# Corner Reflector Plasmonic Nanoantennas for Enhanced Single-Photon Emission
## 3 Results and Discussion
For this \(L\), the peak directivities were essentially the same for the silver and gold CRs, even though the \(L/\lambda_{M}\) value was larger for silver. This indicates a saturating effect regarding the increase in \(D\) with \(L\). In the case of gold, the relative positions of the maxima and minima as a function of \(S/\lambda_{M}\) closely matched those found for \(L=1.5\) um, with a null occurring at \(S=\lambda_{M}\) for \(W=80\) nm. In contrast, for silver, significant shifts in the directivity maxima and minima as a function of \(S/\lambda_{M}\) were observed, and these shifts were highly dependent on the value of \(W\). The normalized radiative emission and loss rates for \(L=3\) um CRs are displayed in Figure 17 for the three values of \(W\) considered. The results closely resemble those obtained  
Figure 2:6 Values obtained of the directivity as a function of the feeder position \(S\) normalized to the corresponding target wavelength for three different reflector film thicknesses when the length of the CR planes was increased to \(L=3\) μm. (**a**) Results for silver CR. (**b**) Results for gold CR. Figure 2:7 (**a**) Purcell, \(f_{R}\), and loss, \(f_{L}\), factors; (**b**) directivity of a \(W=80\) nm, \(L=1.5\) μm CR silver NA with the feeder at \(S=0.55\) μm in the presence of an interfering \(d=70\) nm silver NP at position \((\rho\sin(\alpha),\rho\cos(\alpha),0)\) for different values of \(\alpha\). for \(L=1.5\)\(\upmu\)m, indicating that the impact of the CR on the loss and emission properties was due to the interactions occurring in a localized region near the apex of the CR. Figure 18 shows the gain, \(G\), of the silver and gold CR NAs as a function of \(S/\lambda_{M}\). The gain provides a comprehensive measure of on-axis photon emission, incorporating all three key parameters: \(f_{R}\), \(f_{L}\), and \(D\). For the gold CR NAs, the maximum gain occurred at a metal thickness of \(W=80\) nm. The first gain peak, with a value of \(G=11.8\), was found at \(S/\lambda_{Au}=0.67\) and \(S/\lambda_{Au}=0.75\). The second peak, \(G=21.8\), was located at \(S/\lambda_{M}=1.33\). Figure 2:8 Radiative transition rate enhancement \(f_{R}\) and normalized loss \(f_{L}\) factors of a gold CR with \(L=3\)\(\upmu\)m as a function of the feeder position \(S/\lambda_{M}\) for three different reflector film thicknesses: (**a**) silver CR \(W=10\) nm, (**b**) gold CR \(W=10\) nm, (**c**) silver CR \(W=40\) nm, (**d**) gold CR \(W=40\) nm, (**e**) silver CR \(W=80\) nm, (**f**) gold CR \(W=80\) nm. In the case of the silver CRs, the aforementioned shift of the directivity maxima with respect to \(S/\lambda_{Ag}\) resulted in the highest directivity for \(W=40\) nm rather than for \(W=80\) nm. This shift aligns the directivity peak with a higher \(f_{R}\) value at \(W=40\) nm, leading to the maximum gain being achieved at this thickness. The first gain peak for silver was \(G=12.3\) at \(S/\lambda_{Ag}=0.5\), and the second was \(G=30.0\) at \(S/\lambda_{Ag}=1.25\). The directivity values obtained for the CR NA were, in all cases, well below the bounds set by the Kildal limit for the CR sizes considered [28]. Nevertheless, the proposed scheme offers a significant improvement over a single NP emitter while maintaining high implementation simplicity, which is consistent with the advantages of CR antennas used in radio frequency applications. Although superdirective dielectric NAs would allow for a more compact setup, the proposed scheme enables the full exploitation of plasmonic nanostructures' potential [34].