%ANada, Mohamed%ACapolino, Filippo%BJournal Name: Journal of the Optical Society of America B; Journal Volume: 37; Journal Issue: 8; Related Information: CHORUS Timestamp: 2022-10-06 15:10:08 %D2020%IOptical Society of America %JJournal Name: Journal of the Optical Society of America B; Journal Volume: 37; Journal Issue: 8; Related Information: CHORUS Timestamp: 2022-10-06 15:10:08 %K %MOSTI ID: 10171132 %PMedium: X %TExceptional point of sixth-order degeneracy in a modified coupled-resonator optical waveguide %X

We demonstrate for the first time, to our knowledge, the occurrence of asixth-order exceptional point of degeneracy (EPD) in a realistic multimode optical photonic structure by using a modified periodic coupled-resonator optical waveguide (CROW) at the optical wavelengthλ<#comment/>e=1550nm. The sixth-order EPD is obtained in a CROW without the need of loss or gain, and such an EPD corresponds to a very special band edge of the periodic photonic structure where six eigenmodes coalesce, so we refer to it as the sixth-order degenerate band edge (6DBE). Moreover, we report a new scaling law of the quality factorQof an optical cavity made of such a periodic 6DBE-CROW with cavity length asQ∝<#comment/>N7, when operating near the 6DBE withNbeing the number of unit cells in the periodic finite-length CROW. Furthermore, we elaborate on the application of the 6DBE to ultralow-threshold lasers. We present a novel scaling law of the lasing threshold that scales asN−<#comment/>7when operating near the 6DBE. Also, we show the superiority of the threshold scaling of the 6DBE-CROW to the scaling of another CROW with the same size operating near a fourth-order EPD that is often referred to as the degenerate band edge (DBE). The lasing threshold scaling of the DBE-CROW laser is shown here for the first time to our knowledge. We also discuss the high sensitivity of the proposed 6DBE-CROW to perturbations, which may find applications in sensors, modulators, optical switches, nonlinear devices, andQ-switching cavities.

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