This paper presents a simple method for localization of events on traces of group of optical fibers from the same fiber optic link segment (FOLS) of a fiber-optic transmission line (FOTL). This method is primarily focused on determining the location of the most "problematic" for the automated search events "without reflection," which fit to optic fiber fusion splices with insertion loss significantly less than the standard values and simultaneously related values of backscattering coefficients of fused optical fibers. Proposed solution is based on comparison of tables of events for measured traces with test of condition of check sum of distances to the same event in backward directions relative to optical length of fiber optic link segment and condition of belonging of pair of events on traces of different optical fibers of the same direction to one event. As a result, it is possible to make a conclusion about the presence of this event on all other traces of the group. Further, corresponding corrections are made in tables of traces with missing events.
This work presents results of absolute error estimation performed for non-reflective optical time domain reflectometer (OTDR) event localization during wavelet analysis of optical fiber link trace by continuous Haar wavelet transform. We considered fusion splices of standard singlemode optical fibers with different insertion loss values. Here OTDR indications varied over range 0.020…0.550 dB, while Haar wavelet scaling coefficients were selected from 150 up to 3000. Following comparison of measured and evaluated results allowed for proposition the basic criterion for non-reflective OTDR event localization by wavelet analysis. It is “the center” of this event, and it is characterized by strongly reduced absolute error. During the next step of research, we compared diagrams of event localization error distribution and detected generalized Haar wavelet scaling coefficients that provide mentioned absolute error no more 2 m, which are also presented in this work.
In work results of the survey conducted among professional fiber optic technicians and engineers concerned with skills in fiber optic link testing and measurement are presented. Head count was provided on the basis of the Samara Regional Telecommunication Training Centre (SRTTC) of the Povolzhskiy State University of Telecommunications and Informatics (PSUTI) during the period from February to April, 2017. The developed survey included a set of the questions allowing to estimate an work length and qualification of the engineer, his practical skills, the main activity field, typical work volume on measurements and results processing and, respectively, obligatory and optional actions for grouping, marking, structuring and hosting of the database on this or that trace of the elementary cable section of fiber optic transmission links. More than 40 employees of communication industry, business units of the big companies and also the separate enterprises of medium and small business carry on installation and maintenance of fiber optic transmission links have participated in survey. At the same time part of them have been defective, proceeding from the revealed unacceptably low skill level and/or short work length. The analysis of the received survey results have allowed to establish the corresponding subsections of course programs in the "Measurements on Fiber Optic Transmission Links" demanding, at least, enhanced studying, and in some cases – modifications and carrying out an additional lecture practical training.
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.
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