Coupled-core Multicore Fibers Research Articles

Numerical Estimation of Inter-Core Crosstalk Affected by Stimulated Raman Scattering in Weakly Coupled Multicore Fiber

Numerical Estimation of Inter-Core Crosstalk Affected by Stimulated Raman Scattering in Weakly Coupled Multicore Fiber

Characterization of Effective Nonlinear Coefficient in Randomly Coupled Multi-core Fiber

Characterization of Effective Nonlinear Coefficient in Randomly Coupled Multi-core Fiber

Evaluation of Crosstalk in Nonlinear Regime for Weakly Coupled Multi-Core Fiber With Random Perturbations Using a Split-Step Numerical Model

Evaluation of Crosstalk in Nonlinear Regime for Weakly Coupled Multi-Core Fiber With Random Perturbations Using a Split-Step Numerical Model

Field Trial of SDN-Controlled Probabilistic Constellation Shaping Supporting Multiple Rates Over a Coupled-Core Multi-Core Fiber

Space division multiplexing (SDM) is being investigated in support of traffic growth. SDM networks offer multiplexing over space and spectrum dimensions. Probabilistic constellation shaping (PCS) is a solution to optimize spectral efficiency by adapting the constellation of a M-ary quadrature amplitude modulated (QAM) signal to physical layer impairments. At the control plane, in the recent years NETCONF and YANG have been identified as the protocol and the data modeling language, respectively, for the configuration and management of network devices. Significant effort has also been directed to network disaggregation and vendor neutrality: an example is the work done within the OpenConfig consortium. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this paper, we present a SDM field trial based on a deployed coupled-core four-core fiber, where a software-defined network (SDN) controller configures probabilistic constellation shaping through NETCONF, by optimizing spectral efficiency either with respect to the path length, or in response to degradations due to soft failures. The NETCONF protocol relies on the OpenConfig YANG data model to configure and manage transceivers. In the field trial the integrated data and control planes are demonstrated with multiple rates (800-850-900-950-1000 Gb/s) for optical reach values ranging from 910 km to 2730 km. Soft failures are also introduced and a characterization of their impact on transmission performance is provided in order to design the recovery strategy deployed by SDN controller. Indeed, depending on the changes in the electrical signal-to-noise ratio, the SDN controller reconfigures the constellation shaping to restore the optical connection affected by the failure with a reduced line rate.

Nonlinear impairment scaling in coupled-core multi-core fibers for space-division multiplexing

We study the nonlinear impairment scaling in coupled-core multi-core fibers (CC-MCFs) with core count by evaluating four typical CC-MCFs with different numbers of cores, which have been demonstrated promising for long-haul optical fiber transmissions, using the Gaussian-noise model. The results show that nonlinear signal degradation in CC-MCFs with more cores becomes significantly weaker, which would be of great interest to ultralong-haul transmission in CC-MCFs. We further analyze how the fiber loss, differential group delay and effective mode field area impact on the trend. Moreover, we compare CC-MCFs and few-mode fibers with the same number of spatial modes in terms of nonlinear impairment and find that CC-MCFs tend to achieve better nonlinear performance. It is also shown that few-mode fibers operated in strong coupling regime are quite promising for long-haul transmission.

Weakly Coupled Multicore Fiber Technology, Deployment, and Systems

Space-division multiplexing (SDM) technology is a promising candidate to achieve massive parallelism in optical fiber cables and overcome the capacity limitation of the conventional single-mode fiber (SMF). Among the several kinds of SDM fiber, a weakly coupled multicore fiber (MCF) is advantageous in that it can be easily upgraded for use in existing equipment and requires no complex signal processing for optical multi-input multi-output (MIMO). In this article, we discuss the progress and standardization activity of MCF technologies from the viewpoint of accelerating the practical application of SDM technology. We first describe the possible application areas of SDM fibers and then show the recent progress of the essential technologies to construct the MCF link: the MCF itself, its splicing and connectorization, and the input/output techniques. We also discuss the availability and deployability of MCF as a large-capacity transmission medium and detail the progress on establishing a new international standard for SDM technology, which includes both historical progress and more recent endeavors on the standardization of optical fiber cables and SDM technology in International Telecommunication Union Telecommunication Standardization Sector (ITU-T) and International Electrotechnical Commission (IEC). We close with a summary of MCF technology and its standardization activity with an eye to next-generation transmission systems and the long-term development of ultralarge capacity SDM transmission technology.

Low Loss Ultra-Small Core Pitch All-Fiber Fan-In/Fan-Out Device For Coupled-Core Multicore Fibers

We designed and fabricated all-fiber fan-in/fan-out (FI/FO) devices using a fused taper technique for square lattice structure coupled-core multicore fiber (CC-MCF). A vanishing core bridge fiber with a diameter of 80 μm was tailor-designed to minimize both the mode field mismatch and the required tapering ratio at the same time. In experiment, we succeeded in fabricating FI/FO devices with a core pitch as small as 17 μm and achieving practically low insertion losses of 1.43 dB and 2.28 dB for fan-in and fan-out devices, respectively. The fabricated FI/FO devices can well multiplex and demultiplex 1550 nm light into and out from the CC-MCF without obvious total power fluctuation even when an external perturbation is intentionally imposed on the CC-MCF. The proposed FI/FO device is very useful for both the study and application of CC-MCFs which usually have ultra-small core pitches.

A Comparative Study of Few-Mode Fiber and Coupled-Core Multi-Core Fiber Transmission

Few-mode fibers and coupled-core multi-core fibers are attractive transmission media for space-division multiplexed transmission systems as they enable a high spatial channel multiplicity whilst sustaining the current standard cladding diameter. This paper compares space-division multiplexed recirculating loop transmission using either a 3-mode few-mode fiber or a 3-core coupled-core multi-core fiber. After analyzing the spectral attenuation properties of both fibers, we investigate the wavelength and transmission distance dependence of the transmission channel characteristics. We find that the channel memory length is shorter and mode-dependent loss is lower in the coupled-core multi-core fiber, which can be attributed to the fundamental mode-structure differences between the two fiber types. This leads to a higher data rate at similar transmission distance for the coupled-core multi-core fiber.

Long-Haul Coupled 4-Core Fiber Transmission Over 7,200 Km With Real-Time MIMO DSP

In this work, we present an experimental demonstration of real-time transoceanic space-division multiplexed transmission with coupled-core multicore fibers. To compensate for modal coupling in the coupled-core multicore fibers, we implement real-time multiple-input multiple-output (MIMO) digital signal processing based on field programmable gate array circuits. Using optical receivers with a real-time MIMO, we demonstrate 16-channel wavelength-division multiplexed coupled four-core fiber transmission over 7200 km. The results show the feasibility of real-time coupled-core multicore fiber transmission.

Distribution Characteristics of Inter-Core Crosstalk in Weakly Coupled Multicore Fibers

Distribution Characteristics of Inter-Core Crosstalk in Weakly Coupled Multicore Fibers

Near-Zero Modal-Dispersion (NEMO) Coupled-Core Multi-Core Fibers

Wepropose a design for coupled-core multi-core fibers that allows to achieve extremely low levels of modal dispersion. These fibers, which we dub <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NEar-zero MOdal-dispersion</i> (NEMO) fibers, have an even number of cores regularly distributed on a circle, and the optimal design parameters follow from a simple condition independent of the number of cores. The modal-dispersion reduction trades off some of the fiber mode-mixing effectiveness, yet without compromising its beneficial property of mitigating nonlinear signal distortions. The semi-analytical tool developed for this study allows to effectively characterize the effect of various types of perturbations to the ideal fiber structure.

Space-division multiplexing for optical fiber communications

Research on space-division multiplexing (SDM) came to prominence in early 2010 being primarily proposed as a means of multiplying the information-carrying capacity of optical fibers at the same time as increasing efficiency through resource sharing. Proposed SDM transmission systems range from parallel single-mode fibers with shared amplifier pump lasers to the full spatial integration of transceiver hardware, signal processing, and amplification around a fiber with over 100 spatial channels comprising multiple cores each carrying multiple modes. In this paper, we review progress in SDM research. We first outline the main classifications and features of novel SDM fibers such as multicore fibers (MCFs), multimode fibers, few-mode MCFs, and coupled-core MCFs. We review research achievements of each fiber type before discussing digital-signal processing, amplifier technology, and milestones of transmission and networking demonstrations. Finally, we draw comparisons between fiber types before discussing the current trends and speculate on future developments and applications beyond optical data transmission.

Correlation and Power Distribution of Intercore Crosstalk Field Components of Polarization-Coupled Weakly Coupled Single-Mode Multicore Fibres

The correlation and power distribution of intercore crosstalk (ICXT) field components of weakly coupled multicore fibers (WC-MCFs) are important properties that determine the statistics of the ICXT and ultimately impact the performance of WC-MCF optical communication systems. Using intensive numerical simulation of the coupled mode equations describing ICXT of a single-mode WC-MCF with intracore birefringence and linear propagation, we assess the mean, correlation, and power distribution of the four ICXT field components of unmodulated polarization-coupled homogeneous and quasi-homogeneous WC-MCFs with a single interfering core in a wide range of birefringence conditions and power distribution among the field components at the interfering core input. It is shown that, for homogeneous and quasi-homogeneous WC-MCFs, zero mean uncorrelated ICXT field components with similar power levels are observed for birefringence correlation length and birefringence beat length in the ranges of 0.5m,10m and 0.1m,10m, respectively, regardless of the distribution of power between the four field components at the interfering core input.

Design of High-Density Cable Parameters for Controlling Spatial-Mode Dispersion of Randomly Coupled Multi-Core Fibers

In this work, we propose design parameters for optimized high-density optical cables to control the spatial-mode dispersion (SMD) of randomly coupled multi-core fibers (MCF). The analytical results of our proposed cable demonstrated the controllability of the bending and twisting of the implemented optical fibers by means of tension that is applied for a bundled fiber while keeping the sufficient reliability. An optical characterization showed that appropriate cabling parameters resulted in SMD controllability and a 47% reduction of the SMD coefficient while avoiding undesired loss increase. C-L band transmission experiments using our optical cable showed no degradation of the Q-factor or mode-dependent loss (MDL). Our proposed cable design is beneficial for achieving an SMD-managed large-capacity and long-haul transmission link.

High Capacity Transmission in a Coupled-Core Three-Core Multi-Core Fiber

High-capacity, long-haul transmission over a coupled-core three-core multi-core fiber is investigated in a recirculating loop experiment. We report key system characteristics, such as the optimum launch power as well as the wavelength dependence and distance-evolution of mode-dependent loss and the impulse response time spread. We further performed two high data-rate, long-haul transmission demonstrations with more than 75 nm optical bandwidth in C- and L-bands over distances up to 4800 km. The reported data-rate of 172 Tb/s over 2040 km is the highest demonstrated in any multi-span transmission system employing optical fibers with standard cladding diameter of 125 micro-meter to date. Additionally, transmission of 81 Tb/s over 4800 km distance demonstrates the potential of using coupled-core multi-core fibers in combination with wideband optical signals over long-haul distances.

Simple GDS Estimation Method for Coupled Multicore Fibers with Various Core Layouts

Simple GDS Estimation Method for Coupled Multicore Fibers with Various Core Layouts

Probability Distribution of Intercore Crosstalk in Weakly Coupled MCFs With Multiple Interferers

The statistical behavior of the intercore crosstalk (ICXT) power in weakly coupled multicore fibers (MCFs) with multiple interfering cores is experimentally assessed. The histograms with multiple interfering cores are compared with the probability density function (pdf) of the quadratic form corresponding to the ICXT power considering different correlation coefficients between the in-phase and quadrature Gaussian ICXT field components of the orthogonal polarizations. A very good fitting between experimental histograms and the numerical pdf of the quadratic form occurs when the ICXT field components are modeled as uncorrelated random processes. These results demonstrate that the ICXT power can, with a very low error, be described by a chi-square distribution with 4 degrees of freedom not only with a single interfering core but also with multiple interfering cores. This means that the ICXT contributions induced by different cores of the MCF are uncorrelated.

Efficient Channel Model for Homogeneous Weakly Coupled Multicore Fibers

To analyze a homogeneous weakly coupled multicore fiber (WC-MCF) based transmission system via simulation, we propose an efficient (fast and accurate) WC-MCF's channel model, which can describe the propagation effects including attenuation, walk-off, chromatic dispersion, self-phase modulation (SPM), and especially the frequency-dependent inter-core crosstalk (XT). We speed up the simulation with two orders of magnitude by simplifying the XT's calculation. On one hand, the calculation step size can be greatly increased by utilizing a new XT's coupling matrix. On the other hand, the calculation of XT can be further accelerated by down-sampling XT's coupling matrix in frequency domain. The XT power and average occurrence distance should be set manually based on the existing XT model to describe the frequency-dependent XT the same as a real WC-MCF. We numerically and experimentally observed that XT's de-correlation bandwidth decreases with relative time delay (RTD) by fractional linear function. The range of validity of the proposed channel model is also discussed with different walk-off and coupling strength. We believe the proposed efficient channel model can provide great help for analysis and optimization of homogeneous WC-MCF based optical communication systems.

Decorrelation Bandwidth of Intercore Crosstalk in Weakly Coupled Multicore Fibers With Multiple Interfering Cores

The decorrelation bandwidth of the intercore crosstalk (ICXT) power generated in a weakly coupled multicore fiber (MCF) with multiple interfering cores is studied. For the first time, this is accomplished using a closed-form expression of the equivalent autocovariance function of the ICXT power that enables evaluating the correlation between the ICXT power generated at two different frequencies using a theoretical model to describe the stochastic evolution of the ICXT over time. It provides fast and reliable estimates of the decorrelation bandwidth of the ICXT induced by multiple interfering cores with arbitrary relative time delays (skews) between cores, which represents a crucial tool to assist the design of new MCF systems. Validation of the autocovariance and decorrelation bandwidth expressions by numerical simulation and with experimental results published by other authors is accomplished. In contrast to the single interfering case, the equivalent autocovariance of the ICXT induced by multiple interferers may present several inflexion points along the frequency lag due to the different core contributions that may be characterized by different skews. For MCFs with similar skews between cores, the equivalent autocovariance has, approximately, a sinc-squared shape with the decorrelation bandwidth, defined as the first zero of equivalent autocovariance, occurring at the frequency lag, in Hz, given by the inverse of the skew. When the decorrelation bandwidth of the ICXT induced by multiple interfering cores is much lower or much higher than the signal bandwidth, the ICXT mechanism can be considered as uncorrelated noise or as a static coupling component, respectively. When the decorrelation bandwidth is similar to the signal bandwidth, the ICXT mechanism should be treated as correlated noise.

Coiling Size Dependence of Group Delay Spread in Coupled Multicore Fibers Without Intentional Twisting

Coiling size dependence of group delay spread (GDS) in coupled multicore fibers (MCFs) without intentional twisting is investigated by using a coupled-wave theory. It is shown that the GDS does not simply decrease with increasing bending radius and the optimum coiling size to decrease GDS depends on a core-to-core distance of MCFs. It is also found that a coupled MCF with a trench-assisted profile is suitable for realizing lower GDS with higher spatial density compared with a coupled MCF with a step-index profile.