Section Of Optical Fiber Research Articles

Temperature-insensitive and cost-effective distributed NP-Doped optical fiber sensors

This paper presents the development of a cost-effective distributed optical fiber sensor for temperature-insensitive assessment of mechanical disturbances along an optical fiber cable. The proposed sensor system uses a nanoparticle (NP)-doped optical fiber with enhanced Rayleigh backscattering to provide higher sensitivity and spatial resolution using the transmission and reflection analysis (TRA) approach, where the transmitted and backscattered optical powers are analyzed as a function of the mechanical disturbance. In addition, Fiber Bragg Gratings (FBGs) are used as wavelength filters to provide the wavelength division multiplexing of the proposed device, which enable the use of 3 different NP-doped optical fiber sections for simultaneous detection of multiple curvature conditions in a cost-effective distributed sensing approach. The sensor characterization tests are performed by means of applying curvature angles from 360° to 1080° at different positions along NP-doped fibers (namely 25 mm, 100 mm and 175 mm) at 4 different temperatures of 25 °C, 30 °C, 40 °C and 50 °C. The results indicate the feasibility of the proposed approach, where the temperature variations lead only to a wavelength shift of the Bragg wavelength, whereas the mechanical disturbances (the curvatures) lead only to variations in the transmitted and reflected optical powers. Thus, by analyzing the transmitted and reflected optical powers in conjunction with the Bragg wavelength shift, it is possible to estimate both the mechanical disturbance amplitude (i.e., curvature angle) and the position along each NP-doped optical fiber section. Results indicate a relative error of around 3 % and 4 % for the mechanical disturbance location and absolute value, respectively. Moreover, the temperature cross-sensitivity in this case is below 2 % considering both amplitude and location of the mechanical disturbance. The proposed approach can be applied in structural health monitoring of different types of structures by integrating the fibers in the structures themselves with the possibility of measuring the strain distribution along the fibers (instead of in different points along the fiber) using a lower cost hardware when compared with similar distributed optical fiber sensing approaches.

Optical Fiber Bragg Grating As A Temperature Sensor

The optical fibre sensor (OFS) has become quite well-known and prominent in the sensor technology industry. It is often used to react to outputs from other systems, like those in industrial, monitoring, and chemical analysis applications, and to detect changes in the environment. A Fibre Bragg Grating (FBG) is a device that allows light to be reflected from a short section of optical fiber at a specific wavelength, while the Bragg reflector expands and transmits all other wavelengths. The current effort focuses on the evolving characteristics and behaviors of strain and temperature sensors operating on fiber bragg gratings through computer modeling. The temperature sensor is employed to detect and quantify any variations in temperature on the Fiber Bragg Grating that could result in accidents or fires. This will show how the Fibre Bragg Grating may be used to showcase temperature sensors.

A film composed of PEDOT:PSS/PVA as a sensitive medium for pH sensor in optical fiber

In this work, a pH sensitive transducer element attached to a multimode optical fiber section is proposed. The sensitive element is a PEDOT:PSS/PVA composite film that exhibited sensitivity at low pH values in the range of 1–7 pH. The addition of PVA was important for the adhesion process to the optical fiber surface. The morphology of the PEDOT:PSS polymers allowed characterization at pH stimuli that were based on the optical power transmission generated from the interaction of the light propagating in the optical fiber core and the optical fiber section coated with the sensitive film. A sensitivity of −0.05 dB/pH and a linear fit R2 of 0.93 was obtained, the response time was 3 s, while the sensor recovery time was 50 s maintaining stability higher than 10 min.

Influence of geometry passive Q-switch based on a nanopowder-polymer on the characteristics of an erbium ring fiber laser

The presented work shows an influence of geometry passive Q-switch based on a nanopowder-polymer on the characteristics of an erbium ring fiber laser. The saturable absorber Bi2Te3 was applied to two types of specially prepared samples of thinned sections of optical fiber, and the resulting structures were built into the ring circuit of an erbium fiber laser. In the first case, the surface of the light guide segment was thinned by chemical etching, and in the second, by mechanical grinding. For the first time, the time-domain optical reflectometry technique was used to control the quality of the resulting sample surface and the resulting losses. For a more complete comparison, a set of different optical splitters was used, providing a change in the feedback coefficient in the resonator from 5 to 95 %. A study in the mode of passive Q-switching using polarized light showed that for both types of modulators there are optimal ratios of the amount of energy output from the resonator to obtain the highest values of the average generation power. The d-shape fiber modulator allows mode-locking to be observed without any additional changes to the laser circuit. The pulse duration in this case was 5 ns with a repetition rate of 4 MHz. A Q-switch based on a chemically thinned fiber segment made it possible to obtain narrower pulses in Q-switching mode (up to 700 ns at 38 kHz), a stable peak position in the transmission spectrum, and an average power of 34 mW.

Novel Approach to Phase-Sensitive Optical Time-Domain Reflectometry Response Analysis with Machine Learning Methods.

This paper is dedicated to the investigation of the metrological properties of phase-sensitive reflectometric measurement systems, with a particular focus on addressing the non-uniformity of responses along optical fibers. The authors highlight challenges associated with the stochastic distribution of Rayleigh reflectors in fiber optic systems and propose a methodology for assessing response non-uniformity using both cross-correlation algorithms and machine learning approaches, using chirped-reflectometry as an example. The experimental process involves simulating deformation impact by altering the light source's wavelength and utilizing a chirped-reflectometer to estimate response non-uniformity. This paper also includes a comparison of results obtained from cross-correlation and neural network-based algorithms, revealing that the latter offers more than 34% improvement in accuracy when measuring phase differences. In conclusion, the study demonstrates how this methodology effectively evaluates response non-uniformity along different sections of optical fibers.

High resolution and large measurement range voltage sensing based on an optoelectronic oscillator utilizing an unbalanced Mach-Zehnder interferometer.

A voltage sensor with high resolution and large measurement range based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The key component in the cavity to select the oscillating signal is a finite impulse response (FIR)-microwave photonic filter (MPF) which consists of a sinusoidal broadband optical signal, an unbalanced Mach-Zehnder interferometer (MZI), a section of dispersion compensating fiber, and a photodetector. The center frequency of the FIR-MPF is mainly determined by the free spectral range (FSR) of the FIR-MPF. In the lower arm of the MZI, a cylindrical piezoelectric ceramic (PZT) wrapped with a section of optical fiber acts as voltage sensing head. Due to the inverse piezoelectric effect of PZT, the variation of the voltage will cause radial deformation of the cylindrical PZT and then lead to the change of the FSR of the MZI, determining the shift of center frequency of FIR-MPF as well as the frequency of the oscillating signal of the OEO. Thus, by monitoring the shift of the oscillation frequency of the OEO using an electric spectrum analyzer or a digital signal processor, a high-speed interrogation and high-resolution voltage measurement can be realized. Additionally, in the proposed scheme, an infinite impulse response (IIR)-MPF consisting of a fiber ring resonator is cascaded with the FIR-MPF to ensure the single-mode oscillation of the OEO. The experimental results show that a total range of 1700 V voltage sensing from - 200 V to 1500 V is accomplished with the voltage sensitivity of 0.25 GHz/100 V and the resolution of 0.3 V. By adjusting the proportion of the length of single mode fiber between two branches of MZI, the impact of temperature can be greatly reduced. The proposed sensor offers advantages such as a large measurement range, high resolution, high-speed interrogation, and stability to temperature disturbances, making it highly suitable for sensing applications in smart grids.

Определение разновидностей оптических волокон и ранняя диагностика их физического состояния на основе анализа характеристик рассеяния Мандельштама–Бриллюэна

Research results into the automating the processing of measurement data obtained from the Brillouin optical reflectometer, light guides containing various types of optical fibers are presented in this paper. By analyzing the parameters of the Mandelstam — Brillouin scatter obtained from Brillouin reflectograms, we can classify optical fibers in the studied telecommunication optical cables. This makes it possible to evaluate the change of the Brillouin frequency shift and determine the longitudinal fiber tension. The initial values of the Brillouin frequency shift and the profile of the Mandelstam — Brillouin scatter spectrum are different for each fiber type. The programs for automated processing of Brillouin reflectogram data are discussed. Estimation of the level of the back-reflected signal allows you to identify the factor, that had a predominant effect on the parameters of the Mandelstam — Brillouin scatter signal in the studied sections of optical fibers, and to compensate for the influence of temperature changes in the longitudinal strain distribution graphs. After that, we can plot a graph of the distribution of longitudinal strain along the fiber, caused precisely by mechanical influences on optical fibers. Conclusions about the accuracy of the estimates obtained by various algorithms, based on the accumulated experience in working with the presented programs are drawn.

Investigating the Spectral Response of Fiber Bragg Grating for Strain Sensor Applications

Abstract: The optical fibre sensor (OFS) has become quite well-known and prominent in the sensor technology industry. It is often used to react to outputs from other systems, like those in industrial, monitoring, and chemical analysis applications, and to detect changes in the environment. A Bragg reflector starts to grow and transmit all other wavelengths while a short section of optical fibre with a specific wavelength is reflected with light in a device called a Fibre Bragg Grating. The current study focuses on the evolving characteristics and behaviours of strain and temperature sensors operating on Fibre Bragg Gratings (FBG) through software modelling. This work's primary goal is to investigate the characteristics and behaviour of strain sensor that are used with fibre bragg gratings. A strain sensor can be used to determine the strain in an object whose resistance changes when force is applied.

An automation of the detection processes of the strain characteristics of optical fibers, classification of their varieties and identification the influence factor according to Brillouin reflectograms

Research results into the automating the processing of measurement data obtained from the Brillouin optical reflectometer, light guides containing various types of optical fibers are presented in this paper. By analyzing the parameters of the Mandelstam–Brillouin scatter obtained from Brillouin reflectograms, we can classify optical fibers in the studied telecommunication optical cables. This makes it possible to evaluate the change of the Brillouin frequency shift and determine the longitudinal fiber tension. The initial values of the Brillouin frequency shift and the profile of the Mandelstam–Brillouin scatter spectrum are different for each fiber type. The programs for automated processing of Brillouin reflectogram data are discussed. Estimation of the level of the back-reflected signal allows you to identify the factor, that had a predominant effect on the parameters of the Mandelstam–Brillouin scatter signal in the studied sections of optical fibers, and to compensate for the influence of temperature changes in the longitudinal strain distribution graphs. After that, we can plot a graph of the distribution of longitudinal strain along the fiber, caused precisely by mechanical influences on optical fibers. Conclusions about the accuracy of the estimates obtained by various algorithms, based on the accumulated experience in working with the presented programs are drawn.

Active Thermostatting of the Reference Optical Fiber Section Method in a Distributed Fiber-Optical Temperature Sensor

Active Thermostatting of the Reference Optical Fiber Section Method in a Distributed Fiber-Optical Temperature Sensor

Various Types of Light Guides for Use in Lossy Mode Resonance-Based Sensors

A comparative study of figure-of-merit fiber sensors of the mass concentration of NaCl solutions based on single-mode and multi-mode fibers was carried out. Lossy mode resonance is realized on chemically thinned sections of optical fibers to various diameters (from 26 to 100 μm) coated with ZnTe. Thin-film coatings were applied using the method of metalorganic chemical vapor deposition (MOCVD). Samples of single-mode and multi-mode fiber sensors were created in such a way that the depth and spectral position of resonances in aqueous NaCl solutions coincided. Sensors implemented on a single-mode fiber have a higher sensitivity (5930 nm/refractive index unit (RIU)) compared to those on a multi-mode fiber (4860 nm/RIU) and a smaller half-width of the resonance in the transmission spectrum. According to the results of experiments, figure-of-merit sensors are in the range of refractive indices of 1.33–1.35 for: multi-mode fiber—25 RIU−1, single-mode fiber—75 RIU−1. The sensitivity of the resulting sensors depends on the surface roughness of the ZnTe coating. The roughness of films synthesized on a single-mode fiber is four times higher than this parameter for a coating on a multi-mode fiber. For the first time, in the transmission spectrum during the synthesis of a thin-film coating on a multi-mode fiber, the possibility of separating the first nine orders of resonances into electric and magnetic transverse components has been demonstrated. The characteristics of sensors with the operating wavelength range in the visible (500–750 nm) and infrared (1350–1550 nm) regions of the spectrum are compared. The characteristics of multi-mode lossy mode resonance sensors are demonstrated, which make them more promising for use in applied devices than for laboratory research.

Monitoring the Vital Activity of Microalgae Cells Using a Fiber-Optical Refractometer

Using the technology of metalorganic chemical vapor deposition (MOCVD), fully fiber refractometers based on the lossy mode resonance (LMR) were obtained and investigated. The sensors are made on the basis of a section of optical fiber etched to the core with films of titanium dioxide (TiO2) and tin (TiO2/SnO2) deposited on the side surface. The sensitivity of the obtained sensors to the refractive index of the surrounding liquid medium is compared depending on the composition and thickness of the film coating. The sensitivity of the fiber sensor with a two-layer coating in the wavelength range of 1.33–1.35 microns was 4850 nm/RIU. Before measurements, cells suspended in liquid were concentrated on the surface of the sensor due to the effect of optical tweezer. Particles were attracted from the suspension when launching into the fiber radiation from a diode laser with a power of 10 mW. With the help of fabricated fiber sensors, the change in the refractive index of a suspension containing living cells of the microalgae Chlorella Vulgaris was monitored. The possibility of assessing the influence of external conditions on the life process of algae with real-time control using fabricated fiber sensors is shown.

Adjustable testbench system to stretch optical fiber

Actually, the use of optical fiber has been extended to several applications, not only its use for telecommunications; nowadays, optical fiber is used for sensor construction and instrumentation. For that reason, modifications and deformations in optical fiber sections are required and in order to observe how light transition is performed through to the fiber. The construction of this platform has the main objective to accomplish stretching test with different tensions on the fiber, different exposition terms to the electric arc and finally the gap between electrical electrodes to modify the affectations on the fiber, that are applied on the fiber. The different parts this system is conformed with, are presented in this work and the main features of each stage.

WDM-PON Management and Control by Auxiliary Management and Control Channel for 5G Mobile Fronthaul

The demand for fifth generation (5G) mobile systems has been exploding. There are strict latency and transmission capacity requirements, especially in the optical fiber section called the mobile fronthaul. A wavelength division multiplexing passive optical network (WDM-PON) system is an attractive solution to accommodate the high demand of traffic. However, wavelength management, which is important in a WDM-PON system, has not been sufficiently studied at the system level. In previous studies, control by a management control channel independent of the client signal, called the auxiliary management and control channel (AMCC), has been considered in many cases. In most of these studies, physical layer evaluation, such as the effect of superimposing the management control channel, was conducted for feasibility studies, and it was only confirmed that the effect was minor by measuring the bit error rate. In this paper, we review and compare the superimposition schemes of the AMCC to clarify operating conditions such as modulation format and modulation index of the AMCC signals. In addition, we propose a WDM-PON system managed using AMCC for ONU activation, wavelength adjustment and alive monitoring. We then discuss the connection of a WDM-PON prototype system we developed to a 5G mobile system to evaluate the effect of throughput on user equipment. The results indicate that the WDM-PON prototype system did not degrade (less than 2%) the downlink throughput even when the wavelength adjustment function was used against wavelength drift.

Label-Free Creatinine Optical Sensing Using Molecularly Imprinted Titanium Dioxide-Polycarboxylic Acid Hybrid Thin Films: A Preliminary Study for Urine Sample Analysis

Creatinine (CR) is a representative metabolic byproduct of muscles, and its sensitive and selective detection has become critical in the diagnosis of kidney diseases. In this study, poly(acrylic acid) (PAA)-assisted molecularly imprinted (MI) TiO2 nanothin films fabricated via liquid phase deposition (LPD) were employed for CR detection. The molecular recognition properties of the fabricated films were evaluated using fiber optic long period grating (LPG) and quartz crystal microbalance sensors. Imprinting effects were examined compared with nonimprinted (NI) pure TiO2 and PAA-assisted TiO2 films fabricated similarly without a template. In addition, the surface modification of the optical fiber section containing the LPG with a mesoporous base coating of silica nanoparticles, which was conducted before LPD-based TiO2 film deposition, contributed to the improvement of the sensitivity of the MI LPG sensor. The sensitivity and selectivity of LPGs coated with MI films were tested using CR solutions dissolved in different pH waters and artificial urine (near pH 7). The CR binding constants of the MI and NI films, which were calculated from the Benesi–Hildebrand plots of the wavelength shifts of the second LPG band recorded in water at pH 4.6, were estimated to be 67 and 7.8 M−1, respectively, showing an almost ninefold higher sensitivity in the MI film. The mechanism of the interaction between the template and the TiO2 matrix and the film composition was investigated via ultraviolet–visible and attenuated total reflectance Fourier-transform infrared spectroscopy along with X-ray photoelectron spectroscopy analysis. In addition, morphological studies using a scanning electron microscope and atomic force microscope were conducted. The proposed system has the potential for practical use to determine CR levels in urine samples. This LPG-based label-free CR biosensor is innovative and expected to be a new tool to identify complex biomolecules in terms of its easy fabrication and simplicity in methodology.

The Structure and Preparation Method of Spectrally Shifted Double-Comb Tilted Fiber Bragg Gratings

Tilted fiber Bragg gratings (TFBGs) have peaks in the transmission spectrum associated with cladding modes. The spectral distances between these peaks depend on the geometry of the optical fiber including the cladding, tilt angle and structure period. In this letter we propose to increase the number of peaks in the spectrum without changing the geometry of the optical fiber. Such effect can be achieved by producing two structures on the same section of optical fiber, one of which has shifted spectral peaks relative to the other. The spectral shift occurs as a result of a change in the period of the structure obtained by stretching the optical fiber during its writing. We show here the properties of such a method for increasing the number of modes by analysing both simulated and experimental spectra.

Optical flow sensor based on the thermal time-of-flight measurement.

This paper presents a dielectric, all-optical thermal time-of-flight fluid flow velocity sensor. The proposed sensor utilizes a sequence of three short sections of optical fibers, which are positioned in a direction perpendicular to the measured fluid flow. One of these three fiber sections is highly doped with vanadium and acts as an optically controlled heater, while the other two fiber sections contain fiber Bragg gratings (FBG) that act as dynamic temperature sensors. The vanadium-doped fiber is heated periodically by a laser source, while observing temperature variations within the fluid flow downstream by the two fiber sections with inscribed Bragg gratings. The time delay in temperature variations recorded at both FBG sensors correlates directly with the flow rate of the fluid. When the sensor was placed within the glass capillary with inner diameter of 650 µm, it enabled a flow rate measurement range between 1 ml/h and 1200ml/h. The sensor thus provides a broad flow-rate dynamic range and is insensitive to changes in losses in the lead optical fibers or optical heating source power fluctuations. Furthermore, the thermal properties of the measured liquid, for example, the liquid's thermal conductivity and heat capacity, have mostly limited effects on the measurement results, which allows for thermal-principle-based flow velocity measurements in cases of liquids with variable or poorly defined compositions.

A two-dimensional cantilever beam vibration sensor based on fiber Bragg Grating

A two-dimensional cantilever vibration sensor based on Fiber Bragg Grating (FBG) is proposed. The proposed sensor consists of a section of optical fiber with double FBGs and three different beams. After theoretical analysis and experimental verification, the proposed sensor has a high sensitivity response. The experimental result shows that the natural frequency of the sensor in the x/y direction of vibrations is respectively 505/177 Hz. The flat frequency of the sensor is 60–150 Hz and 30–150 Hz, respectively. And the sensor’s sensitivity is respectively 125.85/82.32 pm/g in the x/y direction of vibration. Compared with the traditional cantilever beam FBG sensor, the proposed sensor has the advantages of multi-directional detection, avoiding chirp and so on. Therefore, it has great application prospects in two-dimensional vibration signal detection of bridges, roads and buildings.

Spatially resolved fibre cavity ring down spectroscopy

This paper presents a fibre cavity ring down spectroscopy probed by Rayleigh scattering optical frequency domain reflectometry (OFDR), which provides spatial location of stimuli and improved signal to noise ratio for distributed sensing measurements. A section of optical fibre was integrated into an active fibre ring cavity with optical gain and interrogated by the OFDR system for 11 cycles with a single laser scan. Through the cavity ring down configuration, root-mean-squared (RMS) noise of distributed temperature and strain measurements was reduced to 6.9 mK and less than 0.1 με, respectively for 1-cm spatially resolved measurements. Our work shows that the active fibre cavity configuration can be combined with distributed fibre sensing schemes to achieve both high spatial resolution and high sensitivity measurements.

Temperature-Insensitive Magnetic Field Sensor Based on an Optoelectronic Oscillator Merging a Mach–Zehnder Interferometer

A temperature-insensitive magnetic field sensor with high interrogation performance and large measurement range based on an optoelectronic oscillator (OEO) merging a Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. In the OEO loop, a finite impulse response (FIR)-microwave photonic filter (MPF) and an infinite impulse response-MPF are cascaded to select the oscillating frequency and further suppress the side mode. The center frequency of the FIR-MPF, which is composed of a non-coherent broadband optical source, a MZI, a dispersion compensating fiber (DCF), and a photodetector, is determined by dispersion of DCF and the free spectral range (FSR) of the MZI jointly. In one arm of the MZI, a section of optical fiber is bonded with a giant magnetostrictive material (GMM) to achieve the magnetic field sensing, where the GMM is acted as a magnetic field-strain transducer. When the magnetic field varies, the FSR of the MZI will be changed, resulting in an oscillating frequency shift of the OEO. Therefore, a high interrogation performance magnetic field measurement can be achieved by simply monitoring frequency change of microwave signal generated by OEO in the microwave domain. Moreover, by placing a section of unprocessed fiber with appropriate length in the other arm of the MZI, the temperature cross-talk for the magnetic field can be alleviated greatly. In the experiment, the magnetic field sensitivity of 1.33 MHz/mT with a large range of 20.9 mT to 58 mT is obtained and the measurement error induced by temperature is as low as 0.09 mT.