PhD defence of Essam Berikaa - Advancing Datacenter Interconnects with High-Speed Silicon Photonic and Thin-Film Lithium Niobate Transmitters
Abstract
The relentless growth of internet traffic demand, along with the rising traction of bandwidth-intensive applications, is driving datacenters to seek higher transmission capacities. The performance of transmission systems has traditionally been limited by the transmitter electro-optic modulator. Therefore, this thesis focuses on studying the architectures and system-level trade-offs for both IMDD and coherent transmission systems utilizing silicon photonics (SiP) and thin-film lithium niobate (TFLN) modulators.
The thesis explores the wavelength-architecture 2脳2 matrix. In the first part, we focus on IMDD systems using both SiP and TFLN MZMs. With early access to TFLN technology, we demonstrate the capability of driving TFLN MZMs with sub 1 Vpp single-ended driving swings, achieving net 300 Gbps transmission rates. Additionally, we propose a transmitter architecture that eliminates the need for separate RF drivers and transmitter DSP, achieving a record net 400 Gbps/位 transmission rate for single DAC operation. Furthermore, we propose and validate the design of a SiP vestigial sideband transmitter (VSB) targeting long-reach C-band IMDD transmission. The proposed SiP VSB transmitter architecture employs pure intensity modulation with a single differential-output DAC, enabling the transmission of 56 Gbaud PAM4 signals over 60 km of dispersion-uncompensated single-mode fiber.
In the second part, we propose and advocate employing TFLN-based coherent transmission systems for short-reach intra-datacenter communications (2 to 10 km). We highlight the challenges facing IMDD to stretch beyond 800 Gbps operation. Moreover, we demonstrate the first O-band transmission system operating at net 1.6 Tbps over a single 10 km optical fiber using a single-carrier TFLN O-band coherent transmitter at 167 Gbaud DP-64QAM. Furthermore, we provide a power consumption comparison between the different IMDD and coherent architectures for 1.6 Tbps operation, strongly supporting our proposal for adopting TFLN-based coherent transmission for short-reach applications.
The third part demonstrates the first net 1 Tbps/位 transmission over 80 km of SSMF using a single-segment SiP IQ modulator with only electronic equalization at 105 Gbaud DP-64QAM. In addition, we study the system-level trade-offs and optimizations that enabled a 30 GHz modulator to support operating beyond 100 Gbaud and achieve this record transmission rate.
In the last part, we propose and validate a method to reduce the equalization-enhanced in-band noise that can be incorporated into the receiver DSP after conventional equalizers and improve transmission performance. In simulations, and validated with experimental data, we observe a gain of 0.5 dB in the signal-to-noise ratio when the proposed method is employed.