Intracavity\nEpsilon-Near-Zero Dual-Range Frequency\nSwitch

Epsilon-near-zero (ENZ) nanophotonic devices with zero\npermittivity\nare known to exhibit adiabatic frequency translation via temporal\nrefraction under extracavity excitation by intense light sources,\nwhich are however hard to integrate on-chip owing to a high demand\nfor energy density. As this class of complementary-metaloxide-semiconductor-compatible\nmaterials is progressing toward on-chip photonic integration, a more\nversatile solution with less intensity requirements needs to be further\nexplored. Here, for the first time, by leveraging the abundant frequency\nmode resources inside a resonant cavity, we experimentally demonstrate\nthe realization of input-dependent dual-range frequency switching\nvia a single intracavity ENZ element. By utilizing the linear and\nnonlinear effects induced by ENZ, the system can perform a small 279.73\nGHz as well as a 13-octave-span larger (3.63-THz) mode-locked frequency\nshift at 196 and 192 THz, respectively, under a pulse energy 2 orders\nof magnitude lower than extracavity schemes with a conversion efficiency\n(in %frequency shift per unit energy density per unit material thickness)\nalso 2 orders of magnitude higher. Additionally, we report for the\nfirst time the real-time observation of the intracavity ENZ frequency\nswitching operation, proving that the mechanism differs from pure\nENZ time refraction. We further discuss that by encoding the states\nof two intracavity components, the optical system can program eight\ntypes of different 1- and 2-operand logic functions, including four\ncomplex noncommutative ones. This work extends the understanding of\nENZ photonics beyond extracavity scenarios. The proposed solution\ncould be extended to photonic integration with a potential for novel\noptical logic gates and photonic computing designs as an efficient\nand simplified alternative to microelectronic counterparts.