A unified decision scheme for the classification and localization of cable faults is proposed based on a two-step procedure. Having basis in the time domain reflectometry (TDR), the proposed scheme is capable of determining not only the locations but also types of faults in a cable without an excessive additional computational burden compared to other TDR-based schemes. Results from simulation and experiments with measured real data demonstrate that the proposed scheme exhibits a higher rate of correct decision than the conventional schemes in localizing and classifying faults over a wide range of the location of faults.

Under the condition of inadequate torque management, contact failure could occur in the interconnecting connector. Contact failure reduces the local immunity and degrades the electromagnetic properties of the equipment. It has been shown in previous reports that connector contact failure causes the parasitic inductance and radiated electromagnetic noise to increase. However, there is not enough discussion about the effects of connector torque fluctuation on the surrounding electromagnetic environment. Thus, in this study, the effects of a changing connector torque value on the circuit response and near field at the contact boundary were investigated. Based on these results, we discuss the influence of torque fluctuation on the electromagnetic environment surrounding the connector.

The contact surface of a loose connector has both contact resistance and low inductance, and the inductance depends on the distribution of the true contacts. The contact resistance and inductance were measured by time-domain reflectometry (TDR) for seven contact distribution models. The resistance was approximately constant, while the maximum inductance varied more than twofold depending on the distribution model.

A loosened connector between interconnected electric devices causes an increase in electromagnetic radiation when the devices operate in high-frequency bands. To develop a high-frequency circuit equivalent to a connector with contact failure, we previously investigated the parasitic elements caused by failure at the contact boundary. From the results of that study, the inductance and resistance at a connection contact boundary are increased by the loosening of a connector. Furthermore, the increase in inductance is the dominant factor in increasing the intensity of the electromagnetic radiation. In this paper, to suppress electromagnetic radiation resulting from a loose contact, we formulate the contact performance requirement needed to maintain a good contact condition when a small loosening has occurred at the interconnection. To this end, we investigate the mechanism of increase in the inductance by loosening the connector.

This paper describes a novel optical fiber line testing system operating at 1.65 µm using test light bypass modules. We show a new testing configuration for add/drop multiplexer (ADM) ring networks. The test light bypass modules were installed in individual customer buildings so the test light can bypass the ADMs. We evaluated the bit-error performance with a 2.48832 Gbit/s ADM ring network using a prototype test light bypass module. We confirmed that this testing system can monitor the optical fiber cables of an ADM ring network, and that it causes no degradation in transmission quality. We show the operating area provided by the system dynamic range expressed in terms of fiber length and customer building number. The prototype system could monitor an ADM ring network linking five buildings with a 5 km loop. We also performed an in-service monitoring field trial in a 2.6 km ring network with three ADM nodes. This testing system enables us to reduce the operating, administration, and maintenance cost and improves the transmission quality of ADM ring networks.

This letter presents the first experimental results that confirm the restorability of Rayleigh backscatter traces from a single-mode fiber measured by using a coherent optical time domain reflectometer (OTDR) with a precisely frequency-controlled light source. Based on this restorability, we can measure the distributed strain and temperature along the fiber with a very high measurand resolution that is one to two orders of magnitude better than that provided by Brillouin-based techniques for a long length of fiber.

A novel technique is proposed for measuring the distributed strain and temperature in a fiber with a very high resolution. This technique makes use of the jagged appearance of Rayleigh backscatter traces from a single-mode fiber measured by using a coherent OTDR with a precisely frequency-controlled light source. Our preliminary experiment indicated the possibility of measuring temperature with a resolution of better than 0.01 and a spatial resolution of one meter. This temperature resolution is two orders of magnitude better than that provided by Brillouin-based distributed sensors.

The changes in fiber strain and fiber loss with temperature are quantitatively evaluated for 0.5 mm UV-coated fiber and three kind of fiber-optic access cables, for dropping and indoor wiring, employing 0.5 mm UV-coated fiber. Measurements of the fiber strain and loss increase are conducted using a quasi-heterodyne interferometer method and a photon-counting optical-time-domain-reflectmeter, respectively, at 1.3 and 1.55 µ m. From the strain characteristics, the following observations are made: (a) In the temperature range from -40 to 20 the fiber strain followed the cable strain quite closely, thus maintaining a tight cable structure and (b) from 20 to 80, the fiber exhibited a lower strain than the cable strain. Furthermore, no loss increase due to temperature change was observed for the 0.5-mm diameter coated fiber and the three type of optical cables.

Discontinuity such as a bend in a micro-strip line is known as one of major radiation sources. The total radiation from the micro-strip line is, however, being generally investigated because of the difficulties in identifying the radiation from some specific location. In this paper, paying attention to the feature of TDR (Time-Domain Reflectometry) measurement, we made an attempt to extract the radiation only from the bend in a micro-strip line. Such an approach is useful in understanding its radiation mechanism. As a result, we found that the larger the bend angle is, the larger the radiation power becomes. The radiation power achieved 3.5% at maximum when the bending angle was 90at the frequencies below 1 GHz. We also examined the validity of the TDR analysis in comparison with network analyzer measurement. We obtained the radiation power versus frequency from the measured scattering parameters, which exhibited a fair agreement with the TDR result.

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.

An optical fiber line testing system is essential for reducing maintenance costs and improving service reliability in optical access networks. NTT has already developed such a system called AURORA (AUtomatic optical fibeR opeRAtions support system). As we already use the 1310 and 1550nm wavelengths for communication, we use the 1650nm wavelength for maintenance testing in accordance with ITU-T recommendation L.41. Recently, a long wavelength band (L-band) that extends to 1625nm has begun to be used for WDM transmission. With a view to monitoring optical fiber cables transmitting L-band communication light, an attractive way of separating the U-band wavelength of the test lights from the L-band wavelength of the communication light is to use a chirped fiber Bragg grating (FBG) filter because of its steep optical spectrum. However, it is difficult to measure fiber characteristics with an optical time-domain reflectometer (OTDR), because multi-reflections appear in the OTDR trace when FBG filters are installed at both ends of an optical fiber line. In this paper, we consider this problem and show that the reflection loss at the port of a test access module (TAM) must be more than 36.6dB. We also describe the system design for an extended optical fiber line testing system using an L/U-band optical coupler, which has two chirped FBGs between two 4-port circulators for L-band WDM transmission. In this system, the reflection loss at a TAM port was 38.1dB, and we confirmed that there was no degradation in the OTDR trace caused by multi-reflections at the optical filters.

This paper describes a method for assessing the structural integrity of International America's Cup Class (IACC) yachts using a fiber optic distributed strain sensor. IACC yachts are made of advanced composite materials designed for high stiffness and lightness, however, a number of critical accidents have occurred during sailing. So we developed a health monitoring system and applied it to two Japanese IACC yachts to measure the distributed strain by using an optical fiber sensor installed in their hulls. We then estimated the three-dimensional distributed strain and compared the results with simulated data obtained by finite element analysis (FEA) to confirm the designed strength of these yachts.

An effective spatial resolution enhancement method for distributed strain measurement by BOTDR is proposed. An optical fiber is glued to a structure by a length less than the spatial resolution defined by the pulse width, and the Brillouin spectrum of the light scattered from the glued optical fiber is investigated theoretically. The apparent strain xp observed in the fiber is found to be proportional to the accurate strain a. The ratio r=xp/a coincides with the ratio of the glued length to the spatial resolution. Spatial resolution as small as 0.2 m is demonstrated experimentally for small strains of less than 10-3.

Low cost optical subscriber systems and effective operation are indispensable to the construction and maintenance of greatly expanded optical fiber networks. An optical fiber line monitoring system is essential for reducing maintenance costs and improving service reliability in optical access networks. To promote cost-effective optical fiber line operation, we propose an extended automatic optical fiber operations support system (AURORA) with a remotely installed fiber selector. We suggest a configuration for extended AURORA and design the dynamic range of the system. We confirmed that testing could be carried out on an extended optical network section of 10 km in length by using extended AURORA when the optical trunk line was less than 15 km. We also discuss the effect on the maintenance cost of optical fiber cables in access networks. We calculated the annual maintenance cost for periodic tests in actual operation areas, and confirmed that this cost could be reduced by 30% compared with that for a conventional system.

A novel technique is developed to reconstruct a nonuniform transmission line by using arbitrary incident waveforms. By discretizing both the incident and reflected waves, we find that the ratio of reflected wave to incident wave has the same form as the reflection coefficient obtained by treating a nonuniform line as a cascaded, multiple-section signal line. A reconstruction scheme is derived to get the impedance profile of a nonuniform line. Some examples are presented to illustrate this new technique.

An improvement of the fiber-optic transceiver having both transmitter and receiver functions of optical time-domain reflectometers is examined. The improvement is achieved by introducing an external optical amplifier without changing the previously reported configuration. The characteristics of the transmitted Q-switched pulse and the receiver gain is studied theoretically and experimentally to estimate the performance improvement. It is found that the introduction of the external optical amplifier is a simple and effective way to the performance improvement.

We investigated the reflection of light caused by sharp bends in optical fiber experimentally. The position distribution of reflection power was measured using an OTDR and an OLCR. We found that the reflection power increased linearly as the logarithm of the bending loss increased, which agrees with expectation from a simple theoretical model. We believe that the light we observed was part of the leaked light, which was reflected between the primary and secondary coatings.

A kind of time domain reflectometry using deconvolution and envelope extraction process is presented for measuring microwave resonator characteristics, where data acquisition and data processing are performed entirely in the time domain. The proposed method may be used to characterize resonators which have Q values in the range between a few dozen and several hundred. The major drawback of the time domain measurement techniques is in general considered to be a low frequency resolution. In the proposed method, it is avoided skillfully.