Space Division Multiplexing Research Articles

Influence of mode coupling on angular division multiplexing in seven-core plastic optical fibers

We propose an angular division multiplexing in new designed multicore plastic optical fiber with seven cores arranged in a hexagonal array. The influence of mode coupling on two-channel angular division multiplexing capability in each of seven cores is investigated by solving the power flow equation. Our numerical results show that mode coupling significantly limits the fiber length at which the angular division multiplexing can be realized in each of seven cores with a minimal crosstalk between two neighbor angular optical channels. Two angular channels in the proposed seven-core plastic optical fiber can be employed with a minimal crosstalk up to the fiber length which is about 20% of the coupling length (fiber length where equilibrium mode distribution is achieved). Such characterization of multicore optical fibers should be considered in designing a multicore optical fiber transmission system for space division multiplexing.

Modeling and performance investigation of 4 $$\times$$ 20 Gbps underwater optical wireless communication link incorporating space division multiplexing of Hermite Gaussian modes

In this work, we report the development of long-haul high-speed underwater optical wireless communication (UOWC) transmission link by incorporating space division multiplexing (SDM) of distinct Hermite Gaussian (HG) modes for enhanced channel-capacity. Four distinct 20 Gbps non-return to zero encoded information signals are transmitted over distinct HG modes of a single wavelength laser at 1800 m underwater link range to realize an 80 Gbps UOWC system. Also, we investigate the performance of the proposed UOWC transmission link under the influence of different operating wavelengths, aperture diameter, attenuation coefficient, and link range. Further, we optimize the proposed UOWC link performance in terms of spatial aperture to stabilize the bit-error rate (BER) performance of the link at high signal attenuation values and varying transmission link reach.

Spatial Density and Splicing Characteristic Optimized Few-Mode Multi-Core Fiber

Few-mode fiber design suitable for long-haul dense space division multiplexing (SDM) transmission is proposed, where the spatial density and the splicing characteristics of the fiber is optimized. We numerically investigate the impact of the number of modes per core in a multi-core structure on the total number of spatial channels possible and the splice loss property. It is shown that increased number of mode per core enables us to improve the spatial density while maintaining feasible splice-induced differential modal attenuation. We then successfully fabricate a 10-mode 12-core fiber with a cladding diameter of 217 μm, that achieves a relative core multiplicity factor (RCMF) of 101.7 and maximum number of spatial channels among the possible few-mode multi-core fiber designs with a cladding diameter of less than 250 μm. Experiments confirm that its splice-induced differential modal attenuation characteristics were better than those of previously reported 114-spatial-channel fiber.

Transmission of Orbital Angular Momentum and Cylindrical Vector Beams in a Large-Bandwidth Annular Core Photonic Crystal Fiber

The stable propagation of orbital angular momentum and cylindrical vector beams in a newly designed annular core photonic crystal fiber (AC-PCF) tailored for the broadband single-radial order beam transmission (within the so-called “endlessly mono-radial” guiding regime) is demonstrated for the first time. It is shown that the vector-vortex beams can maintain high mode purities above 18 dB after propagation in the fiber under test over all of the wavelength range from 805 to 845 nm (over 17 THz bandwidth) investigated with the help of a tunable laser and an S-plate for the generation of singular beams in free space. Our results confirm that the AC-PCF is a promising design for the broadband transmission of vector-vortex beams that have potential applications in space-division multiplexing, quantum communications, optical sensing and trapping.

Spiral-Phased Laguerre-Gaussian Modes Generation in SWDM over Few Mode Fiber based on Electrical Equalization

Space division multiplexing, in conjunction with wavelength division multiplexing, is a powerful mechanism that increases spatial channels significantly in a single optical fiber. Spiral Phased-Laguerre-Gaussian (SP-LG) modes indicate that they effectively reduce mode coupling, thereby increasing the channel response and performance positively. However, mode-coupling influence optical fiber system leads to inter-symbol interference (ISI) between the channels and reduces both capacity and distance. In this paper, we apply the SP-LG modes in a space wavelength division multiplexing over a few-mode fiber system. The results demonstrate significant improvements in reducing channels effects and ISI. The performance evaluations are based on the bit-error-rate (BER), eye diagram and spectrum analyzer.

Modeling and Characterization of Cladding-Pumped Erbium-Ytterbium Co-Doped Fibers for Amplification in Communication Systems

Cladding-pumped optical fiber amplifiers are of increased interest in the context of space-division multiplexing but are known to suffer from low power efficiency. In this context, ytterbium (Yb) co-doping can be an attractive solution to improve the performance of erbium (Er) doped fiber amplifiers. We present a detailed direct comparison between Er/Yb-co-doping and Er-doping using numerical simulations validated by experimental results. Two double-cladding fibers, one doped with Er only and the other one co-doped with Er and Yb, are designed, fabricated and characterized. Using the experimentally extracted parameters, we simulate multi-core fiber amplifiers and investigate the interest of Er/Yb-co-doping. We calculate the minimum gain of the amplifiers over a 35-nm spectral window considering various scenarios.

A novel dual guided modes regions photonic crystal fiber with low crosstalk supporting 56 OAM modes and 4 LP modes

In this paper, a novel photonic crystal fiber (PCF) with dual guided modes regions is proposed, which can support 56 orbital angular momentum (OAM) modes and 4 linear polarization (LP) modes over S + C + L wavelength bands. The introduction of a low refractive index ring enables separation of the guided modes regions and makes the designed PCF easier to fabricate. The characteristics of designed PCF are systematically analyzed by using the finite element method (FEM). The results show that the crosstalk between channels can be ignored and the confinement loss is lower than 5 × 10−8dB/m. Furthermore, dispersion and purity are also analyzed. In summary, the designed PCF has potential applications in the high capacity fiber communication of space division multiplexing (SDM).

On the Analysis and Comparison of Decoupled Modal Gain Equalization Systems for Four-Mode (4M)-EDFAs

SpaceDivision Multiplexing (SDM) has gained considerable interest as a promising means to increase transmission capacity per fiber. For proper use of this technology, optical components of transmission line including Erbium-Doped Fiber Amplifiers (EDFAs) need to be re-examined. In this work we analyze modal gain equalization systems obtained from extended Giles model for 4M-EDFA. We introduced a simpler method of calculation of two radial overlap factors extracted from the model using standard B–V curve thus proposing two decoupled systems for Modal Gain Equalization. In Decoupled Mode Specific Pump Combination (MSPC) system so obtained, Differential Modal Gain (DMG) was reduced to 1.55 dB with mean gain of about 28.72 dB. For Modified Erbium Doped Profile (MEDP) system we obtained an optimum Multi-Well Profile. The DMG here showed further reduction to 1.3254 dB with mean gain of about 24.24 dB. Further we report investigation on evolution of ASE for 4M-EDFA for the first time with new performance metric namely ASE ratio to indicate the deviation of noise between four modes. The ASE levels reached in MEDP are smaller than MSPC system thus enabling reduction in Noise Figure. Simulation results and comparison indicated that in MEDP, DMG is more sensitive to variation in length, concentration and wavelength. Each spatial channel in our designed MEDP and MSPC system as well as simple 4M-EDFA system gave good pre-amplification performance for data rates upto 15 Gb/s.

CR‐QRM‐MLD for SD‐SM Hybrid MIMO systems

AbstractRecently, multiple‐input multiple‐output (MIMO) is studied actively such as a key technology for wireless communications. Space division (SD) multiplexing and spatial modulation (SM) have been proposed as the transmission technique of MIMO systems. In the full maximum likelihood detection (MLD), the QR decomposition with M‐algorithm MLD (QRM‐MLD), and the channel ranking QRM‐MLD (CR‐QRM‐MLD) for the SD‐MIMO, there are the trade‐off between the system performance and the computational complexity. Also, in the SM‐MIMO, the transmission rate is deteriorated due to a small number of transmitted signals. To solve these problems, in this article, we propose the CR‐QRM‐MLD for SD‐SM Hybrid MIMO (SD‐SM‐MIMO) systems. From the computer simulation results, the proposed method shows the reduction of the computational complexity and the good bit error rate performance.

Spatial Channel Cross-Connect Architectures for Spatial Channel Networks

A spatial channel network (SCN) is a novel optical network architecture targeting the space division multiplexing (SDM) era where the optical layer is explicitly evolved into the hierarchical SDM layer and wavelength division multiplexing layer, and an optical node is decoupled into a spatial channel cross-connect (SXC) and a wavelength cross-connect to form a hierarchical optical cross-connect. In this article, we discuss a wide variety of SXC architectures based on optical matrix switches (MSs) and newly proposed core selective switches (CSSs) from the viewpoints of connection flexibility and architectural complexity. After briefly reviewing the architecture and functionalities of an SCN and its building-block optical devices, novel SXC architectures based on sub-MSs and CSSs are described and formulas are derived for each SXC architecture that give the required number of optical devices, switching mirrors, and internal fiber connections. Based on the formulations, these architectures are compared with traditional SXC architectures based on a high-port count full-MS pair and a Clos network from the viewpoints of the freedom of connection functionalities, operational benefits, and potential node costs associated with the architectural complexity in order to obtain insights regarding which network application is suited to each SXC architecture.

Impact of indirect mode coupling on planar lightwave circuit based mode converters/multiplexers

To improve fiber transmission capacity, space division multiplexing has been proposed and demonstrated, in which mode division multiplexing (MDM) is one option. To implement MDM transmission, mode converters/multiplexers are essential, which can be designed using planar lightwave circuits (PLC). In this work, we propose indirect mode coupling for design of mode converters/multiplexers to improve the performance. It is found that the performance of conversion efficiency, extinction ratio, and crosstalk can be significantly improved by using indirect mode coupling.

Survivable time-aware traffic grooming in spatial division multiplexing elastic optical networks with minimized crosstalk

The space division multiplexing (SDM) technology with multi-core fiber (MCF) is a solution to increase the capacity of optical links. MCF undergoes involuntary challenges due to the interference of transmitted signals on congested multiple cores, named inter-core crosstalk (XT). On the other hand, to protect the huge traffic of users, applying survivability and traffic grooming at the same time is necessary. We study dynamic survivable time-aware grooming, routing, spectrum and core allocation considering XT in SDM-enabled elastic optical networks (SDM-EONs) with MCF and propose survivable grooming time-aware XT-unaware/aware (TXTUSG/TXTASG) algorithms. Using these algorithms, full survivability and optimum utilization of network resources are provisioned by the dedicated path protection and grooming strategies. In addition, the quality of receiving signals is assured by overcoming XT. Furthermore, an attempt is made to reduce fragmentation by involving time dimension. Our simulation results affirm that blocking rate always decreases in suggested algorithms owing to fragmentation reduction, spectrum utilization increase, and bandwidth variable transponders performance enhancement.

Network slicing architecture for SDM and analog-radio-over-fiber-based 5G fronthaul networks

The blueSPACE project focuses on the study of innovative technologies to overcome the limitations of current fronthaul networks. The key technology proposed is space-division multiplexing, which makes it possible to increase the capacity available in conventional single-mode fibers, effectively encompassing this capacity to the forecasted bandwidth demands imposed by 5G mobile communications. In this paper, we present the innovative optical fronthaul infrastructure proposed in the project and the tailored extensions to the European Telecommunications Standards Institute network function virtualization management and orchestration architecture for this enhanced infrastructure together with practical implementation considerations.

Design of 12 OAM-Graded index few mode fibers for next generation short haul interconnect transmission

Abstract The exploitation of the spatial dimension in space division multiplexing (SDM) is a promising solution for increasing the transmission capacity and substantially improving the spectrum efficiency. Orbital angular momentum (OAM) is one of the most attractive approaches of SDM that observes increasing interest either in free space or in optical fiber communications. In this work, we design optimized graded index-few mode fibers (GI-FMFs) supporting 20 eigenmodes with high intermodal separation (≥1 × 10−4) between vector modes; hence limiting intermodal coupling and favoring the formation of 12 OAM modes. To the best of our knowledge, this is the highest OAM number reported in the well-known graded index fiber. We investigate numerically the effects of the shape parameter (α) on the supported vector modes and on the properties of OAM channels in the GI-FMFs. We evaluate their associated differential group delay (DGD) and purity. The selected designs are proposed as viable candidates for short haul connections.

Evaluation of optical MIMO transmissions through multicore fiber links with an optical switch

Multiple-input and multiple-output (MIMO) signal processing technique has been introduced to eliminate the interference caused by crosstalk along Space Division Multiplexing (SDM) links. In optical networks, optical paths are set between end-to-end nodes via several switches. Optical switches connect light signals using appropriate switching rules. Consequently, different combinations of light signals transmitted through several coupled Multi-Core Fibers (MCFs) along an end-to-end optical path. In turn, this type of optical transmission results in an increased complexity with respect to the MIMO signal processing at the receiver and also in a reduced transmission capacity of the entire communication system. To analyze this issue in detail, an optical MIMO network model with MCFs and optical switch was considered, and the eigenvalue distribution of channel matrix along with average capacity of MCF links was discussed. The analysis showed that the optical switch disperses the eigenvalue distribution of channel matrix and reduces the capacity by approximately 15% for SDM network with MCFs. This degradation rate is increased noticeably for larger crosstalk in MCF links and is increased moderately with an increasing number of switches.

On routing, modulation format, space and spectrum allocation with protection in space division multiplexing-based elastic optical networks

ABSTRACTThe required upgradation of the optical network capacity, which is constrained by the non-linear Shannon’s limit and the provisioning needed for the future diverse Internet traffic’s required capacity, can be resolved by the deployment of the Space Division Multiplexing (SDM)-based Elastic Optical Networks (EONs) (SDM-b-EONs). However, with an increase in the rates of transmissions, for countering the network failures, there will be a need for protection mechanisms, specifically those, which can protect the routes and also provision solutions which are end-to-end. In the current work, for an SDM-b-EON, we introduce the Routing, Modulation Format, Space and Spectrum Allocation with Protection-with-Protection (RMFSSA-w-P) algorithm which is independent of the failures in protecting the routes and also considers the modulation format adaptation. We conduct extensive simulations considering realistic networks and the obtained results demonstrate the superior performance of the RMFSSA-w-P algorithm than the existing strategies.

Design of High Speed Optical Fiber Cables and Transmission Techniques in Advanced Optical Networks

In the present paper, design of high velocity fiber-optic communication networks with ultra wide-dense wavelength division multiplexing (UW-DWDM), space division multiplexing (SDM) and optical transmission techniques is presented. All connects in the (SDM) are split into subgroups of various chemical and geometrical characteristics .The parameters have been designed at: i) Δn, the relative refractive index difference for both the core and also the clad, ii) x%, the percentage of doping in silicon material by Germanium material. The Δn and x% parameters are also preserved during their technological boundaries of attention. UW-DWDM has 1200 channels that transferred at the fiber-optic wavelengths from 1450 nm up to 1650 nm within 140 connects from UW-SDM wherever every connect is prepared to own the same compressed chromatic dispersion. From this technique, it is noticed that the connect design parameters suffer more nonlinearity with the number of connects. So, two different propagation techniques have been used to investigate the transmitted bit-rate as a criterion to enhance the system performance. The first technique is Soliton propagation, where the control parameters lead to equilibrium between the pulse spreading due to dispersion and the pulse shrinking because of nonlinearity. The second technique is the maximum time division multiplexing (MTDM) technique where the parameters are adjusted to lead to minimum dispersion. Two cases are investigated; no dispersion cancellation and dispersion cancellation. The investigations are conducted over an enormous range of the set of controlling parameters. Thermal effects are considered through three basic quantities, namely: the transmission bit rate, the dispersion characteristics and the spectral losses.

Routing Core and Spectrum Allocation Algorithm for Inter-Core Crosstalk and Energy Efficiency in Space Division Multiplexing Elastic Optical Networks

Elastic optical networks (EONs) and space-division multiplexing (SDM) have emerged as a promising technology to accommodate the high-capacity and dynamic bandwidth demands of next-generation network. However, the problems of high energy consumption and inter-core crosstalk (ICXT) in space-division multiplexing elastic optical networks (SDM-EONs) are also particularly prominent. In this paper, we proposed an energy efficient grooming and hybrid crosstalk solution (EEG-HCS) algorithm. Firstly, in the routing strategy, a candidate path sorting formula combined the path length and path load state is designed to select the candidate paths and balance the network load. According to the sorting result, whether the current candidate path satisfied the energy efficiency grooming condition or not is determined. When the candidate path meet the energy efficiency grooming condition, the energy efficiency grooming algorithm is used to reduce the transmission energy consumption. For traffic request that do not satisfied the grooming condition, a new optical path is established. Through the core priority grouping, combined with crosstalk avoidance strategy and ICXT aware algorithm, the impact of inter-core crosstalk is minimized, and the probability of successful transmission is improved. In order to evaluate the performance of proposed algorithm, ICXT improvement index is defined. The simulation results show that the proposed algorithm can significantly reduce the energy consumption of space-division multiplexing elastic optical network system while ensuring the optimal blocking probability performance.

Research on few-mode PAM regenerator based on nonlinear optical fiber loop mirror

In recent years, the demand for network bandwidth has increased significantly, and the capacity of wave division multiplexing (WDM) systems has reached the nonlinear Shannon limit. In order to adapt to the development of future networks, space division multiplexing (SDM) technology attracts more and more attention. In this paper, we put forward a novel structure of pulse amplitude modulation(PAM) regenerator based on few-mode nonlinear optical fiber loop mirror (FM-NOLM) for the first time, and theoretically analyze the working principle for few-mode reshaping. It can regenerate degraded PAM signals and improve transmission performance in SDM system. The detailed design steps of the regenerator are given, in which the sulfide highly nonlinear fiber and multimode coupler are used to build up the FM-NOLM and their mode characteristics are simulated by COMSOL software. The parameters of the regenerator are determined by taking the few-mode optical fiber supporting LP<sub>01</sub>, LP<sub>11</sub>, and LP<sub>21</sub> modes as an example, and then the power transfer function (PTF) curve of each mode for PAM signals is calculated. We simulate and analyze the noise reduction ratio (NRR) performance of the few-mode regenerator for PAM-4 signals, and compare with the case of single mode fiber. Our simulation shows that: (1) for each spatial mode of PAM signal, all regenerative levels have the same consistent power transfer performance; (2) for the input signal-to-noise ratio (SNR) greater than 20 dB, the NRR for each mode can exceed 3 dB, and increase with the input SNR at the slope of about 1.2; (3) the NRR difference between the three modes is less than 1.1 dB for the same input SNR. In order to illustrate the reshaping function of the regenerator, we also present the power distribution histograms for PAM-4 signals before and after regeneration when the input SNR is 25 dB. This scheme proposed here has some advantages over the existing regenerators in the applicability for the long-haul SDM system with high spectral efficiency and regeneration of any level number of PAM signals in theory due to its uniform multi-level regeneration function, but also is capable of being extended to the wavelength domain for higher transmission capacity.

Design and Characterization of Nanopore- Assisted Weakly-Coupled Few-Mode Fiber for Simpler MIMO Space Division Multiplexing

We report on a novel weakly-coupled 6-LP-mode fiber that features a nanopore-assisted step-index core with double-cladding profile. The purpose of this fiber design is to alleviate modes coupling and bend sensitivity, thus simplifies the multiple-input multiple-output (MIMO) process and the environmental requirements in which the fiber is used. Through numerical simulations, we show that the minimum effective index difference (Δfl eff ) of larger than 1.8*10 -3 among all LP-mode over C and L band can be achieved by a simple nanopore with 170 nm radius in the center of the core. Furthermore, the dependences of both bending loss and chromatic dispersion on fiber structures are investigated by the finite element method (FEM) to show the good broadband performance. The proposed fiber targets applications in simpler MIMO space division multiplexing (SDM) systems such as data center and short-reach large-capacity transmission.