Fiber Optic Applications Research Articles

Applications of Optical Fiber in Label-Free Biosensors and Bioimaging: A Review.

Biosensing and bioimaging are essential in understanding biological and pathological processes in a living system, for example, in detecting and understanding certain diseases. Optical fiber has made remarkable contributions to the biosensing and bioimaging areas due to its unique advantages of compact size, immunity to electromagnetic interference, biocompatibility, fast response, etc. This review paper will present an overview of seven common types of optical fiber biosensors and optical fiber-based ultrasound detection in photoacoustic imaging (PAI) and the applications of these technologies in biosensing and bioimaging areas. Of course, there are many types of optical fiber biosensors. Still, this paper will review the most common ones: optical fiber grating, surface plasmon resonance, Sagnac interferometer, Mach-Zehnder interferometer, Michelson interferometer, Fabry-Perot Interferometer, lossy mode resonance, and surface-enhanced Raman scattering. Furthermore, different optical fiber techniques for detecting ultrasound in PAI are summarized. Finally, the main challenges and future development direction are briefly discussed.

Cylindrical vector beam generation from a passively mode-locked Raman fiber laser

We experimentally investigate cylindrical vector beam (CVB) generation from a passively mode-locked Raman fiber laser. The mode-locked Raman fiber lasers based on nonlinear polarization rotation (NPR), utilize the Raman gain resulted from the stimulated Raman scattering (SRS) effect in passive fibers, instead of stimulated emission amplification of active fibers in conventional mode-locked fiber lasers. With a mode-selective coupler (MSC) incorporated into the mode-locked Raman fiber laser, the generation of CVBs has been realized. In experiment, using a Raman pump source of 1454 nm, mode-locked CVB output with central wavelength of 1562 nm was obtained. The output polarization state can be switched between the radial and azimuthal polarization states, and the beam purity is above 90%. Due to the broadband Raman gain in optical fiber, the CVB output with the desired wavelength is available in principle by selecting a suitable pump source. This kind of flexible wavelength CVB Raman fiber laser may have potential applications in optical communications and fiber optics.

On the study of optical soliton solutions to the three-component coupled nonlinear Schrödinger equation: applications in fiber optics

On the study of optical soliton solutions to the three-component coupled nonlinear Schrödinger equation: applications in fiber optics

Bright Soliton Solution of the Nonlinear Schrödinger Equation: Fourier Spectrum and Fundamental Characteristics

We derive exact analytical expressions for the spatial Fourier spectrum of the fundamental bright soliton solution for the 1+1-dimensional nonlinear Schrödinger equation. Similar to a Gaussian profile, the Fourier transform for the hyperbolic secant shape is also shape-preserving. Interestingly, this associated hyperbolic secant Fourier spectrum can be represented by a convergent infinite series, which can be achieved using Mittag–Leffler’s expansion theorem. Conversely, given the expression of the series of the spectrum, we recover its closed form by employing Cauchy’s residue theorem for summation. We further confirm that the fundamental soliton indeed satisfies essential characteristics such as Parseval’s relation and the stretch-bandwidth reciprocity relationship. The fundamental bright soliton finds rich applications in nonlinear fiber optics and optical telecommunication systems.

Heat treatment and polymer coating effect on Rayleigh scattering based fiber optic temperature measurement

This study experimentally investigates the effect of heat treatment on Rayleigh scattering based distributed single-mode fiber optic temperature measurement. A finite element model was established to investigate the effect of thermal expansion of coatings on the optical fiber core strains and thus, temperature sensitivity before the coatings soften and melt away. A theoretical derivation for the fiber core strains, using Lame equations, was performed to validate the accuracy of the finite element model. It was found that the one-time heat treatment eliminates the hysteresis effect and stabilizes the Rayleigh scattering based fiber optic temperature measurement up to 1000 °C. The typical dual-layer coating effect on the temperature sensitivity of the Rayleigh frequency shift can be neglected at high temperatures in civil engineering application. Numerical parametric studies are performed to design coatings of fiber optic temperature sensors. The present study is promoting distributed fiber optic temperature sensor development and application.

Optical fiber with homogeneous material byside-array cladding.

Optical fibers are the core elements for various fiber-optic applications in communication, lasers, sensors, tweezers, quantum optics, and bio-photonics. Current optical fibers are based on a core-cladding structure with different refractive indices and are mainly fabricated using the stack-draw method. However, such a traditional fabrication method limits the realization of fibers with various advanced optical materials, thereby restricting the utilization of excellent optical properties offered by these materials. In this study, a novel structure for side-array cladding by laser drilling on the side of the fiber with homogeneous material is proposed. Accordingly, the confinement loss, mode characteristics, birefringence, and dispersion of the side-array cladding fiber are investigated based on the numerical simulation performed via the finite element method. Subsequently, an optimal fiber structure is obtained by taking the crystal material as an example. Essentially, our proposed side-array cladding fiber can eliminate the mismatch problem of core-cladding materials in the current stack-draw fabrication method. Potentially, the proposed approach can serve as a standard design and fabrication method of optical fibers with homogeneous material, by utilizing the rapid development of laser processing. In other words, a large number of advanced optical materials can be fabricated into optical fibers with the proposed technique, thus maximizing their technical advantages for different applications.

Intelligent Sensing Analysis Using Mel-Time-Frequency-Imaging and Deep Learning for Distributed Fiber-Optic Vibration Detection

In fiber-optic vibration-sensing applications, intelligent sensing analysis is an important task for reducing costs and improving the overall quality of monitoring. Most existing methods show a low accuracy because their feature extractions significantly relied on the prior knowledge and the ability of the classifier designer. To deal with the challenges, an effective and scalable feature engineering method that uses vibration time-frequency imaging and deep learning has been proposed in this study. In order to improve the effectiveness and scalability, a Mel time-frequency-based vibration imaging approach is developed. This transforms the original time-domain data into a high-dimensional feature space and incorporates more feature information from data with various scales. Moreover, since the vibration-sensing recognition network is designed based on the deep-learning model, more discriminative features from the vibration image can be extracted automatically. The whole sensing recognition procedure includes four key steps: 1) original signal preprocessing of segmentation and denoising; 2) Mel time-frequency image generation; 3) representative feature extraction; and 4) vibration pattern-sensing classifier design. To verify the effectiveness and superiority of the proposed approach, eight datasets are collected, and three comparison schemes are investigated, using a distributed optical fiber interferometer-based vibration-sensing system. Our results demonstrate that the proposed intelligent sensing detection approach can provide higher accuracy and efficiency than other reported schemes.

Physics-Informed Neural Network for Optical Fiber Parameter Estimation From the Nonlinear Schrödinger Equation

For any system that follows rigorous mathematical and physical theories like fiber-optic system, system parameter estimation is crucial for system detection and monitoring. In this paper, a physics-informed neural network (PINN)-based method is proposed for optical fiber parameter estimation by solving the inverse problem of the nonlinear Schrödinger equation (NLSE), i.e., inferring the unknown parameters of NLSE. The proposed method considers both the prior knowledge of physical law and the characteristics of observation data from only the transmitted and received waveforms. In PINN, the NLSE and observation data are set as the loss function, and the typical fiber parameters (attenuation, dispersion, and nonlinear coefficient) are optimized iteratively until they satisfy the inferred NLSE by learning the limited observation data. Three scenarios are validated, including single Gaussian pulse propagation, ultrashort pulse propagation in highly nonlinear fiber, and optical signal transmission in standard single-mode fiber. The launch power of the signal is embedded in PINN as a parametric feature, which makes PINN learn the signal transmissions under different powers simultaneously. The weights of mean square error terms for NLSE and observation data in the loss function are properly adjusted to balance learning difficulties. Moreover, the statistical results of 128 different signals and model performance under different signal-to-noise ratios are analyzed. As an extension, fiber length estimation is also studied, and the error is 0.375% when the launch power is 0 dBm. Our work verifiably shows that the proposed approach performs well and can be further extended to multiple applications in fiber optics.

Raman scattering-based distributed temperature sensors: A comprehensive literature review over the past 37 years and towards new avenues

Over the last 37 years, particular interest has been directed towards exploring the characteristics of the optical environment for sensing, giving rise to what would now be one of the largest applications of well-known optical fibers, typically employed to transmit data at high rates. Sensing temperature, pressure, liquid level, deformation, and other physical parameters utilizing optical fibers has become a growing branch of research and a business competing with well-established electrical sensors in the industry. Optical fiber sensors have all the inherent characteristics of a fiber optic cable, such as electromagnetic immunity, small size and weight, multiplexing, and so on. These exclusive features have made fiber sensors so versatile as to become a transformative technology by enabling several industrial processes to be carried out with higher reliability. Nowadays, there are several optical sensors, including fiber Bragg grating, interferometric, polarimetric, polymer fiber, distributed, and several others. Specifically, Raman-based distributed temperature sensor (RDTS) is a class of fiber optic sensors broadly employed in temperature measurement of large structures such as oil and gas wells, tunnels, and pipelines. Since 1985, many techniques have been proposed to break through the barriers of exploring Raman scattering as a distributed temperature measurement method. Range, spatial and temperature resolutions have been the most investigated parameters. In this perspective, this paper presents a comprehensive review focused on the progress of the RDTS technology over the past 37 years (1985–2022), covering an analysis of over 500 journal papers. First, a brief introduction to fiber optic sensor technology is presented as a theoretical basis, discussing the emergence of distributed sensors. Subsequently, Raman scattering in optical fibers is introduced, as well as how this nonlinear effect can be used to build temperature sensors. Next, RDTS technology is detailed, followed by a discussion of its applications and evolution over nearly four decades of development. Lastly, future perspectives are addressed in this review for the advancements in distributed temperature sensor technologies.

Evaluating Stimulation Effectiveness with Permanent Optical Fiber and Sealed Wellbore Pressure Monitoring: Bakken Shale Case Study

Summary In 2019, the operator embarked on a data acquisition project in the Bakken, an unconventional shale play in the USA, with the goal of mapping far-field drainage and characterizing completion performance. The project consisted of a six-well pad (10,000-ft laterals) with a dedicated observation lateral located in the Three Forks formation instrumented with cemented pressure gauges and external optical fiber along the 10,000-ft lateral. The observation lateral was offset by Middle Bakken (MB) wells ~450 ft on either side (~900-ft MB-MB well spacing). One of the offset MB wells was instrumented with external optical fiber for cluster-level completion measurements and fracture hit detection. Characterizing hydraulic fracture geometry is critical to improving completion designs and optimizing well spacing. Until recently, microseismic has been the primary diagnostic for estimating “bulk” or stage-level fracture geometry (Warpinski 2009) and parent-child interactions for modern multicluster plug-and-perf completions (Cipolla et al. 2018). However, microseismic cannot provide details on individual fractures or cluster-level measurements. With the continued advances in fiber-optic technologies, we can measure cluster-level fracture behavior at the wellbore and in the far field (Ugueto et al. 2016, 2019). Characterizing the relationship between wellbore and far-field fracture geometry, referred to as fracture morphology, is important when simultaneously optimizing completion design and well spacing. Microseismic and fiber optics are very robust, but expensive, technologies, and this limits the frequency of their application. The recent introduction of sealed wellbore pressure monitoring (SWPM) enables lower-cost, higher-volume data acquisition but may not provide the same level of detail compared with microseismic and fiber-optic measurements. This paper presents a case history that details the application of permanent fiber optics and SWPM to characterize fracture geometry and morphology using distributed acoustic sensing (DAS) for near-wellbore (NWB) measurements along with SWPM and crosswell strain for far-field investigation. This is the first example of both NWB and far-field optical fiber measurements being used to evaluate cluster efficiency in conjunction with SWPM. The SWPM results compared favorably with the fiber measurements; stages with more uniform distribution based on the NWB DAS data also had higher volume to first responses (VFRs) measured using crosswell strain and SWPM.

Application of optical fiber sensing technology in bridge detection

This paper introduces the development and application status of bridge detection technology at home and abroad, focuses on the research and application of optical fiber sensing technology in bridge detection at home and abroad, and takes strain detection as an example to introduce the detection principle, method and latest research of optical fiber sensing technology in bridge detection. Finally, the paper points out the development direction of optical fiber sensing technology in bridge detection.

Efficient taper optical hydrogel fiber coupler drawn from suspended photocuring 3D printing

Integrating bio-friendly optical hydrogel fibers (HFs) with solid-state fibers (SFs) could expand the horizons of fiber-optic technology for bio-photonics. However, methods for coupling HF and SF-based systems are inefficient due to the mode field mismatch. Here, a hydrogel fiber coupler with a taper core-cladding structure is demonstrated for efficiently coupling HF to SF and fabricated through suspended photocuring 3D printing. Coupling efficiencies of 8.3 and 9.4 dB are obtained at 632 and 473 nm, respectively, which are 22% better than those of conventional couplers. The working bandwidth covers visible wavelengths, satisfying bioengineering requirements. This research removes obstacles to optical fiber applications in bioscience.

Application of Optical Fiber Sensing Technology in Permeability Test of Three-Dimensional Physical Model of Medium and Long-Distance Diversion Tunnel

In order to accurately simulate the dynamic change law of seepage field during construction, this paper proposes the application of optical fiber sensing technology in the permeability test of three-dimensional physical model of medium and long-distance headrace tunnel. This paper introduces the principle of optical fiber sensing, analyzes and compares the application advantages of optical fiber and general electrical signal sensing in the safety monitoring of long-distance diversion tunnel. Taking the safety monitoring of a 16# long tunnel of a diversion project as an example, the selection of monitoring sections, monitoring items, and the layout and networking of monitoring instruments are studied. In addition, combined with the tunnel project, the physical simulation of the construction process of the deep buried headrace tunnel under high seepage pressure is carried out, and the water pressure automatic control water supply system and the discrete flower tube seepage generation system are designed and manufactured to realize the high simulation of the seepage field. The seepage and evolution law in the surrounding rock of headrace tunnel during dynamic construction are calculated and analyzed. The test results show that the maximum external water pressure of the headrace tunnel is 15 MPa, which is equivalent to 1500 m head pressure, and the similar scale of head pressure is 100. Therefore, taking 15 m constant head water supply pressure for simulation calculation, the excavation of the tunnel is 120 cm, and the two-dimensional seepage of the vertical section of Z = 91 cm . The seepage flow of the two sides of the tunnel is large, and the contour of the hydraulic gradient is dense. The coordinates are 0.7 m, 2.090 m, and 0.9 m. This point in the original rock mass is located at the same elevation point of the four headrace tunnels and directly below the model exploratory tunnel. The head pressure is 1.40 m, and the corresponding prototype point pressure head is 140 M. During construction, such a high external water pressure is a great safety hazard. Conclusion. The test conclusion provides a theoretical basis for the seepage prevention construction technology design of the headrace tunnel and is of great significance to the long-term stability, safety evaluation, and prediction of the headrace tunnel.

Improvement of Fiber Bragg Grating Wavelength Demodulation System by Cascading Generative Adversarial Network and Dense Neural Network

A high-performance, low-cost demodulation system is essential for fiber-optic sensor-based measurement applications. This paper presents a demodulation system for FBG sensors based on a long-period fiber grating (LPG) driven by artificial intelligence techniques. The LPG is applied as an edge filter to convert the spectrum drift of the FBG sensor into transmitted intensity variation, which is subsequently fed to the proposed sensor demodulation network to provide high-precision wavelength interrogation. The sensor demodulation network consists of a generative adversarial network (GAN) for data augmentation and a dense neural network (DNN) for wavelength interrogation, the former addresses the drawback that traditional machine learning models rely on a large-scale dataset for satisfactory performance, while the latter is used to model the relationship between transmitted intensity and wavelength for demodulation. Experiments demonstrate that the proposed system has excellent performance and can achieve wavelength interrogation precision of ±3 pm. In addition, the effectiveness of the GAN is demonstrated. With a wide demodulation range, high performance, and low cost, the system can provide a new platform for fiber-optic sensor-based measurement applications.

Gallium nitride-based resonant cavity light-emitting diode with single-longitudinal-mode emission.

A novel, to the best of our knowledge, gallium nitride (GaN)-based resonant cavity light-emitting diode (RCLED) with single-longitudinal-mode light emission was demonstrated. A Ta2O5/SiO2 dielectric distributed Bragg reflector (DBR) with a filter-film structure was adopted as the top mirror. In contrast to the flat-topped reflectivity spectrum of the conventional high-reflective-structure DBR, for this filter-film-structure DBR, there is a light-transmitting concave band on the reflectivity spectrum. Owing to the modulation effect of this band on the output light, a single-longitudinal-mode light emission with a full width at half maximum as low as 0.63 nm was realized. Furthermore, the novel RCLED exhibited better wavelength stability. With an increase in the injection current from 50 to 500 mA, the redshift of the emission peak was only 0.2 nm. This novel RCLED with ultra-narrowband emission has a high potential for application in optical communication systems and optical fiber sensing applications.

Optimization of VGG16 Algorithm Pattern Recognition for Signals of Michelson–Sagnac Interference Vibration Sensing System

Signal recognition accuracy and recognition time are the two most important parameters of pattern recognition in a fiber optic vibration sensing system. To obtain high recognition accuracy and short recognition time, this paper optimized the VGG16 algorithm and carried out VGG16-1D and VGG16-2D recognition on big data signals generated by a Michelson–Sagnac interferometric vibration sensor system. The results indicate that VGG16-1D has a higher accuracy of 98.44% and a shorter recognition time of 0.03 s. The proposed method is a more accurate and faster pattern recognition method for big data signals from optical fiber vibration sensing systems, which is helpful in promoting further applications of optical fiber sensing systems.

Multimode interferometric sensor based on the no-core tellurite optical fiber for cryogenic temperature detection.

In this paper, a no-core tellurite optical fiber (NCTOF)-based sensor was proposed for cryogenic temperature detection in refrigeration process. The ultraviolet adhesive (UVA) dual-curing method was operated to stablish a sandwich-like composite structure, in which a section of NCTOF was compactly sandwiched between two segments of silica fiber to form multimode interference. The temperature sensing characteristics in cryogenic range were experimentally investigated by monitoring the transmission spectral movement, where a high sensitivity of 105.6 pm/°C was achieved in the range of -20-0 °C and 51.6 pm/°C in the range of -20-25 °C. The excellent performance was consistent with the simulation analysis. The maximum repeatability standard deviation and stability wavelength error of the sensor are 0.9799 pm/°C and 0.1676 nm, respectively. To the best of our knowledge, this is the first report on using tellurite optical fibers for cryogenic temperature detection, and the UVA dual-curing method provides a reliable solution for the integration and practical application of tellurite optical fiber. The proposed sensor is simple in structure, easy in fabrication, low in cost and excellent in performance. It can be expected to be used in food refrigeration, air-conditioning engineering, medical and health, industrial production, etc.

Study on Quantitative Characterization of Coupling Effect between Mining-Induced Coal-Rock Mass and Optical Fiber Sensing.

The monitoring of mine pressure, division of vertical zoning of the overburden, discrimination of key stratum structure of the overburden and monitoring of advanced abutment pressure are still the main research problems in the field of coal mining. Therefore, the promotion of development of a monitoring technology of mining-induced rock mass deformation has important research value in the mining field. There are many problems to be solved in the application of optical fiber sensing (OFS) to deformation monitoring, such as the corresponding relationship between actual deformation and optical parameters, the coupling relationship between the optical fiber and rock mass and the reasonable division of vertical zoning of the overburden. In this study, a quantitative index of coupling action between the mining rock mass and optical fiber is put forward, and the coupling coefficient of different vertical zonings is quantitatively analyzed and discussed. Based on this, five different media in contact with optical fiber are proposed. The relationship between the strain curve form, the development height of the fracture zone and the activity of key stratum is established. It is of great academic value and research significance to establish a characterization system of displacement, deformation and structural evolution of overlying strata based on optical fiber sensing technology.

Optical solitons and stability analysis for the new (3+1)-dimensional nonlinear Schrödinger equation

This paper explores the new [Formula: see text]-dimensional nonlinear Schrödinger equation which is used to model the propagation of ultra-short optical pulses in highly-nonlinear media. This equation is newly derived based on the extended [Formula: see text]-dimensional zero curvature equation. An effective technique, namely, the extended sinh-Gordon equation expansion method is applied to find optical soliton solutions and other solutions for this model. As a result, dark, bright, combined dark–bright, singular, combined singular soliton solutions, and singular periodic wave solutions are obtained. The stability of the model is investigated by using the modulation instability analysis which guarantees that the model is stable and all solutions are stable and exact. Physical explanations of the obtained solutions are presented by using 3D and 2D plots. The reported outcomes are useful in the empirical application of fiber optics.

Air flowing induced thermo-optic effect for thermal sensitivity reduction in anti-resonant hollow core fibers

The signal propagation delay through an optical fiber changes with environmental temperature, imposing a fundamental limit on performances in many fiber-optic applications. It has been shown that the thermal coefficient of delay (TCD) in hollow core fibers (HCFs) can be 20 times lower than in standard single-mode fibers (SSMFs). To further reduce TCD over a broad wavelength range at room temperature, so that to enrich fiber-optic applications in time- synchronization scenarios, the thermal expansion effect of silica glass must be compensated for. Exploiting the thermo-optic effect of air inside an anti-resonant hollow core fiber (ARF) can be a feasible solution. Nevertheless, an accurate description of the air flow in the course of temperature variation is highly needed to predict the influence of this effect. This work develops an analytical model for quantitatively calculating this temperature-induced air-flowing effect. Across a range of parameters of core diameter, fiber length, and temperature change rate, the experimentally measured propagation delay changes agree well with our model. The resultant low thermal sensitivity is also validated in non-steady conditions and in a practically usable SSMF-ARF-SSMF chain. Our model indicates that a >40-fold TCD reduction relative to SSMFs can be realized in a 60-m-long, 50-µm-diameter ARF, and further TCD reduction should be possible by properly engineering the gas type and the ambient pressure.