Photon-counting Optical Time Domain Reflectometer Research Articles

Fast Acquisition Tunable High-Resolution Photon-Counting OTDR

A 15 dB dynamic range and 4.6 cm spatial resolution tunable photon-counting optical time-domain reflectometer (PC-OTDR) is presented along with a Field Programmable Gate Array (FPGA)-based detection management system that allows several regions of the fiber to be interrogated by the same optical pulse, increasing the data acquisition rate when compared to previous solutions. The optical pulse generation is implemented by a tunable figure-8 passive mode-locked laser providing pulses with the desired bandwidth and center wavelength for WDM applications in the C-band. The acquisition rate is limited by the afterpulse effect and dead time of the employed gated avalanche single-photon detectors. The devised acquisition system not only allows for centimeter-resolution monitoring of fiber links as long as 12 km in under 20 minutes but is also readily adapted to any other photon-counting strategy for increased acquisition rate. The system provides a 20-fold decrease in acquisition times when compared with state-of-the-art solutions, allowing affordable times in centimeter-resolution long-distance fiber measurements.

Large Structural Shear Deformation and Failure Monitoring Using Bend Losses in Polymer Optical Fibre

Rapid identification of structural damage positions is essential to the post-disaster rehabilitation of structures and infrastructures. Large shear deformation, e.g., shear failure of bridge piers, shear-slip of slopes, and shear cracking of structural walls, is often the cause of structural instability. Distributed optical fibre sensing (DOFS) techniques have an advantage over point-based sensors in terms of spatial continuous structural condition monitoring. This paper presents the development of new measurement theory and algorithm to evaluate the structural shear deflection based on the large beam deflection and optical bend loss theories. The proposed technique adopted a photon-counting Optical Time Domain Reflectometer (ν-OTDR) with polymer optical fibres (POFs) which has a large deformation measurement range and high spatial resolution. In the experiment, shear deformation events can be successfully detected and evaluated from the proposed technique. When the normalised shear deformation is larger than 0.2, both the event locations and the magnitudes can be accurately determined. When normalised shear deformation is lesser than 0.2, the error in the magnitude evaluation increased, but the event location can be found with an absolute error <0.5 m. Multiple shear events can be treated as independent events when they are separated by more than 5 m. Various configurations of POFs attached to concrete beam specimens for rupture failure monitoring were also studied. The configuration that could maximise the POF curvature at the beam failure produced the largest ν-OTDR signals. In other configurations in which the POFs were only stretched at failure, the signals were less strong and were influenced by the POF-structure bonding strength.

Linearized Bregman Iterations for Automatic Optical Fiber Fault Analysis

Supervision of the physical layer of optical networks is an extremely relevant subject. To detect fiber faults, single-ended solutions such as the Optical Time Domain Reflectometer (OTDR) allow for precise measurements of fault profiles. Combining the OTDR with a signal processing approach for high-dimensional sparse parameter estimation allows for automated and reliable results in reduced time. In this work, a measurement system composed of a Photon-Counting OTDR data acquisition unit and a processing unit based on a Linearized Bregman Iterations algorithm for automatic fault finding is proposed. An in-depth comparative study of the proposed algorithm's fault-finding prowess in the presence of noise is presented. Characteristics such as sensitivity, specificity, processing time, and complexity, are analysed in simulated environments. Real-life measurements that are conducted using the Photon-Counting OTDR subsystem for data acquisition and the Linearized Bregman-based processing unit for automated data analysis demonstrated accurate results. It is concluded that the proposed measurement system is particularly well suited to the task of fault finding. The natural characteristic of the algorithm fosters embedding the solution in digital hardware, allowing for reduced costs and processing time.

Plasma Current Measurement in Thermonuclear Fusion Reactors Using a Photon-Counting POTDR

In this letter, we present a fiber-optic current sensor for the measurement of plasma current in thermonuclear fusion reactors. The sensor includes a low-birefringence optical fiber placed around a section of the vacuum vessel that hosts the fusion reaction. The interrogating unit consists of a polarization-sensitive photon-counting optical time domain reflectometer that enables to determine the light polarization rotation induced by the plasma current. The measurement principle is demonstrated by means of the Jones formalism. The sensor has been experimentally validated on the Tore Supra tokamak fusion reactor for a plasma current range going from 0.6 to 1.5 MA. A maximum error of 13.50% has been observed for the lowest current.

The response of polymer optical fiber (POF) to bending and axial tension for the application of a POF sensor for automotive seat occupancy sensing

The automotive industry is a promising area for innovations in the field of polymer optical fiber (POF) sensors as the industry currently uses the POF mostly for data transmissions. Since an optical fiber sensor has a high bandwidth, is small in size, is lightweight, and is immune to electromagnetic interference, it offers higher performance than that of its electrical-based counterparts such as the strain gage, elastomeric bladder, and resistive sensor systems. This enhanced performance makes an optical fiber sensor a suitable material for sensing seat occupancy for improved safety features in automobiles. The overall goal of this research is to develop a textile-based optical fiber sensor for automotive seat occupancy with high accuracy and reproducibility. In this study, the bending and tensile loading responses of POF were investigated, where two perfluorinated (PF) graded index (GI) POFs with two different core/cladding diameters, 62.5/750 and 62.5/490 μm, were used. The bending loss and the light attenuation against the applied axial stress were measured by a photon counting optical time-domain reflectometer. The critical bending diameters were analyzed: Cytop-1 (62.5/750 μm) ≥ 38.10 mm, Cytop-2 (62.5/490 μm) ≥ 44.45 mm. Furthermore, the elastic sensitive strain regions (x), where the stress-induced loss was recoverable, of the POFs at a 76.2 mm gage length at a strain rate of 4 mm/min were determined: Cytop-1: 3% ≤ x ≤ 3.5%, Cytop-2: 3.1% ≤ x ≤ 3.3%. The Cytop-1 was found to be less sensitive to bending and to have greater elastic sensitive strain range relative to the Cytop-2. In this study, a theoretical approach of the PF GI POF behavior to bending and axial tension was provided. The results demonstrated the feasibility of POFs as optical fiber sensors for automotive seat occupancy sensing.

Investigation of bend loss in single mode fibers with ultra-high-resolution photon-counting optical time domain reflectometer.

An intensity peak associated with fiber bending could be detected thanks to the use of an ultra-high-resolution photon-counting optical time domain reflectometer (OTDR) setup. The peak intensity is shown to be dependent on the curvature radius and angular distance of the bend. To account for such peaks, we propose a model based on modal mismatching and coupling inside the bend region and show that the model is highly consistent with the acquired data. Combining the information of the bend peak and bend loss, and taking advantage of the high dependence of the peak value with the local modal field parameter, the technique could be employed as an optical fiber local-parameter characterization method.

Distributed damage detection of offshore steel structures using plastic optical fibre sensors

In this paper, results demonstrating the potential application of plastic optical fibre (POF) sensors for damage detection of offshore steel structures are summarized. Graded-index perfluorinated plastic optical fibre (GIPOF) was used for crack detection in tubular steel specimens. A high-resolution photon-counting optical time-domain reflectometer (ν-OTDR) was used for interrogating the optical signal. The study will show that the technique adopted in this study is able to determine the position of the crack in the host structure with high accuracy and repeatability. The technique was also found to be capable of monitoring crack growth in the steel specimens used based on a serpentine sensor configuration.

Photon Counting OTDR: Advantages and Limitations

In this paper, we provide a detailed insight into photon-counting optical time-domain reflectometer (¿-OTDR) operation, ranging from Geiger-mode operation of avalanche photodiodes (APD), analysis of different APD bias schemes, to the discussion of OTDR perspectives. Our results demonstrate that an InGaAs/InP APD-based ¿-OTDR has the potential of outperforming the dynamic range of a conventional state-of-the-art OTDR by 10 dB, as well as the two-point resolution by a factor of 20. Considering the trace acquisition speed of ¿-OTDRs, we find that a combination of rapid gating for high photon flux and free running mode for low photon flux is the most efficient solution. Concerning dead zones, our results are less promising. Without additional measures, e.g., an optical shutter, the photon counting approach is not competitive.

High resolution optical time domain reflectometer based on 1.55μm up-conversion photon-counting module

We implement a photon-counting Optical Time Domain Reflectometer (OTDR) at 1.55mum which exhibits a high 2-point resolution and a high accuracy. It is based on a low temporal-jitter photon-counting module at 1.55mum. This detector is composed of a periodically poled Lithium niobate (PPLN) waveguide, which provides a wavelength conversion from near infrared to visible light, and a low jitter silicon photon-counting detector. With this apparatus, we obtain centimetre resolution over a measurement range of tens of kilometres.

Photon-counting optical time-domain reflectometer using a planar InGaAsP avalanche detector

We demonstrate the first room-temperature photon-counting optical time-domain reflectometer, which uses a planar InGaAsP avalanche photodiode. Using a 1.3 μm semiconductor laser source we achieve a one-way loss sensitivity of 20 dB.

1.52 μm room-temperature photon-counting optical time domain reflectometer

We demonstrate the first photon-counting optical time domain reflectometer which operates at room temperature and at a wavelength of 1.52 μm. A range of 50 km is achieved for the detection of an index-matched fibre end.

Optical time domain reflectometer using a photon-counting InGaAs/InP avalanche photodiode at 1.3 μm

We report the first photon-counting optical time domain reflectometer using an InGaAsInP avalanche photodiode. The measured sensitivity at a temperature of −40°C is comparable to that of the best present conventional PINFET receiver results.