Ultrahigh Q-factor Ge_11.5As₂₄Se_64.5 chalcogenide glass photonic crystal cavity embedded in silica

Photonic crystals (PhCs) have attracted much attention for their ability to manipulate light, for example structures containing ultrahigh Q-factor cavities allow low threshold all-optical switching as has been demonstrated in 2-D PhCs fabricated in air-clad silicon membranes. However, the strong two-photon (TPA) and free-carrier absorption (FCA) in silicon has meant that optical switching has so far been due to the slow thermal nonlinearity exacerbated by the low thermal mass and poor heat conduction from the 2-D resonant cavity. To achieve optical switching via the ultrafast Kerr nonlinearity the PhC resonators must be fabricated from materials with negligible TPA and FCA and with better heat conduction from the cavity. This can, in principle, be achieved by replacing the silicon with a highly nonlinear chalcogenide glass membrane embedded in a cladding to increase heat conduction and thermal mass. However, such a structure will have a smaller refractive index contrast which can lead to increased energy loss to modes above the light line and lower the Q value.