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

Abstract

As any physical particle or object, light undergoing a circular trajectory features a constant extrinsic angular momentum. Within strong curvatures, this angular momentum can match the spin momentum of a photon, thus providing the opportunity of a strong spin-orbit interaction. Using this effect, we demonstrate tunable symmetry breaking in the coupling of light into a curved nanoscale plasmonic waveguide. The helicity of the impinging optical wave controls the power distribution between the two counter-propagating subwavelength guided modes including unidirectional waveguiding. We found experimentally that up to 95% of the incoupled light can be selectively directed into one of the two propagation directions of a nanoscale waveguide. This approach offers new degrees of freedom in the manipulation of subdiffraction optical modes and thus appealing new prospects for the development of advanced, deeply subwavelength optical functionalities.

Spin–Orbit Controlled Excitation of Quantum Emitters in Hybrid Plasmonic Nanocircuits

“…Spin-orbit interactions (SOI) of light on the subwavelength scales that couple the polarization and spatial degrees of freedom have recently attracted a great deal of attention due to bringing in novel functionalities to optical nanodevices. [31][32][33][34][35][36] The spin-selective flow of light has been demonstrated with various photonic [37][38][39] and plasmonic [40][41][42] configurations. Very recently, the SOI have also been exploited to realize the on-chip electrical detection of the spin state of incident photons.…”

Dynamical Manipulation of Surface Plasmon Polaritons

“…(b) Directional SPP excitation with interfacial phase discontinuity [49]; (c) Directing SPP flows based on spin and orbit angular momentum interaction [50]; (d) Wavelength dependent directional SPP excitation [79]; (e) Broadband directional SPP excitation with a single compact antenna [80]. Reproduced with permissions from: [48], AAAS, 2013, [49], Springer Nature, 2013, [50], ACS, 2018, [79], Springer Nature, 2011, and [80], ACS, 2015. Figure 1c schematically shows a curved plasmonic waveguide which can realize directional SPP propagation at a deep subwavelength scale [50].…”

“…Two counter propagating modes can be sustained in such a curved single-mode waveguide and, considering the longitudinal angular momentum conservation, the corresponding probabilities of the two modes can be expressed as [79]; (e) Broadband directional SPP excitation with a single compact antenna [80]. Reproduced with permissions from: [48], AAAS, 2013, [49], Springer Nature, 2013, [50], ACS, 2018, [79], Springer Nature, 2011, and [80], ACS, 2015. Figure 1c schematically shows a curved plasmonic waveguide which can realize directional SPP propagation at a deep subwavelength scale [50].…”

“…Reproduced with permissions from: [48], AAAS, 2013, [49], Springer Nature, 2013, [50], ACS, 2018, [79], Springer Nature, 2011, and [80], ACS, 2015. Figure 1c schematically shows a curved plasmonic waveguide which can realize directional SPP propagation at a deep subwavelength scale [50]. The circular slit provides an extrinsic orbital angular momentum (OAM) [89,90] to match the spin angular momentum (SAM) of incident phonon, which enables the spin-orbit interaction (SOI).…”

“…Particularly, for circularly polarized light, the SPPs generated by subwavelength slits are imprinted with a spin-dependent Pancharatnam-Berry (PB) phase which can be tuned by changing the orientation angle of the slits [46,47]. Polarization-controlled dynamical SPP excitation [48][49][50][51][52][53][54][55][56], SPP focusing [46,[57][58][59][60][61][62][63][64][65][66], SPP vortex [21,44,[67][68][69][70][71][72][73], SPP nondiffracting beams [74][75][76], and SPP holography [77,78] have been 2 of 17 realized. Besides, the other degrees of freedom of light-including the wavelength, topological charge, and the spatial frequency-can be taken advantage of to actively control the SPP field [79][80][81][82][83][84][85][86] as well.…”