Study of localized defect-bound excitonic transitions in TMD-WSe2 monolayers and evanescent coupling to tapered optical nanofibers

The project has two main objectives. First, the demonstration of the existence of single photon emitters in WSe2 monolayers. We recognized localized defect-bound excitons as responsible for this. Second, the demonstration of the evanescent coupling of a localized defect-bound exciton emission to a tapered optical nano fiber. To achieve these goals, we produced a detailed study ofWSe2, starting from the fabrication process in the clean room, up to the characterization ofthe emission spectrum and the proof of the existence of single photon emitters. Then, before fabricating the nanofibers and demonstrating the coupling result, we tested the feasibility ofthe evanescent coupling with COMSOL and MATLAB simulations. In particular, we performed a detailed optical characterization of two samples of WSe2 monolayers produced via exfoliation in clean room. We used an all dry deterministic transfer to encapsulate the samples in two layers of hexagonal boron nitride (hBN). We performed micro-photoluminescence, lifetime and degree of second-order temporal coherence measurements. We focused our attention in localized defect-bound excitons due to the high intensity PL signal and sharp linewidth. Moreover, in this work we have demonstrated the evanescent coupling of a single localized defect-bound exciton emitter with a tapered optical nano fiber we produced. For the fabrication of the nanofiber, through COMSOL and MATLAB simulations we found the right size to have a sufficiently intense evanescent field to allow coupling to the emitter. We managed, through several repetitions, to produce autonomously the nanofiber of the desired size. Finally we were able to demonstrate the feasibility of the evanescent coupling of the emission to the fiber from a chosen localized defect-bound exciton. Thus, our results provide evidence of the possibility to integrate quantum emitters in 2D materials with photonic structures.