Optomechanical coupling strength in various triangular phoxonic crystal slab cavities

Enhancement of interaction between optical and mechanical fields is one of the main goals of cavity optomechanics as a newly founded physics context. If the coupling rate between these fields exceeds their decay rates from the cavity, then preparation of quantum entangled states between photons of the electromagnetic field and phonons of the mechanical field becomes feasible. Among different types of cavities, phoxonic crystal (PxC) cavities have attracted attention in recent years because they can confine optical and mechanical fields simultaneously. In this paper, we introduce four PxC slabs which exhibit simultaneous photonic and phononic bandgaps. All of these crystals have a triangular lattice pattern and are formed of periodic air holes inside a silicon slab. Then, we create cavities inside these crystals by filling air holes of a unit cell with silicon and then study the coupling strength between their photonic and phononic modes. We deduce that the crystal slab with circular holes can enhance the coupling strength more than others. We further show that if this crystal can be manufactured with lattice constant a=400 nm, then a single-photon coupling rate of g0≃14 MHz is predicted, which is the greatest value reported for a PxC slab cavity to the best of our knowledge. This cavity would have an effective mass of meff≃35 fg.