Directing Nanoscale Optical Flows by Coupling Photon Spin to Plasmon Extrinsic Angular Momentum

Area of Science:

• Photonics and Nanophotonics
• Plasmonics
• Optical Waveguiding

Background:

• Light's angular momentum can be manipulated in curved trajectories.
• Strong curvatures enable photon spin-orbit interaction.
• Controlling light propagation at the nanoscale is crucial for advanced optical devices.

Purpose of the Study:

• To demonstrate tunable symmetry breaking in light coupling into curved nanoscale plasmonic waveguides.
• To utilize photon spin-orbit interaction for controlling light propagation direction.
• To achieve unidirectional waveguiding in subwavelength structures.

Main Methods:

• Utilizing the extrinsic angular momentum of light in curved trajectories.
• Inducing spin-orbit interaction by matching light's angular momentum with photon spin momentum.
• Experimentally coupling light into a nanoscale plasmonic waveguide with tunable symmetry breaking.
• Controlling power distribution between counter-propagating subwavelength guided modes using optical wave helicity.

Main Results:

• Achieved tunable symmetry breaking in light coupling.
• Demonstrated control over power distribution between two counter-propagating subwavelength guided modes.
• Experimentally directed up to 95% of incoupled light into a single propagation direction.
• Showcased unidirectional waveguiding in a nanoscale plasmonic waveguide.

Conclusions:

• The developed approach offers new degrees of freedom for manipulating subdiffraction optical modes.
• This method provides a pathway for developing advanced, deeply subwavelength optical functionalities.
• Tunable spin-orbit interaction in curved plasmonic waveguides enables efficient unidirectional light control.