Graphene coated subwavelength wires: a theoretical investigation of emission and radiation properties

Abstract

This work analyzes the emission and radiation properties of a single optical emitter embedded in a graphene-coated subwavelength wire. We discuss the modifications of the spontaneous emission rate and the radiation efficiency as a function of the position and orientation of the dipole inside the wire. Our results show that these quantities can be enhanced by several orders of magnitude when the emission frequency coincides with one of the resonance frequencies of the graphene-coated wire. In particular, high-order plasmon resonances are excited when the emitter is moved from the wire center. The modifications by varying the orientation of the dipole in the near field distribution and in the far field intensities are shown.

Spontaneous emission in plasmonic graphene subwavelength wires of arbitrary sections

“…Figure 2 shows both F and F s efficiencies obtained with the integral formalism described in this paper (solid and dashed curves) and with the analytical results obtained using solution for the scattered fields in the form of infinite series of cylindrical harmonics (squares and circles) sketched in Ref. [23]. A good agreement between both formalisms is observed in this Figure. The spectral position of the multipolar plasmon resonances, at a frequency near 0.17µm −1 for the dipolar resonance and near 0.24µm −1 for the quadrupolar resonance, also agree well with those obtained from the quasistatic approximation for which the stationary plasmonic mode condition is fulfilled [24].…”

“…In Figures 7a and 7b we have chosen the emission frequency ω/c = 0.1613µm −1 , for which an enhancement of the emission and the radiation efficiencies occur due to the dipolar resonance excitation (first maximum observed in Figure 4). Unlike the circular case in which, for any location of the source, the values of the decay rates do not show any dependence on the orientation angle α [23], by comparing Figures 7a and 7b we see that, in the case of quasi-square wires, both F and F s values are rather dependent on this angle. At ρ ′ = 0 both the emission and the radiation decay rates are close to 10 4 times larger than in the absence of the wire.…”

“…The scattered field is expressed in terms of two unknown source functions evaluated on the graphene layer, one related to the field interior to the wire and the other related to its normal derivative. In Section 3 we validate the numerical results by comparing them with analytical calculations in the case of a circular wire [23]. To explore the effect that the deviation from the circular geometry has on the emission and the radiation spectra of the single emitter, we consider graphene coated wires of quasi-rectangular shapes.…”

“…In a recent work [23], we have revealed that the interplay between the optical emitter and SP excitations on the graphene layer strongly influences both the spontaneous emission as well as the radiation characteristics of an optical emitter into a graphene coated wire of circular cross section. Since the electric field of the excited SPs reaches similar values inside and outside the graphene wire [24], and taking into account new possibilities of encapsulating single atoms, molecules and compounds into graphene wires [20,21], and the fact that, as a result of the van der Waals force, a graphene sheet can be tightly coated on a fiber surface [25], in that work we deemed appropriate to consider the case in which the optical emitter is localized inside the wire.…”

“…Our primary motivation for this work is to extend the study realized in [23] to the case of wires with an arbitrary cross section. To do this, the calculations have been made using the Green function surface integral method (GSIM) [26,27,28] which enables to solve the scattering problem for structures with a complex shape.…”