Resonantly assisted silicon photonics transceivers for medium-reach interconnects

Nojić, Jovana; Witzens, Jeremy (Thesis advisor); Petrova, Marina (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

Mobile data traffic is on a constant rise, with emerging 5G technologies having to service a broad range of applications that require high throughput, low latency, and high reliability communication. Fiber optic links, based on standard single mode fibers (SMF), are one of the main candidates for transporting data from 5G cell sites to central offices, and further to remote data centers. To reduce infrastructure costs, silicon photonics (SiP) presents itself as the technology of choice for the necessary electro-optical transceivers, with its low per-unit cost for high-volume production, owing to its large degree of compatibility with the well-established complementary metal oxide semiconductor (CMOS) fabrication. Moreover, low power, frequency selective resonantly assisted SiP devices ease the implementation of multi-channel, wavelength division multiplexed (WDM) transceiver systems that increase parallelization. Furthermore, to meet the growing demands for data throughput, flexible, robust modulation schemes that rely on inexpensive direct detection (DD) are of great interest. The single-sideband orthogonal frequency multiplexing (SSB-OFDM), with its high tolerance to dispersion-mediated signal distortion, flexibility in spectral loading, and high spectral efficiency fits well the stated requirements. In that context, we investigate the feasibility and performance of SSB-OFDM links that rely on SiP ring resonator assisted modulation, while carefully taking other typical link components (lasers and amplifiers) into consideration. On the receiver side, we study a SiP WDM receiver system based on optical add-drop multiplexers (OADM) that handles polarization scrambling present in SMF data links. In this work, we present, to the best of our knowledge, for the first time a detailed analytical model for the laser phase noise to intensity noise conversion in resonant ring modulator (RRM) assisted DD data transmission. To validate the model, we perform a set of SSB-OFDM transmission experiments using a SiP RRM assisted modulator. Moreover, we numerically model the same link, including all imperfections associated with individual link components, with the laser phase noise introduced at the link end through the derived analytical expressions. Excellent agreement of experimental and modeling results confirms the validity of our analytical model. Additionally, we study how the optimal biasing point of the RRMs depends on the laser source characteristics, as well as the influence of component nonlinearities on the SSB signal. Lastly, we present a high-speed 10-channel polarization-diverse SiP WDM receiver with a reduced number of OADMs per channel and balanced group delays for orthogonal polarization states and experimentally benchmark the performance of each of the receiver channels.

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