thickness changes in ten retinal layers of Alzheimer\u2019s disease patients based on optical coherence tomography

The retina is an attractive source of biomarkers since it shares many features with the brain. Thickness differences in 10 retinal layers between 19 patients with mild Alzheimer’s disease (AD) and a control group of 24 volunteers were investigated. Retinal layers were automatically segmented and their thickness at each scanned point was measured, corrected for tilt and spatially normalized. When the mean thickness of entire layers was compared between patients and controls, only the outer segment layer of patients showed statistically significant thinning. However, when the layers were compared point-by point, patients showed statistically significant thinning in irregular regions of total retina and nerve fiber, ganglion cell, inner plexiform, inner nuclear and outer segment layers. Our method, based on random field theory, provides a precise delimitation of regions where total retina and each of its layers show a statistically significant thinning in AD patients. All layers, except inner nuclear and outer segments, showed thickened regions. New analytic methods have shown that thinned regions are interspersed with thickened ones in all layers, except inner nuclear and outer segments. Across different layers we found a statistically significant trend of the thinned regions to overlap and of the thickened ones to avoid overlapping.

Low-temperature crosstalk and surrounding refractive index insensitive vector bending sensor based on hole-assistant dual-core fiber.

A low-temperature crosstalk and surrounding refractive index insensitive vector bending sensor based on resonance coupling is proposed and experimentally demonstrated. The sensor is constructed by directly sandwich-splicing asegment of single eccentric hole-assisted dual-core fiber between two single-mode fibers. The transmission characteristicsof the sensor are theoretically analyzed by combining coupled-mode theory and full-vector finite-element method. The bending responses of the sensor are experimentally measured in the curvature range of0-3.6651 m-1. The bending sensitivities are -15.95 nm/m-1 and 14.87 nm/m-1 at 0° and 180° bending orientation, respectively, which are higher than that of most long-period fiber-grating-based and interferometer-based vector bending sensors. Moreover, the temperature and surrounding refractive index responses of the sensor are investigated. The measured results show that the proposed sensor has a low temperature sensitivity of 21.7pm/°C in the range of 15°C-55°C and is insensitive to the surrounding refractive index in the range of 1.335-1.425, which reduces the cross-sensitivity from temperature and surrounding refractive index.

Phase Measurement of Optical Fiber via Weak-Value Amplification

A precision phase detection scheme employing a weak-value amplification (WVA) technique is proposed and demonstrated. With a minimum detectable phase change of $\sim \!10^{-5}$ rad, the present system rivals similar free-space schemes using bulk optical components only. The new setup is tested in a simple hydro-pressure detection experiment, with a short segment of fiber under water, showing a remarkable responsivity to small pressure changes.

A liquid refractive index sensor based on 3-core fiber Michelson interferometer

A liquid refractive index (RI) sensor based on in-fiber Michelson interferometer (MI) is proposed and experimentally demonstrated, which consists of a segment of 3-core fiber (3CF) fusion spliced with a short piece of multimode fiber (MMF). The operation principle of the MI lies in the intermodal interference of the 3CF via employing MMF to excite high-order modes, and the 3CF end face reflects the interference spectrum which loaded the surrounding RI information. By measuring the reflection spectrum variation, the RI can be determined. Experimentally, a linearly RI sensitivity of -151.56 dB/RIU is achieved in the sensing range of 1.3335-1.3720 RIU, and the temperature sensitivity in water is 0.048 nm/°C.

Optimized design of single-pump fiber optical parametric amplifier with highly nonlinear fiber segments using a differential evolution algorithm

Fiber optical parametric amplifiers (FOPAs) are regarded as one of the candidate optical amplifiers for future ultralong-distance, large-capacity, and high-speed optical fiber communication systems. FOPAs provide high signal gain and low noise figures compared with other optical amplifiers. However, they suffer from gain fluctuation, which restricts commercial application. Optimization of the dispersion parameters of highly nonlinear fibers (HNLFs) employed as gain media is essential because they have an immediate impact on the flatness of the amplifier. An optimization method for multiple HNLF segments using the differential evolution algorithm is proposed to minimize spectral gain variation. We theoretically yield an FOPA with an average signal gain of 20 dB and gain fluctuation

Generation of noise-like pulses with 203 nm 3-dB bandwidth.

Raman-scattering-assisted noise-like pulse (NLP) generation was achieved by using an appropriate segment of high nonlinearity fiber in an erbium-doped fiber laser. Broadband spectrum with 203 nm 3-dB bandwidth was obtained, which, to the best of our knowledge, is the broadest bandwidth achieved for NLPs. The broadband operation is the result of tailored cavity design, which optimizes various effects including the Raman scattering effect to maximize the bandwidth of NLPs. Further broadening the NLP spectrum up to 294 nm was achieved by using spectral filtering outside the cavity with a polarization beam splitter.

Effect of a magnetic field on polarisation of light in an optical fibre with a random distribution of linear birefringence

A numerical model is proposed to describe the evolution of polarisation of a light wave propagating through a telecommunication fibre with random linear birefringence in a magnetic field. As a result of statistical processing of a set of numerical simulation results, a convenient phenomenological formula is obtained for the first time for the dependence of the average value of the polarisation rotation angle on the magnetic field, the fibre parameters and its length. It is found that the average value of the polarisation rotation angle in a long telecommunication fibre in the representation of the Stokes vectors linearly depends on the applied longitudinal magnetic field (as in the classical Faraday effect for an isotropic medium) but is proportional to the root of the fibre length. It is theoretically shown and experimentally confirmed that the polarisation rotation angle for an extended segment of a telecommunication fibre (50 km) is two orders of magnitude less than that for an isotropic fibre of the same length and material.

Simulation of generation of ultrashort pulses in a laser based on the nonlinear polarisation evolution in two segments of a polarisation-maintaining fibre

A model describing generation of ultrashort optical pul­ses in a fibre cavity with Kerr nonlinearity and normal dispersion is constructed based on numerical solution of a nonlinear Schrödinger equation. The model makes it possible to investigate the specific features of pulsed generation of a passively mode-locked laser bas­ed on the effect of nonlinear polarisation evolution (NPE) in two segments of a polarisation-maintaining (PM) fibre. It is shown theoretically that the proposed scheme may provide generation of linearly chirped optical pulses with a spectral width of above 25 nm and a centre wavelength of 1030 nm.

Hydrogen Sulfide Gas Sensor Based on Copper/Graphene Oxide Composite Film-Coated Tapered Single-Mode Fibre Interferometer

Abstract A hydrogen sulfide (H2S) gas sensor based on copper (Cu) nanoparticle deposited graphene oxide (GO) composite membrane with two waist-enlarged tapers is proposed. Three segments of the single-mode fibres (SMFs) are sequentially fused to obtain two waist-enlarged bitapers of Mach–Zehnder interferometer (MZI). When the light of a broadband light source transmits through the first bitaper, some light enters the fiber cladding; the lights of core mode and cladding mode are coupled at the second taper and an MZI is successfully fabricated. The copper/graphene oxide (Cu/GO) composite sensing film is coated on the surface of the second SMF, and the effective refractive index of the coating is changed when the sensitive film adsorbs the target gas. The correlation between the gas concentration and the wavelength shift is achieved and the H2S can be measured effectively. The results show that a uniform Cu/GO film is successfully coated on the surface of the fiber, and when the thickness of the sensitive film is about 1.2 μm, the sensor has a sensitivity of 4.42 pm/ppm and a good linearity and selectivity for H2S in the range of 0–60 ppm, and the limit of detection is 2.79 ppm. The response time and recovery time are approximately 31 and 48 s, respectively. The sensor has the advantages of small volume, low cost, simple structure, and easy manufacture and so on, which is suitable for on-line monitoring of H2S.

Effect of the planar coil and linear arrangements of continuous carbon fiber tow on the electromagnetic interference shielding effectiveness, with comparison of carbon fibers with and without nickel coating

The effect of macroscale planar arrangement (planar coil, unidirectional and crossply arrangements, with a gap between tow segments) of continuous polyacrylonitrile-based carbon fiber (7.0-μm diameter) 12 K tow on the electromagnetic interference shielding effectiveness for normal-incident unpolarized plane wave is reported at frequencies ranging from 200 to 2000 MHz. The planar coil configuration, which favors magnetic interaction, has not been previously reported for shielding with any material. For all arrangements, the total shielding effectiveness (SET) is dominated by the absorption loss (SEA), whether the fiber is nickel-coated or not. The nickel coating (0.25-μm thick) increases SET from 2‒6 dB to 13–26 dB for the planar coil configuration, but has little effect for the crossply/unidirectional configuration. Both SET and SEA are greatly increased by the nickel coating, which also reduces SEA's frequency dependence and increases the absorption's fractional contribution to shielding, particularly for the planar coil configuration below 1000 MHz (from 53%‒78% to 83%–94%). The advantage of the crossply configuration over the unidirectional configuration is greater without the nickel coating. Increasing the tow size from 12 K to 24 K (with the gap decreased from 3.0 to 2.0 mm) raises SEA for planar coil and unidirectional arrangements. The results agree essentially with electromagnetic theory.

Математическая модель неравномерной микромеханической деформации участка оптического волокна при осесимметричном поверхностном нагружении

Математическая модель неравномерной микромеханической деформации участка оптического волокна при осесимметричном поверхностном нагружении

Distribution and activation of matrix metalloproteinase-2 in skeletal muscle fibers.

A substantial intracellular localization of matrix metalloproteinase 2 (MMP2) has been reported in cardiomyocytes, where it plays a role in the degradation of the contractile apparatus following ischemia-reperfusion injury. Whether MMP2 may have a similar function in skeletal muscle is unknown. This study determined that the absolute amount of MMP2 is similar in rat skeletal and cardiac muscle and human muscle (~10-18 nmol/kg muscle wet wt) but is ~50- to 100-fold less than the amount of calpain-1. We compared mechanically skinned muscle fibers, where the extracellular matrix (ECM) is completely removed, with intact fiber segments and found that ~30% of total MMP2 was associated with the ECM, whereas ~70% was inside the muscle fibers. Concordant with whole muscle fractionation, further separation of skinned fiber segments into cytosolic, membranous, and cytoskeletal and nuclear compartments indicated that ~57% of the intracellular MMP2 was freely diffusible, ~6% was associated with the membrane, and ~37% was bound within the fiber. Under native zymography conditions, only 10% of MMP2 became active upon prolonged (17 h) exposure to 20 μM Ca2+, a concentration that would fully activate calpain-1 in seconds to minutes; full activation of MMP2 would require ~1 mM Ca2+. Given the prevalence of intracellular MMP2 in skeletal muscle, it is necessary to investigate its function using physiological conditions, including isolation of any potential functional relevance of MMP2 from that of the abundant protease calpain-1.

Two-dimensional microbend sensor based on the 2-core fiber with hump-shaped taper fiber structure

Abstract A novel two-dimensional bending vector sensor formed by cascading two hump-shaped tapers (HSTs) in a segment of 2-core fiber (2CF) is proposed and fabricated, in which the HSTs serve as the mode splitting and coupling. Several modes are excited at the first HSTs, where a part of the light energy is propagated within the center core of the 2CF, and the other part is coupled to the external core. Due to the effective refractive index difference between these core modes, they are recoupled into the lead-out single-mode fiber (SMF) at the second HSTs and interfere with each other. The bulge of the HSTs and two cores of the 2CF are distributed in a triangle. Owing to the asymmetric structure, the sensor can distinguish multiple bending directions. In addition, the linear spectral responses for bending and temperature are observed experimentally. The proposed sensor has many advantages, including compact, inexpensive, and high directional resolution ratio. Experiment results show that the sensor can distinguish bending directions and experience a maximum sensitivity of −6.182 nm/m−1 with a bending range of 0–0.98 m−1 without dead zone.

Temperature- and strain- insensitive transverse load sensing based on optical fiber reflective Lyot filter

For the first time to our knowledge, we propose and experimentally demonstrate a transverse load sensor using an optical fiber reflective Lyot filter. Such an optical fiber reflective Lyot filter consist of a fiber polarizer, a segment of polarization-maintaining fiber and a single mode fiber based fiber reflector. By demodulating the wavelength of the interference dip, the proposed device exhibits a desirable high transverse load sensitivity of 64.72 nm/(N/mm) without temperature and strain confusion, which provides a new option for the transverse load measurement and further expands the application of the fiber Lyot filter.