An all-optical fiber mode converters based on 5-LP mode fiber of weakly coupling and large effective mode area

In this work, an all-optical fiber-based mode converter was created by mating a self-made 5-mode fiber (5MF) with a single mode fiber (SMF) using the fused tapering approach. The 5MF was characterized by weakly coupling and large effective mode area with the attenuation of 0.277 dB/km. By controlling the core size during the pre-tapering process, mode conversions of high efficiency were successfully realized between the fundamental mode in the SMF with the five modes (LP01, LP11, LP21, LP02 and LP31) in the 5MF. At the wavelength of 1550 nm, the reality normalized coupling efficiencies of the five conversion processes were 0.952, 0.930, 0.990, 0.923 and 0.998, respectively. Moreover, a 5-mode-division multiplexer was produced by cascading the five mode converters in terms of descending order (LP01, LP11, LP21, LP02, LP31). The 5MF, mode converters and multiplexers provide a convenient and effective option for constructing the high-capacity mode division multiplexing communication systems.