Abstract

Integrated optical filters such as Bragg gratings are widely used in silicon-on-insulator technology for signal processing [1], telecommunications [2] and quantum processing [3]. Sidewall gratings offer a simple geometry that has been widely used for fabricating TE filters with high extinction ratios and accurate control over the grating stop-band and central wavelength [4]. However, a major drawback of this design stems from the weak interaction of the TM mode with the sidewalls of the waveguides, which makes it unsuitable for fabricating TM filters. This feature severely limits the maximum extinction ratio of the filter because of the strong polarization scattering typical of highly confined optical waveguides [5]. To this aim, top surface relief waveguide gratings provide an interesting alternative as they strongly interact with the TM mode with a negligible influence on the TE polarised mode. Integrating surface and sidewall gratings on the same waveguide not only substantially improves the extinction ratio of the filters but also provides a powerful design tool to independently manipulate TE and TM polarised light.

© 2017 IEEE