Spotlight on "Refractive index engineering with subwavelength gratings for efficient microphotonic couplers and planar waveguide multiplexers"

When approaching the design of an integrated photonic circuit, a critical issue one must deal with is the choice of the most suitable refractive-index contrast of the waveguide. On the one hand, the index should be sufficiently high to guarantee a proper light confinement; on the other hand, using a higher-index contrast than strictly required brings a variety of side effects, such as higher propagation loss, higher coupling loss with optical fibers, higher sensitivity to fabrication imperfections and sidewall roughness, and so on. Unluckily, the refractive index cannot be chosen at will but must be selected within a limited set of optical platforms.