High-refractive-index dielectric particles offer a potential solution to the issue of material (non-radiative) loss. However, the main limitation of metal-based Fano-resonant systems is the large non-radiative loss due to ohmic damping, which limits the achievable Q-factor 17 to <~10. Due to the low radiative loss of the dark mode, the Fano resonance can be extremely sharp, resulting in complete transmission, analogous to EIT 2, 3, 4, 5, 6, 7, 8, 9, 10, or complete reflection 13, from the sample across a very narrow bandwidth.
If these two resonances are brought in close proximity in both the spatial and frequency domains, they can interfere resulting in an extremely narrow reflection or transmission window.
The classical analogue of EIT in plasmonic metamaterials relies on a Fano-type interference 16, 17 between a broadband ‘bright’-mode resonator, which is accessible from free space, and a narrowband ‘dark’ mode resonator, which is less-accessible, or inaccessible, from free space. The transparent and highly dispersive nature of EIT offers a potential solution to the long-standing issue of loss in metamaterials as well as the creation of ultra-high-quality-factor (Q-factor) resonances, which are critical for realizing low-loss slow-light devices 2, 3, 6, 10, optical sensors 13, 14 and enhancing nonlinear interactions 15. This concept was later extended to classical optical systems using plasmonic metamaterials 2, 3, 4, 5, 6, 7, 8, 9, 10, among others 11, 12, allowing experimental implementation with incoherent light and operation at room temperature. Furthermore, we show that the dielectric metasurfaces can be engineered to confine the optical field in either the silicon resonator or the environment, allowing one to tailor light–matter interaction at the nanoscale.Įlectromagnetically induced transparency (EIT) is a concept originally observed in atomic physics and arises due to quantum interference, resulting in a narrowband transparency window for light propagating through an originally opaque medium 1. Due to extremely low absorption loss and coherent interaction of neighbouring meta-atoms, a Q-factor of 483 is observed, leading to a refractive index sensor with a figure-of-merit of 103. Here we experimentally demonstrate a classical analogue of EIT using all-dielectric silicon-based metasurfaces. However, ohmic losses limit the achievable Q-factors in conventional plasmonic EIT metasurfaces to values <~10, significantly hampering device performance. Such resonances are expected to be useful for applications such as low-loss slow-light devices and highly sensitive optical sensors. Metasurface analogues of electromagnetically induced transparency (EIT) have been a focus of the nanophotonics field in recent years, due to their ability to produce high-quality factor (Q-factor) resonances.