Optical limiters transmit low intensity input light while blocking input light with the intensity exceeding certain limiting threshold. Conventional passive limiters utilize nonlinear optical materials, which are transparent at low light intensity and turn absorptive at high intensity. Strong nonlinear absorption, though, can result in over- heating and destruction of the limiter. Another problem is that the limiting threshold provided by the available optical material with nonlinear absorption is too high for many applications. To address the above problems, the nonlinear material can be incorporated in a photonic structure with engineered dispersion. At low intensity, the photonic structure can display resonant transmission via localized mode(s), while at high intensity the resonant transmission can disappear, and the entire stack can become highly re ective (not absorptive) within a broad frequency range. In the proposed design, the transition from the resonant transmission at low intensity to nearly total re ectivity at high intensity does not rely on nonlinear absorption; instead, it requires only a modest change in the refractive index of the nonlinear material. The latter implies a dramatic increase in the dynamic range of the limiter. The main idea is to eliminate the high-intensity resonant transmission by decoupling the localized (resonant) modes from the input light, rather than suppressing those modes using nonlinear absorption. Similar approach can be used for light modulation and switching.
We demonstrate that a family of metamaterials, with a designed complex permittivity and permeability such that their index of refraction is real, have anomalous scattering features as opposed to their lossless passive counterparts with the same index of refraction.
We introduce a class of unidirectional lasing modes associated with the frozen mode regime of non-reciprocal slow-wave
structures.1 Such asymmetric modes can only exist in cavities with broken time-reversal and space inversion
symmetries. The lasing frequency coincides with a spectral stationary inflection point of the underlying passive
structure and it is virtually independent of the size of the cavity. These unidirectional lasers can be indispensable
components of photonic integrated circuitry.