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.

Accurate mode purity measurement of ring core fibers with large mode numbers from the intensity distribution only

Mode purity measurement is crucial for various applications utilizing few-mode fibers and related devices.In this paper,we propose a simple and accurate method for measuring the mode purity of the output optical field in fewmode ring-core fibers(RCFs).Mode purity can be calculated solely from the outgoing intensity distribution with high precision.This method is theoretically capable of measuring the mode purity of RCFs that support orbital angular momentum modes with an infinite number of azimuthal orders and has strong applicability to various RCF types and image qualities simultaneously.We demonstrate our approach numerically and verify it experimentally in a few-mode RCF supporting four(five)mode groups at 1550(1310)nm.A polarization test method is proposed to verify its accuracy.We believe that this straightforward and cost-effective characterization method for RCFs and RCF-based devices can promote the development of mode-division multiplexing technology and its applications.

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.