Low-Loss All-Fiber Mode Multiplexers for Weakly-Coupled 4-Mode Fiber

In this paper, we report an all-fiber 4-mode fiber multiplexer and its measurement, which uses a fused tapering method to fabricate different mode-selective coupler. The insertion loss of a single mode-selective is less than 0.7dB, the insertion loss of LP
01
, LP
11
, LP
21
and LP
02
is less than 3 dB after cascading, while the modal crosstalk is lower than −15dB. This device can be applied in mode-division multiplexing transmission systems.