High-speed Ge/Si electro-absorption optical modulator in C-band operation wavelengths.

Area of Science:

• Photonics and Optoelectronics
• Materials Science
• Semiconductor Devices

Background:

• High-bandwidth optical interconnects are crucial for modern data communication.
• Germanium-on-silicon (Ge/Si) electro-absorption modulators (EAMs) offer potential for compact and high-speed modulation.
• Previous Ge EAMs primarily operated in the L-band, limiting C-band applications.

Purpose of the Study:

• To investigate the performance of a Ge/Si EAM with submicron germanium layer widths.
• To achieve high-speed modulation in the C-band wavelengths.
• To optimize the Ge/Si EAM structure for enhanced optical bandwidth and performance.

Main Methods:

• Fabrication of a lateral pn junction Ge/Si EAM with selectively grown Ge layers below 1 µm.
• Evanescent coupling of the Ge layer with a silicon waveguide (Si WG).
• Photoluminescence and Raman spectroscopy for material characterization.
• High-speed modulation testing at 56 Gbps non-return-to-zero (NRZ) and 56 Gbaud pulse amplitude modulation 4 (PAM4).

Main Results:

• Demonstrated 56 Gbps NRZ and 56 Gbaud PAM4 EAM operation in the C-band.
• Confirmed increased direct bandgap energy in submicron Ge/Si stack structures via spectroscopy.
• Optimized operation wavelength by reducing device width (< 1 µm) and controlling post-growth anneal conditions.

Conclusions:

• Submicron Ge layer engineering in Ge/Si EAMs enables high-speed C-band operation.
• Optimized device geometry and annealing relax tensile strain and broaden the Franz-Keldysh effect bandwidth.
• This work advances Ge/Si EAM technology for future high-bandwidth optical interconnects.