Polarization independent integrated filter based on a cross-slot waveguide.

We investigate an in-line band pass filter, working both for TE and TM polarizations, based on a cross-slot waveguide merged with a Bragg grating and an optical cavity. Different types of cavities (C₂- and C₄-symmetric) are presented in order to optimize the filtering and make the device dependent or independent on the polarization. We show a strong light confinement in an extremely small volume, which offers an advantage for further sensing applications. Moreover, we show how the inclusion of a silicon nanowire in the cavity helps the guiding and increases the amplitude of the resonance. In this study we make use of both the Fourier Modal Method and the Finite Difference Time Domain method to perform the numerical simulations.