Mode division multiplexing of an all-fiber three-mode selective coupler

Abstract

The emergence of space division multiplexing technology has enabled large-scale expansion of fiber transmission capacity, and the mode selection coupler (MSC) based on few-mode fibers (FMFs) has been studied as a promising technique for SDM. In this work, we demonstrated an all-fiber three-mode selective coupler formed with a pre-tapered single-mode fiber and two types of FMF by fused biconical taper technology. The simulation results show that efficient mode conversion can be achieved by optimizing the degree of pre-tapered fibers, fiber core distance, and coupling zone length. Both simulated and experimental results show that the FMF in the MSC is capable of selectively exciting LP11, LP21, or LP31 modes. The simulation illustrates that the conversion purity is higher than 50%, and the bandwidth can reach 360 nm, 395 nm, and 180 nm when the two high-order modes are LP11/LP11, LP11/LP21, and LP11/LP31, respectively. Furthermore, the MSC is capable of mode multiplexing without the need of a mode converter and can generate high-quality orbital angular momentum modes. This MSC design is scalable to accommodate a larger number of mode selective couplings, so it can be easily integrated with broadband fiber optical communication systems.