mechanism that breaks the left vs. right symmetry of the modal response of the array, which in this sense becomes chiral. Plasmon OSO modes are thus launched in counter-propagating directions along the $x$-axis for opposite spins $\sigma$ of the excitation light. In the case of a bare plasmonic OSO resonator, this is clearly observed in Fig. \[fig:2\] (c). We stress that similar arrangements of anisotropic apertures have previously been demonstrated to allow for spin-dependent surface plasmon launching [@Hasman2011; @SZhang2013; @Capasso2013; @Drezet2016].

![(a) White light (WL) microscope image of the sample and photoluminescence (PL) image of the same area under $2.58$ eV excitation. (b) SEM image of the plasmonic OSO resonator fabricated by sputtering $200$ nm of gold on a glass substrate coated by a $5$ nm thick chromium adhesion layer. The array with $\phi$-rotated rectangular apertures is milled through the metallic layers using a focused ion beam (FIB). (c) Real-space leakage radiation microscope [@Drezet2016] images of the surface plasmons launched by $\sigma^+$ and $\sigma^-$ excitations on a OSO plasmonic resonator similar to the one of panel (b). \[fig:2\]](Figure2rev.png){width="1\columnwidth"}

As explained in the Supporting Information (Sec. A), the low transmission measured through our WS$_2$/plasmonic array sample (Fig. \[fig:2\](a)) enables us to 