Solution To OTDR Limitations For Automated Measurement

This work is concerned with research of Haar wavelet threshold sensitivity for detection of non-reflective events corresponding to optical fiber fusion splices on fragments of fiber optic link traces measured by optical time domain reflectometer (OTDR). We performed test series contained 40 step-by-step repeatable splicing of the same couple of standard singlemode fibers of ITU-T Rec. G.652 spools with length 2.2 km and 4.2 km and outer termination by conventional singlemode FC/UPC pigtails for OTDR connection and following bidirectional trace measurement. Results of insertion loss estimation and accomplished by OTDR software automated detection of non-reflective event corresponding to fusion splice of described optical fibers as well as ability of its visual manual localization on trace were recorded. The first 30 splices were realized by fusion splicer conventional program for jointing standard singlemode optical fibers of ITU-T Rec. ITU-T G.652, while the next 10 splices were done under “attenuator” mode with preset increased insertion loss. Described link traces were measured by OTDR operating in a standard mode with high spatial resolution under pulse width 20 ns and appropriate dynamic range with far-end OSNR 6.5 dB at wavelength 1550 nm. As a result 80 traces were analyzed in both automated and manual modes with fusion splice insertion loss varied from 0.002 dB to 0.554 dB. At the next stage we applied continues Haar wavelet transform for detection non-reflective event on measured traces of lab fiber optic link containing described one fusion splice with total length about 6.4 km. According to results, wavelet transform of described link trace provides detection of extremely low loss non-reflective events with OTDR reading down to own error corresponding to 0.020…0.030 dB range under improved scaling over normalized spatial diagram of wavelet coefficients.

Pencil-lead-break transient detecting is demonstrated by phase- optical time domain reflectometer based on coherent detecting and data processing. By using coherent detecting technology, combined with Erbium-doped Optical Fiber Amplifier and high power load Acousto-optical Modulators (AOM), we improves signal detecting sensitive and Signal-noise-ratio by 2∼3dB coherent detection advantage over direct detection of phase-OTDR. Location of pencil-lead-break transient signal was detected with higher spatial resolution in time domain by averaged traces transiently. Using varying power with time of the location, frequency information can be obtained by fast Fourier transforms (FFT) analyzer. With loop geometry fiber, as short as 0.25cm fiber can give effective signal over 12-km long single-mode fiber and as high as 50 kHz frequency component can be detected.

A distributed fiber optic intrusion detection sensor is proposed, in which a nonbalanced Mach‐Zehnder interferometer is used as phase demodulator, and an optical time domain reflectometer is used as a position detector. The experimental results concluded that the positioning error of ±25m can be achieved along an 8.8‐km single mode fiber. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2746–2748, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25602

Study on Multiplexing Ability of Identical Fiber Bragg Gratings in a Single Fiber

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.

교량과 각종 건물을 비롯한 대형 토목 구조물에서 발생하는 수 mm의 변위를 한 개의 광섬유로 간편하게 측정하기 위하여 광커넥터에서 반사가 굽힘 손실에 의하여 변하는 현상을 이용한 새로운 다중화된 광섬유 변위센서를 제안하고 실험하였다. 한 쌍의 광커넥터 양끝에서 반사광의 신호차이가 두 광커넥터 사이에서 발생한 굽힘 변위에 의해서 달라지는 것을 Optical Time Domain Reflectometer로 측정하여 선형으로 그 변화가 측정되는 변위센서를 만들고, 이 센서 4개를 직렬형으로 배열하여 여러 지점의 변위를 동사에 측정이 가능한 다중화 센서 시스템을 구성하고 실험하였다. 그 결과 이 변위센서를 이용하면 4개 지점에서 각각 최대 6 mm까지의 변위를 6%의 오차범위 내에서 0.9942의 선형성을 가지고 변위를 측정할 수 있음을 확인하였다. We propose and present a new multiplexed bend loss type single-mode fiber-optic sensor system for displacement measurement in order to measure the displacement of several mm of civil engineering structures such as bridges and buildings. We make a bend loss type fiber-optic sensor for measuring displacements using the signal difference between two reflection signals due to various bend losses generating at a pair of optical connectors by using the optical time domain reflectometer. And we fabricate a multiplexed bend loss type fiber-optic sensor detecting linear displacements of 4 measuring positions of an object by setting these new 4 fiber-optic sensors on a single mode fiber simultaneously. We find that the multiplexed fiber-optics displacement sensor has linearity of 0.9942, maximum displacement of 6 mm, and accuracy of 6% for 4 measuring points.

Introduction. The relevance of using fiber-optic sensors to monitor the geomechanical state of the mine workings of coal mines of the Karaganda coal-mining field is extremely high, because they are super-categorical and dangerous in a sudden explosion of coal dust and methane gas during mining operations in hazardous mines. Fiber optic sensors have several advantages: explosion safety, high accuracy, measurement speed and have good linearity of characteristics. Aim. The use of optical fiber of the ITU-T G.652.D standard as a sensor for monitoring the geomechanical state of an array of coal mines, which is very promising in terms of creating a distributed monitoring system capable of timely signaling to personnel about the danger of a sudden collapse of a mine. Materials and methods. To develop methods for monitoring and measuring the geotechnical parameters of the workings, a simulation laboratory bench based on fiber-optic sensors was developed. The authors used a quartz single-mode optical fiber 9/125 μm (OS2) Corning SMF-28e + ®. The article proposes systems in two variants, depending on the tasks and functionality. In the first variant, the well-known method of optical reflectometry OTDR (Optical time domain reflectometer) is used. In the second variant, the values of the additional losses caused by the mechanical action on the optical fiber are controlled. Results. During mechanical action on an optical fiber microcracks occur, leading to a change in the properties of light and an increase in additional losses of the light wave passing through it. Conclusion. The use of ITU-T G.652.D standard optical fiber for monitoring the geomechanical state of an array of coal mine workings is very promising, since the VODs developed on its basis have sufficiently high accuracy, measurement speed and good linearity of characteristics.

In this paper we report the splicing losses of a single mode optical fiber at different humid conditions and at different places of Bangladesh Railway West Zone (BRWZ). The location of the splicing points and their losses for a single mode step index optical fiber have been measured by optical time domain reflectometer before re-splicing. Fusion splicer is used to re-splice these points at different humid conditions to analyze the splicing loss dependency. From this study it has been found that different humid conditions affect the splicing losses to a large extent.

Bolted joints of aircraft lug assembly play an important role in connecting the wing and fuselage of an aircraft structure. Generally, the bolted joints get loosened because they are frequently exposed to the dynamic loads induced when an aircraft is in service. For this reason, it is important to monitor the condition of the bolted joints to avoid any critical defect that will lead to any risk in human life. However, it is difficult to conduct the bolted joints’ loosening inspection by an operator. In past few decades, optical fiber based sensor has been widely used due to its advancement over a conventional piezoelectric (PZT) sensor, especially due to its small size and light weight. With regard to this, a loosening monitoring of bolted joints using optical fiber bending sensor for aircraft lug assembly is proposed in this paper. The lug assembly specimen, which consists of a stainless steel lug, CFRP/Nomex honeycomb sandwich panel, carbon-steel bolt, nut and washer, and the monitoring system, which consists of a single mode fiber with ten optical fiber bending sensor nodes and an Optical Time-domain Reflectometer (OTDR) were used to determine the bolt loosening at every 1 degree interval.

In this paper, the optimization tool based on Genetic Algorithms (GAs) to improve the different parameters such as the Attenuation and backscatter coefficients of single mode optical fibre (SMF) is proposed. The method of experimental study which is based on the use of an Optical Time Domain Reflectometer (OTDR) to measure and locate different events that occur in an optical fibre in real time is exploited. The experimental results have been compared with theoretical results in order to validate the proposed methods of modelling.

We describe the implementation of a versatile system and the corresponding method to perform fast postmortem optical attenuation measurements on irradiated optical-fibers (OFs) for dosimetry purposes. The measurement is based on the radiation-induced attenuation (RIA) phenomenon. We use a dual-wavelength optical time-domain reflectometer (OTDR) coupled with a suitable radiation-sensitive OF. We demonstrate that radiation dose levels higher than 100 Gy(SiO2) can be measured efficiently with 1-m-long samples. The accuracy of the measurement increases with the increasing radiation dose if the length of the sample is kept fixed. We also highlight the possible limitations of our approach and, more generally, limitations related to performing accurate RIA measurement (online or postmortem) on short single-mode (SM) OF samples. The technological solution we propose can be tailored to address different radiation environments.

A magnetic field sensor with a magnetic fluid (MF)-coated intermodal interferometer is proposed and experimentally demonstrated. The interferometer is formed by sandwiching a segment of single mode fiber (SMF) between a segment of multi-mode fiber (MMF) and a spherical structure. It can be considered as a cascade of the traditional SMF-MMF-SMF structure and MMF-SMF-sphere structure. The transmission spectral characteristics change with the variation of applied magnetic field. The experimental results exhibit that the magnetic field sensitivities for wavelength and transmission loss are 0.047 nm/mT and 0.215 dB/mT for the interference dip around 1 535.36 nm. For the interference dip around 1548.41nm, the sensitivities are 0.077 nm/mT and 0.243 dB/mT. Simultaneous measurement can be realized according to the different spectral responses.

A new optical fiber bend sensor is proposed and demonstrated based on a sandwich structure created by splicing a segment of twin core fiber (TCF) between two segments of single mode fibers (SMFs). One core of the TCF is aligned with the cores of two segments of SMFs. An incident beam is directed into the TCF by the lead-in SMF. Light couples back and forth between two cores. The bend sensing performance of the sensor is investigated by intensity-modulated method. The intensity of the operation wavelength is modulated by the change of refractive index and geometrical deformation in the bent TCF. Experimental results show such a bend sensor achieves sensitivity of +0.671 /m-1 and resolution of 0.003 m-1 in the range of 0 to 1.25 m-1. In addition, the sensitivity and bend measurement range can be flexibly adjusted through selection of the length of TCF and sensing configuration. As such, the proposed sensor can be further developed for large or small bend ranges measurement.

1. The focal nature of contraction-induced injury to skeletal muscle fibres may arise from heterogeneities in sarcomere length that develop during contractions. We tested the hypothesis that when a maximally activated single permeabilized fibre segment is stretched and a deficit in maximum isometric force (force deficit) is produced, the regions of sarcomeres with the longest lengths of prior to the stretch contain the majority of the damaged sarcomeres when the fibre is returned to optimum length (Lo) after the stretch. 2. Single fibre segments (n = 16) were obtained from soleus muscles of rats. Average sarcomere length at five discrete positions along the length of each fibre was determined by lateral deflection of a diode laser spot. Diffraction patterns were obtained while fibres were relaxed and immediately before, during and after a single stretch of 40% strain relative to Lo. Following the stretch, the regions of each fibre that potentially contained damaged sarcomeres were identified by an increased scatter of the first-order diffraction patterns. The damage was confirmed by light and electron microscopy. 3. While single fibre segments were in relaxing solution, the mean value for all of the average sarcomere lengths sampled (n = 80) was 2.53 +/- 0.01 microns (range, 2.40-2.68 microns). During the maximum isometric contraction before each stretch, the mean sarcomere length decreased to 2.42 +/- 0.02 microns and the range increased to 2.12-3.01 microns. 4. During the stretch of 40% strain, all regions of sarcomeres were stretched onto the descending limb of the length-force curve, but sarcomere lengthening was non-uniform. After the stretch, when the maximally activated fibres were returned to Lo, the force deficit was 10 +/- 1%. Microscopic evaluation confirmed that the regions with the longest sarcomere lengths before the stretch contained the majority of the damaged sarcomeres after the stretch. We conclude that when heterogeneities in sarcomere length develop in single permeabilized fibre segments during a maximum isometric contraction, the sarcomeres in the regions with the longest lengths are the most susceptible to contraction-induced injury.

Based on enhanced Vernier effect, a compact fiber sensor with ultrahigh sensitivity is proposed for simultaneous transverse load (TL) and temperature measurements. A single mode fiber (SMF) is spliced with a segment of hollow-core fiber (HCF) coated with polydimethylsiloxane (PDMS), some PDMS is injected into the HCF, forming a Vernier sensor with an air cavity adjacent to a PDMS cavity. It is shown that TL and temperature changes give rise to opposite and remarkable different variations in lengths of the two cavities, thereby enhancing Vernier effect and in favor of simultaneous measurements of TL and temperature. Moreover, the limited sensitivity magnification due to the length mismatch between the two cavities is compensated for by reconstructing the Vernier envelope with a broadened free spectrum range (FSR) from output signal. As a result, the highest TL sensitivity reported so far of -2637.47 nm/N and a good condition number of 69.056 for the sensitivity coefficient matrix have been achieved.