Optical Time Domain Reflectometer Traces Research Articles

Distributed vibration and temperature sensing system by multiplexed fiber scattering spectra

A new, to the best of our knowledge, distributed optical fiber vibration and temperature hybrid sensing system is proposed and experimentally demonstrated. The proposed system only employs two signal channels, which is more compact and practical. Based on the structure of the optical time domain reflectometer (OTDR), the Rayleigh scattering light and the Raman anti-Stokes scattering light is extracted for vibration and temperature sensing, respectively. For vibration sensing, a new differential location algorithm based on polarization state analysis of the Rayleigh scattering light is proposed to locate the vibration events. It first rectifies the original OTDR traces by fiber attenuation compensation to make each position in it with the same pulse power level. And then, by difference of adjacent traces and threshold discrimination, the vibration positions are identified and located. For temperature sensing, a temperature calibration unit and algorithm are adopted to dynamically correct the trace data and reduce the temperature measurement error caused by the instability of the pulse laser source. The experiment is conducted with a fiber range of about 12 km and laser pulse width of 60 ns, and the experimental results show that the maximum error range for temperature measurement is −0.7∘C to 1.3°C, with a root mean square (RMS) error of 0.85°C in the entire temperature measurement range. Additionally, the spatial resolution (SR) for both vibration and temperature sensing is 6 m.

A hybrid distributed optical fiber vibration and temperature sensor based on optical Rayleigh and Raman scattering

A hybrid distributed optical fiber vibration and temperature sensing system is proposed and experimentally demonstrated. By the system structure of optical time domain reflectometer (OTDR) and wavelength division method, the Rayleigh and Raman scattering light in multi-mode fiber (MMF) are extracted respectively for fiber vibration event detection and hot spot monitoring. The vibration event causes the polarization state and phase of the optical signal propagating in MMF to change, which makes the OTDR trace become smooth from the vibration position to the fiber end, so that it provides a reliable way to locate the vibration events. And then, a data processing method that averages the data within the vibration position and at least 50 continuous positions behind is proposed to improve the signal to noise ratio (SNR) of the vibration signal and finally by fast Fourier transform (FFT), the vibration spectrum is accurately obtained. In addition, the backscattered Raman Stokes and anti-Stokes signals are separated by the wavelength division multiplexer (WDM) and then they are converted into voltage signals. By conventional temperature demodulation algorithm, the temperature information along the MMF is obtained with measurement accuracy of about 1.5 °C. The experimental results show that the proposed hybrid distributed vibration and temperature sensing system possess good performance and as it is compatible with MMF that has been laid on the power cable, it is of great significance for engineering application.

A Novel Distributed Vibration Sensor Based on Fading Noise Reduction in Multi-Mode Fiber.

Multi-mode fiber (MMF) is used in a polarization-sensitive optical time domain reflectometer (OTDR) for vibration event location and spectrum analysis. The vibration events acting on MMF are considered to be the optical polarization state and phase diversifying process for fading noise reduction. In addition, data averaging with continuous positions and the fast Fourier transform (FFT) method is proposed to extract the spectrum of the vibration events. In the experiment, the vibration events are loaded at the positions of 5.167 and 10.145 km, respectively, along MMF. The experimental results demonstrate that the vibration event can effectively diversify the optical polarization state and phase of the Rayleigh scattering light to make the averaged OTDR trace behind the vibration position converge rapidly, which helps to locate corresponding vibration events and extract the vibration spectrum. It is inferred that the new distributed vibration sensor shall have a lower false alarm rate, as it can greatly reduce the errors caused by randomness of the sensing light signals. Additionally, it also saves time in comparison with the method that analyzes the vibration spectra for all the positions along the fiber under test.

Known and unknown event detection in OTDR traces by deep learning networks

Optical fiber links are customarily monitored by Optical Time Domain Reflectometer (OTDR), an optoelectronic instrument that measures the scattered or reflected light along the fiber and returns a signal, namely the OTDR trace. OTDR traces are typically analyzed by experts in laboratories or by hand-crafted algorithms running in embedded systems to localize critical events occurring along the fiber. In this work, we address the problem of automatically detecting optical events in OTDR traces through a deep learning model that can be deployed in embedded systems. In particular, we take inspiration from Faster R-CNN and present the first 1D object-detection neural network for OTDR traces. Thanks to an ad-hoc preprocessing pipeline for OTDR traces, we can also identify unknown events, namely events that are not represented in training data but that might indicate rare and unforeseen situations that need to be reported. The resulting network brings several advantages with respect to existing solutions, as these typically classify fixed-size windows of OTDR traces, thus are less accurate in the localization. Moreover, existing solutions do not report events that cannot be safely associated to any label in the training set. Our experiments, performed on real OTDR traces, show very promising performance, and can be directly executed on embedded OTDR devices.

Optical OFDM Error Floor Estimation by Means of OTDR Enhanced by Front-End Optical Preamplifier.

Optical time-domain reflectometer (OTDR) enables simple identification and localization of a plethora of refractive and reflective events on a fiber link, including splices, connectors and breaks, and measuring insertion/return loss. Specifically, large enough OTDR dynamic range (DR) and thus high signal-to-noise-ratio (SNR) enable clear far-end visibility of longer fibers. We point out here that, under such conditions, the optical bit-error-rate (BER) floor is dominantly determined by reflective events that introduce significant return loss. This complements the OTDR legacy tests by appropriate optical BER floor estimation in the field. As high SNR implies inter-symbol interference as dominating error generating mechanism, we could apply the classical time-dispersion channel model for the optical BER floor determined by the root-mean-square (rms) delay spread of the actual fiber channel power-delay profile. However, as the high-SNR condition is not always fulfilled mostly due to insufficient DR, we propose here inserting a low-noise optical preamplifier as the OTDR front-end to reduce noise floor and amplify the backscattered signal. In order to verify the model for the exemplar test situation, we measured BER on the same fiber link to find very good matching between the measured BER floor values and the ones predicted from the OTDR trace.

Low-cost real-time fiber optic sensor for intrusion detection

PurposeThe purpose of this paper is to introduce a novel intensity-modulated fiber optic sensor for real-time intrusion detection using a fiber-optic microbend sensor and an optical time-domain reflectometer (OTDR).Design/methodology/approachThe proposed system is tested using different scenarios using person/car as intruders. Experiments are conducted in the lab and in the field. In the beginning, the OTDR trace is obtained and recorded as a reference signal without intrusion events. The second step is to capture the OTDR trace with intrusion events in one or multiple sectors. This measured signal is then compared to the reference signal and processed by matrix laboratory to determine the intruded sector. Information of the intrusion is displayed on an interactive screen implemented by Visual basic. The deformer is designed and implemented using SOLIDWORKS three-dimensional computer aided design Software.FindingsThe system is tested for intrusions by performing two experiments. The first experiment is performed for both persons (>50 kg) in the lab and cars in an open field with a car moving at 60 km/h using two optical fiber sectors of lengths 200 and 500 m. For test purposes, the deformer length used in the experiment is 2 m. The used signal processing technique in the first experiment has some limitations and its accuracy is 70% after measuring and recording 100 observations. To overcome these limitations, a second experiment with another technique of signal processing is performed.Research limitations/implicationsThe system can perfectly display consecutive intrusions of the sectors, but in case of simultaneous intrusions of different sectors, which is difficult to take place in real situations, there will be the ambiguity of the number of intruders and the intruded sector. This will be addressed in future work. Suitable and stable laser power is required to get a suitable level of backscattered power. Optimization of the deformer is required to enhance the sensitivity and reliability of the sensor.Practical implicationsThe proposed work enables us to benefit from the ease of implementation and the reduced cost of the intensity-modulated fiber optic sensors because it overcomes the constraints that prevent using the intensity-modulated fiber optic sensors for intrusion detection.Originality/valueThe proposed system is the first time long-range intensity-modulated fiber optic sensor for intrusion detection.

Feasibility study of employing mechanically induced long-period fibre grating as optical-based sensors

The investigation of long-period fibre gratings formed by a 3D printer with several grating periods is presented here. The proposed grating device was pressed on to an optical fibre to observe the resonant wavelengths as a function of different groove periods. Results showed that devices with 700 and 800 nm grating period introduced resonant wavelengths of 1,487 and 1,570 nm with refractive index changes of 2.121 × 10−3 and 1.963 × 10−3, respectively. Once resonant wavelengths were known, an optical time domain reflectometer (OTDR) was employed to determine light behaviour, event positions, and losses. The OTDR trace revealed that the non-reflective event occurred at the grating perturbation position. Consequently, the wavelength-dependent-resonance was caused by the non-contra-directional coupling of light from the fibre core to fibre cladding and its attenuation was a cubic function of an applied force. The proposed approach, therefore, shows a great potential to be used for the sensing applications in the vulnerable environments.

The Reinforced Optical Fiber Sensing with bilayer AuNPs/SiC for pressure measurement: Characterization and Optimization

A cladding modified multimode optical fiber sensor reinforced with bilayers Au:SiC is designed and fabricated for pressure sensing in this presented. The Au thin film was used to enhanced the sensitivity of the sensor while the SiC thin film has been investigated as the reinforced layer at the sensing part to measure the wide range of applied pressure. The data acquisition interrogated using an optical time-domain reflectometer (OTDR). The results showed that the performance of the optical fiber sensor coated with bilayers Au:SiC coating is significantly improved in the measurement of applied pressure at the sensing part. Additionally, the sensor coated with bilayer Au:SiC exhibits linear variation in the return losses measured from OTDR trace with the wide range of applied pressure compare to the sensor coated with Au thin film. Where the maximum value in the sensitivity is equal to 35% dB/um of the sensor coated with bilayers SiC:Au compared to the sensitivity of the sensor coated with Au which equal to 30% dB/um. The high performance showed in results demonstrating that the fabricated optical fiber sensor has the excellent potential application as a sensor to measure a wide range of applied pressure without deform the sensing part.

Effect of strong local stretching of sensing fibre on the operation of a phase-sensitive optical time-domain reflectometer

It has been shown experimentally and confirmed by numerical simulation that strong local stretching of sensing fibre distorts the signal detected by a phase-sensitive optical time-domain reflectometer (OTDR) from the fibre section behind the local disturbance region. Comparison of experimental data with theoretical estimates and numerical simulation results leads us to conclude that the physical mechanism underlying the distortion of the OTDR trace is related to the external disturbance-induced variable shift of the optical carrier frequency of probe pulses.

Analysis of loss levels in a single mode fiber optic cable for some fiber plants in Northern Nigeria

Increasing demand for transmission capacity due to digital revolution is causing an increasing demand for optical fiber systems. However, as bit-error-rate (BER) increases the fiber optic cable signal quality becomes degraded, causing signal delays, jitters, poor quality of service, packet loss, link outage, etc. In this study, the analysis of loss levels in a single mode fiber optic cable was carried out using the optical time domain reflectometer (OTDR), network monitoring system (NMS) and CACTI (V 1.1.38). Various OTDR traces were carried out to determine the loss levels in the fiber cores. Similarly, using the NMS, the actual link losses were calculated and compared with the loss budget to derive the link loss margin of the links; with a benchmark loss margin of 5 dB, high and low loss levels were determined. Lastly, bandwidth utilization was carried out using network graphical solution software (CACTI, V 1.1.38). The results show that, from the OTDR traces, 60% of the tested fiber cores had high losses at the spliced joints, whereas the analysis of the NMS shows 41.7% high losses. The bandwidth utilization analysis shows a reduction in fiber link availability by 8.3%. This work has revealed the different loss levels in the tested fiber cores with high loses leading to increase in BER which negatively impacts the optimum usability of a link. Therefore, maintaining a low and within-budget loss level is very essential for efficient signal transmission and optimization of the fiber optic cable for both manufacturers and the end users.

Optical Time Domain Reflectometer Assessment of Attenuation in Fiber Optics Communication System

Attenuation is an undesirable factor that weakens the strength of signal as it travels down fiber optics. Attenuation level in every fiber communication link must be kept at its tolerable range in order to maintain good signal transmission. When the level of attenuation in a link is higher than the acceptable tolerance value, the transmission suffers some setbacks such as loss of signal, freezing of signal etc. An optoelectronic device, Optical Time Domain Reflectometer (OTDR) was used in the measurement of attenuations in the single-mode fiber using the uni-directional technique. It is a convenient and powerful tool for rapidly assessing attenuation behavior in optical fibers. It combines a detector and laser source to provide an inside view of the fiber link described by a trace. The injected light pulse from the laser source is received at the detector. OTDR traces were produced in accordance with the light pulses received. From these traces, the attenuation levels for the different fiber cores were obtained. An average attenuation limit of 0.188 dB/km and average section loss of 0.3dB for 1550 nm wavelength window over the span length of 1597.35 m were achieved which are within the acceptable standard range of 0.20 dB/km to 0.30 dB/km.

Fabrication and characterization of multimode optical fiber sensor for chemical temperature monitoring using optical time domain reflectometer

In this work, the optical fiber sensor system to measure the optical loss due to temperature variation of gasoline and toluene was papered. The optical fiber sensor was characterized using optical time domain reflectometer (OTDR). The sensor was a 50 cm multimode fiber with about 1–3 cm at its central region being partially unclad. The partial uncladding was carried out using chemical etching technique. The optical loss of sensor was measured when unclad part exposed to gasoline and toluene respectively at different temperature ranging from 25 °C to 60 °C. The optical loss of sensor increases in a step drop of OTDR trace as the temperature is increased. The rate of optical loss was estimated to be 0.01576 dB/°C and 0.02212 dB/°C for gasoline and toluene respectively.

FUEL DETECTION SYSTEM USING OTDR WITH MULTIMODE FIBER

This work presents an optical fiber based sensor for fuel detection and adaptionan optical time domain Reflectometer (OTDR) as an analyzer. The sensing system consists of a portion of removal clad multimode fiber (MMF) as sensing part connected between a receive and launch fiber. The sensing part was prepared by removing 1 cm of the MMF cladding layer using chemical etching technique. Both launch and receive fibers are using single mode fiber (SMF) where OTDR is connected to the Launch Fibre while Receive Fiber has one end with air interface.The sensor response is based on optical return loss recorded from OTDR trace when sensing part in contact with fuel where in this work diesel and benzene were tested. OTDR measurement revealed that the return loss recorded from OTDR increases when etching time of the MMF increases. The highest return loss of 2.462 dB and 3.099 dB were recorded in diesel and benzene respectively with etching time of 20 minutes. The etching time was up to 25 minutes but it was found to cause the fiber core become too thin and at the end the fiber core can completely dissolve. Further enhancement of detection sensitivity was achieved by using two-point MMF sensing system.

Phase-sensitive correlation optical time-domain reflectometer using quantum phase noise of laser light.

We propose and experimentally demonstrate a simple approach to realize a phase-sensitive correlation optical time-domain reflectometer (OTDR) suitable for detection and localization of dynamic perturbations along a single-mode optical fiber. It is based on the quantum phase fluctuations of a coherent light emitted by a telecom DFB diode laser. Truly random probe signals are generated by an interferometer with the optical path difference exceeding the coherence length of the laser light. Speckle-like OTDR traces were obtained by calculating cross-correlation functions between the probe light and the light intensity signals returned back from the sensing fiber. Perturbations are detected and localized by monitoring time variations of correlation amplitude along the fiber length. Results of proof-of-concept experimental testing are presented using an array of ultra-low-reflectivity fiber Bragg gratings as weak reflectors.

The Faulty Optical Fiber Mechanism and Fault Localization Techniques in TDM-PON Network

In this paper, the mechanism of failure (breakdown) detection in an optical fiber line will be studied. The objectives of this paper are to understand in detail the mechanism of faulty fiber and previous recommended fault localization techniques for fiber-to-the-home (FTTH) access network. The detail failure analysis results, failure mechanism, and eliminating solution will be studied and presented. It was reported that any failure in FTTH is affected the triple-play services transmission. Conventionally, a fiber fault in FTTH can be located using optical time domain reflectometer (OTDR) upwardly from customer premises toward central office (CO). Technician is sent to the optical network terminal (ONT) or optical network unit (ONU) side to inject an OTDR pulse into the faulty fiber. This approach would require much time and effort. Moreover, OTDR can only display a measurement result of a line in a time. Therefore, it becomes a hindrance to detect failure of optical line with a large number of customer premises and large coverage area in the fiber plant by using an OTDR. Besides, it is difficult to detect a failure in optical line equipped with passive optical splitter by using a conventional OTDR in the CO downwardly from CO towards the customer premises, because the Rayleigh back-scattered (RBS) light from different branches overlap with each other in the OTDR trace and cannot be distinguished. To overcome these problems to achieve desired network survivability, we introduced a MATLAB-based graphical user interface (GUI) named Centralized Failure Detection System (CFDS), which is potentially used to increase efficiency and flexibility of FTTH, particularly in monitoring the optical signal flow and locating a fiber break downwardly from CO. To perform all the mentioned tasks, interfacing between the developed program with OTDR is required.

Analysis of Line Monitoring Device Network using Centralized Failure Troubleshooting System

An optical time domain reflectometer (OTDR) is an instrument that used to measure parameters such as attenuation, length, connectors and splice losses, reflectance level and locating faults in an optical link. The measurement results are saved in OTDR and then transfer into computer for further analysis by using computer-based emulation software for performing more OTDR trace processing. In this paper, we proposed and demonstrated a new in-line monitoring and testing system based on Line Monitoring Device (LMD) and Centralized Failure Detection System (CFDS) for transmission surveillance and failure detection without affecting the transmission in an optical access network. LMD is passive device for optical signals tapping purpose; meanwhile CFDS is a centralized monitoring and troubleshooting solution with the GUI processing in MATLAB software. The LMD network will be analysis through both programs by means of OTDR installed software and our CFDS. The results are eventually compared and show both are reliable with the second is able to be extended for further analysis. Any fiber failure or breakdown occurs in the network will be determined by CFDS while the LMD is used to determine sharply the point of failure before it is been repaired. The proposed systems are able to improve the service reliability and reduce the repairing cost and time.

A quasi-distributed temperature sensor interrogated by a wavelength-sensitive optical time-domain reflectometer

In this note, we present a quasi-distributed temperature monitoring system based on the concatenation of identical low-reflective fiber Bragg gratings (FBGs) and interrogated by means of an optical time-domain reflectometer (OTDR). An original wavelength-sensitive system placed before the OTDR detector is used to analyze the reflected signal. This system allows the height of the FBG reflection peaks in the OTDR trace to depend on their resonance wavelength, and therefore to the local temperature. In addition, a simple but original reference method is proposed. The configuration of the whole interrogating device is kept very basic, as a standard OTDR and some passive components are used. The cost of the overall system is therefore very limited. In this note, the wavelength-sensitive system is studied in details, as well as the reference method. Experimental results are reported.

Newly Developed Optical Fiber Line Testing System Employing Bi-Directional OTDRs for PON and In-Service Line Testing Criteria

A passive optical network (PON) that provides fiber to the home (FTTH) services is a fundamental access network topology in Japan. An optical fiber line monitoring and testing system is essential if we are to improve service reliability and reduce the maintenance costs of optical access networks. PONs have optical splitters in their optical fiber lines. It is difficult to find a fault in an optical fiber line equipped with an optical splitter by using a conventional optical fiber line testing system, which uses optical time-domain reflectometer (OTDR) in a central office (CO), because Rayleigh backscattering from the branched fibers accumulates in the OTDR trace. This paper describes a newly developed optical fiber line testing method that employs bi-directional OTDRs with two wavelengths at branched fiber regions in a PON to locate a fault precisely. Optical fiber line testing is conducted by two OTDRs that are installed in a CO and on a customer's premises, respectively. The OTDR in the CO has a U-band maintenance wavelength. We present two kinds of maintenance wavelength allocation for OTDRs on a customer's premises, which are in the U-band and C-band respectively. An OTDR whose maintenance wavelength is in the U-band enables us to test in-service PON lines simply by filtering the U-band wavelength. For the maintenance wavelengths in the C-band, we can use a cost-effective conventional OTDR to test the PON from the customer's premises on condition that we clarify the peak pulse power limit and dynamic range. We describe the test procedures for both cases. We also clarify the insertion loss design for an optical filter in the CO when using the U-band to provide the maintenance wavelength and the criteria for in-service line testing when the using C-band to provide the maintenance wavelength. To confirm the feasibility of our approach, we demonstrate a bi-directional OTDR method using the U-band and the C-band, and the test procedure, which successfully detected fault locations in branched fiber regions. We also describe the use of packet loss measurements to investigate the effect of in-service line testing with an OTDR in the C-band on data communication quality.

Distributed measurement of the chromatic dispersion of an optical fiber using a wavelength-tunable OTDR

In this paper, a distributed measurement of the chromatic dispersion (CD) of an optical fiber is presented. The measurement is based on the analysis of a set of bidirectional optical time domain reflectometer traces collected over the wavelength range of interest. To calculate the distributed CD of the fiber, several approximations are required. The validity of these approximations is verified via a numerical simulation for both step-index and dispersion-shifted fibers (DSFs). These simulations allow the placement of an upper bound on the error of the measurement. Experimentally, measurements of both step-index and DSFs are reported.

Suppression of the Cross-Gain Modulation in Remotely-Pumped EDF/DRA Hybrid Inline Amplifier Systems with Online OTDR for Gain Monitoring

Novel gain monitoring scheme in Remotely-Pumped EDF/DRA hybrid inline amplifier is proposed using Optical Time Domain Reflectometer (OTDR). Signal degradation due to cross gain modulation (XGM) caused by an OTDR pulse in the distributed Raman amplifier (DRA) section and remotely-pumped EDF (RP-EDF) unit is analyzed theoretically. The required conditions for suppressing of XGM in the DRA section are derived. We propose the directional bypass configuration to realize OTDR measurement without XGM in the EDF unit. Transmission experiments using the RP-EDF/DRA hybrid inline amplifier demonstrate the absence of transmission impairement induced by OTDR. An analysis of the OTDR trace for each gain medium is also discussed. The theoretical analysis agrees well with the experimental result.