Multichannel Bragg gratings in silicon waveguides with asymmetric sidewall modulation

We demonstrate a new type of on-chip Bragg grating designed to possess multiple stopbands at predetermined wavelengths. By employing sidewall modulation to control the full width half-maximum and extinction ratio, and through the incorporation of multiple spatial frequencies into the gratings' periodicities, we show that Bragg reflection can be achieved at particular wavelengths of interest without compromising spectrally distinct characteristics. Multiple device geometries are theoretically studied using the finite-difference time-domain method, and the results these analyses yield are shown to be in good agreement with experimental data. We additionally demonstrate how such devices may be employed to fabricate so-called dual-mode Bragg gratings, which are capable of reflecting both TE- and TM-like modes at a single wavelength of operation.