  An ultrahigh-Q hybrid cavity using a graded multiheterostructure and space
modulation is designed in this work. Two high Q resonant modes exist in the
cavity and follow separate confinement mechanisms. We have demonstrated an
analytical method for designing the desired multiheterostructure. Space
modulation was used to create a robust and sensitive nanocavity. The
confinement mechanism and resonant characteristics of the resonant modes are
studied using the finite difference time domain method. We have shown that the
modes of the cavity are highly robust with respect to fabrication error. We
have also demonstrated that the nanocavity can act as a highly sensitive
refractive index sensor.
