Ultra-low-loss all-fiber orbital angular momentum mode-division multiplexer based on cascaded fused-biconical mode selective couplers

Mode-division multiplexers(MDMUXs)play a pivotal role in enabling the manipulation of an arbitrary optical state within few-mode fibers,offering extensive utility in the fields of mode-division multiplexing and structured optical field engineering.The exploration of MDMUXs employing cascaded resonant couplers has garnered significant attention owing to their scalability,exceptional integration capabilities,and the anticipated low insertion loss.In this work,we present the successful realization of high-quality orbital angular momentum MDMUX corresponding to topological charges 0,±1,and±2,achieved through the utilization of cascaded fused-biconical tapered couplers.Notably,the measured insertion losses at 1550 nm exhibit remarkable minimal values:0.31,0.10,and 0.64 dB,respectively.Furthermore,the 80%efficiency bandwidths exceed 106,174,and 174 nm for these respective modes.The MDMUX is composed of precisionmanufactured high-quality mode selective couplers(MSCs).Utilizing a proposed supermode propagation method based on mode composition analysis,we precisely describe the operational characteristics of MSCs.Building upon this comprehensive understanding,we embark on a pioneering analysis elucidating the influence of MSC cascading order on the performance of MDMUXs.Our theoretical investigation substantiates that when constructing MDMUXs,MSCs should adhere to a specific cascading sequence.

Low-loss,high-purity,and ultrabroadband all-fiber LP_(41)mode converter employing a mode-selective photonic lantern[Invited]

Broadband mode converters are essential devices for space-division and wavelength-division multiplexing systems.There are great challenges in the generation of higher-order modes above the third order with low loss and high mode purity employing all-fiber devices.In this paper,an all-fiber LP_(41)mode converter is proposed and fabricated by tapering a nine-core single-mode fiber bundle.Experimental results indicate that this all-fiber LP_(41)mode converter is low-loss,high-purity,and ultrabroadband.The insertion loss is less than 0.4 dB.The purity of odd LP_(41)at 1310 nm is 95.09%,and the operating bandwidth exceeds 280 nm.