High-Q photonic crystal nanobeam cavity based on a silicon nitride membrane incorporating fabrication imperfections and a low-index material layer

We detail the optimization of a nanobeam design and show how the fabrication imperfections can affect the optical performance of the device. Then we propose the design of a novel configuration of a photonic crystal nanobeam cavity consisting of a membrane structure obtained by sandwiching a layer of Flowable Oxide (FOx) between two layers of Silicon-Nitride (SiN). Finally, we demonstrate that the presence of a low refractive index layer does not impair the performance of the nanobeam cavity that still exhibits a Q factor and mode volume V of the order of 105 and 0.02 (λ/n)3, respectively.