Mode-Selective by Phase-Matching Coupling to Guided Modes in Multilayer Germanium Grating for Narrow Linewidth in Wavelength Precision Photodetection

High-efficiency and narrow-linewidth photodetectors are critical for advanced optical communication systems, especially in dense wavelength division multiplexing (DWDM) applications. This study introduces a novel photodetector featuring a multilayer structure comprising a subwavelength grating, a Ge absorption layer, and a SiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/Si multilayer. By utilizing the phase-matching coupling of SiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>/Si-confined modes, the devices with the gratings demonstrate a high absorbance peak of ∼97% with an ultra-narrow linewidth of ∼1 nm at 1550 nm. It is 10 times narrower than those of previous works of photodetectors integrated with phase-matching gratings. By utilizing the two-dimensional grating, the device performs polarization independently. Additionally, the inclusion of a Si spacer layer enhances design flexibility while maintaining performance. With a demonstrated bandwidth of approximately 58 GHz, the proposed photodetector is well-suited for high-speed optical communication applications. This work provides a pathway to overcoming current limitations in photodetector efficiency and spectral control, paving the way for future innovations in photonic devices.