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 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 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 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.
A high-precision symmetric optical vector analyzer (OVA) based on amplitude-phase double sideband (DSB) modulation with suppression of an optical carrier is proposed and numerically simulated. Accurate and stable frequency characteristics are achieved by the formation and minimization of such higher-order components in the probe radiation, the difference frequency of which does not coincide with the difference frequency of the two main measuring components of the first order. In comparison with the known solutions, the processing of spectral information is carried out at the modulation frequency, and not at the doubled frequency; the operating range of OVA has been increased by 2 times in terms of the bandwidth of the tested devices; instead of the standard Pound-Drever-Hall technique used to stabilize the laser wavelength with an additional modulator, the technique of controlling the amplitude and phase of the beating envelope of the main probing components is used; the relative error in the reconstruction of the frequency response of the high-Q optical structure at each point does not exceed 5×10–5. The obtained characteristics are confirmed by numerical modeling of the developed OVA when characterizing the spectral parameters of a narrow-band fiber Bragg grating. The presented method is structurally simple, does not require the use of various generators to perform its main functions and monitoring functions, and can be used to characterize both selective fiber-optic structures and high-Q optical Fabry-Perot resonators, resonators based on whispering modes, ring active and passive resonators, transparency windows of nonlinear crystals, plasmon resonances, etc.
In this paper, a two-element sensor of relative humidity of a parallel structure is proposed for consideration, which differs from the existing ones by using address fiber Bragg gratings made in SMF-28 fiber. One of the grids has a quartz shell replaced by polyimide, synthesized using a fiber coating with a full multiplicative response to temperature and deformation caused by humidity. The second grating recorded in a standard fiber and responds to temperature. It is possible to include an additional third grating with a partially etched cladding, which can be used for refract metric measurements of the amount of condensed moisture on the elements of a complete switchgear. All gratings are identical, have the same Bragg wavelength, after manipulating their claddings, but differ in a unique address, which is formed by recording two transparency windows in each of the gratings with different difference frequency space. The transparency windows correspond to phase π-shifts symmetrically located at the same distance from the center of each of the gratings. The structure obtained makes it possible to record information of the measurement conversion at the indicated difference frequencies in the radio range, which significantly increases the speed of measurements of relative humidity and their accuracy by an order of magnitude. In addition to what has been said, it is possible to note the possibility of building a network of these sensors in consecutively arranged switchgear devices, with a different radiofrequency address group being used in each of them.
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 work presents some results of experimental approbation of method for writing of cascaded precision microstructured defects, like "tapers" and "up-tapers", in various configurations and sequences in silica multimode graded index optical fibers by commercially available field fusion splicer with modified software settings. Here we utilized earlier on developed technique for micro-defect geometry parameters estimation via analysis of photo-image, performed after defect writing and displayed on fusion splicer screen, to estimate the least available distance between couples of the “up-tapers” and “tapers” without optical fiber structure deformation. Also, some results of insertion loss measurements for various configuration of 3-element cascaded microstrucured defects are presented.
This work presents an alternative method implemented in software procedure for automated localization of fiber optic connector contaminated ferrule end face image artifacts. Here the main problem is concerned with detection and removing the aureoles of core/cladding and cladding/ferrule boundaries without impact on pixels of contamination particles. We considered typical end face images measured by commercially available fiber optic video probe kit containing video microscope and software, which provides ferrule end-face quality inspection "PASS/FAIL" according to ratified standard IEC 61300-3-35 that is a global common set of quality requirements for the surface of ferrule fiber optic connectors. After removing artifacts, modified image may be utilized for the following estimation of the predicted value of insertion loss. We also present some results of proposed procedure approbation for various order contaminated ferrule end face images.
This work presents method for performing precision macro-structure defects “tapers” and “up-tapers” written in conventional silica telecommunication multimode optical fibers by commercially available field fusion splicer with modified software settings and following writing fiber Bragg gratings over or near them. We developed technique for macrodefect geometry parameters estimation via analysis of photo-image performed after defect writing and displayed on fusion splicer screen. Some research results of defect geometry dependence on fusion current and fusion time values re-set in splicer program are represented that provided ability to choose their “the best” combination. Also experimental statistical researches concerned with “taper” and “up-taper” diameter stability as well as their insertion loss values during their writing under fixed corrected splicer program parameters were performed. We developed technique for FBG writing over or near macro-structure defect. Some results of spectral response measurements produced for short-length samples of multimode optical fiber with fiber Bragg gratings written over and near macro-defects prepared by using proposed technique are presented.
This work presents results of experimental approbation of earlier on proposed modified fiber optic stress sensor based on a few-mode effects occurring during laser-excited optical signal propagation over silica multimode optical fiber (MMF). Modification is concerned with a passage to quasi-interferometric scheme realized by two multimode Y-couplers with equalized arm lengths improved by fiber Bragg grating (FBG) written on preliminary formed precision macrostructure defects in silica multimode graded-index optical fibers and special offset launching conditions providing laser-based excitation of higher-order modes. The “arms” of quasi-interferometer are two equalized lengths of MMF Cat. OM2 with great central dip of refractive index profile and strong pulse splitting due to high differential mode delay (DMD). We tested FBGs with Bragg wavelength both 1310 nm and 1550 nm written over tapers or up-tapers preliminary formed in short pieces of MMF Cat. OM2+/OM3 and further jointed to the end of one of the arms before output Y-coupler. Researches were focused on comparison analysis of pulse responses under changing of selected excited mode mixing and power diffusion processes due to stress distributed action to sensor fiber depending. Here we considered FBGs not only as particular wavelength reflector during spectral response measurement but also as local periodic microstructure defect which strongly effects on few-mode signal components mixing process also improved by combination with macro-defect like taper or up-taper that should provide response variation. Some results pulse response measurements produced for different scheme configuration and their comparison analysis are represented.
This work is concerned with fiber Bragg grating (FBG) writing technique developed for graded-index multimode optical fibers applied in measurement systems based on a few-mode effects. We present some results of experimental approbation of proposed technique with Bragg wavelength 1310 and 1550 nm on samples of graded-index multimode optical fibers 50/125 of both new-generations Cat. OM2+/OM3 and old Cat. OM2 with preliminary measured refractive index profiles. While the first group fibers of Cat. OM2+/OM3 was characterized by almost ideal smooth graded refractive index profile and some fiber profile samples of this group contains thin central peak, the second fiber group profiles of Cat. OM2 differ by great central core defects representing dip or thick peak. Results of described FBG spectral response measurements under excitation of laser pigtailed by single-mode fiber are represented.
This work presents results of experimental approbation of modified fiber optic stress sensor based on a few-mode effects
occurring during laser-excited optical signal propagation over silica multimode optical fiber (MMF). Modification is
concerned with adding of quasi-interferometric scheme realized by two multimode Y-couplers with equalized arm
lengths improved by fiber Bragg grating (FBG) and special offset launching conditions providing laser-based excitation
of higher-order modes. We tested FBGs written on graded-index MMFs 50/125 with Bragg wavelength 1550 nm connected
to different parts of proposed scheme. Researches are focused on comparing analysis of both spectral and pulse
responses under changing of selected mode mixing and power diffusion processes due to stress local and distributed action
to sensor fiber depending on scheme configuration. Here we considered FBGs not only as particular wavelength
reflector during spectral response measurement but also as local periodic microstructure defect strongly effecting few-mode
signal components mixing process that provides pulse response variation. Some results of spectral and pulse response
measurements produced for different scheme configuration and their comparison analysis are represented.
This work presents results of experimental researches of fiber Bragg gratings (FBG) operating in a few-mode regime.
We tested FBGs written on silica graded-index multimode fibers 50/125 Cat. OM2+/OM3 with Bragg wavelength 1550
nm by using them in a set of developed experimental schemes based on excitation of multimode fibers by corresponding
laser sources. The researches were focused on analysis of both spectral and pulse responses under changing of selected
mode mixing and power diffusion processes due to tension and/or stress local and distributed action to FBG or sensor
fiber. Results of spectral and pulse response measurements at the output of schemes with installed described FBGs are
represented.
This paper presents a microwave photonics method for the instantaneous frequency measurement of microwave signals,
based on the generation of a two-frequency laser radiation in the Mach-Zehnder modulator with a difference frequency
equal to the measured, and the "frequency - amplitude" conversion in the π-phase-shifted fiber Bragg grating. Frequency
measurement occurs in two ranges: 0.3 - 3 GHz in the passband of the FBG and 3 - 30 GHz in its reflection band. Using
the specific conversion of two-frequency radiation in the π-phase-shifted fiber Bragg grating allowed us to obtain measuring
characteristics, that are independent of the amplitude fluctuations of the optical carrier and to organize additional
circuit for monitoring the spectral characteristics of the used elements to reduce measurement inaccuracy caused by their
temperature instability.
This paper presents a new two-frequency method for the instantaneous frequency and amplitude measurement of unknown microwave signal. Using the specific interaction of two-frequency radiation with fiber Bragg grating (FBG) in first version and FBG with phase π-shift in second allowed us to obtain measuring characteristics, that are independent of the energy fluctuations of the optical carrier and the microwave signal. Frequency measurement occurs in two ranges: 3-30 GHz in FBG reflection band, and in second version 0,3-3 GHz in the FBG pass band. Additional circuit for spectral characteristics monitoring of the used elements are organized to reduce measurement inaccuracy caused by their temperature instability.
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