Relative Core Multiplicity Factor Research Articles

Low crosstalk 125 μm cladding heterogeneous six-core few-mode fiber with air-hole array and trench structure

In order to be compatible with the current optical fiber communication network, we propose a 125 μm diameter heterogeneous six-core two linear polarization modes fiber with air-hole array and trench (HAT) structure. The coupled power theory and finite element method (FEM) are used to investigate inter-core crosstalk (ICXT), bending loss, and other properties. The HAT structure can effectively suppress ICXT; and the maximum ICXT is less than −38 dB/100 km in C + L band. The effective refractive index difference (Δneff) between modes is greater than 3 × 10-3, inter-mode crosstalk (IMXT) can be ignored. The maximum intrinsic loss is 0.187 dB/km; relative core multiplicity factor reaches 32.21. The relative spatial efficiency is 18 times that of traditional single-mode fibers. This fiber can be produced by chemical vapor deposition and existing optical fiber manufacturing technology. The designed fiber can be directly connected to the communication network to reduce the cost of equipment renewal, and the communication capacity can be increased by 18 times.

Trench-assisted 12-core 5-LP mode fiber with a low refractive index circle and a high refractive index ring.

We propose a homogeneous five-mode twelve-core fiber with a trench-assisted structure, combining a low refractive index circle and a high refractive index ring (LCHR). The 12-core fiber utilizes the triangular lattice arrangement. The properties of the proposed fiber are simulated by the finite element method. The numerical result shows that the worst inter-core crosstalk (ICXT) can achieve at -40.14 dB/100 km, which is lower than the target value (-30 dB/100 km). Since adding the LCHR structure, the effective refractive index difference between LP21 and LP02 mode is 2.8 × 10-3, which illustrates that the LP21 and LP02 modes can be separated. In contrast to without the LCHR, the dispersion of LP01 mode has an apparent dropping, which is 0.16 ps/(nm·km) at 1550 nm. Moreover, the relative core multiplicity factor can reach 62.17, which indicates a large core density. The proposed fiber can be applied to the space division multiplexing system to enhance the fiber transmission channels and capacity.

Low cross talk homogeneous few-mode multi-core fiber with a suspended air-trench and V-type index core

We propose a homogeneous 13-core 4 linear-polarized modes fiber based on a suspended air-trench V-type index core (SA-VC) structure that can suppress inter-core cross talk (ICXT) and inter-mode cross talk. The SA structure is used to control ICXT, and the VC structure is used to control inter-mode cross talk. Cross talk and other properties of the fiber are calculated by coupled power theory and the finite element method. The numerical results demonstrate that the SA-VC structure has stronger cross talk suppression ability compared with traditional trench structure, the ICXT meets the requirement of lower than − 30 d B / 100 k m , the effective refractive index difference ( Δ n e f f ) between modes is greater than 1.52 × 10 − 3 , the maximum intrinsic loss is 0.189 dB/km, and the relative core multiplicity factor reaches 49.09. Based on the current optical fiber fabrication technology, a manufacturing scheme for this fiber preform is proposed. This design structure aims to be applied to communication systems to increase the transmission capacity of optical fibers.

Low cross talk homogeneous seven-core five-LP mode fiber based on a high and low refractive index double ring

We propose a what we believe is a novel, to the best of our knowledge, high and low refractive index double-ring (HL-DR) structure in few-mode multicore fibers (FM-MCFs) to simultaneously suppress intercore cross talk (XT) and intermodal cross talk. The fabrication methods of HL-DR seven-core fiber are introduced. A series of intercore XT values are calculated by the average power coupling coefficient, which shows that the HL-DR structure has a great contribution to meet the intercore XT target of less than − 30 d B / 100 k m in FM-MCFs. Intermodal XT is mainly measured by the effective refractive index difference ( Δ n e f f ) between modes, and the Δ n e f f between any two adjacent modes is larger than 2 × 1 0 − 3 . Other main fiber properties, including bending loss and dispersion, are also simulated by the finite-element method. The results imply that the bending loss can satisfy the requirement of five-LP mode operation over the C + L band. In addition, the dispersion comparison of L P 01 mode illustrates that the fiber dispersion performance is not significantly influenced by the addition of the HL-DR structure. Through numerical analyses, an optimal HL-DR seven-core five-LP mode fiber with low XT is obtained, and it has a relative core multiplicity factor (RCMF) of 62.17. The proposed structure targets the design and application of space division multiplexing fibers with high capacity and independent channels.

Superposition-assisted 125-μm cladding multi-core fibers with ultra-low inter-core crosstalk and high relative core multiplicity factor

We propose a novel superposition-assisted structure (SAS), composed of trench and air holes, in few-mode multi-core fibers (FM-MCFs) to effectively suppress the inter-core crosstalk (XT). The proposed SAS can minimize the inter-core XT to −70.58 dB/100 km in the 7-core fibers, which is 60 dB/100 km lower than the typical trench-assisted structure and 29 dB/100 km lower than the typical hole-assisted structure, respectively. In addition, the SAS does not introduce extra fiber loss and dispersion. In this paper, the key properties of SAS MCFs are numerically simulated using the finite element method (FEM). The large effective area (Aeff) over 90 μm2 enables the suppression of nonlinear effects. The values of dispersion coefficient and differential mode group delay (DMGD) are in the range of 24–42 [ps/(nm·km)] and 5–23 ps/m over C + L band, respectively, which are favorable for fiber communication systems. Such SAS 7-core 5-LP-mode fibers can be further optimized to obtain the cladding diameter of 125 μm, where five propagation modes achieve inter-core XT target below −50 dB/100 km with the bending radius less than 500 mm. Besides, the optimized relative core multiplicity factor (RCMF) can be up to 97.55. The proposed SAS provides a promising solution for the design of FM-MCFs with ultra-low inter-core XT and high capacity for space division multiplexing (SDM).

Manufacturable low-crosstalk high-RCMF 13-core 5-LP mode fiber with graded-index core and stairway-index trench.

We propose a novel scheme of high doped core and stairway-index trench structure to design a manufacturable graded-index 13-core 5-LP mode fiber with low inter-core crosstalk (ICXT) and large mode differential group delay (MDGD). By using the couple power theory and the finite element method (FEM), the change ICXT of with fiber parameters are investigated. The design of core graded profile and trench structure are optimized to achieve better performance and to meet the fabrication conditions. The numerical result demonstrate that this fiber achieves a low ICXT of lower than -30dB/km (Rb≤500 mm). The bending loss values satisfy the ITU-T recommendation G.655 in 195 µm cladding diameter. Furthermore, the dispersion and the MDGD dependences on wavelength are calculated. The relative core multiplicity factor (RCMF) is obtained as 75.17, which realizes the high density multiplexing. The fabrication methods of this fiber are briefly introduced. The designed fiber may be used for Space-division multiplexing (SDM) system to solve the problem of fiber capacity limitation.

Low-DMD and low-crosstalk few-mode multi-core fiber with air-trench/holes assisted graded-index profile

We propose a novel scheme of air-trench (AT) assisted graded-index profile to design a heterogeneous few-mode multi-core fiber (hetero-FM-MCF) with high density of cores and low inter-core crosstalk (XT). By the using of finite element method (FEM), it is revealed that the AT structure can remarkably reduce XT and bending loss, and leaving no significant impact on other fiber properties. The numerical analyses show that the AT hetero-FM-MCF achieves a low XT of about -66 dB/km (15.7% lower than that of trench-assisted (TA) hetero-FM-MCF), the max differential model delay (DMD) over C+L band of 70 ps/km and relative core multiplicity factor (RCMF) of 41.7. To further improve the light confinement ability of individual cores, air-holes (AH) are introduced to the AT structure. The air-trench/hole assisted (AT-AH) hetero-FM-MCF generates a lower XT of -68 dB/km and 6% bending loss values optimization than AT hetero-FM-MCF.

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.

Optimal design of a bend-insensitive heterogeneous MCF with differential inner-cladding structure and identical cores

Abstract We propose a scheme of differential inner-cladding structure and identical cores to design a kind of bend-insensitive heterogeneous multi-core fiber (MCF) with high density of cores and ultra-low crosstalk (XT), which have not been previously reported. Eight cores are arranged in a ring layout in a fiber diameter of 150 μm. The impact of differential inner-cladding structure on fiber performances has been simulated and evaluated in detail. The numerical analyses show that the proposed hetero-MCF achieves an ultra-low XT of less than −50 dB/100 km, mode field area ( A eff ) of larger than 90 μm2, cut-off wavelength ( λ cc ) of less than 1350 nm, bending loss of less than 0.5 dB/100 turns at 1625 nm when bending radius ( R b ) is set to be 30 mm, and relative core multiplicity factor (RCMF) of 6.77. Our proposed hetero-MCF is capable for long distance and high capacity space division multiplexing (SDM) optical transmission systems.

Six-Mode Seven-Core Fiber for Repeated Dense Space-Division Multiplexing Transmission

We propose the optimum design of high spatial density few-mode multicore fiber (MCF) for repeated space-division multiplexed (SDM) transmission. Numerical analyses reveal that a hexagonally arranged six-mode seven-core structure is potentially better than the other possibility, the six-mode multicore structure, in terms of realizing high spatial density and low mode-dependent loss (MDL) characteristics at the splice point; its benefits will enable us to construct long-haul dense SDM transmission links. We fabricate a 171 μ m cladding six-mode seven-core fiber and successfully demonstrate low loss, differential mode delay (DMD), crosstalk, and splice-induced MDL characteristics while maintaining the relative core multiplicity factor of more than 50. Finally, we demonstrate repeated optical 12 × 12 MIMO transmission of more than 100 km using our six-mode MCF and erbium doped fiber amplifier (EDFA).

Optimal design for crosstalk analysis in 12-core 5-LP mode homogeneous multicore fiber for different lattice structure

Abstract 12-Core 5-LP mode homogeneous multicore fibers have been proposed for analysis of inter-core crosstalk and dispersion, with four different lattice structures (circular, 2-ring, square lattice, and triangular lattice) having cladding diameter of 200 µm and a fixed cladding thickness of 35 µm. The core-to-core crosstalk impact has been studied numerically with respect to bending radius, core pitch, transmission distance, wavelength, and core diameter for all 5-LP modes. In anticipation of further reduction in crosstalk levels, the trench-assisted cores have been incorporated for all respective designs. Ultra-low crosstalk (-138 dB/100 km) has been achieved through the triangular lattice arrangement, with trench depth Δ2 = −1.40% for fundamental (LP01) mode. It has been noted that the impact of mode polarization on crosstalk behavior is minor, with difference in crosstalk levels between two polarized spatial modes as ≤0.2 dB. Moreover, the optimized cladding diameter has been obtained for all 5-LP modes for a target value of crosstalk of −50 dB/100 km, with all the core arrangements. The dispersion characteristic has also been analyzed with respect to wavelength, which is nearly 2.5 ps/nm km at operating wavelength 1550 nm. The relative core multiplicity factor (RCMF) for the proposed design is obtained as 64.

Optimal design of 4LP-mode multicore fibers for high spatial multiplicity.

High spatial multiplicity fiber designs are presented for homogeneous and heterogeneous 4LP-mode multicore fibers (MCFs) that support six spatial modes per core. The high-spatial-density 4LP-mode MCF design methodology is explained in detail. The influence of the number of cores on the cladding diameter (Dcl) and relative core multiplicity factor (RCMF) is investigated. The optimal core designs and MCF layouts with square and triangular lattices maintain glass fiber reliability (maximum Dcl = 250 μm). For homogeneous 4LP-mode MCFs, a 19-core triangular-lattice fiber gives the highest RCMF of 61.7. For heterogeneous 4LP-mode MCFs, an RCMF of 65.4 is obtained for a 21-core square-lattice fiber.

Design and optimization of 32-core rod/trench assisted square-lattice structured single-mode multi-core fiber.

We propose and design a kind of heterogeneous rod-assisted and trench-assisted multi-core fiber (Hetero-RA-TA-MCF) with 32 cores arranged in square-lattice structure (SLS), and then we introduce the design method for Hetero-RA-TA-MCF. Simulation results show that the Hetero-RA-TA-32-Core-Fiber achieves average effective area (Aeff) of about 74 μm2, low crosstalk (XT) of about -31 dB/100km, threshold value of bending radius (Rpk) of 7.0 cm, relative core multiplicity factor (RCMF) of 8.74, and cable cutoff wavelength (λcc) of less than 1.53 μm.

Low-Loss and Low-DMD 6-Mode 19-Core Fiber With Cladding Diameter of Less Than 250 μm

We investigate a few-mode multicore fiber structure suitable for realizing a high spatial density while maintaining a feasible cladding diameter. First, we discuss the impact of cladding diameter on mechanical reliability, and set a target cladding diameter of less than 250 μm to maintain a comparable reliability to conventional fiber. We then optimize the 6-mode core profile to obtain a low differential mode delay (DMD) characteristic and reveal that a hexagonally arranged 19-core structure can realize more than 100 spatial channels with a cladding diameter of less than 250 μm. Finally, we fabricate 6-mode 19-core fiber with a 246 μm cladding diameter and realize a relative core multiplicity factor of more than 60 with a low loss and a DMD of less than 0.24 dB/km and 0.33 ns/km, respectively.

Design and optimization of 3-mode×12-core dual-ring structured few-mode multi-core fiber

We adopt dual-ring structure (DRS) for the core arrangement of 3-mode (LP01, LP11a and LP11b)×12-core few-mode multi-core fiber (FM-MCF) and then introduce the design method for this DRS-FM-MCF. After investigating the characteristics such as differential mode delay (DMD), inter-core crosstalk (XT), threshold value of bending radius (Rpk), relative core multiplicity factor (RCMF) and cable cutoff wavelength (λcc), we present an optimized scheme for this DRS-FM-MCF. For the optimized DRS-FM-MCF, |DMD| is ≤100ps/km over C+L band, the maximum XT at wavelength (λ) of 1625nm achieves −33dB/100km, maximum Rpk is 11.03cm, RCMF (LP01, LP11a and LP11b) reaches 25.49 and maximum λcc is ≤1530nm. Compared with one-ring structure (ORS), DRS has much more space to enlarge core pitch (Λ) so that lower XT can be achieved. Furthermore, DRS has less confinement degree on mode than square-lattice structure (SLS) if Λ and cladding diameter (Dcl) are set at similar values. It means that it is easier for DRS to make sure λcc would not be larger than the lower limit of C+L bands. In this paper, DRS is proved as a suitable core arrangement for 3-mode×12-core FM-MCF.

Heterogeneous trench-assisted few-mode multi-core fiber with graded-index profile and square-lattice layout for low differential mode delay.

We propose a kind of heterogeneous trench-assisted graded-index few-mode multi-core fiber with square-lattice layout. For each core in the fiber, effective area (A(eff)) of LP(01) mode and LP(11) mode can achieve about 110 μm(2) and 220 μm(2). Absolute value of differential mode delay (|DMD|) is smaller than 100 ps/km over C + L bands, which can decrease the complexity of digital signal processing at the receiver end. Considering the upper limit of cladding diameter (D(cl)) and cable cutoff wavelength of LP(21) mode in the cores located at the inner layer, we set core pitch (Λ) as 43 μm. In this case, D(cl) is about 220.4 μm, inter-core crosstalk (XT) is lower than -40 dB/500 km and the relative core multiplicity factor (RCMF) reaches 15.93.

Heterogeneous trench-assisted few-mode multi-core fiber with low differential mode delay.

We propose a kind of heterogeneous multi-core fiber (Hetero-MCF) with trench-assisted multi-step index few-mode core (TA-MSI-FMC) deployed inside. After analyzing the impact of each parameter on differential mode delay (DMD), we design a couple of TA-MSI-FMCs with A(eff) of 110 μm2 for LP01 mode. DMD of each TA-MSI-FMC is smaller than |170| ps/km over C + L band and the total DMD can approach almost 0 ps/km over C + L band if we adopt DMD managed transmission line technique by using only one kind of Hetero-TA-FM-MCF. For such Hetero-TA-FM-MCF, crosstalk is about -30 dB/100km at wavelength of 1550 nm as bending radius becomes larger than 15 cm, core number can reach 12, a relative core multiplicity factor (RCMF) is 15.7, and the RCMF can even reach 26.1 if we treat LP11 mode as two special modes thanks to the multiple-input-multiple-output technology.

Large Effective-Area Few-Mode Multicore Fiber

A design concept of few-mode multicore fiber is presented. Cores with a step-index profile are designed to support two LP modes over the C band and the L band with a large effective area larger than 110 μm2. The pitch of cores is determined regarding the inter-core crosstalk related to the LP11 mode. The two LP modes multicore fibers with four cores and seven cores show a relative core multiplicity factor (RMCF) of 7.3 and 9.2, respectively. The RCMF of the proposed two LP modes multicore fiber is larger than that of previously reported single-mode multicore fibers.