Tunable and reconfigurable metadevices constructed by metamaterials and metasurfaces will bring optics and photonics the highly desired on-demand property control. In this talk, I will introduce our recent work on three types of tunable and reconfigurable metadevices based on different principles for different applications. We demonstrated a continuous orbital angular momentum (OAM) transmitter comprising bilaterally symmetric gratings with an aperture to create arbitrary rational-order optical vortex beams without a theoretical limit. The vortex beam has a distinguished spiniform wavefront with phase singularities located equidistant along a line and tunes its average OAM by changing the number of singularities the beam accommodates. The approach realizes both non-integer and arbitrary rational-order generation of OAM and enables the exploration of quantum entanglement using such continuous OAMs. Phase change material GST is known for its huge optical property difference between amorphous and crystalline states. We used fs laser pulse trains to create high resolution multi-level phase changes in GST films and demonstrated reconfigurable optical devices like lens in various types, iteratively modifiable grayscale photomasks and waveguides for bidirectional transport of nanoparticles. Si based photonics with CMOS compatibility is of great interest for the potential integrations with electronics and the benefits from the scalable Si process. We used a CMOS compatible process to create an electrically and thermally tunable Si metasurface for broadband terahertz antireflection application. Perfect antireflection condition can be precisely achieved. The methodology suggests a possibility of using all-silicon platform for making atomically smooth and tunable metadevices in THz and other frequency range.
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