ПІДВИЩЕННЯ ЕФЕКТИВНОСТІ ОПТОВОЛОКОННИХ КАНАЛІВ ЗВ’ЯЗКУ

For several decades silica-based optical fibres have been used for telecommunication and sensor purposes. The single-mode fibre is frequently employed in long-distance networks, whereas the multi-mode fibre is the preferred means of signal transport in campus and in-building networks. Because of the huge bandwidth of optical fibres in comparison to its electrical wireless and copper-based counterparts, the demand for optical fibres keeps increasing. In a competitive market, fibre manufacturers aim to produce ever better fibres that are as cheap and easy to employ as possible. As fibre research, development and manufacturing is a mature discipline, improvements in fibre design can only be achieved through the construction of robust, accurate and efficient numerical fibre models for the computation of those quantities that determine the behaviour of the fibre. We have developed a modular software code, based on Maxwell’s equations, to compute these quantities in a vectorial full-wave way for both single-mode and multi-mode optical fibres. Key is the refractive-index profile, or, more specifically, the dopant profile, as it defines the propagation, splicing and bending-loss characteristics of the fibre. For the single-mode fibre, the fibre quantities that we have concentrated on are dispersion, dispersion slope, mode-field diameter, effective area, bending loss, effective and theoretical cut-off wavelength and MAC-value. We highlight one fibre quantity in particular, viz. the computation of the bending loss in a single-mode fibre. Many approximate modelling techniques have been developed to estimate this loss in a fast way. Our numerical scheme, however, is the first rigorous one, as we have performed a vectorial full-wave analysis of the bent optical fibre. In this context, triple integrals involving products of Bessel functions with large, complex order and argument appear. Due to cancellations in the pertaining computation, a high relative accuracy is needed for the computation of each product. As a result, it takes weeks on a contemporary computer to compute the bending loss as a function of the radius of curvature. We have used the vectorial full-wave bending-loss results to determine the most appropriate approximate method. Subsequently, we have extended that approximate method to compute the bending losses of higher-order modes, since the required effective cut-off wavelength depends on the bending loss of the first higher-order mode. The selected approximate method has been used in the ensuing bending-loss calculations. Since the fibre properties are often conflicting, it is a challenging task to adapt the radial dopant profile to meet a set of predefined design goals. A design goal is a combination of desired values for (some of) the aforementioned fibre quantities, and can mathematically be translated into a cost function. The minimisation of this cost function provides us with the optimal dopant profile for that specific set. For the single-mode fibre, we have performed this minimisation for piecewise-linear profiles, by employing various global and gradient-based local optimisation strategies to speed up the design step considerably. Frequently,these optimisation strategies lead to counter-intuitive dopant profile designs that could not have been contrived otherwise. We have selected a deliberate mix of several optimisation routines and have compared their performances. Perhaps the most important conclusion is that there still appears to be room for improvement in the design of the radial dopant profile of commercially available fibres. For the multi-mode fibre, vectorial full-wave optimisation is not feasible yet because of the long computation times for the large number of propagating modes. Still, our numerical scheme allows for a manual fine-tuning of the popular power-law profile to minimise differential mode delay. Further, we have included mode coupling and differential mode attenuation in our model to obtain intensity patterns that match closely with measurements. We have also analysed the influence of profile variations, e.g. on-axis dips and kinks, on the intensity pattern. A selective excitation of different mode groups in a multi-mode fibre, offers the possibility to create several independent transmission channels, and thus a higher information capacity. Recently, the feasibility of this so-called mode group diversity multiplexing technique has been demonstrated. Simulations provide us with a means to better understand its operation and possibly increase its efficiency. The channel separation may be enhanced by employing a lens between the fibre and the detector, which is called mode-selective spatial filtering. Our numerical simulations of a mode group diversity multiplexing link, with and without mode-selective spatial filtering, are in agreement with the measurements. The above discussion makes clear that the developed software code has a wide range of applicability. Moreover, it is built in a modular way and thus extensions, like the inclusion of more fibre quantities or different profile dopants, are straightforward.

Fiber optic sensors offer a high-performance alternative because they provide a low-cost solution, resistance to electromagnetic interference, multiplexing capabilities, and high integration. The performance of fiber optic sensors applies to measuring physical parameters such as pressure, bending, and temperature. This study aims to determine the optimal value of using optical fiber types in landslide early detection sensors. The method used is bending in the form of deflection on the optical fiber. The deflection values used are 0 mm - 15 mm, 0 mm - 20 mm, and 0 mm - 25 mm. The optical fiber is placed horizontally in the middle of the bending tool. This bending affects the deflection of the optical fiber, resulting in the attenuation of light in the optical fiber. The deflection phenomenon results in light attenuation in the optical fiber. The sensitivity level of a single-mode fiber optic sensor is higher than a multimode. It shows the greater linearity value in each deflection treatment. Single-mode optical fiber linearity data on deflection variations of 0 - 15 mm, 0 - 20 mm, and 0 - 25 mm, respectively, are 0.9833, 0.9871, and 0.9847. At the same time, the linearity data of multimode optical fiber is 0.8926, 0.9841, and 0.9687. Single-mode optical fiber is more sensitive than multimode optical fiber. It is caused by the core diameter of single-mode optical fiber, which is much smaller than that of multimode optical fiber. The difference in core diameter results in differences in light propagation in the optical fiber. The small diameter of the core has a low dispersion level so that more light intensity is reflected into the core. Light attenuation occurs in a single-mode optical fiber due to macro bending treatment. Meanwhile, the attenuation of light in Multimode fiber optics is due to the bending and dispersion of light. Therefore, a landslide early detection sensor design is more optimal by using a single-mode optical fiber.

Data center (DC) and high performance computing (HPC) applications have traditionally used a combination of copper, multimode fiber and single-mode fiber interconnects with relative percentages that depend on factors such as the line rate, reach and connectivity costs. The balance between these transmission media has increasingly shifted towards optical fiber due to the reach constraints of copper at data rates of 10 Gb/s and higher. The percentage of single-mode fiber deployed in the DC has also grown slightly since 2014, coinciding with the emergence of mega DCs with extended distance needs beyond 100 m. This trend will likely continue in the next few years as DCs expand their capacity from 100G to 400G, increase the physical size of their facilities and begin to utilize silicon-photonics transceiver technology. However there is a still a need for the low-cost and high-density connectivity, and this is sustaining the deployment of multimode fiber for links ≤ 100 m. In this paper, we discuss options for single-mode and multimode fibers in DCs and HPCs and introduce a reduced diameter multimode fiber concept which provides intra-and inter-rack connectivity as well as compatibility with silicon-photonic transceivers operating at 1310 nm. We also discuss the trade-offs between single-mode fiber attributes such as bend-insensitivity, attenuation and mode field diameter and their roles in capacity and connectivity in data centers.

A comparison is made between the use of single and multimode optical fibers in a homodyne quasi-elastic light scattering experiment using simple optical hardware. The single-mode fiber is used without a spatial filter and gives a larger signal-to-noise ratio and counting rate than a multimode fiber with a spatial filter.

The optical fibres that will be used in SLHC detectors will be exposed to high doses and low temperatures in the inner detectors. A number of Single-Mode (SM) and Multi-Mode (MM) fibres have been tested for radiation hardness by exposure beyond a full SLHC dose to 500 kGy(Si) in the -25°C operating temperatures expected in the upgraded inner detectors. From these measurements conservative estimates of the level of Radiation Induced Absorption (RIA) have been calculated for these fibres in realistic paths through an upgraded inner detector. Two SM fibres have been found whose total calculated RIAs were much lower than the budgeted 1 dB, despite the high dose rates used in the experiment. The RIAs for the DrakaElite Super RadHard Single-Mode Fiber and Fibre X were calculated to be 0.142 and 0.064 dB respectively. Another SM and a MM fibre showed high levels of RIA during the experiment, however they cannot be ruled out as candidate fibres due the the high dose rate of 27 kGy(Si)/hr used.

Of all the lasers in use today, it is only the semiconductor laser where the quantum noise, inevitable in all lasers, is of major practical concern. This is due to two reasons. The first one is that since semiconductor lasers have a very small physical volume, the cavity quality factor is very small, which results, according the the Schalow-Townes formula, in a large spectral width of the laser output. The second reason is that due to the widespread application of semiconductor lasers in real-life optical fiber comunications systems, the noise aspects are of real concern. The basic physical mechanism of this noise is the addition of spontaneous emission power to the laser field. This effect is compounded and amplified by coupling between intensity and phase fluctuations, which are characteristic of semiconductor lasers. In the talk we will review those physical effects and show some possible ways of reducing the laser linewidth. These ways include the use of large external cavity and/or coupling of frequency dependent loss mechanism into the laser oscillators. The effect of spontaneous emission is also a limiting factor in optical fiber amplifier systems, which are assuming major practical importance. In this case the major noise mechanism is beating between the signal propagating in the fiber and the background amplified spontaneous emission power. The basic limitation on signal to noise ratio in a practical system because of this mechanism will be reviewed. Experiments performed in various laboratories will be discussed and compared to the theory. A limiting noise behavior of the optical amplifier fiber system is shown to consist of a transmission system with uniformly distributed gain along the whole length of the fiber. The penalty factors for using other schemes of optical fiber amplification compared to the ideal system will be discussed. The last mechanism to be discussed will be that of double Rayleigh scattering in fibers. This converts phase noise to intensity noise. The resulting limiting RIN will be discussed and compared with new experiments.

Currently, communication systems are widely used, where optical fiber is used as a transmission medium. In turn, decision and control of optical fiber parameters has become needfull, since these parameters have a significant impact on the quality and quantity of transmitted information using fiber-optic communication systems. One of these parameters is cut-off wavelength of the single-mode optical fiber, which determines the minimum wavelength of optical radiation at which the optical fiber supports only one propagated mode, in other words, operates in single-mode. The problem of decision cut-off wavelength of the optical fiber used in fiber-optic communication systems is quite relevant and demand, since when the optical fiber operates in multimode, its throughput decreases due to inter-mode dispersion. The article describes methods for measuring cut-off wavelength of the optical fiber. Variant of a high- precision apparatus for measuring cut-off wavelength of the optical fiber has been proposed and tested. The measurements were performed based on the reference bending technique described in GOST R IEC 60793-1-44-2013. The analysis of the accuracy characteristics of the developed apparatus is made, a quantitative assessment of the measurement error is obtained.

The aim of this study is to verify the possibility of detecting oil in the bottom sediment using a fibre optic system. The presence of oil is assessed on excitation-emission spectra obtained from spectral fluorescence signals of the sediment sample. A factory spectrofluorometer coupled with an experimental fibre optic measurement system was used. During the determination of spectra, the fibre optic system is set at a 45° angle to the sediment surface and placed above its surface. The light exciting the fluorescence and the light emitted by the sediment are transmitted in a combined bundle of fibre optic threads. The analysis of excitation-emission spectra of sediments contaminated with oil shows variability of the shapes of fluorescence spectra depending on the type and degree of oil contamination, which indicates the feasibility of the sensor design for detecting oil in the sediment in situ.

A detailed investigation of the nonlinear multimodal interference in a short graded-index multimode optical fiber is presented. The analysis is performed for a specific device geometry, where the light is coupled in and out of the multimode fiber via single-mode fibers. The same device geometry was recently used to obtain ultra-low-loss coupling between two single-mode optical fibers with very different mode-field diameters. Our results indicate the potential application of this simple geometry for nonlinear devices, such as in nonlinear switching, optical signal processing, or as saturable absorbers in mode-locked fiber lasers. Saturable absorption in this all-fiber configuration is discussed and it is shown that it provides attractive properties that can potentially be used in high pulse energy mode-locked fiber lasers.

For pt.I see ibid., vol.6, no.2, p.165-71 (1988). For pt.III see ibid., vol.8, no.6, p.977-89 (1990). The results of steady-state /sup 60/Co irradiations of silica core multimode fiber and silica core single-mode and Ge-doped graded index fibers are reported. These data were acquired over the interval of 1987-9. Several significant differences from the results and measurement procedures presented in pt.I must be accounted for in drawing comparisons between the two sets of reported data. Fiber wrap diameter and launched power level were observed to significantly influence the radiation-induced attenuation measured in silica core multimode and single-mode fibers, while the effect was less in Ge-doped silica core multimode fibers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical fibers are the basis of data transmission systems. However, during operation, the optical cable may be damaged, and to eliminate the damage that has occurred in the field, it is necessary to know the wavelength of optical radiation in this fiber and the radiation power for each of the wavelengths used. This determines the relevance of developing a method for recording the wavelength of radiation at the output of an optical fiber that is accessible for use in field conditions, without the use of complex and expensive equipment. A method for determining the wavelength of optical radiation propagating through an optical fiber based on the use of the fiber macrobending is proposed. An experimental setup for implementing the method is developed. It is shown that this method can be used for both single-mode and multimode optical fibers. It is established that for all the studied optical fibers, the deviation of the power values determined using the method from the real ones does not exceed 12.5 %. The results of the work can be used in fiber-optic communication systems to determine the wavelength and power of radiation propagating through an optical cable.

We study the problem of coupling partially coherent radially polarized (PCRP) vortex beams into a single-mode optical fiber. Using the well-known concept of the cross-spectral density (CSD) matrix, we derive a general expression for the coupling efficiency of the partially coherent beam into a single-mode fiber. We adopt PCRP vortex beams for incident beams and use our general results to discuss the effects of the coherence, topological charge, and wavelength on the coupling efficiency of an optical beam focused onto a single-mode fiber with a lens. Our results should be useful for any application that requires coupling of partially coherent beams into optical fibers.

Summary form only given. There have been many displacement sensing methods based on optical fibers such as using mode scrambling of multi-mode fibers or intensity change of single mode fibers due to coupling mismatch. In this work, we used as displacement sensing the mode excitation change caused by spatial variation of input beam. A single mode fiber is used as a point-like input beam source for a multi-mode fiber. Since the core size of the multi-mode fiber is about 10 times larger than that of the single mode fiber, if two fibers are closely located and the multi-mode fiber is sufficiently long, the input beam from the single mode fiber excites many modes of the multi-mode fiber without power loss.

The main objectives of this paper is to improve knowledge of multimode fiber transmission over step-index plastic optical fiber SI POF with 1000 μm core. The thick SI POF fibers seem a very attractive alternative in local computer networks for the “classic” (thin) single- and multimode fibers because of their low price and easy installation. In the paper we show measurements of bandwidth and attenuation of various SI POF optical paths. In particular, there was investigated a cascade of passive components (couplers, patchcords) which can be part of transparent (passive) optical networks. Keywords : plastic optical fibre, passive optical network, multimode coupler. 1. INTRODUCTION Recently there has been publish a number of papers concerning optical data transfer over plastic optical fiber [1][2]. Both point-to-point and WDM passive network configurations are considered. The concept of passive network is well known as it comes to the access networks based on single mode fiber. Such networks were proposed in several standards (APON, BPON networks). Commercial solution have been developed and deployed since. We would like to extend benefits of this network type to home networks based on multimode optical fiber. We consider such networks as a viable solution of the optical home network architecture. Along with a multimode optical cable only multimode compatible elements (couples/splitters, connectors, etc.) may be used in the network. Once deployed the upgrade of such a network should be relatively easy. Unlike to the single mode PON where the bandwidth is not an issue, the multimode network maximum operational range is defined by the fiber bandwidth (related to the intermodal dispersion) rather than by the fiber attenuation [3]. The relation among the modal bandwidth of the fiber, the launching condition and mode coupling is fairly well known for silica GI optical fibers (

The special optical fibers, with large mode field, are developed for fabricating high power optical fibers passive components. If a conventional fiber optical laser is used as optical source, the coupling efficiency between special optical fibers and conventional single mode fibers (SMFs) need to be improved. We investigate the specialty optical fibers property and its effect on the coupling efficiency using an electric arc fusion splicer. Improper splicing parameters can lead to coupling efficiency sharply decreased. Several splicing methods are utilized, and all the results are proposed. Comparing these results, we find a set of splicing parameters for reducing the scattering loss at the splice point. It was demonstrated that properly splicing parameters can make coupling efficiency greatly increased; furthermore, a balance between splicing strength and coupling loss was achieved.