PhD defence of Essam Berikaa - Advancing Datacenter Interconnects with High-Speed Silicon Photonic and Thin-Film Lithium Niobate Transmitters
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 2×2 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/λ 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/λ 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.