Germanium-on-Silicon Waveguide-Integrated Photodiode with Dual Optical Inputs for Datacenter Applications

Area of Science:

• Photonics
• Optical Communications
• Semiconductor Devices

Background:

• Exponential growth in compute workloads necessitates higher intra-datacenter interconnect bitrates.
• Advanced modulation formats like PAM4 are adopted but introduce SNR penalties, requiring higher optical powers.
• High optical powers challenge photodetectors due to the space-charge effect, limiting high-speed performance.

Purpose of the Study:

• To design and fabricate a photodiode that overcomes space-charge limitations under high optical power.
• To enable higher bitrates in optical interconnects by improving photodetector performance.
• To maintain low bit error rates (BER) at increased optical power levels.

Main Methods:

• Design and fabrication of a waveguide-integrated photodiode with dual optical inputs (DIPD).
• Implementation of a dual-fed architecture with cross-sectional geometric optimizations.
• Characterization of photodiode performance under high-power illumination and CMOS driving voltages.

Main Results:

• Demonstrated effective distribution of photocurrent density to delay space-charge saturation.
• Achieved high responsivity of approximately 0.91 A/W for O-band wavelengths.
• Obtained a large electro-optic bandwidth (EOBW) of approximately 58 GHz.

Conclusions:

• The developed DIPD photodiode effectively mitigates space-charge effects in high-power optical links.
• This design enables optical networking equipment to meet increasing bitrate demands in datacenters.
• The photodiode operates efficiently under high optical power and standard CMOS driving voltages, paving the way for next-generation interconnects.