Abstract

The concept of parity-time (PT) symmetry in optics attracts great deal of attention. Recently, a parity-time symmetry-breaking laser consisted of two coupled microrings has been experimentally demonstrated [1, 2]. A single-mode operation in an initially multimode system was achieved through stronger mode discrimination close to a PT-symmetry breaking transition. Further on, a single transverse mode operation in a system of coupled microring lasers was demonstrated near the exceptional point [3]. A possible route to a PT symmetrybased mode-locking has been theoretically discussed in paper [4].

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