Ultrahigh Q-factor Ge11.5As24Se64.5 chalcogenide glass photonic crystal cavity embedded in silica

In this paper, the authors report a design which minimises energy losses and leads to high Q resonant cavities in a Ge_11.5As₂₄Se_64.5 chalcogenide glass PhC membrane completely embedded in a silica cladding corresponding to an index contrast of 1.22. A conventional W1 photonic crystal (PnC) waveguide in this structure had limited bandwidth of only ≈12nm because of the low refractive index contrast between Ge_11.5As₂₄Se_64.5 (2.67) and silica (1.45) and this led to a heterostructure PhC cavity with a Q-factor of only ≈ 8,000. However, it was found in this work that by changing the width of PhC waveguide to correspond to a W0.6 structure the bandwidth of the guided mode increased to over 40 nm and Q-factors could be substantially increased.