UBC Theses and Dissertations
High-speed optoelectronic links for datacenters Ahmed, Abdelrahman Hesham Elsayed
Optoelectronic (O/E) links are necessary for inter/intra-datacenter communication. Driven by the need to support higher data throughput, breakthroughs in Silicon-photonics and innovative circuit techniques are needed to enable efficient, compact, and low-cost links across a wide range of interconnect lengths. For short-reach applications, where energy efficiency is a major concern, microring resonator (MRR)-based transmitters (TXs) promise low cost and dense multiplexing to replace their vertical-cavity surface-emitting laser (VCSEL)-based counterparts. This thesis presents an analysis of MRR-based links from the perspective of optical devices, circuits, and link budget and compares them to VCSEL-based links. On the receiver (RX) side, sensitivity enhancement is necessary to improve the link’s energy efficiency. Due to their multiplication gain, avalanche photodetectors (APDs) improve RX sensitivity. When implemented monolithically with the RX, they reduce cost and parasitics. An RX with noise-canceling active balun is presented. The RX works as part of the APD bias stabilization loop. The integrated O/E-RX achieves a measured sensitivity of -18.8dBm at 0.57pJ/b. A high-sensitivity, high-speed, and low-power RX demands solutions to the gain-bandwidth-power trade-offs. Accordingly, a current-mode receiver that eliminates the noisy and power-hungry front-end is proposed. The proposed design converts the single-ended PD current into differential currents and resolves the data using a current-based sense amplifier. For long-reach applications, where spectral efficiency is critical, coherent O/E links rely on advanced modulation and dual-polarization, leading to stringent link requirements. The TX requires high bandwidth (BW), linearity, swing, and reliability, while the RX requires minimizing noise and total harmonic distortion (THD) across gains and frequency. A linear high-swing driver for Mach-Zehnder modulator is presented. The driver uses a voltage breakdown enhancement technique to ensure reliability, and resistor-based capacitor-splitting technique to enhance BW. It achieves 6Vppd, 3.6% THD, and >40GHz BW, enabling >0.5Tb/s/wavelength operation. An auto-reconfigurable transimpedance amplifier satisfying the stringent noise-linearity conditions is presented. Operating on a single sense-voltage, it reduces base resistor noise, gain peaking, phase margin and fT degradation. Techniques such as collaborative offset and DC current cancellation are also described. The RX achieves a gain of 75.5dBOhm and an input-referred noise of 18.5pA/sqrt(Hz) at 42GHz BW, enabling >0.5Tb/s/wavelength operation.
Item Citations and Data
Attribution-NonCommercial-NoDerivatives 4.0 International