A multi-core optical fiber comprises a plurality of cores each extending along a predetermined axis and arranged on a cross section perpendicular to the predetermined axis; and a cladding region integrally surrounding each of the cores, wherein the plurality of cores rotate around the predetermined axis, and wherein where an average twist rate defined as an average value of absolute values of angles of rotations of the cores per unit length along a longitudinal direction of the multi-core optical fiber is ³ (rad/m), the shortest distance between centers of the respective cores is A (m), a group index for a fundamental mode in each of the cores is ng, an in-use bending radius defined as a bending radius in use of the multi-core optical fiber is R (m), the speed of light in vacuum is c (m/s), and the ratio of the circumference of a circle to its diameter is À, the multi-core optical fiber satisfies at least one of first to third conditions and satisfies at least either of fourth and fifth conditions, the first condition being defined so that Expression: 2 n g › cR ³À is not more than 7.91×10-12 (s/ml/2), the second condition being defined so that in a state in which the multi-core optical fiber is wound on a bobbin with a radius Rbobbin (m), Expression: 2 n g › cR bobbin ³À is not more than 7.91×10-12×1/Rbobbin (s/m1/2), the third condition being defined so that the shortest distance A is not more than approximately 25×10-6 m and the average twist rate ³ is not less than approximately 4.72 rad/m, the fourth condition being defined so that the shortest distance A is not more than approximately 25×10-6 m, and the fifth condition being defined so that crosstalk between closest adjacent cores is not less than - 15 dB.
MULTI-CORE OPTICAL FIBER, MULTI-CORE OPTICAL FIBER CABLE, AND MULTI-CORE OPTICAL FIBER TRANSMISSION SYSTEM