In-depth investigation and applications of novel silicon photonics microstructures supporting optical vorticity and waveguiding for ultra-narrowband near-infrared perfect absorption

We propose a novel concept of designing silicon photonics metamaterials for perfect near-infrared light absorption. The study's emphasis is an in-depth investigation of various physical mechanisms behind the ∼100% ultra-narrowband record peak absorptance of the designed structures, comprising an ultrathin silicon absorber. The electromagnetic power transport, described by the Poynting vector, is innovatively explored, which shows combined vortex and crossed-junction two-dimensional waveguide-like flows as outcomes of optical field singularities. These flows, though peculiar for each of the designed structures, turn out to be key factors of the perfect resonant optical absorption. The electromagnetic fields show tight two-dimensional confinement: a sharp vertical confinement of the resonant-cavity type combined with a lateral metasurface supported confinement. The silicon-absorbing layer and its oxide environment are confined between two subwavelength metasurfaces such that the entire design is well compatible with silicon-on-insulator microelectronics. The design concept and its outcomes meet the extensive challenges of ultrathin absorbers for minimum noise and an ultra-narrowband absorptance spectrum, while maintaining an overall very thin structure for planar integration. With these materials and such objectives, the proposed designs seem essential, as standard approaches fail, mainly due to a very low silicon absorption coefficient over the near-infrared range. Tolerance tests for fabrication errors show fair tolerability while maintaining a high absorptance peak, along with a controllable deviation off the central-design wavelength. Various applications are suggested and analyzed, which include but are not limited to: efficient photodetectors for focal plane array and on-chip integrated silicon photonics, high-precision spectroscopic chemical and angular-position sensing, and wavelength-division multiplexing.