Fiber Optic System Research Articles

Method for Controlling Dispersion in Order to Maintain a Quasi-Soliton Pulse Propagation Mode in High-Speed Fiber-Optic Communications System

Relevance: Every year, there is an increasing need to enhance the bandwidth and range of fiber-optic communication systems. The study of methods to control dispersion is relevant and helps maintain a quasi-soliton regime, which is essential for ensuring high-speed, reliable data transmission. Conducted modeling and calculations make this research practical and applicable. This will enable engineers to accurately predict the system's behavior and optimize its performance before implementing it in real-world networks.Problem statement: Investigation of the processes of maintaining a quasi-soliton regime in fibers with decreasing chromatic dispersion and alternating fibers with different signs of chromatic dispersion, both with and without initial chirping.Goal of the work: The development and analysis of techniques to control dispersion in order to maintain a quasi-soliton mode of light propagation in single-mode optical fibers.Methods: The study of the processes of maintaining a quasi-soliton regime was carried out by mathematical and numerical modeling. To substantiate the methods, theoretical analysis and calculations were carried out and schemes for a quasi-soliton fiber-optic communication system were developed and modeling was carried out.Result: The analysis of the results demonstrated the effectiveness of the proposed method and showed the efficiency and stability of the solutions in conditions that were close to real-world scenarios. Novelty: Models for maintaining a quasi-soliton regime and methods for studying them have been developed. The most effective ways to preserve quasi-soliton pulses over long distances have been analyzed.Practical significance: The developed models and research methods can be applied in the educational process and the development of real fiber-optic communication systems.

Deep Integration of Fiber-Optic Communication and Sensing Systems Using Forward-Transmission Distributed Vibration Sensing and on-off Keying.

The deep integration of communication and sensing technology in fiber-optic systems has been highly sought after in recent years, with the aim of rapid and cost-effective large-scale upgrading of existing communication cables in order to monitor ocean activities. As a proof-of-concept demonstration, a high-degree of compatibility was shown between forward-transmission distributed fiber-optic vibration sensing and an on-off keying (OOK)-based communication system. This type of deep integration allows distributed sensing to utilize the optical fiber communication cable, wavelength channel, optical signal and demodulation receiver. The addition of distributed sensing functionality does not have an impact on the communication performance, as sensing involves no hardware changes and does not occupy any bandwidth; instead, it non-intrusively analyzes inherent vibration-induced noise in the data transmitted. Likewise, the transmission of communication data does not affect the sensing performance. For data transmission, 150 Mb/s was demonstrated with a BER of 2.8 × 10-7 and a QdB of 14.1. For vibration sensing, the forward-transmission method offers distance, time, frequency, intensity and phase-resolved monitoring. The limit of detection (LoD) is 8.3 pε/Hz1/2 at 1 kHz. The single-span sensing distance is 101.3 km (no optical amplification), with a spatial resolution of 0.08 m, and positioning accuracy can be as low as 10.1 m. No data averaging was performed during signal processing. The vibration frequency range tested is 10-1000 Hz.

Machine learning approach in multi-channel fiber-optic SPR sensors

Fiber-optic surface plasmon resonance (SPR) sensors have been increasingly used due to their advantages such as compact size, stable physical and chemical properties, high sensitivity, and resistant to electromagnetic interference. In this paper, a dual-channel side-polished fiber-optic SPR sensor system is established to detect the refractive index of liquids and the liquid temperature. High sensitivity of ∼2000 nm/RIU (refractive index unit) and linear sensitivity of ∼−2.0 nm/°C is achieved for two-channel SPR sensors, which are integrated for simultaneously RI temperature sensing and easily scaled to multi-channel SPR sensor array. The resonant wavelengths of the two sensors are located in the range of 600–700 nm and 700–800 nm respectively, which could avoid overlapping the resonance dips. Then, we propose an approach using five machine learning algorithms to predict the resonant wavelength of the second channel of SPR temperature sensor using the normalized transmission spectrum data with a wavelength range of 760–889 nm. After error analysis, it is found that the Categorical Boosting (CatBoost) is the best among five algorithms in terms of accuracy and resolution. The results provide clear evidence that accurate SPR resonant wavelength can be obtained with machine learning approach using a more compact spectrometer.

An Image Processing-Based Correlation Method for Improving the Characteristics of Brillouin Frequency Shift Extraction in Distributed Fiber Optic Sensors

This paper demonstrates how the processing of Brillouin gain spectra (BGS) by two-dimensional correlation methods improves the accuracy of Brillouin frequency shift (BFS) extraction in distributed fiber optic sensor systems based on the BOTDA/BOTDR (Brillouin optical time domain analysis/reflectometry) principles. First, the spectra corresponding to different spatial coordinates of the fiber sensor are resampled. Subsequently, the resampled spectra are aligned by the position of the maximum by shifting in frequency relative to each other. The spectra aligned by the position of the maximum are then averaged, which effectively increases the signal-to-noise ratio (SNR). Finally, the Lorentzian curve fitting (LCF) method is applied to the spectrum with improved characteristics, including a reduced scanning step and an increased SNR. Simulations and experiments have demonstrated that the method is particularly efficacious when the signal-to-noise ratio does not exceed 8 dB and the frequency scanning step is coarser than 4 MHz. This is particularly relevant when designing high-speed sensors, as well as when using non-standard laser sources, such as a self-scanning frequency laser, for distributed fiber-optic sensing.

Application Of High Bandwidth Two-Stage Amplifier in Communication System

With the rapid development of communication technology, the application of high-bandwidth amplifiers in communication systems becomes more and more important. Currently researchers have applied high bandwidth two-stage amplifier technology in many fields such as cloud computing and data centers, video and audio transmission, virtual reality and augmented reality, Internet of Things, financial transactions, etc., and in this paper we will focus on its application in communication systems. In this paper, the basic principle and structure of two-stage amplifier are firstly described, and then the key theories of high-bandwidth technology including its concept, importance, principle and core technology of high-bandwidth design technology as well as stability analysis and design are elaborated, and the applications of high-bandwidth two-stage amplifiers in wireless communication system, fiber optic communication system, data center network, and satellite communication are enumerated. In summary, high-bandwidth two-stage amplifiers play a key role in a variety of communication systems, helping to provide stable, high-speed, long-range signal transmission. Through the research of this thesis, it is expected to provide new references and ideas for the research and development in the field of communication technology, and to promote the progress and innovation of communication system.

Optical fiber integrated WGM cylindrical cavity resonator.

Whispering gallery mode (WGM) resonators are usually discrete optical devices, which have integration difficulties with an optical fiber system. Here we present a new, to the best of our knowledge, type of optical fiber whispering gallery mode resonator based on a cylindrical cavity, which is located in the multimode fiber core and fabricated by femtosecond laser micromachining together with fast hydrofluoric acid etching techniques. When light traveling in the fiber core is tangent to the cylindrical cavity wall, it is coupled into the cavity and circulates along the cavity wall to excite WGM resonance before being coupled out to the same tangential path and continuing propagation in the fiber core. The device is fully integrated into the optical fiber, simple in fabrication, convenient in operation, low in cost, and has a good quality factor (Q) of 1.06 × 104. The device enriches the family of WGM resonators and is expected to have promising applications in photonics.

Hybrid Fibers with Subwavelength-Scale Liquid Core for Highly Sensitive Sensing and Enhanced Nonlinearity.

Interest grows in designing silicon-on-insulator slot waveguides to trap optical fields in subwavelength-scale slots and developing their optofluidic devices. However, it is worth noting that the inherent limitations of the waveguide structures may result in high optical losses and short optical paths, which challenge the device's performance in optofluidics. Incorporating the planar silicon-based slot waveguide concept into a silica-based hollow-core fiber can provide a perfect solution to realize an efficient optofluidic waveguide. Here, we propose a subwavelength-scale liquid-core hybrid fiber (LCHF), where the core is filled with carbon disulfide and surrounded by a silicon ring in a silica background. The waveguide properties and the Stimulated Raman Scattering (SRS) effect in the LCHF are investigated. The fraction of power inside the core of 56.3% allows for improved sensitivity in optical sensing, while the modal Raman gain of 23.60 m-1·W-1 is two times larger than that generated around a nanofiber with the interaction between the evanescent optical field and the surrounding Raman media benzene-methanol, which enables a significant low-threshold SRS effect. Moreover, this in-fiber structure features compactness, robustness, flexibility, ease of implementation in both trace sample consumption and reasonable liquid filling duration, as well as compatibility with optical fiber systems. The detailed analyses of the properties and utilizations of the LCHF suggest a promising in-fiber optofluidic platform, which provides a novel insight into optofluidic devices, optical sensing, nonlinear optics, etc.

Low complexity and finer granularity quantization scheme for perturbation-based fiber nonlinearity compensation in coherent optical communication systems

In the efficient implementation of perturbation theory-based nonlinearity compensation method for reliable fiber-optic coherent communication systems, different quantization schemes have been proposed to reduce the required computational and implementation complexity. For example, the k-means clustering algorithm focused on reducing the number of perturbation coefficients to alleviate the burden of calculating the perturbation terms. In this paper, from the bit-level architectures of multipliers, we propose a multi-segment mixed-word-length quantization scheme that assigns different word lengths for the quantized perturbative coefficients to save computational resources, where Bayesian optimization is employed to derive the optimal hyperparameters involved in this scheme. The proposed scheme was evaluated by numerical simulations of single-channel and multi-channel optical fiber communication systems with dual-polarization 16-QAM modulation. The comprehensive numerical simulation results show that our proposed scheme demonstrates a complexity reduction of more than 65% without performance degradation compared with the traditional uniform quantization method with fixed-word-length, and was robust to the fiber length and baud-rate. We also carried out an experiment of single-carrier transmission over 18 × 100 km standard single-mode fiber with 20 Gbaud single-polarization 16-QAM signal. Similar to the numerical results, the hardware complexity can be reduced by 70.7% with negligible performance deterioration over the uniform quantization scheme. The proposed scheme shows great potential in real-world applications.

SRS-Net: a universal framework for solving stimulated Raman scattering in nonlinear fiber-optic systems by physics-informed deep learning

As a crucial nonlinear phenomenon, stimulated Raman scattering (SRS) plays multifaceted roles involved in forward and inverse problems. In fibre-optic systems, these roles range from detrimental interference that impairs optical performance to beneficial effects that enables various devices such as Raman amplifier. To obtain solutions of SRS, various numerical methods customized for different scenarios have been proposed. However, these methods are time-consuming, low-efficiency, and experience-orientated, particularly in combined scenarios consisting of both forward and inverse problems. Inspired by physics-informed neural networks, we propose SRS-Net, which combines the efficient automatic differentiation and powerful representation ability of neural networks with the regularization of SRS physical laws, to obtain universal solutions for SRS of forward, inverse, and combined problems. We showcase the intuitive solving procedure and high-speed performance of SRS-Net through extensive simulations covering different scenarios. Additionally, we validate its capabilities in experiments involving the high-fidelity modelling of a wavelength division multiplexing system spanning the C + L-band with approximately 10 THz. The versatility of the SRS-Net framework extends beyond SRS, indicating its potential as a promising universal solution in other engineering problems with nonlinear dynamics governed by partial differential equations.

Eigenfrequency analysis using fiber optic sensors and low-cost accelerometers for structural damage detection

Structural Health Monitoring (SHM) is crucial for infrastructure safety and integrity. Arduino-based sensors are gaining popularity in low-cost SHM structures. Distributed fiber optic systems (DFOS), such as Distributed Acoustic Sensing (DAS), are employed for accurate SHM despite their high costs, computational demands, and energy consumption. The primary objectives of this work are to compare the accuracy of an accelerometer named LARA (Low-cost Adaptable Reliable Accelerometer (LARA)) that utilizes both Arduino and Raspberry Pi technologies with a DAS system in detecting structural damage and to explore the potential advantages of combining LARA and DAS to create an effective SHM tool. This study is the first to enhance the design of LARA. Subsequently, LARA and DAS were used in a laboratory setting to analyze eigenfrequency changes in a beam model with induced localized damage. Finally, this study evaluated the precision and reliability of LARA and its potential role as a trigger for DAS in detecting localized damage. The findings show that both LARA and DAS can identify changes in the eigenfrequencies of damaged structures with deviations as small as 3.68 %. Consequently, LARA demonstrated its potential as a trigger for DAS, significantly reducing the computational demands while enriching the analysis. This approach offers highly accurate eigenfrequency measurements and enhances the analytical capabilities of DAS by identifying the primary axes of the detected eigenfrequencies.

Improving decryption quality of optical chaos communication using neural networks.

Optical chaos communication is a promising secure transmission technique because of the advantages of high speed and compatibility with existing fiber-optic systems. The deterioration of chaotic synchronization quality caused by fiber optic transmission impairments affects the quality of recovery of information, especially high-order modulated signals. Here, we demonstrate that the use of a convolutional neural network (CNN) with a bidirectional long short-term memory (LSTM) layer can reduce the decryption BER in an optical chaos communication system based on common-signal-induced semiconductor laser synchronization. The performance of a neural network is investigated as a function of network parameters and chaos synchronization coefficient. Experimental results show that the BER of 16-ary quadrature-amplitude-modulation (16QAM) signal after 100-km fiber transmission is decreased from 3.05 × 10-2 to below the soft-decision forward-error-correction (SD-FEC) threshold of 2.0 × 10-2.

High speed operation efficiency of doped light sources with the silica-doped fiber channel for extended optical fiber system reach

Abstract This paper demonstrated the high speed operation efficiency of doped light sources with the silica-doped fiber channel for extended optical fiber system reach. The output power and required bias voltage are clarified of AlIn(x)Ga(y)As light source versus injection current variations and indium, gallium dopants concentration variations at room temperature and 1.55 μm wavelength. The output power and required bias voltage are studied of PAl(z)Ge(h)Sb light source versus injection current variations and aluminum, germanium dopants concentration variations at room temperature and 1.55 μm wavelength. Required resonance frequency is measured for AlIn(x)Ga(y)As light source versus injection current variations and indium, gallium dopants concentration variations at room temperature and 1.55 μm wavelength. Required resonance frequency is demonstrated for PAl(z)Ge(h)Sb light source versus injection current variations and aluminum, germanium dopants concentration variations at room temperature and 1.55 μm wavelength.

New Technologies for Monitoring Coastal Ecosystem Dynamics.

In recent years, our view of coastal ecosystems has expanded and come into greater focus. We are currently making more types of observations over larger areas and at higher frequencies than ever before. These advances are timely, as coastal ecosystems are facing increasing pressures from climate change and anthropogenic stressors. This article synthesizes recent literature on emerging technologies for coastal ecosystem monitoring, including satellite monitoring, aerial and underwater drones, in situ sensor networks, fiber optic systems, and community science observatories. We also describe how advances in artificial intelligence and deep learning underpin all these technologies by enabling insights to be drawn from increasingly large data volumes. Even with these recent advances, there are still major gaps in coastal ecosystem monitoring that must be addressed to manage coastal ecosystems during a period of accelerating global change.

Fiberoptic Laser-Induced Breakdown Spectroscopy System for in situ Measurement in a Hazardous Environment

We report the development of a novel fiberoptic laser-induced breakdown spectroscopy (FOLIBS) system for material characterization applications. The system utilizes a 1000-µm optical fiber to transport the laser beam to remote locations for elemental analysis via laser-induced breakdown spectroscopy. Air-fiber interface damage, internal damage, and air breakdown issues during laser-fiber coupling are identified and corresponding solutions are presented. For evaluating the physical properties of the plasma generated by the FOLIBS system, spectroscopic characterization is carried out using a titanium sample. The spectral features collected from a natural uranium sample are also presented. Hence, this rapid, remote, and flexible measurement technique is promising for in situ measurements in hazardous environments in nuclear energy, nuclear safeguards, and nonproliferation applications.

Construction of some new traveling wave solutions to the space-time fractional modified equal width equation in modern physics

Nonlinear fractional evolution equations are important for determining various complex nonlinear problems that occur in various scientific fields, such as nonlinear optics, molecular biology, quantum mechanics, plasma physics, nonlinear dynamics, water surface waves, elastic media and others. The space-time fractional modified equal width (MEW) equation is investigated in this paper utilizing a variety of solitary wave solutions, with a particular emphasis on their implications for wave propagation characteristics in plasma and optical fibre systems. The fractional-order problem is transformed into an ordinary differential equation using a fractional wave transformation approach. In this article, the polynomial expansion approach and the sardar sub-equation method are successfully used to evaluate the exact solutions of space-time fractional MEW equation. Additionally, in order to graphically represent the physical significance of created solutions, the acquired solutions are shown on contour, 3D and 2D graphs. Based on the results, the employed methods show their efficacy in solving diverse fractional nonlinear evolution equations generated across applied and natural sciences. The findings obtained demonstrate that the two approaches are more effective and suited for resolving various nonlinear fractional differential equations.

Dynamic interplay: unveiling inelastic breather collisions and modulation instability enhancement in a periodically gained inhomogeneous fiber optic communication system across temporal frequencies

Examining the impact of inhomogeneity on the propagation of femtosecond ultrafast optical pulses in fiber, we delve into the realm of the modified Hirota nonlinear Schrödinger equation (NLS) with inhomogeneity of variable coefficients (MIH-vc). Employing the Hirota bilinear method, we derive two soliton solutions for the modified Hirota NLS equation and analyze the effect of variable coefficients. The dynamical properties of these soliton solutions come to light as we meticulously analyze the corresponding plots. In our exploration, a noteworthy revelation unfolds as we witness the inelastic collision between two breathers, unleashing profound changes in the trajectory of femtosecond pulses. Furthermore, we showcase a detailed modulation instability analysis, unraveling the gain spectrum for our theoretical model. Through graphical illustrations, we elucidate how inhomogeneous functions intricately shape the modulation instability (MI) gain spectrum. A groundbreaking observation surfaces as, for the first time, we discern the periodic gain enhancement in relation to Group Velocity Dispersion along the fiber and its dynamic interactions.

The amplification effect of four-phonon scattering in CdX (X=Se, Te): The role of mid-frequency phonons

Recently, CdX (X = Se, Te) materials have garnered notable interest owing to their great application potential for high-efficiency solar cells, fiber optic communication systems, and nanoelectronic devices. The performance of optoelectric devices is significantly influenced by the thermal conductivity. In this study, a combination of machine-learning methods and first-principles calculations is utilized to investigate the phonon thermal transport properties of CdSe and CdTe, as well as to give deep insights into the phonon behavior in heat transfer. It is found that acoustic phonons dominate the lattice thermal conductivity (κ) in CdSe, while optical phonons contribute around 50 % to the κ value in CdTe. There are strikingly strong four-phonon scattering phenomena in both materials, which result in 55 % and 66 % reduction in κ values for CdSe and CdTe, respectively. Further analysis shows that the mid-frequency phonons play an important role in amplifying the four-phonon scattering. Its special frequency positions permit an unusually large number of four-phonon scattering processes to occur and cause large scattering of low-frequency phonons. This mechanism differs from earlier proposed features regarding large acoustic-optical gaps, bunching of acoustic branches and four-phonon Fermi resonance, which implies strong four-phonon anharmonicity. Thus, the present work opens up new prospects in the exploration and design of innovative thermoelectric material, which provides a more thorough understanding of the four-phonon scattering mechanisms in crystalline solids.

Real-Time SHM of composite wing in a wind tunnel test using PCA-Based statistics

Structural health monitoring could prove particularly valuable in the case of composite aerostructures, where traditional inspection methods for critical components face challenges due to limited accessibility. An effective online SHM system can be achieved by employing fiber optic sensors, facilitating the integration of a 'fiber optic nervous system' into the composite structure, enabling the detection, measurement, and communication of a number of critical structural parameters. While the success of such system relies on selecting the right parameters to be monitored and the right sensing technology, it can also greatly benefit from on-board, real-time processing of the rather large amount of streamed data that ends with some data-driven real-time and continuous assessment as to the current state of the structure: Normal/Abnormal (based, of course, upon previously selected criteria). In this work we demonstrate fiber-optic-based structural health monitoring of a healthy/damaged composite airplane wing in a wind tunnel test. Real-time health assessment is based on Principal Component Analysis (PCA). We utilize two PCA-based measures, the Hotelling's T-squared distribution and the Q-statistics, as fault indicators. These statistics have been demonstrated to exhibit high sensitivity to structural anomalies. A PCA model accompanied by these statistics form a decision support tool that offers dependable real-time information regarding the health of the airborne structure, including the reporting of deviations from a prescribed flight envelope. We demonstrate the performance of the method on real-time structural data gathered in a wind tunnel test, performed on a composite wing. Here, a PCA model was built based on the wing in its healthy state under a nominal loading regime. During the test, the system, processing the data collected from 10 FBGs, using a standard PC, successfully identified deviations, such as overload and initial damage.

Use of fibre optic systems for detection of small leaks on trunk pipelines

This paper is devoted to the issue of efficiency of application of fibre optic leak detection systems for identification of small leaks on trunk pipelines. The main methods of leak detection currently in use have been considered, and parametric and fibre optic LDS have been selected for comparative analysis. In the course of the research a model of product leakage from an underground oil pipeline equipped with a fibre-optic LDS was built in the COMSOL Multiphysics software package. The result of the simulation was the estimated time of leak identification by the fibre-optic system, which turned out to be much shorter than that of the parametric LDS. Compensable environmental damage for each type of system was then calculated, confirming the effectiveness of fibre optic LDS for detecting small leaks on trunk pipelines due to the significant reduction in compensable damage.

A fiber-wireless integration approach in WDM-PON architecture, boosted with polarization multiplexing and optical frequency comb source

Abstract The paper discusses an optical frequency comb source (OMCG)-enabled hybrid single mode fiber (SMF) and free space optical (FSO) communication system (fiber-wireless) delivering a total capacity of 96 Gbps by incorporating polarization division multiplexing (PDM) in passive optical network (PON) architecture. For the accomplishment of PDM, three diverse states of polarization (SOPs) are explored such as 00, 450, and 900. Performance investigation of proposed system is conducted for assessing Q factor and BER by exploring the different modulation formats in proposed system such as modified duo-binary return to zero (MDRZ), return to zero (RZ), compressed spectrum RZ (CSRZ), and non-RZ (NRZ). Results revealed that presented design can cover 30 km SMF + 3.4 km FSO range by incorporating MDRZ due to its spectral efficient and dispersion tolerant properties.