This PDF file contains the front matter associated with SPIE Proceedings Volume OTT410, including the Title Page, Copyright information, Table of Contents and Conference Committee list and an in memoriam to Vladimir A. Burdin.

6G mobile networks will support a wide range of services with different technical requirements and in different frequency bands. To achieve this goal, the use of radio-over-fiber (RoF) technology together with optical space division multiplexing (SDM) technology is an important basis for creating both a transport architecture and a hybrid radio-optical centralized architecture or cloud radio access network (C-RAN) 6G fronthaul. At the same time, the 6G signals processing technologies and the modulation schemes must meet the stringent requirements for a mobile data transmission network. The paper presents a study and simulation results of the process of signal conversion and retransmission with a promising data processing technology – DFT-s-OFDM with rotated QAM modulation over a fiber-optic line using RoF technology; a numerical estimation of PAPR level is also given.

In line with ETSI's vision, the Fifth Generation Fixed Network F5G can be characterized as enhanced fixed broadband eFBB, full-fiber connection FFC and guaranteed reliable experience GRE. To determine the ways to implement the FFC concept, it is necessary to know the current state and possible options for the development of the national fiber-optic infrastructure. The Fiber Development Index (FDI) is critical to measure the evolution of countries towards Fiber to the Everywhere and Everything (FTTE) in F5G network. The FDI aims to combine selected indicators into a single benchmark. The FDI provides a comprehensive way to measure the evolution of fiber optic links in access, backhaul and core networks, guiding the evolution towards FTTE and F5G networks. The FDI can be used to identify priority investment areas and the national fiber deployment strategy in each network cluster. The article provides an analysis of ETSI research materials on the implementation of the FTTE concept during the transition to F5G networks and an assessment of the FDI value of the current state of the national fiber-optic infrastructure.

This paper describes the OLT virtualization technology in 5G networks. New services, the rapid development of Internet of Things technology and next generation mobile 5G networks are leading to a huge increase of Internet traffic, which requires higher optical network bandwidth and reliability. This means that future optical transport network and access solutions must provide flexible bandwidth for dynamic services through intelligent management. At the same time, optical networks still face difficulties in service deployment and expansion. The main issue is to ensure guaranteed performance, including routing protocols, convergence and route calculation time, path discovery time, reliability and resource utilization. Current solutions for operating and maintaining optical networks is not aligned with growing customer demands. For these reasons, optical virtualization is a promising technology to meet a given set of network requirements while providing the necessary isolation between network segments. The prospective solution in the field of virtualization on 5G networks is the technology of vOLT. The application of vOLT in 5G networks offers several advantages. This paper presents the concept of OLT virtualization in 5G networks and its application in optical networks and transport and access solutions. The paper describes the implementation of vOLT technology, its advantages and existing problems.

At present, fiber-optic communication lines (FOCL) are widely used to transmit information [1]. On their basis, both long (trunk) lines and zonal, metropolitan, intra-object networks are built. Video surveillance, data collection and transmission with high speed require connection to a single (usually fiber-optic) network in a continuous data exchange mode to work in hard industrial production conditions, at oil facilities, to solve the tasks of the "smart city" system, as well as in numerous special applications. However, in many cases it turns out to be either impossible or economically unprofitable to create wired branches to large terminal consumers of information. Therefore, not all objects have the possibility of direct connection to fiber-optic communication lines. The solution to this problem consists in the development and use of methods for interfacing fiber-optic and wireless communication lines using microwave photonics technologies. In particular, it is possible to transfer the spectrum of the information signal to the carrier frequency in the microwave range using optical heterodyning methods. In this way, it is possible to convert modulated optical signals transmitted through optical fiber into modulated radio signals, bypassing the intermediate stages of demodulation and modulation. This leads to a simplification of the communication channel transmitter and a reduction in the distortion of transmitted information related to additional signal conversions.

This article describes a new approach for the estimation of the direction or of the microwave signal reflected from the object, based on radio photonics technologies. The angle of arrival measurement device has the same structure as the classical fiber-optic communication channel and consists of a laser, a block of electro-optical modulators and a photodetector. The block of electro-optical modulators, in contrast to the known solutions based on a two-port Mach- Zehnder amplitude modulator, is based on two parallel subunits, consisting of tandem single-port amplitude and phase modulators (TAPM). A microwave signal reflected from the object with a time delay, the value of which is determined by the AOA, is sequentially received at the radio frequency inputs of two TAPMs through the receiving antennas connected to them. In this case, the initial components of the laser carrier at the output of the TAPM subunits of both channels are completely suppressed, which significantly distinguishes the proposed solution from the known ones for the better in terms of increasing the measurement accuracy. The beats of the output signals of the TAPMs at the output of the photodetector represent a signal reflected from the object, according to the power of which the AOA can be determined.

The article presents further development of radiophotonic sensor systems based on the usage of the addressed (AFBS) and multi-addressed fiber Bragg structures (MAFBS) as sensing elements. Addressed fiber Bragg structure is an emerging type of fiber Bragg grating, which has a spectral response with two or more narrow notches. The presented system comprises two optical filters with linear inclined frequency response, which are used simultaneously to determine the central wavelengths of the AFBSs or MAFBSs. This feature enhances the operating temperature range of the system and allows to simplify its implementation, since the necessity of temperature isolation of the optical filters is eliminated. The algorithm and the mathematical model for the thermal drift compensation of the optical filters are introduced, and their realization is discussed.

We theoretically show how, using a cylindrical lens, a Gaussian beam with a finite number of parallel zero-intensity lines (edge dislocations) is transformed into a vortex beam that carries orbital angular momentum (OAM) and topological charge (TC). Remarkably, while the original beam is assumed to carry a non-zero OAM and have no TC, the latter is shown to appear during free-space propagation. Considering two parallel center-symmetric zero-intensity lines located as an example, we look into the dynamics of generating two intensity nulls at the double focal length: with increasing distance between the vertical zerointensity lines, two optical vortices are first generated on the horizontal axis, before converging at the origin and then diverging along the vertical axis. Irrespective of the between-line distance, such an optical vortex has TC = –2 at any distance from the optical axis, except for the original plane. With changing distance between the zero-intensity lines, the OAM that the beam carries is changing, taking positive and negative values, or a zero value at a certain between-line distance. We also show that if the number of zero-intensity lines is infinite, a vortex beam with finite OAM and infinite TC is generated.

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 article describes a new method for the Doppler frequency shift (DFS) measurement of a radar microwave signal reflected from a moving object, based on radio photonics technologies. The DFS measurement device has the same structure as the sequential radiophotonic link with filtration and consists of a laser, a block of electro-optical modulators, a fiber Bragg grating (FBG), and a photodetector. The block of electro-optical modulators, in contrast to the known solutions based on a two-port Mach-Zehnder amplitude modulator, is based on two subunits, consisting of connected tandem single-port amplitude and phase modulators (TAPM). The general structure of the TAPM subunits is parallelserial. The microwave signal reflected from the object arrives at the first TAPM, which forms the measurement channel. The second and third TAPMs, connected in series, form a reference channel connected in parallel to the measurement one. The second TAPM receives a reference signal from the locator transmitter at the probing microwave frequency, after which the two-frequency radiation, spaced by twice of the probing frequency, is fed to the third TAPM, which generates from each component of the two-frequency radiation two more with a difference frequency equal to twice the maximum possible DFS. The beats of signals from the measurement and reference channels at the output of the photodetector are three high-frequency (GHz) or low-frequency (MHz) electrical signals, the frequencies and powers of which used for the DFS determination.

The diffraction of Laguerre-super-Gaussian (1,0) modes with circular polarization by sub-wavelength silicon optical micro-axicons with relief height change has been studied in this paper. The height of the all relief of the microelements was varied and only the central part. Modeling by the finite difference time domain method showed that, depending on the height of the element, it is possible to form the required size of the focal segment. It was also shown that by adjusting the height of the central part of the axicon relief, the size of the focal spot can be reduced from 0.51λ to 0.24λ.

3D models of piezoelectric and optical elements which assembled from microstructures of a certain geometry were developed. These models were prepared for printing on a 3D printer, considering the specifics of their geometry and the small size of each of the cells. After several printing attempts, designed prototypes were obtained using SLA technology with synthesized plastics. These prototypes were investigated for the presence of defects and the quality of the resulting elements (preservation of the necessary microcell structures). An analysis was carried out and a technology for printing elements of this type on a 3D printer was obtained. These designs can be used in practice as piezoelectric or piezoacoustic elements when a piezoelectric powder is added to a polymer, for example, in ultrasonic flowmeters, or used to create optical structures, for example, diffractive optical elements. They will have properties different from the properties of elements obtained by standard methods, due to using of microcells with a certain geometry in their constructions.

The work is devoted to the problem of three-dimensional models of flow profiles in the hydrodynamic system’s channels restorating. A multichannel ultrasonic flow meter based on the time-pulse method was developed and investigated for measuring velocity and visualizing of liquid and gas flows structures. The device determines the downstream and upstream time of an ultrasonic pulse flight in three channels and converts it into flow velocity and then into volumetric flow. A technology that allows to synchronize parallel tasks is used to organize the stable operation of the microcontroller. The main problems of technology implementation were the large amount of memory occupied and the low "transparency" of processes. The problems of the memory optimization and minimizing of power consumption was solved.

This report theoretically and numerically investigates the properties of autofocusing of chip beams based on a more accurate analytical model. It is shown that the refinement of the model made it possible to obtain a caustic of the second type. At the same time, caustics of the first and second types "do not intersect": in two-parameter beams, they are formed in different ranges of values of the exponent; and in three-parameter ones they are formed in the same range, but they are spatially separated.

The specific characteristics and regularities of the formation of nanostructured arrays of ZnO nanowires on a conductive copper-zinc alloy substrate were determined. Pulsed-periodic CO₂ laser irradiation led to the vibration of the treated samples, which was only a condition for the intensification of nanowires growth during laser heating. The laser irradiation resulted in an increase in temperature in the central region and during this process the arrays of ZnO nanobjects were formed with greater intensity in the central part of the sample than at the periphery. Surface dezincification and a selective oxidation process may represent a new approach in the production of nanomaterials with customizable and controllable electrical and optical properties. In this case, a layer of copper oxide (I) is formed on the surface of the material from which zinc oxide nanowires are emerging. High air humidity, in which an additional hydratogenic layer is formed on the surface of the brass, also contributes to a change in the mechanism of oxide structures formation. Measurements of electrical resistance of the created samples was established that the specific electrical resistance was by 30–40 % greater in the central area of the sample than at the periphery, and it reached 700 Ω × cm. The oxygen adsorbed in the sample increased the electrical resistivity by 70 % up to the value of 1200 Ω × cm. Such arrays can be used to create a periodic localized electric field when a direct current is applied. In turn, this provides the opportunity to produce electrically switchable diffraction gratings with a varying character of zones.

In this research, a plasmonic lens with a concentric relief in thin metal film was numerically studied by the (FD)2TD method. Parameters of the plasmonic lens were optimized. It is shown that the silver plasmonic lens operates better than gold one and focuses laser light with wavelength of 633 nm into a spot with full width at half maximum of 0.38λ and maximum intensity of 4.04 a.u. It is shown that silver plasmonic lens could focus cylindrical vector beams, forming several peaks on the circle.

For refractive index (RI) sensing, a unique cavity design of racetrack combined circular cavity (CC) constructed on metaldielectric- metal waveguide (W/G) is proposed. The best sensing performance can be achieved by using an optimized cavity design. We used the finite element method (FEM) to numerically assess the device design in this paper. Small changes in the device’s geometric parameter might cause a considerable shift in the device’s sensitivity (S) and figure of merit (F.O.M). The predicted device’s S and F.O.M are 1400 nm/R.I.U and 12.01, respectively. We believe that the sensing device described in this research can be used to recognize biological analytes on-chip.

In this paper we present a brief analysis of existing materials and structures with quadratic-nonlinear optical properties that can be used to generate a difference frequency in both THz and sub-THz frequency ranges. This task is actual for future hybrid radio-over-fiber systems exploiting ultra high frequencies (6G etc.). It is shown that such a device may be of interest regarding the problems of generating (preparation) quantum-entangled states of photons, which can find application in high-performance computing and information systems. It is shown that the proposed concept of nonlinear optical-to-radio converter can be applied for entangled photons preparation as well.

The article considers typical problems of determining the Doppler frequency shift (DFS) and its sign in continuous-wave radars using microwave photonic technologies in single target tracking mode. The structure of the hardware-software spectrum analyzer and variants of its software for solving the above problems are proposed. The analyzer is functionally universal, however, its main purpose is to solve the problems of determining the magnitude and sign of the DFS when using a microwave photonic device based on tandem single-port amplitude and phase modulators in the radar receiver. For the single-target continuous radar tracking mode, a hardware linear filter method with an oblique frequency response and analysis of pairwise beating frequencies is proposed. The absolute error in determining the DFS by the frequency of information signals depends on the error of beating frequencies (units of Hz).

The article considers typical problems of determining the Doppler frequency shift (DFS) and its sign in continuous-wave or pulse radars using microwave photonic technologies in multi-target tracking mode. The structure of the hardware-software spectrum analyzer and variants of its software for solving the above problems are proposed. The analyzer is functionally universal, however, its main purpose is to solve the problems of determining the magnitude and sign of the DFS when using a microwave photonic device based on tandem single-port amplitude and phase modulators in the radar receiver. For multi-target tracking, software of receiver is supplemented by an FFT with further analysis of all received components by scanning with an ultra-narrow band filter. The absolute error in determining the DFS from the frequency of information signals depends on the bandwidth of the software ultra-narrow band filter (units of Hz). The relative error in determining the amplitudes of information signals does not exceed ~10^–3 in almost the entire range of amplitudes of the hardware high quality linear filter at the output of receiver. The ratio D of the obtained amplitudes for a pair of associated DFS information frequencies for one specific target allows you to determine its sign: if D < 1, the target is removed, if D >1 , the target is approaching. Using a method similar to the method for multi-target tracking of a continuous wave radar, typical problems of determining the DFS and its sign in pulse radars can be solved.

Currently, the process of introducing photonics into traditional radio frequency systems is in progress. As a result, a new direction has emerged in the field of telecommunications – microwave optoelectronics. Contrasted with standard microwave oscillators, the optoelectronic oscillator (OEO) has a number of advantages. Overcoming the compromise between the frequency tuning band of generation and the level of FM noise is the main one. Another advantage is that the upper limit of the OEO generation frequency is about 110 GHz, which is difficult to realize in the case of integrated transistor microwave generators. This limit in the OEO is caused by the bandwidth of an electrooptical modulator based on a lithium niobate crystal (LiNbO3). At present, the stationary mode of operation of OEO is well studied, but little attention is paid to the study of the process of its self-excitation. Therefore, the purpose of this work is a mathematical description of the process of self-excitation of an optoelectronic autogenerator.

The paper describes the problems of constructing optical branch analyzers. On the example of existing solutions (single-frequency scanning and microwave photonic methods), it is shown that these solutions have a number of limitations, which can be largely removed by a new approach to the construction of probing radiation. A description of the mathematical apparatus for restoring the contour characteristics is presented. A quantitative assessment of the dynamic and nonlinear characteristics of the probing radiation former are given.

We describe iteration algorithm for multidimensional television signals superposition of optical triangulation sensor for speckle reducing, which distorts the measurements of object counter. The object of research is the drill-pipe thread. The measurements of such objects are very sensitive to the speckle. The estimation error can be about 0.20 mm and higher. But value of tolerance is about 0.05 мм. The developed method for speckle reducing includes the preliminary stage of superposition of two multidimensional signals. The location of speckle on signals is different. The different location is defined by object offset relatively the laser of optical triangulation sensor. The multidimensional television signals superposition allows estimating the location of the speckle noise on images. Removing of the image region with the speckle noise reduces the error of object contour estimation. In issue of television signals processing the one of important problem has been distortion of multidimensional signals. It connects with distortion of triangulation sensor optical elements. The method of superposition on background of optical distortions and speckle noise is described in this article.

We describe the iteration algorithm for multidimensional signals superposition of optical triangulation sensor. The multidimensional signals link by transformation. This transformation includes offsets, scale, and rotation. The processing of multidimensional signals has characterized some features, which make superposition difficult. This is an irregular sampling step and no matching between points of processing signals. We developed the algorithm on-base iteration procedure for this issue. The procedure includes the offsets estimation in the Cartesian system, and it includes the scale and rotates in the log-polar coordinate system. The numerical simulation allows the estimate of superposition parameters error. The simulation shows that superposition parameters error of developed algorithm likes error by brute force algorithm, but the developed algorithm is faster. The developed algorithm can use in a system that works in real-time.

We describe the algorithm of multidimensional signals superposition for improving quality images of a multicamera video surveillance system. The quality of images is defined by the resolution of a video surveillance system. The multicamera video system includes the camera with low resolution for surveying in all fields of view and includes the camera with high resolution for recognizing small objects in a video frame. The possibility of switching between the cameras can be provided by the homography superposition of multidimensional television signals. The developed algorithm of the homography superposition includes two stages of processing. The first stage is rough superposition by the feature points. The second stage is accurate superposition by the modified Lucas-Kanade algorithm. The feature of the first stage is longtime of processing. The reason for this is the huge amount of possible variants of superposition. The reduction of processing time is provided by a procedure of removing wrong variants of matching points. The developed algorithm has been tested on real multidimensional television signals and the result of superposition was satisfactory.

Recently, data mining and neural networks are increasingly used for wavefront recognition from interferograms. In this case, there is considerable freedom in choosing the structure of the reference beam. In this work, a comparative study of the effectiveness of using neural networks for solving the problem of recognizing wavefront aberrations based on linear (flat reference beam) and conical (conical reference wavefront) interferograms is carried out. The effectiveness of recognition of types and levels of aberrations by conical interferograms based on the use of neural networks is shown: the average absolute error is reduced by 3 times, compared with linear interferograms. This effect is related to the rotational invariance of the introduced aberrations.

It is known that the astigmatic transformation is used to analyze the topological charge of a vortex beam. In this paper, to implement astigmatic transformations of vortex beams, a multichannel filter is used, which is matched to various aberrations described by Zernike polynomials. Such a filter allows several wave aberrations of various types and levels to be introduced into the analyzed vortex beam at once in order to implement various aberrational transformations, including astigmatism. In this case, a set of aberration-transformed distributions of the analyzed vortex beam is formed in the focal plane in different diffraction orders, which facilitates the determination of the vortex topological charge.

Synthetic Aperture Radar (SAR) interferometry is an active remote sensing technology that uses microwaves to characterize the earth's surface. SAR interferometry allows to measure the 3D profile of the earth's surface, recover surface topography, and determine topographic displacements over time. The microwave SAR signal is usually highly distorted. Distortions can be caused by, for example, atmospheric disturbances and various characteristics of earth's surface scatterers reflectance. Compensation for these distortions is performed by filtering the phase and evaluating the degree of coherence of the original images. This is an important step to improve the accuracy of the subsequent pphase-unwrapping operation. In this paper, we investigate the use of U-net neural networks for preprocessing the SAR interferogram at various parameters of the distortion of the SAR signal. Two neural networks filter the SAR interferogram and determine the degree of coherence, respectively.

The article considers algorithms for determining the location of a sound source (intruder) using a system of distributed acoustic sensors in two-dimensional and three-dimensional space, in particular, the simple triangulation algorithm and the triangulation algorithm when the sound source is displaced. The algorithms proposed in the paper can be used to build auxiliary security systems to prevent theft of information and valuable property. Modeling of the influence of a source of harmonic acoustic impact on a system of distributed acoustic sensors was carried out, according to the results of which the distance from the optical fiber to the location of the source of harmonic acoustic impact (intruder) could be determined with an error of up to 10-15% or less.

In this paper, the effect of different noises on Laguerre-Gaussian (LG) modes recognition by convolution neural network (CNN). A dataset of halftone images with LG modes and noises was prepared during the study. It is shown that not only intensity but also type of noise has high influence on classification process. However, presence of noisy images in the training sample allows to increase the recognition accuracy from 50% to 100% in most cases.

In this paper we present an effective and simple method of image compression based on spectral analysis rather than redundancy reduction. A significant portion of traffic transmitted over communication channels is static and dynamic images, and the volume of this traffic is growing at a faster rate than the capacity of communication channels is increasing. One of the ways to solve this problem is to compress the transmitted images. Data compression can be done in two ways – with and without loss of information. A distinctive feature of images as a form of information presentation is the presence of large internal redundancy, which allows the use of lossy compression methods. To exclude the loss of meaningful information, it is necessary to take into account the specifics of specific signals and divide them into groups according to the predominant concentration of information in the frequency or in spatial domain. To do this, one can use the analysis of the spatial spectrum of images and remove some part of the spectrum with an acceptable loss of information.

The paper discusses a method of error-correcting coding based on the transfer of holographic coding of an arbitrary digital signal into the spectral range. The process of coding a code message consists in generating N radio pulses at orthogonal frequencies (a set of frequencies is determined by a holographic encoder for each message) by switching the outputs of N harmonic signal generators operating in a constant mode. The group signal is formed by summing the manipulated harmonics at the input of the transmitter amplifier or directly in the antenna. Signal decoding in the receiver is performed by calculating the spectrum of the received signal and applying an inverse holographic transform to it, which restores the value of the transmitted data block. Spectral holographic coding provides a 7-8 dB gain in noise immunity compared to coding the signal itself. Another advantage of the spectral code is the lower complexity of encoding and decoding when the redundancy is changed over a wide range, as well as high secrecy due to the use of a noise-like signal.

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.

The article presents the method for predicting the lifetime of an optical cable after the maintenance cycle. The invention proposes a formula for calculating the remaining lifetime of optical fibers of cable, which has been in operation for some time. Proposed formula based on actual estimates of the strength of optical fibers of cable samples selected from the line.

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 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.

The article presents a spectral analysis of the transmission coefficient of an optical fiber in the event of short attenuation jumps. In this case, it is assumed that the time function of the additional loss factor is a symmetrical triangular function with the same rise and fall times. It is shown that the spectral loss density is sensitive to the number of attenuation jumps, has a low-frequency character and has a filtering effect on the useful signal. Approaches to the analysis of performance characteristics of fiber-optic transmission systems under specific operating conditions are considered.

The article analyzes the design experience line-cable structures of transport multichannel communication. It is shown that in Russia the current guidelines cannot be applied to new technologies; therefore, it is necessary to develop recommendations for the design of line-cable structures of transport multichannel communication.

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.

In this paper we propose a design of an integrated wavelength-tunable vortex beam emitter based on the silicon photonics platform. The proposed device utilizes the free-plasma dispersion effect in order to change the effective index of the ring waveguide, which leads to displacement of the resonant wavelengths. This scheme allows to bypass the dependence of the emitter resonant characteristics from the fabrication errors. Our simulations also show that for the micro-ring resonators with a small free spectral range it becomes possible to switch the emitted vortex order keeping the same wavelength. Such capabilities make the proposed emitter useful in a wide applications range from communication systems to sensors.

Twisted fibers provide interesting properties in terms of mode coupling relevant for optical multichannel systems. In this regard, the article provides an overview of the use of space division multiplexing (SDM) technology in radio over fiber data transmission systems in future high-speed scalable 6G wireless networks. The features of using the SDM technology in the radio access network are analyzed. The application of new specialized few-mode fibers in 6G networks for useful information transmission is proposed. The results of experimental and simulation studies of custom twisted (chiral) optical fibers designed for vortex mode generation/maintenance are also presented, which can be used as a basis for hybrid modulation development, using both temporal and spatial properties of the signal.

In optical data transmission, among the information carriers of special interest are laser beams, whose shape does not change on propagation in free space and in a homogeneous medium. In this work, we study a continuous superposition of paraxial propagation-invariant off-axis Gaussian beams. We obtain conditions when this superposition yields an offaxis elliptic beam with a given geometric parameters (center displacement, waist radii, tilt angle), which conserves its shape on propagation and rotates around the optical axis. Properties are derived of the normalized-to-power orbital angular momentum of such beams.

Hybridly polarized beams have attracted increasing attention in recent years. Due to the features of spatial polarization and phase singularity, they can be used in STED microscopy, as optical tweezers, in nanoprocessing, to excite surface plasmon polaritons, in nonlinear optics, in quantum optics, and in telecommunication technologies. In this work, using the FDTD method, we simulated the passage of laser radiation through a binary spiral zone plate with a fractional order m=0.5 and a focal length of 0.532 μm. Quartz glass n=1.5 was assumed as the material for the relief of the zone plate. The zone plate radius was 4 μm. A TE polarized Gaussian beam with a wavelength of 0.532 μm was fed to the input. In this work, the intensity distribution and the Poynting vector in focus were studied. The possibility of forming an optical vortex with a fractional order was demonstrated.

In this article the principle of instrumental (experimental) determination of the parameters of mode compositions of an optical signal propagating along an optical fiber is described. The measurement scheme is based on the use of a wellknown experimental setup designed to obtain the profile of the refractive index of an optical fiber. In addition to that setup, it is proposed to perform measurements for different angular positions of the investigated optical fiber, and for its different longitudinal positions. The proposed method is realizable in the case when the signal propagating through the optical fiber is characterized by increased intensity, which makes it possible to measure a nonlinear (Kerr) caused addition to the refractive index. It is proposed to calculate the desired mode weight coefficients by the method of probabilistic selection according to the developed method.

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.

Pandemic COVID-19 in 2020-2021 led to the largest disruption in education systems in history. Universities, institutes, and other institutions of higher education changed their students to study by using distance learning technologies. The greatest difficulties for educational organizations were caused by the implementation of a laboratory workshop in a distance form. In this work, we share the experience of leading laboratory classes in a remote form, using virtual laboratory installations.

The content of the professional standard of the master's program for training engineers in the field of optical and fiberoptic communication systems is considered; the necessity to include the methods and technologies of developing soft skills into the educational process is justified. The structure of the concept "being ready for creative thinking" is determined; the structural and functional model of the concept "being ready for creative thinking" is analyzed; scientific and methodological recommendations are developed for getting master's students ready for creativity. Approaches to and methods for the development of creative abilities are presented; the results of a diagnostic study of master's students' creativity level are analyzed.

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.