A $\boldsymbol{4} \times \boldsymbol{112}-\mathbf{Gb}/\mathbf{s}$ PAM-4 Silicon-Photonic Transceiver Front-End for Linear-Drive Co-Packaged Optics

The explosive growth of the data-intensive AI computing demands for datacenter interconnects with ever-increasing bandwidth (BW). Traditional pluggable optical modules can hardly meet the DC power and form-factor requirements by the new 51.2T ethernet switch. By tightly integrating the compact optical engine (OE) into the switch package, on-board metal traces are mostly replaced by optical fiber, which thereby saves the signaling power and improves the front-panel BW-density. Depicted in Fig. 1(a), each 3.2T OE employs 4 quad-lane optical transceivers (O-TRX) in the package, enabling $16\times 112\ \text{Gb}/\mathrm{s}$ fiber channels directly attached to the chip edge. Meanwhile, the pluggable optical module has to employ a power-hungry DSP-based O-TRX to compensate for the channel-loss beyond 100 Gb/s per lane. The integrated co-packaged optics (CPO) in contrast, simplifies the transceiver by replacing the DSP with linear driver and amplifier with embedded continuous-time linear equalizers (CTLE). The so-called linear-drive (LD) CPO draws increasing attentions, since it significantly reduces power consumption, cost, and latency. The embedded CTLE needs to equalize 10–12 dB channel loss between the switch and each OE.