Katsuhiro Takenaga

Analytical Expression of Average Power-Coupling Coefficients for Estimating Intercore Crosstalk in Multicore Fibers

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 Δβmn 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 (Δβmn = 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.

Multi- core fiber design and analysis : coupled-mode theory and coupled-power theory

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.

Fabrication of electromagnetic crystals with a complete diamond structure by stereolithography

Three-dimensional electromagnetic or photonic crystals with periodic variations of the dielectric constants were fabricated by a rapid prototyping method called stereolithography. Millimeter-order epoxy lattices with a diamond structure were designed to reflect electromagnetic waves by forming an electromagnetic bandgap in the GHz range. Titanium oxide-based ceramic particles were dispersed into the lattice to control the dielectric constant, resulting in the formation of narrow and deep bandgaps. Crystals of the inverse form that have a network of holes with the diamond structure in a dielectric matrix were successfully fabricated as well. These inverse diamond structures formed the perfect bandgap reflecting electromagnetic waves for all directions. The location of the bandgap agreed with the band calculation using the plane wave propagation method.

Reduction of crosstalk by trench-assisted multi-core fiber

Trench-assisted multi-core fiber (TA-MCF) is proposed to achieve high dense MCF design with a solid structure. The crosstalk value at 1.55 µm of fabricated TA-MCF is estimated to be −35 dB at 100 km.

A large effective area multi-core fiber with an optimized cladding thickness

The cladding-thickness of trench-assisted multi-core fibres was investigated in terms of excess losses. The MCF with an effective area of 110 μm² at 1.55 μm and 181-μm cladding diameter was realised without any excess loss.

Reduction of crosstalk by quasi-homogeneous solid multi-core fiber

Power-conversion efficiency reduction on a quasi-homogeneous solid multi-core fiber is numerically investigated. The fiber length dependence of measured crosstalk of fabricated fibers is in good agreement of simulation result by power-coupled equation.

Design and analysis of large-effective-area heterogeneous trench-assisted multi-core fiber

Based on the overlap integral of electromagnetic fields in neighboring cores, a calculating method is proposed for obtaining the coupling coefficient between two adjacent trench-assisted non-identical cores. And a kind of heterogeneous trench-assisted multi-core fiber (Hetero-TA-MCF) with 12 cores is proposed to achieve large effective area (A(eff)) and high density of cores. As bending radius becomes larger than 50 mm, the crosstalk value at 1550-nm wavelength of the Hetero-TA-MCF is about -42 dB after 100-km propagation and the A(eff) of this Hetero-TA-MCF can reach 100 µm(2).

Boundary element method for analysis of holey optical fibers

By using a full-vector boundary element method (BEM) based on a formulation in terms of transverse magnetic field components, holey fibers (HFs) are numerically analyzed. The BEM provides very accurate solutions with an extremely small number of unknowns. Not only the characteristics of all-silica HFs, but also those of hole-assisted lightguide fibers and field-confined HFs, are investigated and compared with each other.

12-core fiber with one ring structure for extremely large capacity transmission

The feature of a multicore fiber with one-ring structure is theoretically analyzed and experimentally demonstrated. The one-ring structure overcomes the issues of the hexagonal close-pack structure. The possibility of 10-core fiber with Aeff of 110 μm(2) and 12-core fiber with Aeff of 80 μm(2) is theoretically presented. The fabricated 12-core fibers based on the simulation results realized Aeff of 80 μm(2) and crosstalk less than -40 dB at 1550 nm after 100-km propagation. The MCF with the number of core larger than seven and the small crosstalk was demonstrated for the first time.

409-Tb/s + 409-Tb/s crosstalk suppressed bidirectional MCF transmission over 450 km using propagation-direction interleaving

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.