Moiré Effects in Silicon Photonic Nanowires

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Photonic moiré lattices offer an attractive platform for manipulating the flow and confinement of light from remarkably simple device geometries. This emerging field draws inspiration from the rapid research progress observed in twisted bilayer van der Waals materials or “twistronics,” instead of applying moiré physics to photon propagation in wavelength-scale optical media. However, to date, only a limited number of experimental studies have been performed in this area, and there is strong interest in understanding how moiré effects can be tailored in compact and scalable optical technologies such as an integrated photonics platform. In this work, we map the moiré effects of one-dimensional (1D) photonic moiré lattices composed of width-modulated silicon nanowires, including the construction of a 1D experiment analogous to the twisting of a two-dimensional (2D) lattice. Although the twist angle Δθ and/or lattice mismatch ΔΛ are the sole defining parameters for infinite moiré crystals, we demonstrate how the crystal size, symmetry, and moiré fringe phase Δϕ also serve as important degrees of freedom. Through tailoring these parameters, we map a wide range of behaviors including the formation of moiré photonic crystal cavities, the onset of miniband formation and operation as a coupled resonator optical waveguide (CROW), widely tunable Q-factors and group velocities, suppression of grating sidebands, and persistent vs extinguishable tunneling. These results provide insight into the moiré physics of 1D optical systems and highlight various operating regimes relevant to the design of finite photonic moiré lattices and devices.