Broadband LP₀₁-LP₀₂ mode converter for O-, E-, S-, C-, L-, and U-bands

This paper proposes a novel all-optical fiber mode converter for mode conversion from LP₀₁ to LP₀₂ and vice versa. The mode converter is formed by connecting a single-mode fiber, a taper-core multi-mode fiber, and a few-mode fiber (FMF) together. The taper fiber core is designed to convert LP₀₁ mode to LP₀₂. The few-mode fiber is used to cut off the modes that are higher than LP₀₂. It is shown that the proposed mode converter provides 20 dB extinction ratio and low insertion loss in a very broad optical bandwidth of 200 nm, from 1465 to 1665 nm. By further optimizing the FMF radius only for each of the O-, E-, S-, C-, U-, etc. bands, the mode converter can apply to any band of interest with higher performance. It is found that the performance of the mode converter has a large tolerance to structural parameters. The mode converter has the same performance in reciprocal operation, i.e., LP₀₂ to LP₀₁.