Non-volatile MWIR/LWIR beam reconfigurability with all-dielectric metagratings comprising phase-change materials with a high-refractive-index shift

Abstract

We propose an all-dielectric grating paradigm comprising an optical-phase-change-material (O-PCM), functional in the 5 μm to 10 μm spectral range. This system leverages the capabilities of a newly-discovered O-PCM [Nat. Comm. 10, 4279 (2019)10.1038/s41467-019-12196-4], Ge2Sb2Se4Te1, which can be reliably switched between amorphous and crystalline phases at larger thicknesses close to 1 μm, while exhibiting a high-refractive-index shift of about 1.5 and no optical loss in this spectral range. The amorphous-O-PCM grating predominantly responds as an effectively homogeneous slab, letting light through without perturbing its path. The crystalline-O-PCM grating supports leaky Floquet-Bloch modes, which, at certain wavelengths, can simultaneously interfere destructively into the primary light path and constructively into the back-bent diffraction channel, in transmission. This “accidental” interference effect steers the incident beam in the negative direction. At a slightly detuned wavelength, the output power can be evenly split between the primary light path and the back-bent diffraction channel. Hence, our all-dielectric O-PCM-based metagrating can function as a platform for non-volatile reconfigurable beam steering and splitting. We have designed the metagrating paradigm and predicted its reconfigurable behavior with a semi-analytical calculation method and then verified it with a numerical first-principles experiment. We believe these results are relevant to MWIR/LWIR applications, but can also inspire new means for programmable and reconfigurable photonics across the spectrum as new O-PCMs are being developed.