Abstract

In this Letter, we have studied the effect of losses and gains on generation of optical vortices (OVs) in a chiral fiber with an $l$-fold rotational symmetric core. Studying both unequal attenuations and symmetric loss–gain cases for core and orbital angular momentum (OAM) modes, we show that losses may play a constructive role in generation of OVs from a Gaussian input. We study the processes of field evolution at the exceptional point (EP). We show that at the EP any superposition of the fundamental mode and $l$-charge OV evolves in the limit into an equal-weighted superposition of such fields that forms a special attractor mode with average $l/{2}$ OAM per photon. At the generalized Poincare sphere, such a mode is represented by the OAM black hole in analogy with the spin black hole introduced in [Optica 3, 1025 (2016) [CrossRef]  ].

© 2021 Optical Society of America

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