Optical waveguides with apodized sidewall gratings via spatial-phase-locked electron-beam lithography

Abstract

We describe a technique to fabricate Bragg gratings in the sides of optical waveguides using a single lithographic step. This technique is particularly suited to the apodized gratings required for add/drop filters in dense-wavelength-division multiplexing. Apodization minimizes cross talk between channels and improves the filter response. Silicon-on-insulator rib waveguides with both uniform and apodized gratings were fabricated using direct-write spatial-phase-locked electron-beam lithography (SPLEBL). This approach combines SPLEBL’s pattern-placement accuracy with the flexibility of direct-write device prototyping. The resulting grating-based devices exhibited substantially reduced side-lobe levels.