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.

Absorbers such as photonic crystals, metasurfaces, and nanowires have been demonstrated to have important applications in solar cells, detectors, etc. The application of thin-layerbased absorbers to photodetectors is beneficial to simultaneously improve responsivity and 3 dB bandwidth. In this work, we propose a high-contrast-gratings-like absorber to achieve ultra-high absorption based on a thin Germanium layer. High absorption approximately 95% at wavelength 1310 nm is reached for TEpolarized incidence due to the interference of two guided modes, which is 4 times compared to the planar film with the same thickness. The high absorption of the absorber is also experimentally demonstrated. This work shows a new method for enhanced absorption with thin Germanium layer, indicating a promising prospect for high-efficiency photodetection.