Segment Of Optical Fiber Research Articles

Damage detection of Kevlar woven fabric using optical fiber multimode interferometer

Kevlar woven fabric is crucial for the lightweight design of aerospace structures due to its unique advantages. However, it is susceptible to damage during operation, making effective damage detection essential for ensuring structural reliability. Nevertheless, conventional sensors used for damage detection have limitations such as complex manufacturing processes and weight. To address this issue, this paper proposed a simple singlemode-multimode-singlemode (SMS) optical fiber sensor to collect vibration signals and construct a damage recognition model based on natural frequency in order to identify the size of damages in Kevlar woven fabrics. To achieve a highly linear and accurate sensor, a length determination criterion for multimode optical fiber segments based on quasi-image, notch, and transmission spectrum loss was proposed. An optical sensor was fabricated based on this criterion. The feasibility and sensitivity of the sensor for vibration signal measurement were verified by constructing a vibration signal measurement device. An experimental study was conducted to detect damage in Kevlar tapes, where the natural frequency changes measured by the SMS sensor were integrated with an optimized multi-variable gray model for damage size detection. The experimental results indicate that the estimated error in damage size is 0.71%. The damage identification system proposed in this paper offers a simple and cost-effective solution for measuring damage in flexible structures using fiber optic sensors.

Optical Fiber Bragg Grating as a Strain Sensor

Abstract: The sensor technology industry has come to recognize and value the optical fibre sensor (OFS). It is frequently used to detect changes in the environment and to respond to outputs from other systems, such as those in industrial, monitoring, and chemical analysis applications. While a brief segment of optical fiber with a particular wavelength is reflected with light in a device known as a Fibre Bragg Grating, a Bragg reflector begins to grow and transmit all other wavelengths. Through software modeling, the current study focuses on the changing traits and behaviors of temperature and strain sensors that are used with fiber bragg gratings (FBG). The main objective of this work is to study the properties and behavior of strain sensors utilized in conjunction with fiber bragg gratings. A strain sensor can be used to determine the strain in an object whose resistance changes when force is applied

Optical fiber fronthaul segment in open radio access 5G networks: enhanced performance utilizing AFBG

In open Radio access network (oRAN) 5G networks, a fronthaul segment between virtual Distribution unit (vDU) edge cloud and other external Remote radio units (RRUs) sites is very important to transmit high data rate to achieve 5G requirements. Performance parameters such as Quality factor (Q-factor) and Bit error rate (BER) of an optical fiber fronthaul segment are the main important parameters to enhance latency and bit rate. An Apodized fiber bragg grating (AFBG) is utilized with different apodization profiles to optimize linewidth of an optical signal leading to enhance performance. The designed AFBG is used with a data rate of 25 Gb/s optical Ethernet module at the vDU edge cloud to optimize the linewidth of the optical signal between the vDU and the RRU in the fronthaul optical fiber segment. The AFBG is investigated at different connections pre, post, and symmetrical connections, where different apodization functions are used in the AFBG design. It is found that the best results for the maximum Q-factor and minimum BER are 9.2 and 2.72e− 21, respectively, obtained from uniform function in the symmetrical connection. Finally, the proposed model linewidth is 0.408 nm, which is better than 1.56 nm that is evaluated by related work.

Demonstration of a low loss, highly stable and re-useable edge coupler for high heralding efficiency and low g(2)(0) SOI correlated photon pair sources.

We report a stable, low loss method for coupling light from silicon-on-insulator (SOI) photonic chips into optical fibers. The technique is realized using an on-chip tapered waveguide and a cleaved small core optical fiber. The on-chip taper is monolithic and does not require a patterned cladding, thus simplifying the chip fabrication process. The optical fiber segment is composed of a centimeter-long small core fiber (UHNA7) which is spliced to SMF-28 fiber with less than -0.1 dB loss. We observe an overall coupling loss of -0.64 dB with this design. The chip edge and fiber tip can be butt coupled without damaging the on-chip taper or fiber. Friction between the surfaces maintains alignment leading to an observation of ±0.1 dB coupling fluctuation during a ten-day continuous measurement without use of any adhesive. This technique minimizes the potential for generating Raman noise in the fiber, and has good stability compared to coupling strategies based on longer UHNA fibers or fragile lensed fibers. We also applied the edge coupler on a correlated photon pair source and observed a raw coincidence count rate of 1.21 million cps and raw heralding efficiency of 21.3%. We achieved an auto correlation function g H(2)(0) as low as 0.0004 at the low pump power regime.

Extension of Fiber Bragg Grating Ultrasound Sensor Network by Adhesive Couplers

Previous studies demonstrated coupling of acoustic guided waves from one optical fiber to another through a simple adhesive bond coupler. This paper experimentally utilizes such an adhesive bond coupler to easily extend an already existing sensor network. We experimentally demonstrate this concept for detecting simulated cracks growing from circular holes in a thin aluminum plate. A single, remotely bonded FBG sensor is used to detect the original crack growth, followed by the addition of other optical fiber segments using adhesive couplers to detect new crack growth locations on the plate. A laser Doppler vibrometer is also used to measure the guided wave propagation through the plate to verify that the changes in the FBG sensor measurements are due to the growth of the cracks.

Mid-infrared refractive index sensor with high sensitivity and wide detection range based on multimode interference in tellurite optical fibers

In this paper, a section of tellurite no-core optical fiber (NCF) is compactly sandwiched between two segments of tellurite single-mode optical fibers (SMF) to form multimode interference (MMI) sensor for refractive index (RI) measurement. Theoretical investigation reveals that the sensitivity of this MMI-based RI sensor can be enhanced by reducing the diameter of the NCF. As the NCF diameter is lowered to 20 µm, the sensor presents good RI sensing performance in the mid-infrared range of 2–5 µm and the sensitivity rises with the increase of the wavelength. At 4–5 µm and within the detectable RI range of 1.36–1.63, the maximum sensitivity is 3069.1 nm/RIU. The proposed sensor combines the material superiority of tellurite glass and the structural advantage of the SMF-NCF-SMF sensing unit, exhibiting high sensitivity and wide detection range in terms of RI sensing. It provides a new method for detecting the concentration of toxic organic compounds with high RI.

Microwave Photonic Direction-Finding Spectrometer

In this paper, we propose an architecture wherein the radio-frequency (RF) field at the antenna array is up-converted to an optical carrier and passed through an array of optical fibers, after which an analog Fourier transform is taken in a free-space optical processor. Through the use of multiple temporal dispersion projections, implemented through varied-length optical fiber segments, the locations of RF sources in three-dimensional space spanning angle-of-arrival (AoA) and instantaneous frequency may be determined on a millisecond time scale using commercial computing hardware after detection by a charge-coupled device (CCD) camera. We present a mathematical formulation of the problem, followed by simulated and experimental results showing three-dimensional spatial-spectral localization through the solution to a system of equations brought forth through the use of Fourier optics to process the RF field.

An ultraviolet sensor based on surface plasmon resonance in no-core optical fiber deposited by Ag and ZnO film

A new ultraviolet (UV) optical fiber sensor based on surface plasmon resonance (SPR) is suggested in this research, which is fabricated by splicing a segment of no-core optical fiber (NCF) between two multimode optical fibers (MMFs). An Ag film and a ZnO film are successively deposited upon the surface of the NCF by magnetron sputtering, and the UV detection function is accomplished by utilizing SPR's sensitivity to ambient refractive index (RI) and ZnO RI's sensitivity to the UV irradiance. Due to the hydrophilic properties of ZnO, the sensor is encapsulated in absolute ethanol to produce stable SPR and isolate water molecules. The effects of film thickness (Ag and ZnO) and UV irradiance on sensor performance are discussed in detail. It is discovered that the UV sensitivity of the sensor increased with the ZnO thickness. At the deposition of a 10 nm thick ZnO film, the sensitivity can reach -1.462 nm / (mW/cm2), which is 6 times that of 2 nm thick film. The exploratory combination of SPR and UV sensitive materials tremendously simplifies UV detection technology, making the sensor highly reproducible and UV detection more efficient in the fields of environmental monitoring, food hygiene, and medical health.

Exceptional-point-induced asymmetric mode conversion in a dual-core optical fiber segment

The engineering of exceptional points (EPs) in open optical systems has lately attracted much attention for developing future all-optical devices. However, investigation of the fascinating features of EPs in fiber geometries is lacking. We design a fabrication feasible dual-core optical fiber segment, where non-Hermiticity in terms of a symmetric customized gain-loss profile is introduced to modulate the interaction between two corresponding coupled modes toward hosting a dynamical EP encirclement scheme in the gain-loss parameter space. An asymmetric conversion process between two supported modes is reported by exploiting the chirality of the encountered EP. The proposed scheme can lead to an advanced platform to design mode-manipulative all-optical components in communication and all-fiber photonic devices.

QUASI-DISTRIBUTED RECIRCULATED FIBER OPTIC GASEOUS OXYGEN MEASUREMENT SYSTEM

A scheme of a quasi-distributed fiber-optic system for monitoring the oxygen concentration of the recirculation type is proposed. The principle of measurement is to register changes in the recirculation frequency of single optical pulses with periodic regeneration simultaneously at several wavelengths. The operation of the sensor is based on a change in the length of the magnetostrictive strips and the segments of optical fibers associated with them under the influence of a changing magnetic field due to the paramagnetic properties of gaseous oxygen. The numerical estimation of the measurement error has been carried out. It is shown that with a length of the sensitive element of the sensor of 1.5 m and a radius of 0.6 ... 0.7 m, it is possible to obtain a relative error of the measurement method no worse than 0.6% for pure oxygen and 2.5% for an air mixture.

Vector distribution measurement of PMD in optical fiber links employing a wavelength-tunable SOP-OTDR.

A measurement of polarization mode dispersion (PMD) vector distribution is implemented with a wavelength-tunable state-of-polarization-detection-based optical time domain reflectometry (SOP-OTDR). Derived from the dynamic equation between the PMD vector and the birefringence vector with a piecewise approximation method, we present an equation for piecewise expression of the relation between the two vectors based on the approximation that the second-order partial derivative of the PMD vector with respect to the length is negligible in each short-enough segment of optical fiber. Utilizing the birefringence vector distributions at three adjacent wavelengths, both the magnitude and the direction distributions of the PMD vector have been calculated through the numerical solution algorithm. The calculation results indicate that the measured magnitudes of PMD vectors are consistent with the statistical experience, which is the Maxwell probability distribution, and the second-order partial derivative magnitudes of the PMD vectors conform to the lognormal distribution. This method could provide a distributed approach for optical performance monitoring by PMD-related characteristics in optical fiber links.

Estimation of temperature detection delay in a fiber optic gyroscope sensing coil

The use of algorithmic temperature compensation requires that the external temperature sensor data and the thermal response of the fiber optic sensor should be synchronized. The paper considers an approach to estimate the temperature detection delay for the external temperature sensor in a sensing coil assembly of a fiber-optic gyroscope. The delay estimation is based on a cross-correlation of temperature data from an external temperature sensor and temperature data of an optical fiber segment obtained by distributed temperature measurement based on optical frequency reflectometry. The results include the estimation of temperature detection delay between the sensing coil and the temperature sensor. The described approach allows evaluating temperature detection delay in a sensing coil assembly of a fiber-optic gyroscope. In case of using multiple temperature sensors, the delay for each temperature sensor can be estimated and taken into account to improve the efficiency of the thermal drift compensation of the fiber optic gyroscope.

Generation of Subpicosecond Pulse Trains in Fiber Cascades Comprising a Cylindrical Waveguide with Propagating Refractive Index Wave

A cylindrical waveguide structure with the running refractive index wave has been recently demonstrated as a means for the generation of high-repetition-rate pulse trains. The operation mechanism involves a proper combination of the frequency modulation and modulation instability simultaneously experienced by the input continuous wave (CW) signal as it propagates through the cylinder waveguide. Here, we explore the same idea but employ the cylindrical waveguide only as a part of the cascaded optical fiber configuration now comprising both passive and active optical fiber segments. The new system design enables the improved control of the pulse train formation process in the cascaded system elements, relaxes strong requirements for the CW signal power, and provides an additional optical gain for the advanced pulse peak power scaling. In particular, using a low-amplitude, weakly modulated, continuous wave as an input signal we explore and optimize the nonlinear mechanisms underlying its cascaded transformation into the train of kilowatt peak power picosecond pulses.

Frequency-resolved spatial beam mapping in multimode fibers: application to mid-infrared supercontinuum generation.

We present a new, to the best of our knowledge, spatial-spectral mapping technique permitting measurement of the beam intensity at the output of a graded-index multimode fiber (GIMF) with sub-nanometric spectral resolution. We apply this method to visualize the fine structure of the beam shape of a sideband generated at 1870 nm by geometric parametric instability (GPI) in a GIMF. After spatial-spectral characterization, we amplify the GPI sideband with a thulium-doped fiber amplifier to obtain a microjoule-scale picosecond pump whose spectrum is finally broadened in a segment of InF3 optical fiber to achieve a supercontinuum ranging from 1.7 up to 3.4 µm.

Revisiting the nonlinear Gaussian noise model for hybrid fiber spans

We rederive from first principles and generalize the theoretical framework of the nonlinear Gaussian noise model to the case of coherent optical systems with multiple fiber types per span and ideal Nyquist spectra. We focus on the accurate numerical evaluation of the integral for the nonlinear noise variance for hybrid fiber spans. This task consists in addressing four computational aspects: (1) Adopting a novel transformation of variables (other than using hyperbolic coordinates) that changes the integrand to a more appropriate form for numerical quadrature; (2) Evaluating analytically the integral at its lower limit, where the integrand presents a singularity; (3) Dividing the interval of integration into subintervals of size π and approximating the integral over each subinterval by using various algorithms; and (4) Deriving an upper bound for the relative error when the interval of integration is truncated in orderto accelerate computation. We apply the proposed analytical model to the performance evaluation of coherent optical communications systems with hybrid fiber spans composed of quasi-single-mode and single-mode fiber segments. More specifically, the model is used to optimize the lengths of the optical fiber segments that compose each span in order to maximize the system performance. We check the validity of the optimal fiber segment lengths per span provided by the analytical model by using Monte Carlo simulation, where the Manakov equation is solved numerically using the split-step Fourier method. We show that the analytical model predicts the lengths of the optical fiber segments per span with satisfactory accuracy so that the system performance, in terms of the Q-factor, is within 0.1 dB from the maximum given by Monte Carlo simulation.

WITHDRAWN: Real time data on hand grip strength in a population-based study using fiber Bragg grating

Grip strength, also known as wrist angular strength is anthropometric measurement which is an indicator of hand muscle health. The measurement is included in longitudinal studies because it is an indicator of the overall well-being of a person. Grip strength can be used as a screening tool for measurement of upper body strength and overall strength. It is also used as an easy measure of skeletal muscle and neuromuscular functions. The body strength plays an important role in determining the abilities or ailments of the physical human body. We can test the human body with respect to the hand grip measurement which is proportional to the body strength. This is here used to make a gender stratified, hand dominance based comparative study of hand grip strength in individuals of all age groups in different wrist positions such as extension, flexion and normal to produce real time data. Fiber Bragg Grating (FBG) sensor is a type of distributed Bragg reflector, constructed in a segment of optical fiber that reflects specific wavelengths of light and transmits the rest, whose reflections are recorded as change in wavelength in the form of waveforms. The obtained results are later converted to force in kilograms by using a calibration value obtained using load cell. The results obtained by FBG sensor can be accessed directly through a computer which records the real time data both numerically and in the form of graph.

Breaking limitations of fiber identification in traditional OFDR systems via compensation of initial optical frequency instability

As the security of optical fiber lines in data centers has attracted growing attention, it has become increasingly important to accurately characterize the fiber that is used. Optical frequency domain reflectometry (OFDR) has been demonstrated as a means of identifying specific segments of optical fiber; however, OFDR measurements are limited in length due to initial optical frequency (IOF) variations. This Letter describes a detailed analysis of IOF and introduces a method to mitigate it in an OFDR system constructed using a semiconductor laser (SCL). Additionally, an algorithm is described that minimizes the calculating density necessary for OFDR-based optical fiber verification, reducing the calculating time required by an order of magnitude relative to prior techniques. Experiments demonstrate that the described method can be effectively applied to a range of application areas, ranging from centimeter to meter lengths of optical fiber, with an error equal rate (EER) of less than 1%.

Health monitoring of long-haul fiber communication system using chaotic OTDR

A novel chaotic optical time-domain reflectometry (OTDR)-based approach was proposed for monitoring long-haul fiber communication systems with multiple fiber segments. The self-phase modulation and group velocity dispersion effects of the optical cable was considered in demonstrating the proof-of-concept experiment and simulation. In experiments, the correlation peaks are clearly obtained from the correlation trace between the reference and reflected (or scattered) light signals propagating in three optical-fiber segments. The technique affords a high spatial resolution of 2 m, and further long-haul fiber simulations indicate that the sensing distance can be more than 3300 km. Thus, the new proposed technique can be effectively applied for health monitoring of long-haul fiber communication systems.

Investigation of Photonic Integrated Circuits with Low-Loss Bragg Gratings

AbstractThe impact of physical parameters of uniform fiber Bragg grating (U-FBG) like grating period, length of grating, and width of grating on the performance of U-FBG fiber by using finite differences time domain (FDTD) based on surface plasmon polaritons (SPP) is evaluated. An FBG is similar to a distributed Bragg reflector created in a small segment of optical fiber that reflects some particular wavelengths of light and transmits the other wavelengths. It is observed that the maximum received optical power at the reflected port achieved is −1.67×10-6 w/m2 with silver (Ag) profile material of U-FBG at 0.1 w/m2 input transmission power and wavelength of 1.55 μm with 0.9 μm grating length and 0.2 μm grating width. The result shows that the received optical power is changing by optimizing the physical parameters of U-FBG.

Improved algorithms for determining the strain of optical fibers using Brillouin reflectometers

The issues of improved algorithms for determining the strain of optical fibers using Brillouin reflectometers are investigated. Structure charts of devices for early diagnostics of optical fibers are presented. Adaptive algorithms for construction of Brillouin reflectograms: patterns of Brillouin frequency shift and strain distribution along the optical waveguide are considered. Reference Brillouin reflectograms for different optical fibers from the database are required to correctly detect the “problem” segments (segments of optical fibers with increased mechanical strain or with transformed temperature) in the optical waveguide.