Coupled-mode and coupled-power theories are described for multi-core fiber design and analysis. First, in order to satisfy the law of power conservation, mode-coupling coefficients are redefined and ...then, closed-form power-coupling coefficients are derived based on exponential, Gaussian, and triangular autocorrelation functions. Using the coupled-mode and coupled-power theories, impacts of random phase-offsets and correlation lengths on crosstalk in multi-core fibers are investigated for the first time. The simulation results are in good agreement with the measurement results. Furthermore, from the simulation results obtained by both theories, it is confirmed that the reciprocity is satisfied in multi-core fibers.
When few-mode fibers are employed in mode-division multiplexing (MDM), mode coupling between the propagation modes must be suppressed. In this study, the impulse response for a two-mode fiber (TMF) ...is theoretically described to estimate the mode coupling in the fiber and at a splice point. We then propose a technique for measuring the mode-coupling coefficient in a TMF based on the impulse response technique. The mode-coupling behavior in a fiber and at splice points is measured experimentally using the proposed technique for several fabricated TMFs. We clarify the relationship between the effective-index difference Δ n eff between LP 01 and LP 11 modes and the mode-coupling coefficient h for our fabricated TMFs.
In order to realize fast and accurate estimation of intercore crosstalk in bent multicore fibers (MCFs), an analytical expression of the average power-coupling coefficient (PCC) based on an ...exponential autocorrelation function is, for the first time, derived, resulting in no need for heavy numerical computations. It is revealed that, when the bending radius is large and the correlation length is large, the average PCC is inversely proportional to the correlation length and to the square of the propagation constant difference Δβ mn between core m and core n, and when the bending radius is small and the correlation length is large, the average PCC is proportional to the bending radius and is independent of the correlation length. When the correlation length is small, on the other hand, the average PCC is proportional to the correlation length and is independent of the bending radius. For homogeneous MCFs (Δβ mn = 0) with small bending radius, the average PCC coincides with the mean crosstalk increase per unit length derived from the coupled-mode theory of Hayashi et al. that is proportional to the bending radius. Average crosstalk values calculated by using the analytical expression derived here are in excellent agreement with those of numerical solutions of coupled-power equations, irrespective of the values of bending radius and correlation length.
Multicore fibers (MCFs) are expected as a good candidate for overcoming the capacity limit of a current optical communication system. This paper describes the recent progress on the MCFs for ...space-division multiplexing to be utilized in future large capacity long-distance transmission systems. Tradeoff issue between low crosstalk and high core density in MCFs is presented and prospect of large-space multiplicity of MCFs is discussed.
•Designee issues in FM-MCFs are presented.•Proposed FM-MCFs to date are reviewed.•Design and measured characteristics of a fabricated FM-MCF are presented.
Few-mode multicore fibers (FM-MCFs) that ...enable dense space-division multiplexing (DSDM) have the potential to drastically improve the fiber capacity. In designing the FM-MCFs, several issues that originate from multicore fibers and few-mode fibers must be considered. In this paper, these design issues such as inter-core crosstalk (IC-XT) and dispersion mode delay (DMD) are discussed. A three-mode 12-core fiber with low-DMD low-IC-XT achieves long-haul DSDM transmission over 500km. The design concept, fiber design, and characteristics of the fabricated three-mode 12-core fiber are also described.
We demonstrate bidirectional transmission over 450 km of newly-developed dual-ring structured 12-core fiber with large effective area and low crosstalk. Inter-core crosstalk is suppressed by ...employing propagation-direction interleaving, and 409-Tb/s capacities are achieved for both directions.
We experience Internet traffic growth of 100 times every 10 years. However, the capacity of existing standard single-mode fiber is approaching its fundamental limit regardless of significant ...realization of transmission technologies which allow for high spectral efficiencies. Space division multiplexing (SDM) based on multicore fibers (MCFs) has emerged as a solution to the problem of saturation of the capacity of optical transmission systems. This article presents the recent progress on the MCFs for future large capacity long-distance transmission systems. In MCFs, there is a tradeoff relationship between low crosstalk and high multiplicity, therefore the maximum number of cores and the core arrangement have to be carefully determined based on the required crosstalk level and core size. The state-of-the-art of fabricated MCFs and the transmission experiments using MCFs are reviewed. The current maximum capacity-distance product in MCF transmission is 368.2 (184.1+184.1) Pb/s/fiber km with the relative spatial efficiency of 4.7 compared with a standard single-mode fiber. In order to increase the spatial efficiency as well as the capacity-distance product further in MCFs, the possibility of heterogeneous MCFs and few-mode MCFs is also presented.
In this paper, we present long-haul 32-core dense space-division-multiplexed (DSDM) unidirectional transmission over a single-mode multicore transmission line. We developed a low-crosstalk ...heterogeneous 32-core fiber with a square lattice arrangement, and a novel partial recirculating loop system. The span crosstalk of the 51.4-km 32-core transmission line was less than -34.5 dB. This allowed the transmission of polarization-division-multiplexed 16 quadrature amplitude modulation (PDM-16QAM) signals through all 32 cores over a long distance exceeding 1000 km. We demonstrate 32-core DSDM 20 wavelength-division-multiplexed PDM-16QAM transmission over 1644.8 km with a high aggregate spectral efficiency of 201.46 b/s/Hz Additionally, we examine the effect of crosstalk on the transmission performance of each core, and show that the Q-penalty has strong correlation with intercore crosstalk.
Intercore crosstalk of heterogeneous multicore fiber is investigated based on coupled-mode theory. Random twisting model is used for estimating the crosstalk. The crosstalk of two kinds of fibers: ...triangular lattice 30-core fiber with four kinds of cores and square lattice 32-core fiber with two kinds of cores is investigated both theoretically and experimentally. Unlike previous study, measured crosstalk for all the combinations of cores for both fibers is in good agreement with calculated values with single correlation length, showing the validity of the theoretical model used here.
We demonstrate 7-core fiber transmission of 10 x 96-Gb/s PDM-16QAM signals over 1000-km using distributed Raman amplification (DRA). DRA gain of 9-12 dB and equivalent noise figure of less than 1 dB ...are achieved in all cores. We also prove the feasibility of high power multi-core fiber transmission with per fiber power of 6.5 W.
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