wire side facets acting as the Fabry-Perot cavity mirrors. To verify this assumption we assess the effective index for the supported guided mode(s) assuming a 1D waveguide of infinite extensions in $X$- and $Y$-direction. For the case of TM polarized illumination at $\lambda=580\,$nm, the corresponding first order guided mode along the width of the NW has an effective index of $n_{\text{eff}}=3.45$ ($n_{\text{Si}}\approx 4.0$). The first and second order standing wave patters in figure \[fig:fig5\]g and h match perfectly with the nanowire widths of $180\,$nm, respectively $330\,$nm (at $\lambda=560\,$nm for the latter). For more details on the supported guided modes, see [section V in the SI]{}. It is possible to exploit these Fabry-Perot like modes in order to toggle between FW and omni-directional scattering within a narrow spectral window – simply by switching the incident polarization from TE to TM (see *e.g.* around $560\,$nm in figure \[fig:fig5\]d).

Figs. \[fig:fig5\](g-h) (TM: center row) correspond to near-field intensity distributions inside the SiNW at the first two orders of these TM-excited Fabry-Perot resonances. The field patterns inside the NW cross section correspond indeed to standing wave patterns of guided modes, which eventually lead to an almost equal FW and BW scattering in a narrow 