Optical limiter based on PT-symmetry breaking of reflectionless modes

• Published in: Optica 2023-10, Vol.10 (10), p.1302
• Main Authors: Riboli, Francesco, Kononchuk, Rodion, Tommasi, Federico, Boschetti, Alice, Suwunnarat, Suwun, Anisimov, Igor, Vitebskiy, Ilya, Wiersma, Diederik S., Cavalieri, Stefano, Kottos, Tsampikos, Chabanov, Andrey A.
• Format: Article
• Language: English
• ISSN: 2334-2536; 2334-2536
• DOI: 10.1364/OPTICA.497275

The application of parity–time (PT) symmetry in optics, especially PT-symmetry breaking, has attracted considerable attention as an approach to controlling light propagation. Here, we report optical limiting by two coupled optical cavities with a PT-symmetric spectrum of reflectionless modes. The optical limiting is related to broken PT symmetry due to light-induced changes in one of the cavities. Our experimental implementation involves a three-mirror resonator of alternating layers of ZnS and cryolite with a PT-symmetric spectral degeneracy of two reflectionless modes. The passive optical limiting is demonstrated by measurements of single 532 nm 6 ns laser pulses and thermo-optical simulations. At fluences below 10mJ/cm 2 , the multilayer exhibits a flattop passband at 532 nm. At higher fluences, laser heating combined with the thermo-optic effect in ZnS leads to cavity detuning and PT-symmetry breaking of the reflectionless modes. As a result, the entire multilayer structure quickly becomes highly reflective, protecting itself from laser-induced damage. The cavity detuning mechanism can differ at much higher limiting thresholds and include nonlinearity.