Tunable Waveguide Mode of Hyperbolic Phonon Polaritons in α-MoO₃ Flake/Gold Slit Composite Structure
crossref(2024)
摘要
Hyperbolic phonon polaritons (HPhPs) in van der Waals layered polar crystals exhibit extreme light confinement capability, providing an unprecedented research opportunity to manipulate nanoscale mid-infrared photons. Precise tuning of HPhPs propagation characteristics and near-field energy routing are crucial for applying polaritonic devices. Here, we demonstrate a widely tunable waveguide mode of HPhPs in an α-MoO₃ flake/gold slit composite structure. By varying the width of the gold slit from 3 µm to 220 nm, the compression ratio of HPhPs wavelength relative to the incident light wavelength can be adjusted from 35% to 8.6%, respectively. This is attributed to that the introduction of the gold slit can effectively excite and guide HPhPs within α-MoO₃, forming a confined waveguide mode. Notably, the excitation efficiency of HPhPs in the nanoscale ultra-narrow waveguide can be enhanced by integrating an extended port at the waveguide port. In addition, the routing of polaritons in a Y-shaped waveguide is realized by modulating the frequency of the incident light. This work presents a promising platform for manipulating deep subwavelength polaritons in planar photonic devices for infrared applications.
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