This work presents overview of technological issues concerned with drawing of twisted silica microstructured optical fibers. We present results of drawing tower modifications with developed and verified technological modes, that provide fabrication of silica microstructured optical fibers with induced chirality up to extremely high twisting order of 800 revolutions per meter (rpm). Thus, a work package using the original designer technical solutions for upgrade the adapter for supplying overpressure to the cane holes of the microstructured optical fiber (MOF) was carried out. Hence, the target increase in the twisting speed in the cane feed unit to 2000 rpm is ensured while simultaneously target overpressure feeding to the cane holes, which prevents the hole collapsing in the process of MOF drawing. The reliability of the adapter design and the high reproducibility of the specified cross section structure for the MOF at lengths of more than 50 meters with a twist period of 500 rpm have been experimentally confirmed. For the first time in the Russian Federation, prototypes of "stable" chiral MOF lengths (more than 50 m) of a different configuration with a maximum induced twisting of 500 rpm and MOFs prototypes with structure stability at lengths of less than 50 m with a strongly induced chirality of up to 790 rpm were fabricated. The geometric patterns of these fibers are also presented in this work.
This work presents results of test series, performed for earlier on designed and successfully fabricated silica few-mode microstructured optical fibers (MOF) with six GeO2-doped cores, induced twisting 100 revolutions per meter, typical “telecommunication” outer diameter 125 μm, core diameter 8.7 μm, air hole diameter 4.6 μm, pitch 7.2 μm, and core quasi-step / graded refractive index profiles with height 0.0360/0.0275, respectively. Part I introduces attempts for splicing of typical telecommunication optical fibers and fabricated samples of MOFs by commercially available field arc fusion splicer kits and results of differential mode delay map measurements, performed for laser excited large core (multimode) optical fibers with core diameters 50 and 100 μm, jointed via free space to described above 2 m long pilot samples of 6-GeO2-core MOFs at both receiving and transmitting ends under laser-excited gaussian optical pulse launching with precision offset conditions, while Part II is concerned with researches of spectral responses, measured for fiber Bragg gratings, recorded in these MOFs.
This work presents results of test series, performed for earlier on designed and successfully fabricated twisted silica fewmode microstructured optical fibers (MOF) with six GeO2-doped cores. While Part I introduces results of differential mode delay map measurements, Part II is focused on researches of spectral responses, measured for fiber Bragg gratings, recorded in these multi-core MOFs with core graded refractive index profiles and induced twisting 100 revolutions per meter. Specially setup for spectral response measurement for described complicated fiber optic element was developed, that provides selected alignment of matching singlemode optical fiber with particular single core of MOF via free space and reducing of reflection by precision 8 angle cleaving. Comparing analysis of measured spectral responses confirmed written FBGs in 2 of 6 cores, and demonstrated potentiality of fabricated complicated structure, containing multi-core MOF with FBG, for applications in multichannel fiber optic sensors with spatial division multiplexing technique.
This work introduces first time fabricated spun silica microstructured optical fiber (MOF) with inclusion of seven GeO2-doped capillaries, placed in the central part of MOF cross-section, and induced twisting up to 730 revolutions per meter. Part I discusses technological issues for manufacturing of described complicated twisted fiber optic structure, while Part II presents some results of test series, performed for successfully manufactured twisted MOF pilot samples with typical hexagonal geometry under hole radius 4.40 μm and pitch 9.80 μm, outer “telecommunication” diameter 125 μm, and center part, formed by seven hollow GeO2-doped ring cores with inner radius 2.50 μm, pitch 8.80 μm and refractive index difference Δn=0.030. Following measurements were performed: measurements of transmission spectra under various twisting order, far-field laser beam profiles, some attempts of fusion splicing of typical telecommunication optical fibers and fabricated MOF with insertion loss estimation, and spectral response measurements of both single and group WDM (Wavelength Division Multiplexing)-channels of commercially available telecom WDM-system under inclusion of 2 m length MOF into various spans of short-range lab fiber optic link.
This work introduces first time fabricated spun silica microstructured optical fiber (MOF) with inclusion seven GeO2-doped capillaries, placed in the central part of MOF cross-section, and induced twisting. While Part I discussed technological issues for manufacturing of described complicated twisted fiber optic structure, presented some pilot samples of described MOFs with various twisting order and measured their transmission spectra, Part II describes some results of results of experimental researches, performed for successfully manufactured twisted MOF pilot samples with typical hexagonal geometry under hole radius 4.40 μm and pitch 9.80 μm, outer “telecommunication” diameter 125 μm, and center part, formed by seven hollow GeO2-doped ring cores with inner radius 2.50 μm, pitch 8.80 μm and refractive index difference Δn=0.030 with induced twisting 130, 300 and 730 revolutions per meter. Following test series were performed: measurements of far-field laser beam profiles, some attempts of fusion splicing of typical telecommunication optical fibers and fabricated MOF with insertion loss estimation, and spectral response measurements of both single and group WDM (Wavelength Division Multiplexing)-channels of commercially available telecom WDM-system under inclusion of 2 m length MOF into various spans of short-range lab fiber optic link.
This work reports the results of bandwidth measurements and tests, performed for earlier on designed and fabricated pilot lengths of new silica laser-optimized graded-index multimode fibers (LOMFs) with extremely enlarged core diameter up to 100 μm and "typical" "telecommunication" cladding diameter 125 μm. Presented optical fibers are targeted for harsh environment short-range multi-Gigabit onboard cable systems and industrial networks. Proposed LOMF 100/125 differs by specially optimized graded refractive index profile, that provides low differential mode delay (DMD) for selected guided modes. We present some results of tests, performed for fabricated pilot 520 m length of described LOMF 100/125, focused on researches of bandwidth features. They contain DMD map and transfer function measurement as well as 10GBase-LX/SX channels eye-diagram and bit-error-ratio reports with following direct detection of the maximal acceptable optical fiber length for guaranteed 10Gbps channel supporting.
This work considers the issue of creating and promoting student communities focused on attracting young people to modern scientific work and development, in particular in the field of photonics and fiber optics. The materials of the article are based on the experience of implementing the project "Student Community of Photonics and Fiber Optics" and are devoted to management issues in the context of a well-established hierarchical approach to management in classical universities. In the course of the work, tasks were set and ways to solve them were described. Particularly important aspects of the influence on the future career guidance and career aspirations of the youth groups under consideration are reflected.
This work presents some results of pulse and spectral responses, performed for laser-excited pilot sample of earlier on designed and fabricated chiral silica few-mode optical fiber (FMF) with induced twisting 66 revolutions per meter (rpm), typical (for telecommunication optical fibers) cladding diameter 125 μm, weakly increased core diameter up to 11 μm and numerical aperture NA=0.22, corresponding to improved height of quasi-step refractive index profile. Described FMF 11/125 provides propagation of 4 and 6 guided modes over “C” and “O”-bands, respectively. We present results of tests, focused on researches of few-mode effects, occurring under laser-excited optical signal propagation over pilot sample optical fiber, and their influence on pulse and spectral responses, including some measurements, performed for fiber Bragg grating, recorded in tested FMF 11/125.
This work presents method for prediction of laser-excited optical pulse additional distortions, occurring due to contamination of fiber optic connector end-face, under its propagation over short range multi-Gigabit network link with crypto-fibers – couple of special multimode optical fibers “encryptor-decoder”, operating in a few-mode regime. Results of optical pulse response envelop computations, propagating over 1 km link with 500 m crypto-fibers “encryptor” and “decoder” lengths, are compared under various conditions of 10GBase-LX transceiver laser-source fiber optic connector ferrule end-face contamination. Strong pulse splitting additional distortions due to strong ferrule contamination were noticed.
This work is concerned with some aspects of selection of graded refractive index profiles for couple combination of optical crypto-fibers “encryptor”–“decryptor”. We present some results of experimental approbation of method for differential mode delay (DMD) management by selection and recombination of two corresponding refractive index profiles, differing by technological defects in the core center. Here it is supposed, that combined fiber optic link, containing the sequence of two graded-index multimode optical fibers with strong DMD, occurring due to great technological defect of refractive index profile in the core center with a peak (or dip) in the first and, on the contrary, with a dip (or peak) in the second, provide inverting DMD diagram of selected mode components in the second optical fiber in relation to the first. Therefore, according to earlier on proposed alternative method for implementation of secure data transmission channel protected over physical layer for the "first/last mile" segment of intra-corporate network, the first optical fiber with strong unique distortions is considered as “encryptor”, while the second with inverted DMD diagram implements function of “decryptor” in the optical interface.
This work presents fast and simple method for estimation of the reflection at the connection of two singlemode optical fibers with contaminated fiber optic connector ferrule end faces via results of analysis of connector ferrule end face photo-image. Proposed solution is based on discretization of mode field distribution and following passage to representation of the mode field overlap integral in the form of finite nested sums. Proposed approach provides ability of taking into account the mode field distortions, occurring due to the optical fiber end face contaminations, by directly overlapping of connector ferrule end face image over discretized mode field radial distribution. We present some results of developed method approbation on really measured fiber optic connections between standard singlemode optical fibers with various order contaminated ferrules.
The paper presents the research results to assess the efficiency of using MIMO technique in the tasks of detection and location of nonreflecting events on traces of a group of optical fibers of a cable line. The mean values and standard deviations of the detection probability of a splice closure and also the first described efficiency parameters are calculated as evaluation criterion. Calculations are carried out for different values of cable capacity, repeater spacing and dynamic range of reflectometer. The analysis showed that the use of MIMO technique significantly increases the detection probability of a splice closure on traces of optical fibers of a cable line.
We propose and fabricate pilot lengths of two type microstructured optical fibers with chirality, induced during the drawing process under 10 and 66 revolutions per meter. The first one is microstructured fiber with geometry providing quasi-ring radial mode field distribution. So it imitates ring-core optical fiber properties by special formation of designed 2D-periodic structure. The second is fiber with hexagonal geometry and shifted core in relation to central axe. The work presents results of numerical analysis of fabricated samples, performed by rigorous numerical method. Here initial data were set via manufactured optical fiber end face images. We also reports some results of far field laser beam profile images, measured at the output of described fiber samples under laser source excitation at wavelength 1550 nm.
This work presents fast and simple method for estimation of the insertion loss at the connection of two singlemode optical fibers with contaminated fiber optic connector ferrule end faces. Proposed solution is based on the fundamental mode coupling coefficient (or e.g. transmission coefficient) evaluation via discretized mode field overlap integral. It is represented in the form of nested sums on radial mode field distributions, which are described well by Gaussian function under weakly guiding approximation or may be taken from the mode field distribution matrix, computed by rigorous numerical methods during analysis of real optical fiber samples with nonsymmetrical geometry. Proposed approach provides ability of taking into account the mode field distortions, occurring due to end face contaminations, by directly overlapping of connector ferrule end face image over discretized mode field radial distribution. We present some results of developed method approbation on really measured fiber optic connections between standard singlemode optical fibers with various order contaminated ferrules.
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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