Fiber-optic Signal Processing Research Articles

Deep learning-assisted structural health monitoring: acoustic emission analysis and domain adaptation with intelligent fiber optic signal processing

Structural health monitoring aims to detect damage progression in materials. This study focuses on categorizing crack stages, a critical aspect of monitoring structural integrity. By leveraging acoustic emission (AE) monitoring, cracks can be analyzed in a data-driven manner. However, applying AE analysis poses several challenges, including discrepancies between simulated AE data from models and experimental data from the field, as well as class imbalance in crack progression data, with a scarcity of late-stage data. To bridge the gap between theory and experiments, our approach employs domain adaptation to synchronize simulated and actual AE data. The model learns robust domain-invariant features through meticulous experimentation across training epochs. Quantitative analysis of the model’s performance provides key insights. F1 scores vary with feature counts, and domain adaptation outperforms by 20% on highly imbalanced datasets. This emphasizes the model’s adaptability for precise crack classification, even with underrepresented damage classes. In summary, this study advances structural health monitoring by offering a solid AE analysis approach. Core contributions include reconciling simulated and experimental data discrepancies, tackling class imbalance, optimizing feature extraction, and demonstrating robust crack stage categorization. The insights gained highlight the merits of domain adaptation and data-driven AE analysis for predicting crack progression.

Study on a new four‐fiber sensor signal processing algorithm of hydrodynamic characteristics in liquid–liquid two‐phase flow

AbstractIn the process of two‐phase countercurrent flow in the extraction column, the study of the hydrodynamic characteristics of dispersed phase droplets is crucial for the design and scaling up of the extraction column. In a pulsed extraction column with a liquid–liquid system, the four‐sensor optical fiber probe was used to assess the hydrodynamic characteristics of the dispersed phase droplets, including size, mean velocity, and holdup. 1 M HNO3 and 30% TBP/kerosene were used as continuous phase and dispersed phase, respectively. The effects of two‐phase superficial velocities and pulsation intensity were investigated on droplet size, mean velocity, and holdup. The findings show that aside from the local holdup, the pulsation intensity has the greatest impact on the hydrodynamic characteristics. A new and concise algorithm was used to deal with the light signals to determine the droplet size and mean velocity. This algorithm created two Cartesian coordinate systems, each with a separate z‐axis using the leading probe as the origin of the coordinate instead of using the vector approach. Compared to the previous algorithm, both the needed number of the time interval between the voltage peaks and that of the direction angles decrease. The relative error of the droplet size obtained by this improved algorithm is within 7%, and droplet velocity is almost the same, compared to the previous algorithm, which indicates that the new algorithm of the four‐sensor optical fiber signal processing is reliable to the measurement of the hydrodynamic characteristics.

Photoelectric Vibration Monitoring System Using Optical Fiber Sensing/Mathematical Modeling

The optical fiber vibration monitoring system is designed, and the optical fiber with strong anti-interference performance, high stability and corrosion resistance is used as the sensor. Mach-Zehnder with high sensitivity is used for interference counting, and embedded technology is introduced. The extracted spectral characteristics of optical fiber signals are used for pattern recognition through a mathematical modeling method. In the hardware design, embedded technology is introduced. Multi-channel AD collects data, and the processed optical fiber data are communicated with the master computer through the high-speed network port to realize the data transmission without breakpoints, and then reduce the development cost. Fast Fourier transform (FFT) is used as the research method of mathematical modeling in optical fiber signal processing and is improved. The new algorithm can analyze the vibration signal from the frequency domain. In the test, one group of intrusion vibration signals and one group of ordinary vibration signals are taken as the test objects. The results show that the improved mathematical modeling method will not have the situation of false intrusion alarm, nor will it have the situation of common false alarm. Using this algorithm in the vibration monitoring system of optical fiber sensors can accurately identify intrusion signals to distinguish the intrusion vibration situation from the ordinary vibration situation.

Self-Learning Filtering Method Based on Classification Error in Distributed Fiber Optic System

The distributed fiber optic system based on phase-sensitive optical-time-domain reflectometry ( $\Phi $ -OTDR) has attracted extensive interest in the field of perimeter security. However, the noise caused by environmental factors in fiber optic signal processing is a great difficulty due to the complexity and variability of the natural environment. In this paper, an improved wavelet de-noising method based on classification error of training signal data is proposed to solve the difficulty of filtering thresholds selection. By maximizing the true positive rates under selected false positive rates, initial filtering thresholds based on experience are constantly adjusted and optimized. Experimental results prove that improved wavelet filtering thresholds get better performance than traditional wavelet thresholds in indoor and outdoor environments. In addition, the improved method can automatically select and optimize thresholds to adapt to different situations.

Transmission Reliability of Wireless Communication System-Based on Optical Fiber Signal Processing

Abstract With the continuous progress of society, people’s requirements for communication technology are getting higher and higher, and the traditional communication system has not been able to meet the growing data needs of society. Therefore, it is of practical significance and guiding significance to study the transmission reliability of communication system. In this study, the wireless communication system-based on optical fiber and Class-AB technology and non-linear distortion model used for improving communication quality were briefly introduced, and then simulation analysis was carried out on the traditional simulation system and communication system designed in this study using VPI TransmissionMaker software. The results demonstrated that the proposed system had better stability than the traditional system. The comparison of the electricity frequency spectrum between the two systems showed that the proposed system could effectively suppress the third-order distortion current, and 28.6 dBm distortion current was suppressed. The Spurious Free Dynamic Range (SFDR) of the proposed system was higher, and the fit line slope of the distortion current was 5, differing from that of the traditional system, 3. which further demonstrated that the distortion current was inhibited. In conclusion, the optical communication system designed in this study can effectively improve the communication quality and increase the reliability of wireless communication.

Temporal cloak based on tunable optical delay and advance.

A temporal cloak scheme based on tunable optical delay and advance is theoretically proposed. An input optical signal is divided into two parts, and the front part is advanced while the rear part is delayed. A temporal gap which contains negligible optical energy is opened to hide events from observers, which can be closed by doing the inverse process. Different from the previous schemes that use continuous wave light, we use an optical data stream as the probe beam. Simulations have been done to investigate performance of the temporal cloak. The developed scheme can be applied in fiber-optical signal processing and secure communications.

Fault-tolerant polarization-insensitive photonic delay line architectures using two-dimensional digital micromirror devices

A binary multichannel photonic delay line (PDL) module is introduced that gives balanced loss switched states and a polarization-insensitive operation via the use of binary operation Digital Micromirror Devices (DMDs). Experimental demonstration of a DMD-based PDL architecture is performed for a 6.84-ns time delay design. Experimental results include a 25-beam feed interchannel crosstalk test indicating a <−60 dB optical interchannel crosstalk level for a 0.381 mm interchannel distance in the multichannel PDL. An average optical signal-to-leakage noise ratio of 35.33 dB is measured for this PDL. A butterfly design PDL optical architecture is proposed for minimizing loss and improving assembly accuracy. These DMD-based variable PDLs can be used in applications ranging from radio frequency (RF) fiber-optic signal processing systems to adaptive optics for astronomical and laser radar arrays.

International Trends in Optics

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Design and performance optimization of fiber optic adaptive filters

There is a great need for easy-to-fabricate and versatile fiber optic signal processing systems in which optical fibers are used for the delay and storage of wideband guided lightwave signals. We describe the design of the least-mean-square algorithm-based fiber optic adaptive filters for processing guided lightwave signals in real time. Fiber optic adaptive filters can learn to change their parameters or to process a set of characteristics of the input signal. In our realization we employ as few electronic devices as possible and use optical computation to utilize the advantages of optics in the processing speed, parallelism, and interconnection. Many schemes for optical adaptive filtering of electronic signals are available in the literature. The new optical adaptive filters described in this paper are for optical processing of guided lightwave signals, not electronic signals. We analyzed the convergence or learning characteristics of the adaptive filtering process as a function of the filter parameters and the fiber optic hardware errors. From this analysis we found that the effects of the optical round-off errors and noise can be reduced, and the learning speed can be comparatively increased in our design through an optimal selection of the filter parameters. A general knowledge of the fiber optic hardware, the statistics of the lightwave signal, and the desired goal of the adaptive processing are enough for this optimum selection of the parameters. Detailed computer simulations validate the theoretical results of performance optimization.

Bipolar optical modulation and demodulation using dual-mode fiber and a fast diffusion-driven photodetector

A bipolar fiber-optic signal processing and photodetection concept which combines a dual-mode optical fiber with a fast diffusion-driven photodetector is demonstrated. A discussion of the concept is given, and the results of a simple experiment are given. Various permutations of the ideas described can permit different kinds of coherent and incoherent optical-signal processing and optical control of pulsed photodetection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Code division multiple-access techniques in optical fiber networks. I. Fundamental principles

An examination is made of fiber-optic code-division multiple-access (FO-CDMA), a technique in which low information data rates are mapped into very-high-rate address codes (signature sequences) for the purpose of achieving random, asynchronous communications free of network control, among many users. The need for a special class of signature sequences to achieve the multiple-access capability using fiber-optic signal processing techniques is discussed. A class of signature sequences called optical orthogonal codes (OOCs) that provide the auto- and cross-correlation properties required for FO-CDMA is introduced and used in an experiment to show the principles of FO-CDMA. The experiment demonstrates the auto- and cross-correlation properties of the codes. The concept of optical disk patterns, an equivalent way of representing the OOCs, is introduced. The patterns are used to derive the probability density functions associated with any two interfering OOCs. A detailed study of different interference patterns is presented, and the strongest and the weakest interference patterns are determined. >

Deposition of oriented zinc oxide on an optical fiber

Techniques are described by which an oriented zinc oxide film is sputtered directly on one side of an 80-μm-diam fused silica single-mode optical fiber. A 4-GHz piezoelectric transducer incorporating this film demonstrates that the film is oriented. Evidence of acoustic waves in the fiber is given by the swept-frequency vector input impedance of the transducer. Acoustic transducers fabricated directly on a fiber produce fields focused on the fiber core for efficient acousto-optic interactions, making possible many new fiber-optic signal processing devices.

Single-mode waveguide microlenses and microlens arrays fabrication in LiNbO3 using titanium indiffused proton exchange technique

Single-mode planar waveguide microlenses and microlens arrays in LiNbO3 have been fabricated using a combination of titanium diffusion and proton exchange processes. The lenses have demonstrated properties such as very short focal length, micron focal spot size, and large angular field of view that are desirable for applications in integrated and fiber-optic signal processing and computing as well as communication systems.