3-D integrated heterogeneous intra-chip free-space optical interconnect.

Area of Science:

• Optoelectronics
• Integrated Photonics
• Computer Architecture

Background:

• Traditional interconnects face limitations in latency, energy efficiency, and bandwidth density for advanced many-core chips.
• Waveguide-based optical interconnects, while promising, have inherent constraints.
• Free-space optical interconnects (FSOI) offer a potential solution for high-performance intra-chip communication.

Purpose of the Study:

• To present the first chip-scale demonstration of a proposed intra-chip free-space optical interconnect (FSOI).
• To evaluate the performance of the FSOI interconnect and compare it with waveguide-based optical interconnects.
• To highlight the advantages of FSOI for future high-performance computing architectures.

Main Methods:

• Fabrication of a 1x1 cm chip prototype on a germanium substrate with integrated photodetectors.
• 3-D integration of commercial 850-nm GaAs vertical-cavity-surface-emitting-lasers (VCSELs) and fused silica microlenses.
• Experimental evaluation of optical transmission loss, crosstalk, and electrical-to-electrical bandwidth at a 1.4 cm distance.

Main Results:

• Achieved measured optical transmission loss of 5 dB at 1.4 cm distance.
• Demonstrated crosstalk below -20 dB.
• Obtained an electrical-to-electrical bandwidth of 3.3 GHz, primarily limited by the VCSEL speed.

Conclusions:

• The demonstrated FSOI system shows significantly lower loss and higher energy efficiency compared to wavelength division multiplexing (WDM) systems.
• FSOI technology holds promise for overcoming the limitations of current interconnects in future many-core chips.
• The FSOI system provides an all-to-all intra-chip communication fabric with potential for inter-chip scalability.