High-efficiency Ge-based waveguide photodetector integrated with a grating coupler on silicon-on-insulator

Area of Science:

• Optoelectronics
• Materials Science
• Nanotechnology

Background:

• Silicon-on-insulator (SOI) platforms are crucial for integrated photonics.
• Germanium (Ge)-based photodetectors are essential for optical communication wavelengths.
• Improving coupling efficiency and light absorption in Ge-based devices is a key challenge.

Purpose of the Study:

• To design and optimize a composite device structure integrating Ge-based waveguide photodetectors with grating couplers on an SOI platform.
• To enhance the performance of grating couplers and waveguide photodetectors for broader detection ranges and improved light absorption.
• To enable miniaturization of Ge-based waveguide photodetector devices.

Main Methods:

• Utilized the finite-difference time-domain (FDTD) method for simulation and design optimization.
• Optimized grating coupler design by adjusting parameters and combining nonuniform grating with Bragg reflector structures.
• Introduced germanium-tin (GeSn) alloy as the active absorption layer in the waveguide detector.

Main Results:

• Achieved a peak grating coupler efficiency of 85% at 1550 nm and 75.5% at 2000 nm, significantly outperforming uniform gratings.
• The GeSn alloy enabled near-complete light absorption within a 10 µm device length for both 1550 nm and 2000 nm wavelengths.
• Demonstrated broadened detection range and significantly improved light absorption for the waveguide photodetector.

Conclusions:

• The proposed composite device structure offers superior performance for Ge-based waveguide photodetectors.
• The optimized grating couplers and GeSn-based detectors pave the way for highly efficient and compact optoelectronic integrated circuits.
• This work facilitates the miniaturization of Ge-based waveguide photodetectors for advanced photonic applications.