Few-mode fibre device

A few-mode fibre device. A fibre core of the few-mode fibre device is composed of a main fibre core (1) and an auxiliary fibre core (2), wherein there is only one main fibre core (1), and the normalized frequency V m meets the condition that V m > 2.405, i.e. supporting high-order mode transmission; the number of auxiliary fibre cores (2) is M, wherein M ≥ 1; one end of the auxiliary fibre cores (2) intersects with a side face of the main fibre core (1), and the central axis of the main fibre core (1) is in the same plane as the central axis of the auxiliary fibre cores (2); the other end of the auxiliary fibre cores (2) is located on an end face of the fibre, and in the end face, the centre distance between any two fibre cores is greater than the sum of the radii of the two fibre cores; and a parameter between any auxiliary fibre core (2) and the main fibre core (1) meets: the main fibre core (1) at least has a transmission mode of which the effective refractive index is less than the effective refractive index of a fundamental mode of the auxiliary fibre cores (2). A mode in a few-mode fibre can be converted, combined, separated or filtered.