ABSTRACT
Vortex beams are playing an increasingly crucial role in wireless optical communications. Traditional vortex beam generators based on spiral phase plates and metasurfaces have a geometric center in real space, which limit their convenience in practical applications. In this work, we propose that the creation of a vortex beam can be achieved by using the bound state in the continuum (BIC) supported by a photonic crystal slab structure. Theoretical analysis shows that the proposed structure can be used as a kind of "momentum-space resonators" and thus can generate vortex beams. Moreover, higher-order vortex beams can also be achieved by changing the symmetry of photonic crystal slab, thus paving the way for the application of vortex beams in the fields of quantum information processing and micro optical micromanipulation.
ABSTRACT
A device incorporating a series of periscope-like waveguides to achieve bidirectional focusing and plasmon launching is proposed. Optimizing the number, positions, and dimensions of the waveguides and tuning the waveguide optical paths both produce the required phase shifts to shape wavefronts and achieve constructive interference at the desired points. Due to the symmetry and reversibility of the structure, the lens can focus the light incident on both sides. Energy redistribution to a specific multi-focus can also be achieved by applying appropriate phase shifts. This simple and high performance structure makes the bidirectional plasmonic launcher easy to implement in various application situations.
