Fiber Optic System Research Articles

Interfacial fatigue debonding retardation in wrapped composite joints: Experimental and numerical study

Debonding crack propagation at the composite-to-steel interface has been found to be an important failure mechanism for wrapped composite joints under static and fatigue loads. Friction at the interface behind the crack tip may deviate fatigue debonding of the joints from the linear-fracture-mechanics behaviour. This paper presents static and fatigue tests of axial wrapped composite joints. 3D DIC and optical fiber system is employed to monitor displacements and crack propagation. A finite element model is established and validated against static and fatigue test results, where friction is considered at the cracked interface. Through FE modelling, it is proved that the friction at the interface significantly reduce the strain energy release rate (SERR) at the crack tip, leading to retardations of crack growth and stiffness degradation. Parametric study is conducted finally to investigate the influence of friction coefficient, failure modes as well as Paris relationship parameters on the predicted fatigue behaviour of wrapped composite joints.

Fiber-Optik Haberleşme Sistemlerinin Bant Genişliğinin Artırılması için Yeni Bir Yaklaşım

In this study, a theoretical systematic approach is introduced as a solution of the bandwidth problem of multi-tone network systems. This systematic approach proposes the use of unused harmonic components of non-linear harmonic distortion produced by the semiconductor laser diode, which is used as a source in the infrastructure of the fiber optic communication system. In order to separate these unused harmonic distortion frequency components from the others, it is possible to add a protocol to each harmonic distortion difference frequency signal, or by intermodulation distortion (IMD) phase modulation, or to use both protocol and IMD phase modulation together. Thus, all harmonic distortion frequency components can be separated theoretically. Thus, it is recommended to use IMD difference frequency components in multi-tone-input subcarrier fiber optic or similar communication systems in the same transmission medium. We think that if this technique is used, it will make a great contribution to increasing the bandwidth of fiber optic communication and network systems.

Integration of Raspberry Pi and antennas for multiplexing digital signals over a fiber optical communication system

A Fiber Optical Communication System (FOCS) is used to experimentally demonstrate the transmission of multi-channel information of two High Definition (HD) video signals and 18 digital TV channels. These signals are supplied using commercial Raspberry Pi boards and digital TV Antennas, respectively. Both digital signals and lightwaves of a couple of Distributed Feedback (DFB) lasers with wavelengths located at 1547.5 and 1552.5 nm interact with two Mach-Zehnder Intensity Modulators (MZ-IM). The resulting modulated optical signals from each modulator are combined by using an optical coupler. The combined optical field is amplified and transmitted through 30 km of single-mode optical fiber. To demultiplex the combined optical signals, a bandpass optical filter is used, then a PIN-photodetector is connected to recover HD video signals and the 18 digital TV channels. The measured electrical spectrum of the received signals shows that the transmission is performed without interference and the multi-channel information is successfully received in an HD display. The use of wavelengths with linewidths of 10 MHz and an optical fiber with a chromatic dispersion of 17 ps/nm-km allows for a maximum bit rate of approximately 11 Gbps to be achieved numerically. This result guarantees that HD video signals can be experimentally transmitted successfully with Bit Error Rate (BER) values between 10-6 and 10-15 when the optical power of lasers is tuned between 7 and 9 dBm.

Study on stress-deformation mechanism of concrete face rockfill dam based on centrifugal model test

The traditional method of tracking the deformation of centrifugal dam model involves burying marker points on the sidewalls, which is commonly used. However, the method is inaccurate in monitoring the deformation of the model since the constraining effect of boundary effect on the model. In this study, a quasi-distributed fiber optic monitoring system was constructed using fixed-point distributed fiber Bragg grating. Particle image velocimetry, earth pressure cell, and other electromagnetic sensors were combined to examine the rationality of the face rockfill dams centrifugal model tests. Through comparative analysis, the applicability and stability of the fixed-point distributed FBG technique in the centrifugal model test were demonstrated. It is also demonstrated that traditional monitoring methods will underestimate the deformation of face rockfill dams by 2.32 % ∼ 13.55 %. This study addresses the shortcomings of existing monitoring methods with excessive measurement errors and provides a more applicable monitoring tool for developing related experimental studies.

Handling mode and polarization in fiber by fs-laser inscribed (de)multiplexer and silicon switch array

The emergence of dynamic optical switching has opened up new perspectives for lightening the ever growing load on the electrical switches and routers, to meet the increasing demand on high-speed and flexible data processing and management in fiber-optic communications. Despite diversity schemes of optical switching in the single-mode regime, multi-mode switching of the hybrid fiber and chip system enabled by photonic integrated circuits, especially for the fiber-chip-fiber system, is still an outstanding challenge. Here, we propose and demonstrate the mode and polarization transmission and switching fiber-chip-fiber system with few-mode fibers (FMFs), including the FMF links for mode- and polarization-division multiplexing data transmission, the femtosecond (fs)-laser inscribed 3-dimensional (3D) photonic lantern silica chip for (de)multiplexing and coupling between FMFs and chip, and the topology-optimized N × N non-blocking 2-dimensional (2D) silicon switch array chip for switching and routing. Using 30-Gbaud quadrature phase-shift keying signals on wavelength-division multiplexing (WDM) channels, the WDM-compatible hybrid mode/polarization transmission, switching and routing system with FMFs, fs-laser inscribed silica (de)multiplexing chip and silicon switch array chip are demonstrated in the experiment with favorable operation performance. The demonstration may open the door for developing robust multi-dimensional optical data processing in fiber-optic communication systems with versatile fibers and chips.

Toward in-fiber nonlinear silicon photonics

Silicon core fibers (SCFs) offer an exciting opportunity to harness the nonlinear functionality of the semiconductor material within the excellent waveguiding properties of optical fiber systems. Over the past two decades, these fibers have evolved from a research curiosity into established components for use across a wide range of photonic applications. This article provides a comprehensive overview of the evolution of the SCFs, with a focus on the development of the fabrication and post-processing procedures that have helped unlock the nonlinear optical potential of this new technology. As well as reviewing the timeline of advancements in nonlinear performance, a perspective will be provided on the current challenges and future opportunities for in-fiber nonlinear silicon systems.

Transient Strain Monitoring of Weldments Using Distributed Fiber Optic System

The primary objective of this study was to evaluate the capability of a distributed fiber optic sensor to capture in situ dynamic transient strain formation during and post-weldment on the surface of a steel plate. The study involved a vertical manual weld of a bead on a plate on a 300 mm × 300 mm × 6.35 mm A36 steel plate (European equivalent S235J2; Chinese equivalent Q235B) clamped at the corners. A fiber optic distributed sensor was used to measure the surface total and thermal strains on the welded side of the plate adjacent to the weld path. Experimental results show a complex behavior of strain changes during the welding process and the residual strain formation post-welding. This study aims to document the use of distributed fiber optic sensing techniques in welding applications. Validations of the experimental data were performed using VrWeld, a commercial software framework for computational weld mechanics, and an iPhone FLIR One Pro. thermographic camera. The experimental results demonstrated that although distributed fiber optic sensing based on Rayleigh backscattering is an appropriate and useful technique for total strain measurements, the manufacturing and the materials used for the thermal sensors are critical in obtaining optimal results. Finally, this study highlights the challenges encountered in synchronizing large experimental data sets captured with different instruments with computational welding mechanic (CWM) models.

Amplitude-frequency response of a helically-wound fiber distributed acoustic sensor (DAS)

The goals of this study were to analyze the capabilities of DAS (distributed sensors) in resolving mining problems, compare them with existing seismoacoustic data collection systems, and prepare the basis for conducting seismoacoustic studies with recording by a fiber optic distributed system. This paper considers the capabilities of recording seismoacoustic responses using fiber optic distributed acoustic systems (DAS). Based on physical and geometrical analysis, the amplitude-frequency responses (characteristics) of recorded longitudinal waves for straight and helically-wound fibers were obtained. In the case of helically-wound fiber, the frequency response depends on several key factors: integrating the measured value along the fiber based on the measurement; the angle of incidence on the cable; and the winding angle of the fiber in the cable. An increase in the winding angle increases the uniformity of the amplitude-frequency characteristics of longitudinal waves both in terms of frequencies and angles of incidence. At the same time, helical winding changes the effective response spacing (gauge length). This makes it possible, by summing the responses of the straight and helically-wound fibers due to the overlap of the spectra, to record frequencies that are suppressed in case of separate recording. Based on the study results, a cable design was proposed to record broadband seismoacoustic responses enabling a wide range of mining and engineering problems to be resolved, and for seismic surveys both in wells and on the surface to be carried out.

Amplitude-frequency response of a helically-wound fiber distributed acoustic sensor (DAS)

The goals of this study were to analyze the capabilities of DAS (distributed sensors) in resolving mining problems, compare them with existing seismoacoustic data collection systems, and prepare the basis for conducting seismoacoustic studies with recording by a fiber optic distributed system. This paper considers the capabilities of recording seismoacoustic responses using fiber optic distributed acoustic systems (DAS). Based on physical and geometrical analysis, the amplitude-frequency responses (characteristics) of recorded longitudinal waves for straight and helically-wound fibers were obtained. In the case of helically-wound fiber, the frequency response depends on several key factors: integrating the measured value along the fiber based on the measurement; the angle of incidence on the cable; and the winding angle of the fiber in the cable. An increase in the winding angle increases the uniformity of the amplitude-frequency characteristics of longitudinal waves both in terms of frequencies and angles of incidence. At the same time, helical winding changes the effective response spacing (gauge length). This makes it possible, by summing the responses of the straight and helically-wound fibers due to the overlap of the spectra, to record frequencies that are suppressed in case of separate recording. Based on the study results, a cable design was proposed to record broadband seismoacoustic responses enabling a wide range of mining and engineering problems to be resolved, and for seismic surveys both in wells and on the surface to be carried out.

Time-Limited Waveforms With Minimum Time Broadening for the Nonlinear Schrödinger Channel

Simple fiber optic communication systems can be implemented using energy modulation of isolated time-limited pulses. Fundamental solitons are one possible solution for such pulses which offer a fundamental advantage: they preserve their shape along the channel. Furthermore, a simple energy detector can be used at the receiver to detect the transmitted information. However, systems based on energy modulation of solitons are not competitive in terms of data rates. This is partly due to the fact that the effective time duration of a soliton depends on its chosen amplitude. In this paper, we propose to replace fundamental solitons by new time-limited waveforms that can be detected using an energy detector, and that are immune to fiber distortions. Our proposed solution relies on the prolate spheroidal wave functions and a numerical optimization routine. Time-limited waveforms that undergo minimum time broadening along an optical fiber are obtained and shown to outperform fundamental solitons. In the case of binary transmission and a single span of fiber, we report rate increases of 33.8% and 12% over lossy and lossless fibers, respectively. Furthermore, we show that the transmission rate of the proposed system increases as the number of used energy levels increases, which is not the case for fundamental solitons due to their effective time-amplitude constraint. For example, rate increases of 164% and 70% over lossy and lossless fibers respectively are reported when using four energy levels.

Methods and ways for improving the exchange of information in the flight control system

Taking into account the shortcomings of the information exchange system through the ARINC 629 bus, which is widely used in new digital avionics systems (delay of information exchange, program errors, sensitivity to external influences, etc.), the fiber-optic information exchange system proposed in the article reduces the weight of aircraft in aviation systems, it allows solving many problems such as software errors, delays and maintenance problems. This system has a much higher transmission speed than traditional systems, significantly reduces the number of computers and wires, and the transition to modular avionics makes it more compact and easier to maintain.

Enhancing performance of optical chaotic-based secure fiber-optic communication system

Enhancing performance of optical chaotic-based secure fiber-optic communication system

A Novel Millimeter Wave Receiver Enhanced by a Metallic Dipole Antenna and an Electro-Optic Polymer Waveguide Ring Resonator

The ever-demanding requirement for higher data transmission rate has pushed the carrier frequency in wireless communications from centimeter to millimeter waves (MMW) or even terahertz band. Hybrid integration between the wireless and fiber-optic systems can then help realize a seamless signal transition between the access and backbone networks. In this work, we propose a novel MMW receiver with a simple structure consisting of an electro-optic polymer racetrack waveguide ring resonator (WRR) and a metal dipole antenna. Due to Pockels effect within the polymer waveguide, the presence of the MMW electric field can introduce minor refractive index changes in the waveguide, which can affect light phase and the transmission through the WRR. This effect can be employed to effectively detect the presence of MMW based on the optical method. The phase changes can be highly improved by the dipole antenna resonating at the MMW frequency in order to achieve an enhanced detection of the MMWs. As a result, a low-cost, compact and reliable MMW receiver can be realized, which provides an effective functional interface between MMW and optical fiber-optic systems.

Machine Learning-Enabled Intelligent Fiber-Optic Communications: Major Obstacles and the Way Forward

Machine learning (ML) has achieved phenomenal success in revolutionizing a number of science and engineering disciplines over the last decade. Naturally, it is also being reckoned as a powerful technology to transform future fiber-optic communication systems. Over the past few years, we have seen extensive research efforts by both academia and industry to assimilate and gain from ML paradigm in several aspects of optical communications and networking. However, despite years of rigorous research, ML has not yet gained broad acceptance in commercial fiber-optic networks. In this article, we identify major common factors which are currently hindering widespread adoption of ML in practical optical networks. As ML-based methods are inherently data driven, we particularly highlight critical data-related issues as well as intrinsic limitations of the ML algorithms. Taking two important use-cases, i.e., quality-of-transmission estimation, and proactive fault detection and management as examples, we elucidate how these limiting factors shrink the deployment prospects of ML-based solutions. We also briefly discuss main challenges faced by ML-assisted methods in seven other key areas of fiber-optic communications. Finally, we suggest some useful strategies that can help alleviate existing obstacles, thus paving the way for vast deployment of ML -powered tools in real optical network infrastructures.

Highly Dispersive Optical Fiber for Orbital Angular Momentum Modes

Orbital angular momentum (OAM) modes, featured by the unique properties of the helical phase front and annular intensity profile, have shown enormous potential for a wide range of applications. Optical fibers with ring-shape profile have been experimentally proven for supporting stable OAM beam propagation. In most instances, managing the chromatic dispersion is of vital importance in a variety of optical fiber systems. In this paper, we summarize optical fibers with concentric ring cores for extremely dispersive OAM modes. The properties of the OAM mode in double ring-core fiber are presented, including the effective refractive index, effective mode area, power integral ratio, chromatic dispersion, and loss. Photonic crystal fiber and triple ring-core fiber, which share the same operation principle for dispersive OAM modes as the one in the dual-ring fiber, are also briefly introduced.

METHODS FOR THE FORMATION OF SPATIAL TOPOLOGY AND INTERROGATION OF FIBER-OPTIC SENSORS FOR DIAGNOSTICS OF COMPOSITE STRUCTURES (Review)

The paper formulates general requirements for the formation of spatial topologies of quasi-distributed fiber-optic systems of embedded monitoring based on fiber Bragg gratings for monolithic and three-layer structures made of polymer composite materials. The main types of spatial topologies of fiber-optic sensors for the implementation of an effective quasi-distributed system of embedded diagnostics of composite structures are considered. The main methods for interrogating arrays of fiber-optic sensors that form a quasi-distributed system of embedded diagnostics of composite structures are analyzed, an overview and analysis of the technical characteristics of foreign and domestic interrogation equipment is given. It has been established that for practical applications, taking into account the relative simplicity of physical implementation and the availability of interrogation equipment, it is advisable to use a mixed topology of fiber-optic sensors, which includes elements of serial and star topologies, with he spectral channel separation method being the most optimal.

FOSS-Based Method for Thin-Walled Structure Deformation Perception and Shape Reconstruction

To improve the accuracy of deformation perception and shape reconstruction of flexible thin-walled structures, this paper proposes a method based on the combination of FOSS (fiber optic sensor system) and machine learning. In this method, the sample collection of strain measurement and deformation change at each measuring point of the flexible thin-walled structure was completed by ANSYS finite element analysis. The outliers were removed by the OCSVM (one-class support vector machine) model, and the unique mapping relationship between the strain value and the deformation variables (three directions of x-, y-, and z-axis) at each point was completed by a neural-network model. The test results show that the maximum error of the measuring point in the direction of the three coordinate axes: the x-axis is 2.01%, the y-axis is 29.49%, and the z-axis is 15.52%. The error of the coordinates in the y and z directions was large, and the deformation variables were small, the reconstructed shape had good consistency with the deformation state of the specimen under the existing test environment. This method provides a new idea with high accuracy for real-time monitoring and shape reconstruction of flexible thin-walled structures such as wings, helicopter blades, and solar panels.

Distributed Fiber-optic Perimeter Security System of Various Objects

The issues of development of a distributed fiber-optic security system for restricted access objects and other objects of state significance from unauthorized access are considered. The analysis of existing systems developed by foreign scientists is given. A scheme of a passive perimeter security system is proposed for consideration, in which an optical fiber is used as the main element. The principle of operation of a distributed type fiber-optic security system is based on a method for controlling the amount of additional losses during mechanical action on an optical fiber. A laboratory stand was constructed for conducting field experiments and testing the design of the security system. The obtained research results make it possible to further create fiber-optic security systems of a distributed type with a lower cost compared to foreign analogues due to a fundamentally new method of data processing and the use of multimode optical fibers. This will also increase the length of the fiber-optic security system and increase their reliability. The proposed distributed fiber-optic security system uses a completely different principle associated with pixel analysis of the change in the light spot.

Research On High Precision Fiber Optic Platform System Temperature Compensation Technology

In a high-precision fiber optic platform system, temperature changes will have a significant impact on the start-up speed and actual application accuracy. In order to effectively improve the navigation accuracy of the system, the article analyzes the temperature characteristics of the system-level calibration error parameters and establishes a temperature error model. Finally, a temperature compensation test and a platform model calibration test are designed to verify the compensation effect. The test results show that the established temperature error compensation model is accurate and effective. The stability of error parameters has increased by an order of magnitude. The method improves the performance of the fiber optic platform at the start-up stage, and has a small amount of calculation, which has high engineering application value.

Fiber Optic Temperature Sensor System Using Air-Filled Fabry-Pérot Cavity with Variable Pressure.

We report a high-resolution fiber optic temperature sensor system based on an air-filled Fabry-Pérot (FP) cavity, whose spectral fringes shift due to a precise pressure variation in the cavity. The absolute temperature can be deduced from the spectral shift and the pressure variation. For fabrication, a fused-silica tube is spliced with a single-mode fiber at one end and a side-hole fiber at the other to form the FP cavity. The pressure in the cavity can be changed by passing air through the side-hole fiber, causing the spectral shift. We analyzed the effect of sensor wavelength resolution and pressure fluctuation on the temperature measurement resolution. A computer-controlled pressure system and sensor interrogation system were developed with miniaturized instruments for the system operation. Experimental results show that the sensor had a high wavelength resolution (<0.2 pm) with minimal pressure fluctuation (~0.015 kPa), resulting in high-resolution (±0.32 ℃) temperature measurement. It shows good stability from the thermal cycle testing with the maximum testing temperature reaching 800 ℃.