Optical Time Domain Reflectometer Research Articles

Digital Longitudinal Monitoring of Optical Fiber Communication Link

Optical transmission links are generally composed of optical fibers, optical amplifiers, and optical filters. In this paper, we present a channel reconstruction method (CRM) that extracts physical characteristics of multiple link components such as longitudinal fiber losses, chromatic dispersion (CD), multiple amplifiers’ gain spectra, and multiple filters’ responses, only from receiver-side (Rx) digital signal processing (DSP) of data-carrying signals. The concept is to reconstruct a virtual copy of an actual transmission channel in the digital domain, where optical fibers and amplifiers are modeled as the split-step Fourier method for the Manakov equation while optical filters are emulated as complex-valued finite impulse response filters. We estimate the model parameters such as losses, CD, gains, and filter responses from boundary conditions, i.e., transmitted and received signals. Experimental results show that, unlike traditional analog testing devices such as optical time-domain reflectometers and optical spectrum analyzers, CRM visualizes multi-span characteristics of fibers, amplifiers, and filters in Rx DSP, and thus localizes anomaly components among multiple ones without direct measurement.

Machine learning methods for identification and classification of events in ϕ-OTDR systems: a review.

The phase sensitive optical time-domain reflectometer (φ-OTDR), or in some applications called distributed acoustic sensing (DAS), has been a popularly used technology for long-distance monitoring of vibrational signals in recent years. Since φ-OTDR systems usually operate in complicated and dynamic environments, there have been multiple intrusion event signals and also numerous noise interferences, which have been a major stumbling block toward the system's efficiency and effectiveness. Many studies have proposed different techniques to mitigate this problem mainly in φ-OTDR setup upgrades and improvements in data processing techniques. Most recently, machine learning methods for event classifications in order to help identify and categorize intrusion events have become the heated spot. In this paper, we provide a review of recent technologies from conventional machine learning algorithms to deep neural networks for event classifications aimed at increasing the recognition/classification accuracy and reducing nuisance alarm rates (NARs) in φ-OTDR systems. We present a comparative analysis of the current classification methods and then evaluate their performance in terms of classification accuracy, NAR, precision, recall, identification time, and other parameters.

Random coding method for SNR enhancement of BOTDR.

A random coding method for a Brillouin optical time domain reflectometer (BOTDR) fiber sensor is proposed. In this method, a series of pulses modulated by random code are injected into the optical fiber to enhance the signal-to-noise ratio (SNR) and further improve the measurement accuracy. Random coding method allows the sensing range to be extended to several tens of kilometers while maintaining meter-scale spatial resolution and lower detection peak power, without modifying the conventional configuration of BOTDR. The decoding principle and the coding gain of random coding method are analyzed and simulated. We experimentally implement the method and evaluate its influence on the performance optimization of BOTDR. Compared with the single pulse with peak power of 10 mW, the measured BFS uncertainty over 4.93 km sensing fiber is reduced from 5.34 MHz to 0.38 MHz when 512-bit random coding pulses with the same peak power are utilized. The experimental results show that the coding gain of 11.93 dB is obtained by 512-bit random coding. Benefitting from the SNR enhancement, the sensing range is extended from 4.93 km to 64.76 km within a root-mean-square error (RMSE) of 3 MHz, when the pulse peak power is only 10 mW and the spatial resolution is 2 m.

Plasma current measurement in ITER with a polarization-OTDR: impact of fiber bending and twisting on the measurement accuracy.

Using a polarization-sensitive optical time domain reflectometer (OTDR), plasma current in the International Thermonuclear Experimental Reactor (ITER) can be measured by investigating the Faraday effect-induced polarization rotation in a spun fiber placed around the Vacuum Vessel. However, intrinsic birefringence and external effects like fiber bending and twisting generate unwanted polarization changes and decrease the measurement accuracy. In this paper, a simulation-based approach is developed, considering bending and twisting effects to assess the performance of the reflectometer in measuring plasma current at ITER. The results demonstrate that, for a proper choice of spun sensing fiber parameters (intrinsic beat length and spun period), the performance of the sensor satisfies ITER accuracy.

Galloping Vibration Monitoring of Overhead Transmission Lines by Chirped FBG Array

A distributed online fiber sensing system based on the phase-sensitive optical time domain reflectometer (Φ-OTDR) enhanced by the drawing tower fiber Bragg grating (FBG) array is presented and investigated experimentally for monitoring the galloping of overhead transmission lines. The chirped FBG array enhanced Φ-OTDR sensing system can be used to measure the galloping behavior of the overhead transmission lines (optical phase conductor or optical power ground wire), which are helpful for monitoring the frequency response characteristics of the ice-induced galloping, evaluating the motion tendencies of these cables, and avoiding the risk of flashover during galloping. The feasibility of the proposed online monitoring system is demonstrated through a series of experiments at the Special Optical Fiber Cable Laboratory of State Grid Corporation of China (Beijing, China). Results show that the proposed system is effective and reliable for the monitoring of galloping shape and characteristic frequency, which can predict the trend of destructive vibration behavior and avoid the occurrence of cable breaking and tower toppling accidents, and these features are essential for the safety operation in smart grids.

Photonic integrated circuit-assisted optical time-domainreflectometer system

Optical time-domain reflectometers (OTDR) are photonic systems that consist of an interrogator, a receiver and a fiber optical cable and have applications in telecommunications, security, environmental monitoring, distributed temperature and strain sensing. Since OTDR systems are bulk optical setups that consume multiple Watts of power, have large mass and volume footprint and are vulnerable to thermal drift, deployment of OTDR systems in the field is expensive, complicated and may not necessarily yield accurate sensing results. Thus, a compact, low-power, inexpensive and thermal drift-free OTDR system needs to be developed for improving the accuracy and the viability of OTDR in the field. In this study, I present the design and modeling of a photonic integrated OTDR system design based on IMEC's iSiPP50G silicon integrated photonic process design kit. The photonic integrated circuit includes a photonic modulator and a photodetector. Photonic power link budgets and the corresponding electronic signal-to-noise ratios are analyzed for 5-110 km fiber optical OTDR systems and power-efficient OTDR system designs are presented for inexpensive multiproject wafer fabrication.

Fault monitoring in passive optical network through the integration of machine learning and fiber sensors

SummaryAs the deployment of fiber‐based broadband networks continues to accelerate, the number of network facilities too is increasing exponentially. The network of optical fiber cables keeps growing as the number of passive optical network (PON) customers increases, eventually leading to unforeseen faults. Several solutions are offered for monitoring the optical link in PON with the optical time‐domain reflectometer (OTDR) as the most common for point‐to‐point optical link characterization. However, the OTDR approach has been found to be inadequate for point to multipoint network fault characterizations due to numerous back‐reflected signals converging at the power splitter that cannot be identified simultaneously by the OTDR detector. Several machine learning (ML) methods have recently been introduced for successful monitoring of optical communication links, but much of the ML technique depends on data from network transceivers to train ML algorithms to identify and detect faults. However, the use of data information for monitoring purposes can have an impact on the consistency of the services offered. In this article, we consider the deployment of the fiber Bragg grating sensor to acquire the monitoring data samples used to train the ML technique for effective link characterization. The proposed solution has the advantage of having a separate monitoring source that is independent of the data transmission signal and guarantees transparent transmission of information. The proposed ML‐based technique shows up to 99% precision for the identification of fiber defect in the PON optical distribution network.

Design Attention System of Single Mode Aerial Fiber Optic Cable Transmission on Connection Loss on Passive Splitter

In this study, a comparison of the attenuation value of single mode aerial cable with pigtail is made. Perform several types of connections using a 4 cm and 6 cm protection sleeve, with one and two connections and use a barrel adapter connector. How does the connection affect the installation of a 1:2 passive splitter device. The measuring instruments used for the measurement process are Optical Power Meter (OPM) and Optical Time Domain Reflectometer (OTDR). The attenuation value of aerial single mode optical cable is smaller than that of pigtail cable. The measurement results using OPM at a wavelength of 1310 nm, connection using a 4 cm protection sleeve, one connection, the attenuation value is 0.18525dB, this value is smaller than the pigtail cable, which is 1.2728 dB. In the installation of a passive splitter, the attenuation value on the aerial cable is smaller, namely 0.2081 dB compared to the pigtail cable, which is 4.3281. The measurement results using the OTDR obtained the connection loss value for the connection type using a 6 cm protection sleeve, one connection is smaller with a value of 0.155 dB, compared to the connection type using an adapter barrel with a value of 12,216 dB.

Fabrication of biaxial polarization-maintaining optical fiber with ultra-low bending-dependent polarization extinction ratio deterioration

Different applications, including interferometers, gyroscopes, and frequency combs, require a single polarized light transmission by maintaining this property against the environmental perturbation. As a new type of polarization-maintaining (PM) fiber, a biaxial PM fiber was fabricated over 30 dB of high polarization extinction ratio (PER) values among two orthogonal axes over a fiber length of 110 m. The PM fiber was manufactured with a combination of an elliptical core and Panda-type geometries. The PER values were demonstrated to be preserved at harsh temperature conditions from −55 °C to +85 °C. The bending loss measurements indicate the biaxial PM fiber has ultra-low bending dependent PER deterioration (<0.5 %) at various bending diameters from 12 mm to 5 mm. The biaxial PM property was also confirmed by the group beat length measurements and found to be less than 1.5 mm at 1550 nm. The optical time-domain reflectometer (OTDR) measurements show that the optical loss of the biaxial PM fiber was below 1.5 dB/km over 3kmlength. The mode-field diameter (MFD) and the numerical aperture (NA) values were also reported along two polarized axes. This novel PM fiber offers a single solution for the elliptical and Panda-type PM fibers utilized for integrated fiber-based sensors and instruments.

Real-Time Φ-OTDR Vibration Event Recognition Based on Image Target Detection.

Accurate and fast identification of vibration signals detected based on the phase-sensitive optical time-domain reflectometer (Φ-OTDR) is crucial in reducing the false-alarm rate of the long-distance distributed vibration warning system. This study proposes a computer vision-based Φ-OTDR multi-vibration events detection method in real-time, which can effectively detect perimeter intrusion events and reduce personnel patrol costs. Pulse accumulation, pulse cancellers, median filter, and pseudo-color processing are employed for vibration signal feature enhancement to generate vibration spatio-temporal images and form a customized dataset. This dataset is used to train and evaluate an improved YOLO-A30 based on the YOLO target detection meta-architecture to improve system performance. Experiments show that using this method to process 8069 vibration data images generated from 5 abnormal vibration activities for two types of fiber optic laying scenarios, buried underground or hung on razor barbed wire at the perimeter of high-speed rail, the system mAP@.5 is 99.5%, 555 frames per second (FPS), and can detect a theoretical maximum distance of 135.1 km per second. It can quickly and effectively identify abnormal vibration activities, reduce the false-alarm rate of the system for long-distance multi-vibration along high-speed rail lines, and significantly reduce the computational cost while maintaining accuracy.

Mode Dependent Loss Measurement of Few Mode Fiber Based on Mode Multiplexing Power Control

In this letter, we propose and experimentally demonstrate a novel measurement method of mode dependent loss (MDL) in few-mode fiber (FMF) based on mode multiplexing power control. The fiber MDL, between mode groups, is computed from output power of FMF under test by controlling the power of each spatial mode of the photonic lantern. With this method, the MDL between LP₀₁ and LP₁₁ modes in about 9.8km 3-mode fiber is successfully measured. The experimental results obtained with our proposed method agree well with those measured by the FMF optical time domain reflectometer (FMF-OTDR) and the conventional cutback method. And it is also demonstrated that the proposed scheme can be scalable to measure long-distance FMFs with a large number of modes, and be independent of photonic lantern mode crosstalk.

Experimental research on a novel spring-shaped fiber-optic displacement sensor for settlement monitoring

In this paper an innovative spring-shaped fiber-optic displacement sensor (SSFODS) based on optical time domain reflectometer (OTDR) technology with simple construction and cheap cost was proposed for subgrade settlement monitoring. The sensor incorporated a simple spring-shaped fiber bending modulation that increased its sensitivity in bending, light source and detector. The sensing principle between the measured external displacement and bending loss of optical fiber was theoretically explained and its expression was also derived. Sensor calibration was conducted, which showed that the SSFODS was characterized by a large measurement range of 90 mm, minimum displacement resolution of 0.173 mm, maximum hysteresis error of 2.81% and maximum repeatability error of 8.42%, respectively. A soil drainage model test with the SSFODS was performed to study its performance in determining compression deformation of the soil. At last, a simple field monitoring application with two SSFODSs connected in series was conducted and the progressive compaction behavior of the fill slope was accurately captured by two SSFODSs. Additionally, it is possible to connect these SSFODSs in series on one optical link to realize quasi-distributed sensing monitoring. This capability supports a promising application of the sensor in geotechnical engineering for real-time monitoring of the stability of fill slopes, foundation pits and so on.

Reflectometric temperature measurement using a single-mode-multimode-single-mode&amp;quot; fiber optic structure

It is shown the &amp;quot;single-mode-multimode-single-mode&amp;quot; structure allows carrying out remote temperature measurement with optical time domain reflectometer. A multimode fiber length was 10 mm. We used the temperature range from 30 to 70oC and wavelengths of 1310 and 1550 nm. The total length of a single-mode fiber-optic line for reflectometric measurements was 20 km. Keywords: fiber optics, fiber optic sensors, optical fiber reflectometry, multimode interference.

Рефлектометрическое измерение температуры с использованием оптоволоконной структуры одномод-многомод-одномод"

It is shown the "single-mode-multimode-single-mode" structure allows carrying out remote temperature measurement with optical time domain reflectometer. A multimode fiber length was 10 mm. We used the temperature range from 30 to 70oC and wavelengths of 1310 and 1550 nm. The total length of a single-mode fiber-optic line for reflectometric measurements was 20 km.

Applicability of Optical Time Domain Reflectometer for Measuring Differential Modal Group Delay in Few-Mode Fibers

Applicability of Optical Time Domain Reflectometer for Measuring Differential Modal Group Delay in Few-Mode Fibers

Accurate Location of Fiber Cable Fault with OTDR

The paper reviews the factors limiting the accuracy of locating a fiber optic cable fault when using an optical time domain reflectometer (OTDR) and describes an error estimation method for typical use cases. The primary source of errors lies in the complex relationship between the length of the optical fiber (measured by OTDR), its routing, cable design depending on cable design and type of installation (i.e. duct, directly buried, aerial) as well as the spare lengths used for service purposes. The techniques which considerably improve the accuracy of the fault localization processes are presented, the importance of accurate documentation of the network and of referencing the fault location to the nearest splice instead of end of the line are discussed, as is the absence of cable helix factor in data sheets.

Improvement of Performance for Raman Assisted BOTDR by Analyzing Brillouin Gain Spectrum.

We propose a simplified partitioned Brillouin gain spectrum (BGS) analysis method to enhance the spatial resolution and measurement accuracy of a Brillouin optical time-domain reflectometer (BOTDR) assisted by a first-order Raman pump. We theoretically derive the mathematical model of the partitioned BGS and analyze the superposition process of sub-Brillouin signals within a theoretical spatial resolution range. We unified all the unknown constant parameters of the calculation process to simplify the partitioned BGS analysis method and the value of the uniform parameter is attained through the system test data and numerical analysis. Moreover, to automate data processing, the starting point of the temperature/strain change is determined by the first occurrence of the maximum Brillouin frequency shift (BFS), then the position where the partitioned BGS analysis method calculation begins is obtained. Using a 100 ns probe pulse and partitioned BGS analysis method, we obtain a spatial resolution of 0.4 m in the 78.45-km-long Raman-assisted BOTDR system, and the measurement accuracy is significantly improved. In addition, we achieve a strain accuracy of 5.6 με and a spatial resolution of 0.4 m in the 28.5-km-long BOTDR without Raman amplification.

Enhanced fire sprinkler system: Fiber optical monitoring of fire sprinkler heads

A novel fiber optical monitoring concept for real-time localization of activated fire sprinkler heads is presented and discussed in this work. The concept is implemented by a designed fiber optical sensor and standard telecom components, such as optical time-domain reflectometer (OTDR), single-mode glass fiber, couplers, and reflectors. The proposed sensor based on optic reflection and interrupting mechanism allows to monitor the current status of sprinkler head and to differentiate the sprinkler activation from unwanted interferences, for example, glass fiber breakage. According to the experiments and calculations, hundreds of sprinkler heads can be monitored by a single OTDR device that results in net system energy consumption well below 100 mW per sensor point. The proposed monitoring concept opens up new perspectives for applying fiber optical sensors in fire protection methods. It can be used as a self-contained sensor network or in combination with modern fire detection and alarm systems in a primary-secondary-configuration.

Wavelength-Tunable OTDR for DWDM-PON Based on Optimized Wavelet Denoising

In this letter, a wavelength-tunable Optical Time-Domain Reflectometer (OTDR) for Dense Wavelength Division Multiplexing Passive Optical Network (DWDM-PON) is proposed and experimentally demonstrated. An Integrated Tunable Laser Assembly (ITLA) serves as the light source permitting measurements of 80 DWDM channels in the C-band. Dither modulation is added to ITLA to depress coherent noise resulted from the narrow linewidth of the light source. Semiconductor Optical Amplifier (SOA) modulates the continuous light into pulsed light and meanwhile amplifies peak optical power of the pulsed light to 13 dBm. In addition, we optimize the wavelet denoising algorithm for further signal-noise ratio (SNR) enhancement. Dynamic range and spatial resolution of the proposed OTDR reach up to 16.2 dB and 2 m respectively. A DWDM-PON fiber link including an Arrayed Waveguide Grating (AWG) is measured to verify the system performances, and the OTDR profiles of different channels coincide with each other. The designed wavelength-tunable OTDR is shown to be appropriate for DWDM-PON.

On the measurement accuracy of coherent Rayleigh-based distributed sensors

The phase change of back-scattered light due to external perturbations is retrieved in coherent Rayleigh-based distributed sensors by estimating the frequency shift (FS) between the traces of different measurements. The uncertainty associated with the estimator, due to the presence of system noises, can lead to an inaccurate evaluation of the FS. Additionally, in coherent Rayleigh-based sensors, the calculation of the signal-to-noise ratio (SNR) from the jagged back-scattered intensity trace using the statistical estimators can cause an erroneous determination of the absolute value of the SNR. In this work, a method to accurately evaluate the non-uniform SNR caused by the stochastic variation of the back-scattered light intensity along the fibre is presented and validated. Furthermore, an analytical expression to evaluate the uncertainty in the FS estimation using one of the standard estimators, namely cross-correlation, is presented. A direct-detection frequency-scanned phase-sensitive optical time-domain reflectometer (φ-OTDR) is employed for the experimental verification of the expression as a function of two crucial system parameters: the SNR and the spatial resolution. The performance of various distributed sensing system configurations utilising cross-correlation for determining the FS occurring due to the external perturbations can be properly predicted hereafter with the aid of the analytical expression presented in this study.