Compact Optical TX and RX Macros for Computercom Monolithically Integrated in 45 nm CMOS

As the reach of optical communications continues to shrink, photonics is moving from rack-to-rack datacom links to centimeter-scale in-computer applications (computercom) where different architectures are needed. Integrated optical microring resonators (MRRs) are emerging as an attractive choice for fulfilling the more stringent area and efficiency requirements: They offer scaling by wavelength division multiplexing (WDM) and high bandwidth densities. In this paper we present compact electro-optical transmit (TX) and receive (RX) macros for computercom monolithically integrated in 45 nm CMOS. They operate with MRR modulators and photodetectors and include all necessary electronics and optics to enable optical links between on-chip data sources and sinks. A most compact implementation for thermal stabilization was enabled by sensing the optical device's bias currents in the driving electronics instead of using external operating point sensing optics. Using a field-effect transistor as heating element — as is possible in monolithic integration platforms — further reduces area and power necessary for thermal control. The TX macro is shown to work for data rates up to 16 Gb/s with a 5.5 dB extinction ratio (ER) and 2.4 dB insertion loss (IL). The RX macro demonstrates a sensitivity of 71 µA
_pp
at 12 Gb/s for a BER ≤ 10
⁻¹⁰
. An intra-chip link built with the macros achieves ≤2.35 pJ/b electrical efficiency and a BER ≤10
⁻¹⁰
at 10 Gb/s. Both macros are realized within 0.0073 mm
²
which amounts to 1.4 Tb/s/mm
²
bandwidth density per macro.