2-D MMI Devices Based on Integrated Hollow ARROW Waveguides

In this paper, the design, fabrication, and characterization of 2-D multimode interference (MMI) devices based on integrated silicon hollow antiresonant reflection optical waveguides (ARROW) is presented. Unlike conventional waveguides, the field in ARROW is not confined in the core region by total internal reflection but by dielectric cladding layers designed to form-high reflectivity Fabry–Perot mirrors. This peculiar structure permits to realize integrated hollow-core waveguides using standard silicon technology. In this paper, we show that these waveguides can be usefully applied in the fabrication of 2-D MMI devices. With a 130 $\mu$m$\,\times\,$ 130 $\mu$m cross-section waveguide, multiple images are observed from 1$\,\times\,$1 to 6 $\,\times\,$6 image matrices. These devices also exhibit interesting bandpass spectral properties that can be usefully applied in several fields ranging from telecommunications to sensing.