Abstract
Gears are rotating machines, meshing with each other by teeth to transmit torque. Interestingly, the rotating directions of two meshing gears are opposite, clockwise and counterclockwise. Although this opposite handedness motion has been widely investigated in machinery science, the analogue behavior of light remains undiscovered. Here, we present a simple nanophotonic directional coupler structure which can generate two light beams with opposite handedness of polarization states-optical gears. Due to the abrupt phase shift effect and birefringence effect, the angular momentum (AM) states of photons vary with the propagation distance in two adjacent waveguides of the coupler. Thus, by the choice of coupling length, it is able to obtain two light beams with opposite handedness of polarization, confirming the appearance of optical gears. The full control in the handedness of output beams is achieved via tuning the relative phase between two orthogonal modes at the input port. Optical gears thus offer the possibility of exploring light-matter interactions in nanoscale, opening up new avenues in fields of integrated quantum computing and nanoscale bio-sensing of chiral molecules.
Highlights
Our scheme is conceptually different from previous methods for manipulation of angular momentum (AM), such as birefringence effect caused by optical crystals[24] and abrupt phase change introduced by nano-resonators.[25]
We show that, in the coupling region of a directional coupler, the phase lag between the two orthogonally polarized modes is modulated via two factor: the abrupt phase shift and the birefringence effect that happens in the coupling process
Our results uncover an exotic chirality phenomenon buried under the coupling process in a nanophotonic directional coupler, which has not been previously reported in literature
Summary
Already a number of integrated devices have been realized based on directional couplers, such as optical filters,14 3-dB splitters,[15] polarization beam splitters,[16, 17] PT-symmetric nonlinear couplers,[18] entangled photon-pairs sources,[19] two-photon quantum interference,[20] integrated quantum logical gates,[21] and all-optical data processing.[22] a RLC circuits. Most of those demonstrations have been focused on a single quasi-linearly polarized mode and mainly discussed the energy exchange between two adjacent waveguides. We show that, in the coupling region of a directional coupler, the phase lag between the two orthogonally polarized modes is modulated via two factor: the abrupt phase shift and the birefringence effect that happens in the coupling process
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