High-Q and high-absorption photonic crystal nanobeam cavity based on semi-cylinders of air coupled with graphene

In this paper, we present a structure of graphene layer coupled with a One-Dimensional photonic crystal nanobeam cavity (1D-PCNC). The proposed structure constructed of two mirrors, two couplers, and one cavity which all are made of semi-cylinders of air (holes). The placement and rotation of the semi-cylinder holes play very important role in the performance of the proposed 1D-PCNC. In this structure, unlike the previous works that were focused on the size of holes in different areas, the type of placement of the semi-cylinder holes are examined. By applying the three-dimensional finite-difference time-domain (3D-FDTD) simulations, three fundamental parameters (the number of cavity holes \(( {N}_{\text{c}})\), the number of mirror holes (\({N}_{\text{m}})\) and the number of coupler holes (\({N}_{\text{t}})\)) are optimized to achieve the highest absorption rate of monolayer graphene while keeping the quality (Q) factor of the cavity at its high values (unlike the previous works). The graphene layer absorbs over 90% of the incoming light at wavelengths around 1.55 μm and the highest Q-factor of \({1.28\times 10}^{6}\) are obtained when the number of holes in the cavity, mirror and coupler are 10, 9 and 5, respectively. Furthermore, the structure occupies only about 19 µm × 0.9 µm, making this structure applicable for photonic integrated devices based on 1D-PCNC.