Ultrafast beam steering using gradient Au-Ge₂Sb₂Te₅-Au plasmonic resonators.

Beam steering devices have gained extensive interests in the fields of optical interconnects, communications, displays and data storages. However, the challenge lies in obtaining an ultrafast beam steering structure in the optical regime. Here, we propose phase-array-like plasmonic resonators based on metal/phase-change materials (PCMs)/metal trilayers for all-optical ultrafast beam steering in the mid-infrared (MIR) region. We numerically demonstrate an angle beam steering of 11° for transmitted wave (front lobe) and 22° for reflected wave (back lobe) by switching between the amorphous and crystalline states of the PCM (Ge₂Sb₂Te₅). A photothermal model is used to study the temporal variation of the temperature of the Ge₂Sb₂Te₅ film to show potential for switching the phase of Ge₂Sb₂Te₅ by optical heating. Generation of the beam steering in this structure exhibits a fast beam steering time of 3.6 ns under a low pump light intensity of 2.6 μW/μm₂. Our design possesses a simple geometry which can be fabricated using standard photolithography patterning and is essential for exploiting the ultrafast beam steering in various applications in the MIR regime.