This work reports comparative results of mode analysis, performed for earlier on designed silica microstructured optical fiber with ideal equiangular spiral six-ray geometry (ESSR-MOF) and for its real fabricated sample, differing from the model by weak asymmetry and deformed air holes. We discuss issues of input data preparation to specify analyzed complicated non-ideal fiber optic structure for computation by using rigorous finite-element method. Some results of the comparison between mode field patterns as well as guided mode effective refractive index spectral characteristics are represented. It is demonstrated, that potential deviations from the desired MOF geometry, occurring due to features of silica MOF fabrication technological process, should be taken into account during the design to predict real values of mode parameters for manufactured MOF.
The paper presents the study of a phase-sensitive reflectometer's potential for recording acoustic emission signals from the early stages of optical fiber defect growth. The methods of registering acoustic emissions and two possible ways of forming defects in the optical fiber are described. As a result, it is demonstrated that pulsed acoustic emissions can be recorded during the process of defect formation on the optical fiber surface.
The article presents the results of an experimental study of the possibility of application a phase-sensitive reflectometer to register nonlinear acoustic emissions during the formation of defects in optical fibers. The method for control of nonlinear acoustic emission parameters in optical fibers was proposed and the peculiarities of using a phase-sensitive optical reflectometer was considered.
The paper presents a method of underground dielectric optical fiber cable route tracing using a distributed acoustic sensing based on phase-sensitive optical reflectometer. The results of field tests are presented, demonstrating the performance of the method and the ability to determine the location of the cable route with an accuracy of ± 0.2 meters.
The study explores the potential applications of fiber optic sensors for user verification tasks. An experimental validation of the considered methods for recognizing speech signals obtained from acoustic sensors is conducted. In the experiment, voices of four different speakers were recorded. Each speaker sequentially uttered the same text simultaneously using a capacitor microphone and a fiber optic distributed sensor. To create the dataset, each speaker read three prepared texts. After training the system on the dataset and achieving speech signal recognition with sufficiently high accuracy recorded from the capacitor microphone, attention was turned to addressing the challenge of noise elimination. For this purpose, background noise was separately recorded at the experimental site. The conclusion is drawn regarding the applicability of mel-frequency cepstral coefficients for solving the task of identifying individuals based on the sound signal obtained from the fiber optic sensor with a specified accuracy.
The experimental study of attenuation distribution changes of optical fiber in cable due cyclic temperature variations is represented in paper. It was observed that attenuation coefficient changes due temperature effect varies in irregular manner, that can be caused by redistribution of fiber curvature along cable. The fiber segments corresponding to the outer cable coils on the drum are most affected by temperature cycling, that can be due high thermal inertia of cable drum. The length of fiber segment with noticeable attenuation rising is approximately 500 m. The irregular local attenuation changes demonstrate the optical fiber curvature redistribution in cable due cyclic temperature variation and also can be used for estimation of variation of mechanical stresses.
During maintenance of fiber optical communication lines the cyclic seasonal temperature variations can cause movement of optical fibers in loose tubes and redistribution of curvature. This is especially true for aerial suspended optical cables there significant “pushing out” of fiber from tubes in optical closures can be observed after years. In previous papers two methods for estimation of optical fiber curvature distribution based on reflectometric measurement on two wavelength and using polarization reflectometry were proposed. The results of estimation of optical fiber curvature distribution in all-dielectric self-supporting cable during cyclic temperature variation in climatic chamber are represented in paper.
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 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 study aimed to investigate the potential application of distributed fiber-optic acoustic sensors for speech recognition amidst complex audio backgrounds. The experimental measurements were carried out on the mock-up room with a fiberoptic link. The possibility of application the fiber-optic distributed acoustic sensor for localization of sound source and recognition of musical and human speech signals amidst complex audio backgrounds was demonstrated. The signal detected by DAS provides good quality of music composition recognition and clear speech recognition. The difference in spectrum of signals detected by microphone and DAS was analyzed. The signal noise ratios were calculated for test speech signal with different average levels and its influence on the speech recognition was analyzed.
The article discusses the use of Distributed Acoustic Sensing technology in locating underground all-dielectric optic cables. DAS uses fiber optic cables to detect acoustic vibrations along the cable's length caused by digging or drilling, allowing for precise identification of the cable's location and path without excavation or other intrusive search methods. DAS provides high-resolution data over long distances, making it more accurate than traditional search methods like geo-radar or GPS markers. The article proposes a localization algorithm for detecting the path of all-dielectric optical cables using DAS technology, based on a combination of approximate and point estimates of cable location. The algorithm is tested on a testing ground of a section of an optical communication line, demonstrating the ability to determine the area of optical cable laying with a radius of up to 5 meters in real-time.
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.
The methods for estimation of optical fiber curvature distribution based on reflectometric measurement on two wavelength and using polarization reflectometry were proposed. The method for estimation of correction coefficients for bend-insensitive optical fibers for was represented. The approbation of methods on test setup of a fiber-optic communication line including segments with different bending radii was performed.
The testing ground based on the different technologies of optical cable installation is described in paper. The testing ground consist from communication lines based on microduct system and using direct underground installation. The comparison of different methods for cable trace location was performed. The experimental approbation of electromagnetic induction method, ground penetrating radar method and acoustic method was carried out on the testing ground.
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.
The paper proposes a method for localizing the location of an optical cable based on the analysis of the characteristics of a phase-sensitive reflectometer under external acoustic impact. Approbation of the methodology was carried out using a vibroacoustic monitoring system at a test site built on the territory of the university. The results of measurements of the intensity distribution of the acoustic impact along the length of the optical fiber depending on the location of the impact source are presented. The specific features of the method based on the analysis of amplitude characteristics are determined.
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.
The article proposes a method for non-destructive testing of optical fiber strength based on estimates of the energy of nonlinear acoustic emission and the tested optical fiber as an acoustic sensor with phase modulation of the optical carrier. Models of the processes on which the method is based are presented. The results of experimental studies are presented. The data obtained from the results of testing the fiber samples using the proposed method were compared with the results of the same samples' measurements by the known 2-point method. The error in relative estimates of the strength of the tested fiber samples did not exceed 3.0%. This allows us to speak about the correctness of the models used and the potential possibility of using the proposed method for non-destructive testing of the strength of optical fibers, as well as the prospects for the development of the application of the considered approach for measuring optical fibers strength in cable.
In this paper the polarization state analyzer/generator based on the three-stage polarization controller is developed. The method for determination of input state of polarization based on Muller matrix formalism is proposed. The operation algorithm for regime of generation an arbitrary state of polarization is proposed.
The results of theoretical and experimental study of the vibration sensor based on the few-mode optical fiber are represented in paper. The mode composition of telecommunication single mode fiber working in few-mode regime was obtained by theoretical calculation and experimentally approved. The detection of acoustic influence on few-mode optical fiber was demonstrated and impact of relative mode excitation and state of polarization was registered.
In this paper the method for interrogation of Brillouin scattering signal from sensing fiber is proposed. The essence of the method consists in the application of the single pump source to generate reference signal due stimulated Brillouin scattering in thermally stabilized reference fiber spool and for probing the sensor fiber. As result of heterodynes in receiver the signal at beat frequencies is analyzed. The requirements for pump power and reference fiber parameters are defined theoretically and experimentally. The results of experimental estimation of beat signal are represented.
In this paper computer simulation and experimental investigation of the vibration influence on the single-mode optical fiber polarization characteristics was carried out. Measurements were made using a standard optical reflectometer and an external module providing sensitivity to polarization. Based on the obtained data, a measurement algorithm with polarization controller was determined and the method for analyzing the polarization reflectograms was proposed. The possibility of detection and localization of multiple fiber segments under vibration action was demonstrated.
In this paper the analysis of exceed fiber length distribution in loose tube cable and its relation with mechanical stress was carried out. The polarization reflectometry method for estimation of exceed fiber length distribution along cable during manufacturing and maintenance was proposed. The method of measurement local birefringence using polarization optical time domain reflectometer with three stage polarization controller was proposed. Results of computer stimulation are represented.
In this paper the polarization characteristic are investigated. The mathematical model was developed and computer simulation was carried out. The results of experimental investigation of the Brillouin backscattered light are represented. Measurements were made using polarization analyzer based on three stage polarization controller. The measurement algorithm represented.
We present results of experimental research and comparison of differential mode delay (DMD) maps measured for silica graded index multimode optical fibers (MMFs) with strong and weak diameter variation. Preliminary for two synthesized by MCVD fiber preforms were selected by criterion of expected strong DMD due to great profile dip in the core center. Then two lengths of MFMs were drawn. The first one was manufactured according typical operations with automatic control of technological processes, while the second one was drawn under manual maintenance. Therefore two samples of MMFs of ISO/IEC Cat. OM2 with length about 1 km were manufactured with diameter variation ± 0.3 μm and ± 1.2 μm respectively. At the next stage we performed DMD map measurement of described two MMF 50/125 samples by DMD analyzer lab kit R2D2 according to ratified standards TIA-455-220-A/FOTP-220 and IEC 60793-2-10 to research and analyze influence of fiber diameter variation on mode coupling in the form of additional DMD distortions during laser-excited optical pulse propagation over MMF under a few-mode regime.
In this paper, the signal propagation is described by a generalized nonlinear Schrodinger equation take into account linear and nonlinear mode coupling. A modified solution based on split-step Fourier method is considered. The method for simulation of mode coupling coefficients based on statistical characteristics is proposed. Results of bit error rate estimations for space division multiplexing signal propagation in few mode fiber communication line for weak and strong coupling regime are represented.
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.
The paper discusses options for using semiconductor optical amplifiers in the radio-over-fiber systems. The theoretical evaluation of the optical parameters of the amplifier, modulator and detector implemented on the basis of the semiconductor optical amplifier, as well as estimates of the parameters of the device using a semiconductor optical amplifier as a multifunctional optical device power modulator detector.
In this paper an application of Raman reflectometry for distributed temperature measurement on overhead power lines was represented. The modification of standard remote fiber test system scheme and requirements to software was proposed. The results of experimental measurements at fiber optical test set and signal processing algorithm was represented.
This work continues the series of publications devoted to theoretical researches of silica graded-index few-mode optical
fibers with eliminated nonlinearity due to much extended mode effective area by considerably increased core diameter.
We utilized an earlier on developed modified Gaussian approximation generalized for arbitrary order guided mode in
silica optical fiber with arbitrary axially symmetric graded refractive index profile bounded by single solid outer cladding
to calculate researched fiber guided mode staff parameters. Here we present results of chromatic dispersion computation
of higher-order guided modes propagating over large core 6-mode optical fibers with special refractive index profiles
providing low differential mode delay that were synthesized in recent papers.
The analysis of semiconductor optical amplifier applications in Radio-over-Fiber systems of telecommunication
networks is given. In such systems semiconductor optical amplifier can be used for either amplification, modulation or
detection, and also as an universal device.
The distributed control of temperature is an actual task for various application such as oil & gas fields, high-voltage power lines, fire alarm systems etc. The most perspective are optical fiber distributed temperature sensors (DTS). They have advantages on accuracy, resolution and range, but have a high cost. Nevertheless, for some application the accuracy of measurement and localization aren't so important as cost. The results of an experimental study of low-cost Raman based DTS based on standard OTDR are represented.
The investigation of polarization reflectometry sensitivity to detection and localization of new events in fiber optical lines is carried out. The results of numerical simulation and experimental measurements are represented. The estimation of localization accuracy for different events depending on polarization characteristic is represented. The algorithm of data processing and method for measurement using polarization controller are represented.
In this paper the potentiality of nonlinear effects mitigation by increasing of optical fiber core diameter was investigated. The numerical simulation of return to zero differential quadrature phase shift keying optical signals propagation taking into account nonlinear effects was performed. As result the Q-factor dependence from effective mode diameter was obtained for different signal parameters. The results of optical fiber synthesis with given parameters are represented.
This paper is concerned with the applications of polarization reflectometry for identification and localization of defects
of various types in the fiber optical lines. The methods of physical simulations of various defects in optical fibers are
described. The methods and algorithms for polarization optical time domain reflectometer (POTDR) data processing are
represented. The results of laboratory and field tests are represented.
In this paper application of dispersion managed soliton in Radio-over-Fiber system was investigated. The realization of
dispersion management by inserting dispersion compensation fiber spools in optical cable closures was proposed. Numerical
simulation of RoF signal propagation in soliton regime based on system of Nonlinear Schrodinger equations was
carried out. The performance of RoF system for different parameters of dispersion map was estimated by means of eye-diagram
and Q-factor.
In this paper the principles of polarization optical time domain reflectometry and features of developed POTDR
prototype model are described. The approbation of methods for analysis of POTDR trace on experimental setup was
carried out. The results of field inspection of fiber optical communication lines including measurements of chromatic
dispersion and polarization mode dispersion are represented. Specificities of localization of fiber section with high level
of polarization mode dispersion using PODTR are noted.
A well-known dense dispersion management soliton (DDMS) technique is applied to increase bandwidth of metropolitan
area network fiber optic links. This technique requires an installation of optical cables with dispersion compensating
fibers (DCFs), which leads to high costs for upgrading of installed fiber optic links. To become the DDMS more
applicable, we propose to place DCFs in optical fiber closures. Here results of numerical simulations of optical pulse
propagation and following bit-error-ratio estimation in fiber optic link with DCFs in optical closures are represented.
There is no doubt that dispersion management soliton systems (DDMS) are the most applicable for the short-haul
transport. However on practice it is unbelievable to realize an ideal coincidence between projected and installed lengths
of dispersion map fibers, which can be explained, for example, by business problems or an optical closure placement.
Here we present results of numerical simulations of optical pulse propagation and following bit-error-ratio estimation in
a dense dispersion manage optical link with non-perfect dispersion maps.
In this paper influence of DDMS dispersion segment deviations from nominal values on system performance was
investigated. The model of dispersion managed soliton propagation based on variatonal approach was used. The results
of statistical simulation of soliton-like pulse propagation in optical communication lines with different dispersion maps
and taking into account deviation of dispersion map parameters are represented.
In this paper method and equipment for estimation of polarization mode dispersion distribution along optical
communication lines are represented. The polarization optical time domain reflectometer with linear extension of pulse
width is described. The measurement algorithm and data processing algorithm are shown. The prototype model of
PODTR was developed.
In this paper cross-phase modulation in mutichannel dispersion managed soliton systems was investigated. Method for
evolution of main optical soliton parameters for two-channel WDM systems based on variatonal approach was proposed.
Results of soliton propagation simulation in communication lines with different dispersion maps are represented and
comparison with numerical method was carried out.
In this paper experimental research results on ability of localization high-birefringence sections using POTDR based on
standard OTDR are presented. Different method of POTDR reflectograms analysis are compared and conclusions about
criterion of application was made. Algorithm of POTDR traces processing for localization was developed.
In this paper four wave mixing effect in fiber optical communication line with Raman amplifiers is analyzed. Method
and expression for calculation of efficiently interacting channels are presented. Developed model for calculation FWM
power taking into account distributed Raman amplification. An analytical solution for FWM noise allows reducing time
expenses at simulations. Results of calculation FWM noise for different parameters of optical line, WDM system and
Raman amplifier gain are presented.
In this paper noise performance of Raman amplifiers is analyzed. Efficient model and methods for calculation of noises
impact in Raman amplifier of various designs (forward, backward and bidirectional pump schemes) are presented.
Developed models are taking into account features of not uniform amplifier span and cascaded amplifier spans. An
analytical solution for ASE noise allows to reduce time expenses at simulations. Analytical and simplified expressions
for DRB noise can be used to investigate qualitative dependence from different factors. Area of application developed
models was defined as distributed Raman amplifier with standard single mode fiber.
In this paper features of broad-band Raman amplifier design and simulation was considered. Numerical and analytic approaches for Raman amplifier simulation was represented. Such effects as pump-to-pump interaction, signal-to-signal interaction, pump depletion was taking into account. Raman amplifier model take into account any pump direction and arbitrary number of pump sources. Simulation of WDM signal propagation in optical fiber line take into account dispersion, nonlinear effects, and also influence ofdistributed Raman amplification.
This paper describes a methods of simulation of fiber optical communication line with Raman amplifiers. Proposed method allow to consider impact of nonlinear effects, dispersion effects, noise from double Rayleigh backscattering (DRB) and amplified spontaneous emission (ASE). In paper scheme with forward pump Raman amplifier was analyzed and different types of fiber was used for simulation. Single and multichannel system was simulated. Estimation of transmission system performance was made by Q-factor.
The fiber-optical cable installation on aerial high-voltage power lines is widely spread on the territory of Russia and has a huge perspective for development. Designing aerial fiber-optical communication lines there are some problems at choosing of suspension method and fiber-optical cable type. The calculation of aerial fiber-optical cable mechanical characteristics is most actual problem. The calculation should be made due to mechanical parameters of cable and electrical line towers. During service life aerial fiber-optic cable is subject to external influences under different environment conditions: temperature drops, wind pressure, ice loads. For constructing of reliable aerial fiber-optic communication line all those factors must be taken into account. For optical cable installation on towers should be calculated essential value of cable mounting sag and tension.
During realization of plan-prophylactic operations on fiber- optical transmission line (FOTL) at reflectometric measurements, with small duration of outgoing pulse, in a number of optical fiber fusion splicers the inhomogeneities as signals of return reflection were detected by one of the telecommunication operators in Volga region. In paper the results of a research the detected inhomogeneities with the help of full-scale measurements carried out during 1999 - 2000(Gamma) (Gamma) are given. The reasons, which could lead to appearance of return reflection signals on fusion splices, are analyzed, the recommendations on detection such fusion splices are made and the work package preventing appearance of fusion splices with reflections at a stage of FOTL building is offered.
KEYWORDS: Optical fibers, Signal attenuation, Signal to noise ratio, Fiber optic communications, Wavelength division multiplexing, Systems modeling, Optical simulations, Signal processing, Optical amplifiers, Telecommunications
A modeling approach for the simulation of fiber optic communication links is proposed. Simulation model of various signal processing operations and physical noise process is introduced. Influence of link irregularities of different types and orders on transmitted signals is shown. Results of proposed model approaching are compared with known simulation algorithms of modeling fiber optic communication systems.
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