Thin Germanium Waveguide-Array-Like Absorber Based on Localized Resonance

Abstract

Mode overlapping promotes the capability in manipulating optical absorption. Based on such a mechanism, an all-dielectric metasurface has the capability of perfectly absorbing incident optical energy without the assistance of a mirror. Here, an array of thin germanium waveguide-like units is designed as a special absorber possessing some advantages by overlapping two localized resonant modes. Such a thin absorber can realize strong absorption even though the germanium material is of low loss at the O band. It is found that the absorption capability is about three times stronger than that of an unpatterned germanium film with the same thickness, and wideband strong absorption is obtained at the same time. The structure is continuous so that it can conduct carriers in photodetection. The suggested method would be heuristic in the photodetection area.

Enhanced Absorption of a Patterned Thin Germanium Layer as a High-Contrast Grating

“…The wavelength selectivity of this absorber is beneficial to our design of different target wavelengths, which is crucial for practical applications. Our proposed absorbers are expected to be integrated into a surface-illuminated vertical-PIN detector [37], [38], the ultra-high absorption is beneficial to improve the responsivity of the PDs. In addition, the thickness of intrinsic Ge layer is expected to be controlled at 500 nm, and the carrier transit-time-limited bandwidth f T greater than 50 GHz can theoretically be obtained according to f T = 0.45 * v sat /d, where v sat is saturated drift velocity of Ge (6 * 10 6 cm/s) and d is the thickness of intrinsic Ge layer [37], [39], which promise a fast response.…”