Dynamically reconfigurable directionality of plasmon-based single photon sources

We propose a plasmon-based reconfigurable antenna to controllably distribute emission from single quantum emitters in spatially separated channels. Our calculations show that crossed particle arrays can split the stream of photons from a single emitter into multiple narrow beams. We predict that beams can be switched on and off by switching host refractive index. The design method is based on engineering the dispersion relations of plasmon chains and is generally applicable to traveling wave antennas. Controllable photon delivery has potential applications in classical and quantum communication.

Figure 1

(Color online) Sketch of our reconfigurable nanoantenna concept to control single emitters. We consider a single emitter [red (dark gray) dipole] embedded in a set of linear plasmon antennas [metal particles in yellow (light gray)] that intersect at the emitter. In its unswitched state (left), such an antenna funnels spontaneous emission into different beams. The beams can be switched on and off (indicated by “ZAP”) at will by modifying the particle or host material dynamically.

Figure 2

(Color online) (a) Sketch of the emitter-antenna geometry consisting of two identical arms. We consider a single emitter placed in the middle of a 160 nm gap between the antenna arms, oriented perpendicular to the antenna axis. (b) Black [red (dark gray)] curve: dispersion relation for the transverse plasmon modes of an infinite Ag particle chain in glass [pitch $d=160\text{nm}$, radius $R=55$ (58) nm]. The black horizontal line indicates the operation wavelength ${\lambda }_{op}=652\text{nm}$. [(c) and (d)] Emission pattern at ${\lambda }_{op}$ for a single emitter embedded in a linear array antenna with eight silver particles to each side. In (c) both arms are equal $\left(R=55\text{nm}\right)$. In (d) the right arm has $R=58\text{nm}$. (e) Radius/host index (top axis) dependence of the beaming fraction and beam contrast, assuming a collection $\text{NA}=0.32$ $\left(2\theta =36°\right)$.

Figure 3

(Color online) (Color online). Results for an asymmetric two-beam antenna with radius $R=50\text{nm}$, pitch $d=140\text{nm}$ (left arm), and $R=55\text{nm}$, $d=160\text{nm}$ in the right arm. [(a) and (b)] shows the dispersion relation for transverse plasmons for each arm before (black) and after the switch [red (dark gray)]. [(c) and (d)] Emission pattern for a single emitter in the antenna (both arms with eight particles) before (c) and after (d) switching host index from 1.5 to 1.56. (e) Host index dependence of the beaming fraction and beam contrast at $\lambda =662\text{nm}$. (f) Quantum efficiency versus the variation of host index at $\lambda =662\text{nm}$.

Figure 4

(Color online) Contour plot of beaming fraction $F$ versus host index and wavelength. The dashed lines denote the cut-off wavelengths. In a 30 nm band to the red of the cutoff of the right arm, both beams have comparable power. In between the cutoffs, the right beam is off, and the left beam is brighter.