Sensitive Optical Time Domain Reflectometry Research Articles

Voiceprint and position information detection of non-cooperative ship with Φ-OTDR and suspended sensitized optical cable

Target detection is significant in many fields, including oceanic security, marine ecology, etc. In this paper, phase sensitive optical time domain reflectometry (Φ-OTDR) is introduced for the non-cooperative ship detection, with large-scale diversity technology and suspended sensitized optical cable. In outfield experiments, the ship’s voiceprint information is obtained in high fidelity, the ship’s power spectrum is analyzed, and the over-top detection is achieved. Moreover, an array orientation method based on adaptive phase difference correction (APDC) is proposed to track the ship, suppressing the delay jitter influence of acoustic transmission underwater. This is the first time that voiceprint information of the non-cooperative ship is high-fidelity acquired and deeply analyzed with Φ-OTDR and suspended sensitized optical cable, which is conducive to the detection and identification of marine targets, and proves the potential of Φ-OTDR in hydroacoustic detection applications.

Performance improvement of optical fiber sensor based on phase sensitive optical time domain reflectometry

Performance improvement of optical fiber sensor based on phase sensitive optical time domain reflectometry

Vibration Event Recognition Using SST-Based Φ-OTDR System.

We propose a method based on Synchrosqueezing Transform (SST) for vibration event analysis and identification in Phase Sensitive Optical Time-Domain Reflectometry (Φ-OTDR) systems. SST has high time-frequency resolution and phase information, which can distinguish and enhance different vibration events. We use six tap events with different intensities and six other events as experimental data and test the effect of attenuation. We use Visual Geometry Group (VGG), Vision Transformer (ViT), and Residual Network (ResNet) as deep classifiers for the SST transformed data. The results show that our method outperforms the methods based on Continuous Wavelet Transform (CWT) and Short-Time Fourier Transform (STFT), while ResNet is the best classifier. Our method can achieve high recognition rate under different signal strengths, event types, and attenuation levels, which shows its value for Φ-OTDR system.

Low-noise φ-OTDR employing nonlinear optical preamplification for distributed acoustic sensing.

A phase sensitive optical time domain reflectometry sensing scheme employing a two-stage nonlinear optical preamplification system is proposed to reduce the blind spot effect in Rayleigh scattering by improving the optical power distribution and to enhance the resolution at locations of low-backscatter intensity measurements, providing a higher signal-to-noise ratio for distributed acoustic measurements; the developed system has been tested in-laboratory and on in-field monitoring of a survey well in Cottessen, The Netherlands. The characterization shows strain noise levels below 1nɛ for a 10kHz sampling rate.

Distributed multiple vibrations detection with high frequency response assisted by dual NLL sources

Distributed multiple vibrations detection with high frequency response is still a challenging task in distributed optical fiber vibration sensors. In terms of optical interferometer based vibration sensors, the location information can not be directly demodulated. Moreover, the detectable frequency response in the optical reflectometer based vibration sensors is limited by the repetition frequency of the modulated optical pulse. In this paper, an integrated vibration sensing scheme based on two dual narrow line-width laser (NLL) sources with different wavelengths has been theoretically proposed and experimentally demonstrated. In the scheme, one NLL source is used for constructing the phase sensitive optical time domain reflectometry (Φ-OTDR), and the other one is used to build the Michelson interferometer. These two vibration sensors are integrated by using a dense wavelength division multiplexer. Based on the sensing mechanism of the integrated vibration sensor, the multiple simultaneous vibration points can be located by the Φ-OTDR sensing part, meanwhile its corresponding frequencies information can be fully acquired by the Michelson part. Experiments on detection of the piezolelectric transducer (PZT) show that a spatial resolution of ∼20 m is achieved in a 4.95 km sensing fiber link based on the width of the modulated optical pulse in Φ-OTDR part was set as 200 ns. And a maximum frequency response can reach 45 kHz restricted by the vibration source of the PZT. Compared to conventional vibration structure, the proposed vibration sensing scheme can offer a series of unique advantages, such as simple signal demodulation process, high signal to noise ratio of the demodulated frequency spectrum, no high order harmonics in the frequency spectrum, no dead zone in the detectable frequency range and it can be achieved with a common sensing fiber.

Temporal convolution network with a dual attention mechanism for φ-OTDR event classification.

We propose a hybrid model named channel attention based temporal convolutional network combined with spatial attention and bidirectional long short-term memory network (ATCN-SA-BiLSTM) for phase sensitive optical time domain reflectometry signal recognition. This hybrid model consists of three parts: ATCN, which extracts temporal features and preserves causality of time domain signals, the SA mechanism, which re-weights spatial sequences for better feature extraction, and BiLSTM, which extracts spatial relationships considering the bidirectional propagation characteristics of disturbances in space domain signals. Experimental results show that our method achieves better classification performance with an accuracy of 93.4% and zero nuisance alarm rate.

Laser source frequency drift compensation in Φ-OTDR systems using multiple probe frequencies.

Fully distributed fiber sensors, such as phase sensitive optical time domain reflectometry (Φ-OTDR) systems, have drawn significant attention from researchers, especially for use in geophysical applications. Distributed sensing, cost efficiency, wide dynamic range, good spatial resolution, and high accuracy make these sensors ideal for industrial use and for replacing traditional geophones. However, inevitable drifts in the central frequency of laser sources always cause low frequency noise in the output, which could easily be mistaken with real sub-Hertz environmental vibrations. This deteriorates the data accuracy, especially when dealing with low frequency seismic waves. In this study, we propose a method in which adding an extra probe frequency to a Φ-OTDR setup provides a reference frequency. This reference frequency provides information regarding changes in the laser source and other environmental noises, such as humidity and temperature, helping to refine extracted results from low frequency noise. This feature is also very useful for frequency domain analysis, where we may lose the near DC band information during mathematical measurements. Regarding the adjustable properties of this reference frequency, it can be implemented in various Φ-OTDR applications and commercial devices.

Distributed measurement of mode group effective refractive index difference in a few mode optical fibers.

The possibility to perform distributed measurements of the effective refractive index difference between distinct modes in few mode optical fibers is demonstrated using phase sensitive optical time domain reflectometry. Effective refractive index differences between LP02, LP21a and LP21b modes are measured with for a spatial resolution of 24m.

Phase Demodulation Methods for Optical Fiber Vibration Sensing System: A Review

In recent years, phase demodulation methods for optical fiber vibration sensors (OFVS) have attracted more and more attention, aiming to accurately detect vibration signals. The principles of phase modulation and demodulation in OFVS are firstly introduced. Then, three classical phase demodulation methods are described, including phase generated carrier (PGC) demodulation method, <inline-formula> <tex-math notation="LaTeX">${3}\,\,\times \,\,{3}$ </tex-math></inline-formula> coupler demodulation method, and in-phase and quadrature (IQ) demodulation method. Furthermore, the state of art of phase demodulation methods in various OFVS are reviewed. As the results of analysis, different structures of OFVS need appropriate demodulation methods for vibration detection. The Fourier transform method, fringe counting method and PGC demodulation method have strong applicability for Fabry-Perot interference OFVS. The scalability of interferometers provides convenience for PGC demodulation method and <inline-formula> <tex-math notation="LaTeX">${3}\,\,\times \,\,{3}$ </tex-math></inline-formula> coupler demodulation method in the OFVS with composite structure. PGC demodulation method, <inline-formula> <tex-math notation="LaTeX">${3}\,\,\times \,\,{3}$ </tex-math></inline-formula> coupler demodulation method and quadrature demodulation method are good choices for dynamic sensing in FBG-OFVS. The IQ demodulation method is a popular choice for phase sensitive optical time domain reflectometry at present. This paper provides a reference for the OFVS to realize vibration detection with appropriate phase demodulation method.

Optimization of low frequency response performance of phase sensitive optical time-domain reflectometry system

Optimization of low frequency response performance of phase sensitive optical time-domain reflectometry system

Large Dynamic Range Optical Fiber Distributed Acoustic Sensing (DAS) With Differential-Unwrapping-Integral Algorithm

Optical fiber distributed acoustic sensing (DAS) based on phase sensitive optical time domain reflectometry (ϕ-OTDR) has a great demand in many application fields with large signals, such as railway safety monitoring, cable vibration detection, etc. However, due to the inherent limits of phase unwrapping algorithm, the large signal whose phase change exceeds π cannot be recovered correctly by DAS. In this work, the differential-unwrapping-integral (DUI) algorithm is proposed and demonstrated to replace the traditional unwrapping algorithm for large signal recovery. By utilizing differential operation to compress the signal amplitude, the large phase signal can be converted into small signal which can be recovered through unwrapping. Then, multiple integral operations and polynomial fitting compensation algorithm are applied onto the differential signal to recover the original phase signal without any signal-to-noise ratio(SNR) sacrificed. In theory, the maximum measurable phase of DUI can be improved 1390 times compared with traditional DUI algorithm. Further, the experimental results demonstrate that the dynamic range of DAS with DUI can reach up to 131.7 dB. Moreover, DUI algorithm has been tested and verified in the field test for recording the digging signals with large amplitude. This scheme can be applicable for all phase-demodulation-based sensing techniques without increasing the system complexity.

Phi-OTDR Based On-Line Monitoring of Overhead Power Transmission Line

The overhead power transmission line, as an important component of equipment for long-distance power transmission, is threatened by icing and galloping, which will lead to equipment troubles and cause huge economic loss. Thus, there is a great need for on-line monitoring for transmission lines. Because the photoelectric composite cable, such as optical fiber composite overhead ground wire (OPGW) is widely used, it is possible to introduce distributed optical fiber sensors (DOFS) into transmission line status monitoring. Common schemes based on DOFS usually offer low sensing density and are hard to realize global awareness, while phase sensitive optical time domain reflectometry (Φ-OTDR), as a DOFS that has the characteristic of distributed sensing, is hoping to address the limitation. In this paper, by establishing mathematical models, proposing analytical method, and building demonstration devices to analyze the dynamic strain characteristics of overhead power transmission line, an Φ-OTDR based on-line monitoring scheme of transmission line status is presented and experimentally proved for the first time. The estimation error of sag is less than 5.8% on centimeter scale, and the estimation error of ice thickness is no more than 10.84% on sub-millimeter scale, which gives an accurate description of transmission line status and provides strong support for early warning of transmission line failures.

Distributed Optical Fiber Sensing Assisted by Optical Communication Techniques

The development of optical fiber technology has facilitated the technological innovation in optical fiber communication and sensing systems over the past decades. Among all the fiber sensing technologies, distributed optical fiber sensing (DOFS) has attracted great research interests and has been extensively investigated. In optical fiber communication systems, optical parameters such as intensity, phase, polarization, or frequency are modulated to realize data transmission, while for DOFS they are employed to measure the distributed physical parameter variation along the sensing fiber. Due to the similarities shared by optical fiber communication systems and DOFS systems, optical communication techniques, including coherent detection, polarization diversity and multicarrier signaling have been widely used in the DOFS to improve the sensing performance. In this article, principles of coherent detection, polarization diversity and multicarrier signaling are introduced and their applications in phase sensitive optical time domain reflectometry and Brillouin optical time domain analyzer are reviewed. A newly proposed unidirectional forward transmission based DOFS is also presented.

Distributed Optical Fiber Sensor for Dynamic Measurement

Distributed optical fiber sensors (DOFS), which can distributed measure static parameters such as temperature and strain, have been extensively researched and applied in industrial fields over the past several decades. Recently, in consideration of the explosive demand for dynamic sensing, the DOFS with the capability of dynamic phenomena measurement has attracted amounts of attentions. Various techniques that could realize and enhance the dynamic performance of DOFS have been proposed. In this article, DOFS for dynamic measurement is discussed. Firstly, the principles of DOFS based on Rayleigh and Brillouin scattering are introduced. Then, the most recent advances of fast DOFS especially those based on phase sensitive optical time domain reflectometry (φ-OTDR) and Brillouin optical time domain analysis (BOTDA), are analyzed. Furthermore, DOFS for multi-parameter sensing is also reviewed.

Rayleigh Φ-OTDR based DIS system design using hybrid features and machine learning algorithms

There is an increasing interest among the researcher community, and industries on the design, and development of a combined distributed acoustic sensing, and a pattern recognition system to detect, and classify potentially dangerous intrusion events. In this work, we describe the design, and optimization of a distributed intrusion sensing system using Rayleigh-phase sensitive optical time domain reflectometry (Rayleigh Φ -OTDR) technique, and supervised machine learning algorithms. The proposed system can classify an intrusion along with the position of an intrusion caused along a single mode optical fiber. We have considered three different external intrusion events, such as a person walking, digging by pickaxe, and electrical drilling. After training and testing the data samples of the simulated intrusion events, we have achieved an average intrusion classification rate of 100% with a 10 dBm of input laser source power over a 25 km length of sensing fiber. The relevant simulated experiments are carried out using MATLAB 20.0 platform.

Suppression of the Interference Fading in Phase-Sensitive OTDR With Phase-Shift Transform

An approach of phase-shift transform is proposed and demonstrated to suppress the interference fading in phase sensitive optical time domain reflectometry (Φ-OTDR). The phase-shift transform is executed in the digital domain and the complicated frequency modulation is not required. The operation principle is carefully analyzed and a signal with complementary amplitude can be obtained with this method. Through synthesizing the complementary signals, the false phases can be corrected. Benefiting from the flexibility of this approach, multiple transforms are implemented to make sure that all phases are retrieved accurately. Experimental results show that the intensity fluctuation over 60 dB is reduced to 15 dB, which decreases the standard deviation of differential phase to 0.0224. Besides, 30 dynamic measurements are tested and all distorted phases have been corrected, indicating the high reliability of this method.

Fading Noise Suppression in Φ-OTDR Based on Nearest Neighbor Analysis

Phase sensitive optical time domain reflectometry (Φ-OTDR) has been widely used in the precise acquisition of the vibration signal along the sensing optical fiber, and has attracted more and more interest. However, polarization fading and coherent fading usually lead to the phase hopping of the recovered signal, thus it is difficult to realize the continuous measurement of vibration, especially the low frequency vibration. The polarization diversity and multi-frequency detection schemes which are usually used to solve the above problems need additional hardware, thus increasing the cost and complexity of the system. In this article, we propose a statistical method based on nearest neighbor analysis. For each interrogation fiber separation, the phases of the sub-separations are evaluated and selected to reconstruct the vibration. In the experiment, the vibrations with frequencies as low as 0.2 Hz are loaded on the fiber and recovered. The results show that the method can effectively suppress the phase hopping, correct distorted vibration and improve the performance of low frequency vibration measurement of Φ-OTDR system on the basis of only numerical calculation.

Hybrid electronically addressable random fiber laser.

We report here a novel architecture for a random fiber laser exploiting the combination of a semiconductor optical amplifier (SOA) and an erbium doped fiber (EDF). The EDF was optically biased by a continuous wave pump laser, whereas the SOA was arranged in a fiber loop-mirror and driven by nanosecond duration current pulses. Laser pulses were obtained by synchronizing the SOA driver to the returning amplified Rayleigh back-scattered light from a selected short section of the EDF. By tuning the SOA pulse rate, random lasing was achieved by addressing selected meter-long sections of the 81-m long EDF, which was open-ended. Laser oscillation can be potentially obtained with SOA modulation frequencies from several kHz to the MHz regime. We discuss the mechanism leading to the hybrid random laser emission, connecting with phase sensitive optical time domain reflectometry and envision potential applications of this electronically addressable random laser.

Frequency scanned phase sensitive optical time-domain reflectometry interrogation in multimode optical fibers

Standard multimode optical fibers normally support transmission over some 100 modes. Large differences in the propagation constant and the spatial distribution of distinct modes degrade the performance of phase-sensitive optical time-domain reflectometry measurements. In this work, we present a new realization of a coherent time-domain interrogation technique using single-mode operation in multimode fibers. We demonstrate effectively distributed strain sensing on three different multimode optical fibers. Up to 4 km of multimode fiber has been correctly interrogated, featuring a spatial resolution of 20 cm.

Distributed vibration sensing with high frequency response by using WDM based integrated scheme

Distributed vibration sensing measurement with high frequency response is still a challenging task in distributed optical fiber vibration sensing systems. In this paper, a WDM based integrated scheme is proposed to directly demodulate the high frequency vibration signal with high spatial resolution by merging the phase sensitive optical time-domain reflectometry and the Sagnac interferometer. A maximum frequency response of ~2.5 MHz and a spatial resolution of 20 m have been achieved in a 4 km sensing fiber link. Comparison to conventional sensing structure, the proposed scheme shows great application potential in the field of distributed vibration sensing system.