New Horizons for Nonlinear Space-Time Optics with Near-Zero-Index Materials

Very few scientific fields have become as pervasive in basic research and everyday life as nonlinear optics which ushered in tremendous achievements in areas like attosecond physics, ultra-broadband optical communication, and high-resolution sensing. The utility of nonlinear optics has therefore been a compelling motivator to increase generally weak light-matter interactions. In this pursuit, novel materials have been explored including materials where in a particular spectral region the real part of the permittivity ()-epsilon is near zero (ENZ) and materials whose losses in that spectral region are also low leading to a near-zero-index (NZI). ENZs and NZIs increase light-matter interactions via the enhanced fields at the interface between the ‘normal’ and ENZ materials, the “slow-light” effects and relaxed phase matching conditions. One important class of novel ENZ/NZI materials is transparent conducting oxides (TCOs) whose low-losses and high-tunability have made them a leader in ENZ-enhanced nonlinear optics like Kerr-nonlinearities^1,2 and frequency generation³. More recently, transparent conducting oxides have pioneered ultrafast optically-modulated nonlinear optics opening the door to exotic time-varying media phenomena such as negative refraction^4,5, time refraction^6,7, time reflection, and photonic time crystals^8–10.

(1) Alam, M. Z.; et al., Science (1979) 2016, 352 (6287), 795–797.

(2) Caspani, L., et al., Phys Rev Lett 2016, 116 (23), 233901.

(3) Capretti, A., et al., Opt Lett 2015, 40 (7), 1500.

(4) Vezzoli, S., et al.,Phys Rev Lett 2018, 120 (4), 043902.

(5) Bruno, V., Phys Rev Lett 2020, 124 (4), 043902.

(6) Shaltout, A. M., et al., In Optics InfoBase Conference Papers; 2016. doi:10.1364/CLEO_QELS.2016.FF2D.6

(7) Zhou, Y., Nat Commun 2020, 11 (1), 2180.

(8) Shaltout, A. M. In CLEO; Optica Publishing Group, 2016. doi.org/10.1364/CLEO_QELS.2016.FM1D.4.

(9) Lyubarov, M., et al., Science (1979) 2021, 428 (July), 425–428.

(10) Lustig, E, et al., Nanophotonics,  doi.org/10.1515/nanoph-2023-0126