Additive 3D photonic integration that is CMOS compatible.

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Integrated Circuit Design

Background:

• Electronic integrated circuits (ICs) face fundamental miniaturization limits (∼2 nm feature size).
• Energy consumption in electronic ICs, especially for communication and neural networks, is a major challenge.
• Three-dimensional (3D) integration offers a strategy to improve IC architecture beyond 2D limitations.

Purpose of the Study:

• To review advancements in 3D photonic integration using additive photopolymerization.
• To demonstrate CMOS-compatible fabrication of 3D photonic circuits for hybrid integration.
• To explore the application of these circuits in optical neural networks.

Main Methods:

• Utilized additive photo-induced polymerization of standard photo-resin.
• Employed one- and two-photon polymerization (TPP), including flash-TPP, combined with direct-laser writing.
• Fabricated air- and polymer-cladded photonic waveguides and adiabatic couplers.

Main Results:

• Demonstrated 3D-printed polymer-cladded waveguides (up to 6 mm length) with low insertion (∼0.26 dB) and propagation (∼1.3 dB mm⁻¹) losses.
• Achieved broadband, low-loss (∼0.06 dB splitting losses) adiabatic 1 to M couplers.
• Successfully printed integrated photonic circuits on semiconductor samples, confirming CMOS compatibility.

Conclusions:

• Additive photopolymerization enables truly 3D photonic integration compatible with CMOS processes.
• 3D photonic circuits are crucial for scalable interconnects in optical neural networks.
• This approach provides a promising pathway for scalable hybrid photonic-electronic integration.