TECHNICAL FIELD

The present disclosure relates to a multicore optical fiber (hereinafter, referred to as an “MCF”) and an MCF cable including the MCF.

BACKGROUND ART

In recent years, an optical fiber transmission system that compensates for crosstalk between spatial modes by using a multi-input and multi-output (MIMO) signal processing technology and enables space division multiplexed transmission is under development. As one of transmission media applicable to such an optical fiber transmission system, for example, an MCF including a coupled core group in which a plurality of cores are arranged to cause mode coupling between the cores is known, and causing mode coupling between the plurality of cores allows the coupled core group to be regarded as substantially one multimode transmission line.

CITATION LIST

Non Patent Literature

Non-Patent Document 1: ECOC2015, We.1.4.1Non-Patent Document 2: JLT 34(4), 1228 (2016).Non-Patent Document 3: S. Fan and J. M. Kahn, “Principal modes in multimode waveguides,” Opt. Lett. 30(2), 135-137 (2005).Non-Patent Document 4: M. Koshiba, K. Saitoh, K. Takenaga, and S. Matsuo, “Analytical expression of average power-coupling coefficients for estimating intercore crosstalk in multicore fibers,” IEEE Photon. J. 4(5), 1987-1995 (2012).Non-Patent Document 5: T. Hayashi, T. Sasaki, E. Sasaoka, K. Saitoh, and M. Koshiba, “Physical interpretation of intercore crosstalk in multicore fiber:effects of macrobend, structure fluctuation, and microbend,” Opt. Express 21(5), 5401-5412 (2013).Non-Patent Document 6: T. Sakamoto, T. Mori, M. Wada, T. Yamamoto, F. Yamamoto, and K. Nakajima, “Fiber twisting and bending induced adiabatic/nonadiabatic super-mode transition in coupled multi-core fiber.,” J. Lightw. Technol., vol. 34, no. 4, pp. 1228-1237, February 2016.

SUMMARY OF INVENTION

The multicore optical fiber cable (MCF cable) according to the present disclosure contains a plurality of multicore optical fibers (MCFs). Each of the MCFs includes at least one coupled core group and a common cladding surrounding the coupled core group. Note that the coupled core group includes a plurality of cores. Further, each of the MCFs has a core structure adjusted to satisfy the first and second conditions, core arrangement, and average torsion (fiber torsion), where Cavg[m−1] represents an average curvature of bending of the MCF along the longitudinal direction of the MCF no bending applied to the MCF cable, Cf[m−1] represents a pseudo-curvature of the MCF, ftwist[turn/m] represents an average torsion of the MCF, κ [m−11] represents a coefficient of mode coupling between adjacent cores of the plurality of cores, β [m−1] represents an average of propagation constants of the adjacent cores, and Λ [m] represents a core center-to-center distance between the adjacent cores. The first condition is that the core center-to-center distance Λ is set so as to make the coefficient κ of mode coupling between the adjacent cores at a wavelength of 1550 nm fall within a range of from 1×10−1[m−1] to 1×103[m−1]. The second condition is that mode coupling with at least one tenth of the maximum randomness is achieved.

