Co-packaging Digital Readout Integrated Circuits and Photonics for Advanced Infrared Imaging

State of the art infrared digital focal plane arrays (FPAs) can produce >20 Gbps when operated at standard video framerates and in large formats. Designing output drivers for this bitstream in a cryogenic environment is nontrivial. It requires careful balancing of the electrical, mechanical, and thermal constraints of the readout integrated circuit (ROIC). Industry surveys indicate that the current state of practice is limited to just under 3 Gbps per channel and 10 pJ/bit. In a large format FPA, the power consumption for data transfer becomes significant and acts to shorten cryocooler lifetimes. A paradigm shift is required. Photonic integrated circuits (PICs) are viewed as a potential solution to the ROIC output driver issue. PICs can improve the ROIC bandwidth, latency, and energy consumption by a factor of 10 or more compared to standard electronic IO practices. Unfortunately, all demonstrations to date have utilized mostly off-the-shelf ROICs with PIC chiplets on an interposer. While this reduces the thermal load of the electrical wiring, it does very little to change the overall power consumption. A fully monolithic design is needed. Fortunately, several foundries now offer 45-180 nm CMOS/PIC capabilities. The envisioned effort will demonstrate a tri-service ready capability to either completely integrate electronics and photonics on a single silicon wafer, or perform foundry-level integration of both a photonic and an electronic layer before detector hybridization. The primary objective of this effort is to demonstrate high-speed, ultra-low-power optical channel operations within cryogenic environments. The supporting Readout Integrated Circuit (ROIC) design must support high-throughput data generation. To facilitate benchmarking and diagnostic testing, the system should feature independent and configurable electrical and optical outputs. While specialized design hardening for space and high-radiation environments is advantageous to support long-term survivability, it remains an optional parameter.