Heterogeneously-Integrated Electronically-Assisted Photonics for RF and mm-Wave Links

Electronically-assisted photonics have historically played an essential role in high-speed communications and will continue to do so in the predicted 5G paradigm. While millimeter-wave emitters with beam-forming, massive MIMO, and advanced modulation techniques will likely provide the fronthaul wireless links, photonics provides broadband solutions for long-distance backhaul communications. Optical fiber can be extended even closer to the user, providing additional increases in data rates. Additionally, optical and millimeter-wave frequency synthesis systems utilizing tightly integrated optical and electronic circuits can enable a wide range of applications with high complexity chip-scale solutions.

One of the most important blocks in determining the cost and performance of an optical link is the photoreceiver. Photoreceivers with high bandwidths and low noise can enable high speeds for data transmission and lower minimum detectable signals in the optical link. As silicon PDs are inefficient and III-V material-based electronics can become expensive, heterogeneous integration of III-V PDs and silicon CMOS electronics offers an effective solution. This research presents design, simulation, and measurements of several transimpedance amplifier topologies implemented in several CMOS and BiCMOS platforms. Additionally, heterogeneously integrated photoreceivers based on these electronic circuits and III-V PDs are presented. The integration schemes demonstrate increasing levels of integration and SWaP reduction while simultaneously removing previously encountered bottlenecks in photoreceiver performance. Investigations are presented in both high-speed as well as low-noise application spaces.

Further, integrated silicon photonics (SiP) platforms offer high integration potential for optical and electronic circuits. Germanium-on-silicon (Ge-on-Si) PDs are readily integrated and offer high bandwidths and responsivities. Several PDs and PD arrays are fabricated on a developing SiP platform, along with several other circuits including a Mach-Zehnder delay line interferometer.

Lastly, a solution to radio-over-fiber (RoF) high frequency RF and mm-Wave carrier generation is proposed. For use in coherent receivers, an optical phase-locked loop can improve the phase noise and eliminate long-term temperature drift of the RF beat frequency. An electronics CMOS chip is designed and fabricated to implement the necessary control circuits. Additionally, a SiP chip with phase modulators and the necessary optical components is designed and fabricated. The two chips are heterogeneously integrated on-board to create an optical phase-locked loop. This integration will offer a chip-scale solution with high complexity in order to control and improve the operation of the widely-tunable optical sources used in millimeter-wave frequency synthesis.