## 4 Conclusions  
In conclusion, we have demonstrated the emission coupling of the MoS\({}_{2}\) mono- and bi-layer emission with a high Q surface mode. The MoS\({}_{2}\) transition dipoles are oriented in the plane of the 1D photonic crystal, which allows for a perfect matching with the TE-polarized BSW. Coupled mono- and bi-layer emission have the same energy dispersion, which is also identical to the BSW mode dispersion of the bare DBR. Considering the high sensitivity of the BSW to surface perturbations, this result suggests that the coupled emission is mostly propagating out of the small MoS\({}_{2}\) stripe (coupling  
Figure 4: **(a)** In the upper part, a sketch of the leakage radiation microscope setup in a non-resonant configuration. The excitation source (a cw laser at 2.33 eV) is focused on the sample from the organic deposition side. The emission is collected through a microscope objective with NA = 1.49. In the bottom part, a sketch of the resonant configuration. The excitation laser (100-fs laser pulse) is energetically matched with the BSWP mode and focused through the oil immersion objective. **(b)** Space map of the non-resonant excited polariton emission; the white arrows are a guide for the eye indicating the radial directions starting from the excitation spot (i.e., BSWP propagation direction). **(c)** BSWP nonlinearities. **(top left)** Bare experimental data of the BSWP dispersion in reflectance configuration at 150 \(\upmu\)J cm\({}^{-2}\) pumping energy. **(top right)** Energy-resolved signal at in-plane wavevector \(k\) = 10.34 \(\upmu\)m\({}^{-1}\) under 150 \(\upmu\)J cm\({}^{-2}\) and 10 mJ cm\({}^{-2}\) excitation energy densities (blue and red dots, respectively), showing the blueshift of the BSWP resonance. **(bottom left)** Experimental BSWP dispersions with 150 \(\upmu\)J cm\({}^{-2}\) (blue) and 10 mJ cm\({}^{-2}\) (red) resonant pump pulse. The green ellipse depicts the resonant laser central position and size in the energy–momentum domain (FWHM circle). **(bottom right)** The expected blueshift as a function of the excitonic fraction (black dashed line) fits the experimental results (red dots) for a bare exciton blueshift of 8 meV. (Adapted with permission from [42], Nature Publishing Group, 2017)  
with the BSW of the bare DBR). These results pave the way for an on-chip propagation control and manipulation of the TMDC emission signals.  
In the second section, we have reviewed the main results obtained by our group in the field of BSWP. Soon after the first demonstration of the strong coupling between BSW and Frenkel excitons at room temperature, we have demonstrated the in-plane BSWP propagation for macroscopic distances. This result has been achieved thanks to the extraordinary speed of this particular polariton mode, which is close to 50% of the speed of light. Furthermore, we proved the first nonlinear BSWP, which is the dispersion blueshift when increasing the polariton density due to polariton-polariton interactions, demonstrating the extraordinary potential of this system in the field of optical logic devices.  
The authors would like to thank [PERSON] and [PERSON] for useful discussions and scientific support. This work has been funded by the MIUR project Beyond Nano and the ERC project POLAFLOW (Grant No. 308136).  
[PERSON], [PERSON], [PERSON] and [PERSON] conceived and designed the experiments; [PERSON] and [PERSON] performed the experiments; [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] provided the sample; [PERSON] analyzed the data; all the authors contributed to the data discussion; [PERSON] wrote the paper with contributions from all the authors.  
The authors declare no conflict of interest.