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We leverage the all-dielectric, essentially lossless, capabilities of a newly developed phase-change material by Y. Zhang et al. [1], GSS4T1, for dramatic light-path reconfigurability with a metagrating in the MWIR/LWIR spectrum (above 5 microns free-space wavelength) . We show that there are two entirely different governing physical regimes that control the metagrating responses, depending on the phase of GSS4T1, amorphous or crystalline. Specifically, we show that the proposed metagrating paradigm behaves as an effective metamaterial when GSS4T1 in the amorphous phase, while it supports leaky Floquet-Bloch waves when GSS4T1 is in the crystalline phase. These leaky Floquet-Bloch modes can exhibit accidental destructive and constructive interference into the zeroth and first-order Bragg transmitted beams respectively via a mechanism similar to the one responsible for the emergence of accidental bound states in continuum (BIC) phenomena. By utilizing these two different physical regimes, we demonstrate steering the incident beam to the negative direction when GSS4T1 is switched from the amorphous to the crystalline phase [2]. We believe these results are highly relevant to infrared devices and technologies such as long-range lidars, spectroscopic sensors etc.
[1] Y. Zhang et al., Broadband transparent optical phase change materials for high-performance nonvolatile photonics, Nature Comm. 10, 4279 (2019).
[2] N. L. Tsitsas and S. Foteinopoulou, Non-volatile MWIR/LWIR beam reconfigurability with all-dielectric metagratings comprising phase-change materials with a high-refractive-index shift, Opt. Mat. Express 12, pp. 3187-3212 (2022).
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